Cabletron Systems MMAC-Plus 9G426-02, Руководство пользователя, Страница: 35 / 44

3-7
Operation
DC/DC Converter
The DC/DC converter converts the 48 VDC on the system power bus to the
necessary operating voltages for its host network services module. The diagnostic
controller monitors and controls the operation of the DC/DC converter.
INB Interface
The INB Backplane is designed to transport fixed length data blocks between
modules in the MMAC-Plus using a Time Division Multiplexing (TDM) design.
The MMAC-Plus INB bus delivers 2.0 Gbps of true data bandwidth with all
control and management communication being serviced on the 8 bit out-of-band
bus. The INB can time slice its bandwidth using one of three methods. The default
method is standard TDM round-robin bandwidth arbitration, the second method
is for modules to reserve a specific amount of bandwidth using MONARCH,
Cabletron’s INB Bandwidth Arbitrator, the third method permits the lowest slot
number to use any bandwidth not used by the previous two methods.
Arbitration for the backplane is accomplished in the INB Time Division
Multiplexing (ITDM) logic. The arbitration is a three-level scheme that ensures
that no one can get the backplane for more than one time slice at a time.
The ITDM RAM contains 256 4-bit locations. This RAM is used to hold slot
numbers of modules participating in INB backplane arbitration. The arbitration
engine accesses this RAM once every time slice to get a slot number. That slot
number will be granted access on the next time slice if it is requesting. The
arbitration engine is always one time slice ahead, meaning that the value read
from the RAM is for the next time slice, not the current time slice.
The RAM is programmed on system power-up or when ever a module is
inserted/removed from the MMACPlus chassis. There is a module discovery
program running that will detect these events. The amount of RAM to be used
and the position of the slot numbers in the RAM is determined by a higher level
system management program.
ITDM Arbitration Levels
The three levels of arbitration guarantee that a module will get its allocated
bandwidth plus some more depending on what levels of arbitration it is
participating in.