5-121/19/05 ATM Services Configuration Guide for CBX 3500, CBX 500, GX 550, and B-STDX 9000
BCM Closed-loop Flow Control
Beta Draft Confidential
BCM Cell Termination
When you configure the FCP to terminate BCM cells, the FCP decides whether to
increase or decrease the ACR. This decision
is based upon one or more of the
following conditions:
• The local port congestion state
• The current ACR being above the fair bandwidth for the VC
• Whether or not any BCM cells were received within the RM cell generation
interval
The fair bandwidth for a VC is the proportional allocation of the total bandwidth for
managed (non-real time) circuits, based on the MCR of the VC relative to all of the
managed VCs. The total, non-real time bandwidth is the total port bandwidth, less the
bandwidth allocated to unmanaged (real-time) circuits and point-to-point Non-Real
Time (NRT) circuits.
Note that the FCP can increase the ACR well beyond its fair bandwidth. Once other
circuits attempt to use that bandwidth (which causes a congestion condition), the FCP
will throttle back the ACR towards the fair bandwidth for the circuit until the
congestion condition is removed.
For general RM cell termination considerations, see “RM Cell Termination” on
page 5-6.
Note – If BCM cells are received, but the port is not configured for BCM termination,
the BCM cells are forwarded.
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