WO2001045431A2

WO2001045431A2 - System and method for automatically detecting dsl service on multiple telephone lines

Info

Publication number: WO2001045431A2
Application number: PCT/US2000/041473
Authority: WO
Inventors: Ting Sun; Jeffrey Bernstein
Original assignee: 2Wire, Inc.
Priority date: 1999-11-05
Filing date: 2000-10-23
Publication date: 2001-06-21
Also published as: AU4901101A; WO2001045431A3

Abstract

A system (100) and method are disclosed for automatically detecting DSL service on multiple telephone lines. A DSL modem (124) is coupled to multiple telephone lines (106 and 108) and periodically probes the lines until identifying the line having DSL service. In one embodiment, the DSL modem includes relays to periodically switch connection between the lines until the line having DSL service is identified. The DSL modem probes each of the lines for DSL service by transmitting activation tones over each of the lines and waiting for a response from the DSL service.

Description

SYSTEM AND METHOD FOR AUTOMATICALLY DETECTING DSL SERVICE ON

MULTIPLE TELEPHONE LINES

By Ting Sun and Jeffrey Bernstein

CROSS REFERENCE TO RELATED APPLICATION This application is related to co-owned U.S. Patent Application No. 09/353,111 by Ting Sun and Brian L. Hinman, entitled "Odd-Order Low-Pass POTS Device Filter" and filed on July 14, 1999, which is incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention The present invention relates generally to providing DSL service over telephone wires, and more particularly to a system and method for automatically detecting DSL service on multiple telephone lines.

2. Description of the Background Art

It has become increasingly commonplace, m recent years, for homes to have more than one telephone line. Indeed, many homes have multiple telephone lines to accommodate an increased popularity of analog modems, facsimile machines, and telephones, all of which may use telephone lines. For example, having multiple telephone lines in a home permits its residents to receive a facsimile on one telephone line while simultaneously conducting a telephone call on another telephone line. As another example, it may be desirable for one resident to make a telephone call on one telephone line while another resident is simultaneously making another telephone call on another telephone line. Hence, for many, it is advantageous to have more than one telephone line for a single home. Digital Subscriber Line (DSL) is a technology that dramatically increases the digital capacity of ordinary telephone lines into a home or office. The different versions of DSL include, for example, ADSL (Asymmetrical DSL) , CDSL (Consumer DSL) , HDSL (High Bit Rate DSL) , and VDSL (Very High Bit Rate DSL) . Using Frequency Division Multiplexing (FDM) techniques, ADSL generally permits data to ride over the same telephone lines as voice communications with the voice and data signals being split apart at both the customer' s side and the telephone company' s side.

There are numerous advantages to having DSL service in a home. One advantage is that DSL typically permits one to access information over the Internet at rates typically about 10 times faster than rates associated with conventional 56.6K analog moαems in some applications. Another advantage is that DSL usually does not interfere with regular voice-band or POTS telephone or facsimile machine use so that a single telephone line may be used to access the Internet and conduct a telephone call at the same time. For these reasons, and perhaps other reasons, DSL service is becoming increasingly popular in that many households and businesses are signing up for DSL service to be provided to them over a telephone line.

Additional details concerning conventional ADSL equipment are found m Standards Project for Interfaces Relating to Carrier to Customer Connection of Asymmetrical Digital

Subscriber Line (ADSL) Equipment, T1E1.4/97-007R6, T1.413 Issue 2, edited by John Bingham and Frank van der Putten, dated September 26, 1997, which is incorporated herein by reference. One problem associated with the provision of DSL service, however, is that when a home or business has multiple telephone lines, it may be difficult to determine on which of the multiple telephone lines the DSL service is present. Indeed, it is usual for homes and businesses having multiple telephone lines to have DSL service on one and only one of the multiple lines. As such, there is a substantial possibility that DSL equipment, such as an ADSL modem, will not be coupled to the correct line, resulting in failure of the DSL service within the home due to the DSL equipment being coupled to the wrong telephone l ne.

Additionally, m many applications, it may be important that DSL equipment operate with relatively low insertion impedance so as not to unduly attenuate the DSL signal. Hence, it is desirable to reduce, to the extent practical, the insertion impedance of the DSL equipment, such as an ADSL modem, so as not to impair the associated signals. Because DSL equipment is frequently disposed within living areas of a home, it is also advantageous that such equipment operate quietly so as not to disturb the occupants of the home. That is, it is generally desirable for DSL (as well as other home electronic) devices to operate with little or no noise so as not to disturb the occupants of the home.

Consequently, a need exists for a system and method for automatically detecting DSL service on multiple telephone lines. Another need exists to provide a system and method for coupling a DSL device to a telephone line having DSL service without imposing significant impedance and signal attenuation on the telephone line during operation. Yet another need exists to provide a DSL device that operates quietly so as to not disturb the home occupants during operation.

SUMMARY OF THE INVENTION The present invention overcomes or substantially alleviates prior problems associated with coupling DSL equipment to telephone lines in homes or businesses having multiple telephone lines. In general, the present invention connects a DSL modem to the multiple telephone lines and then switches between the multiple telephone lines until detecting DSL service on one of the multiple telephone lines. Pursuant to one embodiment, the invention employs relays to perform the switching function, although other types of digitally controlled switching devices may also be used. The DSL modem transmits activation tones to probe the multiple telephone lines to determine on which of the multiple telephone lines the DSL service is present. In one embodiment, the DSL modem includes a combination of solid state and mechanical relays. The initial switching between the multiple telephone lines is advantageously performed by the solid state relays, which have an essentially silent operation. Solid state relays, however, are typically characterized as having significant insertion impedance, which can significantly impair, or attenuate, the DSL signals passing to and from the DSL modem.

To alleviate the high insertion impeαance of the soliα state relays, the DSL modem mechanical relays are turned on after the DSL modem has identified, or detected, the telephone line having DSL service. Mechanical relays typically have a very low, or negligible, insertion impedance and, therefore, do not significantly impair or attenuate DSL signals that pass over them. Because mechanical relays may generate audible noise when performing their switching function, they are switched in and turned on after the line having DSL service has been identified, or detected, to reduce or avoid the generation of potentially disturbing audible noise by the mechanical relay. Accordingly, m operation, the DSL modem is connected to multiple telephone lines. A solid state relay disposed within the DSL modem then periodically switches between the multiple telephone lines and selectively probes for DSL service on each of these lines until identifying, or detecting, the line on which DSL service is present. After the DSL modem has identified the telephone line having the DSL service, a mechanical relay is positioned in the same position as the solid state relay and turned on. Other advantages and features of the present invention will be apparent from the drawings and detailed description as set forth below.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1A is a block diagram illustrating multiple telephone lines interconnecting a home with a telephone central office in accordance with one embodiment of the present invention; FIG. IB is a block diagram illustrating multiple telephone lines interconnecting a home with a telephone central office in accordance with another embodiment of the present invention;

FIG. 2 schematically illustrates an embodiment of the DSL modem of FIG. 1 in accordance with the present invention; FIG. 3 illustrates details of the switching device controller of FIG. 2;

FIG. 4 schematically illustrates an embodiment of the switching device of FIG. 2;

FIG. 5 is a flowchart that illustrates the operation of the switching device of FIG. 4 ;

FIG. 6 schematically illustrates another embodiment of the switching device of FIG. 2; and

FIG. 7 is a flowchart that illustrates the operation of the switching device of FIG. 6.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT FIG. 1A illustrates a splitterless DSL service network 100 that includes a central office 102 and a home 104 coupled by telephone lines 106 and 108. Telephone lines 106 and 108 may be respectively referred to as "line 1" and "line 2" herein. In one embodiment, the central office 102 provides regular Plain Old Telephone Service (POTS) to the home 104 over both lines 106 and 108. The central office 102 further provides a DSL service, such as ADSL, over only one of the telephone lines 106 and 108.

The home 104 is shown as including a first and second home home networks 120 and 122, which are respectively coupled to lines 106 and 108. As illustrated, a DSL modem 124 is coupled to both home networks 120 and 122. The modem 124 demodulates a DSL signal from the central office 102, and sends the demodulated signal to a computer 126. To transmit data, the computer 126 sends a signal to the DSL modem 124, and the DSL modem 124 modulates the signal to a DSL signal and sends the DSL signal to the central office 102. The home network 120 is further shown as having telephones 130 coupled thereto via filters 132. The filters 132 preferably comprise low-pass filters for separating the telephones 130 from high frequency data signals, such as DSL or home networking signals that might be present on the home network 120. The low-pass filters also prevent POTS device impedance changes from affecting the high frequency signal transmissions .

The home network 122 is further shown as being coupled to a facsimile machine 136 via one of the filters 132. As shown, the line 108 (line 2) serves as a dedicated line for the facsimile machine 136. Those skilled in the art will appreciate, however, that other POTS devices, such as telephones and 56k modems may also be coupled to the home network 122. In the configuration of FIG. 1A, the computer 126 may receive DSL service from the central office 102 along either l ne 106 or line 108. Hence, by using the DSL modem 124 of the present invention, a successful DSL connection will result regardless of whether the DSL service is provided over line 106 or line 108. Details of the DSL modem 124 are discussed in more detail below.

FIG. IB illustrates a splittered DSL service network 150. The DSL service network 150 differs from the DSL service network 100 (FIG. 1A) in that it includes low pass filters 152 disposed between the line 106 and the network 120 and between the line 108 and the network 122. Another difference is that the DSL modem 124 s directly coupled to the lines 106 and 108 via lines 154 and 156. In this configuration, the DSL modem 124 preferably includes high pass filter functionality to prevent POTS signals from passing therethrough.

The low pass filters are identical to the low pass filters 132 (FIG. 1A) discussed above and permit POTS signals to pass between the line 106 and the network 120 and between the line 108 and the network 122 while preventing higher frequency signals, such as DSL signals, to pass therebetween. Since the low pass filters 152 prevent DSL signals from entering onto the networks 120 and 122, the low pass filters 132 disposed between POTS device and the networks 120 and 122 are unnecessary m this embodiment.

Those skilled in the art will appreciate that the low pass filters 152 of FIG. IB may alternative comprise POTS splitters (not shown) , which separate the POTS and DSL signals entering the home 104 over the lines 106 and 108. Where POTS splitters are used instead of the low pass filters 152, the DSL modem 124 is coupled to the splitter via the lines 154 and 156.

In both FIGS. 1A and IB, the DSL modem 124 is coupled to both lines 106 and 108 even though DSL service is only be available, or present, on one of the lines 106 and 108. According to these configurations, and as discussed m more detail below, the DSL modem 124 detects on which line DSL service is present and then provides DSL modem services to the computer 126.

FIG. 2 illustrates details of the DSL modem 124 depicted in FIG. 1 and discussed above. As illustrated, the DSL modem 124 is disposed between the computer 126 and the lines 106 and 108 so that the computer 126 can receive DSL service over either of the lines 106 and 108.

The DSL modem 124 is shown as including seriatim a switching device 202, a transformer 204, an analog front end 206, a codec 208, and a programmed data processor, such as Central Processing Unit (CPU) 210. Although the switching device 202 is illustrated as being disposed between the transformer 204 and the lines 106 and 108, ttose skilled in the art will appreciate that the switching device 202 could also be disposed between the transformer 204 and the analog front end 206. In addition, those skilled m the art will appreciate that the DSL modem 124 may be positioned internal or external (as shown) of the associated computer 126. As discussed m more detail below, the switching device 202 periodically switches the connection between the analog front end 206 and the lines 106 and 108 until DSL service is detected over one of the lines 106 and 108. The analog front end 206 is coupled to the switching device 202 via the transformer 204.

The codec 208 is interposed between the analog front end (AFE) 206 and the CPU 210 to convert the analog output of the AFE 206 to digital signals and to convert the digital output of the CPU 210 to analog signals. Accordingly, in this configuration, the codec 208 provides A/D and D/A signal conversions between the AFE 206 and the CPU 210.

The CPU 210 is illustrated as including a PCI (Peripheral Component Interconnect) controller 220 for controlling communications between the DSL modem 124 and the associated computer 126 (FIG. 1) . The CPU 210 may comprise a digital signal processor or a microprocessor. The CPU 210 also includes a switching device controller 222 for controlling the switching device 202. The CPU switching device controller 222 controls the switching device 202 over lines 230 using digital control. Additional details of the switching device controller 222 are discussed m more detail below.

FIG. 3 illustrates details of one embodiment of the switching device controller 222 m accordance with the present invention. As shown, the switching device controller 222 includes an activation tone generator 302, a response detector 304, a relay control module 306, and a timer 308. Those skilled in the art will appreciate that the functions of the controller 222 may alternatively be included in digital signal processing functionality of the CPU 210 rather than in a separate module as shown.

The activation tone generator 302 generates activation tones to be transmitted over the telephone lines until the response detector 304 detects a response from the central office 102 (FIG. 1) or other DSL service provider. Those skilled in the art will appreciate that the transmission of activation tones is a conventional DSL protocol.

The response detector 304 operates to detect the presence of DSL service on the telephone line to which the switching device 202 (FIG. 2) is switched. As discussed in more detail below, the switching device 202 continues to periodically switch between different telephone lines, such as the lines 106 and 108, until the response detector 304 detects the presence of DSL service.

The relay control module 306 operates to digitally control the operation of the switching device 202 (FIG. 2) over the lines 230. In particular, the relay control module 306 changes the position, or the configuration, of the relay(s), switch (es), multiplexers, or other switching mechanism of the switching device 202. If no DSL service has been detected by the response detector 304, and the predetermined time period of the timer 308 has expired, then the relay control module 306 switches the configuration of the switching device 202. Pursuant to one embodiment, switching the configuration of the switching device 202 includes changing connection from the line 106 (FIG. 1) to the connection with the line 108 or vice versa. Details of the switching device 202 are discussed below.

The timer 308 controls the frequency at which the relay control module 308 switches between multiple lines 106 and 108 in the absence of the response detector 304 detection of DSL service. The timer 308 may include a conventional timer algorithm for signaling the relay control module 306 at the expiration of a predetermined time interval. For example, in one embodiment, the predetermined time interval of the timer 308 is about 30 minutes. Hence, every 30 minutes the timer 308 will signal the relay control module 306 that the predetermined time interval has expired. If the response detector 304 has not detected DSL service over the switching device 202 (FIG. 2) in its current position, the relay control 306 will switch the configuration of the switching device 202 at the expiration of the predetermined time period. Additional details regarding the operation of the switching device 202 and the switching device controller 222 are discussed below.

FIG. 4 schematically illustrates one embodiment of the switching device 202 pursuant to the present invention. As shown, the switching device 202 includes a relay 402, such as a mechanical relay, disposed between the transformer 204 and the telephone lines 106 and 108. In general, switching device 202 periodically switches connection between the transformer 204 and the telephone lines 106 and 108 according to the detection (or non-detection) of DSL service on the current telephone line. As discussed above, the relay controller 306 (FIG. 3) controls the relay 402 over the lines 230 (FIG. 2) . In one embodiment, the relay 402 switches between position A and position B as snown in FIG. 4. Position A is represented by solid lines interconnecting the transformer 204 with the line 108. Position B is represented by dashed lines interconnecting the transformer 204 with the line 106. Hence, the switching device 202 selectively interconnects the transformer 204 with either the line 108 in position A or with the line 106 in position B.

Further, it has been determined that a monolithic CMOS switching device comprising four switches may function satisfactorily in some applications. Preferably, such a switching device will have a relatively low on impedance, such as about 4 ohms or less. In one application, it has been determined that a switching device sold under product designation ADG453 by Analog Devices, Inc. of Norwood, MA will function satisfactorily.

FIG. 5 is a flowchart 500 illustrating one embodiment of a method for identifying or detecting which of a plurality of telephone lines has DSL service available thereon. The method begins at block 502. Initially, a relay, such as the relay 402 is positioned in a default position pursuant to block 504. The default position may be, for example, the position A illustrated m FIG. 4 wherein the relay interconnects the line 108 and the transformer 204. Next, the current telephone line, or the telephone line to which the relay is presently connected, is probed to detect the presence of DSL service pursuant to block 506. That is, the telephone line to which the relay 402 is currently switched is probed for DSL service. In one embodiment, the probing comprises transmitting activation tones, pursuant to conventional DSL protocol, over the current telephone line. As discussed above, the switching device controller 222 (FIG. 3) includes an activation tone generator 302 for generating these activation tones. The switching device controller 222 then detects the presence of DSL service on the current telephone line pursuant to block 508. In one embodiment, the response detector 304 (FIG. 3) detects a response to the transmitted activation tones to determine the presence of DSL service on the current telephone line. If no DSL service is detected pursuant to block 508, then execution proceeds to block 510.

At block 510, the switching device controller 222 (FIG. 3) waits for the expiration of a predetermined time period. As discussed above, the switching device controller 222 includes the timer 308, which periodically notifies the switching device controller 222 of the expiration of the predetermined time period.

After expiration of tne predetermined time period, execution proceeds to block 512 wherein the position of the relay is switched. In particular, the relay control module 306 (FIG. 3) of the switching device controller 222 switches the configuration, or the position, of the relay 402 via digital control along the control lines 230 (FIG 2) . The relay control module 306 then switches the position of the relay 402 from, for example, the position A to the position B (or vice versa) to change the current telephone line from one telephone line to another .

Once the position of the relay has been switched from one position to another pursuant to block 512, execution returns to block 506 wherein the new current telephone line is probed as discussed above. This method then continues until DSL service is detected pursuant to block 508 and the method ends at block 514 with the switching device coupling the DSL modem components to the telephone line having DSL service thereon.

FIG. 6 schematically illustrates another embodiment of the switching device 202. Like the embodiment of the switching device 202 illustrated in FIG. 4, the embodiment of FIG. 6 is shown as being disposed between the transformer 204 and the lines 106 and 108. The switching device 202 of FIG. 6 also includes the mechanical relay 402 described above with reference to FIG. 4.

In addition to the mechanical relay 402, the switching device 202 of FIG. 6 includes a solid state relay 602. Like the mechanical relay 402, the solid state relay is operative to switch connection between the transformer 204 and the telephone lines 106 and 108. That is, the solid state relay 602 may be configured n either the A or the B position and is operative to switch therebetween. The mechanical relay 402 may generate noise, such as a clicking sound, as the mechanical relay 402 switches between the positions A and B. In some conditions, having the switching device 202 periodically generate a noise each time the mechanical relay 402 switches position may be distracting, disturbing, or otherwise undesirable.

Solid state relays, such as the solid state relay 602, however, operate quietly. Indeed, a solid state relay typically has no mechanical parts; all switching mechanisms are semiconductor or thin film components. However, solid state relays also tend to have relatively high on impedances. Some solid state relays, for example, have an insertion impedance of about 20 Ohms, which can adversely affect the DSL transmissions. Mechanical relays, such as the mechanical relay 402, in contrast, typically have relatively low on impedances. Since downstream DSL signals are frequently highly attenuated upon arrival at a DSL modem, such as the DSL modem 124 (FIG. 1), it is generally undesirable to attenuate all downstream signals at a switching device. Consequently, it is undesirable to access a DSL service using the DSL modem 124 over a solid state relay. It is also sometimes undesirable to use a mechanical relay to periodically switch between different telephone lines due to the noise generated thereby.

Accordingly, m the embodiment of FIG. 6, the switching function of the switching device 202 is performed by the solid state relay 602 so that the switching is done quietly. Then, once DSL service is detected over one of the telephone lines, the mechanical relay 602 is turned on and switched to the same position as the solid state relay 602 to provide a low impedance conduit for DSL signals between the current telephone line and the DSL modem 124.

FIG. 7 is a flowchart 700 illustrating another emboαiment of a method for identifying which of a plurality of telephone lines has DSL service available thereon. The method begins at block 702. Initially, a solid state relay, such as the relay 602 (FIG. 6) and a mechanical relay, such as the relay 402 are positioned m a default position pursuant to block 704. The default position may be, for example, the position B illustrated m FIG. 6 wherein the relay 602 interconnects the line 106 and the transformer 204. Next, the current line, or the line currently connected to the relay, is probed to detect the presence of DSL service pursuant to block 706. That is, the line to which the relay 602 is currently switched is probed for DSL service. In one embodiment, the probing comprises transmitting activation tones, pursuant to conventional DSL protocol, over the current l ne. As discussed above, the switching device controller 222 (FIG. 3) includes an activation tone generator 302 for generating these activation tones.

The switching device controller 222 then detects the presence of DSL service on the current line pursuant to block 708. In one embodiment, the response detector 304 (FIG. 3) detects a response to the transmitted activation tones to determine the presence of DSL service on the current line. If no DSL service is detected pursuant to block 708, then execution proceeds to block 710.

At block 710, the switching device controller 222 (FIG. 3) waits for the expiration of a predetermined time period. As discussed above, the switching device controller 222 includes the timer 308, which periodically notifies the switching device controller 222 of the expiration of the predetermined time period.

After expiration of the predetermined time period, execution proceeds to block 712, wherein the position of the relay 602 is switched. In particular, the relay control module 306 of the switching device controller 222 switches the configuration, or the position, of the relay 602 via digital control along control lines 230. The relay control module 306 then switches the position of the relay 602 from, for example, the position B to the position A to change the current telephone line from one telephone line to another.

Once the position of the relay 602 has been switched pursuant to block 712, execution returns to bloc 706 wherein the new current telephone line is probed as discussed above. This method then continues until DSL service is detected pursuant to block 708.

If DSL service is detected pursuant to block 708, then execution proceeds to block 714. According to block 714, the relay control module 306 (FIG. 3) positions the mechanical relay 402 in the same position as the solid state relay 602 so that the mechanical relay 402 is connected to the line over which DSL service is present. The mechanical relay 402 is then activated, or turned on, so that DSL signals may pass between the DSL modem components and the current telephone line over the mechanical relay with relatively low impedance.

The invention has been described above with reference to specific embodiments. It will, however, be evident that various modifications and changes may be made thereto without departing from the broader spirit and scope of the invention as set forth in the appended claims. The foregoing description and drawings are, accordingly, to be regarded in an illustrative rather than a restrictive sense. What is claimed is:

Claims

1. A DSL mode for detecting DSL service on first and second telephone lines, comprising: a data processor; and a switching device coupled to the first and second telephone lines and to the data processor for selectively switching connection between the each of the telephone lines and the data processor until detecting DSL service on either the first telephone line or the second telephone line.

2. The DSL modem according to claim 1, wherein the switching device further comprises at least one solid state relay for selectively switching connection between each of the telephone lines, the solid state relay being controlled by the data processor .

3. The DSL modem according to claim 2, wherein the switching device further comprises at least one mechanical relay for connecting the telephone line detected as having DSL service thereon to the data processor.

4. The DSL modem according to claim 1, wherein the switching device is configured to probe the first and second telephone lines by periodically transmitting activation tones over the first and second telephone lines until the DSL modem receives a response from the DSL service.

5. The DSL modem according to claim 1, further comprising a transformer, the switching device being disposed between the transformer and the first and second telephone lines.

6. A method for detecting DSL service on a plurality of telephone lines, comprising: coupling a DSL modem having a data processor to first and second telephone lines; connecting the data processor to the first telephone line; probing the first telephone line to detect the availability of DSL service on the first telephone line; switching connection of the data processor from the first line to the second line; and probing the second telephone line to detect the availability of DSL service on the second telephone line if no DSL service is detected on the first telephone line.

7. The method according to claim 6, further comprising repeating the probing the first telephone line and the probing the second telephone line until DSL service is detected on either the first telephone line or the second telephone line.

8. The method according to claim 6, wherein the probing the first telephone line and the probing the second telephone line are performed over at least one relay.

9. The method according to claim 6, wherein the probing the first telephone line and the probing the second telephone line are performed by at least one solid state relay.

10. The method according to claim 6, wherein the probing the first telephone line and the probing the second telephone line are performed by at least one solid state relay, further comprising: identifying whether the DSL service s available over the first telephone line or the second telephone line; and connecting the identified telephone line to the DSL modem with a mechanical relay.

lϊ

11. A method of identifying which of a plurality of telephone lines has DSL service available thereon, comprising: coupling the plurality of telephone lines to a switching device; periodically transmitting activation tones via the switching device over each of the telephone lines until receiving a response over one of the telephone lines; and identifying the telephone line over which the response was received as the telephone line having DSL service available thereon.

12. The method of identifying which of a plurality of telephone lines has DSL service available thereon according to claim 11, wherein the periodically transmitting further comprises: providing a relay disposed within the switching device for switching connection between the telephone lines; periodically causing the relay to switch connection between from of the telephone lines to another of the telephone lines until receiving the response.

13. The method of identifying which of a plurality of telephone lines has DSL service available thereon according to claim 12, wherein the relay further comprises a solid state relay.

14. The method of identifying which of a plurality of telephone lines has DSL service available thereon according to claim 13, further comprising: providing a mechanical relay disposed within the switching device; and connecting the mechanical relay to the identified telephone line.

15. A device for identifying which of a plurality of telephone lines has DSL service available thereon, comprising:

DSL modem means coupled to first and second telephone lines ; means for probing the first telephone line to detect the availability of DSL service on the first telephone line; means for probing the second telephone line to detect the availability of DSL service on the second telephone line if no DSL service is detected on the first telephone line.

16. The device for identifying which of a plurality of telephone lines has DSL service available thereon according to claim 15 wherein the means for probing the first telephone line and the means for probing the second telephone line comprise relays.

17. The device for identifying which of a plurality of telephone lines has DSL service available thereon according to claim 15 wherein the means for probing the first telephone line and the means for probing the second telephone line comprise solid state relays.

18. The device for identifying which of a plurality of telephone lines has DSL service available thereon according to claim 15, further comprising: means for identifying whether the DSL service is available over the first telephone line or the second telephone line; and means for connecting the identified telephone line to the DSL modem with a mechanical relay.

19. A device for identifying which of a plurality of telephone lines has DSL service available thereon, comprising: means for coupling the plurality of telephone lines to a switching device; means for periodically transmitting activation tones via the switching device over each of the telephone lines until receiving a response over one of the telephone lines; and means for identifying the telephone line over which the response was received as the telephone line having DSL service available thereon.

20. The device for identifying which of a plurality of telephone lines has DSL service available thereon according to claim 19, wherein the means for periodically transmitting activation tones comprises a data processor.