SIP Protocol is a must for anyone who needs to understand VoLTE/VoWifi calling. However most of the guides and introductions to SIP are focused on enterprise/trunking networks rather than IMS (IP Multimedia Service Core Network). So if you’re working in telco environment, maybe this is a good place to start.
It has been a great archness from me to illustrate anything. 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:
In the first chapter we talk about basic SIP principles and architecture.
In the second post we analyze SIP message and its basic headers.
The third article is about IMS Registration and we discuss basics of SIP 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
The fourth post explains basic SIP/VoLTE session signalling.
In the fifth sip we analyze session routing, including Server location discovery.
More complex flows are explained in
- P-Early-Media – You are running low on credit!
- It is about quality!
- At your service..
- VoLTE Conference Call
- SRVCC – Mind the coverage hole!
Other IMS Protocols: