Cell relay refers to a method of statistically multiplexing small fixed-length packets, called “cells”, to transport data between computers or kinds of network equipment. It is an unreliable, connection-oriented packet switched data communications protocol. Cell relay transmission rates usually are between 56 kbit/s and several gigabits per second. ATM, a particularly popular form of cell relay, is most commonly used for home DSL connections, which often runs between 128 kbit/s and 1.
544 Mbit/s (DS1), and for high-speed backbone connections (OC-3 and faster).Cell relay is an implementation of fast packetswitching technology that is used in connection-oriented broadband integrated services digital networks (B-ISDN, and its better-known supporting technology ATM) and connectionless IEEE 802. 6 switched multi-megabit data service (SMDS). Cell relay is extremely reliable for transporting vital data. Switching devices give the precise method to cells as each endpoint address embedded in a cell. An example of cell relay is ATM, a prevalent form utilized to transfer a cell with a fixed size of 53 bytes.Cell relay systems break variable-length user packets into groups of fixed-length cells, that add addressing and verification information. Frame length is fixed in networking hardware, based on time delay and user packet-length considerations.
One user data message may be segmented over many cells. Frame Relay types: ? ? Variable-length packets Statistical multiplexing Frame Relay often is described as a streamlined version of X. 25, offering fewer of the robust capabilities, such as windowing and retransmission of last data that are offered in X. 25.Internationally, Frame Relay was standardized by the International Telecommunication Union-Telecommunications Standards Section (ITU-T). In the United States, Frame Relay is an American National Standards Institute (ANSI) standard. Devices attached to a Frame Relay WAN fall into the following two general categories: ? ? Data terminal equipment (DTE) Data circuit-terminating equipment (DCE) Frame Relay provides connection-oriented data link layer communication.
This means that a defined communication exists between each pair of devices and that these connections are associated with a connection identifier.This service is implemented by using a Frame Relay virtual circuit, which is a logical connection created between two data terminal equipment (DTE) devices across a Frame Relay packet-switched network (PSN) Frame Relay virtual circuits fall into two categories: switched virtual circuits (SVCs) and permanent virtual circuits (PVCs). The Discard Eligibility (DE) bit is used to indicate that a frame has lower importance than other frames.
The DE bit is part of the Address field in the Frame Relay frame header.DTE devices can set the value of the DE bit of a frame to 1 to indicate that the frame has lower importance than other frames. When the network At any time there is information to be transmitted; the switch basically sends the data units. Connections don’t have to be negotiated like circuit switching.
Channels don’t have to be allocated because channels do not exist in ATM, and on condition that there is an adequate amount of bandwidth to maintain it, there can be indefinite transmissions over the same facility. Cell relay utilizes data cells of a persistent size.Cell relay statems may also carry bitstream-based data such as PDH traffic, by breaking it into streams of cells, with a lightweight synchronization and clock recovery shim. Thus cell relay systems may potentially carry any combination of stream-based and packet-based data.
This is a form of statistical time division multiplexing. becomes congested, DCE devices will discard frames with the DE bit set before discarding those that do not. This reduces the likelihood of critical data being dropped by Frame Relay DCE devices during periods of congestion.
