DSL Access Multiplexers (DSLAMs)

DSLAMs (DSL Access Multiplexers) aggregate traffic from multiple DSL modems and combine it into higher speeds before sending it to the Internet of data networks. DSLAMs are located in carriers' COs or digital loop carriers, also referred to as remote terminals, in neighborhoods and in the wiring closets of large apartment and office buildings. DSLAMs combine DSL traffic into higher-speed streams. These are, for the most part, ATM speeds of optical carrier level 3 (OC-3), 155 million bits per second, but some DSLAMs use slower DS-3 44 Mbps connections.

Customers have dedicated capacity between their DSL modem and the DSLAM that they don't share with other customers. However, capacity between the DSLAM and the Internet or the ISP (Internet Service Provider) is shared by data from other customers. The connection between the DSLAM and an ISP is a potential site for network congestion. If not enough capacity is available, a customer might experience delays. DSLAMs have been manufactured by Adtran, Alcatel, Catena, Lucent, Paradne and Westell.

The links below are the pictures of various DSLAMs

http://www.pssi-us.com/DSLInfo.gif
http://www.tsninternet.com.au/webpages/Prices/images/dslam-image2lg.gif
http://www.nag.ru/2002/2309/img/dslam.jpg


MiniRAM-Mini Remote Access Multiplexer: A newer, lower cost, smaller DSLAM is being deployed to provide DSL over short copper telephone lines. These MiniRAMs are about the size of two pizza boxes stacked on top of each other. They can be located on telephone poles or in standalone boxes on the ground and serve 10 to 24 customers. Power is fed to MiniRAMs through copper telephone lines on the pole or underground.

Because they are closer to customers, MiniRAMs avoid most of the impairments found on copper lines further from COs. These impairments are caused by crosstalk, loading coils that boost signals, and bridge taps used to share copper lines among customers. The dilemma is that the closer the fiber and MiniRAMs are to customers, the higher the overall costs. As they get closer to customers, MiniRAMs serve fewer customers. Overall there are more fiber runs, more MiniRAMs, and more equipment to maintain and install.

Smaller MiniRAMs are connected to CO-based aggregation switches that packetize the data and send it to ISPs. Traffic from larger MiniRAMs is aggregated in DSLAMs. In the future, switches in the DSLAM will provide more of the aggregation function.