What is IPTV Technology
- information, or tutorial about the basics of what is IPTV,
television using Internet Protocol, and distributed over an IP network such as
the Internet.
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.
IPTV Basics
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.
Channel selection
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.
Error correction
Errors will always occur on any network. These need to be
detected and corrected to enable the system to work satisfactorily. Error
correction needs to be handled in different ways according to the type of
broadcast. For Video on Demand, Unicast services it is relatively simple for the
receiver to request a re-send of a packet if errors are detected. However this
cannot be done for a multicast system as it is not possible to request missing
or corrupted packets to be re-sent. It is essential that the integrity of any
network carrying multicast data is high so that few errors occur. In addition to
this a variety of error correction measures are incorporated into the system.
These include forward error correction (FEC) techniques that enable the receiver
to rebuild missing or corrupted data.
Summary
The use of IPTV is on the increase, and with more people
using broadband connections to access an ever increasing number of services, it
seems likely that IP-TV technology will grow in importance over the coming
years. The system offers many advantages including the use of VOD which makes it
particularly attractive to many. When bundled with other services, IPTV will
offer a cost effective way of viewing for many users and in addition to this it
will provide many telecommunications providers with new and lucrative services
to offer. These advantages seem to provide IPTV with a compelling business case.
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