Symptom

The MGCP GW when doing fax switchover using T38 is sending SDP with audio m-line in 200 OK response to MDCX recevied from CUCM. This is not the correct behavior since the SDP of 200 OK response must have image attribute in m-line. NTFY T38 start. NTFY 912383630 aaln/S0/SU2/1@router.abc.edu MGCP 0.1 N: ca@ X: d O: FXR/t38(start) <--- MDCX with SDP MDCX 1588773 AALN/S0/SU2/1@router.abc.edu MGCP 0.1 C: A0000000044feeb6000000F5 I: 224 X: f L: a:image/t38 M: sendrecv R: L/hu, L/hf, D/[0-9ABCD*#], FXR/t38 S: Q: process,loop v=0 o=- 548 0 IN EPN AALN/S0/SU2/1@router.abc.edu s=Cisco SDP 0 t=0 0 m=image udptl t38 c=IN IP4 a=X-sqn:0 a=X-cap:1 image udptl t38 <--- 200 OK SDP.. 200 1588773 OK v=0 c=IN IP4 m=audio RTP/AVP 0 a=X-sqn:0 a=X-cap: 1 audio RTP/AVP 100 a=X-cpar: a=rtpmap:100 X-NSE/8000 a=X-cpar: a=fmtp:100 200-202 a=X-cap: 2 image udptl t38 <---

Conditions

This issue is seen on IOS XE routers when using mgcp t38 fax-relay call.T.38 enabled. IOS-XE version 17.3.3

Workaround

Downgrade to a working release.

Further Problem Description