Thanks for the response , But i am bit confused now ! AFIK any final resopnse should terminate the session, then how came after non-2xx response the ACK still can be part of the same transcation !!
vikram ----- Original Message ----- From: "vimal srivastava" <[EMAIL PROTECTED]> To: <[EMAIL PROTECTED]>; <[email protected]> Cc: <[email protected]> Sent: Tuesday, January 10, 2006 2:25 PM Subject: RE: [Sip-implementors] sip transcation query > Hi > Actually if we look at the intent of ACK in case of 2xx response things > become similar. > the ACK for 2xx resonse may carry SDP and it will un-necessarily congest > the network if it is sent thru all the proxies which are handling the > messaging statefully. Ack is usually exchanged directly > purpose of ACK is also to tell the end UAS that the originator has > received 200 message (which has SDP) so that conversation can begin. so > this signfies the need of ACK. > > in case of non-2xx final response, intent of ACK just to ackknowledge the > previous node that i have received the non-2xx response. and if ACK is not > received retransmit the non-2xx final response. if ACK is not sent then > there is no way to tell the pevious node that final response is received. > > This is not needed in case of 2xx response becos, if 2xx is lost in > between, UAC will not send ACK to the UAS and UAS will re-transmit 2xx > response again. > ACK for 2xx is exchanged directly (normally) between UAC and UAS so it > does not congest the network. > now if for non-2xx we leave the responsiblity of delivery to UAC (the way > it makes sure for 2xx), then even if non-2xx is lost at some intermediate > node, UAS will send non-2xx again and will traverse thru all the nodes > which is not neded. so by using hop-by-hop reliablity mechanism, some > network traffic is saved. > > UAS must know if 2xx is received at UAC or not because its > acknolwedegement of SDP exchanged , else processing at UAS stops > (convesation would not beging) > for non-2xx response UAS does not care. it does not stop any processing > for UAS > > so in essence: > for non-2xx final response (for invite) reliability is ensured hop-by-hope > and > for 2xx final response (for invite) reliablity is ensured end to end. > > > > cheers > v. > > > > From: "VikramB" <[EMAIL PROTECTED]> > To: <[email protected]> > CC: [email protected] > Subject: [Sip-implementors] sip transcation query > Date: Tue, 10 Jan 2006 09:20:06 +0530 > > Hello All, > In rfc 3261 section 6 Definition > > SIP Transaction : > .... > ..... > If the request is INVITE and the final > response is a non-2xx, the transaction also > includes an ACK to the response. The ACK for a 2xx response to > an INVITE request is a separate transaction. > > My query is why ACK is considered as a part of same transaction when in > case of non-2xx response.? > > > > regards > > VIkram > _______________________________________________ > Sip-implementors mailing list > [email protected] > https://lists.cs.columbia.edu/cucslists/listinfo/sip-implementors > > > _______________________________________________ Sip-implementors mailing list [email protected] https://lists.cs.columbia.edu/cucslists/listinfo/sip-implementors
