WO2001058205A9 - Procede et dispositif assurant un service adsl a bande large boucle longue de grande capacite - Google Patents

Procede et dispositif assurant un service adsl a bande large boucle longue de grande capacite

Info

Publication number
WO2001058205A9
WO2001058205A9 PCT/US2001/003459 US0103459W WO0158205A9 WO 2001058205 A9 WO2001058205 A9 WO 2001058205A9 US 0103459 W US0103459 W US 0103459W WO 0158205 A9 WO0158205 A9 WO 0158205A9
Authority
WO
WIPO (PCT)
Prior art keywords
transmission line
adsl
transmission
repeater
atm
Prior art date
Application number
PCT/US2001/003459
Other languages
English (en)
Other versions
WO2001058205A3 (fr
WO2001058205A2 (fr
Inventor
Francis I Akers
Daniel W Agar
Frederick J Brandt
Original Assignee
Godigital Networks
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Godigital Networks filed Critical Godigital Networks
Publication of WO2001058205A2 publication Critical patent/WO2001058205A2/fr
Publication of WO2001058205A3 publication Critical patent/WO2001058205A3/fr
Publication of WO2001058205A9 publication Critical patent/WO2001058205A9/fr

Links

Classifications

    • 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
    • H04Q2213/13039—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
    • H04Q2213/13094—Range extender
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04Q—SELECTING
    • H04Q2213/00—Indexing scheme relating to selecting arrangements in general and for multiplex systems
    • H04Q2213/13191—Repeater
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04Q—SELECTING
    • H04Q2213/00—Indexing scheme relating to selecting arrangements in general and for multiplex systems
    • H04Q2213/13202—Network termination [NT]
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04Q—SELECTING
    • H04Q2213/00—Indexing scheme relating to selecting arrangements in general and for multiplex systems
    • H04Q2213/13203—Exchange termination [ET]
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04Q—SELECTING
    • H04Q2213/00—Indexing scheme relating to selecting arrangements in general and for multiplex systems
    • H04Q2213/1329—Asynchronous transfer mode, ATM

Definitions

  • ADSL Digital Subscriber Line
  • the present invention relates to method and apparatus for providing extended range broadband ADSL service for multiple users over a single twisted copper pair line.
  • DSL Digital Subscriber Line
  • An ADSL system uses the existing twisted copper pair telephone lines to transmit digital signals in addition to the analog telephone signals between the users and the telephone companies, or in some circumstances, between the users and internet service providers (ISPs).
  • ISPs internet service providers
  • ADSL systems can achieve access speeds that are approximately 150 times faster than the analog modems.
  • a significant advantage of ADSL systems is that they can exist concurrently with the telephone signals such that a user connected to the internet via an ADSL modem can, at the same time, place or receive telephone calls using the same existing telephone line. This eliminates the need for installation of a second or third telephone line as would be the case when using an analog modem. In turn, this translates to substantial savings to the user, not to mention the much faster data access.
  • DSL type services which provide digital access to the internet connections speed ranging from around 128 kbps up to 8 Mbps.
  • DSL systems include IDSL, HDSL,
  • HDSL-2 HDSL-2, SDSL, VDSL and RADSL, ADSL and ADSL Lite systems.
  • IDSL is an ISDN (Integrated Services Digital Network) based DSL system which uses 2B1Q line coding and typically supports duplex data transfer rates of 128 to 144 Kbps.
  • HDSL refers to High Bit-Rate DSL which is generally used to deliver Tl/El services, and supports full-duplex symmetric data transmission at rates up to 1.544 Mbps over 2 pairs of existing twisted copper pair telephone lines depending upon the transmission distance. While traditional Tl (El in Europe) requires repeaters at every 6,000 ft to boost the signal strength, an HDSL system can accommodate longer distances without the use of repeaters to support data transmission over approximately 12,000 kft.
  • HDSL-2 is a relatively new transmission technology that has recently become an ANSI standard for transmission of Tl (1.544 Mbps) rate data over a single copper pair. Unlike HDSL, HDSL-2 does not use 2B1Q encoding, but rather uses PAM-16 coding approach which allows for the same transmission bandwidth as HDSL, but using half as much copper plant (for example, one twisted copper pair instead of two). Similar to HDSL-2, G.shdsl has been recently developed as an ITU standard for data transmission using PAM-16 coding scheme.
  • SDSL is a symmetric DSL system that is essentially a 2-wire implementation of a 2B 1Q HDSL system.
  • One implementation of symmetric DSL supports Tl/El on a single twisted copper pair to a transmission distance of approximately 10,000 ft.
  • a more common implementation of SDSL transmits sub-Tl speeds (for example, 384 kbps) to greater distances (up to 18,000 feet).
  • VDSL Very High Bit-Rate DSL, has been proposed to support data rates exceeding 10 Mbps for comparatively shorter distances, such as 3,000 Kft.
  • ADSL or Asymmetric DSL
  • ADSL is defined by its ability to provide much faster downstream transmission rates (of up to approximately 8 Mbps) compared to upstream data transmission rates (of up to approximately 1 Mbps) Since most residential computer users connected to the internet generally spend the majo ⁇ ty of the time downloading information from the internet rather than uploading (or sending) information, this system is amenable to most users Moreover, given its applicability for the residential mass-market, ADSL is projected to be the dominant form of DSL in the future.
  • CAP modulation Car ⁇ erless amplitude and phase modulation
  • DMT modulation Discrete Multitone modulation
  • QAM Quadrature Amplitude Modulation
  • DMT modulation is a multicainer modulation system in which incoming data is collected and then distnaded over a large number of small individual earners each of which uses a form of QAM modulation, and creates these channels using Discrete Fast- Founer Transform
  • the ITU has specified DMT-based ADSL in its standards, and at the present time, the populanty of CAP-based ADSL appears to be on the decline.
  • ADSL-Lite also known as "G. te"
  • G. te is an ITU standard (G 992.2) for providing a lower-speed, lower-power, widely interoperable form of ADSL-DMT. Its speeds are limited to 1 5 Mbps downstream and 512 kbps upstream. This limitation results in a simpler chipset, thus enabling low-power operation and wide interoperability among the DSL products of multiple vendors.
  • a RADSL system is a Rate Adaptive DSL system that supports a wide range of DSL transmission rates. Onginally, RADSL systems were ADSL systems that used CAP modulation rather than DMT modulation
  • the existing telephone plant includes twisted copper pairs extending from telephone central offices to subscribers. This is known as the outside plant (OSP) and may reach 25 miles or more Statistically, 50% of subscnbers reside within a 12,000- foot radius of the central office, 85% reside within 18,000 feet and approximately 99% of subscribers are within 40,000 feet.
  • OSP outside plant
  • the transmission distance of a RADSL/ADSL system varies according to the transmission bandwidth. At short distances (less than 8,000 feet), the ADSL systems can transmit at their full rates. However, at longer distances, the speeds available with ADSL systems decrease. Indeed, the longer the copper loop, the less bandwidth the system can support. As the loop length increases, a point is reached at which the system ceases to function altogether. This point is generally somewhere between 15,000 and 18,000 feet, depending on wire gauge and condition.
  • ADSL systems and other DSL systems discussed above are generally limited to a transmission distance of up to 18,000 feet without the use of repeaters. It should be noted that the transmission distance is generally measured from the telephone company's central office to the customer premise equipment (CPE). In the United States, as discussed above, 18,000 feet covers less than 85% of subscribers. With higher transmission frequencies attenuating faster than at lower frequencies (for example, 784 kbps (SDSL) travels about 12,000 feet, while 256 kbps may travel up to 18,000 feet), and given a rapid rise in customer demands for higher speed internet access, customers are restricted ever more by their distance from the central office.
  • CPE customer premise equipment
  • an ADSL system at a transmission rate of 1.5 Mbps downstream may only work to a distance of 14,000 feet, serving approximately 60% of all potential subscribers.
  • the GDSL-8 system available from GoDigital Networks Corporation, the assignee of the present invention provides multiple (for example, eight) telephone channels over a single copper pair, using a GDSL ® Symmetric DSL transmission scheme transmitting at 544 kbps. Additional information related to the GDLS-8 system can be found in pending application no. 09/510,050 entitled Multiple Digital Subscriber Carrier System with Drop and Insert Repeater System, assigned to the assignee of the present application, and the disclosure of which is incorporated herein by reference in its entirety for all purposes.
  • the GDSL- 12 is configured to run at 784 kbps with a payload of 12 telephone channels.
  • the SDSL chips may transport anywhere from 160 kbps up to 2 Mbps in both directions simultaneously (symmetrical transmission) and are deployed in the telephone network for Tl, ISDN, DAML, xDSL and other services.
  • ADSL service is generally provided to the user with the downstream rate greater than the upstream rate.
  • one ADSL service from Pacific Bell provides 784 kbps downstream and 384 kbps upstream.
  • an asymmetric form of ADSL-DMT may be deployed to end- users.
  • US West currently offers some symmetric services to residential users that are not SDSL, but actually are ADSL-based. These services do not use 2B1Q transmission, but rather CAP modulation, and thus, fall into the category of ADSL systems discussed above.
  • ADSL high speed service for internet access uses an ATM (asynchronous transfer mode) transport from the subscribers' terminal (such as personal computers), through the ADSL system, an into the telephone company's ATM switching network.
  • ATM asynchronous transfer mode
  • ITU standards for ADSL transmission call for ATM to be the transport protocol.
  • An ATM network uses short, fixed-length cells with minimal headers, to allow calls to be routed at high speed by routing tables at each switch.
  • the header of each ATM cell typically consists of 5 bytes and the cell information field includes 48 bytes, making a total cell length of 53 bytes. Accordingly, the header of each ATM cell is configured to provide two main routing functions - a Virtual Path Identifier (VPI) and a Virtual Call Identifier (VCI).
  • VPN Virtual Path Identifier
  • VCI Virtual Call Identifier
  • ADSL Advanced Driver Assistance Systems
  • DMT-based repeaters may be developed to extend the range of ADSL transmission (i.e., repeating ADSL with additional ADSL spans), a separate circuit including the related hardware cost and a separate copper pair for each user is necessary.
  • a data loop extension in a communication system including a symmetric bidirectional transmission line having a first end and a second end; a remote termination unit coupled between the first end of the transmission line and a plurality of customer premise equipment, the remote termination unit configured to receive a plurality of ATM data from each customer premise equipment over a respective ADSL link for transmission over the transmission line; and a line card coupled to the second end of the transmission line configured to receive the ATM data transmitted from the remote termination unit over the transmission line; and at least one repeater coupled between the first and second end of the transmission line configured to detect the ATM data received from the remote termination unit and to regenerate the ATM data for transmission to the line card.
  • a method of providing data loop extension in a communication system comprising the steps of: providing a symmetric bi-directional transmission line having a first end and a second end; coupling a remote termination unit between the first end of the transmission line and a plurality of customer premise equipment, the remote termination unit configured to receive a plurality of ATM data from each customer premise equipment over a respective ADSL link for transmission over the transmission line; coupling a line card to the second end of the transmission line configured to receive the ATM data transmitted from the remote termination unit over the transmission line; and coupling at least one repeater between the first and second end of the transmission line configured to detect the ATM data received from the remote termination unit and to regenerate the ATM data for transmission to the line card.
  • the GDSL-8 and GDSL-12 systems presently available from GoDigital
  • the GDSL ® links are provided to transmit multiple services on a single copper loop are implemented using 2B1Q technology (i.e., the SDSL described above).
  • 2B1Q technology i.e., the SDSL described above.
  • PAM-16 technology for example, the G.shdsl or the HDSL-2 described above
  • GDSL links The connections over copper pairs using GDSL which transmit data in both directions between two pieces of telecommunications equipment as referred to as GDSL links.
  • the long loop broadband system in accordance with the present invention allows data from different ADSL users to be shared across a group of symmetric DSL trunks (GDSL links).
  • the group of trunks could, in one embodiment, may only include a single GDSL link (single copper pair).
  • multiple ADSL users may share the bandwidth on the GDSL links between RTU and CTU by taking ATM cells from the ADSL transmissions, properly addressing them and sending them over the GDSL links. While ATM is a convenient and inexpensive approach to provide the addressing, any scheme that addresses the data and allows it to be sent over any available trunk would be equally effective.
  • Figure 1 illustrates a block diagram of the overall system architecture in accordance with one embodiment of the present invention.
  • FIG. 2 illustrates a block diagram of the Remote Termination Unit (RTU) in accordance with one embodiment of the present invention.
  • RTU Remote Termination Unit
  • FIG. 3 illustrates a block diagram of the Central Termination Unit (CTU) in accordance with one embodiment of the present invention.
  • CTU Central Termination Unit
  • Figure 4 illustrates one embodiment of the present invention shows the geographic locations and distances between its elements, including total system reach.
  • Figure 5 illustrates one embodiment of the present invention implemented in GDSL-8 telephony pairgain system producing a mixed data plus voice line-powered system.
  • FIG. 1 illustrates a block diagram of the overall system architecture in accordance with one embodiment of the present invention.
  • CTU central termination unit
  • CO central office
  • ATM switch 105 configured to communicate with ATM controller 102 and data network 107, and Digital Subscriber Line Access Multiplexer (DSLAM) 106 coupled to four ADSL links 113 to each CTU line card 101.
  • backplane bus 103 supports time domain multiplexing (TDM) for transporting ATM cells.
  • alarm card 104 that communicates with CTU linecard 101 to provide alarm information such as channels out of service to the central office. It should be noted that the number of CTU line cards 101 in the overall system may be increased as long as there are available slots in the CTU shelf 100.
  • RTU remote termination unit
  • CPE Customer Premise Equipment
  • STR straight-through repeaters
  • the ATM cells from customer's CPE 109 are transmitted to RTU 108 and then transported over the line powered twisted pair 111 (the GDSL link) with intermediate stops at STRs 112, as needed, to the central office side.
  • the ATM cells received by CTU linecard 101 are decoded from the GDSL link into bit streams, still in the ATM cell format, and transmitted over backplane bus 103 to ATM controller 102.
  • ATM controller 102 is configured to connect to a single ATM link to ATM switch 105 to transmit and receive data from data network 107.
  • ATM cells received at CTU linecard 101 are converted into ADSL format and transported over a two-wire connection to an ADSL port (not shown) of DSLAM 106 which, then connects to ATM switch 105 for data communication with data network 107.
  • ADSL port not shown
  • one or more STRs 112 may be used as necessary between CTU linecard 101 at the central office side and RTU 108 at the remote end to extend the range of the system to 40,000 feet or even further, depending on wire gauge.
  • each deployed STR 112 in the network increases the overall range of the system by approximately 9,000 feet (the range, using G.shdsl or HDSL-2 transmission on 26 gauge wire).
  • STRs 112 may be configured to read the contents of an incoming HDSL-2 or G.shdsl GDSL connection and then to regenerate the signal and send it down to the next GDSL link. It should be noted that STRs 112 do not decode or process any of the ATM cells. Furthermore, STRs 112, similar to RTU 108, may be line powered by the dc voltage on the twisted copper pair 111 supplied from the central office.
  • Figure 2 illustrates a block diagram of Remote Terminal Unit 108 of Figure 1 in one embodiment of the present invention. As shown, RTU 108 is provided with GDSL link section 210, control section 220 and ADSL link section 230. In one embodiment, GDSL link section 210 is provided with transceiver 211 and transformer 212 which allows RTU 108 to be connected to single twisted copper pair 111 transmission path. Moreover, ADSL link section 230 which may be provided for communication with CPE
  • ADSL link section 230 in one embodiment allows RTU 108 to connect to each ADSL link 110 to respective CPEs 109.
  • control section 220 which includes processor 223 coupled to field programmable gate array (FPGA) 221 and flash SRAM 222, and in the manner shown, controls RTU 108 to property address incoming and outgoing data between GDSL link section 210 and ADSL link section 230 for connection between the twisted pair transmission path 111 and the plurality of ADSL links 110, respectively, at either side of RTU 108.
  • FPGA field programmable gate array
  • RTU 108 may be provided with a separate power supply 240 to provide power thereto.
  • RTU 108 may be powered by the dc voltage on twisted copper pair line 111 supplied from the CTU 100 at the central office side.
  • RTU 108 is configured to transmit and receive ATM cells on a GDSL link such as twisted copper pair 111.
  • the other end of RTU 108 is connected to a plurality of ADSL links 110, each configured to communicate with an ADSL modem at CPE 109 of each customer over a standard
  • the ADSL link section 230 may be configured with ADSL transceiver such as Copper Lite transceiver available from Centilium Corporation which are provided with an ADSL port on one side and an ATM port on the other, and the ATM port may be configured to communicate with multiple physical interfaces using 5-bit addressing.
  • each ADSL transceiver 232 may be configured to write ATM cells into a buffer.
  • RTU 108 is configured to transmit all cells with a given VPI down a particular ADSL link 110 as ATM cells.
  • RTU 108 may be configured to transmit idle cells down the ADSL link 110 when there are no valid data cells available, and these idle cells are discarded at CPE 109 at the customer's location
  • RTU 108 does not need to understand internet protocol (IP) and does not need to use an ATM Adaptation Layer (AAL) 3&4, a standard for adapting other types of data transmission (similar to TCP/IP) to be carried over an ATM network.
  • IP internet protocol
  • AAL ATM Adaptation Layer
  • CPE 109 may be configured to reassemble the data packets using AAL 3&4 standard to convert IP packets to ATM cells and vice versa.
  • FIG. 3 illustrates a block diagram of CTU line card 101 in accordance with one embodiment of the present invention.
  • ADSL link unit 310 there are provided ADSL link unit 310, control unit 320 and GDSL link unit 330.
  • power supply unit 340 coupled to control unit 320 for powering CTU line card 101 as well as for providing dc voltage on the twisted copper pair transmission path 111 to provide line powering to RTU 108 and STRs 112.
  • ADSL link unit 310 is provided with SRAM 311 and ADSL transceiver 312, while control unit 320 includes FPGA 321, Flash SRAM 322 and processor 323.
  • GDSL link unit 330 is provided with transceiver 331 and transformer 332.
  • CTU line card 101 the components of CTU line card 101 are substantially similar to that of RTU 108, but connected in the opposite direction of data transmission.
  • GDSL link unit 330 is coupled to twisted copper pair transmission path 111 ( Figure 1) to receive data from RTU 108 and in turn, to transmit data thereto under the control of control unit 320.
  • ADSL link unit 310 coupled to control unit 320 is configured to interface with the ADSL links 113 to
  • DSLAM 106 ( Figure 1).
  • ATM cells transmitted from the customer's CPE 109 to RTU 108 and sent over GDSL link 111 to CTU line card 101 are decoded into bit streams, still in the ATM format, and transmitted over TDM backplane bus 103 to ATM controller 102.
  • ATM controller 102 connects to a single ATM link that is then provided to ATM switch 105.
  • Table 1 below is a data transport table for the first upstream data link approach in accordance with the present invention.
  • Layer 1 format refers to the physical layer, for example, related to the speed of the transmission connection
  • Layer 2 format refers to the data link layer.
  • IP Internet Protocol
  • each CTU line card 101 carries one GDSL link 111 at 1,544 kbps each.
  • Each ATM cell is 53 bytes long, but can be allocated a space of 64 timeslots on the backplane 103.
  • line card 101 receives a bit clock (master clock) and a quadrature bit clock from the ATM controller 102 as well as a timeslot address and an ATM cell enable as will be discussed in further detail below.
  • Line card 101 receives the DSL bitstream from the associated RTU 108 and generates a corresponding serial bitstream.
  • an ATM cell is transmitted with additional address bits associated with it. In one embodiment, some of these bits may be used as address bits to indicate the proper destination ADSL link while others are used to indicate cell priority.
  • ATM controller 102 transmits 53 bytes during 53 timeslots, and receives 53 bytes during 53 timeslots (for example, interleaved with the first 53).
  • Line card 101 has no knowledge of routing and does not know how to read ATM cell headers, and thus, all cells are transferred whether valid, idle, or errored.
  • CTU 100 is configured to provide line powering for the system.
  • CTU 100 is provided with a power supply capable of supplying approximately 30 watts of power to the loop, via either a 260V or 380V interface.
  • backplane data bus 103 in one embodiment may be 8 bits wide. Moreover, as discussed above, each ATM cell is 53 bytes long, but each GDSL link section 330 carrying an ATM data stream may be allocated 64 timeslots
  • each GDSL link section 330 can be allocated 1,600 cells per second in both transmit and receive directions with a total of 32 GDSL link sections 330 available in a CTU shelf 100. Then, the total throughput requirement would be 51,200 cells in each direction per second.
  • One frame has 32*64 or 2,048 timeslots in each direction, or a total of 4,096 timeslots which can transfer 102,400 cells per second.
  • one frame transfers a total of 64 cells per second (32 each way, one for each GDSL link section 330), resulting in 625 usecond frame length.
  • the timeslots may be clocked in a period of 500 useconds followed by 125 useconds reserved for other uses. With a total of 4,096 timeslots in 500 useconds, the timeslot length and thus, the bit time, is 122 nseconds.
  • the master clock which shifts bits across the backplane bus 103 would run at 8.192 MHz. Accordingly, there may be a 250usecond transmit frame and then a 250 usecond receive frame, or the backplane direction can be reversed for every timeslot.
  • line cards 101 may be configured to receive an 8.192 MHz clock from the master clock with its rising edge at 0 degrees, and furthermore, may be configured to write and read the data on the rising edge of this clock. Additionally, line cards 101 may be configured to also receive a quadrature clock with its rising edge at 270 degrees relative to the first clock.
  • ATM controller 102 is configured to read and write the data in a similar manner, but in alternate timeslots. In this manner, a total of 3/4 of each timeslot is available for the data to cross the backplane 103 rather than only 1/2, which, at 8.192 MHz, translates to a time of 90 nseconds instead of 60 nseconds.
  • backplane 103 carries a GDSL span counter that counts from 1 to 32 using 5 bits (expandable to 64 if needed).
  • the span counter increments at every 128 timeslots allowing enough time to transmit and receive one ATM cell from a single span.
  • There can also be an ATM cell enable which can be configured to be active for 53 of each 64 timeslots. The remaining 11 timeslots are reserved for future use. For example, the first and last timeslots can be used as guardband for timing glitches as the timeslot counter is changing, and the other nine timeslots can carry overhead messages.
  • ATM controller 102 may be configured to generate the clock and timeslot information.
  • the master clock operating at 8.192 MHz does not need to be synchronized to a stratum clock (the network synchronization clock). Rather, it may derive its ATM cell timing from the network where available interface chips have a loop timing mode.
  • ATM controller 102 may include one FIFO which receives all of the cells from line card 101 across the backplane 103 in sequence.
  • the input of ATM controller 102 is gated by the ATM cell enable line.
  • Other timeslots which occur when ATM cell enable is inactive are not loaded into the FIFO, but can be used for other functions.
  • the output of ATM controller 102 is read by the ATM UNI chip itself, which does understand headers and addresses. All cells are sent to the external ATM switch 105 except for OAM (Operations, Administrations, and Maintenance) cells, which are a part of the ATM cell stream, coming from RTU 108. To use the OAM cells properly, it must know the timeslot from which they arrived.
  • OAM Operations, Administrations, and Maintenance
  • each RTU 108 is configured with its own unique serial number, for example, a Dallas Semiconductor's Silicon Serial Number.
  • RTU 108 may be configured to communicate this serial number in an OAM cell approximately once every second across each link to which it is connected, causing a negligible reduction in through traffic rate (1/1600).
  • the ATM UNI chip receives the OAM cell and associates that unique ID from the particular RTU 108 with a certain group of timeslots, that is, with a particular GDSL link unit 330.
  • RTU 108 may be associated with more than one GDSL link unit 330.
  • the software on the line cards 101 may be configured to compare switch settings with these identifiers, and display an address error if there is a mismatch. This would be helpful to field personnel when they wire the shelf.
  • each FIFO may be configured to drive a particular RTU 108, that is, multiple groups of 64 timeslots that are not necessarily sequential.
  • One FIFO may be enabled for 64 timeslots (one group), another for 192 timeslots (three groups), and so on.
  • Cells destined for a particular ADSL end user may be placed in a particular FIFO, and may thus be carried across any of the links to which that ADSL user is connected.
  • ATM controller 102 generates idle cells and sends them in all timeslots for which an actual cell is not available. It is much easier do this function once on ATM controller 102, rather than on every CTU line card 101.
  • the maximum number of RTUs 108 may be governed by the number of FIFOs in ATM controller 102.
  • Each group of GDSL trunks leading to RTU 108 is considered to be a VPI while each ADSL user is considered to be a VCI. Then, the maximum bandwidth of each VPI is programmed into the external ATM switch 105 and the committed information rate of each VCI is also programmed into the external ATM switch 105. These numbers can be altered as more links are added, or as the customer requests a higher grade of service, respectively.
  • the lowest 5 bits of the VCI can be reserved to indicate which user on a given RTU 108 receives the cell (giving a possible 32 users), with the higher order bits available to the external ATM switch 105 for other purposes.
  • the lowest 7 bits of the VPI may be reserved to indicate which RTU 108 receives the cell (giving a possible 128 RTUs 108), with the higher order bits available to the external ATM switch 105 for other purposes, among those being other GDSL shelves.
  • ATM controller 102 communicates with a single external ATM switch 105. It should be noted that if there is a connection to only one external ATM switch 105, that ATM switch 105 can perform all of the bandwidth management.
  • ATM controller 102 does not need a SAR (Sequestration, Assembly and Reassembly function), and thus, an ATM user network interface chip such as PMC-
  • the CTU shelf 100 must know which VPI to associate with a given RTU 108.
  • the logical place is RTU 108, but this approach may be impractical because the RTU 108 is sealed and may already be installed far away when ATM switch 105 is configured.
  • the VPI may be set by a set of front panel DIP switches on line card 101, which, in one embodiment, may be a bank of 8 switches per DSL link. It should be noted that this approach would render the Silicon Serial Number identification as discussed above unnecessary, thus simplifying the system design, and rendering redundant providing address error information as discussed above. Moreover, adding another trunk to an existing RTU 108 would simply require connecting the wires, then setting the VPI switches.
  • the ATM controller 102 loads all cells with a given VPI into a particular FIFO, and that FIFO is configured to send cells to multiple DSLs (i.e., GDSL links 111 to each respective RTU 108).
  • Table 2 For a given network having up to 22 Mbps of valid cells in each direction, at which rate several interfaces are available, Table 2 below illustrates some available connections.
  • the IBM interface may not be desirable because the total bandwidth required is too close to the actual amount necessary. There must be room for a few OAM cells as well as for possible future expansion. Additionally, the physical interface should match the available ATM switching equipment. As can be seen from the above, the SONET/SDH 155Mbps interface can handle different physical media running different distances, providing sufficient bandwidth, and interface SONET/SDH framers may be configured to add the necessary additional overhead bits for clocking and framing, for example. Furthermore, in one embodiment, network ATM switch 105 may be configured to handle all of the bandwidth management at the central office side and allow the system to simply to pass the cells along.
  • ATM cells are decoded from GDSL link 111 into bit streams, still in ATM format, and transmitted over a TDM backplane to ATM controller 102 which connects to a single ATM link to ATM switch 105.
  • CTU line card 101 may be configured to receive ATM data from two-wire ADSL connection to DSLAM 106 as discussed below.
  • the incoming cell traffic at the central office side may be handled without a separate ATM switch 105.
  • ATM cells are taken from ADSL-DMT connections to DSLAM 106 that resides in the same central office as CTU line card 101.
  • the connections are industry-standard ADSL-DMT 2-wire connections.
  • CTU line card 101 includes circuits that operate as ADSL CPE.
  • CTU line card 101 may operate in a similar manner as CPE 109 at the remote end, and thus, ATM cells may be read off of these connections and then processed by CTU line card 101 in a manner similar as described above.
  • CTU line cards 101 provided in the first upstream data link approach discussed above may co-exist physically side by side in the same central office system as CTU line cards 101 for the second upstream data link approach set forth below.
  • Table 3 below is a data transport table for the second upstream data link approach.
  • each CTU line card 101 is configured with four ADSL link sections 310, providing four 2-wire connections to ADSL ports on DSLAM 106, which resides in the same central office as CTU line card 101. Then, CTU line card 101 may be configured to send and receive its ATM cells over these links instead of sending the data across the backplane 103 and into ATM Controller 102 as in the case of the first approach.
  • ATM controller 102 is not necessary in this embodiment, and DSLAM 106 may be configured to perform the functions assigned to ATM switch 105 in the first embodiment.
  • the incoming downstream ATM cells are received and then replicated in parallel FIFOs at CTU line card 101, with one FIFO for each ADSL port.
  • more than one FTFO can be used for each ADSL port if ATM QoS priority mechanisms need to be implemented (i.e., to give real-time traffic priority over non-real-time traffic in a congested state).
  • Each FTFO within an ADSL channel would have a different priority level, and cells would be put into priority categories based on their Cell Loss Priority (CLP) bit, or based on their VPI/VCI information.
  • CLP Cell Loss Priority
  • the address information indicating the destination ADSL port within the GDSL system, as well as the priority is carried in bits associated with each ATM cell, but not as part of it.
  • the address information are transmitted in bytes 54 through 64 of the 56 bits available per 5 link frames in which a cell is sent. It can be seen that this approach requires a higher data rate on CTU line card 101, but still much lower than the buses (i.e., Utopia PHY bus shown in Figure 3) are equipped to handle.
  • ADSL transceiver 312 may be configured to handle 155Mbps at ATM UTOPIA interface between control section 320 and ADSL link section 310.
  • the total bandwidth needed in this mode is 5,455.48 kbps which equals 4 x 1363.87 kbps, with a minimum byte clock speed necessary at 681.935 kHz, with the maximum clock speed supported by ADSL transceiver 312 such as the Copper Lite transceiver from Centilium Corporation operating at 25 MHz.
  • UTOPIA Universal Test and Operations Physical Interface for ATM
  • UTOPIA Universal Test and Operations Physical Interface for ATM
  • ADSL transceivers 232, 312 in ADSL link sections 230, 310, respectively are available from their manufacturers with electrical interfaces that meet the UTOPIA specifications. These transceivers 232, 312 may be directly connected to other parts that use the UTOPIA bus scheme, or can be connected to programmable logic devices, such as the
  • CTU line card 101 may be configured to receive ATM data from ATM controller card 102 for upstream data link, while in accordance with another embodiment, CTU line card 101 may be configured to receive ATM data from two-wire
  • ADSL connection to DSLAM 106 ADSL connection to DSLAM 106.
  • RTU 108 and CTU line card 101 may be configured with their respective ADSL link units 230, 310 to transmit approximately 384 kbps (or, one-quarter of the total available GDSL bandwidth) in each direction at all times.
  • the address byte would still be used to determine which of the four users the ATM cells belong to, but cell traffic from each user's ADSL connections would be limited by the ADSL speed itself so that the total capacity of the GDSL link(s) is never exceeded.
  • ADSL link unit 230 cannot insert idle cells on demand (i.e., in the upstream direction if the physical layer requests a cell and no cell is available), then FPGA 221 in
  • RTU 108 may be configured to perform the same operation without the need for ATM switch 105.
  • This approach uses a simple and inexpensive technique for upstream bandwidth control at RTU 108.
  • this approach limits customers to their fraction of the bandwidth available. For example, with one GDSL trunk handling 1,544 kbps upstream, each of the four users would be limited to a payload of 1/4 of 1,544 kbps, or about 384 kbps upstream.
  • Each customer's connection may alternatively burst to a higher bandwidth, but if the total bandwidth demanded by all customers exceeds the trunk capacity, the excess cells would simply be dropped, without buffering or notification to the customer's equipment that data was being lost.
  • the TCP layer of the internet site to which the customer is connected would normally request retransmission in this scenario. It should be noted that ATM are not suited to bursting beyond the OR - a limitation of ATM.
  • the system in accordance with one embodiment of the present invention can be configured to handle more upstream data by limiting the number of RTU connections, or increasing the number of trunks. For example, with only two customers connected and one GDSL trunk (or 4 customers and 2 trunks), the maximum upstream rate would be approximately 750 kbps. It should be noted that this is also a committed rate and it is always available.
  • RTU 108 may be configured to open ATM cells, reassemble EP packets, terminate the IP packets, understand TCP, and respond using TCP for flow control, add ATM header back to upstream cells and calculate, or retrieve from storage, the HEC.
  • FPGA 221 of RTU 108 may be configured to select an ADSL channel and poll it for an available cell. If there isn't one available, it polls the next channel, and the next, and so on. When it receives an indication that there is a cell ready, it pulls it from the ADSL link section 230, buffers it, and sends it during 5 frames. On the other hand, if it doesn't receive a cell, it sends the idle cell, which it can generate itself.
  • RTU 108 configures ADSL link section 230 to send as much downstream data as possible over the ADSL link. Moreover, RTU 108 may be configured to send its ports' ADSL connect rates to CTU 100. CTU 100 then slows its connection to DSLAM 106 as needed to keep it at or below the rate at which RTU 108 sends data downstream to CPE 109 on the corresponding port. When downstream bursting is implemented, RTU 108 may be configured to use ADSL link section 230 at RTU 108 to insert idle ATM cells to fill the downstream channels.
  • CTU 100 configures its ADSL link section 310 to send as much data as possible to DSLAM 106. This amount is lower than the downstream rate, as it is in the reverse channel.
  • CTU 100 can communicate the result of the setup to RTU 108, which ensures that the maximum allowed upstream rate from CPE 109 to RTU 108 does not exceed the rate from CTU 100 to DSLAM 106.
  • ADSL data transmission from multiple users may be transmitted over a single twisted transmission path 111 to RTU 108 using the addressing schemes and FIFOs for effectively multiplexing the ATM data.
  • the use of a single twisted pair for multiple user access provides significant savings in the usage of the twisted pairs in the copper network.
  • Figure 4 illustrates one embodiment of the present invention showing the geographic locations and distances between its elements, including total system reach.
  • STRs symmetric straight-through repeaters
  • FIG. 4 it can be seen that using 26 awg twisted pair wire and two symmetric straight-through repeaters (STRs) 112 in the transmission path 111, a total of 41,000 feet can be achieved from the central office to the customer's Customer Premise Equipment.
  • the overall ADSL system reach may be further extended an additional 30% to 55,000 feet, 75,000 feet on 22 gauge wire, and finally, as far as
  • RTU 108, and STRs 112 deployed between CTU line card 101 and RTU 108 may be powered from the copper pair on which they transmit their GDSL signals.
  • CTU line card 101 residing in the telephone company's central office, may be provided with a line-powering circuit which supplies ample voltage and current to the copper pair to power the remote units.
  • the system may have outside plant elements, either STRs 112 or RTUs 108, which use local power sources instead of taking their power from the copper twisted pair 111. In this case, the distance reach of the overall system may be further extended beyond that described above.
  • FIG. 5 illustrates one embodiment of the present invention which incorporates ADSL data service and ordinary POTS service to be provided to the user's residence on the same ADSL pair 110.
  • RTU 108 configured to operate with GDSL-8 line card 502 of the GDSL-8 system available from GoDigital Networks Corporation.
  • the GDSL-8 system is a line-powered, repeatered system that carries 8 POTS circuits on a single twisted pair.
  • the system is configured to provide 8 POTS services and 4 ADSL services on two pairs 111.
  • LPF low pass filter
  • LPF 501 may be standard low pass filter circuitry commercially available from third-party vendors. With ordinary ADSL deployments on short loops, this configuration is deployed at the telephone company's central office, thus combining the POTS and ADSL signals onto the same wire pair before the pair leaves the central office. In this embodiment, the combining of the ADSL and POTS is instead accomplished remotely, at RTU 108. In this manner, simultaneous transmission of data and baseband POTS on the same pair, a significant advantage of ADSL service, is preserved. By contrast, presently available xDSL services which use repeaters do not have this feature, since they do not allow for the combining of POTS and ADSL at their outside plant elements.
  • the POTS circuits may be a pairgain device supplied by other manufacturers, a DLC (digital loop carrier) supplied by another manufacturer, or they could simply be POTS lines on individual pairs from the central office to the location of RTUs 108. Any of these scenarios will function properly for creating an ADSL plus
  • POTS service on the pair 110 which runs to the customer's premises. It is also important to note that the inclusion of POTS is not necessary for the ADSL circuit to function; it will work equally well in the absence of a POTS circuit on the same pair 110. Accordingly, the cost of common equipment can be shared among ADSL users.
  • each user will appear to have the full bandwidth of the GDSL links (approximately 1.5 Mbit/second symmetric in one embodiment for each link) when downloading in most cases, although the guaranteed information rate would be less (a proportional share of the total GDSL bandwidth).
  • the benefits of networking and shared facilities beyond their normal domain can be realized, effectively providing pair gain for ADSL data instead of for voice telephony.
  • the present invention provides a system and method for extending the reach of ADSL (or other) internet access from its present 15 to 18 Kft to over 40,000 feet (approximately 99% of all subscribers) using line-powered repeaters and remote terminal units.
  • the long loop broadband system in accordance with the present invention allows data from different ADSL users to be shared on a single copper distribution pair.
  • ADSL users may share the bandwidth on the symmetric GDSL links connected between RTU 108 and CTU line card 101 by taking ATM cells from the ADSL connection, which are properly addressed and sent over the symmetric DSL links.
  • ADSL services described above may be deployed in symmetric or asymmetric speeds.
  • ADSL-based repeaters in one embodiment, using G.shdsl PAM-16 coding
  • G.shdsl PAM-16 coding transmission of ADSL service over longer distances
  • ADSL-based repeaters i.e., ADSL-based repeaters
  • intermediate transmission units ADSL-based repeaters
  • one advantage of ADSL systems is that, since
  • ADSL systems transmit in different bands upstream and downstream, they are generally not subject to near-end crosstalk from other ADSL systems operating at the same end- point locations. However, in the presence of far-end crosstalk from other ADSL transmitters, the system performance degradation is noticeably significant. Further information on the impact of ADSL's performance in the presence of far end crosstalk from other ADSL transmitters can be found in a contribution to Tl committee T1E1.4, contribution T1E1.4/2000-336, available at www.tl.org.
  • the range of ADSL service can be significantly extended which preserving compatibility With non- repeatered ADSL transmission.
  • the upstream and downstream link distances between the transmission units i.e., the distance between the repeaters STRs 112 themselves, or the distance between a repeater STR 112 and CTU line card 101 or RTU 108), are substantially the same, it is easier to determine repeater spacings and thus deployment of the repeaters such that robust transmission performance is maintained.

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Abstract

L'invention concerne un procédé et un dispositif assurant un service à bande large boucle longue permettant de partager et de transporter des données provenant de différents utilisateurs d'ADSL dans un groupe de paires (éventuellement un groupe composé d'une seule paire) de fils de cuivre à répéteur téléalimenté, à l'aide de techniques de transmission symétrique. De multiples utilisateurs d'ADSL peuvent partager la bande passante sur une ou des paires, entre une unité terminale éloignée (RTU) et une unité terminale centrale (CTU), grâce à la conversion des données ADSL en cellules ATM qui sont adressées de manière adéquate et envoyées sur la ou les paires. Des répéteurs directs peuvent être utilisés entre l'unité terminale centrale et l'unité terminale éloignée sur chacune des paires, afin d'étendre la portée su système. De cette manière, on peut accroître la portée d'accès Internet par ADSL (ou par d'autres moyens), actuellement limitée entre 15000 et 18000 pieds, à plus de 40000 pieds, au moyen d'un fil de diamètre 26 permettant d'atteindre efficacement 99 % des abonnés.
PCT/US2001/003459 2000-02-02 2001-02-01 Procede et dispositif assurant un service adsl a bande large boucle longue de grande capacite WO2001058205A2 (fr)

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