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FDDI Technology
(Fiber Distributed Data Interface)



Commonly used Acronyms



CDDI Copper Distributed Data Interface

CMIP Common Management Information Protocol

CON Concentrators

DAC Dual Attached Concentrators

DAS Dual Attached Station

DMAC Dual - Media Access Control

FDDI Fiber Distributed Data Interface

MAC Media Access Control

MIB Management Information Base

MIC Media Interface Connector

NMS Network Management Stations

PMD Physical Medium Dependent

SMAC Single - Media Access Control

SAC Single Attached Concentrators

SAS Single Attached Station

SMT Station Management

SNMP Simple Network Management Protocol

SONET Synchronous Optical Network

TP/DDI Twisted Pair/Distributed Data Interface


FDDI as a LAN Standard


LAN Backbone

Host to Host connection

Host to I/O connection

Client/Server applications


FDDI is a token-passing, fiber ring, network. The fiber optic media can be multimode fiber and can be as large as 100 kilometers - with no more than 2 kilometers between nodes. On class A devices, all fiber connections will be on a dual counter-rotating rings, (which are on independent fiber cables). More information on FDDI standards can be obtained from the ANSI - X3T9.5 committee @ 1430 Broadway, New York N.Y. 10018, (212-354-3300) or from Global Eng. Documents, 2805 McGraw Ave. Box 19539, Irvine, CA. 92714, (714-261-1455).




More Powerful Workstations and Servers
Resource Intensive Network Applications
Growing Distributed Client/Server Applications
Larger Spans of Distributed Networks
Increasing Numbers of Network Users
Bigger and More Powerful Software Applications


FDDI Benefits


Higher Capacity and Performance than older LANs
More Simultaneous Transactions
Higher Availability (dual ring topology)
Predetermined Performance (adding users have minimal impact on throughput)
Longer Distance Loops (2 kilometers to 100 kilometer)


What is FDDI


Ethernet Token-Ring FDDI

Max Data Rate 10 Mbps 4-16 Mbps 100-200 Mbps

Typical Rates 1-2 Mbps 1-15 Mbps 80-160 Mbps

Fault Tolerance No No Yes

Topology Bus Ring Ring

Access Method CSMA/CD Token Timed Token

Token Release N/A Delayed Immediate

Max Frame Size 1.5kb 18Kb 4.5Kb

Num. of Media Single Single Dual


Making the Decision for FDDI

To understand the FDDI needs of your company or department, ask the following questions:

Where do you need the bandwidth?

What is the traffic load on your existing network?

What is the traffic load projected to be in one year? In three years?

What are your network connectivity plans for the future?

What are your geographic spans?

What systems could provide better services or greater accessibility by a direct connection to FDDI?

Do you need better performance and greater flexibility for communities of workgroups

What types of applications will run on your workstations?

Do you need to optimize the use of server systems?

Can you take advantage of copper media as an alternative to fiber?

How will you troubleshoot your network and monitor network performance?


Planning for FDDI

Implementing a FDDI in a multi-LAN environment should address the following areas:



FDDI will operate best with nonproprietary, structured cabling system that supports multivendor environments and a variety of communication applications (voice, 802.3/Ethernet, 802.5/Token ring). One cost-effective way to approach cabling for FDDI is to implement a staged, hybrid solution, with fiber as the backbone and copper for the local loop from the FDDI concentrators to the desk top. Using a tiered approach (fiber/copper) might make cost of a FDDI system more palatable in todays budgets




The selection of FDDI components is dependent upon your FDDI network needs. In any implementation, though, FDDI devices should be simple, reliable, manageable, and interoperable in a multivendor environment. The use of concentrators in the FDDI backbone, for example, provides topology flexibility and management. Concentrators provide maximum management and control to a network where moves, adds, and changes are an everyday event and where network mangamnet (SMT/SMNP), security, integrity, and configurablity are of critical importance. Concentrators can improve network reliability by isolating the FDDI backbone from station failures and "whimsical" end user behavior.




An FDDI network must be manageable within the context of the entire enterprise network. When planning for FDDI, look for a standards-based management protocol (SMT/SMNP) or architecture for managing the entire extended LAN and for FDDI configurations that are easy to change without disruption.


Service and support


FDDI products and systems should conform to industry standards and protocols. When planning FDDI implementations, look for vendors with demonstrated commitment to interoperabiolity.






MAC = Media Access Control Sublayer

(defines the data link packets and protocols)

X3.139-1987/ISO 9314-2:1989

PHY Physical Protocol Sublayer

(defines the encoding and framing of data for

transmission between stations)

X3.148-1988/ISO 9314-1:1989

PMD Physical Media Dependent Sublayer

(defines media requirements such as fiber, connectors, driver/recivers)

X3.166-1990/ISO 9314-3:1990

SMT Station Management

(defines protocols for managing the PMD, PHY, MAC functions)

(SMT revisions 5.1 and the latest 6.2)


SMF-PMD Single Mode Fiber PMD Optics

(defines media requirements for single mode fiber and connectors)



FDDI Architecture


(PMD Physical Media Dependent Sublayer)

specifies physical hardware and related characteristics

Optical Media Characteristics

Copper Media Characteristics

LED Transmitter and Receiver Levels

Connector and Cable Specifications

Optical Bypass Provisions



PMD Specifications


Optical Media (recommended)

1300 nm wavelenght

Multimode fiber

62.5/125 micron

0.275 numerical aperture

Fiber has a BER of 10-12th

Overall network BER of 10-9th

Optical Media (alternative)

50/125 micron

0.20, 0.21, 0.22 0.26, 0.29 numerical aperture

85/125 micron

100/140 micron


(two-level NRZI, IBM)

type 1, 100 meters

UnShielded twisted pair

("NEW" three-level MLT-3 [Multi-Level-Three])

type 5, 50/100 meters

Single-mode fiber


Maximum Distance




1300nm LED on Multimode fiber

50/125 500 Mhz per Km 1.9 miles

62.5/125 500 Mhz per Km 2.9 miles

85/125 300 Mhz per Km 1.5 miles

100/140 200 Mhz per Km 1 mile


1300nm Laser on Multimode fiber

50/125 1,400 Mhz per Km 16.3 miles

62.5/125 1,400 Mhz per Km 16.3 miles

85/125 400 Mhz per Km 1.8 miles

100/140 600 Mhz per Km 2.7 miles


1300nm Laser on Single Mode fiber

8/125 100,000 Hhz per Km 29.8 miles


Type 1 Shielded NRZI modulation = 100 meters

Type 5 UnShielded MLT-3 modulation = 70 to 100 meters