FIBER DISTRIBUTED DATA INTERFACE (FDDI)

Introduction

٭ Shared media network like Ethernet ( IEEE 802.3) &

IBM token ring (IEEE 802.5)

٭ 100 mbps speed

٭ Runs on optical fiber

٭ American National Standards Institute (ANSI) standard

FDDI Basic Principle

• Token ring network like IEEE 802.5

• Token: a special sequence of bits

• Token circulates around the ring

• A station removes the token from ring before transmission

• After transmission, the station returns the token to the ring

• Collisions are prevented as there is only one token in the ring

TOKEN RING NETWORK

FDDI Basic Principle

• Token ring network like IEEE 802.5

• Token: a special sequence of bits

• Token circulates around the ring

• A station removes the token from ring before transmission

• After transmission, the station returns the token to the ring

• Collisions are prevented as there is only one token in the

ring

FDDI Physical Properties

• Dual-counter-rotating token ring architecture

• One ring is primary and the other secondary

• Up to 500 stations with a maximum distance of 2 km

between any pair of stations for multimode fiber

• With single-mode fiber the distance can be up to 40 km

• Maximum ring length is 100 km (total fiber length is 200

km for two rings)

• Uses 4b/5b encoding

FDDI Dual Ring Architecture

Operation On Failure Of The Primary Ring

FDDI Architectural Model

• According to the OSI-RM, FDDI specifies layer 1 (physical

layer) and part of layer 2 (data link control layer)

• The physical layer handles the transmission of raw bits

over a communications link

• The data link control (dlc) layer is responsible for

maintaining the integrity of information exchanged

between two points

Relationship Between FDDI and OSI-RM

The PMD Layer

• PMD layer defines the type of media interconnection and its

characteristics such as transmitter power, frequencies, receiver

sensitivities, bit error rates (per), optical components etc.

• PMD-MMF: MultiMode (62.5 micron core diameter) Fiber

• PMD-SMF: Single-Mode (8-10 micron core diameter) Fiber

• Also defines STP, UTP as media and FDDI on SONET

The PHY layer

• Provides the media independent functions associated with

the OSI physical layer

• Reception: decodes the received bit stream from PMD into a

symbol stream for use by the mac layer

• Transmission: encodes the data and control symbols

provided by mac using 4b/5b encoding for the PMD layer

• Also provides SMT the services required for the

establishment and maintenance of the FDDI ring (by

continuously listening to the incoming signal)

The MAC Layer

• Provides fair & deterministic access

• Fair: no node has advantage over another in accessing the

medium

• Deterministic: under error-free conditions, the time a node has

to wait to access the medium can be predicted

• Medium access is controlled by a token

• Token permits the node that receives it to transmit frames

• The mac layer of the node that generated the frame is responsible

for removing the token

The SMT Layer• A sophisticated, built-in network monitoring and

management capability

• SMT is not an OSI-RM specification

• Making use of the services provided by PMD, PHY, and

MAC, it carries out many functions such as node

initialization, bypassing faulty nodes, coordination of node

insertion and removal, fault isolation and recovery

• SMT is most commonly implemented as a software process

running on the FDDI device

FDDI Benefits

• High bandwidth (10 times more than Ethernet)

• Larger distances between FDDI nodes because of very low

attenuation ( 0.3 dB/km) in fibers

• Improved signal-to-noise ratio because of no interference from

external radio frequencies and electromagnetic noise

• Per typical of fiber-optic systems (10^-11) is substantially

better than that in copper (10^-5) and microwave systems

(10^-7)

• Very difficult to tap signals form a fiber cable

Comparison Of Transmission Media

FDDI Limitations

• High cost of optical components required for

transmission/reception of signals (especially for

single mode fiber networks)

• More complex to implement than existing low

speed LAN technologies such as IEEE 802.3 and

IEEE 802.5

Applications of FDDI

• Office automation at the desktop

• Backbones for factory automation

• Backend data center applications

• Campus LAN interconnection

• Intercampus Backbones Or Metropolitan Area Networks

(mans)

• Interconnection of private branch exchanges (pbxs)

• Workgroup and departmental LANs

• Integrated transport for multimedia applications

A FDDI Backbone Network Example

Comparison With Other Networks

FEATURES FDDI ETHERNET TOKEN RING

Transmission rate

125 mbaud 20 mbaud 8 & 32 mbaud

Data rate 100 mbps 10 mbps 4 & 16 mbps

Signal encoding

4b/5b (80% efficient)

Manchester (50% efficient)

Differential manchester (50%

efficient)

Maximum coverage

100 km 2.5 km Configuration dependent

Maximum nodes

500 1024 250

Maximum distance between nodes

2 km (multimode fiber)

40 km (single-mode fiber)

2.5 km 300 m (recommended

100 m)

The End

……. Thank You …….