SIP-Session Initiation Protocol – “Sick & Tired”

February 5, 2008
Do you ever get “sick and tired” of explaining the same stuff over and over. I seem to be caught in a SIP “sink hole” of trying my best to explain SIP and people still don’t get it. I concede that SIP is not easy and the entire concept of signaling is, outside of technical audiences, as much magic as why planes can fly. Here I go again, trying one more time to provide a tutorial to help because while the “propeller heads” get it, many others don’t but they often control the purse strings. Here goes and always appreciate feedback if you have any ideas on how to make it better. This tutorial describes the steps in a SIP Signaling and SIP Media Session.
 
SIP Signaling
User dials number 303-594-1694. SIP-URI-Uniform Resource Identifier is retrieved from DNS-Domain Name System - sip:tom@xyz.com;Transport=UDP. The SIP INVITE along with the SDP-Session Description Protocol is formatted into an Internet Message Format and encapsulated into ethernet and sent via the LAN Switch to the router and encapsulated into IP or IP-MPLS and UDP and the SIP INVITE is sent via TCP, UDP and other protocols to the destination proxy. The caller receives a 100 (Trying) response indicates that the INVITE has been received and that the proxy is working "on behalf of" to route the INVITE to the destination. The caller receives a 180 (Ringing) and begins ear ringing using an audio ringback tone or by displaying a message on the telephone screen. When the person called picks up the handset, the SIP phone sends a 200 (OK) response to indicate that the call has been answered. The 200 (OK) message contains a SDP-Session Description Protocol media description of the type of session that the other party is willing to establish.
SIP Media Session
User begins talking. Voice is transcoded into a CODEC, e.g. G.711, G.729. Voice is packetized. RTP is added and encapsulated in Ethernet and sent via the LAN Switch to the router and encapsulated into IP or IP-MPLS and UDP. If on-net IP network, converted to an optical data stream and sent via optical fiber to an internet or internal router. If off-net, channelized using a MG-Media Gateway to a TDM-Time Division Multiplexed channel and sent via an optical data stream to a Class 5 CO-Central Office switch for connections to the PSTN-Public Switched Telephone Network.
 

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Comments to SIP-Session Initiation Protocol – “Sick & Tired”


  1. Rich Guard :
    February 7, 2008 11:37 AM

    Tom,

    I enjoyed your tutorial on SIP signalling.
    Is there a hand-on course available where I can spend more time with it, and work with the logs?

    Thanks,
    Rich


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