WO2001008376A1

WO2001008376A1 - Signaling mechanism for modem connection holding and reconnecting

Info

Publication number: WO2001008376A1
Application number: PCT/US2000/010483
Authority: WO
Inventors: Sverrir Olafsson; Keith Chu; Burk Beadle; Yair Kerner; Iddit Shalem
Original assignee: Conexant Systems, Inc.
Priority date: 1999-07-27
Filing date: 2000-04-19
Publication date: 2001-02-01

Abstract

A quick startup procedure for a modem system utilizes known characteristics of a previously established communication channel to reduce the initialization period associated with subsequent connections over the same channel. In response to the establishment of a call, the modem devices determine whether the quick connect protol is supported. If so, then the called modem transmits a modified answer tone to the calling modem. The calling modem analyzes the signal received in response to the modified answer tone to determine whether characteristics of the current channel are similar to stored characteristics associated with a previous connection over the same channel. If a channel 'match' is found, then the modem devices carry out a quick initialization routine that eliminates, abbreviates, or modifies a number of procedures or protocols that are carried out in conventional modem startup processes. The general quick startup techniques may also be applied in the context of a quick reconnect procedure that can be performed in response to a temporary pausing or disconnecting of the data modem mode.

Description

SIGNALING MECHANISM FOR MODEM CONNECTION HOLDING AND RECONNECTING

FIELD OF THE INVENTION The present invention relates generally to modem systems More particularly, the present invention relates to the initialization and reconnection of a V 90 modem system

BACKGROUND OF THE INVENTION

56 kbps modems are now standardized in accordance with the ITU V 90 Recommendation However, many 56 kbps modems particularly end user modems may only be compatible with legacy modes such as K56flex V 34, V FC, and V 32 Such legacy modems, and downwardly compatible V 90 modems, may have an undesirably long connect or initialization time between dial-up and full rate data mode The startup time can be up to 30 seconds, which can be rather annoying and unattractive from the perspective of the end user, especially in light of other data communication protocols that appear to operate in an "always connected" manner

V 90 modems that support legacy modem protocols typically perform the functions shown in Table 1 during initialization The time periods associated with the operations set forth in Table 1 may vary from connection to connection depending upon various factors such as the server speed and channel conditions

Table 1 - Conventional V 90 Modem Startup The V 8bιs operation includes a relatively long timeout period that encompasses much of the time period associated with the operation This operation is described in detail in ITU-T Recommendation V 8bιs (International Telecommunication Union, August 1996), the content of which is incorporated bv reference herein The V 8bιs protocol is an extension of the V 8 protocol, as described in ITU-T Recommendation V 8 (International Telecommunication Union, February 1998), the content of which is incorporated by reference herein In accordance with V 8bιs and/or V 8, the two modem devices exchange their individual capabilities such that compatible protocols may be utilized during subsequent initialization and data communication procedures The various V 90 startup phases are utilized to determine the analog and digital channel characteristics, to train the modem equalizers and to otherwise attempt to optimize the current communication session The details of the V 90 startup phases and other aspects of a V 90 modem system may be found in ITU-T Recommendation V 90 (International Telecommunication Union, September 1998), the content of which is incorporated by reference herein Although a portion of the V 90 startup segments shown in Table 1 are required without regard to the location or status of the client modem, many of the operations could be eliminated or shortened upon repeated connections associated with the same (or nearly identical) channel characteristics

In a conventional λ^r 90 modem system, error correction and data compression techniques are performed during the V 42/V 42bιs stage The specifics of V 42 are contained in ITU-T Recommendation V 42 (International Telecommunication Union, October 1996), the content of which is incorporated by reference herein The specifics of V 42bιs are contained m ITU-T Recommendation V 42bιs (International Telecommunication Union, January 1990), the content of which is incorporated by reference herein The V 42 operation is desirable such that the modem system can perform the login procedure in a substantially "error free" mode The login procedure may be conducted with CHAP and PAP protocols, both are utilized for security purposes in the context of point-to-point protocol ("PPP") connections, e g , a connection between a client computer and an internet service provider server From the perspective of the V 90 modem devices the login information is transmitted as data Once the login procedure is performed, the dial-up connection is complete and data may be transmitted between the server and the host software associated with the client

The widespread use of the internet as a daily research, entertainment, and communication tool has increased the deployment of 56 kbps modems However, many channels can only support legacy modes such as V 34 Thus, although most newer modems

? (particularly those sold with new personal computers) are compatible with the V 90 Recommendation, many legacy modes are still in use The long initialization period associated with V 90 modems that fall back into legacy modes may be annoying and undesirable in many applications and can be a serious hindrance where a user would like to establish an immediate connection after an unanticipated disconnect In addition, even in the context of a connection between two V 90 modem devices, the long V 90 startup phases may test the mettle of an impatient end user Accordingly, it would be highly desirable to reduce the initialization time normally associated with a conventional V 90 modem system

A given modem communication session may be interrupted or disconnected for any number of reasons For example, a call waiting signal may disrupt a modem connection to the extent that the modem call must either be reconnected or reinitialized As another example, it may be possible to place a current modem connection on hold to enable the user to answer an incoming call in response to a call waiting signal or to enable the user to place an outgoing call without disconnecting the modem connection Ideally, the modem connection could be re- established in an instantaneous manner However, in a practical system, a retraining or reinitialization procedure must be carried out to ensure that the two end devices are properly synchronized and to ensure that the channel is adequately equalized As discussed above, conventional V 90 modem systems may spend more than 20 seconds during such retraining and reinitialization Accordingly, it would also be desirable to reduce the reconnection time between the same modem devices in response to a temporary disconnect or a temporary pause in the data communication

SUMMARY OF THE INVENTION The present invention provides techniques to shorten the startup and reconnection times associated with a data communication system that employs a modem The quick reconnect technique leverages the known channel characteristics of a previous connection to reduce the reinitialization period associated with subsequent attempts to reconnect the same two modem devices In accordance with one illustrative embodiment, the techniques of the present invention are utilized to reduce the reconnection time for a communication session that follows an upper layer protocol, e g , PPP Although not limited to any specific modem application the quick startup and reconnect procedures may be used to eliminate portions of the initialization protocols or processes normally employed by a V 90 modem, e g , V 8bιs V 8, digital impairment learning, initial training, probing and ranging, or the like In addition, the quick startup and reconnect techniques may perform certain operations at a different time or in a different order in comparison to a conventional modem startup technique

The above and other aspects of the present invention may be carried out in one form by a method for reducing the reconnection time associated with a data transmission system having a first device configured to communicate with a second device over a communication channel The illustrative method involves establishing a communication session between the first device and the second device over the communication channel, obtaining a number of operating parameters for the data transmission system, where the operating parameters are associated with the communication channel, and storing at least one of the operating parameters at the second device After a temporary pause in the communication session, the operating parameters are recalled at the second device

BRIEF DESCRIPTION OF THE DRAWINGS

A more complete understanding of the present invention may be derived by referring to the detailed description and claims when considered in connection with the Figures, where like reference numbers refer to similar elements throughout the Figures, and

FIG 1 is a block diagram depicting a general modem system environment capable of supporting point-to-point protocol ("PPP") connections,

FIG 2 is a flow diagram of a general quick startup process according to the present invention,

FIG 3 is a block diagram depicting an illustrative modem system configured in accordance with the present invention,

FIG 4 is a flow diagram illustrating portions of a quick startup process performed by two modem devices, FIG 5 is a timing diagram corresponding to a quick startup process performed by two modem devices,

FIG 6 is a timing diagram corresponding to a quick reconnect process performed by two modem devices,

FIG 7 is a flow diagram illustrating a quick reconnect process performed by two modem devices,

FIGS 8-15 are timing diagrams corresponding to different modem-on-hold, reconnect, and clear down situations,

FIG 16 is a block diagram of a modem system environment in which various aspects of the present invention may be incorporated, FIGS 17-19 are timing diagrams corresponding to other an alternate embodiment of the present invention

DETAILED DESCRIPTION OF PREFERRED EXEMPLARY EMBODIMENTS The present invention may be described herein in terms of functional block components and various processing steps It should be appreciated that such functional blocks may be realized by any number of hardware components configured to perform the specified functions For example, the present invention may employ various integrated circuit components, e g , memory elements, digital signal processing elements, logic elements, look-up tables, and the like, which may carry out a variety of functions under the control of one or more microprocessors or other control devices In addition, those skilled in the art will appreciate that the present invention may be practiced in any number of data communication contexts and that the modem system described herein is merely one illustrative application for the invention Further, it should be noted that the present invention may employ any number of conventional techniques for data transmission, signaling, signal processing and conditioning, and the like Such general techniques that may be known to those skilled in the art are not described in detail herein

It should be appreciated that the particular implementations shown and described herein are merely exemplary and are not intended to limit the scope of the present invention in any way Indeed, for the sake of brevity, conventional encoding and decoding, timing recovery, automatic gain control ("AGC"), synchronization, training, and other functional aspects of the data communication system (and components of the individual operating components of the system) may not be described in detail herein Furthermore, the connecting lines shown in the various figures contained herein are intended to represent exemplary functional relationships and/or physical couplings between the various elements It should be noted that many alternative or additional functional relationships or physical connections may be present in a practical communication system

FIG 1 is a block diagram depicting a general modem system 100 m which the techniques of the present invention may be practiced For purposes of this description, modem system 100 is assumed to be capable of supporting connections associated with an upper layer protocol, e g , point-to-point protocol ( 'PPP") connections PPP connections are typically associated with internet communications between, e g , an individual end user and an internet service provider In this respect, modem system 100 includes a plurality of server modems (identified by reference numbers 102a, 102b, and 102n) and a client modem 104 Server modems 102 may each be associated with an internet service provider or any suitable data source Client modem 104 may be associated with a suitable data source, e g , a personal computer capable of running host software 105 For purposes of this description, host software 105 may be an operating system such as MICROSOFT WINDOWS, or any application program capable of functioning in conjunction with modem system 100 Although not shown in FIG 1, client modem 104 may be integrated with the personal computer

In the context of this description, modem system 100 may employ 56 kbps modems that are compatible with the V 90 Recommendation, legacy 56 kbps protocols, the V 34 Recommendation, or the like Although the present invention is described herein in the context of a V 90 modem system, the techniques can be equivalently applied in a V 34 modem system or in any number of legacy modem systems V 90 or 56 kbps modem devices are suitable for use in modem system 100 where a given server modem 102 utilizes a digital connection 106 to the digital telephone network 108 The client modem 104 is connected to a local central office 110 via an analog local loop 112 Thus, the communication channel established between client modem 104 and any server modem 102 is digital up to the central office 110 Thereafter, the digital signals are converted to an analog signal for transmission over the local loop 112

If an end user desires to establish an internet connection, host software 105 may perform any number of operations in response to a user command For example, host software 105 may prompt client modem 104 to dial the telephone number associated with server modem 102a (which, for this example, is the server modem associated with the user's internet service provider) Server modem 102a and client modem 104 perform a handshaking routine that initializes the equalizers, echo cancelers, transmit power levels, data rate, and possibly other operational parameters associated with the current communication channel In addition, host software 105 may cause client modem 104 to transmit and receive authentication data that enables the user to log onto the internet via the service provider As mentioned above, the authentication data may be exchanged between server modem 102a and client modem 104 in accordance with the known CHAP or PAP techniques In an alternate embodiment that employs a non-PPP upper layer protocol a suitable login procedure may be conducted instead of the CHAP or PAP procedures As discussed previously, the dial-up connection time (and reconnection time) associated with conventional modem systems may be undesirably long The present invention takes advantage of the repeated use of a communication channel between modem devices, e g , the communication channel that is established between server modem 102a and client modem 104 Assuming that client modem 104 is associated with a desktop personal computer resident at a specific location, the connection to any given server modem 102 will necessarily be established over the same analog communication channel In other words, client modem 104 will always establish an analog channel between the user premises and central office 110 Disregarding slight variations in the analog channel due to temperature and other environmental effects, the initialization of client modem 104 (with respect to the analog channel) will remain substantially constant from connection to connection

FIG 2 is a flow diagram of a general quick startup process 200 that may be performed by a data communication system such as modem system 100 In a practical system, process 200 may be cooperatively performed by server modem 102, client modem 104, host software 105, and/or any functional component of modem system 100 In addition, process 200 may be realized in the context of an overall initialization procedure that follows any number of conventional modem protocols

Quick startup process 200 may begin with a task 202 which relates to the establishment of a call between client modem 104 and a server modem 102 In the context of this example, client modem 104 is considered to be the calling device Accordingly, host software 105 and/or client modem 104 dials the telephone number associated with, e g , server modem 102b Assuming that server modem 102b is capable of making an additional connection, it will go off hook and generate a suitable answer tone in a conventional manner When both modem devices are off hook and communicating with each other, a communication channel is established via digital connection 106 telephone network 108, central office 1 10, and analog local loop 112 The dialing, ringing, and answering procedures utilized during task 202 may follow conventional protocols

Following task 202, a query task 204 mav be performed by modem system 100 to ascertain whether a quick connect protocol is supported Query task 204 may be necessary to enable different server modems and different client modems to be interoperable and compatible For example, server modem 102b may be a V 90 modem device that supports the quick connect features of the present invention, while client modem 104 may be a legacy 56 kbps modem device that does not support the quick connect features Portions of query task 204 may be performed by server modem 102b or client modem 104 An illustrative technique for performing query task 204 is described in detail below Task 204 may be equivalently performed when client modem 104 initiates the call or when server modem 102 initiates the call

If query task 204 determines that the quick connect protocol is not supported by both modem devices then a task 206 may follow Task 206 prompts modem system 100 to begm a conventional initialization routine For example, in the context of a V 34 or V 90 modem system, task 206 may begin a capabilities exchange protocol such as V 8bιs Alternatively, some modem systems may only implement the V 8 capabilities exchange protocol Older legacy modem systems may skip the V 8 and V 8bιs procedures altogether and perform an appropriate initialization routine according to the legacy mode Following task 206, modem system 100 may conduct a known startup procedure in accordance with an applicable modem specification For example if modem system 100 supports V 90, then task 208 may be associated with conventional V 90 equalizer training, echo canceler training, constellation design, power level verification, and other startup operations If tasks 206 and 208 are performed, then the startup time associated with the communication session is essentially the same as the startup time for a conventional V 90 connection

If query task 204 determines that the quick connect protocol is fully supported, then a query task 210 may also be performed Query task 210 tests whether the characteristics of the established communication channel are similar to corresponding characteristics of a previously established communication channel Briefly, query task 210 compares one or more attributes of a received sequence to stored attributes of a previously received sequence associated with the previously established channel The received signal conveys information regarding the characteristics of the communication channel In particular, the received signal conveys information relative to analog local loop 112 In the illustrative embodiment described herein, where one modem device is connected digitally to the digital telephone network 108, analog local loop 112 affects signals in a substantially consistent manner from connection to connection Although the analog characteristics will be similar for repeated connections to the same server modem 102, slight variations in temperature, humidity, other environmental changes, physical changes in the system hardware, and other operational parameters contribute to random fluctuations in the current channel characteristics used for comparison purposes Nonetheless, the comparison procedure performed during query task 210 is preferably designed to accommodate such fluctuations For purposes of this description, "similar ' characteristics means that query task 210 will assume that the current channel matches a previous channel notwithstanding normal variations due to the uncontrollable and unpredictable factors mentioned above

If query task 210 determines that the parameters of the current communication channel do not match the parameters of a previous communication channel, then a task 212 may be performed Task 212, like task 206, prompts modem system 100 to begin a conventional initialization routine In a preferred embodiment, if modem system 100 verifies that the quick connect protocol is fully supported (query task 204), then most, if not all, of the V 8bιs procedure may be skipped Accordingly, the V 8 capabilities exchange protocol may be prompted by task 212 Thereafter, a task 214 may be performed to cause modem system 100 to enter the conventional V 90 startup procedure Task 214 is similar to task 208 described above If tasks 212 and 214 are performed, then the startup time associated with the communication session may be reduced by approximately three seconds, which is the typical time period required to conduct the V 8bιs procedures Accordingly, even if query task 210 determines that the current channel is not similar to a previous channel, quick startup process 200 reduces the overall initialization time of modem system 100 If query task 210 finds that the current channel characteristics "match" the stored characteristics of a previously established channel, then a task 216 may be performed An abbreviated training procedure is conducted during task 216 As described in more detail below, modem system 100 leverages the known characteristics of the current channel such that the modem devices can be immediately trained For example, although the specific timing phase of digital impairments (e g , robbed bit signaling) may be unknown, the types of digital impairments will be consistent for repeated connections Thus, in the context of a V 90 modem system, the lengthy digital impairment learning procedure need not be fully implemented In addition, the initial training of equalizers and echo cancelers, and the initial determination of PCM codec transmit levels and data rates need not be performed A task 218 may be performed to enable modem system 100 to operate at an initial data rate It should be appreciated that portions of the training associated with task 216 may be performed at the initial data rate associated with task 218 Modem system 100 is able to quickly operate at the initial data rate by recalling the initialization parameters associated with the previously stored channel During task 218, modem system 100 may perform final training of the equalizers and echo cancelers, exchange modulation parameters, and exchange constellation signal points for use during the full rate data mode In accordance with the present invention, PPP data may be transmitted during task 218 in connection with one or more final training sequences For example, the PPP data may be associated with the exchange of log-in authentication information, e g , CHAP or PAP information In view of the transmission of data during task 218, this portion of quick startup process 200 may be considered to be a first data mode or a data phase one

Following task 218, quick startup process 200 causes modem system 100 to operate at a final data rate (task 220) In the context of this embodiment, this portion of process 200 may be considered to be a second data mode or a data phase two The transition between the initial and final data rates preferably occurs in a seamless manner, modem system 100 employs a suitable signal timing or synchronization technique to enable such a data rate transition During the full data mode, modem system 100 utilizes the signal point constellation exchanged during task 218 Once modem system enters the final data mode, quick startup process 200 ends FIG 3 is a block diagram depicting an illustrative modem system 300 configured in accordance with the present invention Modem system 300 is preferably configured to carry out quick startup process 200 and other processes described herein By way of example, modem system 300 is described herein in the context of a 56 kbps or V 90 system (or a system substantially similar to a V 90 system) However, it should be appreciated that the particular implementation shown in FIG 3 is not intended to limit the scope of the present invention in any way

Generally, modem system 300 includes a first modem, e g , modem 302, and a second modem, e g , modem 304 In the context of this description, modem 302 is considered to be a server modem and modem 304 is considered to be a client modem (see FIG 1) It should be appreciated that modems 302 and 304 may be similarly configured such that both can function in either a transmit or receive mode Modems 302 and 304 are generally configured in accordance with known principles to communicate over a telecommunication network, such as the public switched telephone network ("PSTN") 306, via at least one communication channel (e g , channels 308 and 310) For purposes of this description, modem 302 is connected digitally to PSTN 306 while modem 304 is connected to PSTN via a central office (not shown) and an analog local loop, as described above in connection with FIG 1 For the sake of clarity, FIG 3 does not show the various encoder, decoder and other functional elements that would typically be present in a practical modem system

Modem 302 may include a processor element 312 while modem 304 may include a processor element 314 In addition to the specific operations described herein, processors 312 and 314 are suitably configured to carry out various tasks associated with the operation of modem system 300 Indeed, modem system 300 may incorporate any number of processors, control elements, and memory elements as necessary to support its functionality Such processor, control, and memory elements may suitably interact with other functional components of modems 302 and 304 to thereby access and manipulate data or monitor and regulate the operation of modem system 300

Processor 312 may be operatively associated with a quick connect confirmation routine, which is illustrated as a functional block 322 Quick connect confirmation routine 322 may be employed during query task 204 (see FIG 2) Processor 312 is also operatively associated with a number of training routines 324 Training routines 324 may be utilized for initial and/or final training of modem system 300 Training routines 324 may be employed during task 216, as described above Processor 312 may also operate in conjunction with a dial-up authentication scheme 326, e g , information exchanging in accordance with PAP or CHAP The CHAP/PAP functionality may be alternatively (or additionally) realized in one or more software applications maintained by the server corresponding to modem 302 These illustrative operations are not intended to limit the applicability of processing element 312 which is preferably configured to support any number of additional operations

Modem 302 includes a transmitter 316, which is configured to transmit encoded symbols in accordance with conventional data transmission techniques Such symbols may represent data, training sequences, synchronization signals, control signals, information exchange sequences, and any suitable communication signal utilized by modem system 300 Modem 302 also includes a receiver 318, which may be configured in accordance with any number of known modem technologies Receiver 318 is configured to receive communication signals from modem 304, such signals may include encoded information bits, control signals, information exchange sequences, training sequences, and the like Receiver 318 may include or be functionally associated with an equalizer structure 317 and an echo canceler structure 319 The configuration and operation of equalizer structure 317 and echo canceler structure 319 may be consistent with any number of conventional techniques, e g , adaptive filtering algorithms Modem 302 is preferably configured to generate, process, and transmit different data and signals associated with the operation of modem system 300 Such data, signals, and sequences may be suitably stored, formatted, and produced by any number of microprocessor-controlled components For illustrative purposes, FIG 3 depicts a number of blocks related to different operational features of modem system 300, such operational features may have specific data sequences, control signals, or the like, associated therewith Although a practical system may process and transmit any amount of additional or alternative data, the particular embodiment described herein functions in cooperation with at least the following types of data a transition sequence 328, an answer signal point sequence 330, authentication information 332, a quick connect identifier 334 training information 336, and user data 338 This data, and the handling of the data by modem system 300, is described in detail below

Modem 302 also includes a suitable amount of memory 320 necessary to support its operation Memory element 320 may be a random access memory, a read only memory, or a combination thereof Memory element 320 may be configured to store information utilized by modem system 300 in connection with one or more processes related to the present invention For example, memory element 320 may be configured to store a suitable answer signal point sequence 338 Memory 320 may store specific signal points, transmit levels, a pattern utilized to format a sequence for transmission, or the like In the preferred embodiment, answer signal point sequence 338 corresponds to sequence 330 (described above) Memory element 320 may also be configured to store a number of parameters related to the training of receiver 318 These receiver parameters, which are depicted as block 340, may be associated with the initialization of equalizer structure 317 and/or echo canceler structure 319 As a practical matter, memory element 320 may store information related to the analog and/or digital characteristics, e g , filter tap coefficients, of equalizer structure 317 and echo canceler structure 319, and transmit codec level estimates

In accordance with a preferred embodiment of the present invention, memory element 320 is also capable of storing a number of parameters, attributes, and/or characteristics of a previously established channel (illustrated as a previous channel block 342) The previous channel parameters 342 may be stored at any suitable time during a communication session or periodically updated during a session Indeed, modem 302 and modem 304 may both be configured to save the current channel parameters to anticipate a temporary interruption, delay, or disconnection associated with the current communication session (whether such interruption, delay, or disconnection is intentional or unintentional) As described in more detail below, in response to a temporary disconnection or pause in the modem data transmission mode, modem 302 can be placed "on hold" until the communication session is to be reinitiated At that time, modems 302 and 304 mav access the stored channel parameters rather than conduct a lengthy retrain procedure

Modem 304 includes a receiver 350, which is operatively associated with an equalizer structure 352 and an echo canceler structure 354 Receiver 350 is configured to receive communication signals from modem 302 Modem 304 also includes a transmitter 356 configured to transmit communication signals to modem 302 These components of modem 304 may be similar to the corresponding components of modem 302 Thus, for the sake of brevity, the description of features and functions that are common to modems 302 and 304 will not be repeated in this description of modem 304 Processor 314 may be operatively associated with a quick connect confirmation routine

358, one or more training routines 360, and a dial-up authentication scheme 362 These processing functions are similar to the corresponding functions described above in connection with processor 312 In addition to these features, processor 314 may be operatively associated with a digital impairment learning routine 364 Digital impairment learning routine 364 may be compatible with the digital impairment learning procedure earned out by conventional V 90 modems Routine 364 may be utilized to enable modem 304 to analyze a digital impairment learning sequence transmitted by modem 302 and to determine the types of digital impairments present in the communication channel and any timing phases associated with such digital impairments Routine 364 mav interact with a memory element 366 such that modem 304 can store the digital impairment profile associated with a given communication channel Routine 364 may enable modem 304 to select appropriate signal points (or a signal point) that function to illuminate or highlight robbed bit signaling present in the channel For example, if modem 304 determines that the network forces robbed bits (typically the least significant bit of a symbol) to zeros, then a signal point having a least significant bit of one may be selected such that the robbed bit signaling phases can be easily detected

Processor 3 14 may also be configured to conduct a channel comparison routine 368, which may be performed during task 210 described above in connection with FIG 2 Channel comparison routine 368 preferably determines whether the characteristics of the current communication channel are similar to stored characteristics associated with a previously established communication channel In the context of this description, the current channel is a repeated connection of the previously established channel, and a number of stored characteristics may be resident in memory element 366 Routine 368 is described in more detail below As with processor 3 12, the illustrative operations set forth herein are not intended to limit the applicability of processing element 314, which is preferably configured to support any number of additional operations

Like modem 302, modem 304 is configured to generate, process, and transmit different data and signals associated with the operation of modem system 300 Such data, signals, and sequences may be suitably stored, formatted, and produced by any number of microprocessor-controlled components Although a practical system may process and transmit any amount of additional or alternative data, transmitter section 356 is illustrated in conjunction with the following types of data a quick connect identifier 370 a transition sequence signal point identifier 372, training information 374 authentication information 376, and user data 378 This data, and the handling of the data by modem system 300, is described in detail below

As mentioned above, modem 304 includes a suitable amount of memory 366 necessary to support its operation Memory element 366 is similar to memory element 320 In the preferred embodiment, memory element 366 is configured to store an answer signal point sequence 380 that is related to the corresponding answer signal point sequence 338 utilized by modem 302 In this embodiment, the same answer signal point sequence is predetermined and known at both modems 302 and 304 Memory element 366 may also store a number of parameters, attributes, and/or characteristics of a previously established channel (illustrated as a previous channel block 382) The previous channel parameters 382 may be stored at any suitable time during a communication session or periodically updated during a session Like memory element 320, memory element 366 may also be configured to store a number of parameters 384 related to the training of receiver 350 These stored receiver parameters 384 are preferably accessed by modem 304 to effectively reduce the startup latency typically experienced with conventional V 90 modem systems

A number of features of the present invention contribute to the reduction in conventional V 90 modem startup and/or reconnect times, e g , the elimination or abbreviation of the V 8bιs procedure, the elimination or abbreviation of the initial training procedure, and the exchanging of login authentication data earlier in the initialization process (rather than waiting until the full data rate is achieved) In one embodiment, the login authentication data is exchanged while the modem system is in an initially trained mode associated with an intermediate data rate Any one of these (and other) features of the present invention may be implemented in modem system 300

FIG 4 is a flow diagram illustrating portions of a quick startup process 400 performed by two modem devices, and FIG 5 is a timing diagram 500 corresponding to an illustrative quick startup process performed by two modem devices Timing diagram 500 includes acronyms and abbreviations that are often used in the context of V 8, V 8bιs, V 34, V 90, and other data communication protocols The use of such terminology herein is intended to illustrate the concepts of the present invention in the context of one practical embodiment However, the present invention may be employed in any suitable context, and the specific signals, number of sequences, timing of the sequences, data rates, and interaction between the two modem devices shown in FIG 5 are not intended to limit the scope of the invention in any way

Quick startup process 400 is depicted in a manner that indicates tasks associated with a client modem, e g , an analog pulse code modulation modem ("APCM"), and a server modem, e g , a digital pulse code modulation modem ("DPCM") Similarly, timing diagram 500 shows the general sequencing of signals transmitted by an APCM and a DPCM In FIG 5, the arrows between the two major sequences represent responses or interactions between the APCM and the DPCM Quick startup process 400 may begin with a task 402, which causes the APCM to dial the telephone number associated with the DPCM As described above, the call will be established over local loop 112, central office 110. and digital telephone network 108 (see FIG 1) In response to the initial ring tone, the DPCM may be placed in an off hook state (task 404), l e , the DPCM will answer the call Of course, the APCM and the DPCM may be configured to place, answer, and process calls in accordance with conventional telephony protocols Following task 404, a task 406 may be performed to initialize a capabilities exchange protocol such as V 8 or V 8bιs In the embodiment described herein, a capabilities request signal (represented by CRe' in FIG 5) may be transmitted during task 406 The CRe' signal may function to inform the APCM that the DPCM supports the quick connect procedure The CRe' signal may be a modified version of the conventional V 8bιs signaling tones, e g , the V 8bιs tones may be amplitude modulated Alternatively, the frequency associated with a signaling tone may be jittered in a periodic manner or a low-level wideband signal may be added to a tone In this manner, legacy modem systems will recognize the CRe' signal as the normal V 8bιs CRe' signal

In response to the establishment of a call associated with the current communication channel, the APCM may perform a task 408 to suitably transmit a quick connect identifier (QC) to the DPCM In the practical embodiment described herein, the transmission of the quick connect identifier may be prompted in response to the detection of the CRe' signal by the APCM The QC signal is preferably designed such that legacy modems and modems that do not support the quick connect protocol are not adversely affected by the QC signal, l e . the QC signal should be ignored by non-compatible devices (If the APCM does not support the quick connect techniques described herein, then it will not generate the QC signal and the startup will proceed in a conventional manner, as described above in connection with FIG 2) In a preferred embodiment, the QC signal also convevs a signal point identifier that identifies signal points (or one point) for use by the DPCM in a transition sequence (represented by QTS and QTS\ in FIG 5), where the signal points function to highlight, illuminate, or make apparent the digital impairments present in the communication channel Thus the QC signal sequence performs a dual function Assuming that the DPCM also supports the quick connect methodology, it preferably performs a task 410 in response to the reception of the QC signal In connection with task 410, the DPCM transmits a quick connect acknowledgment (represented by the QCA signal in FIG 5) As described above in connection with FIG 2, if the DPCM does not acknowledge the QC signal, or if the APCM somehow fails to receive the QCA signal, then the modem system will proceed with a conventional startup procedure The format, configuration, and processing of the QC and QCA signals may be carried out by the respective portions of the individual modems, as described above in connection with modem system 300 (see FIG 3) If the DPCM and the APCM both support the quick connect technique, then any number of initialization routines may be eliminated, modified, or abbreviated, depending upon the specific application For example, in the context of a V 90 compatible modem system, the transmission of the QC signal may inherently indicate that the APCM is V 90 compliant Similarly the transmission of the QCA signal may inherently indicate that the DPCM is also V 90 compliant Consequently, the modem system may eliminate portions or the entirety of the normal capabilities exchange protocol or protocols, such as V 8 and/or V 8bιs This feature by itself can reduce the startup latency by as much as five seconds (for a typical connection)

It should be appreciated that the quick connect identification and verification scheme described above in connection with task 402 through task 410 can be equivalently applied when the DPCM initiates the call to the APCM Such a situation may arise when, in response to an initial call or request from the APCM, the DPCM calls the APCM to establish the communication channel In this situation, the APCM will transmit the CRe' signal, the DPCM will transmit the QC signal, and the APCM will transmit the QCA signal In contrast to the above description where the APCM initiates the call, the APCM may transmit an additional signal or sequence to suitably identify the transition sequence signal points to the DPCM (rather than embedding the signal points in the CRe' or QCA sequences)

Following task 410 the DPCM mav perform a task 412 to obtain the signal points (or point) for use in a transition (or synchronization) sequence Λ.s discussed above, the QC signal preferably conveys information that identifies signal points that make the presence of robbed bit signaling easily detectable by the APCM The determination of the particular signal points may be carried out by the .APCM, as described above in connection with the digital impairment learning procedure 364 (see FIG 3) This determination mav be based on past analyses of the digital impairments associated with a previous connection over the same channel Task 412 may be performed by processor 312 after the APCM receives the QC signal In response to task 412, a task 414 may be performed such that a suitable transition sequence is transmitted by the DPCM In an exemplary embodiment, the transition sequence includes positive and negative values of the signal points obtained in task 412 Accordingly, the DPCM may utilize the signal points selected by the APCM and a suitable sign pattern (which may be predetermined) to generate the transition sequence The transition sequence is configured and formatted such that the APCM, upon detecting the transmission sequence, can synchronize itself to the subsequent signal or sequence transmitted by the DPCM In this manner, the APCM receiver can obtain its timing from the transition sequence The transmission sequence may be of any predetermined length and have any predetermined sign pattern For example, in the embodiment depicted in FIG 5, the transition sequence is represented by the quick timing sequence (QTS) and QTS\ signals where QTS represents a specific signal point sequence and QTS\ is the same sequence having opposite signs In FIG 5, the QTS sequence is repeated for 810 svmbols while the QTS\ sequence is repeated for 30 symbols

In accordance with one practical embodiment of the present invention, the QTS sequence is formatted such that the period of the QTS root sequence and the period of the robbed bit signaling ("RBS") associated with the network connection have no common denominator (other than one) For example, one suitable QTS root sequence is 0, +A, -A, +A. - A (where A represents a signal point that highlights the presence of RBS Thus, for the embodiment illustrated in FIG 5, this QTS root sequence, which has a period of five, is repeated 162 times while the QTS\ sequence includes six repetitions of the root QTS sequence with inverted signs

For the above example, where the RBS period is assumed to be six, the received transition sequence may be subjected to a 30-pomt discrete Fourier transform ("DFT") to obtain the timing phase of the DPCM In addition, the presence of RBS will be revealed at certain discrete frequencies associated with the DFT result In this manner, timing and RBS information can be extracted from the received transition sequence In addition, the timing phase information is obtained independently from the RBS information The DPCM is preferably configured to transmit a specific signal point sequence during a task 416 The signal point sequence may be considered to be a modified answer tone, as that term is understood by those familiar with modem protocols In FIG 5, this signal point sequence is represented by the ANSpcm signal As depicted in FIG 3, a predetermined ANSpcm sequence 338 may be stored in memory element 320 for transmission by transmitter section 316 In a practical embodiment, the DPCM transmits the ANSpcm signal following the transition sequence This mav be desirable to enable the APCM to anticipate the signal point sequence once it detects the transition sequence In other words, the detection of the transition sequence by the APCM will indicate that the signal point sequence will follow In a preferred embodiment, the ANSpcm signal comprises a sequence of pulse code modulation signal points or a sequence of signal points associated with pulse code modulation signal points For example, the ANSpcm signal may be formatted as a sequence of mu-law or A-law codewords or a sequence of universal codewords (U-codes) The APCM and the DPCM are preferably configured such that the ANSpcm signal is predetermined and known prior to the initiation of quick startup process 400 In an alternate embodiment, a number of different ANSpcm signals mav be suitably stored in lookup tables or the ANSpcm signal may be designed by one of the modem devices and communicated in a suitable manner to the other modem device prior to task 416 For example, the ANSpcm signal may be designed such that the presence of RBS can be easily detected bv the APCM by analyzing the received ANSpcm signal In such an embodiment it may not be necessary for the transition sequence (QTS and QTSY) to identify or highlight the RBS

In the context of V 8 the answer tone is generated as an amplitude modulated 2100 Hz tone In contrast, the present invention utilizes the ANSpcm signal to generate a tone (e g , a 2100 Hz tone) in a digital manner using pulse code modulation signal points In other words, the ANSpcm signal is a digital representation of an analog signal The ANSpcm signal is preferably constructed with known pulse code modulation points such that the ANSpcm signal may be used for purposes other than a mere answer tone In a preferred embodiment, the ANSpcm signal includes many of the available pulse code modulation points associated with the particular telephone network This aspect of the ANSpcm signal is desirable such that the ANSpcm signal mav be used to determine or identif, the characteristics of the current communication channel, particularly digital pads The use of a large number of the possible codewords ensures that the ANSpcm signal will detect digital pads that may merge two input levels into one output level The ANSpcm signal is also configured to provide a tone suitable for disabling the network echo cancelers and disabling the network echo suppressors

If the ANSpcm signal is defined using look-up tables a practical implementation may be difficult where multiple transmit levels are contemplated or required For example, ITU-T Recommendation V 90 allows the DPCM to specify 32 different transmit levels Storing a separate table for each transmit level mav thus lead to excessive memory requirements Accordingly, in an alternate embodiment, a procedure mav be defined for mapping a plurality of codewords associated with one transmit level into a corresponding plurality of codewords associated with the other transmit levels For example, given a table of PCM codewords defining the ANSpcm signal for a level of -0 5 dBmO, the procedure may involve mapping each individual PCM codeword to its corresponding PCM level scaling that level according to the desired transmit level reduction, quantizing the resulting level back to the closest PCM level, and converting to the corresponding PCM codeword Thus a corresponding ANSpcm signal can be constructed using the same mechanism in both the DPCM transmitter and the APCM receiver, hence producing the identical sequence of PCM codewords on each side Note that, in accordance with this embodiment, the quantizing rule should be exact in dealing with "ties" in the quantization 1 e , if two PCM levels are equidistant from the scaled level For example, the rule may dictate that, in case of a tie, the PCM level closer to zero is selected

In accordance with yet another embodiment, the overall method of defining the ANSpcm signal could be based on a predetermined algorithm that generates the sequence of PCM codewords representing the ANSpcm signal For example, the signal could be defined as a collection of tones, 2100 Hz being the strongest, where the tones have predefined amplitudes and initial phases The sum of the tones would then be scaled according to the desired transmit level, and the resulting signal would be quantized to the closest PCM level, again using an exact quantizing rule in case of a tie However, this method would also employ an exact definition of either the sine or cosine function, as well as how many bits were accumulated in summing the tones, to ensure that the calculations proceed in a consistent manner at both ends such that the ANSpcm signal can be properly detected

As described above, the APCM anticipates the transmission of the ANSpcm signal The digital impairments and analog characteristics associated with the communication channel will affect the ANSpcm signal as it is transmitted from the DPCM to the APCM A task 418 may be performed by the APCM to obtain a received sequence that is related to the ANSpcm signal point sequence The APCM mav then perform a task 420 to compare a number of attributes of the received sequence with a number of stored attributes of a previously received sequence associated with a previously established communication channel In an illustrative embodiment, the previously received sequence is a digital impairment learning ("DIL") sequence which is a line probing sequence In this respect, task 420 determines whether a characteristic of the current channel is similar to a corresponding characteristic of a previously established channel In a preferred embodiment, the channel characteristics compared in task 420 are related to the digital impairments in the channel In other words, task 420 validates a current digital impairment channel profile with a stored digital impairment channel profile Task 420 may be performed by a suitable processor element of the APCM (see FIG 3 )

During task 420, any measurable characteristic of the points/levels, any measurable characteristic of the received sequence as a whole, and/or any measurable signal or quantity associated with the points/levels may be analyzed by the APCM For example, any number of individual points or levels contained in the received sequence may be compared to corresponding points or levels stored at APCM (the stored points or levels may be associated with a prior DEL procedure) If the received points/levels "match" the stored points/levels or if the differences between the received and stored points/levels are within a certain threshold, then the APCM mav assume that the current channel attributes match the stored channel attributes (see query task 210 in FIG 2)

The APCM may perform a procedure 421 to suitably obtain and save a number of attributes or characteristics of a previously established connection to the current channel As described above procedure 421 may cause the APCM to store the characteristics of the points/levels contained in a received DIL sequence These past values are thereafter used during task 420 In this respect, procedure 421 may update the previous values with new DIL values after the comparison in task 420 is completed, e g , in response to a subsequent DIL procedure associated with the current connection

As described above in connection with FIG 2, if task 420 determines that the channel characteristics do not sufficiently match, then the modem system may revert to a conventional V 90 startup procedure FIG 5 illustrates that the APCM may fall back into the V 8 protocol and transmit a conventional V 8 call menu (CM) message to the DPCM The conventional V 8 startup for the APCM then follows along a sequence 502 In response to the CM message, the DPCM generates a conventional V 8 joint menu (JM) message and proceeds in accordance with the conventional V 8 initialization (indicated by a sequence 504) For the sake of illustration, quick startup process 400 assumes that task 420 determines that the current communication channel is similar to a previously established communication channel

If the APCM validates the current channel characteristics with a previous channel, then it mav trigger a quick startup routine to further reduce the initialization time associated with the modem system Alternatively, the DPCM may be configured to trigger the quick startup routine Accordingly, a task 422 may be performed, during which the modem system is initially trained (For the sake of clarity and brevity, portions of task 422 and portions of the subsequent tasks mav be performed by both the APCM and the DPCM, quick startup process 400 depicts such combined functionality in the context of single process tasks) Task 422 may cause the APCM and the DPCM to be initialized in response to a number of stored parameters associated with the previously established communication channel As mentioned above, the stored parameters may be related to the initialization or training of the equalizers, echo cancelers, transmit power levels, initial signal point constellations, or the like Task 422 may operate in conjunction with procedure 421, which preferably functions to obtain and store the initialization parameters associated with the previous connection In this respect, procedure 421 may be suitably designed to periodically save such parameters during the normal data mode of the previous connection, after a renegotiation process, or in response to any condition or event associated with the previous communication session Procedure 421 may also be configured such that erroneous settings or initialization parameters are not inadvertently saved

In the context of a tvpical V 90 connection task 422 may be related to a two-point training phase Using the previous parameters the modem system may be able to skip or abbreviate the conventional V 90 Phase 2 probing and ranging procedure and to skip or abbreviate the conventional V 90 Phase 3 digital impairment learning and initial training procedures As shown in FIG 5 the APCM and the DPCM mav each transmit training sequences (represented by the TRN1 signals) during task 422 These training signals may be utilized to adaptivelv adjust the equalizer and echo canceler filter taps and to otherwise facilitate training of the modem system Thus, one of the most time consuming procedures of a V 90 startup (the training of the APCM equalizer) can be performed in an efficient manner that allows ample time for fine tuning and training

In addition to the initial training that occurs during task 422, a task 424 may be performed During task 424, the modem system may conduct error correction and/or data compression protocols In a conventional V 90 modem system, the V 42 Recommendation is followed for purposes of error correction and the V 42bιs Recommendation is followed for purposes of data compression For example, in a normal V 90 operating mode associated with a PPP connection, the V 42 and V 42bιs procedures are performed after final training and before the CHAP PAP authentication procedure V 42 and V 42bιs are performed prior to the CHAP/PAP procedure because the CHAP/PAP procedure is better suited to an "error free" channel In contrast to conventional V 90 systems, task 424 may perform V 42bιs during Phase 3 of the V 90 startup The shifting of V 42bιs forward in the startup process contributes to the reduction in connection time In FIG 5, the XID I signal represents a modified version of the conventional V 42 XID signal For example, the XIDZ signal may utilize a subset of the XID parameters used to negotiate compression and the like Portions of the V 42bιs procedure may also be conducted in connection with various modified signal sequences shown in FIG 5 For example, the CPt_I signal mav represent the conventional V 90 CPt signal combined with one or more V 42bιs signals

In the preferred embodiment, the V 42bιs procedures are performed to provide a substantially "error free" channel Following task 424, a CONNECT message is issued to the host software The CONNECT message indicates that the modem system is ready to transmit data at an initial data rate at this time The CONNECT message may be formatted, generated, and transmitted in accordance with known techniques

In response to the CONNECT message, the host software begins a "simultaneous" upper layer protocol login procedure, e g , a CHAP or PAP procedure (task 428) Task 428 may be initiated automatically by the host software or in response to a user entry The CHAP/PAP data transmission occurs in conjunction with a final training process In the preferred embodiment, the APCM and the DPCM transmit the CHAP/PAP authentication data as scrambled digital data over the communication channel The scrambling of the authentication data enables the modem devices to perform final training on the authentication data In a conventional V 90 modem system, the final training signals are formatted as scrambled "ones" The scrambled ones carry no information, the final training signal is merely utilized as a spectrally white source The present invention leverages the final training signals to carry user data while the modem devices complete the training process Although CHAP PAP data is one preferred form of user data, the present invention is not limited to the transmission or exchange of authentication data In addition, the particular scrambling algorithm may vary from application to application

In FIG 5, the dual function signals are represented by the TRN2A/PPP and TRN2D/PPP signals In this respect, the receiver sections in the modem devices may be trained at an initial data rate during a first time period, e g , during a data phase one, such that they may seamlessly transfer to operating at a final data rate during a subsequent time period, e g , during a data phase two Furthermore, the PPP log-in procedure can be performed at the initial data rate during the first time period rather than after the modem system has been fully initialized

During the initial data rate period, a task 430 may be performed to enable the APCM and the DPCM to exchange constellation parameters and modulation parameters (represented by the CP and MP signals in FIG 5) in a suitable manner Task 430 may be performed in a conventional V 90 manner These parameters may be utilized by the modem devices during the subsequent data mode After the training and authentication procedures are completed, the modem system preferably transitions to a full data rate in a seamless manner A task 432 may be performed to conduct data transmission at the full data rate This period may be referred to as the data phase two Once the modem s stem enters the full data mode, quick startup process 400 ends

In contrast to the conventional V 90 modem startup summarized in Table 1, a modem system according to the present invention may experience a reduced startup latency, as set forth in Table 2 below Notably, the startup time summarized in Table 2 is approximately half of the startup time summarized in Table 1 The considerable reduction in startup latency would be desirable in many situations, particularly in the context of a PPP dial-up internet connection using V 90 or legacy 56 kbps modem systems

Table 2 - Quick V 90 Modem Startup

The techniques of the present invention may be implemented in other contexts to reduce the reinitialization time associated with reconnects after a line corrupting event or a channel interruption For example, many telephone customers subscribe to call waiting, caller identification, and other telephony services However, such services may be disabled or nonfunctional if the telephone line is being utilized for a modem connection If call waiting is not disabled during a modem connection, then the signal tones may interrupt the modem connection If the user decides to answer the waiting line, then the off-hook and on-hook flash may cause the modem system to retrain its receivers or prompt a full reconnect procedure

Rather than perform a time consuming reconnect or retrain procedure, a modem system may be configured to utilize stored analog and digital impairment information, equalizer settings, power levels, echo canceler settings, constellations, and the like Such stored information can be used to immediately reset the modem system parameters if the channel connection is interrupted by a call waiting procedure, by an off-hook condition at an extension telephone device, by a caller identification request, or by any channel corruption event, whether such event is planned or unintentional In this scenario, both the client modem and the server modem may store the relevant system attributes, modem operating parameters, channel characteristics, and/or network characteristics In one practical example, in response to a call waiting tone, the client modem may signal the server to enter a standby mode The server modem can then switch into an FSK mode to suitably detect the Class 2 caller identification information while the server idles If the user wants to answer the second call, then the client modem may periodically transmit standby signals or heartbeat tones to the server to instruct the server to continue holding When the second call ends and the user desires to commence the data call, the client modem would commence a quick reconnect handshaking protocol (described below) On the other hand, if the user wants to terminate the first call, then a clear down message mav be sent (alternatively, the periodic hold signal may end) The quick reconnect handshake causes the modem devices to recall the saved parameters and attributes of the 'held" channel and the saved operating parameters associated with the modem devices as described briefly above in connection with previous channel parameters 342 and 382 With this technique, the modem system can be reconnected in a matter of seconds Thus, the data mode user will not suffer the long reconnect penalty after handling an incoming call waiting or caller identification signal The data mode user, using call waiting in this fashion, would be capable of accepting intermittent interruptions without noticeable delays associated with the modem connection

This feature may be utilized to simulate an "always connected" mode with conventional PPP modem connections For example, pertinent channel compensation information may be periodically saved for a given connection between a client modem and a server modem The client user may answer incoming second line calls while pausing the data mode as described above In addition the data mode mav be gracefully terminated if the client user initiates an outgoing voice call After the voice call terminates, the client modem may re-dial or otherwise re-contact the server modem and establish a quick connection using the stored parameters FIG 7 is a flow diagram illustrating portions of a quick reconnect process 700 performed by two modem devices, and FIG 6 is a timing diagram 600 corresponding to an illustrative quick reconnect process performed by two modem devices Timing diagram 600 may include acronyms and abbreviations that are often used in the context of conventional data communication protocols The use of such terminology herein is intended to illustrate the concepts of the present invention in the context of one practical embodiment However, the present invention may be employed in any suitable context, and the specific signals, number of sequences, timing of the sequences, data rates, and interaction between the two modem devices shown in FIG 6 are not intended to limit the scope of the invention in any way Quick reconnect process 700 may be performed by a modem system after such modem system has established a communication session and, typically, after the modem system has entered a full-rate data mode For purposes of this description it may be assumed that the modem system is configured as described above (or is configured in an appropriate manner to support the various process tasks described below) It mav be assumed that the two modem devices that perform process 700 are compatible with the quick reconnect techniques described herein Thus, process 700 need not perform any verification or signaling to determine whether the quick reconnect procedure can be carried out

Although not a requirement of quick reconnect process 700, the modem system may have been initialized in accordance with the quick startup techniques set forth above Accordingly, process 700 assumes that both modem devices have stored any number of appropriate channel characteristics, receiver parameters, and other information relevant to the initialization training, and synchronization of the modem system As described above, such information may be suitably saved during a startup procedure or periodically during a suitable data mode Process 700 may be utilized to enable the current modem connection to be quickly re-established following a temporary pause in the modem data mode or any interrupting event In this context, a practical system can maintain a communication link or connection between the modem devices while allowing a user of the client modem device to temporarily pause the modem connection (or the modem data communication mode) During the temporary holding period, the user may be able to answer another incoming call in response to a call waiting signal, initiate a new outgoing call or the like, while the client side modem device idles

Quick reconnect process 700 may begin with a task 702, during which a reconnect indication is received by the DPCM (e g , modem 302 shown in FIG 3) The reconnect indication may be generated in response to a request (e g , a user-initiated request) to terminate a temporary pause in the modem communication session For example, a suitable reconnect signal may be generated by the APCM (e g , modem 304) in response to a hook flash initiated by the user of the APCM or in response to an instruction generated bv application software associated with the APCM Alternatively, the APCM or a data access arrangement (DAA) associated with the APCM may generate a reconnect signal in response to a change in line current related to the on-hook status of telephone set Such ne-in-use detection techniques are generally known to those skilled in the art The reconnect indication informs the DPCM that the user desires to re-establish the current modem connection, which has been placed on temporary hold In a practical embodiment, the DPCM receives the reconnect indication and initiates a task 704 in response to the reconnect indication During task 704, the DPCM transmits a suitable reply signal that preferably informs the APCM that the quick reconnect procedure is supported In the illustrative embodiment described herein, such a reply signal mav include a suitable transition sequence as described above Accordingly, quick reconnect process may perform a task 704, which may be similar to task 414 described above in connection with FIG 4 For example, task 704 may cause the DPCM to transmit the QTS signal to enable the APCM to again determine the timing phase of the DPCM (the QTS signal is identified b\ reference number 602 in FIG 6) In addition, the retransmission of the QTS signal enables the APCM to obtain RBS characteristics of the data communication network (if necessary or desirable to do so) It should be noted that, for many practical modem connections, the network connection

(and the associated effects of digital pads and RBS) will remain consistent during the modem hold period Of course there may be some situations where the network connection is cleared down during the modem hold period to conserve network resources In such situations, particularly if the same network connection is not re-established, the digital impairment profile of the network may not remain consistent Furthermore, even if the network characteristics do not change, the APCM may lose its RBS synchronization if the modem connection is put on hold (particularly if the APCM does not receive a signal from the DPCM during the holding period) In this respect, even if the APCM can properly resynchromze itself to the network clock after a holding period, the specific RBS phases may still be unknown Accordingly, quick reconnect process 700 is preferably arranged to contemplate that the network connection and the RBS timing has changed

The reply signal mav also include a suitable signal point sequence that follows the transition sequence Accordingly, following task 704, the DPCM may perform a task 706 to suitably transmit a signal point sequence to the APCM As described above in connection with task 416, the signal point sequence may be considered to be a modified answer tone, e g , the ANSpcm signal (identified by reference number 604 in FIG 6) The ANSpcm signal 604 may be configured as described above, e g , the ANSpcm signal 604 may be suitably formatted to enable the APCM to determine or identify the characteristics of the current communication channel or network, particularly digital pads and/or other digital impairments The ANSpcm signal 604 is also configured to provide a tone suitable for disabling the network echo cancelers and disabling the network echo suppressors

In a practical embodiment, the APCM anticipates the transmission of the ANSpcm signal 604 For example, the APCM may be configured to condition its receiver to receive the ANSpcm signal 604 after it transmits the reconnect indication to the DPCM Accordingly, quick reconnect process 700 may include a query task 708, which preferably determines whether the ANSpcm signal 604 has been received by the APCM and/or whether the DPCM receives a suitable acknowledgment that the APCM received the ANSpcm signal 604 If not, then process 700 may exit and the modem system may proceed with a traditional reconnection routine If query task 708 determines that the ANSpcm signal 706 was properly received, then the APCM may process the received signal as described above to enable the APCM to determine the digital impairments associated with the re-established channel

A task 710 is preferably performed to cause both modem devices to recall and obtain the characteristics and parameters associated with the previous channel connection, I e , the channel before the modem connection was placed on temporary hold Task 710 may cause the DPCM to access previous channel information 342 and may cause the APCM to access previous channel information 384 As described above, this information may include one or more parameters related to the current channel conditions (as previously determined), any number of settings associated with the modem receivers, characteristics of the communication network, or the like Task 710 enables the modem system to quickly retrieve these stored parameters and reset the modem devices in an appropriate manner in lieu of an independent reassessment of the channel and in lieu of a full retraining process Task 710 may be performed by the DPCM once it receives the reconnect identifier from the APCM, while task 710 may be performed by the APCM before it receives the ANSpcm signal 604 If task 710 is performed by the APCM, the APCM equalizers are initialized according to the previous channel information 384 such that the ANSpcm signal 604 can be properly received and analyzed

The DPCM may reacquire its timing synchronization in accordance with any number of techniques, such as the conventional V 34 half-duplex primary channel resynchronization procedure set forth in ITU-T Recommendation V 34 (International Telecommunication Union, September 1994), which is incorporated by reference herein In other words, as shown in FIG 6, the APCM may be configured to transmit a PP signal 610 to enable the DPCM receiver to synchronize its timing recovery and carrier recovery The S and S\ preamble signals (reference numbers 606 and 608, respectively) may be used to initialize an automatic gain control element or the like The Bl signal 612 may be considered to be a preamble sequence that may be employed to initialize the DPCM scrambler, trellis coder, and the like These signals and sequences are set forth in detail in the V 34 Recommendation and will not be described in detail herein

Concurrently, the DPCM may transmit an R signal 616 followed by an R\ signal 618 and a B 1 signal 620 These sequences also serve as suitable preamble sequences that enable the APCM to prepare for the data mode These signals and sequences are set forth in detail in the V 90 Recommendation and will not be described in detail herein

In response to the resynchronization sequences, the modem system enters the data mode and the system can begin transmitting data at the full data rate (task 712) In other words, the data transmission mode is re-established without completely clearing down the previous connection The data mode is identified by sequences 614 and 620 in FIG 6 Notably, in contrast to quick startup process 400, quick reconnect process 700 need not perform a comparison of the channel characteristics (see task 420), an initial training procedure (see task 422), an error correction and data compression procedure (see task 424), a final training procedure (see task 428), an authentication exchange (see task 428), or an exchange of constellation and modem parameters (see task 430) With respect to the PAP/CHAP authentication information, the modem system may be suitably configured to maintain the PPP/TCP/IP protocol layer during the hold period such that the PPP authentication data need not be retransmitted Accordingly, the modem system may re-establish its modem connection without wasting time performing several traditional initialization tasks In a typical practical system, the quick reconnect process can be employed to reestablish the data mode in less than 1 5 seconds

An alternate version of the quick reconnect procedure may employ a timing diagram similar to timing diagram 500 (see FIG 5) However, in such an embodiment, several of the signal segments described above in connection with timing diagram 500 can be reduced in length, thus reducing the conventional reconnect time For example, the various TRN training sequences and the parameter exchange signals may be shortened considerably because they need not convey essential information For practical implementation reasons, it may be desirable to keep the general sequence structure intact in this manner (instead of eliminating segments from timing diagram 500) Indeed, from a software implementation standpoint, segment lengths can be adjusted in a relatively straightforward manner, while the removal of entire segments from an existing protocol may be a time consuming and arduous task Although the reconnect time for such an alternate embodiment may be longer than that described above in connection with timing diagram 600 (e g , up to 2 5 seconds), it is still significantly less than the time required to perform a conventional reinitialization procedure

As mentioned previously, call waiting and related telephony features can be troublesome when the line is being used for a modem connection In response to a call waiting alert signal, the modem connection is often disrupted without the modem devices being aware of the cause of the disruption The call waiting alert signal may cause the modem devices to disconnect or to enter a lengthy retraining mode Furthermore, in many scenarios the consumer is unable to take advantage of the call waiting service itself Generally, the present invention addresses this problem in the following wavs (1) by allowing either modem device to request an immediate clear down in response to a call waiting alert, (2) by allowing a first modem device to request the second modem device to go on-hold, and allowing the second modem device to grant or deny the request, and (3) by allowing either modem device to request a quick reconnect procedure (as described above) With this signaling technique in place, the modem connection can either be cleared down, put on hold, or quickly reconnected in response to an alert signal, e g , a call waiting alert Similarly, if the modem connection is put on-hold, then the same signaling mechanism can be employed to reconnect the modem session after the holding period

Assuming that both end devices (e g , the DPCM and the APCM in a V 90 system) are compatible with the modem-on-hold feature, an appropriate signaling scheme is utilized to enable the end devices to switch operating modes as necessary Although the signaling scheme and various processes are described herein in the context of a modem system having an APCM at the client end and a DPCM at the server or central site end, the present invention is not so limited For example, the techniques described herein may be equivalently applied in the context of a communication session between two client modem devices or in the context of a V 34 modem system FIG 16 is a schematic representation of an exemplary environment in which a modem system 1600 may operate Modem system 1600 generally includes a first modem device 1602, which may be associated with a central site, and a second modem device 1604, which may be resident at a customer site 1670 In the context of a typical V 90 system, first modem device 1602 may be the DPCM and second modem device 1604 may be the APCM DPCM 1602 is coupled to a central office 1606 via a digital link and APCM 1604 is coupled to central office 1606 via an analog link, e g , the local loop It should be appreciated that modem system 1600 may include additional elements and functionality associated with the quick startup routine and/or the quick reconnect procedure described above

FIG 16 also depicts a calling device 1608 (which is capable of placing an incoming call to the customer site), a parallel answer device 1610 located at the customer site and a series answer device 161 1 located at the customer site As shown in FIG 16, parallel answer device 1610 is connected such that it receives the same calls as APCM 1604 in a concurrent manner In contrast, series answer device 1611 is connected such that APCM 1604 routes calls to it, APCM 1604 may control or regulate the call traffic to and from series answer device 1611 in a conventional manner A call may be established between calling device 1608 and answer devices 1610 and 1611 via central office 1606, and a modem connection may be established between DPCM 1602 and APCM 1604 via central office 1606

Generally, the modem system is configured to support a signaling mechanism that responds to call waiting and other situations that may call for an interruption in the modem connection For example, APCM 1604 mav transmit a suitably formatted signal to initiate a modem-on-hold state, DPCM 1602 mav transmit a different signal to acknowledge the modem-on-hold request APCM 1604 may transmit yet another signal to request that a quick reconnect procedure (as described above) be initiated, and either modem device may transmit a signal that represents a clear down request For the sake of clarity and brevity, FIG 16 depicts APCM 1604 and DPCM 1602 in a manner that relates to the example processes described herein In practical embodiments, each of the modem devices may be capable of functioning as a transmit or receive modem, and each of the modem devices mav be capable of originating the various signals described herein DPCM 1602 includes a transmitter section 1612 and a receiver section 1614, both of which may be configured in accordance with conventional technologies and in accordance with the above description of modem system 300 (see FIG 3) DPCM 1602 is capable of transmitting a number of signals, sequences, and tones during initialization procedures, the data mode, the hold mode, and transition modes As described above, DPCM 1602 may be configured to transmit a suitable transition sequence 1616 and a characteristic signal point sequence (such as the ANSpcm signal 1618) associated with a quick startup routine or a quick reconnect procedure During the data mode DPCM 1602 transmits data 1620 in accordance with a suitable data transmission scheme

DPCM 1602 is also capable of transmitting a number of signals that may be received by APCM 1604 and/or by central office 1606 For example, DPCM 1602 is capable of transmitting an "A" tone 1622 and a "B" tone 1624 as described herein In one practical embodiment. "A" tone 1622 is a 2400 Hz tone and "B' tone 1624 is a 1200 Hz tone (as set forth in ITU-T Recommendation V 34) Of course, the modem devices may generate and process any suitable tones or signals in lieu of (or in addition to) these predefined tones DPCM 1602 is also configured to transmit a number of additional signals associated with the initiating of a modem-on-hold mode, the reconnection of a modem session after a holding period, and the clearing down of a modem connection For example, DPCM 1602 may be capable of transmitting a modem hold request 1626, a modem hold acknowledgment 1628, a quick reconnect request 1630, and a disconnect signal 1632 (referred to herein as "modem status signals") The format and function of these signals are described in more detail below

DPCM 1602 may also include a signal detection element 1634, which may employ any number of known techniques to detect, analyze, and interpret control signals, requests and tones transmitted by APCM 1604 and/or by central office 1606 For example, signal detection element 1634 may utilize a conventional tone detector and/or a conventional V 34 or V 90 differential phase-shift keying (DPSK) receiver configured to detect and distinguish the different signals described herein

For purposes of the signaling scheme described herein, APCM 1604 is preferably configured in a manner similar to DPCM 1602 In other words, APCM 1604 is capable of transmitting an "A" tone 1642, a "B" tone 1644 a modem hold request 1646, a modem hold acknowledgment 1648, a quick reconnect request 1650, and a disconnect signal 1652 In addition, APCM 1604 may be configured to generate a caller ID tone 1654 that informs central office 1606 that the customer site supports a caller ID feature (as depicted by the caller ID component 1656) In accordance with current standards, caller ID tone 1654 is a DTMF "D" tone having a length of approximately 55-65 milliseconds Of course, APCM 1604 transmits data 1658 during the data mode

As described above in connection with DPCM 1602, APCM 1604 preferably includes a signaling detection element 1660 that enables APCM 1604 to receive, detect, and analyze the various signaling tones and sequences transmitted by DPCM 1602 In this manner, both APCM 1604 and DPCM 1602 are capable of receiving the signals and are capable of switching operating modes in response to the particular signal or signals that are received

Central office 1606 is configured in a conventional manner to perform circuit switching associated with modem, voice, and facsimile calls Central office 1606 may support any number of customer sites and central office 1606 may be operatively coupled to any number of other central offices, central site modems, or the like As described briefly above, APCM 1604, answer device 1610, and caller ID component 1656 may reside at customer site 1670 Accordingly, APCM 1604, answer device 1610, and caller ID component 1656 are all supported by central office 1606 Central office 1606 includes a suitable switching fabric 1672 for routing calls between the appropriate parties For example, switching fabric 1672 may switch to a first state to establish a modem connection between DPCM 1602 and APCM 1604 and to a second state to establish a voice connection between calling device 1608 and answer device 1610 Furthermore, switch fabric 1672 may be capable of temporarily interrupting a connection to impress control signals, data, or tones onto the current circuit or line In this respect, central office 1606 may transmit a number of ring signals 1674, alert signals 1676, caller ED data 1678, and other information depending upon the particular situation For example, in accordance with current methodologies, central office 1606 may temporarily interrupt a voice call and transmit a call waiting alert signal 1676 to the customer site 1670 If the customer accepts the incoming call, then switch fabric 1672 may be reconfigured to route the incoming call the customer site 1670 while the original call is placed on hold As described in more detail below, a similar routine may be employed to place modem calls on hold

As mentioned previously, the signaling scheme preferably employs Phase 2 signaling tones that are also used by conventional V 34 and V 90 modem systems In addition, the signaling scheme uses DPSK transmission techniques, which allows the signaling to integrate in a seamless manner with V 34 and V 90 retraining procedures The signals are configured such that they can be detected bv either a V 34/V 90 DPSK receiver or by a relatively simple tone detector In one practical embodiment, modem hold requests, modem hold acknowledgments, quick reconnect requests, and disconnect signals are preceded by a period (e g , at least 50 milliseconds) of either tone A or tone B This technique leverages the use of the A and B tones, which are employed by conventional V 34 and V 90 modem systems, and takes advantage of the modulation scheme that is already in use by the modem system Thus, because DPCM 1602 will typically be conditioned to receive DPSK signals, the signaling mechanism is easy to implement

The modem status signals that follow the A or B tones are preferably transmitted as DPSK signals based on a repeated bit pattern In the preferred embodiment, a modem status signal is a DPSK signal associated with eight repetitions of a four-bit pattern, where different patterns correspond to different modem status signals The use of a four-bit pattern is desirable to enable the use of a simple tone detector for signaling detection elements 1634 and 1660, shorter bit patterns result in a fewer number of frequency components associated with the DPSK signal Consequently, the signal detection scheme need not employ a complex processing routine that analyzes a large number of frequencies for spectral content Illustrative bit patterns for the different modem status signals are set forth in Table 3 below

Table 3 - Modem Status Signals The particular bit patterns are preferably selected such that the resultant DPSK signal is distinguishable over DPSK signals that are "reserved" for use in the context of other data communication protocols For example, a DPSK pattern of all zeros is equivalent to the A or B tones, and a DPSK pattern of all ones is equivalent to the V 34 INFOMARK signal In addition, the particular bit patterns may be suitably selected such that the resultant DPSK signal is easy to detect by a tone detector For the example bit patterns set forth in Table 3 the modem status signals will have the frequency content listed in Tables 4 and 5 below, where the frequencies are in Hertz, an "X" indicates spectral content greater than a threshold level, and a slash indicates spectral content that is lower than the threshold level For the example DPSK bit patterns shown in Table 3, a lower spectral energy component is at least 8 dB down from a higher spectral energy component at the same frequency Consequently, the different modem status signals can be distinguished notwithstanding the existence of some shared frequency components

Table 4 - Frequency Components for Modem Status Signals (APCM)

Table 5 - Frequency Components for Modem Status Signals (DPCM)

J . The different frequency ranges employed by the APCM and DPCM are related to an exemplary application where different carriers are used by the two modem devices For example, in a conventional V 90 system, the DPCM uses signaling near 2400 Hz (tone "B" and the DPSK carrier), while the APCM uses signaling near 1200 Hz This feature was deπved from the conventional V 34 scheme where the calling modem uses signaling near 1200 Hz and the answer modem uses signaling near 2400 Hz Consequently, the two spectral patterns are the same but for the shift between 1200 Hz and 2400 Hz This methodology ensures that the end devices can properly detect the signals even where both ends are transmitting the same type of signal In a practical system, the modem status signal detection need not detect the entire

"spectral fingerprint" for the given signals Rather, signal detection elements 1634 and 1660 may be configured to detect and analyze a distinctive number of the spectral components for purposes of indicating a match For example, as shown in Table 4, if a signal contains relatively high spectral energy at 1050 Hz and 1350 Hz, then the signal may be a disconnect signal or a modem hold request Accordingly, the signal detection routine will continue to analyze the signal for spectral content at 900 Hz, 1200 Hz and/or 1500 Hz and make the appropriate decision

FIG 8 is a timing diagram that depicts the situation where a current modem connection is interrupted by a call waiting indication and the modem connection is placed on hold while the incoming call is answered by the client end FIG 8 is applicable regardless of whether customer site 1670 employs parallel answer device 1610 or series answer device 161 1 The progression of signals, sequences, tones, commands, and the like are shown with respect to an APCM. a DPCM, and a central office (the central office may be associated with signals to the APCM and signals to the DPCM) For convenience, the process associated with FIG 8 is described herein in the context of modem system 1600

During the data mode, central office 1606 temporarily interrupts the modem connection and sends an alert signal 802 to APCM 1604 The alert signal may be a conventional call waiting alert and it may include a component that is audible to humans (e g , an audio tone) and a component that is detectable by data communication devices or machines In accordance with most call waiting protocols, the alert signal components are transmitted in series In response to alert signal 802, APCM 1604 may send a DTMF tone 804 to request caller ID information from central office 1606 As described above, tone 804 may be a short burst of a DTMF "D" tone having a duration of about 55-65 milliseconds Assuming that central office 1606 receives and recognizes DTMF tone 804, it will format and transmit the caller ED data 805 back to the customer site 1670 As shown in FIG 16, the caller ID data 805 (represented by reference number 1678 in FIG 16) may be received and processed in a suitable manner for display or analysis by caller ED component 1656

In response to the switching out of APCM 1604 by central office 1606, DPCM 1602 begins a retrain procedure by transmitting an appropriate signal, e g , a "B" tone 806 In a practical application, the "B" tone 806 is usually transmitted while the caller ID request 804 and caller ID data 805 is being received, processed, and transmitted by central office 1606 The "B" tone 806 is continuously transmitted while DPCM 1602 waits for APCM 1604 to reply with an "A" tone 808 APCM 1604 may transmit the "A" tone 808 if it receives the "B" tone 806 from DPCM 1604 As mentioned above, the "A" tone 808 is preferably transmitted for at least a minimum duration, e g , 50 milliseconds, to give DPCM 1602 the opportunity to receive it If DPCM 1602 does not receive an "A" tone 808 within a specific time period, then it may eventually disconnect itself

Assuming that the user of APCM 1604 desires to answer the incoming call, then a modem hold request 810 is transmitted following the "A" tone 808 Modem hold request 810 may be prompted automatically by a suitable device resident at the customer site 1670 or it may be prompted in response to a user command Modem hold request 810, which may be formatted as described above, is preferably transmitted for at least a minimum period of time In one practical embodiment, modem hold request 810 is transmitted for approximately 53 milliseconds (all of the modem status signals described herein may have a similar minimum duration) In contrast to a conventional V 34 or V 90 modem system, an actual retraining procedure is not performed upon receipt of the "A" tone 808 by DPCM 1602 Rather, in response to modem hold request 810, DPCM 1602 may transmit a modem hold acknowledgment 812 for a minimum period of time, e g , approximately 53 milliseconds After DPCM 1602 transmits modem hold acknowledgment 812, it preferably continues to transmit the "B" tone 806 while it maintains a hold state In response to modem hold acknowledgment 812, APCM 1604 may generate a suitable flash signal 814 to instruct central office 1606 to switch out the modem connection and to switch in the incoming call 816 In addition, the handset (or other suitable answer device) begins to receive the incoming call, APCM 1604 may be configured to route the incoming signal to parallel answer device 1610 or serial answer device 1611 in an appropriate manner In addition, APCM 1604 may be placed in an idle or "on-hook" state while the handset is connected (during period 818) Accordingly, the user at customer site 1670 may proceed with the incoming call 816 while DPCM 1602 remains on hold The modem connection may be re-established by way of a quick modem reconnect procedure (described below)

FIG 9 is a timing diagram that depicts a situation where DPCM 1602 is to be reconnected in response to the termination of the incoming call The process shown in FIG 9 assumes that (1) DPCM 1602 is in a hold state, (2) answer device 1610 is connected in parallel with APCM 1604, and (3) answer device 1610 terminates the incoming call, e g , answer device 1610 is placed "on-hook" before calling device 1608 is placed "on-hook" For purposes of this description, the parallel connection means that APCM 1604 and answer device 1610 receive the same signals from central office 1606 in a concurrent manner In response to the termination of the incoming call, central office 1606 will detect the

"hang up" in a conventional manner e g , using well known line detection techniques Eventually central office 1606 switches out or disconnects the incoming call, switches in DPCM 1602, and generates a suitable signal, e g , a ring signal 902 Ring signal 902 serves to alert the user at customer site 1670 that the original call is still holding and is ready to be reconnected In response to ring signal 902, APCM 1604 is placed "off-hook" such that it can again receive signals from central office 1606 Thus, ring signal 902 may inform APCM 1604 that the incoming call has been cleared and/or that APCM 1604 may proceed with a modem reconnect procedure As described above in connection with FIG 8, APCM 1604 generates an "A" tone 904 (for at least 50 milliseconds) in response to the detection of a "B" tone 906 Following the "A" tone 904 APCM 1604 may transmit a quick reconnect request 908 to initiate a quick reconnect procedure (as described above in the context of FIGS 6 and 7 Accordingly, in response to the detection of quick reconnect request 908, DPCM 1602 preferably transmits a QTS signal 910 followed by an ANSpcm sequence 912 The characteristics, format, and function of QTS signal 910 and ANSpcm sequence 912 are as described above Assuming that both modem devices support the quick reconnect feature described above, the held modem connection may be re-established in a relatively short period of time

FIG 10 is a timing diagram that depicts the situation where the incoming call is terminated before parallel answer device 1610 is placed "on-hook" In this scenario, when the termination of the incoming call is initiated by the calling device 1608, central office 1606 will reconnect the customer site 1670 to the original call (which is a modem connection in this example) Consequently, the "B" tone transmitted by DPCM 1602 will again be made available at APCM 1604 Regardless of whether APCM 1604 is currently in an "on-hook" or an "off- hook" state, it preferably detects that DPCM 1602 has been reconnected It should be appreciated that APCM 1604 mav employ any number of known techniques (which can vary depending upon the specific implementation) to detect the reconnection For example, DPCM 1602 may detect the "B" tone from DPCM 1602, it may automatically react after a predetermined timeout period, or it mav utilize hne-in-use techniques to sense the termination of the incoming call Once the two modem devices have resumed communicating with one another, the quick reconnect routine proceeds as described above in connection with FIG 9

With respect to the situation depicted in FIG 10, it may be necessary to have APCM 1604 respond within certain time periods to ensure that central office 1606 does not consider the reconnect attempt to be a hook flash or a disconnect For example, in a preferred embodiment, APCM 1604 is configured to respond to the termination of the incoming call within 200 milliseconds such that central office 1606 does not interpret the delay as a conference call request (which may cause DPCM 1602 to be placed on hold) or a disconnection (which may cause a clear down of the connection) The particular time periods may be selected in accordance with any suitable telecommunication recommendation, standard, or operating protocol, such as the BELLCORE Technical Reference GR-506-CORE (related to general telecommunication signaling) and the BELLCORE Technical Reference TR-NWT-000575 The contents of these references is incorporated by reference herein

In general, any of the procedures utilized in the context of a system using parallel answer device 1610 may also be used in the context of a system using series answer device 1611 However, the converse may not always be true For example, FIG 1 1 is a timing diagram that depicts the situation where the incoming call is terminated by series answer device 1611 As described above, a communication line at customer site 1670 initially provides APCM 1604 with a signal from central office 1606, and APCM 1604 routes the signal to answer device 1610 In most practical applications APCM 1604 will remain "off-hook" even if it is merely routing the call to series answer device 161 1 Accordingly, APCM 1604 is capable of monitoring the line for the presence of a "B" tone or a suitable signal associated with DPCM 1602 In this scenario, if the incoming call is terminated (by calling device 1608 or by series answer device 1611), APCM 1604 is capable of receiving signals from central office 1606 Furthermore, central office 1606 responds to the detection of the call termination by switching DPCM 1602 to communicate with the customer site 1670 Thus, if the "B" tone is detected by APCM 1604, it can immediately decouple the series answer device 161 1 Once the two modem devices resume the communication session, the quick reconnect routine proceeds as described above in connection with FIG 9

FIG 12 is a timing diagram that depicts the situation where DPCM 1602 responds to a modem hold request with a clear down instruction (FIG 12 is applicable to a system that uses either serial answer device 1611 or parallel answer device 1610) Up to the point where a modem hold request 1202 is transmitted from APCM 1604 to DPCM 1602, the process is similar to that described above in connection with FIG 8 In contrast to the scenario where DPCM 1602 acknowledges modem hold request 1202, the situation depicted in FIG 12 calls for the transmission of a disconnect signal 1204 from DPCM 1602 DPCM 1602 may transmit disconnect signal 1204 after contemplating or considering any number of operating parameters, e g , the current call traffic, the functional capabilities of DPCM 1602, the channel characteristics, or the like

After DPCM 1602 transmits disconnect signal 1204, it idles or waits without transmitting any meaningful signals In response to disconnect signal 1204, APCM 1604 clears down the modem connection in an appropriate manner If central office 1606 does not detect activity from APCM 1604 after a suitable timeout period, e g , 1550 milliseconds, then it may assume that APCM 1604 has been disconnected Thereafter, central office 1606 switches out DPCM 1602 and generates ring signals 1206 and caller ID data 1208 to customer site 1670 such that the incoming call can be answered DPCM 1602 may clear down its modem connection after a suitable timeout period, e g , two seconds, during which it receives no signals from APCM 1604 Accordingly, DPCM 1604 will typically hang up once central office 1606 begins generating ring signal 1206 As described above, prior to clear down, APCM 1604 and/or DPCM 1602 may save any number of relevant operational parameters to facilitate a quick startup for subsequent connections

Under certain conditions, the end user may wish to immediately terminate the modem connection and accept an incoming call FIG 13 is a timing diagram that depicts a situation where, in response to an alert signal 1302, .APCM 1604 transmits a disconnect signal 1304 rather than a modem hold request FIG 13 is applicable to a system that uses either serial answer device 1611 or parallel answer device 1610 APCM 1604 may generate disconnect signal 1304 in response to a user command or automatically in accordance with a predetermined protocol or setting The progression of signals and operations associated with FIG 13 is substantially similar to the progression associated with FIG 12 However, unlike the process depicted in FIG 12 APCM 1604 transmits disconnect signal 1304 to DPCM 1602 FIG 14 is a timing diagram that depicts the scenario where, in response to an alert signal 1401, APCM 1604 prompts a quick reconnect procedure and ignores the incoming call FIG 14 is applicable to a system that uses either serial answer device 161 1 or parallel answer device 1610 Such a situation may occur when the quality of the modem connection is important when the end user does not want to be disturbed by incoming calls, and/or if the modem connection is severely affected by the alert signal 1401 Furthermore, such a situation may occur in response to the caller ED data, 1 e , the answering party may choose to ignore incoming calls from certain calling parties Up to the point where an "A" tone 1402 is transmitted, the procedure of FIG 14 is similar to the procedure of FIG 8 Following the transmission of "A" tone 1402. APCM 1604 generates a quick reconnect request 1404, which is eventually received by DPCM 1602 In response to quick reconnect request 1404, DPCM 1602 may transmit a QTS signal 1406 followed by an ANSpcm signal 1408 to facilitate the quick reconnect routine (as described above in connection with FIGS 6 and 7) It should be noted that APCM 1604 may alternatively transmit a suitable modem status signal, e g , a phase reversal, that indicates a full retrain procedure rather than a quick reconnect procedure In such an embodiment, the retrain procedure would proceed in a conventional manner

Under some conditions, DPCM 1602 may not "automatically" enter the initial retrain mode in response to an alert signal In other words, DPCM 1602 may continue transmitting data as though no interruption has occurred FIG 15 is a timing diagram that illustrates this situation (FIG 15 is applicable to a system that uses either serial answer device 1611 or parallel answer device 1610) As described above in connection with FIG 8, APCM 1604 may respond to an alert signal 1502 by transmitting a DTMF "D" tone 1504 (associated with a caller ID request) during an interruption in the data mode Unlike the situation of FIG 8, where DPCM 1602 begins to transmit a "B" tone as a result of the interruption, DPCM 1602 continues to transmit data 1506 to APCM 1604 When APCM 1604 is reconnected by central office 1606, it preferably transmits an "A" tone 1508 for a suitable time period to allow DPCM 1602 to respond with a "B" tone 1510 When APCM 1604 detects the "B" tone 1510 from DPCM 1602, it then follows the "A" tone 1508 with a SIGNAL_Λ 1512, where SIGNAL^ 1512 may be a modem hold request, a quick reconnect request, or a disconnect signal In response to SIGNAL _Λ 1512, DPCM 1602 transmits a SIGNAL_D 1514, where SIGNAL_D may be a modem hold acknowledgment, a short period of silence followed by a QTS signal and an ANSpcm sequence, or a disconnect signal In this manner, the different situations described above can be handled even though DPCM 1602 does not initially enter the retrain mode with the transmission of a "B" tone The signaling routines and procedures described above in connection with FIGS 8-16 can be equivalently applied to accommodate various requests that originate at customer site 1670 For example, the user of APCM 1604 may desire to place a current modem connection on hold, to prompt a quick reconnect, or to prompt a full retrain in an independent manner In one practical embodiment, the modem hold request and modem hold acknowledgment signals can be incorporated into the conventional Phase 4 CP and MP sequences Accordingly, if either modem device wants to place the other modem device on hold (e g , for three-way calling), then the requesting modem device can perform a rate renegotiation and transmit the hold signal in an appropriate manner This technique may be performed in a similar manner as the conventional V 34 and V 90 clear down procedure, where a special code (data rate = 0) is used to indicate a clear down However, the modem hold signaling technique may utilize a different bit combination or leverage a number of reserved bits

In response to such a user request, APCM 1604 may generate an "A" tone followed by an appropriate modem status signal (e g , a modem hold request, a quick reconnect request, or the like) for receipt bv DPCM 1602 As described above in connection with FIG 15, DPCM 1602 may then respond with a "B" tone followed by an appropriate status signal reply (e g , a modem hold acknowledgment a QTS signal, or the like) In this manner, the techniques of the present invention can be applied in any number of situations unrelated to a call waiting alert, a line interruption, or a line corrupting event In accordance with another embodiment of the present invention, a signaling scheme obviates the need of the remote modem (usually an ISP server) to change its ATS 10 default, which typically occurs with previous MOH specifications More particularly, it usually takes several seconds for the user to respond after a call-waiting application pops up a message box According to previous MOH specifications, during that time the client modem is silent Whenever the server modem detects a carrier-loss, it will not know whether the client has disconnected or is merely waits for the user decision regarding the call-waiting Therefore, in order to prevent disconnecting everv user that gets a call-waiting, the server typically waits Y seconds before it makes a carrier-loss decision (where Y is significantly larger than the usual 1 4sec default) The price is unnecessary time spending whenever the user disconnects abruptly In accordance with one aspect of the present invention, the ambiguous carrier-loss period is reduced to the minimum of about 0 9 seconds by sending a simple alert to the server, and then continues in a manner similar to the methods disclosed in above The alert can be any agreed upon signal, such as a tone or bits over DPSK

In general a Modem Hold Alert signal (MHA) is used to inform the remote modem about the reception of call-waiting alert The MH signal is then used to request that the Remote Modem go into "hold" state The MH signal is used to indicate that the Call Waiting user has decided to answer the incoming call and informs the Remote Modem that a disconnection procedure will commence The Fast Reconnect signal (FRR) is used to request the Remote Modem to re-establish a data connection by using the Quick Connect procedure The MH signal is used to acknowledge the MHA message from the APCM and to indicate that the Remote Modem will agree to stay on hold if the Call Waiting Customer wishes to switch to the incoming caller The DC signal is used to acknowledge the MHA message from the APCM and to indicate that the Remote Modem wishes will disconnect if the Call Waiting Customer wishes to switch to the incoming caller Tone B is defined in ITU Recommendation V 34 In the exception of APCM connected in V 34 originate mode, this signal should be Tone A as defined in ITU Recommendation V 34 During the period when the network switch indicates to the call-waiting customer that an incoming call is being received and optionally sends CID, the remote modem receives silence from the switch In order to avoid disconnection bv the DPCM due to its detection of carrier loss, the APCM should inform the remote modem as soon as possible about the reception of call-waiting alert The remote modem has three options when the APCM indicates that an incoming call is being received (1) The remote modem agrees to stay on hold if the APCM wishes to switch to the incoming caller, (2) The remote modem will disconnect if the APCM wishes to switch to the incoming caller, or (3) The remote modem does not support MOH signaling and expects the APCM to ignore the incoming caller and re-establish a V 34 or V 90 connection using the retrain procedure

After reception of a response 1 from the remote modem, the APCM has three options

(a) The APCM wishes to switch to the incoming caller and place the remote modem on hold,

(b) The APCM wishes to switch to the incoming caller and disconnect the remote modem, or

(c) The APCM wishes to ignore the incoming caller and re-establish a V 34 or V 90 connection with the remote modem using the Quick Connect procedure

Alternatively, after reception of a response 2 from the remote modem, the APCM has two options, l e , options (a) and (b) above

After reception of a response 3 from the remote modem, the APCM has two options (a) The APCM wishes to switch to the incoming caller and let the remote modem disconnect, or (b) The APCM wishes to ignore the incoming caller and re-establish a V 34 or V 90 connection with the remote modem using the retrain procedure

After reception of the network Call Waiting signaling and decoding the network caller ID information, if any, the APCM modem will send A for a minimum of 50 ms and condition its receiver to detect Tone B from the DPCM If Tone B is detected, the APCM will transmit MHA and condition its receiver to detect a DPSK signal from the DPCM If the APCM detects MH or DC, the APCM will stay silent until it sends MH, DC or FRR This procedure is shown in Figures 17-19

If the APCM does not detect a valid DPSK signal from the DPCM within t ms, the APCM shall attempt to retrain the DPCM according to Recommendation V 34 or V 90, depending upon which mode was previously established

After detecting the loss of signaling from the APCM, the DPCM starts a timer, t, for 1400 ms, and begin transmitting Tone B The DPCM shall configure its receiver to detect both Tone A and a DPSK signal Referring now to Figure 17 if the DPCM detects MHA 1702, timer t shall stop and timer .2 shall commence If MHA 1702 is not detected within / ms, the DPCM shall disconnect If the server wishes to allow a possible host request to go into "hold" mode, the DPCM shall transmit MH 1704

Referring to Figure 18 if the server wishes to disallow a possible hold request, the DPCM shall transmit DC 1804 after receiving MHA 1802 In any event, after finishing MH or DC, the DPCM shall transmit B (1706 and 1806), and condition its receiver to detect a DPSK signal

The APCM can request the remote modem to go on hold only if the Remote Modem agreed to stay on hold while the APCM switches to the incoming caller Referring again to Figure 17, after reception of the DPSK signal from the DPCM, and within y seconds the APCM modem will transmit MH 1708

Next, zz msec after ending the MH 1708 transmission the APCM will flash its relay (1710) which causes the network to switch the connection over to the incoming caller (1712) After detecting MH 1708 from the APCM, the DPCM shall put itself in 'hold" mode In another scenario, the APCM requests that the modem connection be cleared down

This request can be sent whether the Remote Modem agreed to stav on hold or not Referring to Figure 18 after reception of the DPSK signal from the DPCM, and within y seconds, the APCM modem will transmit DC 1808 Then, zz msec after ending the DC 1808 transmission, the APCM shall go on-hook for a predetermined minimum (e g , 1 566 seconds) to signal a disconnect to the network switch After detecting MH from the .APCM the DPCM shall wait x msec and then disconnect

Referring not to Figure 19, in the case where the APCM requests FRR, the APCM requests that the modem connection be re-established using the Quick Connect method After reception of the DPSK signal from the DPCM, and within y seconds, the APCM modem will transmit FRR 1902 After ending the FRR 1902 transmission the APCM shall condition its receiver to detect a QTS signal (1904)

If the APCM detects QTS 1904, the APCM shall continue with the Quick Connect handshake as described in the Quick Connect specification (or any other suitable handshake method) If the APCM does not detect QTS 1904 from the DPCM within x ms it will try to reestablish a V 34 or V 90 connection using the retrain procedure

After detecting FRR from the APCM, the DPCM shall wait a suitable amount of time, e g , 70 msec, and then re-establish the data connection If the server wishes to allow the re- estab shment of the data connection via Quick Connect the DPCM shall continue according to the Quick Connect specification Otherwise the DPCM shall continue according to the retrain procedure in ITU Recommendation V 90 or V 34

In summarv in accordance with this embodiment, the remote DPCM modem will, in response to a call-waiting alert, send an agreed upon signal that states whether it agrees or refuses to stay on hold if the customer switches to the incoming call This signal can be used to inform the Call Waiting customer how long the remote modem will wait in the "on hold" state This avoids the situation where the APCM sends MHA without knowing whether the DPCM will or will not hold This also allows the remote modem to support Modem on Hold specifications without needing to sacrifice its configuration of period length before carrier loss decision In summary, the present invention provides techniques to reduce the initialization period and reconnect period normally associated with a V 90 modem system and to accommodate a Modem on Hold configuration The quick startup and quick reconnect techniques leverage the known channel characteristics of a previous connection to reduce the training time associated with subsequent attempts to establish the same connection Although not limited to any specific modem application, the quick startup procedure may be used to eliminate portions of the initialization protocols or processes normally employed by a 56 kbps modem e g , V 8bιs V 8, digital impairment learning, initial training, probing and ranging, or the like In addition, the quick startup technique may perform certain operations at a different time or in a different order in comparison to a conventional modem startup technique The present invention has been described above with reference to a preferred embodiment However, those skilled in the art will recognize that changes and modifications may be made to the preferred embodiment without departing from the scope of the present invention These and other changes or modifications are intended to be included within the scope of the present invention, as expressed in the following claims

Claims

What is claimed is

5 1 A signaling method for changing operating modes in a data communication system having a first device configured to communicate with a second device via a communication link, said method comprising the steps of transmitting a modem status signal from said first device to said second device, said modem status signal being configured as a differential phase-shift keying (DPSK) signal 10 based on a predetermined bit pattern, detecting said modem status signal at said second device, and initiating a procedure associated with a change in the operating mode of said data communication system in response to said modem status signal

15 2 A signaling method according to claim 1, wherein said modem status signal represents a modem hold request

3 A signaling method according to claim 1, wherein said modem status signal represents a modem hold acknowledgment n 0

4 A signaling method according to claim 1, wherein said modem status signal represents a quick reconnect request

5 A signaling method according to claim 1 wherein said modem status signal 25 represents a disconnect signal

6 A signaling method according to claim 1, wherein said modem status signal is configured as a DPSK signal based on a repetitive sequence of a predetermined bit pattern

0 7 A signaling method for changing operating modes in a data communication system having a first device configured to communicate with a second device via a communication link, said method comprising the steps of receiving a modem status signal in response to a change in the operating mode of said data communication system, detecting said modem status signal by analyzing a number of spectral components associated with said modem status signal, and initiating a procedure associated with said change in the operating mode of said data communication system in response to said modem status signal

8 A signaling method according to claim 7, wherein said modem status signal is configured as a differential phase-shift keying (DPSK) signal based on a predetermined bit pattern, and said detecting step is performed by a tone detector

9 A signaling method according to claim 7, wherein said modem status signal is configured as a differential phase-shift keying (DPSK) signal based on a predetermined bit pattern, and said detecting step is performed by a DPSK receiver

10 A signaling method according to claim 7, further comprising the step of receiving an A-tone prior to receiving said modem status signal

1 1 A signaling method for changing operating modes in a data communication system having a first device, resident at a client site, configured to communicate with a second device via a communication link, said method comprising the steps of receiving, at said first device, an indication related to the termination of an incoming call directed to said client site, transmitting a modem status signal from said first device to said second device, said transmitting step being performed in response to said receiving step, detecting said modem status signal with said second device, and initiating, in response to said detecting step, a quick reconnect procedure to recall a stored operating parameter for said data communication system, said stored operating parameter being associated with a previous communication session between said first and second devices

12 A data communication device comprising a receiver configured to receive a first indication related to an interruption in a current data mode, a transmitter configured to transmit a first modem status signal to a remote data communication device in response to said indication, said first modem status signal being formatted as a differential phase-shift keying (DPSK) signal based on a first predetermined bit pattern, wherein said receiver is further configured to receive a second modem status signal indicative of a modem hold mode, said second modem status signal being formatted as a DPSK signal based on a second predetermined bit pattern

13 A data communication device according to claim 12, wherein said receiver is further configured to receive a second indication related to the termination of an incoming call, said transmitter is further configured to transmit a third modem status signal to said remote data communication device in response to said second indication, said third modem status signal being formatted as a DPSK signal based on a third predetermined bit pattern, and said third modem status signal is formatted to initiate a reconnect procedure to recall a stored operating parameter for said data communication system, said stored operating parameter being associated with a previous communication session conducted by said data communication device

14 A method for reducing startup latency associated with a data transmission system having a first device configured to communicate with a second device over a communication channel, said method comprising the steps of establishing a call between said first device and said second device, determining whether a characteristic of said communication channel is similar to a corresponding characteristic associated with a previously established communication channel, and initializing at least one of said first and second devices in response to a number of stored parameters associated with said previously established communication channel said initializing step being performed if said determining step determines that said characteristic is similar to said corresponding characteristic

15 A method according to claim 14, further comprising the step of ascertaining, for said call, whether said first device and said second device support a fast connect protocol, said ascertaining step being performed prior to said determining and initializing steps 16 A method according to claim 14, wherein said determining step comprises the steps of transmitting a signal point sequence from said first device to said second device, obtaining a received sequence at said second device, said received sequence being related to said signal point sequence, and comparing attributes of said received sequence with stored attributes of a previously received sequence associated with said previously established communication channel

17 A method according to claim 14, wherein at least a portion of said initializing step is performed at an initial data rate, and said method further comprises the step of entering a data mode at a full data rate, said entering step being performed after said initializing step

18 A method according to claim 14, further comprising the step of identifying at least one signal point for use by said first device in a transition sequence, said at least one signal point being capable of highlighting the presence of digital impairments in said communication channel

19 A method according to claim 14, further comprising the steps of conducting final training of at least one of said first and second devices during a time period, said conducting step being performed after said determining step, and exchanging authentication information between said first and second devices during said time period

20 A method according to claim 14, wherein said determining step determines whether digital impairments associated with said communication channel are similar to digital impairments associated with said previously established communication channel

21 A method for reducing startup latency associated with a data transmission system having a first device configured to communicate with a second device over a communication channel, said method comprising the steps of establishing a call between said first device and said second device, determining whether a characteristic of said communication channel is similar to a corresponding characteristic associated with a previously established communication channel, training at least one of said first and second devices at an initial data rate dunng a first time period, and exchanging authentication information between said first and second devices during said time period, said exchanging step being performed if said determining step determines that said characteristic is similar to said corresponding characteristic

22 A method according to claim 21, further comprising the step of initializing at least one of said first and second devices in response to a number of stored parameters associated with said previously established communication channel, said initializing step being performed if said determining step determines that said characteristic is similar to said corresponding characteristic

23 A method according to claim 21, further comprising the step of ascertaining, for said call, whether said first device and said second device support a fast connect protocol, said ascertaining step being performed prior to said determining, training, and exchanging steps

24 A method according to claim 21, wherein said determining step comprises the steps of transmitting a signal point sequence from said first device to said second device, obtaining a received sequence at said second device said received sequence being related to said signal point sequence, and comparing attributes of said received sequence with stored attributes of a previously received sequence associated with said previously established communication channel

25 A data transmission device comprising a receiver section configured to receive communication signals transmitted by a remote device, a transmitter section configured to transmit communication signals to said remote device and to transmit a fast connect identifier in response to the establishment of a call associated with a current communication channel, said current communication channel having a first channel characteristic associated therewith, a memory element configured to store a second channel characteristic associated with a previously established communication channel, and a processor element configured to determine whether said first channel characteristic is similar to said second channel characteristic, said processor being further configured to trigger a fast startup routine in response to a validation of said first channel characteristic with said second channel characteristic

26 A device according to claim 25, wherein said receiver section is configured to obtain a received sequence related to a signal point sequence transmitted by said remote device, and said processor element is configured to compare attributes of said received sequence with stored attributes of a previously received sequence associated with said previously established communication channel

27 A device according to claim 25, wherein said transmitter is further configured to transmit a signal point identifier that identifies at least one signal point for use by said remote device in a transition sequence, said at least one signal point being capable of highlighting the presence of digital impairments in said current communication channel

28 A device according to claim 27, wherein said transmitter is configured to transmit said fast connect identifier and said signal point identifier as one sequence

29 A device according to claim 25, wherein said receiver is further configured to receive a fast connect acknowledgment from said remote device, said fast connect acknowledgment being generated in response to said fast connect identifier

30 A device according to claim 25, wherein said processor element is further configured to initialize said receiver section in response to a number of stored parameters associated with said previously established communication channel, wherein an initialization of said receiver section occurs if said processor element determines that said first channel characteristic is similar to said second channel characteristic

31 A device according to claim 25, wherein said processor element is further configured to train said receiver section at an initial data rate and to exchange authentication information with said remote device during a first time period, wherein an exchange of authentication information with said remote device occurs if said processor element determines that said first channel characteristic is similar to said second channel characteristic

32 A data transmission device comprising a receiver section configured to receive communication signals transmitted by a remote device and to receive a fast connect identifier in response to the establishment of a call associated with a current communication channel, said current communication channel having a first channel characteristic associated therewith, a transmitter section configured to transmit communication signals to said remote device and to transmit a signal point sequence if said receiver section receives said fast connect identifier, said signal point sequence being configured to identify said first channel characteristic to said remote device, and a processor element configured to trigger a fast startup routine in response to a validation of said first channel characteristic with a second channel characteristic associated with a previously established communication channel

33 A device according to claim 32, wherein said receiver section is further configured to receive a signal point identifier that identifies at least one signal point for use in a transition sequence, said at least one signal point being capable of illuminating digital impairments present in said current communication channel

34 A device according to claim 32, wherein said transmitter section is further configured to transmit said transition sequence, said transition sequence comprising positive and negative values of said at least one signal point

35 A device according to claim 32, wherein said signal point sequence transmitted by said transmitter section comprises a sequence of pulse code modulation signal points

36 A device according to claim 32, wherein said transmitter section is further configured to transmit a training sequence to said remote device at an initial data rate during a first time period, said processor element is further configured to exchange authentication information with said remote device during said first time period, and an exchange of authentication information with said remote device occurs if said processor element determines that said first channel characteristic is similar to said second channel characteristic

37 A method of reducing time for reconnecting a first device to a second device via a communication link, said method comprising the steps of establishing a communication session between said first device and said second device over a communication channel, obtaining an operating parameter for said data transmission system, said operating parameter being associated with said communication channel, storing said operating parameter at said second device as a stored operating parameter, and recalling said stored operating parameter, in response to the termination of a temporary pause in said communication session, to thereby obtain a recalled operating parameter

38 A method according to claim 37, wherein said obtaining step comprises the step of initializing at least one of said first and second devices

39 A method according to claim 37, further comprising the steps of setting said second device utilizing said recalled operating parameter, and subsequently re-establishing a data transmission mode between said first and second devices

40 A method according to claim 37, further comprising the steps of receiving a reconnect indication at said first device, said reconnect indication being generated in response to a request to terminate said temporary pause in said communication session, transmitting a signal point sequence from said first device to said second device in response to said reconnect indication, acquiring a received sequence at said second device, said received sequence being related to said signal point sequence, and determining characteristics of said data communication network in response to said received sequence 41 A method according to claim 40, wherein said signal point sequence comprises a sequence of pulse code modulation signal points

42 A method according to claim 37, wherein said obtaining step further obtains a second operating parameter for said data transmission system, said second operating parameter being associated with said communication channel, said storing step further stores said second operating parameter at said first device as a second stored operating parameter, and said recalling step further recalls said second stored operating parameter, in response to the termination of a temporary pause in said communication session, to thereby obtain a second recalled operating parameter

43 A method according to claim 37 wherein said stored operating parameter comprises initialization data associated with a receiver resident at said second device

44 A method of reducing time for reconnecting a first device to a second device via a communication link, each of said first and second devices being configured to maintam a number of stored operating parameters associated with a data transmission mode, said method comprising the steps of receiving a reconnect indication at said first device, transmitting a reply signal from said first device to said second device in response to said reconnect indication, recalling a stored operating parameter at said second device in response to said reply signal to thereby obtain a recalled operating parameter for said second device, and subsequently re-establishing said data transmission mode between said first and second devices using said recalled operating parameter for said second device

45 A method according to claim 44, further comprising the step of resetting said second device utilizing said recalled operating parameter for said second device

46 A method according to claim 44, wherein said recalling step further recalls a stored operating parameter at said first device in response to said reconnect indication to thereby obtain a recalled operating parameter for said first device, and said re-establishing step further re-establishes said data transmission mode between said first and second devices using said recalled operating parameter for said first device

47 A method according to claim 44, wherein said reply signal comprises a signal point sequence configured to enable said second device to determine characteristics of digital impairments associated with said data communication network

48 A method according to claim 47, wherein said signal point sequence comprises a sequence of pulse code modulation signal points

49 A method according to claim 44, wherein said reply signal comprises a transition sequence configured to enable said second device to determine robbed bit signaling characteristics of said data communication network

50 A data transmission system comprising a first device and a second device configured to communicate with each other over a communication channel via a data communication network, said first device comprising a memory element configured to maintain a first number of stored operating parameters associated with a data transmission mode of said data transmission system, a receiver section configured to receive communication signals transmitted by said second device and to receive a reply signal in response to a request to terminate a temporary pause in said data transmission mode, and a processor element configured to recall at least one of said first number of stored operating parameters at said first device in response to said reply signal to thereby obtain at least one recalled operating parameter for said first device, and to reset said first device utilizing said at least one recalled operating parameter for said first device

51 A data transmission system according to claim 50, wherein said second device comprises a second memory element configured to maintain a second number of stored operating parameters associated with said data transmission mode, a second receiver section configured to receive communication signals transmitted by said first device and to receive a reconnect indication, said reconnect indication being generated in response to said request, and a second processor element configured to recall at least one of said second number of stored operating parameters at said second device in response to said reconnect indication to thereby obtain at least one recalled operating parameter for said second device, and to reset said second device utilizing said at least one recalled operating parameter for said second device

52 A data transmission system according to claim 51 wherein said second device further comprises a second transmitter section configured to transmit communication signals to said first device and to transmit said reply signal

53 A data transmission svstem according to claim 50, wherein said reply signal comprises a transition sequence configured to enable said second device to determine robbed bit signaling characteristics of said data communication network

54 A data transmission system according to claim 50, wherein said reply signal comprises a signal point sequence configured to enable said first device to determine characteristics of digital impairments associated with said data communication network

55 A data transmission system according to claim 50, wherein at least one of said first and second devices is compatible with ITU-T Recommendation V 90

56 A data transmission device comprising a memory element configured to maintain a stored operating parameter associated with a data transmission mode of said data transmission device, a receiver section configured to receive communication signals transmitted by a remote device and to receive a reply signal in response to a reconnect request, and a processor element configured to recall said stored operating parameter in response to said reply signal to thereby obtain a recalled operating parameter, and to reset said data transmission device utilizing said recalled operating parameter 57 A data transmission device according to claim 56, wherein said reply signal is associated with a request to terminate a temporary pause in said data transmission mode

58 A data transmission device according to claim 56, wherein said recalled operating parameter is used to re-establish said data transmission mode

59 A data transmission device according to claim 56, wherein said stored operating parameter comprises initialization data associated with a receiver resident at said data transmission device

60 A data transmission device according to claim 56, wherein said data transmission device is further configured such that it is compatible with ITU-T Recommendation V 90

61 A signaling method for changing operating modes in a data communication system having a first device configured to communicate with a second device via a communication link, said method comprising the steps of transmitting a modem hold alert signal (MHA) from said first device to said second device, detecting said MHA at said second device, transmitting a modem hold signal (MH) from said first device to said second device, initiating a procedure associated with a change in the operating mode of said data communication system in response to said modem hold signal

62 The method of claim 61, wherein said change in the operating mode includes said second device entering a hold state

63 The method of claim 61, wherein said change in the operating mode includes said second device entering a cleared down mode