SIP Illustrated: SIP by sip

It has been a great archness from me to illustrate anything, as I’m not able to draw practically anything. Really you would have a hard time to say whether my drawing is supposed to be an apple or a cat. Yet I couldn’t help myself. I simply believe that graphics help to understand complex IMS flows. And unfortunately there are nearly none in telecom standards. Hope this gentle guide will provide you into the world of SIP protocol in VoLTE environment and you’ll gain some new and useful information.

Have a tea/coffee, take it slowly, sip by sip. Enjoy!


If you are new to IMS and VoLTE, please read firstly these posts:


SIP Illustrated 1: Basics

In the first chapter we talk about basic SIP principles and architecture.


SIP Illustrated 2: SIP Message

In the second post we analyze SIP message and its basic headers.

SIP Request

SIP Illustrated 3: Routing and IMS Registration

The third post article is about IMS Registration and we discuss basics of SIP Routing

SIP Loose Routing

I’d recommend also to go through other related posts, which are not directly focused on SIP, but which you might find useful:

SIP Illustrated 4: SIP Session

The fourth post explains basic SIP/VoLTE session signalling.

SIP Session signalling flow

To deepen your knowledge you could read VoLTE flows – close encounters and It is about quality!

SIP Illustrated 5: SIP Session Routing

In the fifth sip we analyze session routing, including Server location discovery.

SIP INVITE Routing – Terminating IMS