CHAPTER 10. QoS186 © SAMSUNG Electronics Co., Ltd.Traffic PolicingPolicing controls the traffic by dropping packets or marking down theirpriority when the configured profile is exceeded. Shaping controls the trafficby delaying packets using a queuing mechanism when they arrive faster thanthe configured rate. Therefore shaping can smooth out the burstiness in a flow,helping to minimize buffer overruns in intermediate routers. Policing does notsmooth out bursts, but it can control bursts by dropping packets or markingthem down.Since shaping delays packets, thereby throttling the packet rate instead ofdropping them, adaptive applications(those using TCP) perform better.Dropping packets can cause exponential back off of TCP, which can adverselyaffect the throughput. This problem with policing can be minimized byconfiguring the burst parameter of the policer to be a sufficiently large value.Policing has the advantage of providing low latency since it does not queuepackets. This makes policing a good choice for interactive and streamingvoice and video applications. Policing also uses much less resources in therouter than shaping. It is a better method to provide QoS for incoming trafficon an interface.In the iBG2016 system, policing can be enabled in both the ingress and egressdirections, on the WAN interfaces, MAN interfaces, FE interfaces and the GEinterfaces on the main board. For LAN GE interfaces, traffic policing will bedone in hardware. The policing feature can be more appropriately described as‘Class Based Policing’. Traffic Policing can be enabled individually for eachtraffic class that defines a flow. This includes any inbound or outbound ‘leaf’class created on an interface. Policing can be enabled in either srTCM ortrTCM mode.The supported policing features in software enables to rate limit the trafficcorresponding to micro flow, aggregate flow, or behavior flow. For example,VLAN ID based policing can be enabled on ingress traffic by configuringtraffic class with VLAN ID is the classification key and setting appropriatepolicing parameters for traffic class. Similarly for application-based ratelimiting, configuring traffic class with application identifier as a classificationkey and configuring policing parameters for traffic class can achieve ratelimiting.
