VoIP calls disconnect after roughly 30 seconds

Measure the interval

Record the exact time from answer to disconnection over several calls. A repeatable interval near a signaling timer can be informative, but thirty seconds is a symptom rather than a diagnosis. Record which side ends the call and whether audio worked beforehand.

Check answer and acknowledgement

Look for retransmitted final success responses and whether the corresponding ACK reaches the participant expecting it. An incorrect Contact, routing address or NAT path can send acknowledgement to the wrong place while earlier signaling still appeared to work.

A PBX has separate legs. Confirm receipt on the leg that is retransmitting, rather than observing an ACK somewhere else in the trace and declaring the transaction healthy.

Check alternative timers

If acknowledgement is correct, inspect media inactivity and session behavior, device logs and carrier-side termination. A firewall state timeout or configured media timeout can produce a similar user-visible interval. Identify the BYE source and any useful reason information.

Verify the actual fix

Correct the demonstrated routing or timer problem and test calls longer than the previous failure window. Include incoming and outgoing calls and hold behavior. Do not disable all timeouts or raise every timer arbitrarily; that can hide abandoned calls and leave chargeable sessions active.