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Session Selection for Conversations

When an allocation request targets a particular link an attempt is made to locate a session to be used by the conversation. If an idle contention winner session is located then it is assigned. If not, the conversation goes into a pending allocation state, awaiting a session for the conversation.

For a pending allocation on a parallel session link, further efforts are made to isolate a usable session. Where the number of contention winners can be increased (according to the session limits) then a new session is started. Otherwise, if an idle contention loser session is located, a bid is made to use that session.

For a pending allocation on a single session link, if the session is a contention loser session and it is idle, a bid is made to use that session.

In general, when a conversation enters a pending allocation state, one of three events can occur to provide a session for its use:

• An active conversation ends, freeing up a contention winner session for the pending conversation.
• A new contention winner session starts and becomes available for the pending conversation.
• A response to previous bid indicates that the remote end will allow the conversation to commence on a contention loser session.

Conversations remain pending until one of these events frees a session for use, or until the allocation request is otherwise canceled. An allocation may time out (if a time-out period is specified on the allocation), or a link termination condition may cause the cancellation of all pending requests for the link.