Specifications

A.1 Configuration Guidelines and Rules
A–2 FDDI Configuration Capabilities
A.1 Configuration Guidelines and Rules
This section details the configuration capabilities that are supported in the DEChub
900 family of FDDI products.
A.1.1 Individual FDDI Networks
Individual FDDI networks can be configured as either a dual ring or a tree. This
allows compliancy with FDDI configuration rules which operate at the module level
and are independent of MultiChassis Manager.
A.1.2 Multiple FDDI Networks
In DEChubs supporting multiple FDDI networks on the backbone, some of the net-
works can be configured as dual rings and others can be configured as trees, but each
of the individual networks can be of only one type. Dual rings of trees can be con-
structed by interconnecting the various networks across the front panel.
A.1.3 Single Attachment Concentrator (SAC)
Digital’s DEChub 900 family of FDDI products include Single Attach Concentrators
(SACs) and Dual Attach Concentrators (DACs). A SAC has one S port and can have
up to 15 M ports. A DAC has an A and B port, and can have up to 14 M ports.
Implications:
FDDI rules specify that stations with M ports are concentrators. Consequently, when
a FDDI switch (such as, a DECswitch 900EF or a PEswitch 900TX) is configured
with M and S ports, it reports as a concentrator in FDDI NIF (Neighbor Information
Field) and SIF (Signaling Information Field) frame, and in the FDDI and SNMP
MIBs.
MultiChassis Manager, FDDI monitors, and FDDI Ring Maps announce the station
type of a treed DECswitch 900EF or PEswitch 900TX as a Single Attach Concentra-
tor (SAC), rather than as a Single Attach Station (SAS).
A.1.4 Dual Ring and Trees
The terms, Dual Ring and Tree, are physical descriptions of the network topology.
However, in all cases, the FDDI is a logical ring that enables a token to be passed
from station-to-station in the ring. The physical implementation can be configured as
a tree or a dual ring, but in all cases a logical ring exists.