IPTV Testings A Guide to Testing IPTV: Technologies and Challenges Part 1 By Winfried Schultz H igh consumer expectations have put pressure on content producers, network operators and equipment manufacturers to deliver consistently high quality audio and video to their end users. The proliferation of enabling technologies has resulted in a wide variety of formats and standards adding to the complexity of the challenges faced in establishing new services and entering new markets. Despite the maturing of enabling technologies, the deployment of IPTV presents many technical challenges to those required to successfully provide these services. This article series will explore some of the challenges and describe how test and measurement equipment can be used to facilitate the design, rollout and management of these systems. Before we examine the technical challenges however, we should begin by providing a background to IPTV. cable companies may deliver "Digital Voice" over QAM and DOCSIS systems. IPTV is a component of the Triple Play. IPTV is used to describe the delivery of broadcast quality video over an IP network. Note this is not the same as streaming video over the public Internet, which relies on third party decoders to be used, or downloaded on to the decoding device (e.g. a PC). How IPTV Works In standard broadcast systems all of the normal broadcast channels are delivered to the set-top box in the home via cable, satellite or terrestrial. There could be hundreds of channels, all of which are delivered simultaneously. The set-top box tunes to the desired channel in response to requests from the viewer's remote control. As a result of this local tuning the channel changes are almost instantaneous. IPTV systems on the other hand are designed to deliver only the requested channel to the set-top box (in order to preserve bandwidth over the final link to the house). Note there could be several programmes (or channels) delivered to different IP addresses in the same home (i.e. separate set-top boxes or other IP enabled receivers). In order to change channels, special commands are sent into the access network requesting a change of channel. There is a complex protocol exchange (using IGMP "Leave" and "Join" commands) associated with this technique. This exchange requires a finite time to complete, and Figure 1: Various Unicast / Multicast Scenarios. IPTV and the Tripleplay Triple play is a term used to describe the delivery of voice, video and data services to the home. There are a number of commercial offerings that deliver these services to the consumer over different access technologies to the home, but true Triple Play normally provides these services through a single connection (e.g. fibre) to the home. IP technologies are not necessarily used to deliver these services, for example, the time taken is heavily influenced by transmission delays in the network which in turn has a direct impact on the channel change timings of the system. In essence, in IPTV systems the channel change is made in the network and not on the local set-top box. While preserving precious last mile bandwidth, this approach presents a number of challenges to the scalability and usability of the system. Further challenges are presented by the fact that within IPTV there are two different ways of delivering programmes. Broadcast TV makes use of IP Multicasts (and IGMP) to deliver the programming efficiently through the IP system. A Multicast is designed to allow multiple users simultaneous access to the session. Video on Demand (VoD), on the other hand, employs unicast IP services using the RTSP control mechanism. At the request of the viewer, the selected programming is located from within the network (from a server) and a unique unicast is set up to deliver the programme to the user. This is in effect a private network connection between the server and the viewer's set-top box. The >> Page 42 of 100