Networking and Telecommunication Terms

Circuit Switching

Circuit switching dominates the public switched telephone network or PSTN. Network resources set up calls over the most efficient route. That might mean a call from New York to San Francisco goes through switching centers in San Diego, Chicago, and Saint Louis. But no matter how convoluted the route, that path or circuit stays the same throughout the call. Got it? One call, one circuit. It's like having a dedicated railroad track with only one train, your call, permitted on the track at a time.

Packet Switching

Packet switching dominates data networks like the internet. A data call or communication from San Francisco to New York is handled much differently than with circuit switching. With circuit, all packets go directly to the receiver in an orderly fashion, one after another on a single track. Like the train we mentioned before, hauling one boxcar after another. With packet switching routers determine a path for each packet or boxcar on the fly, dynamically, ordering them about to use any railroad track available to get to the destination. Other packets from other calls race upon these circuits as well, making the most use of each track or path, quite unlike the circuit switched calls that occupy a single path to the exclusion of all others.

LAN

A local area network (LAN) is a group of interconnected computers that share the same geographic location, such as an office. This is opposed to a wide area network (WAN), which connects computers over greater distances, and would be used to link branch offices.

Each computer connected to a LAN is able to access the other connected computers' hard drives, as if they were installed internally. Also, you can connect your LAN to a file server, which is specifically designed to house shared files and resources for all the networked computers to access.

WAN

A WAN is a data communications network that covers a relatively broad geographic area and often uses transmission facilities provided by common carriers, such as telephone companies. WAN technologies function at the lower three layers of the OSI reference model: the physical layer, the data link layer, and the network layer.

A point-to-point link provides a single, pre-established WAN communications path from the customer premises through a carrier network, such as a telephone company, to a remote network. A point-to-point link is also known as a leased line because its established path is permanent and fixed for each remote network reached through the carrier facilities. The carrier company reserves point-to-point links for the private use of the customer. These links accommodate two types of transmissions: datagram transmissions, which are composed of individually addressed frames, and data-stream transmissions, which are composed of a stream of data for which address checking occurs only once.

T1

T1 is a telecommunications industry term for a data connection at 1.544 Megabits per second. They are commonly used to connect companies to Internet Service Providers or other offices. T1 data circuits can let an office-full of people have full-time high-speed connections to the net.

T1 uses two pairs of copper wires (four individual wires) to carry up to 24 simultaneous conversations ("channels") that would normally need one pair of wires each. Each 64Kbit/second channel can be configured to carry voice or data traffic. Most telephone companies allow customers to buy just some of these individual channels, a service called fractional T1. Typically, fractional T1 lines are sold in increments of 56 Kbps (the extra 8 Kbps per channel is used for administration).

E1

Similar to the North American T-1, E1 is the European format for digital transmission. E1 carries signals at 2 Mbps (32 channels at 64Kbps, with 2 channels reserved for signaling and controlling), versus the T1, which carries signals at 1.544 Mbps (24 channels at 64Kbps). E1 and T1 lines may