The Architecture of IPTV in an IMS Deployment

By Tsahi Levent-Levi

Categories: IPTV

September 18th, 2008

You can’t discuss communication protocols nowadays without bringing up IMS. Although IMS started as a mobile-centric protocol, it is now all encompassing and also includes IPTV. Since both Packet Cable and TISPAN make use of IMS, IPTV also has an IMS architecture connected to it.

IMS for IPTV starts simply from the fact that operators today are mostly triple-play or quad-play players: their services include telephony, television, internet browsing and mobile phones.

Quad-play doesn’t mean convergence in any way - these packaged deals are business related; they might exist on separate networks with separate usage plans that are simply aggregated and offered to users at certain price points.

Since telephony is included, IMS is required. And once you have IMS, you can use it for the core services of IPTV as well.

Let’s look at TISPAN’s IPTV architecture to understand how it works:

Taken from ETSI TS 182 027 specification and beautified

This is the most I could make of the original, but it still looks ugly. I guess when it comes to IMS there’s no way to beautify the network - probably because when you want to build a network for deploying services it gets complex very quickly.

There are, however, several things I’d like to point out in this architecture:

1. IPTV-related services are now coupled with the core IMS network itself.
2. The User Equipment - be it the set-top box itself, a residential gateway or any other access device - still interfaces with the network with the Gm interface of the IMS. The only difference is that it still uses RTSP for some of the specialized IPTV services.
3. The transport functions are quite boring - they simply deal with how to get to the point of having an IP network to work with. Still, they are important, since they provide QoS for the services used.
4. The HSS in IMS, which holds our user accounts in cellular networks, is replaced - or should I say “extended” - by a UPSF (User Profile Server Function), a similar kind of database that holds the information of the subscribers (a kind of HSS).

If the tricky part of a mobile IMS network is handling switchovers, roaming and legacy circuit switched networks, then the tricky part of an IPTV IMS network is managing additional services that are not directly related to telephony.

And while we are at it, once we have IMS in IPTV’s architecture, we can improve the types of combinational services we allow.

You can find more information in a PowerPoint presentation by Dr. M. Oskar van Deventer.