18-12-2012, 12:11 PM
Fiber Distributed-Data Interface (FDDI)
1Fiber Distributed.pptx (Size: 133.36 KB / Downloads: 26)
Introduction
a standard for data transmission on fiber optic lines in that can extend in range up to 200 km (124 miles)
protocol is based on the token ring protocol
An FDDI network contains two token rings, one for possible backup in case the primary ring fails. The primary ring offers up to 100 Mbps capacity. If the secondary ring is not needed for backup, it can also carry data, extending capacity to 200 Mbps. The single ring can extend the maximum distance; a dual ring can extend 100 km (62 miles)
functions
100-Mbps token-passing, dual-ring LAN using fiber-optic cable.
CDDI is the implementation of FDDI protocols over twisted-pair copper wire
FDDI uses a dual-ring architecture with traffic on each ring flowing in opposite directions (called counter-rotating)
Specifications
FDDI's four specifications are :
the Media Access Control (MAC),
Physical Layer Protocol (PHY),
Physical-Medium Dependent (PMD),
Station Management (SMT)
The MAC specification defines how the medium is accessed, including frame format, token handling, addressing, algorithms for calculating cyclic redundancy check (CRC) value, and error-recovery mechanisms
The PHY specification defines data encoding/decoding procedures, clocking requirements, and framing, among other functions
The PMD specification defines the characteristics of the transmission medium, including fiber-optic links, power levels, bit-error rates, optical components, and connectors
The SMT specification defines FDDI station configuration, ring configuration, and ring control features, including station insertion and removal, initialization, fault isolation and recovery, scheduling, and statistics collection.
FDDI Station-Attachment Types
One of the unique characteristics of FDDI is that multiple ways actually exist by which to connect FDDI devices. FDDI defines three types of devices: single-attachment station (SAS), dual-attachment station (DAS), and a concentrator.
An SAS attaches to only one ring (the primary) through a concentrator. One of the primary advantages of connecting devices with SAS attachments is that the devices will not have any effect on the FDDI ring if they are disconnected or powered off. Concentrators will be discussed in more detail in the following discussion.
Each FDDI DAS has two ports, designated A and B. These ports connect the DAS to the dual FDDI ring. Therefore, each port provides a connection for both the primary and the secondary ring. As you will see in the next section, devices using DAS connections will affect the ring if they are disconnected or powered off..
An FDDI concentrator (also called a dual-attachment concentrator [DAC]) is the building block of an FDDI network. It attaches directly to both the primary and secondary rings and ensures that the failure or power-down of any SAS does not bring down the ring. This is particularly useful when PCs, or similar devices that are frequently powered on and off, connect to the ring