XID Retries

When the local node specifies that the SNALink is to send an XID, either by supplying it on the Open(LINK) Request or by sending it on a Send-XID message, it is the responsibility of the SNALink to perform any retries.

XIDs need to be retried because:

• The remote station has not been started yet.
• Frames may be lost on the line due to noise.

SDLC SNALinks should implement a contact time-out and a retry limit—values for these are provided on the Open(LINK) message. The time-out specifies how often the XID should be retried, and the retry limit specifies how many XIDs should be sent before abandoning the connection activation and sending an Outage message to the local node. The SNALink should stop retrying the XID when one of the following occurs:

• It receives an XID from the remote station.
• An Open(STATION) message is received from the node.
• A mode-setting command is received on the link.