SIP reference, written by people who debug it.

Reference material that pairs with the SIP Flow analyzer. Look up an error code, learn how to capture a trace, then bring the trace back here to render the ladder.

• Reference

  SIP error codes

  Plain-English explanations of the SIP response codes you actually see in production, with vendor-specific causes and fixes for Asterisk, FreeSWITCH, Kamailio, Cisco CUBE, Twilio, and friends.

  Browse SIP error codes

• How-to

  Capture SIP traces

  Short, opinionated step-by-step guides for every tool real VoIP engineers reach for: Wireshark, sngrep, Homer/sipcapture, Asterisk, FreeSWITCH, Cisco CUBE, Twilio. Get a clean .pcap or text log fast.

  Browse capture guides