FDDI, or Fiber Distributed Data Interface, is a high-speed network technology that operates at 100 Mbps via fiber-optic cabling and is commonly used for network backbones in a local area network (LAN) or metropolitan area network (MAN).


FDDI (Fiber Distributed Data Interface) is a network standard that use fibre optic connections to create a local area network (LAN) with a range of up to 200 kilometers (124 miles). The token ring protocol is the foundation of the FDDI protocol. Thousands of people can connect to an FDDI LAN. While FDDI is widely used as the backbone for a wide area network (WAN) or a campus area network (CAN), alternative networking technologies have essentially replaced it.

Fiber Distributed Data Interface is the acronym for Fiber Distributed Data Interface. It is a set of ANSI and ISO specifications for data transmission via fiber-optic cables in a Local Area Network (LAN) with a range of up to 200 kilometers (124 miles). The token ring protocol is the foundation of the FDDI convention.

An FDDI neighbourhood region arrangement can serve thousands of clients in addition to being geographically expanded. For a Wide Area Network, FDDI is commonly used on the spine (WAN).

An FDDI network has two token rings, one for backup in the event that the primary ring fails.

The primary ring has a capacity of up to 100 Mbps. If the secondary ring isn’t needed for backup, it can also be used to transfer data, increasing capacity to 200 Mbps. A single ring may amplify the greatest distance; a double ring can increase 100 kilometers.

Because FDDI networks are made up of two counter-rotating rings, they are extremely dependable. In the case that the primary ring fails, a secondary ring provides an alternative data flow. To route traffic around the problem, FDDI stations add this auxiliary ring into the data line. FDDI with token passing and a ring topology. In the form of a token ring over optical fibre, it is a cutting-edge technology. FDDI was created for two main reasons: to support and help extend the capabilities of older LANs like Ethernet and Token Ring, as well as to provide a stable infrastructure for enterprises, allowing them to move even mission-critical applications to networks.

FDDI Characteristics

  • FDDI provides a data rate of 100 Mbps.
  • FDDI is made up of two interfaces.
  • It’s used to connect the ring to the equipment over extended distances.
  • FDDI could be used to create a LAN with Station Management.
  • Allows all stations to have reached a point of parity in terms of the amount of time it takes to transmit data.
  • FDDI distinguishes between synchronous and asynchronous traffic.
  • Topology and design of fibre distributed data interfaces

A FDDI network has two token rings:

one that serves as the primary ring and another that serves as a backup. The primary ring has a capacity of up to 100 megabits per second (Mbps),

while the secondary ring can also carry data and has a capacity of up to 200 Mbps. One ring will rotate in a clockwise motion, while the other will rotate counterclockwise. A single ring can reach up to 200 kilometers (124 miles); a twin ring can extend up to 100 kilometers’ (62 miles). Thousands of devices can be connected to a single FDDI network.

The FDDI topology is a token ring network, although it can alternatively be implemented as a star topology. The Institute of Electrical and Electronics Engineers 802. FDDI is derived from the Institute of Electrical and Electronics Engineers 802. Token protocol with four tokens and a four-token bus.

Only the device that has the token is allowed to communicate in a token network. The usage of a timed token guarantees that each device has the maximum amount of time to broadcast. Users can configure FDDI as synchronous with guaranteed timings for latency-sensitive networks or as asynchronous, which does not rely on exact token timings, depending on the network latency needs.

FDDI is based on the Open Systems

Interconnection model Layer 1 (physical) and Layer 2 (logical) and is a product of the American National Standards Committee X3T9 standard (media access control data link). It has a 4,352 bytes maximum transmission unit frame size.

FDDI’s principal connecting medium is single-mode fibre optic cable. Copper Distributed Data Interface, Twisted-Pair Physical Medium-Dependent, and Twisted-Pair Distributed Data Interface are examples of FDDI specifications that use nonfiber optic connection.

Users connect the principal routers and devices to the network’s two rings in an FDDI network. Dual attachment stations are the name for these nodes. Single attachment stations allow users to link several nodes with a single fibre optic connection. FDDI can also be connected to other networks via different protocols, allowing for the creation of a wider WAN or the interconnection of multiple customers.

The history and application of the Fiber Distributed Data Interface

FDDI was a good option for big CANs and metropolitan area networks when it was developed in the late 1980s. Its relatively high speed of 100 Mbps was significantly faster than ordinary Ethernet’s 10 Mbps. Users could also use FDDI to connect servers to a single backbone network in a single server room.

FDDI-II is a variant of FDDI that adds the ability to bring circuit-switched service to a network, allowing for the transmission of voice and video signals. FDDI networks are being connected to the Synchronous Optical Network, which is being supplied as leased fibre optic lines.

FDDI has been mainly replaced by other networking technologies. Fast Ethernet, for example, provides the same speed at a reduced installation cost, but most firms employ Gigabit Ethernet and 10 Gigabit Ethernet server or workstation interconnects. Meanwhile, high-speed connections for end devices are being replaced by fibre to the workstation or passive optical networks, and newer fibre optic standards allow faster backbone interconnects.

How Does FDDI Work?

The Fiber Distributed Data Interface (FDDI) is often implemented as a dual token-passing ring within a ring topology (for campus networks) or a star topology (for enterprise networks) (within a building). A primary and secondary ring make up the dual ring. The data is carried on the primary ring. The counter-rotating secondary ring can carry data in both directions, but it is more typically used as a backup in the event that the primary ring fails. FDDI has the fault tolerance required for network backbones as a result of this. FDDI automatically reconfigures itself to use the secondary ring in the event of a primary ring loss, as indicated in the example. Beaconing is a fault isolation technique that can be used to discover and remedy faults.

The secondary ring, on the other hand, can be set to carry data, increasing the maximum possible bandwidth to 200 Mbps.

A media interface connector connects stations to one (or both) rings (MIC). Depending on the implementation, the two fibre ports can be male or female. Depending on whether stations are connected to one or both rings, there are two possible FDDI implementations:

  • Stations with only one connection (Class B stations):

M ports can be used to connect to either the primary or secondary ring. Single-attached FDDI employs only the primary ring and is not as common as dual-attached FDDI for network backbones. Single-attached stations are typically used to connect Ethernet LANs or single servers to FDDI backbones.

  • Stations with two connections (Class A stations):

Join the two rings together. The A port is where the primary ring enters and the secondary ring exits, whereas the B port is the opposite. For single-attached stations, M ports provide connection points. Both rings are used in dual-attached FDDI, with the secondary ring acting as a backup for the primary. FDDI with dual connections is generally utilised for network backbones that require fault tolerance.

A dual-attached device known as a concentrator or multiplexer can connect single-attached stations to dual-attached FDDI backbones.

FDDI employs a timed token-passing protocol similar to that of token ring networks as defined by IEEE 802.5. FDDI stations generate a token that determines how other stations acquire access to the wire in the future. The token moves from one node to the next as it moves around the ring. When a station wishes to send data, it captures the token, sends as many frames as it needs (within the defined access time), and then releases the token. In contrast to the priority system employed in the IEEE 802.5 token ring standard, this characteristic of delivering several data frames per token capture is known as a capacity allocation scheme. The frames are checked by each node on the ring.

The information from the frames is read by the recipient station, and the frames are stripped from the ring when they return to the originating station.

A dual-ring FDDI network can have up to 500 stations. An FDDI ring can have a maximum circumference of 100 kilometres (or 200 kilometres if both rings are merged), and repeaters must be spaced every 2 kilometres or less. To connect the FDDI backbone network to Ethernet or token ring departmental LANs, bridges or routers are used. For these reasons, FDDI is more commonly employed as a network backbone in campus-wide networks than as a wide area network (WAN) solution.

FDDI frames are used to encapsulate LAN traffic for transmission over FDDI backbones. An FDDI frame can have a maximum size of 4500 bytes.

One of three possible framing formats is used in FDDI implementations:

  • FDDI-raw: Cisco routers using Internetwork Operating System (IOS) versions 11.1 and later, as well as some third-party vendors, support this feature.
  • LLC and FDDI: IOS versions 10.0 and earlier are supported.
  • FDDI in conjunction with LLC and SNAP: FDDI’s default encapsulation format for Internetwork Packet Exchange (IPX) packets.
  • Copper Distributed Data Interface refers to FDDI that is done via copper cabling rather than fiber-optic cabling (CDDI). For an Ethernet or Token Ring network, FDDI is an excellent backbone. To improve server performance, connect your servers directly to the FDDI ring. When connecting Ethernet LANs to FDDI backbones, keep in mind that there are two types of bridges:
  1. Bridges encapsulated: FDDI frames can be encapsulated with Ethernet frames.
  2. Bridge translation: Convert the MAC addresses of the source and destination into FDDI addresses.

Incompatibilities between these two FDDI bridging technologies are possible. Cisco FDDI bridges, for example, can normally work with translating bridges from other vendors, but their encapsulation technology is proprietary and won’t work with encapsulating bridges from other companies. In FDDI networks, both types of bridging mechanisms are commonly utilised.

Passing of FDDI Tokens

Token passing on an FDDI network operates similarly to token passing on a Token Ring network: nodes carry a token around the ring, and only the node having the token is authorised to send a frame. This has a twist to it. That, however, is linked to FDDI fault tolerance. When a ring node senses an issue, it does not sit idle. Instead, it generates a beacon, which is a control frame that is sent to the network. When surrounding nodes notice the beacon, they, too, start transmitting beacons, and so on. When the node that started the process receives its beacon back, usually after the network has shifted to the secondary ring, it assumes the problem has been isolated or addressed, generates a new token, and restarts the process.

FDDI has a number of advantages.

  • Signals are transmitted via fibre optic cables over distances of up to 200 kilometres.
  • It is possible to meet the demand at the workstations linked to the chain.
  • As a result, a few stations are bypassed based on the requirement in order to provide faster service to the rest.
  • FDDI makes use of a variety of tokens to organise speed.
  • It has a greater capability for transmission (up to 250 Gbps). As a result, it can manage data speeds of up to 100 Mbps.
  • Because spying on the fiber-optic link is difficult, it provides high security.
  • Fiber optic cable is less likely to break than other types of cable.

FDDI’s disadvantages

  • FDDI is a complicated topic. As a result, setup and support necessitate a tremendous amount of knowledge.
  • FDDI is not cheap. Fiber optic cable, connections, and concentrators are typically extremely expensive.

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