When television by ADSL allows it access to a bunch of Channel television directly on his television.
On the cable and satellite all channels are transmitted to the subscribers. It is then the decoder to do the sorting. The operation is different by the ADSL.
Limited flow on the local loop, the DSLAM transmits only a single string to the Subscriber's home.
Therefore, it is not possible to watch two channels simultaneously, or record one channel on the VCR while you watch another.
When the user wants to change the channel, the set-top-box forwards the request to the DSLAM. It charged to select the good flow.
But the DSLAM either receives all the channels.
It only gets the channels it transmits at this time to these subscribers, and cela to avoid saturating the network.
Television is the most critical in terms of bandwidth for offers Triple play of ADSL. Indeed she is greedy in bandwidth,
and requires a rate guaranteed for good viewing. We must find a compromise between image quality and constraints due to the flow.
Thus the operators reserve about 4 to 5 Mbps of bandwidth for the video stream, although support is used at the same time for other technology
This bandwidth allocated to television on ADSL is thus expected to get a decent image quality.
This compression rate and guaranteed 3.5 to 4 Mbps throughput allow for a definition of 576; 480 points.
The passage in MPEG4 is now envisaged. This will allow for a better quality in a halved bandwidth.
ISPs could then envisaged to allow the Subscriber to receive two channels simultaneously.
Content providers deliver their content directly to the ISP.
These live encode these audio-video in MPEG2 streams. This is a tricky part which can be at the origin of a great loss of quality.
But this encoding is necessary to bring the digital stream to dimensions allowing the transmission via ADSL. Once this encoding is done, the stream can be sent over the network.
The VOD (Video On demand) service offered by ISPs allows a user to rent a movie without moving from home, and the watched from his television screen.
The use is very simple for the Subscriber. It can select a catalogue films, documentaries or television archives offered to him by his ISP.
For this, he used his equipment, connection and set-top-box. He made his choice on his television thanks to its set-top box remote control.
It can thus select a video and watch it fee.
The ISP offers its subscribers a series of video. These videos are owned by content providers, the companies managing the rights to these videos.
It is they who are responsible for the compression of the video. This encoding is performed in MPEG2 or MPEG4. They can also make a video stream encryption, to protect against copying videos.
The most used for realized this encryption is DRM, Data Rigth Management of Microsoft technology. The broadcast files are then encrypted before they are broadcast on the Internet.
The customer must have a key, or license, to read. This key is unique and defines the use that make this video the user and including the number of reading and the period of validity.
Once completed, the ISP is responsible for the delivery of these flow data to the Subscriber. Using the Multicast technology provider may lighten the load of transmission on the network.
It will install all over its network of servers video relay. With computers are very large capacity of storage and high-speed interfaces.
They can simultaneously send multiple instance of the same video to different Subscribers.
Originally the cable was developed to convey TV shows : he was so analog, unidirectional and deployed in residential areas.
Becoming digital television cable operators wanted to follow. They then quickly wanted to develop their offer to offer their subscribers the Internet and telephony.
The cable becomes two-way and will deploy in the industrial zones to open businesses.
Originally the networks serving the Subscriber consisted of coaxial cable TV. They have an impedance of 75 ohms and offer a bandwidth of 400 Mhz about.
Their rate of impairment is important. The number of Repeater needed to transport of the signal just limit the bandwidth.
A new architecture was built to increase this bandwidth : HFC architecture, Hybrid Fiber Coax.
The HFC architecture combines the two transmission media are optical fiber and coaxial cable. The coaxial cable is then used for the final kilometre to the Subscriber.
This architecture opposes a network coaxial end, ultimately and architecture FTTH, Fiber To The Home or only the last meter is coaxial.
The cable was originally planned to only bring television at the Subscriber. It was therefore working in half duplex mode of the provider to the Subscriber.
Communications in the opposite direction were possible only via a telephone line.
This system was efficient for the delivery of television alone.
But the half-duplex is not suitable for Internet services or telephony. Cable operators have therefore invested heavily to pass in full-duplex, developing HFC architectures.
They thus highlight service road to return of their cables, which previously served as the maintenance or testing.
This allows to get rates from 27 to 36 Mbps in top-down way and 320 Kbps to 10 Mbps uplink.
These full-duplex lines so now provide sufficient flows to allow providers to offer their customers Internet and telephony.
For the HFC architecture arteries are in optical fiber and distribution to the Subscriber through the coaxial. The coaxial cable is so more than for the last kilometre used to most.