ADSL Max
Encyclopedia
ADSL Max is a cover term for the UK telco
BT's
range of commercial ADSL services that are rate-adaptive and are deployed over BT phone lines. BT's ADSL Max services were launched in March 2006.
on lines of sufficient quality. Various kinds of lower speed rate-limited adaptive services are also available as a reduced cost option. Customers with long lines or poor quality lines or who experience high levels of noise
or interference
will be limited to much slower transfer rates, and some customers whose lines are very poor or who are affected by high levels of noise may be unable to obtain service at all.
which aids error correction. Several factors dictate the sync rate, which limits the maximum attainable speed, such as the presence of noise within the frequency spectrum used by ADSL, but chiefly it is the distance from the Central Office (telephone exchange) which has the largest influence on the line's performance.
Software within the BT Wholesale
network limits the rate at which inbound IP
packets are delivered to the user, this rate being based on a parameter termed the IP Profile. The IP profile mechanism imposes an upper limit on the rate at which data destined for the user is transmitted. This rate restriction is imposed at the point where inbound data enters the BT Wholesale IP network from the Internet. The rate is chosen so that throughput can not exceed the throughput of the ADSL link. The IP Profile set by DLM may unfortunately be set to a figure that is somewhat below that which the DSL modem could support, which will limit the maximum inbound data delivery rate over the ADSL link to be below the maximum achievable rate.
The IP profile changes over time, and is derived from a consideration of the worst downstream sync rate used by the DSL modem during some recent period of time. If circumstances cause a drop in sync rate, the IP profile decreases immediately. If conditions later improve, the IP profile will only increase after a certain delay time. The time taken for this increase to occur depends on a number of factors and can be between 75 minutes and several days.
IP Profile values are chosen from a certain fixed list of rate values taken from a table and are determined by the downstream sync rate of the ADSL connection. Many sync rate values will correspond to the same IP Profile figure. It is often the case that a user's downstream sync rate, when overheads are accounted for, equates to a true maximum inbound throughput figure that falls between two permitted IP Profile levels and, in such a case, the lower level is used. As an example, if the downstream sync rate of a DSL modem is set to 1984 kbit/s, the associated IP Profile is 1500 kbit/s so the maximum permitted inbound data rate is 1500 kbit/s, but if the sync rate were to rise to 2016 kbit/s the IP Profile would be 1750 kbit/s.
Telephone company
A telephone company is a service provider of telecommunications services such as telephony and data communications access. Many were at one time nationalized or state-regulated monopolies...
BT's
BT Group
BT Group plc is a global telecommunications services company headquartered in London, United Kingdom. It is one of the largest telecommunications services companies in the world and has operations in more than 170 countries. Through its BT Global Services division it is a major supplier of...
range of commercial ADSL services that are rate-adaptive and are deployed over BT phone lines. BT's ADSL Max services were launched in March 2006.
Rate-adaptive service
Rate-adaptive services are intended to offer the best possible speed attainable, which may vary over time. The maximum speed permitted is determined both by current line conditions and the level of noise, and also by recent history based on factors including the rate of communications errors and the best and worst DSL modem sync speeds achieved during some recent period of time. The highest speed ADSL Max services enable customers to receive up to 7.15 Mbit/s (termed 'downstream') over a standard BT telephone lineLandline
A landline was originally an overland telegraph wire, as opposed to an undersea cable. Currently, landline refers to a telephone line which travels through a solid medium, either metal wire or optical fibre, as distinguished from a mobile cellular line, where transmission is via radio waves...
on lines of sufficient quality. Various kinds of lower speed rate-limited adaptive services are also available as a reduced cost option. Customers with long lines or poor quality lines or who experience high levels of noise
Noise
In common use, the word noise means any unwanted sound. In both analog and digital electronics, noise is random unwanted perturbation to a wanted signal; it is called noise as a generalisation of the acoustic noise heard when listening to a weak radio transmission with significant electrical noise...
or interference
Interference (communication)
In communications and electronics, especially in telecommunications, interference is anything which alters, modifies, or disrupts a signal as it travels along a channel between a source and a receiver. The term typically refers to the addition of unwanted signals to a useful signal...
will be limited to much slower transfer rates, and some customers whose lines are very poor or who are affected by high levels of noise may be unable to obtain service at all.
Max 'Premium'
ADSL Max services are available to both residential and business customers. Aimed at business users, the IPStream Max Premium service offers prioritised delivery of traffic over the BT network compared to traffic from non-'Premium' customers and allows a maximum transmit speed of 832 kbit/s (notional, DSL 'upstream' sync rate). The non-'Premium' services, aimed at residential users, offer a lower maximum transmit speed of a notional 448 kbit/s (notional, DSL 'upstream' sync rate).Rate adaptation and BT Wholesale's 'Dynamic Line Management' (DLM)
During the first ten days after the service has been provided, the line's performance is monitored and the lowest connection speed is noted. This figure is used from then on to define minimum service standards below which the service can be considered to have a fault. Both during this period and afterwards a system known as dynamic line management (DLM) constantly assesses the performance of the line in order to provide information to the end user's DSL modem to allow it to choose a suitable sync rate with which to connect to the DSLAM, balancing speed against the risk of errors due to changing noise conditions. DLM can make adjustments to the DSLAM output power, suggested target signal-to-noise-ratio (SNR) margin and sync rate and can choose to apply a technique known as interleavingInterleaving
In computer science and telecommunication, interleaving is a way to arrange data in a non-contiguous way to increase performance.It is typically used:* In error-correction coding, particularly within data transmission, disk storage, and computer memory....
which aids error correction. Several factors dictate the sync rate, which limits the maximum attainable speed, such as the presence of noise within the frequency spectrum used by ADSL, but chiefly it is the distance from the Central Office (telephone exchange) which has the largest influence on the line's performance.
Software within the BT Wholesale
BT Wholesale
BT Wholesale is a division of BT Group responsible for the wholesale leasing of PSTN lines, broadband services and other telephony services to retail customers such as BT Retail, Vodafone and Carphone Warehouse.-External links:*...
network limits the rate at which inbound IP
Internet Protocol
The Internet Protocol is the principal communications protocol used for relaying datagrams across an internetwork using the Internet Protocol Suite...
packets are delivered to the user, this rate being based on a parameter termed the IP Profile. The IP profile mechanism imposes an upper limit on the rate at which data destined for the user is transmitted. This rate restriction is imposed at the point where inbound data enters the BT Wholesale IP network from the Internet. The rate is chosen so that throughput can not exceed the throughput of the ADSL link. The IP Profile set by DLM may unfortunately be set to a figure that is somewhat below that which the DSL modem could support, which will limit the maximum inbound data delivery rate over the ADSL link to be below the maximum achievable rate.
The IP profile changes over time, and is derived from a consideration of the worst downstream sync rate used by the DSL modem during some recent period of time. If circumstances cause a drop in sync rate, the IP profile decreases immediately. If conditions later improve, the IP profile will only increase after a certain delay time. The time taken for this increase to occur depends on a number of factors and can be between 75 minutes and several days.
IP Profile values are chosen from a certain fixed list of rate values taken from a table and are determined by the downstream sync rate of the ADSL connection. Many sync rate values will correspond to the same IP Profile figure. It is often the case that a user's downstream sync rate, when overheads are accounted for, equates to a true maximum inbound throughput figure that falls between two permitted IP Profile levels and, in such a case, the lower level is used. As an example, if the downstream sync rate of a DSL modem is set to 1984 kbit/s, the associated IP Profile is 1500 kbit/s so the maximum permitted inbound data rate is 1500 kbit/s, but if the sync rate were to rise to 2016 kbit/s the IP Profile would be 1750 kbit/s.