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!
Prerequisites
If you are new to IMS and VoLTE, please read firstly these posts:
IMS in VoLTE
SIP Illustrated 1: Basics
In the first chapter we talk about basic SIP principles and architecture.
SIP B2BUA
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:
- Much Ado about Registration
- How to read tcpdump – Registration
- Third Party Registration
- Sh Interface
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
Real Time Communication 