Closed-loop Flow Control
ATM Services Configuration Guide for CBX 3500, CBX 500, GX 550, and B-STDX 9000 1/19/055-5
Beta Draft Confidential
Closed-loop Flow Control
Lucent’s closed-loop, flow control architecture is based on hop-by-hop control loops
with binary feedback. The hop-by-hop control loops push congestion at central nodes
to switches at the edge of the network, thereby providing more efficient use of
network bandwidth. In addition, with less network congestion at central nodes, there is
increased network throughput.
Flow Control Mechanisms
The ATM FCP supports three closed-loop, flow control mechanisms:
Cascade Communications Resource Management (CCRM) Cells — A subset of
the ABR RM cells described in the ATM Forum’s ATM Traffic Management
Specification, Version 4.0. The Protocol ID field in each RM cell is defined as the
CCRM ID, indicating that it is a CCRM cell. The default value for the CCRM ID is
always set at a value of 6 and cannot be modified. Refer to “Enabling the FCP” on
page 6-2 for more information about CCRM cells.
Backward Congestion Message (BCM) Cells — Provide a different RM cell
mechanism and may also provide interoperability with non-Lucent ATM switches.
The Protocol ID field in each BCM cell is defined as the BCM ID. The default value
for the BCM ID is always set at a value of 5 and cannot be modified. Refer to
“Enabling the FCP” on page 6-2 for more information about BCM cells.
Available Bit Rate (ABR) RM Cells — The Protocol ID for an ABR RM cell is
one (1). The ATM FCP identifies any RM cell with a Protocol ID of 1 as an ABR RM
cell. ABR RM cells received by a Lucent switch will be passed transparently through
the network.
Note – Because the FCP communicates with both CCRM and BCM cells for
hop-by-hop control loops, CCRM and BCM cells are both configured within a single
network to allow for conversion between one closed-loop, flow control algorithm to
another.
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