Diagnosing SIP issues: one way audio, gaps in sound, registration errors, SIP ALG

April 26, 2017 by voxbit-admin

Session Initiation Protocol (SIP) can get quite complicated, especially when products from different suppliers are mixed.  SIP issues are difficult to diagnose!

A SIP call relies on DNS, NTP, routers, switches, SIP proxies, media proxies and end devices.  Each component must work as expected… There are a lot of ways that this can break!

The usual suspects for the weird failure of call setup:

  1. Network MTU and SIP UDP
  2. Router: SIP ALG
  3. DNS failure
  4. NAT / Port Forwarding

The usual suspects for call quality issues:

  1. Network dropping packets
  2. Router load
  3. Prioritising Traffic /QOS

There are a few tools which are very useful in figuring out why a call or message did not flow as expected:

  1. SIP dialogs and transactions
  2. Call flow visualization
    1. homer
  3. Commandline tools
    1. ngrep
    2. sngrep
    3. tcpdump
  4. Network issues
    1. NAT
    2. Packet loss / jitter / latency
    3. wireshark

Automated test environment: SIPP, SIP Treadmill …

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