Policing drops or marks packets when a predefined limit is reached

Policing or shaping mechanisms are often used to condition traffic before transmitting traffic to a network or receiving traffic from a network.

Policing is the ability to control bursts and conform traffic to ensure that certain types of traffic get certain types of bandwidth.

Policing drops or marks packets when predefined limits are reached. Policing mechanisms can be set to first drop traffic classes that have lower QoS priority markings.

Policing mechanisms can be used at either input or output interfaces. These mechanisms are typically used to control the flow into a network device from a high-speed link by dropping excess low-priority packets. A good example would be the use of policing by a service provider to throttle a high-speed inflow from a customer that was in excess of the service agreement. In a TCP environment, this policing would cause the sender to slow its packet transmission.

Tools include class-based policing and committed access rate (CAR).

Note The tools for policing are covered in detail in the "Traffic Policing and Shaping" module in this course.

Shaping queues packets when a predefined limit is reached.

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Shaping helps smooth out speed mismatches in the network and limits transmission rates.

Shaping mechanisms are used on output interfaces. These mechanisms are typically used to limit the flow from a high-speed link to a lower-speed link to ensure that the lower-speed link does not become overrun with traffic. Shaping could also be used to manage the flow of traffic at a point in the network where multiple flows are aggregated. Service providers use shaping to manage the flow of traffic to and from customers to ensure that the flows conform to service agreements between the customer and provider.

Cisco QoS software solutions include two traffic-shaping tools to manage traffic and congestion on the network: Generic Traffic Shaping (GTS) and Frame Relay traffic shaping (FRTS).

Note The tools for shaping are covered in detail in the "Traffic Policing and Shaping" module in this course.

Link Efficiency Mechanisms

This topic describes the functions of compression and identifies where compression is commonly implemented in the network.

Compression

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