Cabletron Systems CyberSWITCH CSX150 User Manual

Also see for CyberSWITCH CSX150: User guide Quick start guide

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USER’S GUIDE196 CyberSWITCHconfigured in the device table. It will find the PVC and the line protocol that corresponds to thePVC name and change its PVC name to match the corresponding device name.Notes: VRA Manager is currently the only off-node device database supported by theCyberSWITCH for Frame Relay.The management of Frame Relay permanent virtual circuits requires the use of some formof security. Therefore, systems with frame relay remote devices cannot select No Securityfor the security level.Frame Relay uses ISDN to provide backup redundancy for failed Frame Relay links. In the eventthat a Frame Relay link fails, an ISDN call is brought up and all traffic that was to be forwarded onthe Frame Relay link is forwarded over the ISDN call. Once the Frame Relay link comes back upthe ISDN call will be taken down and transmission of data will resume over the Frame Relay link.When using FR_IETF data encapsulation, LMI is used to determine the status of failed Frame Relayvirtual circuits. When using PPP data encapsulation, Link Failure Detection can be enabled for theFrame Relay access. Link Failure Detection is only supported across PPP permanent virtual circuits.Some Frame Relay networks have a per packet charge, therefore, the administrator should becautious when enabling this feature.The three main operational components of a frame relay access are the Local Management Interface(LMI), Data Rate Control, and Congestion Control. The following three sections provide anoverview of the role that each of these components plays in the function of frame relay access.THE LOCAL MANAGEMENT I NTERFACE O VERVIEWBesides the steady state data transfer portion of the frame relay module, the standards haveprovided for a frame relay management function, known as the Local Management Interface (LMI).The purpose of this interface is to provide a controlled means of verifying both link integrity andthe network status of all PVCs configured on the frame relay access defined by a given physicallink.The elements of this management interface are the STATUS and STATUS_ENQUIRY messages.The STATUS_ENQUIRY messages are sent out by the user equipment at regular intervals. Theinterval at which these status messages are sent, the polling interval, is a configurable value. Thenetwork will respond to these STATUS_ENQUIRY messages with its own STATUS messagecontaining a link integrity verification information element. The user equipment will request viathe STATUS_ENQUIRY either a Link Integrity Verification STATUS message from the network ora full report STATUS message. The link integrity verification STATUS message simply functions asa signal to verify that the link is still operable. This full report signals the user equipment when aPVC is no longer usable, and also when a previously non-active PVC has become available.D ATA R ATE C ONTROL O VERVIEWTo handle congestion within the network and at the endpoints, the frame relay protocol providescertain congestion control features.A frame relay PVC has two transmission rates associated with it: the Committed Information Rate(CIR) and an Excess Information Rate (EIR). The committed information rate is the bandwidthrequested for a PVC at service subscription time. It is essentially the guaranteed transmission rate