Cabletron Systems MMAC-5FNB, Networking Manual

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Designing with the MMAC 4-29
Network Design
Figure 4-10. Chassis, Slots, and Modules
Power Redundancy
Fault-tolerance is also necessary in the supply of electrical power to the modular
chassis. The chassis supplies all modules with electricity. The supply of power in
the correct amperages and voltages for the modules in the chassis is performed by
modular power supplies. As power supplies have high demands placed upon
them by their operation, they are perhaps more susceptible to failure than other
components. Since they are also a key system of the chassis, the loss of a power
supply can mean a catastrophic chassis failure in the same way that a backplane
failure could. To reduce the danger of this occurrence, Cabletron Systems’ larger
MMAC chassis, the MMAC-M5FNB and MMAC-M8FNB, allow for the
configuration of redundant, load-sharing power supplies.
The use of the redundant power supplies gives additional tolerance to the system.
Simple redundancy means that two power supplies are available to the modules
in the chassis. One acts as the primary power supply, while the other remains in
standby. In the event that the primary power supply fails, the secondary power
supply senses its failure and takes over. While this is a valuable feature, it is a
flawed treatment of the problem. If the primary power supply is active while the
secondary is inactive, there is no way of knowing that the secondary power
supply is indeed functional. It also creates a short but significant length of time
that the chassis is without power between the failure of the primary power
supply and the warm-up and activation of the secondary power supply.
Module Guide Channels
MMAC-M8FNB
ETHERNET
C
O
M
2
SN
PRT1
XMT
XMT
XMT
XMT
XMT
XMT
RCV
RCV
RCV
RCV
RCV
RCV
1
2
3
4
5
6
1
2
3
4
5
RESET
RJ45
CH A
CPU
C
O
M
1
Module "slot"
Module
1706n20