An Introduction to FDDI (Fiber Distributed Data Interface)

What Is FDDI?

What is FDDI? FDDI is the abbreviation of the Fiber Distributed Data Interface. It is a set of ANSI and ISO standards for transmitting data in a local area network (LAN) through fiber optic cables. It is suitable for large LANs with a diameter of up to 200 kilometers. You can continue to read this post from MiniTool to get more detailed information about FDDI.

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The following are some features of FDDI.

• It provides a high data rate of 100 Mbps and can support thousands of users.
• It is used in a LAN of up to 200 kilometers for long-distance voice and multimedia communications.
• FDDI technology can also be used as the backbone of a wide area network (WAN).
• FDDI uses optical fiber as its physical medium.
• It runs in the physical and media access control (MAC layer) of the Open Systems Interconnection (OSI) network model.

The fields of an FDDI frame are as follows:

• Preamble: 1 byte for synchronization.
• Start Delimiter: 1 byte that marks the beginning of the frame.
• Frame Control: 1 byte that specifies whether this is a data frame or control frame.
• Destination Address: 2-6 bytes that specify the address of the destination station.
• Source Address: 2-6 bytes that specify the address of the source station.
• Payload: A variable-length field that carries the data from the network layer.
• Checksum: 4 bytes frame check sequence for error detection.
• End Delimiter: 1 byte that marks the end of the frame.

Besides, there are some FDDI standards. You can take reference.

• ANSI X3.139-1987: Media Access Control (MAC) – also ISO 9314-2.
• ANSI X3.148-1988: Physical Layer Protocol (PHY) – also ISO 9314-1.
• ANSI X3.229-1994: Station Management (SMT) – also ISO 9314-6.
• ANSI X3.166-1989: Physical Medium Dependent (PMD) – also ISO 9314-3.
• ANSI X3.184-1993: Single-Mode Fiber Physical Medium Dependent (SMF-PMD) – also ISO 9314-4.

How Does FDDI Work?

Now, let’s see how Fiber Distributed Data Interface works. FDDI is usually implemented as a dual-token transferring in a ring topology (for campus networks) or a star topology (inside buildings). The double ring is composed of the main ring and auxiliary ring.

The main ring carries data. A reverse-rotating auxiliary ring can transmit data in the opposite direction, but it is more common to reserve a backup ring to prevent the main ring from dropping. This provides FDDI with the degree of fault tolerance necessary for the network backbone.

If the primary ring fails, FDDI will automatically reconfigure to use the secondary ring. However, the auxiliary ring can also be configured to carry data, extending the maximum potential bandwidth to 200 Mbps.

The workstation is connected to one (or two) ring using the media interface connector (MIC). Depending on the implementation, its two fiber ports can be male or female. There are two different FDDI implementations, depending on whether the site is connected to one or two rings.

Single-attached stations (Class B stations): Use the M port to connect to the main ring or auxiliary ring. Single-link FDDI only uses the main ring, unlike the dual-link FDDI that is commonly deployed on the network backbone. A single connection station is mainly used to connect an Ethernet LAN or a single server to the FDDI backbone network.

Dual-attached stations (Class A stations): Connect to two rings. Port A is the point where the primary ring enters and the secondary ring leaves; port B is the opposite. M ports provide a connection point for a single connection station. Dual-link FDDI uses two rings, the auxiliary ring is used as a backup for the main ring. Dual connection FDDI is mainly used for network backbones that need fault tolerance.

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Final Words

What is FDDI? The first section tells you the definition and features of FDDI. Then, you can know how it works in the second part. Read here, you may have an overall understanding of FDDI. Hope the above information can be helpful for you. Here comes the end of the post.