The SIP specification handles loops in two ways: Max Forwards (mandatory) Loop detection (optional)
MAX FORWARDS The Max-Forwards header field serves to limit the number of hops a request can transit on the way to its destination. It consists of an integer that is decremented by one at each hop. If the Max-Forwards value reaches 0 before the request reaches its destination, it will be rejected with a 483 (Too Many Hops) error response. The default initial value for Max-Forwards is 70. This solution requires minimal processing by proxies and UACs, but has the disadvantage of stopping the loop only after the message has been forwarded enough times to exhaust the Max-Forwards value (70 hops by default). LOOP DETECTION A proxy can optionally check for loops by employing a special loop detection algorithm. The algorithm affects the way the proxy builds the Via-branch field and mandates the proxy to do certain validations of the Via list in incoming requests. Loop detection requires some extra processing per message, but guarantees immediate detection of the loop as the proxy receives the message for the second time. you can also refer to 3261 for specifics. here the section that would give you some detail. 8.2.2.2 Merged Requests 4. Optional Loop Detection check cheers v. From: Manju S <[EMAIL PROTECTED]> To: [email protected] Subject: [Sip-implementors] What is the use of via header. Date: Fri, 16 Dec 2005 21:23:44 +0530 Hi all... I have some basic question on sip. 1) what is the use of VIA header field? 2) how is loop is detected by proxy? thanks in advance Regards Manju _______________________________________________ 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
