ADSL

ADSL or Asymmetric Digital Subscriber Line is one form of DSL technology, which sends data over copper wires at a faster rate than legacy modems. ADSL differs from other DSL technologies in that it provides an asymmetric distribution of bandwidth for one of the two routes within the interactive architecture. ADSL broadband is crucial to IPTV services since it allows interactivity, but is perhaps the preferred IPTV delivery technology because it allows the service provider more bandwidth for the delivery than it does for the user to interact. Initially, most analysts believe IPTV services will remain mostly a delivered medium with interactivity at a minimum. Video on Demand (VoD) and p2p delivery services would not require as much bandwidth as the download of content from the service provider's head end would. A more interactive architecture whereby the user sends as much data to the service provider as it receives would require a different DSL technology with equal bandwidth for both routes. Currently ADSL is popular in Europe and Asia. The reason for ADSL's asymmetry is that in an ADSL deployment there is likely to be more crosstalk from other circuits at the DSLAM end (where the wires from many local loops are close together) than at the customer premises. The upload signal is therefore weakest at the noisiest part of the local loop, while the download signal is strongest at the noisiest part of the local loop. So technically, its makes sense to have the DSLAM transmit higher bit rates than the modem on the customer end and since the user would typically prefer to have faster download rates than upload speeds—the telcos called it ADSL and branded it accordingly. ADSL is distance-sensitive. The conventional ADSL rates start near 256 Kbps and reach 8 Mbps within 5000 feet of the DSLAM. Upstream rates start at 64 Kbps and typically reach 256 Kbps but can go as high as 1024 Kbps—ASDL Lite sometimes designates a slower version. Outdoor DSLAM can increase the area of coverage. However, DSL in the US and the ADSL in many European countries are not a viable transport medium for delivering video transmission (IPTV) because their data speeds max out at around 8 megabits per second. Want more? The Fierce IPTV weekly newsletter monitors ADSL advances and more DSL news.