Timer T310, in milliseconds, is the window this port waits for a CONNECT (or RELEASE COMPLETE) after it has already received a CALL PROCEEDING for an outgoing SVC request. This is the timer that catches a callee switch that acknowledged the call but then never actually answers it, so tuning it controls how long a caller-side port will hold call-setup resources open for a party that appears to be stalling. If this is left at a long value like 30000 milliseconds on a network with slow far-end call agents, users may perceive a long ring-before-fail delay instead of a fast busy/failure indication.