Hi,
I have similar questions on Retransmission over TCP, Section 14.4.2, bis-4.
Suppose the following scenario.
[A] --- TCP---- [Proxy1]------UDP ----- [Proxy2] ----TCP------[B]
(1) A sends an INVITE which gets eventually proxied to B. B doens't send
any response.
Does Proxy1 retransmit INVITE following retransmission algorithms used for
UDP?
(2) A sends an INVITE which gets eventually proxied to B. B sends 200 OK
which gets eventually forwarded to A.
A doesn't send ACK. Does Proxy2 retransmit 200 OK following retransmission
algorithms used for UDP?
(3) Section 14.3,2, Reliable Transport Protocol, does not say anything
about retransmission of responses for non-INVITE messages. Does the UAS
using TCP need to retransmit a final response when receiving a
retransmitted non-INVITE request?
YoungSun
[EMAIL PROTECTED] on 07/26/2001 01:41:05 PM
To: [EMAIL PROTECTED], [EMAIL PROTECTED]
cc: (bcc: Youngsun Song/Telcordia)
Subject: RE: [Sip-implementors] Query on tags in From field and Retransmis
sion of INVITE responses in TCP !!
Here is the explanation in bis-04 for re-transmitting responses:
14.4.2 Reliable Transport Protocol
A user agent using a reliable transport protocol such as TCP, SCTP or
TLS MUST NOT retransmit requests, but uses the same algorithm as for
unreliable transport protocols (Section 14.4.1) to retransmit
responses until it receives an ACK. A client MAY give up on the
request if there is no response within a client-defined timeout
interval.
It is necessary to retransmit 2xx responses as their
reliability is assured end-to-end only. If the chain of
proxies has an unreliable transport protocol link in the
middle, it could lose the response, with no possibility of
recovery. For simplicity, we also retransmit non-2xx
responses, although that is not strictly necessary.
-----Original Message-----
From: Viswanathan, Sriram C (Sriram) [mailto:[EMAIL PROTECTED]]
Sent: Thursday, July 26, 2001 11:16 AM
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.
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.
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?
Would appreciate if anyone could throw some light on this or even if
possible any web site which indicates a link to this kind of info.
Thanks,
Sriram
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