There are now many ways in which television material can be delivered these days. One method that is set to make a huge impact is IPTV. As the name indicates, IPTV, or Internet Protocol Television, is based around the use of Internet Protocol, and this means that the service tends to be used in conjunction with telecommunications services of which broadband internet lines are the most widely used, although any service that can carry packet data can be used.
IPTV has many advantages. It provides a potentially lucrative market in view many telecommunications providers are looking keenly at the possibilities of providing new services and generating new revenue streams. This means that in the years to come IPTV seems certain to become a major player in the entertainment market.
There are two basic ways in which the material for IPTV can be handled. It can be sent out as broadcast or "multicast" material to many users simultaneously or it can be used to provide video-on-demand where the material is sent to just one subscriber who has requested that particular item.
It is also necessary to ensure that bandwidth is used efficiently. To achieve this, the IPTV video is compressed and two main formats are used for this. One is MPEG-2, and the other is the newer MPEG-4 standard. Of these the MPEG-4 standard is being used increasingly in view of its superior performance.
Basic IPTV system
For the user, an IPTV system is based around a set top box or an equivalent such as a computer. This receives the incoming data and re-assembles the data packets and decodes them to provide the required output for passing on to a television or other form of screen for viewing.
The system at the service provider end is considerably more complicated and requires a number of elements to ensure that the system operates correctly under both unicast and multicast conditions.
The core for any IPTV system is the operator's central distribution centre. Here the material is assembled and encoded.
Once encoded, the video stream is split into packets, so that it can enter the IP network system and routed to the relevant destination or destinations. The video streams consisting of these packets then travel from the centre of the network to outlying local exchanges and routing centres before being routed on to the individual subscribers. It is typically at these local centres that where authentication, channel change requests, billing and video-on-demand requests are handled.
One important aspect of multicasting is the ability of the system to be able to select the required channel and change it as required. In order that vast amounts of data are not set to the set top box, or any other form of IP receiver, one a single channel is sent to a given receiver.
Channel selection is accomplished by using a special protocol known as IP Group Membership Protocol (IPGMP). This is a communications protocol used to manage the membership of Internet Protocol multicast groups. It is used by IP hosts and adjacent multicast routers to establish multicast group memberships.
When a local routing centre receives a request to receive multicast data or to change from one channel to another, it checks to ensure that the user is authorised to connect to the channel and then it directs its routers to add the particular user to its distribution list. In this way only the channels that are being used are routed to the receiver, and this saves enormous amounts of data.
Unicast / video on demand
In order that users can connect to a video on demand service a different set-up is needed. The local server operates in a fashion that enables single streams of data to be drawn off as required and it is controlled using a different protocol to that used for multicasting is used. Known as Real Time Streaming Protocol, RTSP, it controls the data stream and allows DVD-style control over the media stream, enabling the user to play, pause and stop the programme being watched.
Quality of Service (QoS)
One of the major elements of any IP network is the control of the Quality of Service. To enable the video stream to be maintained and to prevent delays and fragmentation of the packets on the network, it is necessary to ensure that the Quality of Service is maintained. The Quality of Service tags assign the required priority to different packets on the network, and in this way enable time sensitive packets such as live video or voice traffic to have a higher priority than those such as Internet browsing where delays can be tolerated. By using QoS tags and tools, the required data streams can be transmitted to make maximum use of the available bandwidth, while still maintaining the required level of performance.