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 QoS features like contention, diffserv, and priority queues.
The end subscribers connect to the DSLAM via DSL modems or DSL routers, which are further connected to the PSTN network using unshielded twisted pair cabling. Each DSLAM has multiple DSLAM aggregation cards, and each such card can have multiple ports. 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
. 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. V DC
From a router perspective, the DSLAM acts like a massive network switch, since its functionality is purely Layer 2.
As the following figure shown, DSLAM is equipped with 24
ADSL/ADSL2/2+ ports with built-in POTS splitters so that it provides broadband
data service over existing copper wires without affecting the conventional voice
service. DSLAM 4824, therefore, is a perfect solution for both central office collocation and MTU/MHU markets.