Cabletron Systems CSX1200 User Manual

Also see for CyberSWITCH CSX1000: User guide Quick start

Contents

USER’S GUIDE214 CyberSWITCHFRAME RELAY ACCESS BACKGROUND I NFORMATIONFrame Relay is a frame mode service in which data is switched on a per frame basis, as opposed toa circuit mode service that delivers packets on a call-by-call basis. This feature will allow the systemto efficiently handle high-speed, bursty data over wide area networks. It offers lower costs andhigher performance than a X.25 packet switched network for those applications that transmit dataat a high speed in bursts.In private line network implementations, network bandwidth is dedicated to a particulardestination, whether via private lines or circuit switched connections. In any event, these resourcesare only available to traffic bound for that location and are reserved for that traffic whether thattraffic is present or not. Conversely, in a frame relay network, bandwidths within the network andin the access lines are only allocated between any two end devices if there is traffic moving betweenthose devices. At other times, this bandwidth is made available to other network devices.Therefore, the performance in a frame relay network is then only limited by the bandwidthavailable at the access point to the frame relay network and not necessarily by any preallocatedend-to-end bandwidth as would be the case of a private line network. In a manner of speaking, thisprovides bandwidth on demand since network bandwidth is allocated to this data path (virtualcircuit) only when traffic is present.Bandwidth is provided by the network’s Permanent Virtual Circuit (PVC) service: each data frameto be transmitted by an endpoint contains and is identified by a Data Link Connection Identifier(DLCI). The DLCI identifies a pre-established path, or permanent virtual circuit, within the accessline to the frame relay network. The frame relay switch at the edge of the frame relay network, theone to which the access line is directly connected, routes the packet to the intended destinationbased upon the DLCI therein. Hence, each packet is routed independently through the networkbased on the addressing information provided by this identifier.The two line protocols used for data encapsulation on a permanent virtual circuit are Point to PointProtocol or FR_IETF. PPP specifies the operation of the PPP protocol over Frame Relay links.Although the CyberSWITCH supports this method of encapsulation, Inband ProtocolDemultiplexing is not performed when a PVC is initiated because the system statically configuresthe line protocol used for a PVC. FR_IETF is a multiprotocol encapsulation for Frame Relay,currently specified by RFC 1490. FR_IETF protocols include IP, MAC Layer Bridge, IPX, andAppleTalk.Although Frame Relay is transparent to each of the protocols specified by FR_IETF, there are a fewspecial considerations to note. ARP, RARP, and IARP are protocols provided by FR_IETF for IPover Frame Relay. These protocols are used to determine the IP and DLCI information used on thevirtual circuits. However, since this information is configured in the CyberSWITCH, theseprotocols are not supported. The CyberSWITCH’s implementation of FR_IETF supports the BridgePoint to Point model. The Virtual port model or Extended Spanning Tree is not supported.The PVC name associates the permanent virtual circuit with a device table entry, whether it isdefined in an on-node or off-node database. If an on-node device database is used, the PVC namemust match the device name if outbound authentication has been disabled for a device associatedwith a PPP virtual circuit, or if FR_IETF has been configured as the line protocol. However, ifoutbound authentication has been enabled for a PPP device, the PVC name isn’t required to match.If an off-node device database is used, the PVC name must match the device name for both lineprotocols. FR_IETF requires that all PVC names match a configured device database entry, since noidentification mechanism is provided by this line protocol. When upgrading from a previousrelease of the UAA software, the CyberSWITCH will process the previous PVC name, which was