Unable to Receive Incoming Calls from the SIP trunk – Session Timer Required

Applicability

  • Firmware version: Any
  • Model: S-Series, U-Series

Problem Description

When receiving the incoming call through the SIP trunk, S-series PBX reply ‘421 Extension Required’, then the incoming call fails.

Analysis

The PCAP log shows S-Series PBX refused the call, then required ‘Timer’, which means S-series PBX requires the SIP provider sends ‘session timer’ at the INVITE field. 

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Solution

Since the SIP provider is not easy to do the changes, then we disable the Session timers at S-Series PBX side.

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