2009/2/5 Andrew Wood <[email protected]>:
>
> In a call between two phones A & C through one proxy B if B inserts an
> RR into the invite C will rcho it back in the reslonses should or
> shouldnt this be removed when passibg it downstream to A? The example
> im looming at in Johnstons book shows the proxy removing it from the
> 180 but leaving it in the 200
Imagine the following:
C proxy
A
INVITE (require: 100rel) --------->
INVITE (require: 100rel
+ RR) -------->
<-------------------
180 (Contact + RR)
<-------------------- 180 (Contact)
PRACK
---------------------------------------------------------------------------->
If the 180 arriving to C has no RR, then the PRACK will be sent
directly to A instead of the proxy. this is not desirable in cases of
NAT and so.
In RFC3261, a 1XX response doesn't require to contain RR and Contact,
but for using some SIP extensions (as PRACK) it's needed.Other case
would be:
C proxy
A
INVITE ---------------------------->
INVITE (RR)
------------------------------>
<-------------------
180 (Contact + RR)
<-------------------- 180 (Contact)
INFO
---------------------------------------------------------------------------->
This is, C can send an in-dialog request during an early-dialog only
in case C has received a Contact header in the 1XX response. But as
above, in case the 1XX doesn't contain RR then the INFO will be sent
*directly* to the UAS instead of the proxy.
So, I see no reason for a proxy removing RR in 1XX responses. It has
no advantage at all, but some disavantages.
Regards.
--
Iñaki Baz Castillo
<[email protected]>
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