-----Original Message-----
From: Viswanathan, Sriram C (Sriram) [mailto:[EMAIL PROTECTED]]
Sent: Thursday, July 26, 2001 1:16 PM
To: [EMAIL PROTECTED]
Subject: [Sip-implementors] Query on tags in From field and Retransmission
of INVITE responses in TCP !!
>
>Hi,
>I have question on the RFC related to the "From" field. In the "From" field
>there is a requirement to define a "tag" parameter (MUST). I am unable to
>create a
>scenario wherein this would be required from the UAC perspective.
As Brett has correctly pointed out, it is required for re-INVITEs in the
reverse direction to be distinguished from a new INVITE. Note that usage of
>From tags is now mandatory in bis.
>
>Also, could anyone indicate as to why the retransmission of INVITE
responses
>are done for a TCP connectivity. TCP itself is a reliable transport. Even
if
>we have intermediate proxies or other carriers I am assuming that when they
>implement UDP on the way, they would have retransmission logic built in.
John has answered this one.
>The
>other thing is if a SIP message indicates that the transport is TCP and if
any
>proxy on the way does not support this transport there is supposed to be an
>error code returned back. Is this correct?
What does it mean to "indicate"? If a user sends a request of the following
form:
INVITE sip:[EMAIL PROTECTED];transport=tcp SIP/2.0
to its local outbound proxy, and that proxy doesn't support TCP, then yes,
an error is generated (404 is probably appropriate). THis usually won't
happen, though. Transports are not arbitrarily placed into URLs. They only
get there, in general, if a proxy record-routes with a transport parameter.
bis-04 clarifies that a proxy should only do that if its sure the elements
which will use that record-route actually support TCP.
-Jonathan R.
---
Jonathan D. Rosenberg, Ph.D. 72 Eagle Rock Ave.
Chief Scientist First Floor
dynamicsoft East Hanover, NJ 07936
[EMAIL PROTECTED] FAX: (973) 952-5050
http://www.jdrosen.net PHONE: (973) 952-5000
http://www.dynamicsoft.com
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