In a real world situation you will most likely be connected to an ethernet switch where MTU is 1500 bytes. So you can compute the likely maximum sip message off of that: 8 bytes UDP, 20 bytes IP, 26 bytes ethernet DIX. That leaves you 1446 bytes for a real world SIP message.
-----Original Message----- From: Mehul Jain [mailto:[EMAIL PROTECTED] Sent: Friday, August 11, 2006 3:43 PM To: Romel Khan; [email protected] Subject: RE: [Sip-implementors] Max Size of an INVITE message using UDP Thanks for the info, but that's the ideal case. In the real network with gateways, routers and proxies in between, the situation changes. I wanted to know if there is a known max value in such a real network scenario. -----Original Message----- From: Romel Khan [mailto:[EMAIL PROTECTED] Sent: Friday, August 11, 2006 12:35 PM To: Mehul Jain; [email protected] Subject: RE: [Sip-implementors] Max Size of an INVITE message using UDP Based on the RFC quote, implementation must be able to accept sip message up to the maximum size allowed per UDP. UDP header can consume 8 bytes, IP header 20 bytes typically. So SIP messages could theoretically use 65,535-28 = 65,507 bytes in a hypothetical environment where there is no MTU constraint. -----Original Message----- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf Of Mehul Jain Sent: Friday, August 11, 2006 1:41 PM To: [email protected] Subject: [Sip-implementors] Max Size of an INVITE message using UDP Am not clear what is the max supported size of SIP Request (INVITE) sent using UDP. Went through the RFC 3261 (18.1.1 Sending Requests ). MTU (1500 Bytes for Windows) looks to be the limiting factor for UDP, while later its written that implementations must support messages of the max datagram size (65,535 bytes). Any pointers as to what is the accepted max length in the proxies, servers etc. Mehul. If a request is within 200 bytes of the path MTU, or if it is larger than 1300 bytes and the path MTU is unknown, the request MUST be sent using an RFC 2914 [43] congestion controlled transport protocol, such as TCP. If this causes a change in the transport protocol from the one indicated in the top Via, the value in the top Via MUST be changed. This prevents fragmentation of messages over UDP and provides congestion control for larger messages. However, implementations MUST be able to handle messages up to the maximum datagram packet size. For UDP, this size is 65,535 bytes, including IP and UDP headers. The 200 byte "buffer" between the message size and the MTU accommodates the fact that the response in SIP can be larger than the request. This happens due to the addition of Record-Route header field values to the responses to INVITE, for example. With the extra buffer, the response can be about 170 bytes larger than the request, and still not be fragmented on IPv4 (about 30 bytes is consumed by IP/UDP, assuming no IPSec). 1300 is chosen when path MTU is not known, based on the assumption of a 1500 byte Ethernet MTU. _______________________________________________ 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
