3Com 3C780 User Guide - Page 30

Physical Medium Dependent PMD Protocol

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1-4 Overview Physical Medium Dependent (PMD) Protocol The Physical Medium Dependent protocol provides all of the services necessary to exchange data across the cable medium. PMD also specifies an optional optical bypass facility that enhances reliability. This bypass capability is invoked when an FDDI station is powered off. (For information on the optical bypass switch, see Chapter 2, "Installing the Hub.") The PMD services included for each type of media supported by the LinkBuilder FDDI Workgroup Hub are listed below. Fiber-Optic The PMD standard provides these services for fiber media: s Optical power and cable requirements for 62.5/125 µm fiber-optic cables s Power requirements for optical bypass switches and fiber-optic transceivers s FDDI cable connector (the Media Interface Connector [MIC]), mating requirements, and keying s Light wavelength of 1300 nm (nanometers) Shielded Twisted Pair (STP) The PMD standard uses the SDDI de facto standard and provides these services for STP: s Transmit signal amplitude of 350-700 mV, peak-to-peak s Cable fault detect s DB-9 cable connector, specifying M as a male connector and A, B, and S as female connectors

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1-4
Overview
Physical Medium Dependent (PMD) Protocol
The Physical Medium Dependent protocol provides all of the services necessary
to exchange data across the cable medium.
PMD also specifies an optional
optical bypass facility that enhances reliability.
This bypass capability is
invoked when an FDDI station is powered off.
(For information on the optical
bypass switch, see Chapter 2, “Installing the Hub.”)
The PMD services included for each type of media supported by the
LinkBuilder FDDI Workgroup Hub are listed below.
Fiber-Optic
The PMD standard provides these services for fiber media:
■
Optical power and cable requirements for 62.5/125 μm fiber-optic cables
■
Power requirements for optical bypass switches and fiber-optic transceivers
■
FDDI cable connector (the Media Interface Connector [MIC]), mating
requirements, and keying
■
Light wavelength of 1300 nm (nanometers)
Shielded Twisted Pair (STP)
The PMD standard uses the SDDI de facto standard and provides these services
for STP:
■
Transmit signal amplitude of 350–700 mV, peak-to-peak
■
Cable fault detect
■
DB-9 cable connector, specifying M as a male connector and A, B, and S
as female connectors