Traffic Policing Example

Rate-limit file-sharing application traffic to 56 kbps. Do not rate-limit traffic from mission-critical server.

You can use traffic policing to divide the shared resource (the upstream WAN link) between many flows. In this example, the router FastEthernet interface has an input traffic-policing policy applied to it, in which the mission-critical server traffic rate is not rate-limited, but the User X file-sharing application traffic is rate-limited to 56 kbps. All file-sharing application traffic from User X that exceeds the rate limit of 56 kbps will be dropped.

Example: Traffic Shaping

Traffic Shaping Example

Remote Sites

• Central to remote site speed mismatch

• Remote to central site over subscription

• Both situations result in buffering and in delayed or dropped packets

Traffic-shaping tools limit the transmit rate from a source by queuing the excess traffic. This limit is typically a value lower than the line rate of the transmitting interface. Traffic shaping can be used to account for speed mismatches that are common in nonbroadcast multiaccess (NBMA) networks such as Frame Relay and ATM.

In the figure, these two types of speed mismatches are shown:

■ The central site can have a higher speed link than the remote site. You can deploy traffic shaping at the central-site router to shape the traffic rate out of the central-site router to match the link speed of the remote site. For example, the central router can shape the permanent virtual circuit (PVC) outgoing traffic rate (going to the top remote-site router) to 128 kbps to match that remote-site link speed. At each remote-site router, traffic shaping is also implemented to shape the remote-site outgoing traffic rate to 128 kbps to match the committed information rate (CIR).

■ The aggregate link speed of all the remote sites can be higher than the central-site link speed, thereby over-subscribing the central-site link speed. In this case, you can configure the remote-site routers for traffic shaping to avoid oversubscription at the central site. For example, you can configure the bottom two remote-site routers to shape the PVC outgoing traffic rate to 256 kbps to avoid the central-site router from being over-subscribed.

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