Im not going to mention what DSLAM stands for again, and instead i am going to show what role it plays in
DSL connectivity. And now, some
ASCII art
Local Loop
_________________|___________________
| |
_________
SNI | |
| | |
| | |
/--\| _ ______ | |
| |] | | | | | |
| |____| |____| |_____| |
---------------------------------------
^ ^ ^ ^ Central Office
| | |-- Crossbox
| |----Pedastal
|-- Customer Premise
The DSLAM is a piece of equipment that sits in the
Central Office. Next on to the
anatomy of the central office.
_________________________________
| | |
| ATM Edge Switch-> | |
| | |
|_____ |________|
| | | |
| | <- Voice Switch | |
| | _________|__ |
|_____| |ATU-C -> || | |
| | DSLAM -> | __|| | |
| | | | | |
| | | | | |
| | Lim Port --|---> || | |
__|_|_|_____________|_____|| | |
Ok, my
poopy ASCII art out of the way, I am gonna talk through this. The
local loop, as I have had it explained to me is a pair of
copper wires that runs between the
SNI and the
CO (Central Office). When the pair hits the
CO, voice traffic is routed to a
voice switch, while
DSL traffic heads for the DSLAM. The first hit it makes in the DSLAM (usually) is a
LIM port. From the
LIM port, it gets sent to an
ATU-C. The ATU-C converts the signal into
ATM cells, which then get sent to the
ATM Edge Switch. The signal then gets sent through a
myriad of switches referred to as the
ATM Cloud. Then the signal hits the
ISP, and goes out to the internet. Reverse for downstream.
My simplified drawing shows a DSLAM with one lim port and one ATU-C. In reality there are racks of LIM ports and ATU-Cs. That's where the
multiplexer part comes in. The DSLAM takes a bunch of
DSL signals, converts them into
ATM cells, and sends it off to the
Edge Switch.
The DSLAM I work with is a
Cisco 6100. I also work with
Lucent DSLAMs, though only rarely. We refer to the
Lucent ones as
stingers, and they are typically used to extend
DSL availibility. The main difference between the two is the
Ciscos are typically in the
CO, while the
Lucents are out in the field.
Another
point worth mentioning is that it is possible to chain muliple DSLAMs together. The process is called
subtending and allows a
DSL provider to allow more
DSL connections through a
CO