Hi Santosh, The responses are always send as per VIA only. When the initial request as in which can establish a dialogue is coming from UAC to UAS via a proxy, during the traversal, each hop's IPaddress is appended in the VIA header field. The hop's are can be determined by pre existing route set and DNS lookups. Say
UAC------->P1-------->P2--------->P3---------->UAS. In this example say P1 and P2 were part of pre configured route set and P3 as part of DNS lookups. All UAC, P1, P2, P3 will be in the marked in VIA field. Also there is a concept of Record Route as well. SIP entities which are part of initial routing of the message can mark themselves in Record route which means they will receive all further requests and their responses for that particular dialog/session. You can read in detail about this. Coming back to the scenario, now when UAS sends back the response to the request, The response will go through P3, P2, P1 and finally UAC(pls notice the order). The VIA header reuses the effort of routing the initial request to the UAS and thus ensures that all those elements which were part of the initial request also know about the response. UAC<------P1<------P2<-------P3<-------------UAS. The if suppose the dialog is established b/w UAC and UAS and for all further requests and its responses, the route field will be used to route the call. Route is calculted by the Record Route header field. For more details, refer RFC 3261 for this. On Thu, Oct 7, 2010 at 10:16 PM, Santosh Kal <[email protected]> wrote: > Hello All, > > To send response back to initiator proxy uses Route header and Via > header. > > Could you please help me understand which field is used in which scenario. > > Thanks, > Santosh > =====-----=====-----===== > Notice: The information contained in this e-mail > message and/or attachments to it may contain > confidential or privileged information. If you are > not the intended recipient, any dissemination, use, > review, distribution, printing or copying of the > information contained in this e-mail message > and/or attachments to it are strictly prohibited. If > you have received this communication in error, > please notify us by reply e-mail or telephone and > immediately and permanently delete the message > and any attachments. Thank you > > > _______________________________________________ > Sip-implementors mailing list > [email protected] > https://lists.cs.columbia.edu/cucslists/listinfo/sip-implementors > -- cheers!!!! sarvpriya http://sarvpriyak.blogspot.com/ _______________________________________________ Sip-implementors mailing list [email protected] https://lists.cs.columbia.edu/cucslists/listinfo/sip-implementors
