RFC 3665 SIP Basic Call Flow Examples December 2003 These call flows are based on the current version 2.0 of SIP in RFC 3261 [] with SDP usage described in RFC 3264 [].Other RFCs also comprise the SIP standard but are not used in this set of basic call flows. Call flow examples of SIP interworking with the PSTN through gateways are contained in a companion document, RFC 3666 [].. There are various forms of SIP call flows depending on the software involved—basic SIP to SIP, proxy servers, SIP Gateways, etc. Here we've focused on the basic SIP call flow: a direct call from one SIP user to another. Source. Without knowing the usual SIP requests and response codes, this diagram may be confusing.
SIP is based on a request/response transaction model where each transaction consists of a request that invokes a particular method or function on the server and at least one response. Diagram of a request, acceptance, setup and termination of a call. SIP typically sends these messages in UDP (User Datagram.. This will then display the SIP call flow diagram for that call. SIP Call Flow for Outbound Call. In Figure 2 below you will find the SIP message flow for an outbound call from a phone through the PBX and out to the PSTN (Public Switch Telephone Network). The SIP messages used in the outbound call flow are as follows: