Well I think It depends on the SIP Traffic basically. SIP messages are transported over UDP/TCP/SCTP. Each has its own advantages and disadvantages. Following are some which I could think of. There may be more also. * * *1. SIP-OVER-UDP:*
*Advantages:* If the amount of data to be sent at once is not huge then UDP is the simplest and best way of transmission which is quite fast as well. *Disadvantages:* 1. We get Maximum throughput but at the cost of network or application congestion. 2. Obvious drawback of UDP that we know is absence of acknowledgment of received datagrams or retransmission mechanisms. So SIP application needs to take care of this. *2. SIP-OVER-TCP* *Advantages:* 1. TCP has lot more to offer when compared to UDP when w.r.t congestion/retransmission/error control. *Disadvantages:* 1. TCP socket reads and writes needs to be serialized. 2. Reading SIP messages from the TCP stream is much more complicated compared to UDP because it may arrive in different TCP segments wherein payloads are not delivered all at once. 3. Internal Timer Configuration is not permitted in TCP which for that matter Timing in SIP messages are very crucial. *3. SIP-OVER-SCTP:* *Advantages:* 1. This offers a combo of both UDP and TCP. Features like unordered message delivery are one belonging to UDP legacy. 2. Like retransmission of lost data, flow control, congestion control as in TCP. But in addition to above SCTP standard features like multihoming, built-in heartbeats etc (may be more features) are helpful. *Disadvantages:* 1. As its new, Depends on SCTP stack implementation and complexity as well. 2. SCTP performance in terms of throughput may not be upto the mark with the one offered by TCP. I think we need to select kind of transport for SIP based on its keeping trade offs mentioned above or what we actually can expect from the given type of SIP Traffic. Regards, Vikas Jayaprakash On Mon, Jun 21, 2010 at 11:42 PM, Harsha. R <[email protected]>wrote: > > > > > > > > I'm still a bit confused. With RFC3261 should retransmits be used over > > reliable transports? > > > > > I have seen SIP-I (SIP with ISUP encapsulation - ITU-T Q.1912.5 or ANSI > T1.679) requests/responses retransmitted even over reliable transports like > SCTP. > Most often, its driven by operator needs. > > However, care should be taken that SCTP retransmission timers are larger > than SIP retransmission timers by a system engineered factor, otherwise > there might a flood of both transport/application layer retransmissions. > -- > Regards > Harsha > _______________________________________________ > Sip-implementors mailing list > [email protected] > https://lists.cs.columbia.edu/cucslists/listinfo/sip-implementors > -- Thanks & Regards, Vikas Jayaprakash _______________________________________________ Sip-implementors mailing list [email protected] https://lists.cs.columbia.edu/cucslists/listinfo/sip-implementors
