Hi,

I have few doubts in sip-protocol. It will be helpful if any one can help me in clearing my doubt.

1.  RFC 3261 says in 13.2.1 that :-
        "If the initial offer is in an INVITE, the answer MUST be in a reliable non-failure message from UAS back to UAC which is correlated to that INVITE.". 
        - Does this mean that if an INVITE is sent with SDP(offer) and then if reliable provisional response (180/183/...) comes with SDP, then the SDP in reliable provisional response must be considered to be answer and any SDP that comes in 200 OK should be blindly ignored ?

2. RFC 3261 says in 13.2.1 that :-
        "The UAC MUST treat the first session description it receives as the answer, and MUST ignore any session descriptions in subsequent responses to the initial INVITE."

        - Does this mean that if an INVITE is sent with SDP (offer) and then if it receives a non reliable provisional response with SDP and then it gets a 200 OK with SDP, then only the SDP in non-reliable provisional response must be considered as answer and the SDP in 200 OK must be blindly ignored ?

3.  Is the following scenario possible :-

         A                      B
         |                      |
         |  INVITE (SDP OFFER)  |
         |--------------------->|
         |                      |
         |                      |
         |   183 (SPD ANSWER)   |
         |<---------------------|
         |    PRACK (NO SDP )   |
         |--------------------->|
         | PRACK 200 OK(NO SDP) |
         |<---------------------|
         |                      |
         |                      |
         |                      |
         |   183 (SDP OFFER)    |
         |<---------------------|
         |  PRACK ( SDP ANSWER) |
         |--------------------->|
         | PRACK 200 OK(NO SDP) |
         |<---------------------|
         |                      |
         |                      |
         |                      |
         |     200 OK(NO SDP)   |
         |<---------------------|
         |     ACK (NO SDP )    |
         |--------------------->|
         |                      |
In the above diagram, I specifically wanted to know whether calle party (B) can send an OFFER SDP in the second reliable provisional response ?
 
 
4. RFC 3261 says in 19.1.1 that :-
        "Even though an arbitrary number of URI parameters may be included in a URI, any given parameter-name MUST NOT appear more than once."
 
          If this is the case, then how is tel uri format mentioned in RFC 2806 compatible with above definition. Tel uri says that :-
 
       global-phone-number = "+" base-phone-number [isdn-subaddress] [post-dial] *(area-specifier /service-provider / future-extension)
       area-specifier = ";" phone-context-tag "=" phone-context-ident
       phone-context-tag = "phone-context"
 
      Here he says that area-specifier (which is nothing but a tel - uri parameter) can appear more than once. But the above definition is not compatible with that of given in the rfc 3261. What to do in this case ? How to handle multiple tel-uri parameters with the same parameter name ?.
 
 
Rgds
 Krishna
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