How to read Initial Filter Criteria

There are hunters and there are gatherers. My wife she is a gatherer. When she goes shopping, she is gathering (and bet that it requires some time 🙂 ). I hate it, I’m hunting. I need to have a clear goal. A list of things I have to buy. It doesn’t need to be on paper, but I need to know. As a gatherer I’m lost and I always forget something.

In IMS most of the network elements work as state machines. Some of their logic is based on the configuration, some is stored in databases (HSS, DNS). This is also the case of Initial Filter Criteria. Simply said the S-CSCF has a list which tells it what messages forward to what application servers.

IFCs are described in the 3GPP TS 29.228, Annex B. As you probably know (Registration, 3rd Party Registration, HSS-FE), during the registration S-CSCF retrieves in the SAA message from HSS the Subscriber profile.  The profile itself is an XML document which contains information about the user’s identities and also a set of routing rules – IFCs. Note it is also possible to configure iFCs directly on S-CSCF and transfer only id (Shared IFC).

IMSSubscription

News: more than HD

T-Mobile USA is on the cutting edge. It was the the first operator who came with HD Voice back in 2013. This month they announced a new upgrade of their network – to Enhanced Voice Services (EVS). From the customer perspective it means a better audio quality – even better than HD. EVS does this with a broader audio frequency range, which translates to richer, more realistic-sounding voice audio. The EVS is supported for both VoLTE and VoWifi. Additionally for the LTE technology it also brings a higher reliability in areas of weaker signal.

T-Mobile has a pending patent for their solution where their customers with EVS compatible phones will benefit even if the B-party  doesn’t have an EVS-capable device. Currently the technology is available for LG G5,  Samsung Galaxy S7 and S7 edge. T-Mobile plans to support four more smartphones by the end of 2016. I wonder what will be the response of Alliance for Open Media for webRTC.

ePDG and IPSec

It seemed that once we have IMS in place we can add the VoWifi service for free. Of course, there is hardly ever anything for free. As we have is in the VoWifi Overview there are quite a few things we need to take into account. In IMS we have to be more sensitive when it comes to routing, forking, location services etc. In the access network we have to make sure that the communication is secure enough and that we can trigger an access transfer when needed. In this post we’ll go through the security part of it and describe the basic flows.

It is not that difficult to get lost among all the security frameworks, protocols and procedures we have implemented in ePDG. In order to establish an IPSec tunnel we have to use IKEv2 for encryption and then some form of EAP for authentication and then we can start with ESP encryption.

Security over SWu

So let’s start with a short dictionary: