inline. ----- Original Message ----- From: "Revathi K" <[EMAIL PROTECTED]>
> Hi, > I have some basic doubts about the To-tag processing by proxy. > When will a proxy ever need to insert a To-tag in a response? > > Section 16.7 of the RFC says that: > > 3-6xx responses are delivered hop-by-hop. When issuing a 3-6xx > response, the element is effectively acting as a UAS, issuing > its own response, usually based on the responses received from > downstream elements. An element SHOULD preserve the To tag > when simply forwarding a 3-6xx response to a request that did > not contain a To tag. > A proxy MUST NOT modify the To tag in any forwarded response to > a request that contains a To tag. > While it makes no difference to the upstream elements if the > proxy replaced the To tag in a forwarded 3-6xx response, > preserving the original tag may assist with debugging. > > 1) The above section seems to be contradictory. On the one hand, > it says that 3xx-6xx responses are hop-by-hop and the proxy > would act as a UAS hen delivering these. This would mean that > the proxy can, if it wants, insert/replace the To-tag in the > response. However, the section also says that a proxy must not > modify the To tag in any forwarded response. So which of the above > interpretations is correct? The key is whether the request had a to-tag. If it did, it is an in-dialog request (e.g. re-INVITE, BYE, etc). In that case the to-tag in the response MUST always match the to-tag in the request no matter whether the response is generated by a UA or a proxy. For the case of an out-of-dialog request (i.e. no to-tag in the request), if the proxy is forwarding one of the responses it received from a downstream UAS, it SHOULD retain the to-tag from that response, unless there is a really good reason not to. > > 2) Also, this above section seems to talk about tha case where > the proxy forward a 3xx-6xx respone from a downstream element. > What should be the behaviour when the proxy is generating a > 3xx-6xx response on its own (i.e. without forwarding the > request out)? Should the proxy insert a To-tag on it own > in this case? When the proxy is responding to the request, it is truly the UAS for the request, and UAS rules apply (see 8.2.6.2). If the request had a to-tag, the response MUST have the same to-tag. If the request did not have a to-tag, a to-tag MUST be added to the response. > > > Any help in understanding the above section of the RFC correctly > will be appreciated. > > thanks in advance > Revathi > > > -------------------------------------------------------------------------- ------ > Get your own space on the web. Logon to MSN Spaces. Share files, photos, ideas etc ---------------------------------------------------------------------------- ---- > _______________________________________________ > Sip-implementors mailing list > [email protected] > http://lists.cs.columbia.edu/mailman/listinfo/sip-implementors > _______________________________________________ Sip-implementors mailing list [email protected] http://lists.cs.columbia.edu/mailman/listinfo/sip-implementors
