Cabletron Systems Cabletron CyberSWITCH CSX5500 User Manual

Also see for CyberSWITCH 5500: Quick start Manual

Contents

USER’S GUIDE252 CyberSWITCHX.25 R ESTRICTION F ACILITIESThese facilities are used to place restrictions upon incoming and outgoing X.25 calls.BARRING I NCOMING C ALLSAllows to you bar X.25 calls coming in to the system. The default configuration is to not barincoming X.25 calls.BARRING O UTGOING CALLSAllows you to bar X.25 calls going out of the system. The default configuration is to not baroutgoing X.25 calls.X.25 M ISCELLANEOUS FACILITIESThese facilities are used for fast select acceptance for incoming and outgoing X.25 calls. Fast selectis a calling method that allows the device to send a limited amount of information along with a “callrequest packet” rather than after the packet.FAST SELECT ACCEPTANCE - INCOMING CALLSAllows you to chose whether fast select acceptance should be done on incoming calls. Thedefault configuration is to not perform fast select acceptance on incoming calls.FAST SELECT ACCEPTANCE - OUTGOING CALLSAllows you to chose whether fast select acceptance should be done on outgoing calls. Thedefault configuration is to not perform fast select acceptance on outgoing calls.After all of the above X.25 facilities have been specified, the configuration of the X.25 access itselfhave been completed. You may now configure the virtual circuits associated with the X.25 access.PVC C ONFIGURATION ELEMENTSOnce the above X.25 configuration elements have been configured, the associated virtual circuitsshould be configured. Note that virtual circuits may be configured with any combination of SVCsand PVCs, adding up to a maximum of 48 virtual circuits.A PVC is similar to a dedicated line. At subscription time, the subscriber gives the network theaddress to be associated with that virtual circuit. A logical channel is permanently assigned. Fromthat point on, no call set up is needed. Data to be sent to that destination are simply sent in datapackets using the assigned logical channel.LOGICAL CHANNEL NUMBER (LCN)X.25 uses LCNs to distinguish the connections between DTEs at either end of a communication.These LCNs make it possible to send a packet into a packet-switched network at one end (with nocontrol over the packet’s journey) and then to pick the packet out at the receiving end. LCN valuesfor PVCs are obtained from the PPSN carrier.NONSTANDARD DEFAULT TRANSMIT WINDOW SIZEThe number of frames that a DTE can send without receiving an acknowledgment. Using modulo128, the DTEs can send up to 127 frames without receiving an acknowledgment. Using modulo 8,the DTEs can send up to 7 frames without receiving an acknowledgment. The default value for bothmodulo 8 and modulo 128 is 2.