FDDI: Fiber Distributed Data Interface

(Fddi:fiber distributed Data Interface)

Optical Fiber Distributed Data Interface (FDDI) is a set of protocols that are developed by the United States National Standardization Organization (ANSI) to send digital signals on optical cables. FDDI uses a dual-loop token, with a transmission rate of up to 100Mbps. Because of its support for high-bandwidth and long-distance communication networks, FDDI is often used as a backbone network. CCDI is a variant of FDDI, which uses twisted-pair copper cables as a transmission medium with a data transmission rate usually 100Mbps.

FDDI-2 is an extended protocol for FDDI that supports voice, video, and data transmission. Another variant of FDDI, called FDDI Full-duplex Technology (FFDT), uses the same network structure as FDDI, but the transfer rate can reach 200Mbps.

FDDI uses a dual-loop architecture, and traffic on two loops travels in the opposite direction. The double ring consists of a main ring and a spare ring. Under normal circumstances, the main ring is used for data transmission and the standby loop is idle. As described later in this article, the use of double loops is intended to provide high reliability and robustness.

FDDI details the physical layer and media access layer of the OSI Reference Model. In essence FDDI is not a single specification, but consists of four parts, each with its own specific function. The parts together allow FDDI to provide high-speed connections between upper-layer protocols such as TCP/IP, IPX, and media such as optical cables.

FDDI Four sub specifications are media access control (MAC), Physical layer protocol layer (PHY), physical media related layer (PMD), and station management (SMT). The MAC prescribes how to access the media, including the frame format, addressing, token processing, cyclic redundancy check algorithm (CRC) and error recovery mechanism required by the Protocol. PHY prescribes the transmission coding and decoding procedures, clock requirements and other functions; PMD prescribes the characteristics of the transmission medium, including fibre link (fiber-optic link), power level, BER (bit-error rate), Fiber optic devices (optical component) and connectors (connector). SMT provides the characteristics of FDDI station configuration, ring configuration and loop control, including insertion and deletion of stations, start-up, fault separation and recovery, pattern arrangement and statistic collection.

Protocol structure

2	6	6	0-30	Variable	4 bytes
Frame Control	Destination Address	Source Address	Route Information	Information	Fcs

Frame control― The field structure is as follows:

C

L

F

F

Z

Z

Z

Z

C-Class bit: 0 asynchronous frames; 1 Sync Frames L address Length: 0 16 bits (never), 1 48 digits (always) FF Frame bit ZZZZ control bit Destination address― The Address field structure is as follows:

I/g

u/l

Address Bits

Source address― The Address field structure is as follows:

I/g>

Ui.

Address Bits

I/g Personal/Group address: 0 Group address; 1 person address Rii Routing Information indicator: 0 ri not in; 1 ri in The Route information― Routing information field structure is as follows:

3	5	1	6	1	16	16		16
Rt	LTH	D	LF	R	RD1	RD2	...	RDn

RC-Route Selection control (16-bit) RDn-Route Descriptor (16-bit) RT-Route Selection type (3-bit) LTH-Length (5-bit) D-Direction bit (1-bit) LF-Maximum frame (6-bit) R-Reserved (1-bit) The Information―information field may be an LLC, MAC, or SMT protocol. fcs― frame Check sequence.

Related agreements	IEEE 802.5
Organization Source	FDDI is x3t9.5 by ANSI (http://www.ansi.org).
RELATED LINKS	Http://www.cisco.com/univercd/cc/td/doc/cisintwk/ito_doc/fddi.htm:Fiber Distributed Data Interface