Forum Discussion

DayneJake's avatar
DayneJake
Brass Contributor
Sep 28, 2022

Teams devices (deskphones) Throwing 488 error regarding media bypass

Have a Direct routing setup that is using media bypass. Calls using PC client or web client are fine. Calls using any model\mfg of Teams phone throws the following every 10 minutes and then the cal...
calling
microsoft teams
Satyamsoft7's avatar
Satyamsoft7
Copper Contributor
Sep 07, 2026

The useful clue is not just “488”; it is BackToBackBypass offer was declined by Peer, plus desktop/web working while Teams desk phones fail. That points at the media-bypass renegotiation / ICE path on the phone↔SBC leg, not a basic voice route or carrier codec problem.

Capture around the first ~10-minute re-INVITE/UPDATE and compare original SDP with the bypass offer. Confirm the SBC returns reachable ICE candidates on the Teams-facing leg (public media address, no 0.0.0.0 / unusable private-only candidates), and that SRTP + Media Bypass settings match on the trunk the phones actually use.

Controlled test: disable Media Bypass on that online gateway/trunk and retry one desk phone. If the periodic 488 disappears, fix ICE/public media reachability (or SBC firmware support for phone bypass) before turning bypass back on. The SBC trace showing which peer declined the re-INVITE beats guessing at client firmware alone.

Field notes on reading 488 / Not Acceptable Here in Direct Routing: https://skypeexchange4u.com/teams-direct-routing-488-not-acceptable-here/