CA2327118A1 - Access multiplexer for digital subscriber loops - Google Patents
Access multiplexer for digital subscriber loops Download PDFInfo
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- CA2327118A1 CA2327118A1 CA002327118A CA2327118A CA2327118A1 CA 2327118 A1 CA2327118 A1 CA 2327118A1 CA 002327118 A CA002327118 A CA 002327118A CA 2327118 A CA2327118 A CA 2327118A CA 2327118 A1 CA2327118 A1 CA 2327118A1
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- access apparatus
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04Q—SELECTING
- H04Q3/00—Selecting arrangements
- H04Q3/58—Arrangements providing connection between main exchange and sub-exchange or satellite
-
- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04Q—SELECTING
- H04Q1/00—Details of selecting apparatus or arrangements
- H04Q1/02—Constructional details
- H04Q1/10—Exchange station construction
-
- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04Q—SELECTING
- H04Q11/00—Selecting arrangements for multiplex systems
- H04Q11/04—Selecting arrangements for multiplex systems for time-division multiplexing
-
- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04Q—SELECTING
- H04Q2213/00—Indexing scheme relating to selecting arrangements in general and for multiplex systems
- H04Q2213/1301—Optical transmission, optical switches
-
- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04Q—SELECTING
- H04Q2213/00—Indexing scheme relating to selecting arrangements in general and for multiplex systems
- H04Q2213/13039—Asymmetrical two-way transmission, e.g. ADSL, HDSL
-
- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04Q—SELECTING
- H04Q2213/00—Indexing scheme relating to selecting arrangements in general and for multiplex systems
- H04Q2213/13107—Control equipment for a part of the connection, distributed control, co-processing
-
- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04Q—SELECTING
- H04Q2213/00—Indexing scheme relating to selecting arrangements in general and for multiplex systems
- H04Q2213/13383—Hierarchy of switches, main and subexchange, e.g. satellite exchange
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- Engineering & Computer Science (AREA)
- Computer Networks & Wireless Communication (AREA)
- Physics & Mathematics (AREA)
- Astronomy & Astrophysics (AREA)
- General Physics & Mathematics (AREA)
- Data Exchanges In Wide-Area Networks (AREA)
Abstract
In order to reduce complexity and equipment costs, access apparatus for connecting a plurality of DSL lines to a data network comprises a plurality of interface units connected to a plurality of DSL lines, respectively, for converting DSL signals to digital signals, or vice versa; at least one digital signal processor (DSP) unit for processing the digital signals and routing the processed signals to the data network, and for processing signals from the data network and supplying the resulting digital signals to the interface units, respectively, and a session switch for making virtual connections between respective ones of the interface units whose associated DSL lines are active and the DSP. The session switch maintains each connection for the duration of a session. With such an arrangement, a pool of DSPs may be shared by a much larger number of DSL lines.
Description
ACCESS MULTIPLEXER FOR DIGITAL SUBSCRIBER LOOPS
DESCRIPTION
TECHNICAL FIELD:
The invention relates to access multiplexers for use with digital subscriber loops (DSLAMs) and is especially applicable to DSLAMs for use in central offices to interface a plurality of digital subscriber loops (DSLs) with a high speed data network operating with SONET, ATM and so on.
BACKGROUND ART:
In known access apparatus for digital subscriber loops, generally known as DSL access multiplexers (DSLAMs), each DSL has a dedicated high speed modem. This is very expensive, involves high power consumption and is difficult/expensive to upgrade. In addition, it allows only one dedicated specific line code per line, which means that, as standards change, it is necessary to change line cards. Moreover, as a general rule, each DSL line is connected to a modem device within the DSLAM even when it is not used, which leads to redundancy.
Because existing systems are so hardware intensive, known systems have only a small number of lines per DSLAM. It is believed that, at present, 1344 DSL lines is the maximum and the line cards occupy a rack approximately 2 metres high.
Typically, the access apparatus at the central office comprises an input splitter, i.e., a bank of filters, for separating the high frequency data signals from the low frequency "POTS" signals, analog interface circuitry (hybrids, amplifiers, and so on), for processing the high frequency data signals in the usual way, a bank of analog-to-digital (A-D) converters for digitizing the high frequency data signals and supplying the resulting digital signals to a digital signal processor and a bank of digital-to-analog (D-A) converters for converting digital signals from the DSP to analog signals for transmission via the DSLs.
It has been proposed to reduce the number of DSPs for a particular number of DSL lines by sharing each DSP between several DSL lines. Thus, in US
6,084,885 issued July 4, 2000, which is incorporated herein by reference, R.E.
Scott disclosed apparatus for sharing a DSP using statistical properties of data received from DSL. From the input splitter, several data streams are routed to a plurality of hybrid circuits capable of operating at high speeds (above 25 kilohertz). A bank of DAA interface circuits provide the usual amplification etc.
and then supply the data streams to a bank of D-A converters which convert respective ones of the data streams to digital signals and supply them to a digital multiplexer (DMUX). The DMUX is coupled to a DSP which can select only one of the digital signals from the DMUX at any given time. Hence, the DSP is shared by the plurality of data streams. According to Scott, this is feasible because the data is "bursty" in nature. In fact, over the time intervals concerned, i.e., during a particular session, DSL signals are not particularly bursty in nature, so any improvement would be limited. Also, the system introduces significant overhead. Consequently, this DSP sharing scheme is not entirely satisfactory.
DISCLOSURE OF INVENTION:
An object of the present invention is to eliminate or at least mitigate the disadvantages of the known systems and, to this end, provides a DSLAM
apparatus in which each modem can serve a plurality of DSL lines.
According to the present invention, there is provided access apparatus for connecting a plurality of DSL lines to a data network, comprising a plurality of interface units connected to a plurality of DSL lines, respectively, for converting DSL signals to digital signals, or vice versa; a plurality of digital signals processor (DSP) units for processing the digital signals and routing the processed signals to the data network and for processing signals from the data network and supplying the resulting digital signals to the interface units, respectively, and a session switch for making virtual connections between respective ones of the interface units whose associated DSL lines are active and selected ones of the DSPs, the session switch maintaining each said connection for the duration of a session.
In preferred embodiments of the invention, a plurality of DSPs are connected to the session switch which may select any one of the DSPs for connection to a particular active DSL.
DESCRIPTION
TECHNICAL FIELD:
The invention relates to access multiplexers for use with digital subscriber loops (DSLAMs) and is especially applicable to DSLAMs for use in central offices to interface a plurality of digital subscriber loops (DSLs) with a high speed data network operating with SONET, ATM and so on.
BACKGROUND ART:
In known access apparatus for digital subscriber loops, generally known as DSL access multiplexers (DSLAMs), each DSL has a dedicated high speed modem. This is very expensive, involves high power consumption and is difficult/expensive to upgrade. In addition, it allows only one dedicated specific line code per line, which means that, as standards change, it is necessary to change line cards. Moreover, as a general rule, each DSL line is connected to a modem device within the DSLAM even when it is not used, which leads to redundancy.
Because existing systems are so hardware intensive, known systems have only a small number of lines per DSLAM. It is believed that, at present, 1344 DSL lines is the maximum and the line cards occupy a rack approximately 2 metres high.
Typically, the access apparatus at the central office comprises an input splitter, i.e., a bank of filters, for separating the high frequency data signals from the low frequency "POTS" signals, analog interface circuitry (hybrids, amplifiers, and so on), for processing the high frequency data signals in the usual way, a bank of analog-to-digital (A-D) converters for digitizing the high frequency data signals and supplying the resulting digital signals to a digital signal processor and a bank of digital-to-analog (D-A) converters for converting digital signals from the DSP to analog signals for transmission via the DSLs.
It has been proposed to reduce the number of DSPs for a particular number of DSL lines by sharing each DSP between several DSL lines. Thus, in US
6,084,885 issued July 4, 2000, which is incorporated herein by reference, R.E.
Scott disclosed apparatus for sharing a DSP using statistical properties of data received from DSL. From the input splitter, several data streams are routed to a plurality of hybrid circuits capable of operating at high speeds (above 25 kilohertz). A bank of DAA interface circuits provide the usual amplification etc.
and then supply the data streams to a bank of D-A converters which convert respective ones of the data streams to digital signals and supply them to a digital multiplexer (DMUX). The DMUX is coupled to a DSP which can select only one of the digital signals from the DMUX at any given time. Hence, the DSP is shared by the plurality of data streams. According to Scott, this is feasible because the data is "bursty" in nature. In fact, over the time intervals concerned, i.e., during a particular session, DSL signals are not particularly bursty in nature, so any improvement would be limited. Also, the system introduces significant overhead. Consequently, this DSP sharing scheme is not entirely satisfactory.
DISCLOSURE OF INVENTION:
An object of the present invention is to eliminate or at least mitigate the disadvantages of the known systems and, to this end, provides a DSLAM
apparatus in which each modem can serve a plurality of DSL lines.
According to the present invention, there is provided access apparatus for connecting a plurality of DSL lines to a data network, comprising a plurality of interface units connected to a plurality of DSL lines, respectively, for converting DSL signals to digital signals, or vice versa; a plurality of digital signals processor (DSP) units for processing the digital signals and routing the processed signals to the data network and for processing signals from the data network and supplying the resulting digital signals to the interface units, respectively, and a session switch for making virtual connections between respective ones of the interface units whose associated DSL lines are active and selected ones of the DSPs, the session switch maintaining each said connection for the duration of a session.
In preferred embodiments of the invention, a plurality of DSPs are connected to the session switch which may select any one of the DSPs for connection to a particular active DSL.
Preferably, each interface apparatus is arranged to exchange signalling with a user modem connected thereto by the associated DSL line so as to set up a session and maintain the connection therebetween. An activity processor in the session switch detects user activity indicative of the user's desire to establish a session and connects the corresponding DSL to a selected one of the DSPs. The activity processor can be programmed so that, in normal circumstances, the duration of the session may be determined by the user, either by setting the session duration at its commencement, or simply by ending the session at will.
Preferably, each of the DSL lines can be connected to any DSP that is not busy.
With the present disparity between DSL rates and DSP processing capabilities, each DSP may process signals from several of the DSL lines simultaneously.
Preferably, the apparatus comprises one or more pools of DSPs and a plurality of groups of said interface circuits, the interface circuits in a particular group being connected to said one or more DSP pools by means of a high bandwidth communications channel, for example an optical fiber, optical free space link, and so on. Typically, the groups of interface circuits will be at different physical locations which may be within a particular central office, in remote distribution boxes, or even in different central offices.
Each interface circuit then may comprise means for extracting the digital signals and an optical fiber interface for effecting parallel to serial conversion of the digital signals and routing the serial digital signals via the high bandwidth link. Advantageously, this arrangement reduces the need for data buses between the interface circuitry and the DSPs, thereby reducing physical requirements and allowing a large number of interface units at remote locations to be connected easily to one DSP pool. The interface circuitry may be arranged to route signals from only active lines onto the high bandwidth data link.
The foregoing and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description, taken in conjunction with the accompanying drawings, of preferred embodiments of the invention which are given by way of example only.
BRIEF DESCRIPTION OF THE DRAWINGS:
Figure 1 is a simplified block schematic diagram illustrating an existing central office connecting a plurality of DSL users to a broadband data network;
Figure 2 is a simplified schematic diagram of a digital subscriber loop access module (DSLAM) according to an embodiment of the present invention and which comprises a bank of analog interface units and a pool of DSPs;
Figure 3 is a simplified block diagram of a second embodiment of the invention in which several banks of analog interface units are coupled to pools of DSPs by optical communications channels; and Figure 4 is a much-simplified block schematic diagram of a system in which banks of analog interface units associated with different central offices are coupled to a common DSP pool.
BEST MODES) FOR CARRYING OUT THE INVENTION:
In the following description, identical or similar items in the different Figures have the same reference numerals.
In the portion of the telecommunications system illustrated in Figure 1, a plurality of user stations 10,, ..., 10N, comprising, for example, conventional analog telephone sets 11 ~, ..., 11 N, respectively, and computers 12,, ..., 12N, respectively, are connected to a central office 13 by digital subscriber loops DSL,, ..., DSLN, respectively. Within the central office 13, the DSL lines terminate at a POTS splitter 14 which comprises a bank of lowpass and high pass filters for separating each signal received from the corresponding one of the DSL lines DSL~, ..., DSLN into a respective one of high frequency data signals HF,, ..., HFN and a corresponding one low frequency POTS telephone signals P~, ..., PN. The splitter 14 routes the POTS signals P,, ..., PN to the conventional telephone network (PSTN) 15 and routes the high frequency data signals HF~, ..., HFN to a bank of digital subscriber loop access multiplexers (DSLAMs) AM,, ..., AMN, respectively. The access multiplexers AM,, ..., AMN
convert the high frequency signals HF~, ..., HFN to corresponding digital signals D~, ..., DN, respectively, and supply them to a switching device 16 which routes them to the broadband "backbone" data network 17. The nature of the switching device 16 will depend upon the data network 17, for example an Asynchronous Transfer Mode (ATM) or a Synchronous Optical Network 5 (SONET).
In existing DSL systems, the access multiplexers AM,, ..., AMN are dedicated to respective ones of the DSLs DSL~, ..., DSLN, which is disadvantageous for a number of reasons explained hereinbefore.
Figure 2 illustrates a DSLAM embodying the present invention which may replace one or each of the DSLAMs AMA,..., AMN shown in Figure 1, i.e., which may be connected between the POTS splitter 14 and the switching device 16. The DSLAM shown in Figure 2 comprises a bank of analog interface units AFE~,..., AFEN connected to the digital subscriber loops DSL,,..., DSLN, respectively, a pool 18 of digital signal processors DSP,, ..., DSPM, a session switch 19 connected between the analog interface units AFE~, ..., AFEN and the processors DSP~, ..., DSPM, and a network interface unit 20 connecting the processors DSP,, ..., DSPM to the network switch 16 (Figure 1 ) via an optical fiber 21. An activity and accounting processor 22 associated with the session switch 17 monitors the analog interface units AFE,, ..., AFEN
for activity on the loops DSL,, ..., DSLM (Figure 1 ) and, when activity is detected, controls the session switch 19 to connect the corresponding one of the analog interface units AFE,, ..., AFEN to a selected one of the processors DSP,, ..., DSPM which is not busy. The session switch 19 maintains the connection for either a predetermined time determined by the user when initiating the session, or until activity ceases for a preset interval.
A memory 23 is associated with the network interface unit 20 and the DSP pool 18. The network interface unit 20 may write to the memory 23 whereas the processors DSP,, ..., DSPM can both write to, and read from, the memory 23. The memory 23 stores line codes, line condition information, and other operational data.
It is possible, therefore, to select different line codes from memory 23 for use by a particular DSP to process a particular digital signal. Indeed, if the DSP is fast enough to process several digital signals simultaneously, the same DSP may use different line codes simultaneously for the different digital signals.
The line code selection may be initiated by the activity processor 22 in response to a demand from the user station when setting up the session. For example, the user station might select either Asynchronous DSL or Synchronous DSL according to the nature of the session.
The DSLAM shown in Figure 2 allows any one of the DSL lines DSL,, ..., DSLN to be connected to any one of the processors DSP~, ..., DSPM. It is envisaged that, under normal traffic conditions, only ten per cent of the DSL
lines DSL,, ..., DSLN will be active so the number M of DSPs need be only one tenth of the number N of DSLs.
Figure 3 illustrates a second embodiment of the invention in which L
groups G,...G~ of analog interface units AFE,, ..., AFEN and associated ones of L session switches 19',, ..., 19'~ and L activity processors 22',, ..., 22'x, respectively, are physically separate, for example in different racks at different locations within the central office, but connected to a remote common DSP
unit pool 18'. Optical interface units 24,,..., 24~, respectively, connect the session switches 19'x, ..., 19'x, respectively, to the DSP unit pool 18' via optical fibers 25,,..., 25~, respectively. Each of the optical interface units 24,, ..., 24~ converts the digital signals of only the "active" DSLs from the corresponding group of interface units AFE,, ..., AFEN into a serial optical signal and transmits the serial optical signal via the associated one of the optical fibers to the DSP unit 18'. In the DSP unit 18', the optical fibers 25~, ..., 25~
are connected to an optical interface unit 24" which converts the group of serial optical signals into electrical signals again and routes the electrical signals via a bus 26 to the bank of DSPs 18.
In effect, the session switch 19 of the DSLAM shown in Figure 2 has been divided into session switch unit 19" associated with the processor pool 18 and session switch units 19'x, ..., 19'x, respectively. Likewise, the activity and accounting processor 22 shown in Figure 2 has been replaced by a session processor 22" associated with session switch 19" and activity processors, 22',, ..., 22'~ associated with session switches 19',, ..., 19'x, respectively.
In operation, each of the activity processors 22',,...,22' will supply to the corresponding one of the user stations 10,,...,10 a DSL tone, having a frequency higher than the limit of the lowpass fitters, for example at least 25kHz. The tone indicates that service is available. When a particular user station, say user station 10N (not shown) in group G,, wishes to begin a session, it will detect the first tone and emit its own tone, requesting service.
The activity processor 22', will detect the tone and send to the session processor 22" a request to set up a virtual connection via one of the processors DSP,,...,DSPM. Assuming, for example, that DSPM has free capacity, the session processor 22" will send a reply to the activity processor 22', to the effect that processor DSPM, whereupon activity processor 22, will advise the modem of user station 10N that a connection is available and the user station may begin transmitting.
The session will continue until the user station 1 ON terminates it, perhaps by sending a suitable signal to activity processor 22', which then will send a signal to the session processor 22" advising it to terminate the virtual connection and, once the connection has been terminated, providing the DSL
tone again on the corresponding DSL line. The DSL line then is available and the processor DSPM has capacity to handle another session. Alternatively, the activity processor 22', may cause termination if and when there has been no activity on the line for a predetermined "time out" period.
It should be appreciated that each of the digital signal processors may process several signals simultaneously and that, as before, different line codes from memory 23 may be used for the different signals. An advantage of this arrangement is that it allows the user stations to select different line codes according to the kind of session being requested and, for example, the kind of bandwidth required. For example, a user might select Asynchronous DSL for Internet browsing and Synchronous DSL for networked video games or "video-on-demand".
The selected DSP may demultiplex the serial digital signals for processing and then multiplex them again for transmission to the data network. If the processing speed of the DSP is sufficient, it may process several serial data streams simultaneously.
It is envisaged that, where the analog interface units are in physically separate groups, the groups need not be housed within the same central office but rather could be housed in other central offices or in distribution boxes.
Thus, Figure 4 illustrates a system in which the DSP unit 18' is located in a main central office and the groups A...L of analog interface units are housed in respective ones of a plurality of remote central offices. The analog interface units and the central DSP unit 18' will be similar to those shown in Figure 3.
In this case, however, the optical fibers 25,, ..., 25~ interconnect the groups of interface units in a ring configuration. While such a ring connection is particularly suitable when the data network is a SONET network, it should be appreciated that alternative interconnection configurations could be used instead.
INDUSTRIAL APPLICABILITY
It will be appreciated that embodiments of the present invention require less costly equipment, specifically fewer modems, than existing designs and can be upgraded relatively easily. A significant advantage is that the line codes can, if desired, be selected on a "per call" basis and the set of line codes form which the selection is made, i.e. stored in memory 23, can be changed relatively easily, which facilitates upgrading to accommodate new line codes or simply changing line codes according to specific requirements.
Preferably, each of the DSL lines can be connected to any DSP that is not busy.
With the present disparity between DSL rates and DSP processing capabilities, each DSP may process signals from several of the DSL lines simultaneously.
Preferably, the apparatus comprises one or more pools of DSPs and a plurality of groups of said interface circuits, the interface circuits in a particular group being connected to said one or more DSP pools by means of a high bandwidth communications channel, for example an optical fiber, optical free space link, and so on. Typically, the groups of interface circuits will be at different physical locations which may be within a particular central office, in remote distribution boxes, or even in different central offices.
Each interface circuit then may comprise means for extracting the digital signals and an optical fiber interface for effecting parallel to serial conversion of the digital signals and routing the serial digital signals via the high bandwidth link. Advantageously, this arrangement reduces the need for data buses between the interface circuitry and the DSPs, thereby reducing physical requirements and allowing a large number of interface units at remote locations to be connected easily to one DSP pool. The interface circuitry may be arranged to route signals from only active lines onto the high bandwidth data link.
The foregoing and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description, taken in conjunction with the accompanying drawings, of preferred embodiments of the invention which are given by way of example only.
BRIEF DESCRIPTION OF THE DRAWINGS:
Figure 1 is a simplified block schematic diagram illustrating an existing central office connecting a plurality of DSL users to a broadband data network;
Figure 2 is a simplified schematic diagram of a digital subscriber loop access module (DSLAM) according to an embodiment of the present invention and which comprises a bank of analog interface units and a pool of DSPs;
Figure 3 is a simplified block diagram of a second embodiment of the invention in which several banks of analog interface units are coupled to pools of DSPs by optical communications channels; and Figure 4 is a much-simplified block schematic diagram of a system in which banks of analog interface units associated with different central offices are coupled to a common DSP pool.
BEST MODES) FOR CARRYING OUT THE INVENTION:
In the following description, identical or similar items in the different Figures have the same reference numerals.
In the portion of the telecommunications system illustrated in Figure 1, a plurality of user stations 10,, ..., 10N, comprising, for example, conventional analog telephone sets 11 ~, ..., 11 N, respectively, and computers 12,, ..., 12N, respectively, are connected to a central office 13 by digital subscriber loops DSL,, ..., DSLN, respectively. Within the central office 13, the DSL lines terminate at a POTS splitter 14 which comprises a bank of lowpass and high pass filters for separating each signal received from the corresponding one of the DSL lines DSL~, ..., DSLN into a respective one of high frequency data signals HF,, ..., HFN and a corresponding one low frequency POTS telephone signals P~, ..., PN. The splitter 14 routes the POTS signals P,, ..., PN to the conventional telephone network (PSTN) 15 and routes the high frequency data signals HF~, ..., HFN to a bank of digital subscriber loop access multiplexers (DSLAMs) AM,, ..., AMN, respectively. The access multiplexers AM,, ..., AMN
convert the high frequency signals HF~, ..., HFN to corresponding digital signals D~, ..., DN, respectively, and supply them to a switching device 16 which routes them to the broadband "backbone" data network 17. The nature of the switching device 16 will depend upon the data network 17, for example an Asynchronous Transfer Mode (ATM) or a Synchronous Optical Network 5 (SONET).
In existing DSL systems, the access multiplexers AM,, ..., AMN are dedicated to respective ones of the DSLs DSL~, ..., DSLN, which is disadvantageous for a number of reasons explained hereinbefore.
Figure 2 illustrates a DSLAM embodying the present invention which may replace one or each of the DSLAMs AMA,..., AMN shown in Figure 1, i.e., which may be connected between the POTS splitter 14 and the switching device 16. The DSLAM shown in Figure 2 comprises a bank of analog interface units AFE~,..., AFEN connected to the digital subscriber loops DSL,,..., DSLN, respectively, a pool 18 of digital signal processors DSP,, ..., DSPM, a session switch 19 connected between the analog interface units AFE~, ..., AFEN and the processors DSP~, ..., DSPM, and a network interface unit 20 connecting the processors DSP,, ..., DSPM to the network switch 16 (Figure 1 ) via an optical fiber 21. An activity and accounting processor 22 associated with the session switch 17 monitors the analog interface units AFE,, ..., AFEN
for activity on the loops DSL,, ..., DSLM (Figure 1 ) and, when activity is detected, controls the session switch 19 to connect the corresponding one of the analog interface units AFE,, ..., AFEN to a selected one of the processors DSP,, ..., DSPM which is not busy. The session switch 19 maintains the connection for either a predetermined time determined by the user when initiating the session, or until activity ceases for a preset interval.
A memory 23 is associated with the network interface unit 20 and the DSP pool 18. The network interface unit 20 may write to the memory 23 whereas the processors DSP,, ..., DSPM can both write to, and read from, the memory 23. The memory 23 stores line codes, line condition information, and other operational data.
It is possible, therefore, to select different line codes from memory 23 for use by a particular DSP to process a particular digital signal. Indeed, if the DSP is fast enough to process several digital signals simultaneously, the same DSP may use different line codes simultaneously for the different digital signals.
The line code selection may be initiated by the activity processor 22 in response to a demand from the user station when setting up the session. For example, the user station might select either Asynchronous DSL or Synchronous DSL according to the nature of the session.
The DSLAM shown in Figure 2 allows any one of the DSL lines DSL,, ..., DSLN to be connected to any one of the processors DSP~, ..., DSPM. It is envisaged that, under normal traffic conditions, only ten per cent of the DSL
lines DSL,, ..., DSLN will be active so the number M of DSPs need be only one tenth of the number N of DSLs.
Figure 3 illustrates a second embodiment of the invention in which L
groups G,...G~ of analog interface units AFE,, ..., AFEN and associated ones of L session switches 19',, ..., 19'~ and L activity processors 22',, ..., 22'x, respectively, are physically separate, for example in different racks at different locations within the central office, but connected to a remote common DSP
unit pool 18'. Optical interface units 24,,..., 24~, respectively, connect the session switches 19'x, ..., 19'x, respectively, to the DSP unit pool 18' via optical fibers 25,,..., 25~, respectively. Each of the optical interface units 24,, ..., 24~ converts the digital signals of only the "active" DSLs from the corresponding group of interface units AFE,, ..., AFEN into a serial optical signal and transmits the serial optical signal via the associated one of the optical fibers to the DSP unit 18'. In the DSP unit 18', the optical fibers 25~, ..., 25~
are connected to an optical interface unit 24" which converts the group of serial optical signals into electrical signals again and routes the electrical signals via a bus 26 to the bank of DSPs 18.
In effect, the session switch 19 of the DSLAM shown in Figure 2 has been divided into session switch unit 19" associated with the processor pool 18 and session switch units 19'x, ..., 19'x, respectively. Likewise, the activity and accounting processor 22 shown in Figure 2 has been replaced by a session processor 22" associated with session switch 19" and activity processors, 22',, ..., 22'~ associated with session switches 19',, ..., 19'x, respectively.
In operation, each of the activity processors 22',,...,22' will supply to the corresponding one of the user stations 10,,...,10 a DSL tone, having a frequency higher than the limit of the lowpass fitters, for example at least 25kHz. The tone indicates that service is available. When a particular user station, say user station 10N (not shown) in group G,, wishes to begin a session, it will detect the first tone and emit its own tone, requesting service.
The activity processor 22', will detect the tone and send to the session processor 22" a request to set up a virtual connection via one of the processors DSP,,...,DSPM. Assuming, for example, that DSPM has free capacity, the session processor 22" will send a reply to the activity processor 22', to the effect that processor DSPM, whereupon activity processor 22, will advise the modem of user station 10N that a connection is available and the user station may begin transmitting.
The session will continue until the user station 1 ON terminates it, perhaps by sending a suitable signal to activity processor 22', which then will send a signal to the session processor 22" advising it to terminate the virtual connection and, once the connection has been terminated, providing the DSL
tone again on the corresponding DSL line. The DSL line then is available and the processor DSPM has capacity to handle another session. Alternatively, the activity processor 22', may cause termination if and when there has been no activity on the line for a predetermined "time out" period.
It should be appreciated that each of the digital signal processors may process several signals simultaneously and that, as before, different line codes from memory 23 may be used for the different signals. An advantage of this arrangement is that it allows the user stations to select different line codes according to the kind of session being requested and, for example, the kind of bandwidth required. For example, a user might select Asynchronous DSL for Internet browsing and Synchronous DSL for networked video games or "video-on-demand".
The selected DSP may demultiplex the serial digital signals for processing and then multiplex them again for transmission to the data network. If the processing speed of the DSP is sufficient, it may process several serial data streams simultaneously.
It is envisaged that, where the analog interface units are in physically separate groups, the groups need not be housed within the same central office but rather could be housed in other central offices or in distribution boxes.
Thus, Figure 4 illustrates a system in which the DSP unit 18' is located in a main central office and the groups A...L of analog interface units are housed in respective ones of a plurality of remote central offices. The analog interface units and the central DSP unit 18' will be similar to those shown in Figure 3.
In this case, however, the optical fibers 25,, ..., 25~ interconnect the groups of interface units in a ring configuration. While such a ring connection is particularly suitable when the data network is a SONET network, it should be appreciated that alternative interconnection configurations could be used instead.
INDUSTRIAL APPLICABILITY
It will be appreciated that embodiments of the present invention require less costly equipment, specifically fewer modems, than existing designs and can be upgraded relatively easily. A significant advantage is that the line codes can, if desired, be selected on a "per call" basis and the set of line codes form which the selection is made, i.e. stored in memory 23, can be changed relatively easily, which facilitates upgrading to accommodate new line codes or simply changing line codes according to specific requirements.
Claims (20)
1. Access apparatus for connecting a plurality of DSL lines to a data network, comprising (i) a plurality of interface units connected to a plurality of DSL lines, respectively, for converting DSL signals to digital signals, or vice versa.
(ii) a set of one or more digital signal processor (DSP) units for processing the digital signals and routing the processed signals to the data network and for processing signals from the data network and supplying the resulting digital signals to respective ones of the interface units, and (iii) a session switch unit for making virtual connections between respective ones of the interface units whose associated DSL lines are active and said one or more DSP units, the session switch maintaining each said connection for the duration of a session.
(ii) a set of one or more digital signal processor (DSP) units for processing the digital signals and routing the processed signals to the data network and for processing signals from the data network and supplying the resulting digital signals to respective ones of the interface units, and (iii) a session switch unit for making virtual connections between respective ones of the interface units whose associated DSL lines are active and said one or more DSP units, the session switch maintaining each said connection for the duration of a session.
2. Access apparatus according to claim 1, wherein a plurality of DSP units are connected to the session switch unit and the session switch unit is operable to select any one of the DSP units for connection to a particular active DSL.
3. Access apparatus according to claim 1, wherein each interface unit is arranged to exchange signalling with a user station connected thereto by the associated DSL line so as to set up a session and maintain the connection therebetween.
4. Access apparatus according to claim 1, 2 or 3, further comprising an activity processor associated with the session switch unit detecting user activity indicative of an attempt to establish a session and connecting the corresponding DSL to said one of the DSPs.
5. Access apparatus according to claim 4, wherein the activity processor is arranged to permit, in normal circumstances, the duration of the session to be determined by the user.
6. Access apparatus according to claim 5, wherein the activity processor is arranged to permit the user to set a predetermined session duration when initiating the session.
7. Access apparatus according to claim 5, wherein the activity processor is arranged to determine session duration by terminating the session when there has been no activity for a predetermined interval.
8. Access apparatus according to claim 5, wherein the activity processor is arranged to terminate the session in response to a termination request from the user station.
9. Access apparatus according to any preceding claim, wherein each DSP
is arranged to process signals from several of the DSL lines simultaneously.
is arranged to process signals from several of the DSL lines simultaneously.
10. Access apparatus according to any preceding claim, comprising a plurality of groups of said interface circuits, the interface circuits in a particular group being connected to at least one said DSP by means of a high bandwidth communications channel.
11. Access apparatus according to claim 10, wherein the high bandwidth communications channel uses optical transmission.
12. Access apparatus according to claim 11, wherein the high bandwidth communications channel comprises an optical fiber.
13. Access apparatus according to claim 10, wherein the groups of interface circuits are each at a different physical location within the same central office.
14. Access apparatus according to claim 10, wherein at least one of the groups of interface circuits is at a physical location remote from the central office.
15. Access apparatus according to claim 10, wherein the groups of interface circuits are each located at a different central office.
16. Access apparatus according to any one of claims 10 to 15, wherein each interface circuit group comprises means for extracting the digital signals of active DSL lines and an optical fiber interface for effecting parallel to serial conversion of said digital signals and routing the serial digital signals via the high bandwidth link communications channel.
17. Access apparatus according to any preceding claim, further comprising memory means for storing a selection of different line codes for use by said one or more digital signal processors, the or each digital signal processor using a particular one of the line codes in dependence upon the digital particular signal to be processed thereby.
18. Access apparatus according to claim 17, further comprising means for loading said line codes into said memory.
19. Access apparatus according to claim 17 or 18, wherein said particular line code is selected in dependence upon information supplied by a corresponding interface unit when the session is being initiated.
20. Access apparatus according to claim 8, wherein the or each DSP uses different line codes for different ones of the plurality of digital signals.
Priority Applications (3)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA002327118A CA2327118A1 (en) | 2000-11-30 | 2000-11-30 | Access multiplexer for digital subscriber loops |
| PCT/CA2001/001698 WO2002045383A2 (en) | 2000-11-30 | 2001-11-30 | Apparatus for connecting digital subscriber lines to central office equipment |
| AU2002223347A AU2002223347A1 (en) | 2000-11-30 | 2001-11-30 | Apparatus for connecting digital subscriber lines to central office equipment |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA002327118A CA2327118A1 (en) | 2000-11-30 | 2000-11-30 | Access multiplexer for digital subscriber loops |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA2327118A1 true CA2327118A1 (en) | 2002-05-30 |
Family
ID=4167772
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA002327118A Abandoned CA2327118A1 (en) | 2000-11-30 | 2000-11-30 | Access multiplexer for digital subscriber loops |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA2327118A1 (en) |
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| EP2059016A1 (en) * | 2006-08-28 | 2009-05-13 | Huawei Technologies Co., Ltd. | Method,system and device for xdsl crosstalk cancelation |
-
2000
- 2000-11-30 CA CA002327118A patent/CA2327118A1/en not_active Abandoned
Cited By (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| EP2059016A1 (en) * | 2006-08-28 | 2009-05-13 | Huawei Technologies Co., Ltd. | Method,system and device for xdsl crosstalk cancelation |
| EP2059016A4 (en) * | 2006-08-28 | 2010-01-20 | Huawei Tech Co Ltd | Method,system and device for xdsl crosstalk cancelation |
| CN101136659B (en) * | 2006-08-28 | 2012-01-25 | 华为技术有限公司 | Method, system and equipment for crosstalk elimination of xDSL multiple lines |
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