3Com CoreBuilder 7000 Operation Manual page 136

136 C 6: ATM S
HAPTER WITCHING
The EFCI bit in the Payload Type Identifier (PTI) field in the cell header is
set when congestion is encountered. The EFCI bit is set based on one of
the following defined output queue levels: 20% full, 50% full, 80% full.
These output queue levels can be configured only for the CoreBuilder
7000 (REV-C). For the CoreBuilder 7000HD, the level is hardcoded as
50%.
The EFCI function is only implemented on the low priority queue. When
the CoreBuilder 7000 family ATM switch receives notification of
congestion and the output queue levels defined are reached, it sets the
EFCI bit.
Priority Output Queues
The CoreBuilder 7000 ATM switch assigns its output queues two levels of
priority: high priority and low priority. It processes the address bits
associated with each cell and determines whether the associated cell is
loaded into the high priority or low priority queue. Each virtual circuit can
be connected through the high or low priority queues. High priority
channels are used for delay sensitive data. Each output port is serviced by
a high/low priority multiplexer that removes cells from the high and low
priority queues. The multiplexer always gives preference to high priority
cells.