[dispatch] Proposal for a mew SIP 4xx Error code

[Ranjit Avasarala <[e-mail]>]

Hello all

Many times I experienced scenarios where SIP requests (e.g. INVITE, PUBLISH
or PRACK or any other) have either invalid parameters in the header or a
particular header is missing in the request or the header value is
incomplete.  Some e.gs are

   - SIP Route header in INVITE contains additional "lr" parameter.
   Ideally, "lr" parameter needs to be associated with a particular route -
   i.e. sip URI
   - the Accept header is missing in SIP PUBLISH
   - the Allow header misses UPDATE method
   - .....  many more

Currently, in all the above cases the SIP Proxy server that receives the
request, responds with a 400 Bad Request.
Though 400 Bad Request is acceptable given that there is some issue in the
SIP request, a more detailed error would be more useful - as sometimes
interpreting 400 Bad Request is harder
E.g.
a  4xx Invalid header/parameter may be more appropriate with reason
E.g. if there is additional "lr" parameter in SIP INVITE, then the proxy
can return a 4xx Invalid Header/parameter with Reason:  SIP code=4xx;
Text="Invalid lr parameter in Route header"

Let me know your thoughts on if this proposal can be taken forward as an
Internet draft.

Thank you
Ranjit