Cisco 3825 Software Configuration Guide - Page 38

New Features in Cisco IOS Release 12.4(16)MR Chapter 1 Overview of the Cisco 3825 Mobile Wireless Edge Router 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 1-28 Cisco 3825 Mobile Wireless Edge Router Software Configuration Guide OL-15667-03