Hi Dave, You can refer IETF draft 'draft-ietf-sip-outbound-01' for your reference. Abstract of the draft is: Session Initiation Protocol (SIP) allows proxy servers to initiate TCP connections and send asynchronous UDP datagrams to User Agents in order to deliver requests. However, many practical considerations, such as the existence of firewalls and NATs, prevent servers from connecting to User Agents in this way. Even when a proxy server can open a TCP connection to a User Agent, most User Agents lack a certificate suitable to act as a TLS server. This specification defines behaviors for User Agents, registrars and proxy servers that allow requests to be delivered on existing connections established by the User Agent. It also defines keep alive behaviors needed to keep NAT bindings open and specifies the usage of multiple connections for high availability systems.
Regards, Pravesh -----Original Message----- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf Of David Stuart Sent: Thursday, December 01, 2005 5:31 AM To: [email protected] Subject: [Sip-implementors] Question about NAT/FW and UDP Hello, I have noticed that some SIP User Agents are sending UDP keep-alive packets in order to keep the pinhole on the NAT from closing. But because of the fact that most of these NATs are either port restricted cone or, in the worst case, symmetric, it means you need to send the packets to their intended destination (including the port number). So, I worry about these packets because I think that maybe the implementation of the receiving side might not account for packets which are essentially "garbage" (for instance, a phone might interpret this as a lost packet and do silence suppression, or a video codec may try to conceal packet loss etc).. Therefore I am wondering if any standards (or even best practices) exist for the sending of such packets. Dave -- David Stuart, SIPquest Email: dave (at) sipquest (dot) com Phone: 254-8886 x234 Web: http://www.sipquest.com/ Address: 300 - 350 Terry Fox Drive, Kanata Ontario, K2K 2P5 _______________________________________________ Sip-implementors mailing list [email protected] http://lists.cs.columbia.edu/mailman/listinfo/sip-implementors __________________________________ Start your day with Yahoo! - Make it your home page! http://www.yahoo.com/r/hs _______________________________________________ Sip-implementors mailing list [email protected] http://lists.cs.columbia.edu/mailman/listinfo/sip-implementors
