Dual-Homed Single-Attached Station - Cabletron Systems 3F00-01 User Manual

Chapter 2: Connecting to the Network

2.1.2 Dual-homed Single-attached Station

Dual-homing is a method of connecting concentrators and stations that
permits an alternate or backup path to the dual ring in case the primary
connection fails.
The connection is normally made via dual-attached concentrators (DACs)
which are connected to both the primary and secondary FDDI rings.
Other FDDI stations or concentrators are connected to the DAC master
(M) ports.
Figure 2-2 shows the ATX, with a 3F00-01 installed, connected to the
master ports of two DACs.
Network
DAC 1 DAC 2
M M
M M M
M
SAS SAS
SAS SAS
Port A Port B ATX
FastNET ATX
PACKET PROCESSING ENGINE
NMS PORT POWER
FDDI MIC A OPTICAL BYPASS FDDI MIC B
RING A RING B
1876 05
Figure 2-2 Dual-homed Single-attached Configuration
In this configuration, the ATX accesses the FDDI ring through port B and
DAC 2. FDDI standards for DASs such as the ATX state that if the B port
cannot be used, the device will automatically use its A port. Therefore, if
DAC 2 fails, the ATX is still connected to the ring through port A
(DAC 1).
FDDI Dual-Attached Intelligent Module User's Guide Page 2-3