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<b>Chapter 5</b>

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<b>Overview</b>

• <b><sub>Introduction</sub></b>

• <b>Technical basics</b>

• <b>Frame Relay network </b>

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<b>Introduction </b>

<b>What is Frame Relay?</b>

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<b>What is Frame Relay ?</b>

• 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 1 & Layer 2 of OSI model

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<b>Applications of Frame Relay</b>

• 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

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<b>Technical Basics</b>

• <b><sub>Network Interfaces</sub></b>

• <b>Frame Format</b>

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<b>Frame Relay Layers</b>

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

– Specifies what CPE must do to connect

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<b>Network Interfaces</b>

• <i><b>UNI – User Network Interface</b></i>

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

• <i><b>LMI – Local Management Interface</b></i>

– Ensures valid operation of the local frame relay UNI

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

• <i><b><sub>NNI – Network-to-Network Interface</sub></b></i>

– Specifies signaling and management functions between 2 FR
networks

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<b>PHY Layer</b>

• Layer 1 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

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<b>Layer 2 – Frame Format</b>

• FLAG – Indicates beginning and end of the frame

(01111110 binary = 7E hexadecimal)

• HEADER – Contains addressing and status information

• INFORMATION FIELD – User data

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<b>Frame Format - Header</b>

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

•EA – Extended Address Bit

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<b>DLCI Mapping</b>

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<b>Frame Relay Network Implementation</b>

• <b><sub>Equipments</sub></b>

• <b><sub>Virtual Circuits</sub></b>

• <b>Congestion</b>

• <b>Public, Private Networks</b>

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<b>Frame Relay Equipments</b>

• <b>DTE</b>

– Frame Relay Access Devices (FRAD)
– Routers

• <b>DCE</b>

– Frame relay switches
•<b> Others</b>

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

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<b>Routers in FR Networks</b>

•<b>Traditional Router</b>

Typically transports

packets from LAN to other
local or wide area ports

corresponding to address

•<b>Frame Relay Router</b>

Takes packets from LAN to a
single Frame Relay port

provisioning multiple virtual

connections, each to a destination
network corresponding to the

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<b>Frame Relay Virtual Circuits</b>

• 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)

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<b>Switched Virtual Circuits (SVC)</b>

• 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
3. 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

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<b>Permanent Virtual Circuits (PVC)</b>

• 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

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<b>FR Terms and Acronyms</b>

• <b>CIR (Committed Information Rate): </b>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

• <b>Bc (Committed Burst): </b>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

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

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

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<b>FR Terms and Acronyms (2)</b>

• <b><sub>Tc</sub></b>

<sub>: is the time period calculated by dividing Bc by CIR</sub>

– Used to determine the period from which data will be

measured

• <b><sub>Access Rate</sub></b>

<sub>: is the actual interface speed to which the </sub>

users equipment connects

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<b>Private and Public Networking</b>

• 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

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<b>Public Carrier-Provided Networks</b>

• 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

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<b>Private Enterprise Networks</b>

• 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

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