> Looking for the views on, if the media format
> description <fmt> are mandatory to mention in
> the media descriptions (m=) line of SDPs.
Yes; the ABNF indicates that it is mandatory.
media-field = %x6d "=" media SP port ["/" integer]
SP proto 1*(SP fmt) CRLF
> how a state-full proxy/SBC should react, who is
> receiving the m= line having no fmt values like,
>
> |v=0
> |o=ABC-SIP 2000 1000 IN IP4 192.168.180.10
> |s=SIP Call
> |c=IN IP4 192.168.180.10
> |t=0 0
> |m=audio 25218 RTP/AVP
> |a=sendrecv
> |a=rtpmap:0 PCMU/8000
> |a=ptime:20
The SDP is malformed; thus it can basically act how it wants.
In general, a proxy is not expected to act as protocol police or route based
upon SDP. Thus it would typically just relay the malformed SDP.
An SBC, may provide a media function and be a B2BUA. Thus it may have a reason
to decode/use the SDP. The malformed SDP may cause it to a request or release
the call.
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