Troubleshooting ladders, captures, and debug

Rooms

1. Match a ladder before you change anything

   A ladder is one dialog only after Call-ID, CSeq, the Via branch, and the To tag agree.

2. Status codes you will actually see

   Read provisional and final codes from RFC 3261 section 21, and keep 422 with RFC 4028.

3. Display filters for SIP and RTP

   Filter the capture with sip, rtp, and sip.Method, and confirm sip.CSeq.method in the SIP display-filter reference.

4. IOS ccsip and ccapi debug

   debug ccsip messages prints SIP on IOS voice. debug voip ccapi inout prints call-control API output, which is not a SIP RFC.

5. 488 codecs and 422 session timers

   488 is this UA refusing the session description. 422 is a session interval below Min-SE.

6. TLS names, trust anchors, and version

   Handshake failures stay below SIP. A Teams 403 is the Contact FQDN rule after TLS is up.

7. Read an RFC header before you cite it

   Number, category, and Obsoletes or Updates. The RFC Editor header beats a remembered month.

Ecosystem

SIP does not replace workforce management, quality monitoring, CRM, emergency policy, or a messaging registry. It is the session seam those systems hang from. Compliance notes on this page are educational and are not legal advice.

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