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So where would you use polices and where would you use shapers?

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Polices are generally used as ingress tools.

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In other words, the traffic is dropped before it's processed so that you don't waste a valuable resources.

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If a packet is going to be dropped anyway, you might as well drop it on the ingress or incoming interface

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of a router so that you don't waste valuable bandwidth and CPU cycles to move it from one interface

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to another, do a writing lookup and so forth, and then drop the packet.

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Polices can be used on egress to control the amount of traffic sent out of an interface, but are generally

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used to enforce a traffic policy on ingress.

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As an example, your service provider may have an ingress police to ensure that you don't send too much

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traffic.

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As an example, you could have paid for 100 megabits per second internet link, but the physical interface

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that connects you to your service provider could be gigabit Ethernet.

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So to ensure that you don't transmit more than a hundred megabits per second, the service provider

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on the ingress interface on the ISP side will implement a police to drop traffic that exceeds 100 megabits

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per second when traffic is exceeded.

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The police can either drop the traffic or remark the traffic.

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The disadvantage of a police is its dropping traffic which results in TCP resents.

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TCP is designed to retransmit traffic that's been dropped.

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So when a police is dropping a lot of traffic, it causes a lot of TCP transmissions or rescinds polices.

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Don't introduce jitter or delay because they simply drop the packet.

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They don't delay it with shapers introduce delay and jitter by slowing down packets or buffering them

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for a period of time before transmitting them.

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Shapers are a lot gentler than polices, so generally they are deployed between an enterprise customer

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and the service provider to ensure that you don't exceed the contracted rate.

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Again, using the example of a customer connected to a service provider via a gigabit interface, the

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customer will slow itself down under the 100 megabits per second threshold to ensure that it doesn't

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send traffic to the service provider who will simply drop.

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The traffic shapers result in fewer TCP transmissions because they're not dropping the traffic, they

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are delaying it or slowing the traffic down.

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So in summary, policing drops or remarks.

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It doesn't buffer, it causes TCP transmissions, it doesn't introduce data and delay.

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Shippers don't drop traffic.

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They delay the traffic.

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But that can result in additional delay or jitter.

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Shaping is a lot gentler on traffic.

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Policing is very harsh.

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Causes transmissions.