>From RFC.
Since 2xx is retransmitted end-to-end, there may be hops between
UAS and UAC that are UDP. To ensure reliable delivery across
these hops, the response is retransmitted periodically even if the
transport at the UAS is reliable.
The 2xx response and its ACK receive special treatment. This
response is retransmitted only by a UAS, and its ACK generated only
by the UAC. This end-to-end treatment is needed so that a caller
knows the entire set of users that have accepted the call. Because
of this special handling, retransmissions of the 2xx response are
handled by the UA core, not the transaction layer. Similarly,
generation of the ACK for the 2xx is handled by the UA core. Each
proxy along the path merely forwards each 2xx response to INVITE and
its corresponding ACK.
Vivek
-----Original Message-----
From: [EMAIL PROTECTED]
[mailto:[EMAIL PROTECTED] On Behalf Of Rhys D
Ulerich
Sent: Friday, January 07, 2005 1:47 AM
To: [email protected]
Subject: [Sip-implementors] Section 13.3.1.4 The INVITE is Accepted
>From Section 13.3.1.4 "The INVITE is Accepted"
"Once the response has been constructed, it is passed to the INVITE
server
transaction. Note, however, that the INVITE server transaction will be
destroyed as soon as it receives this final response and passes it to
the
transport. Therefore, it is necessary to periodically pass the response
directly to the transport until the ACK arrives. The 2xx response is
passed to the transport with an interval that starts at T1 seconds and
doubles for each retransmission until it reaches T2 seconds (T1 and T2
are
defined in Section 17). Response retransmissions cease when an ACK
request
for the response is received. This is independent of whatever transport
protocols are used to send the response."
Re: the last sentence. Why is this behavior independent of the
transport
protocol? It seems like re-submitting the 2xx to the transport is
completely meaningless for TCP/TLS transports since the 2xx was
guarenteed
to arrive when it was initially passed to the transaction state machine.
I'd expect this special case to only be necessary for UDP.
Comments? Explanations?
- Rhys
__________________________________
Rhys Ulerich
Telecommunications Solutions Software Development
Email: [EMAIL PROTECTED] Office: 512-838-1428
IBM Software Group - Austin, TX
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