ANSI Standard X3T9.5

Application

Presentation

Session

Network

Data Link

Physical

Data Link

LLC

MAC

Media Access Control

Medium Addressing

Data Checking

Data Framing

Physical

PHY

Physical Layer Protocol

Symbol Coding/Decoding

Symbol Framing

Clock Rate

PMD

Physical Layer Medium Dependent

Power Levels

Transmitter

Receiver

Optical Interface

Connector Types

SMT

Station Management

Fault Isolation and Recovery

Station Configuration

Scheduling Procedures

Figure A-3. FDDI Structure and the OSI Network Model

The PMD standard establishes the physical characteristics of the network connection, including the fiber optic transmitter power levels, receiver sensitivity, the fiber optic cable type, the type of connectors, and acceptable losses between nodes. The PMD converts the optically encoded information that it receives to electrically encoded information and presents it to the PHY sublayer. The layers reverse this process when transmitting information.

The PHY entity implements the physical layer protocol. The PHY receives data frames from the MAC as a series of 4-bit symbols and encodes each 4-bit MAC symbol as a 5-bit symbol for transmission. This encoding occurs to ensure each symbol has at least two bit transitions for bit-cell synchronization at the remote receiver. Decoding reverses this process for the received frames.

BRIM-F6 User’s Guide

Page A-5

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Cabletron Systems manual Ansi Standard X3T9.5, BRIM-F6 User’s Guide A-5