Cabletron Systems TRMM-2, Руководство пользователя

Страница: 55 / 82

A-1
APPENDIX A
INTRODUCTION TO MULTIPLE-RING MMAC
FUNCTIONALITY
This appendix explains the closely related concepts of port switching and
the four-ring Flexible Network Bus (FNB). It also compares port
switching MIMs with single ring MIMs. The appendix concludes with a
sample configuration.
A.1 WHY USE MULTIPLE RINGS?
Port switching MIMs allow network users to be distributed among many
rings. The efficiency of a Token Ring network is increased by dividing
large numbers of users among multiple rings. A topology that groups
users among many small rings offers the following advantages:
• Provides more bandwidth for each station.
•
Reduces contention for the token.
•
Prevents the propagation of errors across the network.
A.2 THE FLEXIBLE NETWORK BUS (FNB)
The FNB is a data bus which spans the entire width of the MMAC. The
FNB contains four vertically stacked independent Token Rings. Only
port switching MIMs can access FNB Rings 2 through 4. The FNB
provides connectivity between MIMs on the same ring.
A.2.1 New Terminology
The four vertically stacked FNB rings are now referred to as FNB
Rings 1, 2, 3, and 4. Single ring MIMs (e.g., TRMIM-24A) can only
insert into and communicate across FNB Ring 1. This ring was referred to
in earlier manuals as the “FNB ring,” or simply “FNB.” The term “FNB”
now refers collectively to the channels and connectors of the MMAC
backplane’s communications bus which supports FNB rings,
interconnects MIMs, and carries all user-data.