Timer T313, in milliseconds, applies on the network (callee) side and bounds how long the port waits for a CONNECT ACKNOWLEDGE after it has transmitted CONNECT, i.e. after the callee has accepted the call. If T313 expires with no CONNECT ACKNOWLEDGE, the switch treats the acceptance as failed and releases the SVC even though the callee thought it had answered, so a value that is too aggressive here can cause calls to drop right at the moment they should become active. Because this is the last handshake step before billing/active-call state, an admin troubleshooting calls that connect and immediately disconnect would look at this timer first, alongside svcAtmConfigQ93bNumConnectAckPduRx to see if the ack is arriving late.