From a TV watcher's point of view, IPTV is very simple: instead of receiving TV programs as broadcast signals that enter your home from a rooftop antenna, satellite dish, or fiber-optic cable, you get them streamed (downloaded and played almost simultaneously) through your Internet connection. Not the kind of connection you have today, which can probably handle only 1–10 Mbps (million bits per second—roughly the amount of information in an average novel entering your computer every second!), but a broadband line with about 10 times higher bandwidth (information carrying capacity) of maybe 10–100Mbps. You watch the program either on your computer or with a set-top box (a kind of adapter that fits between your Internet connection and your existing television receiver, decoding incoming signals so your TV can display Internet programs).
From the viewpoint of a broadcaster or telephone company, IPTV is somewhat more complex. You need a sophisticated storage system for all the videos you want to make available and a web-style interface that allows people to select the programs they want. Once a viewer has selected a program, you need to be able to encode the video file in a suitable format for streaming, encrypt it (encoding it so only people who've paid can decode and receive it), embed advertisements (especially if the program is free), and stream it across the Internet to anything from one person to (potentially) thousands or millions of people at a time. Furthermore, you have to figure out how to do this to provide a consistently high-quality picture (especially if you're delivering advertising with your programming—because that's what your paying advertisers will certainly expect).
When you stream a program, you're not downloading it like an ordinary file. Instead, you're downloading a bit of a file, playing it, and, while it's playing, simultaneously downloading the next part of the file ready to play in a moment or two. None of the file is stored for very long. Streaming works because your computer (the client) and the computer it's receiving data from (the server) have both agreed to do things like this. The Internet successfully links practically all the world's computers because they all agree to talk to one another in the same way using prearranged technical procedures called protocols. Instead of using the ordinary, standard, web-based protocols for downloading (technically, they go by the names HTTP and FTP), streaming involves using protocols adapted for simultaneous downloading and playing, such as RTP (Real-Time Protocol) and RTSP (Real-Time Streaming Protocol). Multicast streaming involves using IGMP (IP Group Membership Protocol), which allows one server to broadcast to members of a group of clients (effectively, lots of people all watching the same TV channel).
The future of broadcasting?
There's no great clamor from ordinary TV viewers for IPTV, although that's not unusual where new inventions and innovations are concerned; no-one can truly appreciate something they haven't yet experienced. But the huge popularity of VOD websites such as BBC iPlayer and time-shifting personal video recorders (PVRs) such as TiVO (and Sky+ in the UK) strongly suggest TV will move increasingly away from broadly defined channels and rigid schedules to more narrowly focused, pay-per-view programming.
Even so, consumer demand won't be the main driving force in the transition from 20th-century broadcast TV to 21st-century IPTV—at least, not to begin with. In the last decade or so, traditional telephone companies, faced with competition from cable-based rivals, have had no choice but to redefine themselves as information service providers, offering Internet connectivity as well as phone services. The more powerful and enterprising among them now see a further business opportunity by redefining themselves so they offer telephone, Internet, and TV services simultaneously. Cable companies already offer all three services in attractive bundles; IPTV makes it possible for telephone providers and broadcasters to join forces and compete. In the longer term, who knows whether people will even regard TV, telephone, and the Internet as separate entities, or whether they will continue to converge and merge?
Delivering IPTV sounds easier than it may prove in practice. The biggest inhibitor at the moment is that too few homes have broadband connections with enough capacity to handle a single high-quality TV stream, never mind several simultaneous streams (if there are several TVs in the same home). Upgrading ordinary broadband connections to fiber-optic broadband, so they routinely provide homes with 10–100Mbps, will take time and considerable investment. Until that happens, IPTV providers will not be able to guarantee a "quality of service" (often referred to as QoS or sometimes a "quality of experience," QoE) as good as TV delivered through cable, satellite, or across the airwaves. Latency (delays in packet arrival) and packet loss are problems enough for VoIP (Voice Over Internet Protocol) telephones, and they become much more of an issue when broadcast-quality video is added into the stream. Since IPTV uses compressed video formats such as MPEG2 and MPEG4, packet loss has a much more serious effect than it would have on uncompressed video or audio streams: the higher the compression rate, the bigger the effect every lost packet has on the picture you see.
With luck, IPTV may take off in exactly the same way as broadband Internet did in the early 2000s: back then, as more people used the Internet, they felt hampered by the limitations of dial-up connectivity, demanded (and showed they were willing to pay for) higher-quality broadband, and provided enough revenue for the telecommunications companies to upgrade their networks. Once viewers start to experience the convenience, control, and interactivity of IPTV, higher bandwidth Internet connections that make it possible seem certain to follow.