ADSL (Asymmetric Digital Subscriber Line) is currently the most widely used technology for Internet access by individuals.
Although it was not historically on this type of technology that the Triple Play offers were developed, that today is the first provider of this kind of offer.
ADSL is a technology developed to be able to pass data through the telephone lines (this allows then to re - use a network of already existing cable).
To do this, it uses the high frequency bands used by telephony (300-3400Hz), using multiplexing and modulation techniques suitable for telephone lines.
Using high frequencies of the phone line however involves the use of a filter on part and on the other of the phone line so that telephony signals does not disrupt the ADSL signals (and vice versa).
Flows are asymmetrical, which means that in ADSL, a Subscriber may send data (uplink) to a lower data rate can receive (way down).
The ADSL led to rates of 10 to 500 times greater than the previous techniques of Internet access for individuals (V92 : 56 kbps;) ADSL2+ : 25Mbps).
offering then the possibility ISPs to offer services other than Internet access, as is the case with the offers Triple Play.
Currently, Subscribers whose telephone line is not unbundled can, at best, that benefit from a rate of 2Mbps, which is not enough to get the audio/video stream.
Rates offered by ADSL are ideals rates because ADSL is very sensitive to the mitigation of telephone lines. So, more a line will be long between a Subscriber and its central office,
and less flow it can get via ADSL will be great. For even if the line is damaged, or has electronic devices
The Set-Top Box (STB) is a device that the ADSL ISP (sometimes free) provide their subscribers to qualify for the Triple Play offers.
It is a box that connects to the telephone line, and who has at least a TV output (SCART or RCA), a telephone connector (RJ11 or phone jack), and an Internet Connector (RJ45, USB, WiFi, etc.).
The STB is somehow a mini-computer capable to communicate via ADSL with the ISP, and offer services to subscribers.
Some STB have extra services (sometimes paying) and features (Routing IP/NAT) Internet connection sharing, Media Player (destined for television), streaming multipost (i.e., receive more than one TV channel), etc...
Access to the Internet
Access to Internet is the first type of service offered through ADSL. Other services of a Triple Play by being dependent on one, ADSL offer
We will focus on the operation of this service initially.
The connection between the user and the STB can usually be done in three different ways :
• USB connection : he is a serial link that allows the user to directly connect his computer to the STB. It does not specify any particular communication protocol to use. However, communication with the STB is done, most of the time, using either the ATM protocol, Ethernet protocol. It can also be that the STB works only as a classic ADSL modem using this type of connection, then forcing the use of the PPP protocol over ATM (PPPoA) or Ethernet (PPPoE) in this case.
• Ethernet connection : it is in fact a Fast Ethernet (100 Mbps) connection that allows the user to connect to the STB with a network card.
• WiFi connection : most of the time, this is an optional module paying that allows the user to connect to the STB using a wireless connection, type 802 .11b/g.
Of course, network used here is the IP protocol. His level of the user's computer configuration is performed using a DHCP server,
implemented in the STB, either within the premises of the ISP.
In general, the suppliers provide only a single IP address per subscriber (subscriber can however get more by paying, but it is not common with all suppliers). The latter can also change in time (dynamic IP),
but given the nature almost permanent dynamic ADSL, IP connections offer no benefit to providers.
To share the connection Internet between different computers, there are usually two solutions :
If we want to be able to connect Ethernet to the Internet, please then allow sharing the link Ethernet (hub or switch) devices. In WiFithe link is naturally shared. Finally, using the USB connection.
There must be a device that makes the bridge between the USB link and a link (mainly Ethernet) network, and is compatible with the STB USB drivers.
This course does not work if the connection to the Internet depends on the Protocol PPP.
This type of connection sharing allows to use the three types of access to the STB at the same time to connect to the Internet.
Connection to the Set-Top-Box
The STB is connected to the telephone line from the user. At the other end of the phone line is DSLAM 8, which has the task to make the bridge between the equipment of the users
(via the STB) and the service provider's network. The DSLAM at the level of the local telephone exchange (more technically known as the node of the Subscriber connection), and can be equipment belonging to the supplier or to the historical operator,
(it depends on the level of unbundling of the Subscriber). A same DSLAM is connected to a set of subscribers (from the same ISP).
The number of subscribers by DSLAM Depending on the manufacturer.
The communication between the STB and the DSLAM is performed using ADSL technology. This technology from telecommunications, it almost always involves the use of the ATM protocol at the top,
the latter being simple enough to be implemented easily in telecommunication devices and offering very good management of the 9QoS.
In the case of an offer Triple Play, it may also be an extension of the ATM that is used (RFC 2684) Protocol to allow the transport of several streams (protocols) different via ATM.
These flows are usually four in number :
• one audio (telephony)
• one for the video data (TV)
• one for Internet data
• a final for the three previous flow control data.
The ADSL throughput depends on the subscriber contract, but above all, the distance between the installation of the user and the central office where the DSLAM to which it is connected.
Currently, this will of 128 kbit/s to 25 Mbit/s (ADSL2 +) for the stream down (download), and 128 Kbps to 1 Mbps (ADSL2 +) for the flow amount (upload), knowing that only users living near their central office can benefit from the best rates.
The limits of flow rates per user are carried out at the level of the DSLAM.
Thus, in ADSL, sold flow is only seldom guaranteed. Moreover, it is specified by a debit ATM, which does not match the IP flow, and, indeed, still less useful flow available to the user.
Finally, it should be noted that all of the sold DSL speed is not totally dedicated to Internet access in a Triple Play offer. Indeed, this flow is shared between the flow of data (Internet),
Audio (telephony) and the video stream (television), knowing that the latter is extremely greedy.
However, this share is adaptive, that is to say that while a stream is to use the connection, it can enjoy all of the flow (that is specific to ATM).