FRAME RELAY

Department of Electrical Engineering

Bahria University Islamabad campus

OBJECTIVES

• Introduction• Drawbacks of x.25 and leasing t-1 or t-

3 lines• Features of frame relay• Architecture • FR layers• FR frame• DTE (Data Terminal Equipment)

OBJECTIVES

• DCE (Data Communications Equipment)

• FR Terminology• FR topologies• Conclusion

INTRODUCTION

• Frame relay is a VC wide-area network that was designed in response to demands for a new type of wan in the late 1980s and early 1990s.

• It operates at the data link layer of the OSI reference model.

• Frame Relay uses a subset of the high-level data link control (HDLC) protocol called Link Access Procedure for Frame Relay (LAPF).

• Frames carry data between user devices called data terminal equipment (DTE), and the data communications equipment (DCE) at the edge of the WAN.

Drawbacks of X.25

• X.25 has a low 64-kbps data rates.

• Flow and error control at both layers create a large overhead and slow down transmission

• Originally X.25 was designed for private use, not for internet.

Drawbacks of T1or T3 lines

• Very costly

• T1 and t3 lines has fixed rate data all the time, but the user needs different bandwidth allocations at different times.

Features of FR• FR operates at higher speed. (1.544 Mbps and recently 44.376).

• FR operates in just the physical and data link layers.

• FR allows bursty data.

• FR allows a frame size of 9000 bytes.

• Less expensive.

• There is no flow control and error control.

ARCHITECTURE

FR LAYERS

FR FRAME

DTE (Data terminal equipment)

• DTEs generally are considered to be terminating equipment for a specific network and typically are located on the premises of the customer.

• The customer may also own this equipment.• Examples of DTE devices are routers and Frame

Relay Access Devices (FRADs).

DCE (Data connecting equipment)

• DCEs are carrier-owned internetworking devices. • The purpose of DCE equipment is to provide clocking

and switching services in a network. • In most cases, these are packet switches, which are

the devices that actually transmit data through the WAN.

FR Terminology

SVC PVC• Switched Virtual Circuits (SVCs) are Virtual circuits may be

established dynamically by sending signaling messages to the network.

• However, SVCs are not very common. • Permanent Virtual Circuits (PVCs) are more common.• PVC are VCs that have been preconfigured by the carrier are

used. • The switching information for a VC is stored in the memory of

the switch

Conclusion

• Frame relay protocol is a simplified X.25 WAN protocol. It is a kind of statistical multiplexing protocol that can establish multiple virtual circuits (VC) over a single physical cable.

• A frame relay network can be a public network, a private enterprise network, or a network formed by direct connections between data devices.