A Digital Subscriber Line Access Multiplexer (DSLAM) is a network device, usually located at a telephone company central office, or within a neighborhood SAI as part of a digital loop carrier, that receives signals from multiple customer Digital Subscriber Line (DSL) connections and aggregates the signals on a high-speed backbone line using multiplexing techniques. Depending on the product, DSLAM multiplexers connect DSL lines with some combination of Asynchronous Transfer Mode (ATM), frame relay, or Internet Protocol networks.

A DSLAM may offer the ability to tag VLAN traffic as it passes from the subscribers to upstream routers. Though not a full stateful firewall, some DSLAMs also offer packet filtering facilities like dropping inter-port traffic and dropping certain protocols.

The DSLAM also supports quality of service (QoS) features like contention, diffserv, and priority queues.

Customers connect to the DSLAM through DSL modems or DSL routers, which are connected to the PSTN network via typical unshielded twisted pair telephone lines. Each DSLAM has multiple aggregation cards, and each such card can have multiple ports to which the customers lines are connected. Typically a single DSLAM aggregation card has 24 ports, but this number can vary with each manufacturer. The most common DSLAMs are housed in a telco-grade chassis, which is supplied with −48 V DC. Hence a typical DSLAM setup may contain power converters, DSLAM chassis, aggregation cards, cabling, and upstream links. The most common upstream links in these DSLAMs use gigabit ethernet or multi-gigabit fiber optic links.

From a router perspective, the DSLAM acts like a massive network switch, since its functionality is purely Layer 2.

Path taken by data to the DSLAM

1. Residential/commercial source: DSL modem
2. The local loop: the lines between a customer and the telephone company's central office, often called the "last mile".
3. Central office (CO): a central office device for ADSL service that intermixes voice traffic and DSL traffic onto a customer's DSL line. It also separates incoming phone and data signals and directs them onto the appropriate carrier's network.
4. Main Distribution Frame (MDF): a wiring rack that connects outside lines with internal lines. It is used to connect public or private lines coming into the building to internal networks. In a telco central office, the MDF is generally in proximity to the telephone switch.

The role of the DSLAM

The central office (CO) must now collect all the different digital signals from its modems and combine them into a single signal, via multiplexing.

The aggregate signal then loads onto backbone switching equipment, traveling through an access network (AN)—also known as a Network Service Provider (NSP)—at speeds of up to 1 Gbit/s and emerging at a destination Central Office (CO).

At this point, the signal is then fragmented into its component parts and transmitted via telco modems to its final residential / commercial receivers. The device that performs these functions of signal combination and fragmentation is called the Digital Subscriber Line Access Multiplexer, or DSLAM.

• The DSLAM, functioning as a switch, collects the ADSL modem data (connected to it via twisted pair copper wire) and multiplexes this data via the gigabit link that physically plugs into the DSLAM itself, into the Telco's backbone.
• DSLAMs are also used by hotels, lodges, golfing estates and residential neighbourhoods setting up their own private telephone exchange.

See also

• Asymmetric Digital Subscriber Line (ADSL)
• Symmetric Digital Subscriber Line (SDSL)
• IDSL
• G. Symmetric High-speed Digital Subscriber Line (SHDSL)
• Broadband Internet access
• Broadband Internet access worldwide
• Triple play (telecommunications)

External links

• Google Directory: DSL Vendors

Telecommunications | Digital Subscriber Line

DSLAM | DSLAM | DSLAM | DSLAM | DSLAM | DSLAM | DSLAM | DSLAM | DSLAM