3Com 3C780 User Guide - Page 31

Physical PHY Protocol, Media Access Control MAC Protocol

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Overview 1-5 Unshielded Twisted Pair (UTP) The ANSI TP-PMD standard provides these services for UTP: s Cable requirements for category 5 UTP as defined by EIA/TIA-568 s Electrical requirements for UTP transceivers s FDDI-UTP cable connector Physical (PHY) Protocol The Physical protocol is responsible for encoding and decoding of data and control information on the FDDI network. It specifies the following: s 4B/5B nonreturn to zero inverted (NRZI) encoding scheme (for fiber and STP modules) s MLT-3 with stream cipher encoding scheme (for UTP modules) s Clocking rules s Clocking frequency of 125 MHz s Serial-to-parallel conversion rules Media Access Control (MAC) Protocol The Media Access Control protocol controls the flow of data on the FDDI ring. The MAC typically exists in every hub and station accessed by the FDDI ring, but stations without MACs are allowed. This protocol specifies the following: s Token-passing protocol s Capture and retransmission of token s Packet formation and framing of data s Address generation and recognition s 32-bit cyclic redundancy check (CRC) verification and error detection s Recovery mechanisms

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1-5
Overview
Unshielded Twisted Pair (UTP)
The ANSI TP-PMD standard provides these services for UTP:
■
Cable requirements for category 5 UTP as defined by EIA/TIA-568
■
Electrical requirements for UTP transceivers
■
FDDI-UTP cable connector
Physical (PHY) Protocol
The Physical protocol is responsible for encoding and decoding of data and
control information on the FDDI network.
It specifies the following:
■
4B/5B nonreturn to zero inverted (NRZI) encoding scheme (for fiber and
STP modules)
■
MLT-3 with stream cipher encoding scheme (for UTP modules)
■
Clocking rules
■
Clocking frequency of 125 MHz
■
Serial-to-parallel conversion rules
Media Access Control (MAC) Protocol
The Media Access Control protocol controls the flow of data on the FDDI ring.
The MAC typically exists in every hub and station accessed by the FDDI ring,
but stations without MACs are allowed. This protocol specifies the following:
■
Token-passing protocol
■
Capture and retransmission of token
■
Packet formation and framing of data
■
Address generation and recognition
■
32-bit cyclic redundancy check (CRC) verification and error detection
■
Recovery mechanisms