A student's open lab: learning and sharing, free for everyone.

SIP UniverseFree University

Home / Troubleshooting ladders, captures, and debug / 488 codecs and 422 session timers

488 codecs and 422 session timers

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

Learn in 5 minutes

  1. Read 488 as an offer/answer refusal at this UA
  2. Retry 422 with a large enough session interval
  3. Keep telephone-event in the overlap you meant to keep

Visual

422, then a taller session interval · study drawing · cyphermonkeylabs.com AliceSBC INVITE 422 ACK INVITE 200

SVG HTML PNG

They are different requests to the next INVITE.

Worked example

See the overlap Negotiate this synthetic offer and answer. PCMU and telephone-event are on both sides. PCMA is only in the offer.

  1. Run Negotiate.
  2. Find the shared audio codec.
  3. Confirm telephone-event on both sides.

Fault

The UAS returned 488 Not Acceptable Here. The next INVITE only changes Session-Expires from 90 to 1800 and repeats the same SDP.

488 points at this UA and the SDP. 422 would have been Session Interval Too Small with Min-SE.

Quiz

488 Not Acceptable Here often means


A 422 asks the UAC to


606 differs from 488 because


telephone-event names


PCMU static payload 0 is assigned in


The ACK on the 422 hop uses


Ecosystem

Glossary, sister systems, and the integration seam for this room.

CRM Screen pop uses data the contact center already has: ANI, DNIS, case id. Those values may arrive in SIP headers or in a CTI event after the call is up. The CRM is not a SIP element.

Glossary · Ecosystem map · Ports · Troubleshooting

Sources and go deeper