How Data Communications Really Work
Routing On A Frame Relay Network For Data

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Definitions For Terms On This Page
 Carrier
Competitive Access Provider (CAP)
Competitive Local Exchange Carrier (CLEC)
Channel Service Unit (CSU)
DS1 or T1
Data Services Unit (DSU)
Facilities
Frame Relay
Interexchange
Local Area Network (LAN)
Local Exchange Carrier (LEC)
Local Loop
Permanent Virtual Circuit (PVC)
POP (Point of Presence)
Router
Switch

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Carrier - A long distance telephone company which uses it's own transmission facilities and network lines for the majority of it's customer's calls. Many people refer to any long distance company as a carrier, even if it does not own or operate it own transmission facilities or network. [Back to Diagram]

Competitive Access Provider (CAP) and Competitive Local Exchange Carrier (CLEC) - Companies that compete with the local telephone company (LEC). Most CAP's and CLEC's were created around the time the Telecommunications Reform Act of 1996 opened up local telephone services to competition. Prior to the 1996 Act, the LEC's generally had a monopoly on providing local exchange services (dial tone, hunt groups, local loops, etc.) [Back to Diagram]

CSU (Channel Service Unit) - A piece of equipment that provides line isolation between the customer premise equipment and a local telephone company services. Also provides alarms, loopback, signal regeneration, line build out, and surge protection. A CSU typically sits between a T1 digital circuit and a telephone system (digital PBX or switch) controlling the T1's 24 voice grade channels. Click here for more information about Frame Relay Services. [Back to Diagram]

DS1 or T1- "T1" is actually a speed of digital signal transmission over telephone lines. But the term is often used to describe various types of high speed and/or high volume telecommunications service including Dedicated local access to long distance facilities, Point-to-Point data services and for regular local service. A T1 has the capacity of 24 regular telephone lines. Sometimes also called a "DS-1" or "T-Span". Click here for more information about Frame Relay Services. [Back to Diagram]

DSU (Data Services Unit) - A piece of equipment that converts digital signals from data terminal equipment to a type that can be transmitted through a digital phone line. A DSU typically sits between a 56Kbps or T1 digital circuit and computer(s) to allow data communication over a point-to-point circuit or frame relay permanent virtual circuit. [Back to Diagram]

Facilities - Typically refers to transmission switches and equipment used by long distance carriers to handle a long distance call. [Back to Diagram]

Frame Relay - Frame Relay service is a data communications interface standard for wideband packet-switching. It is a data transmission service which uses a single physical interface to support multiple logical connections from one locations to other remote location(s). It provides transmission of variable-length packets across a virtual digital private network. Click here for more information about Frame Relay Services. [Back to Diagram]

Interexchange - The part of long distance voice and/or data transmission carried over the long distance carrier's facilities. Also called a "Frame Relay Cloud" when related to Frame Relay Services. [Back to Diagram]

LAN (Local Area Network) - A network, which is usually contained within a building or campus, that connects personal computers, printers and other data communications equipment. [Back to Diagram]

Local Exchange Carrier (LEC) - Your Local Telephone company. [Back to Diagram]

Local Loop - That part of a communication circuit that connects the customer's telephone equipment to the long distance carrier's POP through the local telephone company (LEC). [Back to Diagram]

Permanent Virtual Circuit (PVC) - A virtual data connection related to Frame Relay service that is dedicated for a customer's use between two specified locations. [Back to Diagram]

POP (Point of Presence) - 1) Physical place where a long distance carrier interfaces with the network of the local telephone company (LEC). 2) The point at which the local telephone company terminates customer's circuits for long distance calls or leased line communications. [Back to Diagram]

Router - A piece of equipment that routes packetized data to it's intended destination. Used in conjunction with Frame Relay service. [Back to Diagram]

Switch - Guess we ought to explain what this is, even though it's not technically involved in a frame relay network. A switch is a device that handles calls. When long distance data is carried over a frame relay network, the local telephone company does not "switch" the data across the dedicated local loops. Rather the dedicated local loops provide a dedicated connection between the customer's computer equipment and their long distance carrier's Point of Presence (POP) on both ends of each permanent virtual circuit (PVC). [Back to Diagram]