CA2231919A1

CA2231919A1 - Improvements relating to voice and data transmission

Info

Publication number: CA2231919A1
Application number: CA002231919A
Authority: CA
Inventors: Brian Harold William Phillips; Pater Anton Jan Kolf; Mark Gadsby Henson; Craig Ian Morley; James Mcallister
Original assignee: Telefonaktiebolaget LM Ericsson AB
Current assignee: Telefonaktiebolaget LM Ericsson AB
Priority date: 1997-11-25
Filing date: 1998-03-13
Publication date: 1999-05-25
Also published as: US6243377B1

Abstract

Methods and apparatus for enabling simultaneous transmission of voice and data signals over a single subscriber line. Signals are time division multiplexed preferably using an ISDN access format such as the Basic Access or Primary Rate formats, but are treated separately at the exchange. Subscriber equipment combines signals from local computer and telephone devices for separation at corresponding exchange equipment. Similarly the exchange equipment combines signals from one or more packet networks and the public telephone network for separation at the subscriber equipment. Data signals are therefore passed by the exchange directly to or from a packet switched network while voice signals are passed directly to or from a telephone switched network. Channels available over the subscriber line are dynamically allocated with telephone signals generally taking preference over data signals.

Description

IMPROVEMENTS RELATING TO VOICE AND DATA TRANSMISSION

FIELD OF THE INVENTION

This invention relates to voice and data co....,.l~..ication systems, and in particular but not solely to systems which enable simultaneous voice and data tr~n~mi~sion over a single telephone line. More particularly the invention relates to improved methods which enable residential subscribers to telephone and Internet services to access both services simultaneously over a single two wire copper line.

BACKGROUND TO THE INVENTION

The traditional method of Internet access from a subscribers home is by way of a dialled up connection to a modem pool at a server operated by an Internet Service Provider. A
connection of this kind is set up in the PSTN (Public Switched Telephone Network) and infonn~tinn is transferred in the form of TCP/IP (Tr~ncmission Control Protocol/Internet Protocol) packets. The subscriber typically uses a PC (Personal Colllpuler) connected through their telephone line by way of a modem at speeds of around 33 kb/s or possibly up to 56 kb/s in some cases. However, once the connection is set up the telephone line is generally unable to be used for other incoming or outgoing calls. Further, the connection does not make efficient use of PSTN resources in that Internet sessions are relatively long and bursty in nature.

A wide range of systems have been proposed to enable use of a single telephone line for multiple simultaneous data and/or voice related calls. Subscribers to ISDN (Integrated Services Digital Network) can access the Internet using DSL (Digital Subscriber Line) techniques which provide one, two or more B channels. ISDN basic access provides a 2B+D tr~nsmi~sion format in which the B and D channels form a TDM (Time DivisionMultiplexed) signal and operate at speeds of 64 kb/s and 16 kb/s respectively. If one B
channel is in use for Internet access another can carry incoming or outgoing telephone calls siml-lt~neously, and both B ch~nnels may be used for Internet data when notelephone call is underway. However, ISDN requires an entirely new network solution, and for Internet access generally makes the same relatively inefficient use of PSTN
resources as the traditional modem connection.

There is rapid development of other DSL access technology, such as ADSL (Asymmetric Digital Subscriber Line) which provides up to about 9 Mb/s downstream to subscribers and up to about 640 kb/s u~sl~ n depending on length of the copper pair. VDSL (Very high rate DSL) provides up to about 20 Mb/s in both directions. These are more expensive and complex than ISDN in that frequency bands above that of the PSTN are generally used, and are less able to operate effectively over long lines. Still other developments for simultaneous use of a single telephone line include Pairgain systems, DSVD (Digital Simultaneous Voice and Data) modems, and IP modems by which data and voice signals are combined in an IP data stream at the subscribers home. Most of these except the IP modem, also make inefficient use of PSTN circuit switching resources.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide for telephone line communication systems which are improved over existing siml-lt~neous voice and data systems in terms of cost, complexity, availability or efficiency of connection, or which at least provide a useful alternative to existing systems.

Accordingly in one aspect, the invention broadly consists in a method of tr~ncmitlin~
voice and data signals simultaneously over a single telephone line between subscriber premises and a co~ ication service provider, wherein the signals occupy two or more ch~nnelc of a TDM format. The signals are multiplexed or demllltiplexed at the service provider premises so that an incoming or outgoing data signal for the subscriber passes through a packet network rather than the PSTN. Although an incoming or outgoing voice signal passes through the PSTN generally in the usual way, the data signal is received directly from or sent directly into the packet network and so avoids the relative inefficiency of the PSTN for such signals. Preferably the TDM format makes use of ISDN basic access channels although the ISDN network solution itself is not used.
Preferably the TDM signal is encoded using a compressed tr~nsmission format such as 2BlQ.

In another aspect the invention consists in appa~lus for the subscriber and service provider premises which enable tr~n~mission of TDM signals over the subscriber telephone line, and multiplexing or d~multiplexing of outgoing or incoming signals respectively at each premises. At the exchange premises connections are made such that voice signals pass through the circuit switched public telephone network in the usual way while data signals pass through a packet switched network and avoid the telephone network. Remote terminal equipment is provided for installation at the subscriber premises while corresponding central terminal equipment is installed at the service provider or exchange premises.

Further aspects and advantages ofthe invention will become apl)a.elll from the following description and drawings which are provided by way of example only.

BRIEF DESCRIPTION OF THE DRAWINGS

A preferred embodiment of the invention will be described with reference to the accompanying drawings, of which:
Figure 1 schematically shows use of the invention to enable simult~neous tr~n~micsion of voice and data signals over a single telephone line between a subscriber and an exchange, Figure 2 illustrates time division multiplexing using ISDN basic access channel format, Figure 3 illustrates a digital tr~ncmi~sion signal using 2BlQ format, Figure 4 shows a remote device which may be installed at the subscriber premisesin Figure 1, Figure 5 shows an exchange device which may be installed at the exchange premises in Figure 1, Figure 6 is a software diagram outlininp~ generally how control over data flow is m~int~ined by microprocessors in the subscriber and exch~nge equipment, Figure 7 illustrates data flow control between devices at the subscriber and exchange premises, and Figure 8 illustrates multiple subscriber services at an çxch~nge.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring to the figures it will be appreciated that the invention need be described in a high-level form only. Most details of the required apparatus will be readily understood by the skilled reader.

Figure 1 is an overview of a cn. ~ ication system according to the invention, by which a telephone subscriber is able to use an existing copper pair line 100 for simultaneous access to both the telephone and Internet networks. The subscriber installs a remote terminal 10 at his or her premises 11 while a communication service provider installs a corresponding exchange terminal 14 at a local exchange premises or central office 15.
Components of the subscriber-based equipment 10 are similar in many ways to those of the provider-based equipment 14 as will described below. Both may be considered as a DCE (Data Communication Equipment) for the purposes of their interaction with other DTE (Data Terminal Equipment) at their respective premises. The subscriber unit 10 and the exchange unit 14 each have two channels, namely a digital data channel and an analogue voice channel. The subscriber thereby connects a home computer device 12 such as a PC and a telephone device 13 such as DTMF telephone to the unit 10. The service provider also thereby connects unit 14 at the exchange premises to a packet switching device 16 such as a router and a circuit switching device 17 such as typically found as part of the Main Distribution Frame structure at an exchange. The router 16 in turn acts a gateway to one or more wide or local area packet networks 18 such as the Internet or an Intranet. The switch 17 passes telephone voice-grade signals into the PSTN
19.

Figure 2 indicates how the data and voice channels may be time division multiplexed for tr~ncmicsion over the subscriber line DSL 100. The two channels are preferably multiplexed through an ISDN "U" or basic access interface which carries two B or bearer channels at 64 kb/s each and a D or data channel at 16 kb/s which is normally used for control sign~lling A combined 2B+D format signal therefore provides a 144 kb/s stream, and when framing information F is included the actual bit rate of a basic access charmel is 192 kb/s. Other formats are also provided under ISDN and may generally be expressed xB+D. In North America for example, a primary rate access format is 23B+D.
Use of a more general format enables multiple individual data and or voice channels, or faster combined channels, to be made available. In the context of Figure 1, when the subscriber's telephone device 13 is not in use both bearer channels B 1 And B2 of the U
interface are available for data tr~ncmitted to and from the co~ ul.,l 12. When the telephone goes off hook at the subscriber premises 11, or an incoming ring signal is received at the exchange premises 15, one of the B channels is dynamically allocated to the telephone 13. Flow control signals via the D channel reduce the total capacity of the data channel which is available for the computer from 2B to lB and 128 kb/s to 64 kb/s.
It may be noted that the actual data rate of each B channel is less than the bit rate due to additional processing bits which are required, with the actual data rate being typically 57.6 kb/s.

Figure 3 indicates how tr~ncmicsion over DSL 100 may be encoded using a compressed digital format such as 2B lQ. According to this preferred format two binary bits "2B" are encoded in one quaternary symbol "lQ". Up to four signal levels can therefore occur with each level defining the code for two bits of a multiplexed signal being tr~ncmitted between the subscriber premises 11 and the exchange premises 15. This figure is simply an example of a particular digital encoding format, namely the 2B lQ relationship between quaternary symbols and their encoded binary pairs. The previous figure is similarly simply an example of a possible TDM frame format.

Figure 4 shows components of the subscriber eq--ipm~nt RU 10 indicated in Figure 1.
This eqllipm~nt includes a multiplexer/d~m--ltiplexer circuit M/D 40, preferably an ISDN
U interface chip arrangement, under control of a microprocessor 41 with suitablememory. The equipment is mains powered through an input 45. Data signals from the computer device 12 are received by the M/D 40 through data interface 42. The computer device will typically produce and receive asynchronous digital signals through an RS-232 or similar serial port, for example, and the interface 42 converts these to and from a synchronous data flow as required by the M/D 40. Voice-grade signals from the telephone device 13 are received by the M/D 40 through a subscriber line interface circuit 43. The telephone device typically generates and receives analogue signals through a BT
socket for example, and the SLIC 43 converts these to and from digital signals as required by the M/D 40. TDM signals passing between the subscriber premises 11 and the exchange 15 are transmitted and received on the subscriber line 100. These signals are preferably in 2B+D and 2BlQ formats as described above. A bypass circuit 44 is able to provide a direct connnection 46 between the subscriber line and the output to the telephone device 13 in the event of a failure of equipment 10 or power failure. Each of the data interface 42, SLIC 43 and bypass circuit 44 are under control of the microprocessor 41 which also activates a ring signal generator 49 for the telephone device when an incoming call is detected at the exchange premises 15.

Figure 5 shows exchange equipment EU 14 as indicated generally in Figure 1. Thisequipment is similar in many ways to the subscriber equipment 10. A
multiplexer/demultiplexer M/D 50, once again preferably an ISDN U interface chiparrangement, is under control of a microprocessor 51 with suitable memory. The equipment is powered from the exchange through an input 55. Data signals from the packet network 18 in Figure 1 are received by the M/D 50 through interface 52. The router 15 will typically produce and receive asynchronous digital signals by way of an RS-232 or similar serial port, and the interface 52 converts these into synchronous form as required by the M/D 50. Voice grade signals are received from the public telephone network 19 by the M/D 50 through subscriber line interface circuit 53. The telephone switch circuit 17 typically passes analogue signals and these are converted to and from digital form as required by the M/D 50. TDM signals passing between the exch~ngepremises 15 and the subscriber premises 11 are tr~n~mitted and received over thesubscriber line 100 as described. A bypass circuit 54 provides a direct connection 56 between the subscriber line and the output to the telephone network 19 in the event of failure of either the subscriber or exchange equipment, or a failure in power supply from the exchslnge. Each of the data interface 52, SLIC 53 and bypass 54 are under control of the microprocessor 51.

Figure 6 outlines software which may be implemented in the microprocessors 41 and 51 in Figures 4 and 5 respectively, for controlling data flow between the subscriber equipment 10 and exchange equipment 14. Control is required to manage data rate modification between the generally asynchronous (eg. RS-232) data passing into and out of the eqllipm~nt via interfaces 42 and 52, and the generally synchronous (eg. U interface) data passing into and out of the equipment onto DSL 100 via the M/Ds 40 and 50.
Control is also required to manage variation in the available rates of tr~n~mi~sion and reception of data by the data tPrmin~l eqllipm~nt at each premises, generally the col.lpuler device 12 and the router 16. The overall rate of data tr~n~mi~sion between premises depends on whether one or both of the B ch~nnçls are available. In operation themicroprocessors 41 and 51 cycle continuously through a main program loop 60 such as shown in Figure 6, following largely repetitive routines and a number of il~tellupl service routines. Initialisation routine 61 configures input/output pins, watchdog timer, timer modules, interrupts and register variables after reset of the equipment at the particular premises. Self test routine 62 then runs to ensure that all components of the data channel are functioning correctly. The microprocessor then acquires frame synchronisation across the data link between the equipment in synchronising routine 63. The ongoing functions of assembling and analysing frames is then handled by framing and deframing routines 64 and 65 respectively. A UART (Universal Asynchronous Receiver/Tr~ncmitter) llu~l service routine 66 deals with data transfer to the DTE devices 12 and 16 via the RS-232 or similar port. An SPI (Serial Peripheral Interface) Inlell u~l service routine 67 is responsible for data transfer between the M/D 40 or 50 and the microprocessor 41 or 51. A BER (Bit Error Rate) routine 68 is generally run only in the microprocessor 51.
A communication protocol between the microprocessor in each M/D and the respective microprocessors 41 and 51 is enabled by a serial communications routine 69.

Figure 7 is an overview of data channel flow between the con~puler device 12 and remote eq lipm~nt RU 10 at the subscriber premises 11 in Figure 1, and the router device 16 and exchange eq -ipm~nt EU 14 at the exchange premises 15. The devices 12 and 16 are DTE
and the equipment 10 and 14 are DCE. Local flow control between DCE and DTE is preferably hardware based while control between DCE and DCE is generally impl~m~nted in software. Hardware control makes use of standard RS-232 cign~lling by way of I/O pins sign~lling Ready To Send (RTS) and Clear To Send (CTS) which arereadily checked by the microprocessors 41 and 51. Software flow control makes use of a single signal Peer Enable (PREN) which is checked via the status of particular bits in the latest received SPI frame. If DTE 12 cannot process or buffer all of the data arriving from RU 10, then DTE 12 signals RTS which appears as CTS to the DTE 16. A CTS isalso signalled by EU 14 to DTE 16 should the RU 10 or EU 14 detect an outgoing or incoming telephone call respectively, requiring fallback to less than the maximum number of TDM channels on DSL 100. Similarly if DTE 16 cannot process or buffer all of the data arriving from EU 14, then DTE 16 signals RTS which appears as CTS to DTE 12.
In general, the bit rates of both DTE will be fixed and the RTS/CTS sign~lling produces an on/off effect in the transmissions.

Figure 8 shows by way of highly simplified example, an arrangement of exchange eql-irmPnt for multiple subscribers, and gives more detail as implied by the arr~ngPmçnts of Figures 1 and 5. A main distribution frame structure (MDF) 80 supports cross connections between external lines such as DSL 100 and various items of equipment internal to the exchange premises 15. A backplane shelf 81 connected to the MDF
typically supports a number of exchange termin~lc EU 14 for respective subscribers, perhaps alongside items related to other systems enabling simultaneous voice and data tr~n~miccion by other subscribers. The shelf has a management controller MC 82 and a power supply PS 83. Each EU 14 has a data connection to the shelf (eg. RS-485) which communicates with the respective MC 82 and enables incoming and outgoing DSL
transmissions to the subscriber. Each EU 14 has a plain old telephone (POTS) voice connection to the shelf to carry subscriber telephone calls, and a connection to a router 16 which carries subscriber data, either incoming or outgoing, as processed by the M/D
50. Subscriber telephone calls may be connected to the MDF by one of many circuit switches 17 for tr~n~mi~cion to the PSTN 19. Subscriber data tr~n~mi~sions typically pass through an exchange network segment, such as part of an Ethernet system 85, and through a gateway router 86 to an extern~l packet network 18. The packet network is typically part of the Internet, an intranet or an extranet, and may be a fixed permanent or dial-on demand driven network. An Internet service provider ISP is indicated by way of further example.

The invention of a communication system as described above is able to provide two or more channels for data and telephone tr~n~mi~sions between subscriber premises and a telephone exchange or central office. This enables ~imlllt~neous access by the subscriber to both data and telephone services, and in particular enables access to the Internet at relatively high data rates without interruption by incoming and outgoing telephone calls at the subscriber premises.

Claims

1. A method of simultaneously transmitting voice and data signals over a single telephone line between subscriber premises and a communication service provider,comprising:
receiving subscriber generated voice and data signals at the subscriber premises, converting the signals into two channels of a time division multiplexed (TDM) signal in subscriber-based equipment, transmitting the TDM signal over the single telephone line from the subscriber premises, receiving the TDM signal from the telephone line at service provider premises, converting the TDM signal into separate voice and data signals in provider-basedequipment, passing the voice signal from the provider-based equipment into a public telephone network, and passing the data signal from the provider-based equipment into one or more wide or local area packet networks.

2. A method according to claim 1 wherein the data signal from the provider-basedequipment is passed into a fixed permanent network or a dial-on demand driven network.

3. A method according to claim 1 wherein the data signal is dynamically allocated more than one channel of the TDM signal in the absence of a voice signal.

4. A method according to claim 1 wherein the subscriber generated data signals include asynchronous serial data.

5. A method according to claim 1 wherein the TDM signal is an ISDN signal in xB+D format such as Basic Access or Primary Rate formats.

6. A method according to claim 1 wherein the TDM signal is encoded using a quaternary transmission format such as 2BlQ.

7. A method according to claim 1 further comprising:
converting voice and data signals received at the provider-based equipment into a TDM signal for transmission to the subscriber, transmitting the TDM signal over the single telephone line to the subscriber premises, and converting the TDM signal into separate voice and data signals at the subscriberequipment.

8. Apparatus for transmitting and receiving voice and data signals over a singletelephone line between subscriber premises and a communication service provider,comprising:
remote terminal equipment for the subscriber premises, adapted to receive separate outgoing voice and data signals from the subscriber, and to transmit the signals as a time division multiplexed (TDM) signal over the telephone line to the service provider; and central terminal equipment for the service provider premises, adapted to receivethe TDM signal transmitted by the remote terminal equipment, separate the TDM signal into voice and data signals, and direct the separated signals into a public telephone network and one or more wide or local area packet networks respectively.

9. Apparatus according to claim 8 wherein:
the central terminal equipment is adapted to receive incoming voice and data signals from the telephone and packet networks respectively, and transmit the signals as a TDM signal over the telephone line to the subscriber premises; and the remote terminal is adapted to receive the TDM signal transmitted by the central terminal equipment and separate the TDM signal into incoming voice and data signals for the subscriber.

10. Apparatus according to claim 8 wherein:
the central terminal equipment is adapted to pass the separated data signal directly into a fixed permanent network or a dial-on demand driven network.

11. Apparatus according to claim 8 wherein:
the data signal is dynamically allocated more than one channel of the TDM signalin the absence of the voice signal.

12. Apparatus according to claim 8 wherein:
the TDM signals are in an ISDN access format.

13. Apparatus according to claim 8 wherein:
the remote terminal equipment is adapted to process outgoing and incoming data signals in asynchronous serial form.

14. Apparatus according to claim 8 wherein:
the remote and central terminal equipment transmit TDM signals to each other using 2BlQ format.

15. A method of processing a subscriber signal at a telephone exchange, comprising:
receiving a time division multiplexed (TDM) signal from the subscriber over a single line, demultiplexing the TDM signal into separate voice and data signals, passing the voice signal into a public telephone network, and passing the data signal into a packet network.

16. A method according to claim 15 further comprising:
receiving a voice signal from the public telephone network, receiving a data signal from the packet network, forming a TDM signal from the received voice and data signals, transmitting the TDM signal to the subscriber over the single line.

17. A method according to claim 16 further comprising:
receiving and transmitting the TDM signals in 2BlQ format.