As per table-3 of RFC-3261 Page 163. ACK must have via. Via header carries minimum two information. One is the address where the response should be sent. The second is the branch identifier which is used to identify transaction at the peer element ( UAS/Proxy )
So I think the SIP elements which would not include via in the ACK, they are incorrect. For e.g consider the INVITE-3XX case. Here UAS is waiting for an ACK with a via header carrying the same branch as in INVITE-3xx to stop transaction retransmission timers. Without a via header the transactions can not be identified and transaction retransmission timers can not be stopped. Regards, Indresh K Singh ------------------------------------------------------------- Sr. Software Engineer SIP Media Control and Signaling Nokia Siemens Networks Boca Raton, FL-33487 Ph: 561-923-5085 (o), 561-923-2048 (o) ------------------------------------------------------------- >>-----Original Message----- >>From: [EMAIL PROTECTED] >>[mailto:[EMAIL PROTECTED] On Behalf >>Of ext Diego B >>Sent: Saturday, May 19, 2007 12:59 AM >>To: [EMAIL PROTECTED] >>Cc: Sip-implementors@cs.columbia.edu >>Subject: Re: [Sip-implementors] Is the VIA header mandatory >>in all request messages >> >>Hi; >>For example the ACK request. >>I saw several SIP elements that sends ACK without a Via header. >> >>[EMAIL PROTECTED] wrote: >>> From: "Rami Eitan" <[EMAIL PROTECTED]> >>> >>> My question is does anyone know of or has ever come across a >>> request message without the VIA header in it? >>> >>> If there was no Via header, the recipient would have no way to know >>> where to send the response. >>> >>> Dale >>> _______________________________________________ >>> Sip-implementors mailing list >>> Sip-implementors@cs.columbia.edu >>> https://lists.cs.columbia.edu/cucslists/listinfo/sip-implementors >>> >> >>_______________________________________________ >>Sip-implementors mailing list >>Sip-implementors@cs.columbia.edu >>https://lists.cs.columbia.edu/cucslists/listinfo/sip-implementors >> _______________________________________________ Sip-implementors mailing list Sip-implementors@cs.columbia.edu https://lists.cs.columbia.edu/cucslists/listinfo/sip-implementors
