What do these three lines indicate in the SIP header

FreePBX
1

I’m still have trouble with a select few of our inbound callers. What I’ve noticed is the inbound SIP header will have these three lines at the end:

a=sqn: 0
a=cdsc: 1 audio RTP/AVP 0 8 15 18 96 97 98 2 99 101
a=cdsc: 11 image udptl t38

The caller hears a “your call cannot be completed as dialed” message, and our staff members hear our on hold music when they try to answer the call.

2

These are capabilities declarations (0 = PCMU, 8 = PCMA, few dynamic payload types… also T.38 faxing) and shouldn’t do harm (https://tools.ietf.org/html/rfc3407). I’ve seen these only with faxing so far (perhaps not paying attention to “regular” calls).