Cabletron Systems CSX1000, CSX1200 manual PVC Configuration Elements

USER’S GUIDE

X.25 RESTRICTION FACILITIES

These facilities are used to place restrictions upon incoming and outgoing X.25 calls.

BARRING INCOMING CALLS

Allows to you bar X.25 calls coming in to the system. The default configuration is to not bar incoming X.25 calls.

BARRING OUTGOING CALLS

Allows you to bar X.25 calls going out of the system. The default configuration is to not bar outgoing X.25 calls.

X.25 MISCELLANEOUS FACILITIES

These facilities are used for fast select acceptance for incoming and outgoing X.25 calls. Fast select is a calling method that allows the device to send a limited amount of information along with a “call request packet” rather than after the packet.

FAST SELECT ACCEPTANCE - INCOMING CALLS

Allows you to chose whether fast select acceptance should be done on incoming calls. The default configuration is to not perform fast select acceptance on incoming calls.

FAST SELECT ACCEPTANCE - OUTGOING CALLS

Allows you to chose whether fast select acceptance should be done on outgoing calls. The default 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 itself have been completed. You may now configure the virtual circuits associated with the X.25 access.

PVC CONFIGURATION ELEMENTS

Once the above X.25 configuration elements have been configured, the associated virtual circuits should be configured. Note that virtual circuits may be configured with any combination of SVCs and PVCs, adding up to a maximum 8 virtual circuits.

A PVC is similar to a dedicated line. At subscription time, the subscriber gives the network the address to be associated with that virtual circuit. A logical channel is permanently assigned. From that point on, no call set up is needed. Data to be sent to that destination are simply sent in data packets 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 no control over the packet’s journey) and then to pick the packet out at the receiving end. LCN values for PVCs are obtained from the PPSN carrier.

NONSTANDARD DEFAULT TRANSMIT WINDOW SIZE

The number of frames that a DTE can send without receiving an acknowledgment. Using modulo 128, 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 both modulo 8 and modulo 128 is 2.

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