Information Technology Reference
In-Depth Information
Figure5-6
The Use of an Optical Bypass Switch
Station 1
Station 1
Failed station
A
B
B
A
Optical bypass switch
“bypassed configuration”
Optical bypass switch
“normal configuration”
Ring does
not wrap
Station 4
Station 2
Station 4
Station 2
A
A
A
A
B
B
B
B
AB
AB
Station 3
Station 3
Critical devices such as routers or mainframe hosts can use another fault-tolerant technique called
dual
homing
to provide additional redundancy and help guarantee operation. In dual-homing situations, the
critical device is attached to two concentrators. One pair of concentrator links is declared the active link;
the other pair is declared passive. The passive link stays in backup mode until the primary link (or the
concentrator to which it is attached) is determined to have failed. When this occurs, the passive link is
automatically activated.
Frame Format
FDDI frame formats (shown in Figure 5-7) are similar to those of Token Ring.
