It has been 3 years since I started this blog. It was around that time back in 2014 when I heard about 5G for the first time. It was funny, we were just doing the first 4G/VoLTE deployments, everything was new to operators and someone was already dreaming about the next version 🙂 In 2017 the 5G is still not finalized but we have done quite a few steps forward and 3GPP has created a lot of specifications (Rel-15) which uncover the concept (actually we have 5GPP too!). Maybe you have already heard about some features as Dynamical Network Slicing, CloudRAN, Network-as-a-Services, … Some basic principals we’ll briefly discussed also in this post. However my question is: What will be the change from the real-time communication point of view? Is the IMS to stay in the operators’ networks?
Seems that at the first stage the change will be less dramatic than when we introduced 4G. 4G was in many ways a revolution, whereas 5G is “only” an evolution. In fact 4G and 5G, at least in the beginning, will coexist and complement one each other. Still 5G will have a big impact on our existing technologies and the way we work with telecommunication networks.
5GS + EPC + IMS
Before I’ll finish a new post about 5G I decided to take a break and create a presentation which would complement VoLTE Basic Flows.
Btw. I can’t find the option on slideshare which would allow to update the material .. does anyone know??
I have never planned to talk about such an operator specific matter as KPIs. But since I posted NEWS: Telco Monitoring I’m receiving many questions related to this topic and I guess we can discuss at least the basic principles.
If you have read the VoLTE standards such as GSMA IR.92 or VoLTE Service Description and Implementation Guidelines, you probably noticed that performance monitoring is more or less ignored. And at the same time all operators are asking about it. What KPIs to watch, how, what are the guidelines?
I’ve just recently changed my job and that reminded me, what it means to start from the beginning again. To help those of you who have just started with VoLTE/IMS I’ve created a short presentation.
Let me know if it works (and maybe one day I’ll find some to make a recording too 🙂 ). Good luck!
Even in 2017 the telephone number remains the most universal identifier for real-time communication. And as the word is moving to be All-IP, we have to be able to translate the number into something more meaningful for routing in IP networks. The GSMA organization selected for this purpose the Electronic Number Mapping System (ENUM) and in 2007 released the first version of PRD IR.67.
ENUM based Routing
Moreover Mobile Operators in over 50 countries have to support Mobile Number Portability (MNP). Although for MNP is a great feature for end subscribers, it makes the signalling more complex and costly for the Operators. The MNP is not just a problem for signalling (routing) but also for billing and management of interconnect agreements. Last but not least it can be a significant issue for content and application providers who may not be aware of the change of the operator for a particular user.
In the last post we have seen a basic SIP (VoLTE) session. This time we should analyze in more detail, what headers are used by network elements for their routing decisions and how they discover what port and IP to use. In practice that’s what people are not always sure about. They know the flow, order of signalling messages, but when something goes wrong, they are just guessing what could be the reason.
SIP Message Routing
Let’s recap what we have learnt so far. We use loose routing. So if a SIP message contains a Route header, we will use the top most one for the routing. If there is no Route header the routing is done based on the Request-URI, which contains the address of the final recipient. Don’t forget, network elements are able to add and modify the headers. The way how we handle the messages and modify their content within the IMS is described in 3GPP standards.
To describe a single SIP Session in IMS is not that easy as it maybe sounds and in the beginning it requires a lot of simplification. The purpose of the signaling over SIP is to establish a multimedia session over RTP (or MSRP). That means that SIP helps to locate the recipient and to negotiate the parameters of the RTP session. To do that we need one more protocol, called Session Description Protocol (SDP) which SIP carries in its body. The procedures for IMS describing this mechanism can be found in 3GPP 24.229.
SIP 3 Way Handshake
To set up a session the SIP protocol mandates the SIP INVITE request. It has to be answered by some final response – ideally with 200 OK. To confirm, that the client received the 200 OK message, it sends a special request SIP ACK. The SIP ACK is the only SIP request which doesn’t trigger any response on the server side. The procedure is also known as SIP 3-way handshake.
In this post we will go through a basic VoLTE flow from the SIP and SDP point of view.