X.25 Configuration 7-3

Virtual Circuit Service

X.25 uses two mechanisms, providing a logical path between end points, called virtual circuits. A virtual circuit provides a connection-oriented service, similar to that of circuit switching but with the following exceptions:

Limited to a connection between two end points.

Economical statistical multiplexing for establishing a logical path through the network.

There are two virtual circuits types: switched virtual circuits (SVCs) and permanent virtual circuits (PVCs). An SVC is a dynamically established virtual circuit using “call setup” and “call clearing” procedures. A PVC is a permanent, network-assigned virtual circuit that requires no call setup or clearing and operates like a logical leased line.

Using mixed protocols, the router can maintain multiple connections using SVCs between multiple sites. SVCs can be set up to operate automatically or on demand as data and call requests dictate. The router can automatically establish and disconnect on-demand IP connections using SVCs.

The types of connections supported by Emulex X.25 for various protocols are shown in the following table.

Protocol

PVC

Permanent

On-Demand SVC

 

 

SVC

 

IPX

X

X

X

IP

X

X

RFC 1356

APPLETALK

X

X

X

BRIDGE

 

X

X

 

 

 

 

A permanent SVC is established at initialization and is left in a connected state until the user or application brings it down. An on-demand SVC is established only when data is present for the associated virtual circuit and is brought down after the data has been transmitted and the configured idle timer has expired. An on-demand SVC remains down until more data is queued up to be sent, at which time the connection is reestablished.

Once a virtual circuit is established, data packets using this circuit are automatically sent to the appropriate destination

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Emulex DCP_link manual Virtual Circuit Service, Protocol, Permanent On-Demand SVC