DSL Glossary
 

bridge tap ­ an accidental connection of another local loop to the primary local loop. It is generally harmful to DSL connections and should be removed. Extra phone wiring within one's house is a combination of short bridge taps.

CO ­ Central office.

COLO - Co-location.

carrier - See DAML.

cross talk ­ noise from one telephone line that is audible on another line. Caused when lines are too close, touching, not twisted, or by bad punch-downs or other wiring problems. Can allow noise bleed-through from the DSL line to other voice lines in the same location.

DAML ­ The telephone company uses DAML (a pair amplifier) to multiplex two or more phone numbers onto one physical pair (or line). It is a solution for those who want a second line, but for whom the telco found no facilities in their area. A DAML will destroy 56k modem performance, and has to be removed to get DSL. This means you may have to give up one of your telephone numbers when the carrier device is removed from your telephone line.

DHCP - Dynamic Host Configuration Protocol, by which IP addresses are assigned dynamically (when requested by the client) rather than statically (one by one, in advance). A DHCP server is a device that assigns your computer (or router) its IP configuration. The purpose of using this protocol is reduce the amount of work involved in administering a large IP network.

DSL - digital subscriber line.

DSLAM - Digital Subscriber Line Access Multiplexer. The device placed in the CO that accepts all the DSL lines.

demark ­ Demarc or demarcation; the service entrance for your telephone service. Often a box on the outside of your house.

FAQ - Frequently asked question(s).

firewall - a device that protects a network from unwanted traffic, including hackers etc. Can also be used to administer privilege: who gets to see what on the Internet. Generally also used as a DHCP server and for IP translation (NAT).

gateway - a device, at the entrance of your network, that routes packet traffic. On a DSL LAN, it would be the router or firewall with the external IP.

IP - Internet protocol, as in "IP address".

LAN ­ Local area network; the computers in your location. For instance, the LAN side of your router is attached to your local computers and it has an internal IP address.

link - a light indicating that a good connection is present, as in "there is a link between the modem and the router."

load coil - A load coil is an inductor placed on the local loop by the phone company. Coils are generally placed starting at 3.000 feet in 6.000 feet intervals to suppress exactly the signal that DSL modems need to transmit high speed data on -- high frequency. The effect of a load coil is similar, from the perspective of the DSL equipment, to adding 20k feet to the line length. No DSL equipment now works through load coils.

loop ­ telephone wire, also called a pair. The local loop is the term for the line between your house and the local switching center. Since telephone travels on twisted pair, you can imagine one phone line to your house as a big loop of wire, hence the name.

modem - modulates outgoing digital signals from a computer or other digital device to analog signals for a conventional copper twisted pair telephone line and demodulates the incoming analog signal and converts it to a digital signal for the digital device.

NAT - Network address translation: the translation of an Internet Protocol address used within one network to a different IP address known within another network. For instance, a DSL router has two NIC cards. The external card will have a LISCO (public) IP address. The internal card (connected to your LAN) will have an internal IP address. The router will do NAT to route traffic to the correct computer in your LAN.

NIC ­ Network interface card. Also called an Ethernet card.

noise filter ­ Removes the high-frequency whine of DSL data from your line.

POTS - "plain old telephone service"

pair - see loop.

private subnet - There are three IP network addresses reserved for private networks. The addresses are 10.0.0.0/8, 172.16.0.0/12, and 192.168.0.0/16. They can be used by anyone setting up internal IP networks, such as home LAN behind a NAT or proxy server or a router. It is always safe to use these because routers on the Internet will never forward packets coming from these addresses.

remote - A switch at which LISCO does not maintain a DSLAM.

SLC (“slick”) or DLC - DLC stands for Digital Loop Carrier. (An SLC is an AT&T variety.) Beginning in the 1980s, to save money -- copper loops are relatively expensive -- telcos began to install DLC frames around their existing wire centers, particularly in fast-growing districts, to provide for the flood of new lines required. These local concentrators, although digital and fiber optic, were designed before DSL was popular and do not support it. It is estimated that nationally around 20% of US telephone lines are served from a DLC (the percentages vary slightly depending on the telephone company in question).

sync - term used to indicate two devices are communicating, "the modem synched with the DSLAM."

TCP/IP - Transmission Control Protocol/Internet Protocol; the basic communication language or protocol of the Internet.

tip and ring ­ The name for the two wires on a telephone line, derived from the electrical contacts on old-style telephone plugs (one electrical contact is at the tip of the plug, and the other is a ring just above it). A usually low amount of voltage is carried on one of these wires, enough to make an old-style mechanical phone’s bell ring. Reversal of these wires in certain situations can cause excess noise on your extensions after your DSL becomes active.

WAN ­ Wide area network; the Internet. For instance, the WAN side of your router is on the Ethernet port connected to the Internet and it has an external IP address.

Where can I learn more?

If you'd like to learn more technical vocabulary, we recommend Whatis and DSL Reports, or visit our DSL Links page.