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– FR backbone into an existing network; FR is used to pass all network traffic.. Voice over Frame Relay.[r]

Chapter 5

Overview

• Introduction

• Technical basics

• Frame Relay network

Introduction

What is Frame Relay?

What is Frame Relay ?

• A high speed communication technology used in networks to connect LAN, SNA, Internet & carry voice traffic

– Speeds: 56Kbps – 1.54Mbps

• Information is divided into “frames” before transmitting

• “Frames” are simply “relayed” through series of switches within the network

– Each has an address that the network uses to determine the destination

– No error correction or recovery, discards data if there’s problem – Relies on higher layer protocol to recover

• Operates at Layer & Layer of OSI model

Applications of Frame Relay

• File Transfer

– Character-interactive traffic (e.g text editing) – High Resolution graphics

• Access to Internet and Intranet

• Multimedia, Real Time Voice, Video, Fax • LAN Peer-to-Peer, WAN Interconnection • Multi-protocol networking applications

– ATM, SNA, TCP/IP

Technical Basics

• Network Interfaces

• Frame Format

Frame Relay Layers

• F.R operates at PHY and MAC layers of OSI model • It is an interface standard

– Specifies what CPE must to connect

Network Interfaces

• UNI – User Network Interface

– a set of procedures that allow a frame relay access equipment to communicate with the FR network

• LMI – Local Management Interface

– Ensures valid operation of the local frame relay UNI

– Provides the end user with network management information related to the local access circuit

• NNI – Network-to-Network Interface

– Specifies signaling and management functions between FR networks

PHY Layer

• Layer handles the actual physical transmission of bit-stream • Major components required for connecting a customer site to

frame relay network

– Access Circuit: connects customer to service provider’s switch – Port Connections: physical interface to backbone network, logical

entry point to virtual circuit

– CPE: Customer Premises Equipment

• FR Forum implementation agreement allows several physical interfaces for connecting CPE to Access Circuits

Layer – Frame Format

• FLAG – Indicates beginning and end of the frame (01111110 binary = 7E hexadecimal)

• HEADER – Contains addressing and status information • INFORMATION FIELD – User data

Frame Format - Header

•DLCI – Data Link Connection Identifier (10 Bits) •C/R – Command/Response Indication Bit

•EA – Extended Address Bit

DLCI Mapping

Frame Relay Network Implementation

• Equipments

• Virtual Circuits

• Congestion

• Public, Private Networks

Frame Relay Equipments

• DTE

– Frame Relay Access Devices (FRAD) – Routers

• DCE

– Frame relay switches • Others

– Add on devices, such as adapter cards, testing and monitoring

Routers in FR Networks

•Traditional Router

Typically transports

packets from LAN to other local or wide area ports

corresponding to address

•Frame Relay Router

Takes packets from LAN to a single Frame Relay port

provisioning multiple virtual

connections, each to a destination network corresponding to the

Frame Relay Virtual Circuits

• A virtual circuit (VC) is a logical connection created between two DTE across a packet switched network

– VCs provide bi-directional communication path, uniquely identified by a data-link connection identifier (DLCI)

– Several VCs can be multiplexed into a single physical circuit for transmission across the network, reducing equipment and network complexity

– A VC can pass through a number of intermediate switches within the PSN

• Frame Relay virtual circuits fall into two categories – Switched Virtual Circuits (SVC)

Switched Virtual Circuits (SVC)

• SVCs are temporary connections used in situations requiring only sporadic data transfer between DTE devices across the network • A communication session across an SVC consists of four

operational states

1 Call setup: VC between two DTE devices is established

2 Data Transfer: Data transmitted between the DTE over the VC Idle: Connection between DTE remains active, but no data is

transferred

4 Call Termination: VC between DTE devices is terminated

• SVCs save companies money because the circuit is not open all the time

Permanent Virtual Circuits (PVC)

• PVC are used for frequent and consistent data transfers between DTE devices across the network

• PVC operate in one of the following two operational states:

– Data Transfer: Data is transmitted between the DTE devices over the VC

– Idle: The connection between DTE devices is active, but no data is transferred

• Communication across a PVC does not require the call setup and termination states that are used with SVCs

– DTE devices can begin transferring data whenever they are ready because the circuit is permanently established

FR Terms and Acronyms

• CIR (Committed Information Rate): is the average throughput rate that a user can expect from a VC

– User should be able to transmit data continually without problems at this “average bits per second” rate

– CIR is uniquely configurable for each VC

• Bc (Committed Burst): is the total number of bits the user is allowed to transmit onto the FR circuit in a set time period, Tc – Bc is uniquely configurable for each VC

• Be (Excess Burst): is an amount of data in bits above Bc that if transmitted by the user within Tc, the network will attempt to deliver

– ANSI, ITU-T consider anything above Be to be data that will be discarded

FR Terms and Acronyms (2)

• Tc: is the time period calculated by dividing Bc by CIR – Used to determine the period from which data will be

measured

• Access Rate: is the actual interface speed to which the

users equipment connects

Private and Public Networking

• Frame Relay may be implemented in a public carrier-provided networks and in private enterprise networks • Many factors influence the decision

– Public services are inexpensive, but few absolute guarantees of QoS from service providers

– Adding FR network to nodes of existing private network may not provide the most efficient use of FR

– New FR network will require significant investment of time and money

• Choice depends on corporate policy, the particular

Public Carrier-Provided Networks

• The DTE is located in the central offices of a telecommunications carrier

– Subscribers are charged based in their network use (CIR, – They are relieved from administering and maintaining the

network equipment and service

• The DCE may be customer-owned or provided by telecommunication providers as service to customer • Majority of today’s Frame Relay networks are public

Private Enterprise Networks

• The administration and maintenance of the network are the responsibilities of the enterprise (a private network) – All equipments, including the switch equipment is owned by the customer

• More organizations worldwide are starting to implement private networks

• Various methods of implementation include

– Complete private frame relay network (no other protocols)

– Partial FR network, utilizing existing network infrastructure to pass FR over

Summary

• FR takes advantage of the low error rates in present-day optical fiber landline networks for supporting flexible networking configurations and feature-rich

enhancements such as CIRs (Committed Information Rates), video-over-FR, IP multicasts, voice-over-FR (VoFR) services, and VPN implementations

• Frame Relay platform facilitates network consolidation by enabling LAN-to-LAN connections, LAN integration with backbone networks, and LAN interconnectivity