Beta Draft Confidential
2-181/19/05 ATM Services Configuration Guide for CBX 3500, CBX 500, GX 550, and B-STDX 9000
About ATM Logical Ports
About Logical Port Bandwidth
Example
If you send 100% line rate traffic over an ATM DS3 interface that uses HCS direct
mapping, the cells arrive at a rate equal to 44209.694 Kbps or 104268.15 cps. Because
of NMS rounding, the maximum peak cell rate (PCR) you can provision for this PVC
is 104266. If you enable UPC on this PVC, approximately two cells every second are
lost. For these cases, you may want to either adjust the traffic rate or disable UPC for
this circuit.
Modifying Logical Port Bandwidth
You can modify logical port bandwidth on UNI and NNI logical ports even after you
configure PVCs on this port. However, if you reduce the logical port bandwidth such
that the new value is not sufficient to support all of the PVCs traversing the port, the
available bandwidth enters a negative state. The PVC remains active until it has to be
reestablished (that is, trunk reroute, IOM reboot). If at this time the logical port does
not have enough bandwidth to support the PVC, the PVC remains inactive due to
insufficient bandwidth.
CBX 500 SP Thread Bandwidth Available for Logical Ports
The NMS and CAC enforce the switch processor (SP) fabric thread bandwidth such
that each SP fabric thread is limited to 599.040 Mbps. This enforcement ensures that
service is guaranteed even when two IOMs are placed on the same SP fabric thread.
The 599.040 Mbps number is derived from the maximum user cell bandwidth that the
OC-12c/STM-4 interface supports (the OC-12c/STM-4 physical layer bandwidth is
622.080 Mbps, but the maximum user traffic that any OC-12c/STM-4 port can support
is 599.040 Mbps). This 599.040 Mbps thread limitation is also derived from the
maximum user cell bandwidth that the four OC-3c/STM-1 interfaces support (the
OC-3c/STM-1 physical layer bandwidth is 155.020 Mbps, but the maximum user
traffic that any OC-3c/STM-1 port can support is 149.76 Mbps).
For example, this NMS enforcement is noticeable whenever you attempt to provision
two OC-3c/STM-1 cards on the same SP fabric thread. As you provision logical ports,
the NMS subtracts the assigned bandwidth from the 599.040 Mbps total. After you
provision four OC-3c/STM-1 logical ports at the maximum 149.76 Mbps bandwidth
value, there is no bandwidth left for the other OC-3c/STM-1 card and its logical ports.
Because of this, when you use two cards on the same fabric thread, Lucent
recommends you allocate the bandwidth accordingly across all of the IOM ports.
Note – You can oversubscribe the logical ports to avoid any negative implications
associated with this restriction. You can use the QoS tab (accessible from the Add
Logical Port dialog box) to oversubscribe a logical port.
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