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(Fiber Distributed Data Interface)
Commonly used Acronyms
CDDI Copper Distributed Data Interface
CMIP Common Management Information Protocol
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
Host to Host connection
Host to I/O connection
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
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
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.
FDDI OSI Layers
MAC = Media Access Control Sublayer
(defines the data link packets and protocols)
PHY Physical Protocol Sublayer
(defines the encoding and framing of data for
transmission between stations)
PMD Physical Media Dependent Sublayer
(defines media requirements such as fiber, connectors, driver/recivers)
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)
(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
Optical Media (recommended)
1300 nm wavelenght
0.275 numerical aperture
Fiber has a BER of 10-12th
Overall network BER of 10-9th
Optical Media (alternative)
0.20, 0.21, 0.22 0.26, 0.29 numerical aperture
(two-level NRZI, IBM)
type 1, 100 meters
UnShielded twisted pair
("NEW" three-level MLT-3 [Multi-Level-Three])
type 5, 50/100 meters
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