----- Original Message ----- From: <[EMAIL PROTECTED]> To: <[EMAIL PROTECTED]> Cc: <[EMAIL PROTECTED]>; <[EMAIL PROTECTED]> Sent: Saturday, August 04, 2001 4:45 PM Subject: RE: [Sip-implementors] Query on tags in From field and Retransmis sion of INVITE responses in TCP !! > > Hi, > > I have similar questions on Retransmission over TCP, Section 14.4.2, bis-4. > Suppose the following scenario. > > [A] --- TCP---- [Proxy1]------UDP ----- [Proxy2] ----TCP------[B] > > (1) A sends an INVITE which gets eventually proxied to B. B doens't send > any response. > Does Proxy1 retransmit INVITE following retransmission algorithms used for > UDP? Yes, if it is a stateful proxy. > > (2) A sends an INVITE which gets eventually proxied to B. B sends 200 OK > which gets eventually forwarded to A. > A doesn't send ACK. Does Proxy2 retransmit 200 OK following retransmission > algorithms used for UDP? Actually, it is the UAS [B] that re-transmits the 200-OK (in accordance with section 14.4.2 of bis-04 which applies to UAs not proxies). > > (3) Section 14.3,2, Reliable Transport Protocol, does not say anything > about retransmission of responses for non-INVITE messages. Does the UAS > using TCP need to retransmit a final response when receiving a > retransmitted non-INVITE request? You cannot retransmit responses for non-invite requests because there is not an ACK for responses to non-invite requests and thus there is no way to know whether or not the response got back to the UAC. > YoungSun > > > > > > [EMAIL PROTECTED] on 07/26/2001 01:41:05 PM > > To: [EMAIL PROTECTED], [EMAIL PROTECTED] > cc: (bcc: Youngsun Song/Telcordia) > Subject: RE: [Sip-implementors] Query on tags in From field and Retransmis > sion of INVITE responses in TCP !! > > > > > Here is the explanation in bis-04 for re-transmitting responses: > > > 14.4.2 Reliable Transport Protocol > A user agent using a reliable transport protocol such as TCP, SCTP or > TLS MUST NOT retransmit requests, but uses the same algorithm as for > unreliable transport protocols (Section 14.4.1) to retransmit > responses until it receives an ACK. A client MAY give up on the > request if there is no response within a client-defined timeout > interval. > > It is necessary to retransmit 2xx responses as their > reliability is assured end-to-end only. If the chain of > proxies has an unreliable transport protocol link in the > middle, it could lose the response, with no possibility of > recovery. For simplicity, we also retransmit non-2xx > responses, although that is not strictly necessary. > > > > -----Original Message----- > From: Viswanathan, Sriram C (Sriram) [mailto:[EMAIL PROTECTED]] > Sent: Thursday, July 26, 2001 11:16 AM > To: [EMAIL PROTECTED] > Subject: [Sip-implementors] Query on tags in From field and Retransmission > of INVITE responses in TCP !! > > > > Hi, > > I have question on the RFC related to the "From" field. In the "From" field > there is a requirement to define a "tag" parameter (MUST). I am unable to > create a > > scenario wherein this would be required from the UAC perspective. > > Also, could anyone indicate as to why the retransmission of INVITE > responses > > are done for a TCP connectivity. TCP itself is a reliable transport. Even > if > we have intermediate proxies or other carriers I am assuming that when they > implement UDP on the way, they would have retransmission logic built in. > The > other thing is if a SIP message indicates that the transport is TCP and if > any proxy on the way does not support this transport there is supposed to > be > an error code returned back. Is this correct? > > > Would appreciate if anyone could throw some light on this or even if > possible any web site which indicates a link to this kind of info. > > Thanks, > Sriram > > _______________________________________________ > 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 > _______________________________________________ Sip-implementors mailing list [EMAIL PROTECTED] http://lists.cs.columbia.edu/mailman/listinfo/sip-implementors
