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Thursday, May 26, 2005

DSL Broadband Definitions


By: The Editor

Many people get confused with the alphabet soup of DSL broadband terminology. It's explained here in easy to understand terms.

ADSL:
Asymmetric Digital Subscriber Line - asymmetric meaning it's faster downstream than upstream.

ASAM:
Advanced Services Access Manager -Whether you have a DSLAM or ASAM in your exchange doesn't really matter. They do the same thing. See DSLAM's as well. (continued...)

ATM:
Asynchronous Transfer Mode - a method of encapsulation which is capable of many virtual circuits. With these, providers (ISP's) can split an ATM connection (155Mbit or 622Mbit) up into many connections. ATM isn't just used for DSL but in the case of DSL it's used to provision each customer.

Contention Ratios:
A contention ratio is the number of users to xMbit of bandwidth. For example some providers offer 2Mbit DSL, with a ratio of 50:1, meaning 50 users to 1Mbit of bandwidth.

CPE:
Customer Premises Equipment, the term that describes the equipment used on the customer end of a connection, for example your DSL modem/router or cable modem.

DSL:
Digital Subscriber Line.

DSLAM:
Digital Subscriber Line Access Multiplexer – They are placed in DSL enabled Telecomm exchanges, when your modem syncs up and the DSL light comes on, it means you are connected. When data travels down your connection, it goes from the CPE -> DSLAM -> RAN -> ISP

ERX:
Edge Routing Exchange. See RAN.

IPNet:
Telecommunications backhaul networks for carrying traffic from the customer to the ISP, i.e. carrying traffic from RAN's to ISP's.

Ping or Latency:
A ping measures the time in milliseconds that it takes for a packet to travel from your computer to a remote computer and back to you again. Just because you can't ping a given host, quite a lot of providers are beginning to filter ICMP (pings come under this protocol) traffic because it is commonly used to attack hosts and wastes a lot of bandwidth. Many providers also give low priority to ping (ICMP) traffic which may mean your ping at a command line isn't very good, but in say a game, things may be fine.

RAN:
Regional Access Node - These aggregate many DSLAM's connections and then feed the data to an ISP

RTT
Round Trip Time - the time it takes in milliseconds for a packet to go from A to B and back again. See ping.

SDSL
Symmetrical Digital Subscriber Line - symmetrical meaning the same speed up and down.

Units

There is a major difference between UPPER and lowercase

MB = MegaBytes
Mb = Megabits
kB = KiloBytes
kb = Kilobits

MB/s = MegaBytes per second
Mb/s = Megabits per second
kB/s = KiloBytes per second
kb/s = Kilobits per second

There is 8bits to a Byte, 8kb = 1kB

1Meg connections only transfer at 128kB/sec or an 8Mb connection only transfers at 1024kB/sec or 1MB/s