Fiber Distributed Data Interface(FDDI)
Sequence of Presentation
1. Timeline for development of FDDI
3. Transmission Media
4. FDDI Specifications/component of FDDI
5. Features of FDDI
4. FDDI basic principle
5. Cable Types
6. FDDI Devices
5. FDDI Frame Format
6. FDDI Architectural Model
7. FDDI - II
8. Benefits & limitations
Timeline for FDDI
• project initiated in October 1982 by James Hamstra at Sperry.
• two proposals for media access control (MAC) & physical (PHY) layers submitted in
• FDDI MAC became an ANSI standard in late 1986
• FDDI PHY won ANSI standardization in 1988
• FDDI- ii proposal was made in early 1986
• first public demonstrations at advanced micro devices (AMD) in 1989
FDDI is a standard developed by the American National Standards Institute
(ANSI) for transmitting data on optical fibers
Supports transmission rates of up to 200 Mbps
Uses a dual ring
First ring used to carry data at 100 Mbps
Second ring used for primary backup in case first ring fails
If no backup is needed, second ring can also carry data, increasing the data
rate up to 200 Mbps
Supports up to 1000 nodes
Has a range of up to 200 km
FDDI uses three basic topologies Ring, Star, and Tree
FDDI uses optical fiber as the primary transmission medium, but it also can run over
FDDI over copper is referred to as Copper-Distributed Data Interface (CDDI).
FDDI defines two types of optical fiber: single-mode and multimode.
Multimode fiber uses LED as the light-generating device.
Multimode fiber allows multiple modes of light to propagate through the fiber..
multimode fiber is generally used for connectivity within a building or a relatively
geographically contained environment.
single-mode fiber generally uses lasers.
Single-mode fiber allows only one mode of light to propagate through the fiber.
Therefore, single-mode fiber is capable of delivering considerably higher performance
connectivity over much larger distances, which is why it generally is used for connectivity
between buildings and within environments that are more geographically dispersed.
FDDI Specifications/component of FDDI
FDDI is defined by four separate specifications:
1. Media Access Control (MAC)---Defines how the medium is accessed, including
frame format, token handling, addressing, algorithm for calculating a cyclic redundancy
check value, error recovery mechanism
2. Physical Layer Protocol (PHY)---Defines data encoding/decoding procedures,
clocking requirement, framing and other function.
3. Physical Layer Medium (PMD)---Defines the characteristics of the transmission
medium, including the fiber-optic link, power levels, bit error rates, optical components,
4. Station Management (SMT)---Defines the FDDI station configuration, ring
configuration, and ring control features, including station insertion and removal,
initialization, fault isolation and recovery, scheduling, and collection of statistics.
Features of FDDI
Dual Token Rings
FDDI Basic Principle
• Token circulates around a ring in network.
• A station first capture the token ,send packet of data to network.
• After transmission token is released.
• Every station on the network will receive the transmission and repeat it.
• The transmission will travel around the ring until it is received by the station which
originally sent it, which removes it from the ring.
• If a station does not receive its transmission back, it assumes that an error occured
• To solve this problem fault isolation techniques is used.
There are four cable types which can be used with FDDI. They are:
Multimode Fiber Optic Cable
Fiber optic cable, usually with a core size of 62.5 microns. It allows distances up to 2000 meters
Single-mode Fiber Optic Cable
Fiber optic cable with a core size of 7 to 11 microns. It allows distances up to 10,000 meters
Category 5 UTP
An unshielded copper cable, usually with eight wires. The wires are twisted together in pairs,
and the cable is rated at frequencies up to 100 MHz. It allows distances up to 100 meters
IBM Type 1 STP
A heavy, shielded copper cable. It consists of four wires, twisted in to two pairs. Each pair is
covered with an individual shield, and an overall shield covers the entire cable. It allows
distances up to 100 meters (330 feet).
DAS: dual attach station (usually attaches directly to FDDI dual ring)
SAS: single attach station (attaches to the FDDI ring through a
DAC: dual attach concentrator (usually attaches directly to the FDDI dual
SAC: single attach concentrator (attaches to the FDDI ring through another
3. optical bypass switch
FDDI Frame Format
The FDDI frame format is similar
to the format of a Token Ring
FDDI frames can be as large as
The following descriptions summarize the FDDI data frame and token fields
illustrated in the above figure.
• Preamble (16 bits)- Gives a unique sequence that prepares each station for an
• Start delimiter (8 bits)- - Indicates the beginning of a frame by employing a
signaling pattern that differentiates it from the rest of the frame.
• Frame control (8 bits)- - Indicates the size of the address fields and whether
the frame contains asynchronous or synchronous data, among other control
• Destination address (48bits)- - Contains a unicast (singular), multicast
(group), or broadcast (every station) address. As with Ethernet and Token
Ring addresses, FDDI destination addresses are 6 bytes long.
• Source address (48 bits)- - Identifies the single station that sent the frame. As
with Ethernet and Token Ring addresses, FDDI source addresses are 6 bytes
Data - Contains either information destined for an upper-layer protocol or
Frame check sequence (FCS) (32 bits)- - Is filed by the source station with a
calculated cyclic redundancy check value dependent on frame contents (as with
Token Ring and Ethernet). The destination address recalculates the value to
determine whether the frame was damaged in transit. If so, the frame is
End delimiter (16 bits)- - Contains unique symbols; cannot be data symbols
that indicate the end of the frame.
Frame status (16 bits)- - Allows the source station to determine whether an
error occurred; identifies whether the frame was recognized and copied by a
The physical layer defines the electrical, mechanical, and logical characteristics
for transmitting bits across the physical medium. Examples of physical media
include twisted pair, coaxial, and fiber optic cable. Dual ring FDDI specifies fiber
optic cable as the physical medium.
The data link layer specifies the way a node accesses the underlying physical
medium and how it formats data for transmission. FDDI specifies formatting data
into frames, using a special set of symbols and following a special set of rules. The
MAC sublayer within the data link layer specifies the physical address (MAC
address) used for uniquely identifying FDDI nodes
enhanced fddi that handles data, voice, and video
same features as basic FDDI (FDDI - I), including maximum number of
modes, 100 mbps data transfer bit rate, and the dual ring
defines the physical layer and the lower half of the data link layer similar to
FDDI supports only packet mode (synchronous and asynchronous) traffic,
fddi-ii supports both packet data as well as isochronous data traffic (in fddi
isochronous indicates a class of traffic for voice and video.
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• high bandwidth (10 times more than ethernet).
• larger distances between fddi nodes because of very low attenuation.
• improved signal-to-noise ratio because of no interference from external radio
frequencies and electromagnetic noise
Limitation of FDDI
high cost of optical components required for transmission/reception of signals
(especially for single mode fiber networks)
more complex to implement.
Application of FDDI
backbones for factory automation
backend data center applications
campus lan interconnection
workgroup and departmental lans
integrated transport for multimedia applications