SIP - Application layer protocolSIP RequestsSIP responsesSession Description Protocol  (SDP)SIP transactions, dialog , branchMatching in-dialog transactions/requestsRecord Routing strict routingloose routing Mobility and Location ServiceNetwork Address Translator ( NAT)Far End TraversalNear End TraversalSIP Call Flows RegisterationCall RedirectionForkingclick to Dial SIP for Instant Messaging and Presence Leveraging Extensions ( SIMPLE) Update : At the time of writing … Continue reading SIP ( Session Initiation Protocol )