Data Communication & networking

This blog is for undergraduate/graduate students who require some basic information about their subjects or any other topic related to data communication.

Tuesday, 29 March 2011

Frame Relay

Frame Relay is a standardized wide area network technology that operates at the physical and logical link layers of OSI model. Frame relay originally designed for transport across Integrated Services Digital Network (ISDN) infrastructure, it may be used today in the context of many other network interfaces.
Frame relay is an example of a packet switched technology. Packet switched network enables end stations to dynamically share the network medium and the available bandwidth. 
Frame Relay is often described as a streamlined version of X.25, it is because frame relay typically operates over WAN facilities that offer more reliable connection services. Frame relay is strictly a layer 2 protocol suite, where as X.25 provides services at layer 3.
Some important characteristics of frame relay are,
1- It allows bursty data.
2- It allows the frame size 9000bytes, which can accumulate all LANs.
3- It is less expensive than other traditional WANs.
4- It has eror detection only at data link layer, there is no any flow control and error control.
5- There is also a retransmission policy if frame is damaged.
6- 56 kbps, 64 kbps, 128 kbps, 256 kbps, 512 kbps and 1.5 Mbps.

Frame Relay Devices:
Devices attached to a frame relay WAN are of two categories.
1- Data terminal equipment (DTE).
2- Data Circuit Terminating equipment (DCE)

DTEs generally are considered to be terminating equipment for a specific network and typically are located on the premises of a customers. e.g. PC, routers, bridges.
DCEs are carrier owned internet working device. The purpose of DCE equipment is to provide clocking and switching services in a network.

Frame Relay Virtual Circuits:
Frame Relay provides connection-oriented data link layer communications. This means that a defined communication exists between each pair of devices and that these connections are associated with a connection identifier (ID).This service is implemented by using a FR virtual circuit, which is a logical connection created between two DTE devices across a Frame Relay packet-switched network.
Virtual circuits provide a bidirectional communication path from one DTE device to another and are uniquely identified by a data-link connection identifier (DLCI). A virtual circuit can pass through any number of intermediate DCE devices (switches) located within the Frame Relay Packet Switched Network.
Frame Relay virtual circuits fall into two categories: switched virtual circuits (SVCs) and permanent virtual circuits (PVCs).

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