Cisco 3825 - Manual (Page 38)

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Cisco 3825 Mobile Wireless Edge Router Software Configuration Guide
OL-15667-03
Chapter 1 Overview of the Cisco 3825 Mobile Wireless Edge Router
New Features in Cisco IOS Release 12.4(16)MR
UMTS Congestion Management Control
The purpose of Congestion management control is to protect the most important traffic when congestion
happens. Typically signaling and voice traffic are configured as the highest priority in QoS, and usually
you do not expect these two types of combined traffic to congest the backhaul. But, if it does happen,
some traffic will be dropped. The QoS on the Cisco 3825 router does not differentiate between signaling
and voice traffic, which means the packets will drop randomly. Dropping signaling traffic could have
much more severe results than voice traffic. If the RNC and Node B lose signaling communication, the
Node B device could be reset. Signaling traffic needs to be passed through during this time. Congestion
management control throttles any other traffic but the signaling traffic, thus leaving the backhaul
resource for signaling traffic.
Typically, UMTS Congestion Management Control protects the most important PVC traffic (usually
signalling pvc) during backhaul congestion. Each PVC can be configured with a congestion priority.
There are nine congestion control priority levels, protected and priority 2- 9. The protected priority has
the highest priority and priority 9 has the lowest priority.
When congestion happens, all other PVC traffic except protected PVC(s) traffic will be throttled to save
the backhaul resource for the protected PVC traffic. If after a certain period (200 ms) and there is no
congestion reported, a recovery mechanism is triggered. Recovery gradually includes back throttled
PVC traffic in the order of their congestion control priority level (priority 2 being first and 9 being last).
Recovery will unthrottle the traffic gradually every until all traffic is recovered or congestion happens
again.
It is recommended that you configure UMTS QoS as your first line of defense when congestion happens
so that the low priority/best effort traffic be dropped by the QoS during congestion. Congestion control
will be triggered when combining priority traffic (signalling and voice) congested backhaul, and it will
throttle relatively less important traffic (voice) to protect most important traffic (signaling) based on the
congestion control priority configuration.
With UMTS Congestion Management Control, you can configure the UMTS congestion based on
priority. Two new commands (umts-iub congestion priority and umts-iub congestion-control) are
added using the PVC Configuration mode and Interface Configuration mode, respectively (see
Appendix A, “Cisco 3825 Mobile Wireless Edge Router RAN-O Command Reference” ).
interface ATM0/IMA0
no ip address
atm bandwidth dynamic
atm umts-iub
no atm ilmi-keepalive
pvc 2/1 qsaal
umts-iub congestion priority protected
!
pvc 2/2
encapsulation aal0
umts-iub congestion priority protected
!
pvc 3/1
encapsulation aal0
umts-iub congestion priority 4
!
pvc 3/2
encapsulation aal0
umts-iub congestion priority 5
!
pvc 3/100
encapsulation aal2
!
umts-iub congestion-control
umts-iub set dscp 8