DSLAM
DSLAM stands for Digital Subscriber Line Access Multiplexer. At the IPTV service provider’s regional office, the DSLAM receives the subscriber’s connections over copper cable, aggregates them, and connects back to the central IPTV data center through a high speed fiber based network backbone. For IPTV deployments it is typical that the DSLAM supports multicast transmission. This negates the need to replicate channels for each request originating from an IPTV viewer. The DSLAM has overall responsibility for distributing the IPTV content over the “last mile” to theIPTV subscribers. DSLAMs fall into two broad categories: Layer 2 and IP-aware.
(1) Layer 2 DSLAMs operate at level 2 of the OSI (Open Systems Interconnection) communications model and perform functions such as switching traffic between Ethernet and ATM, passing network traffic up-stream, and preventing interference between IPTV subscribers. The switching between ATM virtual circuits and upstream Ethernet packets is facilitated through the used of a bridging mechanism.
(2) IP-awa re DSLAMs include limited support for level 3 IP networking protocols. Advanced functions supported by this category of DSLAMs include replication of broadcast TV channels and executing channel changing instructions.
ADSL technology is ideal for a range of different interactive services; however,
it is not an optimal solution for delivering IPTV content due to the following
reasons:
Data rates An ADSL maxes out at around 8 Mbps, which supports two SD channels and some Internet traffic; however, it will not be able to meet the needs of IPTV providers who plan to deliver high definition programming to their subscribers.
Interactivity Because the technology is ADSL the upload data rate is lower than the download rate. This limitation means that ADSL is unsuitable for applications, such as peer-to-peer services that require as much upstream bandwidth as download bandwidth. Therefore, network service providers are starting to deploy more advanced DSL technologies that overcome these limitations.
ADSL2
The ADSL2 family of standards was created to address the increased demand for capacity to support bandwidth intensive applications such as IPTV. There are three different members of the ADSL2 family:
ADSL2 The initial version of ADSL2 was approved by the ITU in 2003 and included a number of enhancements to the original ADSL standard, namely, higher downstream data rates and longer reach from the CO to the subscriber’s modem.
ADSL2þ Soon after the standardization of ADSL2, a further avor of DSL was adopted by ITU known as ADSL2þ. This standard builds on ADSL2 and allows network service providers to offer speeds up to 20 Mbps to subscribers that live within a distance of approximately 5000 ft (1.5 km) away from the CO. ADSL2þ operates within the signal bandwidth of 138 kHz to 2.208 MHz.
ADSL-Reach Extended The deployment of ADSL2þ is of no use to subscribers who live over 5000 ft (1.5 km) away from the CO. Therefore, a technology called ADSL-Reach Extended, also known as RE-ADSL2 was standardized in 2003 to allow IPTV service providers to increase the range of their offerings to subscribers that are up to 19,000 ft (6 km) away from their nearest CO. It shows good performance in terms of reach and speed over long copper lines.
DSLAM stands for Digital Subscriber Line Access Multiplexer. At the IPTV service provider’s regional office, the DSLAM receives the subscriber’s connections over copper cable, aggregates them, and connects back to the central IPTV data center through a high speed fiber based network backbone. For IPTV deployments it is typical that the DSLAM supports multicast transmission. This negates the need to replicate channels for each request originating from an IPTV viewer. The DSLAM has overall responsibility for distributing the IPTV content over the “last mile” to theIPTV subscribers. DSLAMs fall into two broad categories: Layer 2 and IP-aware.
(1) Layer 2 DSLAMs operate at level 2 of the OSI (Open Systems Interconnection) communications model and perform functions such as switching traffic between Ethernet and ATM, passing network traffic up-stream, and preventing interference between IPTV subscribers. The switching between ATM virtual circuits and upstream Ethernet packets is facilitated through the used of a bridging mechanism.
(2) IP-awa re DSLAMs include limited support for level 3 IP networking protocols. Advanced functions supported by this category of DSLAMs include replication of broadcast TV channels and executing channel changing instructions.
ADSL technology is ideal for a range of different interactive services; however,
it is not an optimal solution for delivering IPTV content due to the following
reasons:
Data rates An ADSL maxes out at around 8 Mbps, which supports two SD channels and some Internet traffic; however, it will not be able to meet the needs of IPTV providers who plan to deliver high definition programming to their subscribers.
Interactivity Because the technology is ADSL the upload data rate is lower than the download rate. This limitation means that ADSL is unsuitable for applications, such as peer-to-peer services that require as much upstream bandwidth as download bandwidth. Therefore, network service providers are starting to deploy more advanced DSL technologies that overcome these limitations.
ADSL2
The ADSL2 family of standards was created to address the increased demand for capacity to support bandwidth intensive applications such as IPTV. There are three different members of the ADSL2 family:
ADSL2 The initial version of ADSL2 was approved by the ITU in 2003 and included a number of enhancements to the original ADSL standard, namely, higher downstream data rates and longer reach from the CO to the subscriber’s modem.
ADSL2þ Soon after the standardization of ADSL2, a further avor of DSL was adopted by ITU known as ADSL2þ. This standard builds on ADSL2 and allows network service providers to offer speeds up to 20 Mbps to subscribers that live within a distance of approximately 5000 ft (1.5 km) away from the CO. ADSL2þ operates within the signal bandwidth of 138 kHz to 2.208 MHz.
ADSL-Reach Extended The deployment of ADSL2þ is of no use to subscribers who live over 5000 ft (1.5 km) away from the CO. Therefore, a technology called ADSL-Reach Extended, also known as RE-ADSL2 was standardized in 2003 to allow IPTV service providers to increase the range of their offerings to subscribers that are up to 19,000 ft (6 km) away from their nearest CO. It shows good performance in terms of reach and speed over long copper lines.
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