Subject: [SIP] SIP Queries

From: Varadarajan Srinivasan <[email-masked]>
Date: Tue, 05 Jun 2001 08:51:36 +0531

Hi All,

      I have some basic queries regarding RFC2543. I have used pdf
version of the draft bis02,
and the page nos are for the same.

     1) Is it not the Route header and Via contains redudant
information?

      Via is needed only to set route or just to send responses in the
same path as that of the
      request.After route is
      set, I think proxies can take this info from route header and via
contains redundant
      information.

      2) Are Max_Forwards header and ttl parameter, mean similar things
? Can we take
      one out?

      3) In chapter 16, RFC2543[100], in example,  Why Via headers of
the response 180
      Ringing to the
      Invite request (in the previous page) are not the same??

      4) In chapter 16.5, [106](Page 106) of RFC2543, under the SIP
message 487 Request
      Terminated, it is written as the response should terminate at
Proxy. I think it is Client.

      5) Why statefull proxies require TCP?

      6) In Appendix A, in minimal implementation, [110] of RFC2543, for
Clients,
      it is said Contact header is not a minimum requirement. Without
that how do you
      register?
      Why BYE is not a part of minimum requirement?How will you
terminate a call then?

      7) In Appendix A, in minimal implementation, for Servers, OPTIONS
is categorised as
      Minimal requirement.
      I dont think so as it is only a sophistication.

      8)

INVITE 11:02:32
              UAC/UAS 1   ------------------------------ > UAC/UAS 2

                                                                    180
RINGING 11:02:34
                                         < -----------------------------

CANCEL 11:02:36

----------------------------- >

200 OK for INVITE
                                          <
-----------------------------

      A user 1 invites another user 2. It gets the 180 ringing and later
wants to cancel the
      invitation by sending
      cancel method. Before, the Cancel method reaches user 2, it picks
up the call and
      hence sends a 200 OK.
      Now, at this situation, what to do next?

      9) I have attempted certain clarrifications on RFC2543 for
Appendix I. I just want the
      group to check whether mine is correct or open the problem to the
group.

      i) In Appendix I, [127] of RFC2543, II paragraph, the author
specify that the request
      URI for
      Register is just the domain name wihtout @ but a format of request
line demands that
      it is a URL which requires @ in its syntax.
      The person who raised this query, is suggesting that To: header
field can be processed
      instead of Request URI by
      REGISTRAR and Request URI can be omitted in the REGISTER method ..
I think
      this is right.

      ii) In another clarrification in Appendix I, the last but one
query before Appendix J,
      the person who raised the query is WRONG. Table 5 does contain
      www-Authenticate as a response as well
      as Request header.

Mr. Varadarajan Srinivasan,
Senior Systems Engineer,
Wipro Technologies.

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