As mentioned in the chapter overview, a stateless filter can evoke a traffic policer action to rate limit traffic according to user-specified bandwidth and burst size settings. Rate limiting is a critical component of a CoS architecture and a primary mechanism for ensuring that a broad range of Service Level Agreements (SLAs) can be honored in a modern, multiservice internetwork. In such networks, it’s critical that you meter and limit ingress traffic flows to protect the shared resources in the network’s core to ensure that each subscriber does not consume excessive bandwidth, leading to poor performance for users that honor their contracts.

Rate Limiting: Shaping or Policing?

The basic idea of rate limiting is rather straightforward. The goal is to limit the amount of traffic that can be sent by a given device in a given unit of time. Simple enough from 20,000 feet, but there are several ways to achieve rate limiting, namely shaping versus policing. While both provide similar effects at the macro level, they have distinct operational differences that can be seen at the micro level when looking at the way packets are placed onto the wire. Most pronounced is shaping introduced delay in an attempt to control loss, making them better suited for use with TCP-based applications, while a policer does the opposite, trading loss for delay, making it better suited to real-time applications.


Traffic shaping attempts to reduce the potential for network congestion by smoothing ...

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