PCI FDDI Administrator's Guide

PCI FDDI
FDDI Architecture
Chapter 1 21
A Timed Token Protocol (TTP) is used to control when a station can
transmit data to the network. A station can transmit until the message
is transmitted or until the TTP timer expires. This allows all stations
fair access to the ring. Once the message is sent or the timer expires, the
station generates a new token and releases it on the ring. Any
downstream station with data to send can capture the token and repeat
the timed-transmission cycle.
A dual ring configuration for the network media provides a secondary
backup ring in case of a fault on the primary ring. It is typically
implemented as a campus backbone or within buildings where a failure
in the primary ring would have serious consequences. A break in the
primary ring causes the two stations on each side of the fault to
automatically wrap the data to the secondary ring. Stations in a single
ring configuration can only attach to the primary ring. No secondary
backup path is available in the event of a failure.
The PCI FDDI standard pertains to the Physical and Data Link layers of
the OSI model.
FDDI Architecture
The following figure shows the FDDI architecture and the most
commonly used topologies.
Table 1-1 Physical and Data Link Layers - OSI Model
Data Link 802.2 Logical Link Control
(LLC)
Media Access Control - (MAC) Station
Management
Physical Physical Layer Protocol (PHY)
Physical Layer Medium
Dependent (PMD)