Lucent Technologies CBX 3500 Configuration Manual page 807

Beta Draft Confidential
Allocating Logical Port Bandwidth on
CBX 500 Shared SP Threads
CBX 500 chassis slots 3-4, 5-6, 7-8, 9-1, 10-2, 11-12, 13-14, and 15-16 are associated
with the switch processor (SP) threads. This means that if you have an input/output
module (IOM) installed in slots 3 and 4, you are "sharing" an SP thread. If you have
an IOM in slot 9 or 10, you are sharing a thread with the SP itself. In this case, there
are no thread limitations; the IOM has the full 599.040 megabits per second (Mbps) of
bandwidth available.
If two IOMs share the same SP thread, the maximum user cell bandwidth available to
the two IOMs is 599.040 Mbps (599040 Kilobits per second [Kbps] or 1412830 cells
per second [CPS]). The NMS now enforces this limit such that the combined sum of
all logical port bandwidth on the two IOMs cannot exceed 599.040 Mbps. These
bandwidth limitations ensure the QoS guarantee even when you install two IOMs on
the same SP fabric thread. Even with this thread bandwidth enforcement, you may still
oversubscribe the VBR and UBR service classes on some or all of the IOM ports to
utilize the statistical multiplexing gains that are an inherent part of running with two
IOMs on one SP thread. However, you should carefully plan such oversubscription
according to the intended service offerings and network engineering considerations of
the different logical ports that share the thread.
The 599.040 Mbps number is derived from the maximum user cell bandwidth
supported by the OC-12/STM-4 interface. The OC-12/STM-4 physical layer
bandwidth is 622.080 Mbps, but the maximum user traffic bandwidth that any
OC-12/STM-4 port can support is 599.040 Mbps. This 599.040 thread limitation is
also derived from the maximum user cell bandwidth that the four OC-3/STM-1
interfaces can support. OC-3/STM-1 physical layer bandwidth is 155.020 Mbps, but
the maximum user traffic bandwidth that any OC-3/STM-1 port can support is 149.76
Mbps. Refer to
description of mapping physical port bandwidth to logical port bandwidth.
ATM Services Configuration Guide for CBX 3500, CBX 500, GX 550, and B-STDX 9000
"About Logical Port Bandwidth" on page 2-16
C
for a detailed
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