Abstract:
A method that provides for multicast delivery of information in a DSL network includes creating transmission paths between a single source port and multiple destination ports in a DSL network; receiving information at the source port; determining which of the destination ports is to receive the information; and distributing the information from the source port to selective ones of the destination ports based on the prior referencing step. A DSL system for providing multicast delivery of information includes an ATM network layer for sending information, a digital subscriber line access multiplexer (DSLAM) coupled to the ATM network layer for receiving the information, and a network control system for controlling selective multiplexing of the information through the digital subscriber line access multiplexer (DSLAM).

Description:
FIELD OF THE INVENTION 
     The present invention generally relates to network communications and, more particularly, to a method of ATM multicast distribution at an ATM network layer. 
     BACKGROUND OF THE INVENTION 
     Changing communications demands are transforming the existing public information network from one limited to voice, text and low resolution graphics to bringing multimedia, including full motion video, to everyone&#39;s home. A key communications transmission technology that is enabling transformation of existing public information networks to accommodate higher bandwidth needs is Asymmetric Digital Subscriber Line (ADSL), a modem technology. ADSL converts existing twisted-pair telephone lines into access paths for multimedia and high-speed data communications. ADSL can transmit up to 8 Mbps (Megabits per second) to a subscriber, and as much as 960 kbps (kilobits per second) or more in both directions. Such rates expand existing access capacity by a factor of 50 or more without new cable installations. 
     Asymmetric Digital Subscriber Line ADSL technology involves modems attached across twisted pair copper wiring in which transmission rates can be up to 8 Mbps downstream (to the subscriber) and from 16 kbps to 960 kbps upstream (from the subscriber), depending on line distance, can be achieved. Asynchronous Transfer Mode ATM is an ultra high-speed cell based data transmission protocol that may be run over ADSL. A Digital Subscriber Line Access Multiplexer (DSLAM) is a device that takes a number of ADSL subscriber lines and concentrates them to a single ATM line. Plain old telephone service POTS refers to basic analog telephone service. POTS takes the lowest 4 kHz bandwidth on twisted pair wiring. Any server sharing a line with POTS must either use frequencies above POTS or convert POTS to digital and interleave with other data signals. 
     Audio, video and other information is increasingly being distributed over networks from a single source to multiple destination points on the network. Networks have finite bandwidth capacities associated with them. Sending multiple copies of the same information to multiple destinations can become demanding on the network and does not constitute an efficient use of resources. 
     Accordingly, there is a need for implementing a multicast delivery service in a DSL network to make efficient use of the network. 
     SUMMARY OF THE INVENTION 
     A method that provides for multicast delivery of information in a DSL network includes creating transmission paths between a single source port and multiple destination ports in a DSL network; receiving information at the source port; determining which of the destination ports is to receive the information; and distributing the information from the source port to selective ones of the destination ports based on the prior referencing step. 
     A DSL system for providing multicast delivery of information includes an ATM network layer for sending information; a digital subscriber line access multiplexer (DSLAM) coupled to the ATM network layer for receiving the information; and a network control system for controlling selective multiplexing of the information through the digital subscriber line access multiplexer (DSLAM). 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The advantages, nature, and various additional features of the invention will appear more fully upon consideration of the illustrative embodiments now to be described in detail in connection with accompanying drawings wherein: 
         FIG. 1  is an exemplary digital subscriber line (DSL) system architecture capable of offering integrated multi-line telephony services such as voice, data and video. 
         FIG. 2  is a block diagram of the inventive method of multicast delivery of information in a DSLAM at the head-end of a DSL network. 
         FIG. 3  is an example of a multimedia setup request to network to join a point-to-multipoint ATM virtual circuit. 
     
    
    
     It should be understood that the drawings are for purposes of illustrating the concepts of the invention and are not necessarily the only possible configuration for illustrating the invention. 
     DETAILED DESCRIPTION OF THE INVENTION 
     The present invention is a method of ATM multicasting at the ATM network layer in a DSLAM at the head-end network for the purpose of distributing information, such as real-time data, video or audio, to the customer premise equipment CPE. The ATM layer multicast delivery service enables a source to transmit ATM cells from a single point to multiple destinations (point-to-multipoint), rather than using traditional broadcast or uni-cast distribution methods. This can be viewed as an ATM virtual path/virtual circuit with a single source and multiple destinations. The ATM network layer will deliver the ATM cells (on a multicast basis) to the destination points specified in the ATM virtual path/virtual circuit connection profile. By implementing a multicast delivery service in a DSLAM at the head-end of a DSL network it is possible to make efficient use of network resources for the purpose of distributing audio, video and other information to the customer premise. 
     A DSL system architecture  1  for integrating voice, data and video services, shown in  FIG. 1 , is presented as an exemplary DSL environment for employing the inventive method of enabling video phone communication and similar multimedia communication over a DSL link. Details of the individual block components making up the system architecture are known to skilled artisans, and will only be described in details sufficient for an understanding of the invention. The system block diagram  1  is composed of several functional blocks. The system domain is composed of Central Office (CO) Equipment  100  and Customer Premise Equipment (CPE). The component blocks within the system domain and their respective interfaces are: customer premise equipment (CPE), Digital Subscriber Line Access Multiplexer (DSLAM)  9 , an ATM switch  2 , an IP router  13  and DSL terminator  12 , and a network control system (NCS)  11 . 
     The current customer premise equipment (CPE)  2  includes a DSL modem unit that interfaces with four separate analog telephones  3 - 6  over a plain old telephone service (POTS), a 10 Base-T Ethernet connection to a PC desktop system  7 , and an Ethernet or RS-422 connection to a set-top box with a decoder  8  for connection to a television or video display  8 ′. From the customer&#39;s analog end, the CPE device  2  accepts the analog input from each of the telephones  3 - 6 , converts the analog input to digital data, and packages the data into ATM packets (POTS over ATM), with each connection having a unique virtual channel identifier/virtual path identifier (VCI/VPI). Known to skilled artisans, ATM is a connection oriented protocol and as such there is a connection identifier in every cell header which explicitly associates a cell with a given virtual channel on a physical link. The connection identifier consists of two sub-fields, the virtual channel identifier (VCI) and the virtual path identifier (VPI). Together these identifiers are used at multiplexing, de-multiplexing and switching a cell through the network. VCIs and VPIs are not addresses, but are explicitly assigned at each segment link between ATM nodes of a connection when a connection is established, and remain for the duration of the connection. When using the VCI/VPI, the ATM layer can asynchronously interleave (multiplex) cells from multiple connections. 
     The Ethernet data is also encapsulated into ATM cells with a unique VPI/VCI. The ATM cell stream is sent to the DSL modem to be modulated and delivered to the DSLAM unit  9 . 
     Going in the other direction, the DSL signal is received and demodulated by the DSL modem in the customer premise equipment  2  and delivered to VPI/VCI detection processing. The ATM cell data with VPI/VCI matching that of the end user&#39;s telephone is then extracted and converted to analog POTS to be delivered to the telephone. The ATM cell data with VPI/VCI matching that of the end user&#39;s Ethernet is extracted and delivered to an Ethernet transceiver for delivery to the port. 
     The Digital Subscriber Line Access Multiplexer DSLAM  9  demodulates data from multiple DSL modems and concentrates the data onto the ATM backbone network for connection to the rest of the network. That DSLAM provides back-haul services for package, cell, and/or circuit based applications through concentration of the DSL lines onto ATM outputs to the ATM switch  10 . 
     The ATM switch  10  is the backbone of the ATM network. The ATM switch  10  performs various functions in the network, including cell transport, multiplexing and concentration, traffic control and ATM-layer management. Of particular interest in the system domain  100 , the ATM switch provides for the cell routing and buffering in connection to the DSLAM, network control system  11  and the Internet gateway (Internet Protocol IP router  13  and DSL terminator  12 ), and T1 circuit emulation support in connection with the multiple telephony links switch  15 . A T1 circuit provides 24 voice channels packed into a 193 bit frame transmitted at 8000 frames per second. The total bit rate is 1.544 Mbps. The unframed version, or payload, consists of 192 bit frames for a total rate of 1.536 Mbps. 
     The ATM switch  10  is shown coupled to a program guide server/video server  16  to satellite  17 , radio broadcast  18  or cable  19  networks. The ATM switch  10  is also coupled over the DSL terminator  12  and IP router  13  pair to receive Internet Protocol IP packet data from the Internet  14 . 
     The network control system  100  provides for address translation, demand assignment and call management functions. The Network Control System&#39;s principle function is to manage the DSL/ATM network including the origination and termination of phone calls. The NCS is essentially the control entity communicating and translating control information between the class 5 PSTN switch (using the GR-303 protocol) and the CPE. The network control system  100  is available for other functions such as downloadable code to the CPE, and bandwidth and call management (e.g., busy) functions, as well as other service provisioning and set up tasks. 
     Turning now to  FIG. 2 , the block diagram  20  illustrates ATM multicasting at the ATM layer at the head-end of the network for the purposes of distributing audio, video and other information to the customer premises equipment CPE. Multicasting is an efficient method of data delivery that simultaneously sends information to a group of interested destination points. Networks have finite bandwidth capacities. Sending multiple copies of the same information to multiple destinations can become demanding on the network and does not constitute an efficient use of resources. 
     The DSLAM of  FIG. 2  is configured with an ATM trunk port  21  and multiple destination ports  22 - 28 . The ATM trunk port  21  is a single virtual path/virtual channel, illustratively assigned a VPI of 39 and a VCI of 12. In this exemplary ATM multicast/point-to-multipoint distribution information is delivered from the ATM trunk port  21  to multipoint destinations: ADSL port  1   22 , ADSL port  2   23 , ADSL port  4   25  and ADSL port N  28 . ADSL port  1   22  is assigned a VPI of 36 and VCI of 21. ADSL port  2   23  is assigned a VPI of 36 and VCI of 20. ADSL port  4   25  is assigned a VPI of 45 and VCI of 9. ADSL port N is assigned a VPI of 37 and a VCI of 4. 
     ATM multicasting can be done at the ATM network layer. The ATM network layer is responsible for cell header generation and extraction, cell VPI/VCI translation and cell multiplexing and de-multiplexing. When a cell arrives at the trunk port it is identified as a channel of video or other information. This is based upon the arrived cell&#39;s VPI/VCI pair indicated in the cell header, which is a relationship known by the network control system. A connection profile  30  can be referenced to find the subscribers to this particular ATM virtual circuit. Based upon the connection profile, ATM cells can be duplicated to the group of customers subscribing to this channel. 
       FIG. 3  shows an example of a multimedia setup request to network to join a point-to multipoint ATM virtual circuit. 
     The Customer Premise Equipment (CPE) sends a request to the network for a multimedia program on an ATM signaling virtual circuit ( 1 ,  FIG. 3 ). The message is sent to the ATM switch based on the ATM signaling virtual circuit ( 2 ,  FIG. 3 ). The message is sent to the Network Control System (NCS) based on the ATM signaling virtual circuit ( 3 ,  FIG. 3 ). The Network Control System (NCS) determines if the request is valid ( 4 ,  FIG. 3 ). If it is a valid request, it sends a request to the Multimedia server for the CPE to join/build a multicast/point-to-multipoint ATM virtual circuit for the selected channel ( 5 ,  FIG. 3 ). The Network Control System (NCS) sends a request to the ATM switch for the CPE to join a multicast/point-to-multipoint ATM virtual circuit for the selected channel ( 6 ,  FIG. 3 ). The Network Control System (NCS) sends a request to the Digital Subscriber Line Access Multiplexer (DSLAM) for the CPE to join a multicast/point-to-multipoint ATM virtual circuit for the selected channel ( 7 ,  FIG. 3 ). Once this connection has been made, the multimedia information will flow to one or more CPE end-nodes ( 8 ,  FIG. 3 ). 
     In order to provide support for the delivery of multimedia services in a DSL network, an economies of scale needs to be achieved for the service provider in order to cost effectively deliver these services to the end user. This economies of scale can be achieved by efficiently using network resources during the delivery of this multimedia information to the end user. In order to efficiently deliver multimedia to the end user a concept known as multicast can be employed in the network. The basic principle of multicast is the delivery of a single stream of information to many while efficiently using the resources of the network. It efficiently uses the resources of the network by having the server only send a single copy of the multimedia program and having downstream intermediate nodes replicate this program until it reaches the necessary end users. Broadcasting is ineffective at providing this, unless every end user is requesting the multimedia. 
     The ideal place for effective multicasting is at the edge of the network. The edge device in a Digital Subscriber Line (DSL) network is the Digital Subscriber Line Access Multiplexer (DSLAM). The DSLAM shall have the capabilities of setting up point-to-multipoint connections at the ATM layer (i.e., a multicast connection). By having this function, the DSLAM can replicate data and send it to multiple subscribers on different ports. 
     The uniqueness of this invention is the method by which the multicast/point-to-multipoint ATM virtual circuits are set up for the delivery of information to the end user. Also, that the system provides the control for the multicast/point-to-multipoint delivery of information to the end user. 
     Although the embodiment which incorporates the teachings of the present invention has been shown and described in detail herein, those skilled in the art can readily devise many other varied embodiments that still incorporate these teachings.