A virtual circuit is a common transport that provides port-to-port communication in an OpenVMS cluster at the TR (transport) layer of the NISCA protocol. A virtual circuit is maintained by everyt port with every other remote port and ensures:
- the delivery of messages without duplication or loss
- the sequential ordering of messages by using virtual circuit sequence numbers on each transmitted message (duplicates are discarded).
Virtual circuits are layered on channels established between each pair of adapters. The choice of channel is determined by the sender (PEDRIVER) of the messages.
To examine information about the virtual circuit (VC) that carries messages between the local node (where you are running SDA) and another remote node, enter the SDA command SHOW PORT/VC=VC_remote-node-name.
The SHOW PORT/VC=VC_remote-node-name command displays a number of performance statistics about the virtual circuit for the target node. The display groups the statistics into general categories that summarize such things as packet transmissions to the remote node, packets received from the remote node, and congestion control behavior.