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An Internet protocol digital subscriber line access multiplexer, more commonly known as IP DSLAM, is a piece of technological equipment that channels and directs Internet-based traffic over a telephone exchange. These sorts of devices are usually situated at the headquarters of the access provider, usually a phone or cable company. Users who subscribe to cable or digital subscriber line (DSL) services for their Internet use these pretty much every time they get online, but they don’t usually realize it; they aren’t like modems or other devices that have a more visible role on the user’s end. The way the device works from a technical perspective can be very complex. In the simplest sense, it acts as a sort of mediator of the digital traffic coursing through a network. It allows individual machines and devices to send and receive data packets, and works as part of the team of tools and coding devices that prioritize traffic and enable things like high-speed access. IP DSLAM technology is constantly growing and changing to keep up with increases in user number, file sizes, and overall network sophistication.
A digital subscriber line access multiplexer (DSLAM) isn’t necessarily configured for Internet protocol, and the original iterations weren’t. This device is a core part of modern telephone exchanges, but as more and more telephone companies have begun expanding their offerings to include cable Internet access and other digital communications, the IP component has become increasingly important.
Telephone exchanges are basically centers where calls are routed and directed. Some of the earliest exchanges were actually manned by people; operators worked a switchboard and manually routed calls to their intended recipients. Simple analog technology made this work more efficient, and DSLAMs were some of the first machines to take on this tasking in the digital age.
There are two main types of core network in most countries. The older network is a mixture or analog and digital technologies and carries most of the voice traffic, while the newer IP network handles most online requests and data transfers. The older network is a hybrid of old analog equipment coupled with newer digital equipment all sharing the same space. This network has been around for years, and is upgraded as money and technology allow.
Digital signals are more compact and move faster than their analog counterparts, and can also travel at a much higher density. Among other things, the advent of digital technology has made telecommunications much more efficient. Most network traffic today is digital; even telephone conversations in most places are digitized, which means that they are encoded into IP and sent across a network in small packets. They can travel much faster as small particles, and they’re always almost instantly rearranged on arrival.
An IP DSLAM is a necessary part of this process as it sorts the traffic coming from users and sends it on its way. It can be though of as the on-ramp to the IP highway; it allows customers to use their DSL line to access the wider network by combining their lines with others and sending them onto the telephone backbone network.
Traditionally, a DSLAM would pass the IP traffic to the core network, where it would be extracted and passed on to its destination. This meant every carrier needed lots of DSLAMs to cope with the demands of their users. IP-specific models extract the IP traffic at the first telephone exchange. As IP traffic takes up less space than other traffic, each DSLAM can cope with more users. More users using less equipment means more savings for the carrier, and in most cases also a faster connection for the user.
As an analogy, say someone drove to work one morning during rush hour when the highway was busy and the car got stuck in traffic. It takes a while to get through, but eventually the person arrives at work. The next day he rides his motorcycle instead of taking the car, and most other drivers do, too. Motorcycles take up less space, so the highway can cope with more motorcycles than cars. As a result, everyone gets to their destinations more quickly. In this example, the car is traditional analog traffic, and the motorcycle is IP or digital packets.
Many carriers are building brand new networks based entirely on IP. These consist of large optical fibers and routers that can carry hundreds of gigabytes of data every second, and typically allow for that traffic to be carried quite quickly. Since the majority of today’s traffic is digital, these networks can be used to carry the most data, which is becoming increasingly important as old networks are phased out. Digital traffic uses less space than analog, which means that the network can cope with more users and more traffic. An IP DSLAM is an important part of this process since it takes digital signals early in the process and allows the same network to carry more traffic. Ideally this helps improve the user experience while also making more money for the carrier.
To clarify on @roser's point, this doesn't mean street distance; it actually comes down to the length of cable. You can call your ISP to find out. What we're basically talking about is called attenuation, which is signal loss due to distance. You want this to be as low as possible.
The DSLAM being a crucial component in regards to internet speed, where your local exchange is located in regards to you is an important thing to consider.