Abstract:
In a method for providing protection switching in a voice-over-broadband (VOB) gateway, egress traffic is multicast from a switch fabric to a working port and to a protection port. The working port forwards the egress traffic to a network in a working mode of operation, and the protection port forwards the egress traffic to the network in a protection mode of operation. Also, the working port forwards ingress traffic to the switch fabric in the working mode of operation, and the protection port forwards the ingress traffic to the switch fabric in the protection mode of operation. In one aspect, ingress traffic is forwarded from the protection port and not from the working port in the protection mode of operation. In another aspect, the working port and the protection port share status information, and the status information is used to select between the working mode of operation and the protection mode of operation.

Description:
TECHNICAL FIELD OF THE INVENTION 
     This invention relates generally to the field of telecommunications and, in particularly, to gateway systems for voice over broadband. More particularly, the present invention relates to a system and method for using switch fabric to support redundant network ports in a gateway system. 
     BACKGROUND OF THE INVENTION 
     Digital subscriber line (DSL) technology was initially deployed to provide data-only service as a replacement for slower-speed, dial-up modems. Incumbent local exchange carriers (ILECs), competitive local exchange carriers (CLECs), and other telecommunication providers have begun to explore offering voice-over-Digital Subscriber Line (VoDSL) service, and other voice-over-broadband services, to deliver integrated voice and data services. 
     A central component of a typical VoDSL system is the voice gateway, or simply “gateway.” The gateway receives Voice over Internet Protocol (VoIP) or Voice over ATM (VoATM) information from the customer premises via network ports. The gateway then reformats the telecommunication information and sends it to a public switched telephone network (PSTN) via telecommunication ports. Likewise, telecommunication information from the PSTN is received at the telecommunication ports, packetized, and then transmitted to users via the ATM ports. Thus, the telephones, computers, and other telecommunication equipment at the customer premises are typically connected to the gateway via an ATM network, and the ATM ports in the gateway are wide area network (WAN) ports. The network ports typically reside on cards that plug in to the gateway. The network ports may, for example, connect to an ATM/IP network, a Digital Subscriber Line Access Multiplexor (DSLAM), or a Cable Modern Termination System (CMTS). Regarding specific techniques for encoding telecommunication information, there are several means available for carrying packetized voice over broadband, including the ATM Adaptation Layer Type 2 Broadband Loop Emulation Service (AAL2 BLES) protocol for carrying voice directly over ATM and the Voice over IP over ATM (VoIPoATM) protocol for transporting IP over ATM Adaptation Layer Type 5 (AAL5). 
     Gateways are now available with the capacity to process, bridge, and/or switch thousands of users. Network designers may also wish to oversubscribe the number of users based on statistical analysis of a network&#39;s behavior. In both cases, a large amount of user traffic passes through a typical gateway at any given time. Due to this large concentration of traffic, it is becoming increasingly important to maintain service, despite failure of components such as network ports. 
     One technique used to increase gateway reliability is to implement network port redundancy with automatic protection switching (APS). For conventional APS, the gateway is generally provided with at least one primary network port, known as the working port, and at least one redundant network port, known as the protection port. If the working port experiences a fault, the working port automatically passes the bearer traffic through to the protection port. Specifically, according to conventional APS, resources residing in the working port utilize a communication path that links the working port and the protection port to forward traffic received by the working port through to the protection port. Resources residing on the protection port receive the forwarded traffic and pass it through to the ATM network. 
     A disadvantage associated with this technique, however, is that additional resources must be provided on the network ports to support passing bearer traffic from the working port to the protection port. For example, the working port must include logic and hardware for detecting faults and forwarding traffic to the protection port. Thus, this method adds cost to the network ports. Furthermore, it may be necessary to remove the working port to cure the fault. However, removal of the working port will interrupt the bearer traffic that the working port passes through to the protection port unless additional steps are taken to otherwise reroute that traffic. There is therefore a need for improved protection-switching technologies that do not increase the cost of network ports and that allow working ports to be replaced easily without interrupting bearer traffic. 
     SUMMARY OF THE INVENTION 
     In accordance with the present invention, a system and method for supporting redundant network ports is provided that substantially eliminates or reduces disadvantages or problems associated with previously developed systems and methods. In a method according to the present invention for providing protection switching in a voice-over-broadband (VOB) gateway, egress traffic is multicast from a switch fabric to a working port and to a protection port. The working port forwards the egress traffic to a network in a working mode of operation, and the protection port forwards the egress traffic to the network in a protection mode of operation. Also, the working port forwards ingress traffic to the switch fabric in the working mode of operation, and the protection port forwards the ingress traffic to the switch fabric in the protection mode of operation. In one aspect, ingress traffic is forwarded from the protection port and not from the working port in the protection mode of operation. In another aspect, the working port and the protection port share protection status information, and the protection status information is used to select between the working mode of operation and the protection mode of operation. 
     A technical advantage of the present invention is the elimination of extra hardware and/or software on the working port and the protection port, which reduces the cost of the network ports. Another technical advantage is that faulty ports can be removed without interrupting a connection that has been rerouted to a protection port, which increases gateway reliability. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Additional features, functions, and technical advantages will become apparent upon review of the following description, claims, and figures, in which: 
         FIG. 1  presents a block diagram of an example embodiment of a gateway system with protection switching according to the present invention; 
         FIG. 2  presents a more detailed block diagram of portions of the gateway system of  FIG. 1 ; and 
         FIG. 3  presents a flowchart of an exemplary process for providing protection switching in a voice gateway according to the present invention. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  depicts an example embodiment of a gateway  30  with protection switching according to the present invention. Gateway  30  includes one or more telephony modules  38  with telephony ports. Gateway  30  sends and receives traffic (i.e., telecommunication information) to and from a telecommunication system  18 , such as a PSTN, via the telephony ports. The traffic on telecommunication system  18  may be referred to generally as voice data, and the telephony ports may send and receive the voice data in a time-division multiplexed (TDM) format, for example. 
     Gateway  30  also includes two or more network modules  36 A– 36 C, each of which includes at least one network port. Gateway  30  sends and receives traffic to and from a network  16  via the network ports. For example, network  16  may be an IP or ATM network. In the example embodiment, the network port on network module  36 A serves as a working port  46 A and the network port on network module  36 B serves as a protection port  46 B, as described in greater detail below with reference to  FIG. 2 . A network port on network module  36 C may serve as an active port with no associated protection port. The traffic on network  16  may be referred to generally as packets, even though networks other than ATM or IP networks may carry that traffic in alternative embodiments. 
     Also included in gateway  30  are a control module  34  and a backplane  40  that includes communication paths which interconnect network modules  36 A– 36 C and control module  34 . Additional communication paths in backplane  40  interconnect control module  34  with telephony modules  38 . In the example embodiment, each telephony module  38 , each control module  34 , and each network module  36 A– 36 C resides on a distinct adapter card. 
     Control module  34  reformats the voice data from telephony modules  38  into a format suitable for transmission on network  16  and reformats the packets from network modules  36 A– 36 C into a format suitable for transmission on telecommunication system  18 . For instance, in the example embodiment, control module  34  encapsulates the voice data into packets for transmission on network  16  and extracts voice data from packets received from network  16  for transmission on telecommunication system  18 . 
     Control module  34  includes a switch fabric  32  that controls how traffic flows between telephony modules  38  and network modules  36 A– 36 C. The traffic flowing from gateway  30  to network  16  is known as egress traffic, and the traffic that gateway  30  receives from network  16  is known as ingress traffic. In the example embodiment, switch fabric  32  is a high-capacity switch fabric  32  capable of IP and/or ATM multicast, and gateway  30  utilizes the multicast functionality to provide protection switching without adding extra components, and hence cost, to the system. 
     Referring now to  FIG. 2 , certain portions of gateway  30  are shown in greater detail. For instance,  FIG. 2  shows that backplane  40  includes separate data paths  54 A and  54 B for switch fabric  32  to communicate with network modules  36 A and  36 B respectively. Also, network module  36 A includes a data interface  56 A, and network module  36 B includes a data interface  56 B. Data path  54 A carries telecommunication information between switch fabric  32  and network module  36 A via data interface  56 A, and data path  54 B carries telecommunication information between switch fabric  32  and network module  36 B via data interface  56 B. 
     Also, network ports  46 A and  46 B are shown residing on network modules  36 A and  36 B, respectively. Network ports  46 A and  46 B are also referred to as working port  46 A and protection port  46 B, respectively. For ingress traffic as well as egress traffic, both working port  46 A and protection port  46 B maintain a copy of the same connection tables. For egress traffic, switch fabric  32  simply multicasts traffic to both working port  46 A and protection port  46 B. Consequently, in the case of a fault on the working port, no new bearer connections to re-route traffic to protection port  46 B are necessary. All traffic entering the switch fabric is simply copied to both ports  46 A and  46 B. 
     As  FIG. 2  also indicates, network ports  46 A and  46 B include status ports  50 A and  50 B, respectively. Status ports  50 A and  50 B communicate status information between network ports  46 A and  46 B via a status path  52 . Status ports  50 A and  50 B may also be referred to as status interfaces  50 A and  50 B. Network ports  46 A and  46 B also include protection switches  44 A and  44 B, respectively. In operation, network ports  46 A and  46 B provide protection switching by opening or closing respective protection switches  44 A and  44 B, based on the status information, as described below with reference to the flowchart of  FIG. 3 , which depicts an example process for providing protection switching in gateway  30 . 
     The process of  FIG. 3  begins at block  200  with network ports  46 A and  46 B operating in working mode and monitoring network communications to evaluate line conditions such as loss of signal, bit error rates (BERs), etc. Network ports  46 A and  46 B also monitor for internal failure conditions. In working mode, switching fabric  32  multicasts egress traffic for network port  46 A to network module  36 A via data path  54 A and to network module  36 B via data path  54 B. Further, in working mode, network port  46 A keeps protection switch  44 A closed, and network port  46 B keeps protection switch  44 B open. Consequently, the traffic passes between network  16  and switch fabric via working port  46 A but not via protection port  46 B. 
     As indicated at block  202 , network ports  46 A and  46 B then use status ports  50 A and  50 B and status path  52  to share status information reflecting the results of the monitoring. As depicted at block  210 , network ports  46 A and  46 B then determine whether to switch from working mode to protection mode, based one the status information. For example, gateway  30  may use the Bellcore GR-253-CORE SONET (Synchronous Optical Network) standard for network communications, and network ports  46 A and  46 B may determine which mode should be used (i.e., working or protection), in accordance with that standard. For instance, network ports  46 A and  46 B may share bearer and APS status signals, such as loss of service (LOS), signal fail (SF), and signal degrade (SD). Nevertheless, although status signals may be passed between status ports  50 A and  50 B, the telecommunication information is not passed between status ports  50 A and  50 B but is instead sent and received directly to and from switch fabric  32  via data paths  54 A and  54 B. 
     If it is determined to switch to protection mode, working port  46 A opens protection switch  44 A and protection port  46 B closes protection switch  44 B, as depicted at blocks  212  and  214 . Consequently, in protection mode, only protection port  46 B carries the ingress traffic and egress traffic between network  16  and switch fabric  32 . The process then returns to block  202 , with network ports  46 A and  46 B monitoring conditions and sharing status information as described above. 
     However, the determination depicted at block  210  whether to switch to protection mode may be negative. For example, communications may be flowing in a satisfactory manner through working port  46 A, or gateway  30  may already be operating in protection mode. If the determination at block  210  is negative, it is determined whether to revert to working mode, as indicated at block  220 . If the current mode is protection mode and it is determined to revert to working mode, working port  46 A closes protection switch  44 A and protection port  46 B opens protection switch  44 B, as depicted at blocks  222  and  224 . Switch fabric  32  consequently communicates ingress traffic and egress traffic with network  16  only via working port  46 A. The process then returns to block  202 . Network ports  46 A and  46 B then continue to monitor conditions and share status information, and gateway  30  continues to provide protection switching in response to changing conditions, as described above. 
     Thus, in working mode, ingress and egress traffic passes between network  16  and switching fabric  32  through components including working port  46 A, protection switch  44 A, data interface  56 A, and data path  54 A. In protection mode, by contrast, ingress and egress traffic passes between network  16  and switching fabric  32  through components including protection port  46 B, protection switch  44 B, data interface  56 B, and data path  54 B. Ingress and egress traffic may pass between network ports  46 A and  46 B and network  16  via a Y cable that includes a junction  42  and a network connector  48 . The example embodiment thus provides automatic equipment protection for working port  46 A. By filtering ingress traffic before it reaches switch fabric  32 , network ports  46 A and  46 B prevent traffic sequencing errors that might otherwise result because the ingress traffic is routed to the same output port. 
     In an alternative embodiment, independent working and protection lines exist back to network  16 . That is, the working and protection ports have independent connections or lines to network  16 , and the egress traffic is not affected by protection switches  44 A and  44 B. However, the ingress traffic is still filtered at least on the inactive port (e.g., by switches like protection switches  44 A and  44 B) to avoid sequencing errors at switch fabric  32 . Such an alternative embodiment may therefore provide line and equipment protection, in accordance with protection standards such as 1+1 SONET APS. 
     Among the advantages of the above embodiments is that they make more effective use of the bandwidth between the switch fabric and the network ports, rather than requiring bandwidth for telecommunication information between the working port and the protection port. In addition, since multicast is used for egress traffic, the software or other control logic for the gateway does not need to provision any new bearer connections to re-route traffic to the protection port. Further, the embodiments allow for component cost savings, since no components for bridging traffic between network ports are required. Also, in the described embodiments, faulty ports can be replaced without interrupting traffic flow between the switching fabric and the network. For example, when a gateway is in protection mode, a new working port may be swapped for a defective working port without interrupting traffic flow between the switch fabric and the protection port. 
     Although an example embodiment of the present invention has been described, myriad changes and variations may be made and used without departing from the scope and spirit of this invention. For example, although the discussion above refers to VoDSL service, alternative embodiments of the invention provide the functionality and advantages described above for gateways that utilize other types of broadband connections. Products that may benefit from the invention include, without limitation, DSLAMs, ATM switches, Routers, Voice Gateways, CMTSs, high-capacity packet transport products, and SONET Add-Drop Multiplexors. Likewise, it should be understood that the number of network modules, telephony modules, and control modules can be varied from that depicted in the example embodiment according to the needs of a particular implementation. 
     In addition, the example embodiment depicts the working and protection ports as physically residing on separate cards that are each connected to a backplane of a chassis that also houses the control module. In an alternative embodiment, however, the working and protection ports may reside on the same card. Nevertheless, in that alternative embodiment, the switch fabric would still use a first communication path of the backplane to send the telecommunication information to the working port and a second communication path of the backplane to send the telecommunication information to the protection port. 
     Furthermore, in the illustrated embodiment, the modules and components depicted within the gateway represent functional elements that are reasonably self-contained so that each can be designed, constructed, and updated substantially independently of the others. In a particular embodiment, some or all of those modules and components are implemented on one or more separate printed circuit boards or cards that may be coupled to a backplane in chassis. However, in alternative embodiments, the gateway may include different hardware, software, or combinations of hardware and software for providing the functionality described and illustrated in this application. The invention is therefore not to be limited to the example embodiment, but is to be defined by the following claims.