This question sometimes pop up, because its difficult to understand, what the purpose of maddr really is, or was. mAybe th following helps:
Look at RFC 3261 18.1.1: A client that sends a request to a multicast address MUST add the maddr parameter to its Via header field value containing the destination multicast address, and for IPv4, SHOULD add the ttl parameter with a value of 1. Usage of IPv6 multicast is not defined in this specification, and will be a subject of future standardization when the need arises. These rules result in a purposeful limitation of multicast in SIP. Its primary function is to provide a "singlehop-discovery-like" service, delivering a request to a group of homogeneous servers, where it is only required to process the response from any one of them. This functionality is most useful for registrations. In fact, based on the transaction processing rules in Section 17.1.3, the client transaction will accept the first response, and view any others as retransmissions because they all contain the same Via branch identifier. My comment: >From there you see, that maddr is or was never used for media conferencing. Another comment on a similar question (Can somebody pls tell me the purpose of maddr in the Request-URI?) was: It was used in the early days of sip as a mechanism for forcing requests to traverse an alternative destination to that specified in the host part of the R-URI. This mechanism has been replaced by preloaded route headers, and it's use is not recommended. Again this answer shows, that maddr was never used for multiparty conferencing. Franz -----Original Message----- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf Of Oleksandr Sakada Sent: Montag, 22. September 2003 16:30 To: [EMAIL PROTECTED] Subject: [Sip-implementors] maddr parameter and multiparty conference Hi! I am confused a little bit with a multicast support in SIP. Consider, we need to establish a multiparty conference with the use of SIP. If I understand right, we need to have a central mixing unit, having it's own IP address. This address can be taken from external source (such as WEB or e-mail) and is carried in SDP encoded body of the INVITE request or 200 OK responce. Each UA performs a unicast "call" to this address. If it is correct, what is the role of "maddr" parameter of the Via header field or Request-URI. How does this paramer relate to the multicast conference address, via which media is transmitted/received? Does this parameter contain the same (multicast) address? Can you clarify this point, please? Thank you!!! _______________________________________________ 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
