Abstract:
System and method for partitioning a DSLAM network. In this regard, one such network can be broadly summarized by a representative communication system comprising a digital subscriber line access multiplexer (DSLAM) that is communicatively coupled on its line-side to a high-speed digital link. The DSLAM is communicatively coupled through the high-speed digital link with the trunk side of a remote line access unit (RLAU). The RLAU is communicatively coupled on its line-side to a first digital subscriber line (DSL).

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of U.S. Provisional Patent Application Ser. No. 60/309,993 filed on Aug. 3, 2001, and entitled “DSL Extender” which is hereby incorporated by reference in its entirety. 
    
    
     FIELD OF THE INVENTION 
     The present invention generally relates to digital subscriber line (DSL) systems. More specifically, the invention relates to a system and method for partitioning a digital subscriber line access multiplexer (DSLAM) system. 
     DESCRIPTION OF THE RELATED ART 
     First generation digital subscriber line access multiplexers (DSLAMs) were typically located within the wire centers, also known as central offices (CO), to provide digital subscriber line (DSL) services to multiple customers located within a customer serving area (CSA) centered around the CO. The CO environment provided advantages related to DSLAM installation, service, and maintenance. As DSL architectures evolved, DSLAMs were installed in alternative locations such as remotely-located digital loop carrier (DLC) cabinets, so as to extend DSL coverage to subscribers served by DLC systems. The DSLAMs installed in these alternative remote locations have been generally connected to a CO through a high-speed digital link, such as a synchronous optical network (SONET) optical link. 
     While there are several advantages in placing DSLAMs at remote locations so as to provide larger DSL coverage, merely moving a DSLAM that has been designed for CO use to a remote location may not provide an optimum solution. Some of the issues related to such remotely-located DSLAMs include poor serviceability, space constraints, environmental constraints, and powering constraints. An improved architecture that provides a different partitioning of a DSLAM network is desirable to reduce the impact of such issues. 
       FIG. 1  illustrates a typical CO providing DSL service to multiple customers. The DS LAM  100 , shown located inside the CO  110 , is a principal component of a communication system that is designed to provide DSL service to multiple customers from a centralized location. 
     ADSL is a popular service provided for residential customers due to the asymmetric nature of data usage by such customers. Business users may prefer a more symmetric data flow, and Symmetric DSL (SDSL) provides one solution to this requirement. To service both asymmetric as well as symmetric users, a DSLAM typically incorporates a limited number of ADSL line cards together with additional line cards corresponding to other DSL standards. The various DSL standards are generally referred to collectively as a group, by the term xDSL, where the letter “x” may be suitably replaced by an appropriate letter to define one particular type of DSL. The xDSL group includes DSL technologies such as SDSL, ISDN digital subscriber line (IDSL), very-high speed DSL (VDSL) and high-speed DSL (HDSL). 
       FIG. 1  illustrates DSLAM  100  providing ADSL service to residences  130  and  135  using local loops  160  and  185 . Residences  130  and  135  are located within the CSA of CO  110 . HDSL service is provided to a business customer, XYZ Inc., located in a business location  140 . DSLAM  100  provides this HDSL service using a HDSL link  165 , which is typically longer than a telephone local loop. HDSL is a symmetric baseband transmission system with the upstream and downstream data rates being identical. While earlier versions of HDSL utilized two or more pairs of wires, recent developments in HDSL technology permit simultaneous upstream and downstream transmission over a single pair of wires. 
     On the trunk side of DSLAM  100 , a high-speed data link  190  is shown connecting the DSLAM  100  to the edge switch  105 , which is connected to the Internet. Data link  190  may, for example, carry data packets contained inside an ATM transport mechanism. 
       FIG. 2  illustrates the DSLAM  100  located in a remote cabinet  200  that is connected to CO  110  via a high-speed digital link  205 . Residences  230  and  235  that are being provided ADSL service by DSLAM  100  are located in the extended CSA of CO  110 . Business location  240  is also shown in this extended CSA, and is provided HDSL service by DSLAM  100 . 
       FIG. 3  is a block diagram representation of the main functional blocks inside a typical DSLAM such as DSLAM  100 . The various blocks shown in  FIG. 3  generally represent circuit packs that are plugged into a DSLAM chassis. The circuit pack architecture permits easy insertion and/or removal, thereby permitting a certain degree of flexibility in configuring the DSLAM  100  to provide various types of DSL service. It also allows relatively easy replacement of defective circuit packs, a replacement that may be carried out while the DSLAM is in operation without simultaneously affecting all of the multiple customers that are being provided DSL service. 
     The high-speed data link  190  of the trunk-side interface circuit  305 , connects DSLAM  100  to an edge switch located in the CO. Data link  190  may carry data packets over various transport protocols, such as ATM and TCP/IP. On the line-card side of the trunk-side interface circuit  305 , data links such as links  307 ,  309 , and  317  connect the interface circuit  305  to multiple line cards. 
     Three xDSL line cards  310 ,  315 , and  320  are shown in  FIG. 3 . While xDSL line cards  310  and  315  may be designed to provide ADSL service to two independent residential customers, xDSL line card  320  may be designed to provide HDSL service to a business customer. 
     A typical circuit inside an xDSL line card, is shown inside xDSL line card  320 . Framer  322 , digital signal processor (DSP)  324 , and analog front end (AFE)  326  elements are used to convert a binary digital signal being carried on link  317  from the trunk-side interface circuit  305 , into a downstream signal that is suitably formatted for transmission into link  180 . For providing ADSL service, this conversion scheme may incorporate a discrete multi-tone (DMT) encoding system, while for HDSL service a 2B1Q format may be used. 
     Framer  322 , digital signal processor (DSP)  324 , and analog front end (AFE)  326  are also used to implement a complementary upstream conversion scheme for DSL data received via link  180 . 
     Host processor  328  is used to control the various elements such as framer  322  and DSP  324 , located in the xDSL line card  320 . This control is generally implemented by firmware and/or software that is stored in memory devices (not shown) that are associated with host processor  328 . 
     While one form of software upgrade may be carried out through remote downloads using suitable circuitry, firmware upgrades generally necessitate physical access to the xDSL line card  320 . Such firmware upgrades are typically carried out by service personnel who travel to the remote location and unplug the xDSL line card  320  to upgrade the appropriate hardware. 
     System processor  330  is used for operations, administration, maintenance and provisioning (OAM&amp;P) of the various circuit packs inside the DSLAM  100 . For example, provisioning the DSLAM  100  may include such procedures as would be necessary to provide various types of DSL service via different types of xDSL line cards. Maintenance may include inventory procedures as well as failure reporting. System processor  330  interacts with various processors, such as the host processor  328 , inside DSLAM  100  using system-level software and/or firmware. This system-level software may be remotely upgraded through a suitable communication medium (not shown) that links DSLAM  100  to the CO  110 . Firmware upgrades typically require physical access by service personnel. 
     Service visits, whether for repair, maintenance, or upgrade purposes, constitute a significant monetary expense that telephone companies strive to minimize. It is therefore desirable that circuitry incorporated into remotely-located equipment, such as DSLAM  100  of  FIG. 3 , should be designed robustly to minimize expensive service visits, and to maximize mean-time-between-failures (MTBF). 
     Maximizing MTBF encompasses various actions such as reducing hardware circuitry, reducing circuit complexity, reducing packaging size, and reducing heat dissipation. 
     SUMMARY OF THE INVENTION 
     The present invention provides a system and method for partitioning a DSLAM network. In this regard, one such system can be broadly summarized by a representative communication system comprising a digital subscriber line access multiplexer (DSLAM) that is communicatively coupled on its line-side to a high-speed digital link; and a first remote line access unit (RLAU) that is communicatively coupled on its trunk-side to the DSLAM through the high-speed digital link, and is communicatively coupled on its line-side to a first digital subscriber line (DSL). 
     Another embodiment can be described as a digital communication system that includes a first circuit comprising a portion of a digital subscriber line access multiplexer (DSLAM) line card, the first circuit located at a first location; and a second circuit comprising a remainder portion of the DSLAM line card, the second circuit located at a second location. 
    
    
     
       DESCRIPTION OF THE DRAWINGS 
       Many aspects of the invention can be better understood with reference to the following drawings. The components in the drawings are not necessarily drawn to scale, emphasis instead being placed upon clearly illustrating the principles of the present invention. Moreover, in the drawings, like reference numerals designate corresponding parts throughout the several views. 
         FIG. 1  is an illustration of a typical central office providing DSL service to multiple customers located within a customer serving area. 
         FIG. 2  is an illustration of a DSLAM located in a remote cabinet providing DSL service to multiple customers located within an extended customer serving area. 
         FIG. 3  is a block diagram representation of the main functional blocks inside a typical DSLAM. 
         FIG. 4   a  illustrates a communication system that provides partitioning of a DSLAM network by using a remote line access unit of the invention. 
         FIG. 4   b  illustrates a remote line access unit of the invention with splitter functionality integrated inside it. 
         FIG. 5  illustrates a communication system incorporating a DSLAM in a CO, together with a remote line access unit (RLAU) of the invention located inside a business location. 
         FIG. 6  is a block diagram representation of the main functional blocks inside an exemplar remote line access unit. 
         FIG. 7  is a block diagram representation of the main functional blocks inside a DSLAM that incorporates the present invention. 
         FIG. 8  illustrates a communication system located in a college campus that incorporates a DSLAM and multiple RLAUs. 
         FIG. 9  illustrates a “hybrid” DSLAM located at a CO, and integrates traditional xDSL service with xDSL service using RLAUs. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Having summarized various aspects of the present invention, reference will now be made in detail to the description of the invention as illustrated in the drawings. While the invention will be described in connection with these drawings, there is no intent to limit it to the embodiment or embodiments disclosed therein. On the contrary, the intent is to cover all alternatives, modifications and equivalents included within the spirit and scope of the invention as defined by the appended claims. 
     DSL network coverage over an extended CSA is traditionally provided by installing a DSLAM in a remote cabinet. The DSLAM typically communicates with an edge switch located in a CO via a high-speed digital trunk such as a SONET fiber-optic trunk. 
       FIG. 4   a  illustrates a communication system  400  that provides DSL service over an extended CSA, by utilizing a DSLAM  450  that incorporates the present invention and is located in central office  440 , together with a remote line access unit (RLAU) of the present invention located in a remote cabinet  420 . 
     On its trunk side, DSLAM  450  communicates with an edge switch  415  using high-speed digital trunk  410 . On its line side, DSLAM  450  communicates with RLAU  460  through a high-speed digital link  430  that has a large bandwidth. DSLAM  450  incorporates suitable hardware to interface into this high-speed digital link  430 . An example of a communication link that may be used for implementing high-speed digital link  430 , is a fiber-optic link capable of supporting wavelength-division-multiplexing (WDM) and utilizing technologies such as SONET and Gigabit Ethernet. The use of such communication links in ring configurations and in long-distance inter-city communication systems, is known to persons of ordinary skill in the art. The bandwidth of such communication links has been under-utilized due to lack of customer demand in certain cases and due to over-providing in certain other cases. The high-speed digital link  430  may be used to exploit such unused bandwidth. 
     RLAU  460  provides a simplified and robust architecture to deliver DSL services from remote cabinet  420 . Communication links  462  and  464  are two examples of communication links that provide ADSL service from the RLAU  460  to residential customers residing in residences  455  and  460 . Links  462  and  464  connect the RLAU  460  to the splitter function  435 . It may be relevant to point out, that while  FIG. 4   a  depicts the splitter function  435  as existing external to RLAU  460 , several system configurations may physically incorporate the splitter functionality inside the RLAU  460 . The links  462  and  464  individually transport downstream as well as upstream ADSL data. 
     Splitter  436  used here for explanation purposes in a full-rate ADSL application, combines the downstream ADSL signal that is transmitted by the RLAU  460  over link  462 , with the analog voice frequency (VF) signal carried from the plain-old-telephone-system (POTS) network over link  467 . The combined downstream signal is then transmitted to the wiring panel  425  via link  436 . 
     Wires entering and exiting the remote cabinet  420  are interconnected using jumpers, such as jumper  426 , in the wiring panel  425 . The downstream ADSL signal together with the downstream analog VF signal that is present at jumper  426  is connected by the twisted wire pair  445  to the residence  455 . Splitter  456  is located on the outside wall of residence  455 , and splits the signal transmitted via twisted wire pair  445 , into an analog VF signal and a downstream ADSL data signal. The analog VF signal may be routed to a telephone  457 , while the downstream ADSL data signal is connected to a PC  458 . The downstream ADSL signal entering PC  458  is generally routed to an ADSL modem that may be installed inside the PC  458  or may be installed as an external modem that is connected by a cable to the PC  458 . 
     An upstream ADSL data signal generated by PC  458 , together with the upstream analog VF signal from telephone  457  is transmitted from the residence  455  towards the remote cabinet  420  over the same external twisted wire pair  445 . 
       FIG. 4   a  also illustrates a HDSL connection that connects RLAU  460  to business location  465 . The PC that is shown inside business location  465  illustrates a customer premise equipment (CPE)  467 . CPE  467  typically incorporates a modem, which in this case is a HDSL modem. The modem may be an independent device serving one individual user or may be a modem that is incorporated into a server that is a part of a local area network (LAN) inside business location  465 . 
       FIG. 4   b  illustrates an RLAU  461  with the splitter function  435  incorporated inside. In addition to the high-speed digital link  430 , RLAU  461  is provided with a voice link  468 , shown by the dotted line connection from POTS system  466 . POTS system  466  is pictorial representation of various voice processing elements, such as a CO switch. While  FIG. 4   b  illustrates POTS system  466  inside a CO, it will be recognized by persons of ordinary skill in the art, that it may be replaced by other voice processing elements, such as a DLC, a private branch exchange voice switch located outside a CO, or a voice gateway. It will also be recognized that voice link  466  may be implemented in a variety of ways using a variety of signaling formats. Accordingly the voice processing elements may also be selected to accommodate such formats. For example, a GR-303/V5.2 voice gateway may be used to implement one of several standards that are known to people of ordinary skill in the art. 
     Voice link  468  may be physically implemented as a communication link that is distinct from high-speed digital link  430 , or it may be integrated into the high-speed digital link  430 . Voice link  468  carries POTS-related voice information in the form of analog base-band signals, and/or as signals in other transmission formats. Transmission formats encompass a variety of technologies such as derived-voice transmission, carrier-based transmission, and base-band digital data transmission. 
       FIG. 5  illustrates a communication system  500  incorporating a DSLAM  450  in a CO  440 , together with a RLAU  460  located in a basement  510  of a customer premise  515 . Customer premise  515  of  FIG. 5 , represents several types of structures, encompassing residential as well as business customers. Such structures which include for example, dormitories, apartment buildings, condominium complexes, hotels, and public housing units, are sometimes referred to as multi-tenant units (MTU) or as multi-dwelling units (MDU). 
     While DSLAM  450  is shown located inside basement  510 , it will be apparent to persons of ordinary skill in the art, that the DSLAM  450  may be installed in other facilities such as utility poles, curb-side cabinets, or office closets. When installed in basement  510 , the links  522 ,  524  and  526  that are shown together with DSLAM  460  may be installed as part of an existing inter-building wiring network. This wiring network may utilize, for example, CAT-5 cabling, fiber-optic cabling, or twisted pair wires to interconnect various offices and various floors. The inter-building wiring network may also incorporate other devices such as multiplexers and de-multiplexers, and encompass various LAN architectures such as star, daisy-chain, or bus structures. The PCs shown in  FIG. 5 , constitute the CPEs that are served by RLAU  460 . The type of DSL service provided in this application may for example, be SDSL rather than ADSL, and may encompass various transport technologies such as Ethernet and ATM. RLAU  460  can be provisioned with the appropriate line cards to cater to the particular type of DSL service used. 
       FIG. 6  is a block diagram representation of the main functional blocks inside an exemplar RLAU. RLAU  460  includes several RLAU-xDSL line ( 620 ,  625 ,  630 ), which are suitably configured to provide DSL service via links  662 ,  664 , and  666 . Links  662 ,  664 , and  666  are selected to accommodate transport of the appropriately-selected DSL technologies. For example, if ADSL service is to be provided over link  662 , this link  662  is selected to be a POTS twisted wire pair. On the other hand, if HDSL service is to be provided over link  662 , twisted wire pair suitable for long-distance signal transport similar to that used for T-1 transport, may be selected instead. 
     Using RLAU-xDSL line card  620  as an example, the AFE functionality, as well as functionality of other circuitry that may be typically incorporated into an xDSL line card of RLAU  460 , is explained. 
     AFE  624  on RLAU-xDSL line card  620  provides an xDSL interface for RLAU  460  into link  662 . One of the functions incorporated into AFE  624  is a transceiver circuit, which is associated with line-driver functionality in certain applications. Other circuit elements contained in AFE  624  may include 2 wire-to-4 wire hybrid converters, and impedance matching circuitry. 
     AFE  624  is designed to accommodate the particular flavor of DSL that is supported on link  662 . For example, AFE  624  may be designed to accommodate signal characteristics related to line-length and line-impedance matching that are necessary to transmit and receive DSL signals over link  662 . AFE  624  may also include digital-to-analog (D/A) conversion as well as analog-to-digital (A/D) conversion that may be needed to convert the line signals carried on link  662 , into binary digital signals that can be interfaced into the DLSAM interface block  615  associated with RLAU-xDSL line card  620 . 
     In the upstream direction (from RLAU  460  towards CO), the DSLAM interface block  615  accepts digital signals that are transmitted upstream by the one or more RLAU-xDSL line cards ( 624 ,  629 ,  634 ) inside RLAU  460 , aggregates these signals, and converts the aggregated signal into a format that is appropriate for transmitting into the high-speed digital link  430 . A complementary process is carried out for downstream signals that are received from the CO over high-speed digital link  430 . 
     RLAU  460  is designed to provide robustness and to minimize cost. Towards this end, the embodiment shown in  FIG. 6 , eliminates hardware circuitry that uses systems operating software. The costs and service issues related to systems operating software installed within communication systems located inside remote cabinets, is fairly significant, and the minimization and/or elimination of such software is very desirable. Also, the use of relatively simple hardware such as shown in  FIG. 6 , allows greater packaging density while minimizing heat dissipation from the RLAU  460 . Greater packaging density translates to providing DSL service to a larger number of customers from a single unit such as RLAU  460 . 
       FIG. 7  is a block diagram representation of the main functional blocks inside an exemplar DSLAM that incorporates the present invention. DSLAM  450  includes several DSLAM-xDSL line cards ( 720 ,  725 ,  730 ) that constitute the CO-end equipment to complement the RLAU-xDSL line cards installed inside an RLAU at a corresponding remote end. 
     For example, DSLAM-xDSL line card  720  may be an ADSL line card that complements an RLAU-xDSL line card that has been configured to serve an ADSL customer from a remotely-located RLAU. The DSLAM-xDSL line card  720 , used here for example purposes, has an RLAU interface block  760  that accepts an upstream digital signal from the high-speed digital link  430  and carries out the complementary function to that executed by the DSLAM interface block  615  inside RLAU  460  ( FIG. 6 ). 
     A line-formatted digital signal appearing on high-speed digital link  430  is converted by the RLAU interface block  760  into a binary digital signal that is selectively routed to one of the several DSLAM-xDSL line ( 720 ,  725 ,  730 ). DSLAM-xDSL line card  720  is connected to RLAU interface block  760  via link  762 . A binary digital signal, which may be carried over link  762 , is connected to a digital signal processor (DSP)  724  in xDSL line card  720 . DSP  724  carries out multiple processing functions upon this binary digital signal. These functions typically include filtering and modem operations. 
     Framer  722  implements a suitable framing format to convert this binary digital signal into a signal format that can be carried over the high-speed digital trunk  410 . Trunk-side interface circuit  710  aggregates multiple binary digital signals from one or more DSLAM-xDSL line cards that are installed in DSLAM  450  and transfers this aggregated signal into high-speed digital trunk  410 , which typically connects DSLAM  450  to an edge switch located in a CO. 
     While the functioning of the DSLAM  450  is explained with reference to the upstream signal transmission path, it will be understood that the explanation will be applicable with corresponding equivalency in the downstream signal transmission path as well. 
     Both framer  722  and DSP  724  may be implemented as programmable devices that may be dynamically configured through the use of software and/or firmware to implement various hardware functions. Framer  722 , for example, may be implemented using a field-programmable-gate-array (FPGA), or alternatively, using an application-specific-integrated-circuit (ASIC). It can also be implemented via a programmable processor or engine that may be embedded inside a DSL processing engine. 
     It will be understood that the functionality of devices such as framer  722 , DSP  724 , and host processor  726 , located on the DSLAM-xDSL line card  720  may be collectively referred to as a digital signal processing circuit. In this context, the term “digital signal processing” is not merely confined to the DSP  724  device. 
     Software and/or firmware that is typically stored in memory devices (not shown) in the DSLAM-xDSL line card  720 , is used by the host processor  726  located in DSLAM-xDSL line card  720 , to carry out OAMP functions. These OAMP functions are coordinated through the system processor  750  located in DSLAM  450 . System processor  750  may have suitable communication interfaces that enable devices external to DSLAM  450 , to interact with DSLAM  450 , for providing various functions such as software downloads for DSLAM system upgrade. Use of such communication interfaces is known to persons of ordinary skill in the art. 
     As DSLAM  450  is located locally inside a CO, OAMP operations may be carried out by service personnel, in a manner that is much easier and convenient in comparison to carrying out such operations upon a DSLAM installed at a remote location. 
       FIG. 8  illustrates a communication system located in a college campus that incorporates a DSLAM and multiple RLAUs. DSLAM  820  communicates with one or more RLAUs that are connected to a high-speed digital link, such as the campus LAN backbone  840 . While DSLAM  820  may communicate with an edge switch  415  at CO  440 , through high-speed digital trunk  805  in a industry-standard format, using technologies such as SONET and ATM, the campus LAN backbone  840  will be a large-bandwidth network typically using an Ethernet-oriented structure. 
     The DSLAM architecture highlighted in communication system  800  of  FIG. 8 , optimizes the bandwidth usage on campus LAN backbone  840 . The RLAUs shown inside various buildings of college campus  880 , may be installed as stand-alone communication equipment or may be incorporated into existing equipment that interact with the LAN backbone  840 . For example, RLAU  1   850  may be a plug-in card that is installed inside a PC used by a student in building  1   845 . This RLAU  1   850  is connected via DSL link  847  to a modem that may be installed inside a PC used by the student in his off-campus residence. Links  857  and  867  are DSL links that connect RLAUs  860  and  870  to modems in other off-campus residences. 
       FIG. 9  illustrates a “hybrid” DSLAM architecture  900  that is an exemplar application incorporating RLAUs into an existing DLSAM serving DSL customers from a CO  905 . DSLAM  910  provides ADSL service to residence  915  via POTS link  920  using a traditional ADSL line card inside DSLAM  910 . HDSL service is provided in a traditional architecture using a HDSL line card installed in DSLAM  910 , to business  947  via HDSL link  945 . 
     RLAU  980  is connected to CO  905  through a high-speed digital link  950  that is associated with DSLAM  910 . RLAU  980  provides xDSL service to multiple customers located in an extended CSA. xDSL service is provided to these customers via links  955 ,  960  and  965  that are shown as example links. A second RLAU  985  is also shown connected to DSLAM  910 . RLAU  985  may provide xDSL service to a second set of customers located in a second extended CSA. 
     It should be emphasized that the above-described embodiments of the present invention are merely possible examples of implementations and merely set forth for a clear understanding of the principles of the invention. Many variations and modifications may be made to the above-described embodiment of the invention without departing substantially from the spirit and principles of the invention. 
     For example, it will be appreciated by persons of ordinary skill in the art that the partitioning of circuit functions between the DSLAM-xDSL line card in the DSLAM, and the complementary RLAU-xDSL line card in the RLAU, may be carried out in many different ways. This circuit partitioning is dependent on overall system design. For example, while in one case software at the RLAU may be completely eliminated, in a second case software related to some limited functions, such as failure-reporting, may be included. In a third case, the circuit functions of the RLAU line cards may be integrated into circuit packs containing traditional DSL line card circuits. In yet another case, software associated with an RLAU may be integrated into software for other equipment that may be installed in a remote location. All such modifications and variations are intended to be included herein within the scope of the present invention and protected by the following claims.