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traffic shaping

By Andrew Froehlich

What is traffic shaping?

Traffic shaping, also known as packet shaping, is a congestion management method that regulates network data transfer by delaying the flow of less important or less desired packets. Network professionals can control traffic flow with the following methods:

Network professionals use traffic shaping to optimize network performance by prioritizing certain traffic flows to ensure the traffic rate doesn't exceed the bandwidth limit. In addition to bandwidth, three major factors affect the quality of a network: latency, jitter and loss.

Traffic shaping attempts to prevent delay, jitter and loss by controlling the burst size and uses a leaky bucket algorithm to smooth the output rate over at least eight time intervals. If traffic arrives slower than the configured rate, it will forward normally. If traffic arrives faster than the configured rate, it will hold in a buffer until it can travel without going over the limit.

What is traffic shaping used for?

Traffic shaping is a quality of service (QoS) technique configured on network interfaces to enable higher-priority traffic to flow at optimal levels even when links become overutilized. Traffic shaping creates a bandwidth limit for less critical packets and, in turn, lessens the possibility for more important packets to delay or drop as they leave the interface.

Common uses of traffic shaping include the following:

Importance of traffic shaping

Traffic shaping is important when network uplinks become congested with data traveling out of an interface. Without traffic shaping, networks can drop or queue any excess traffic that can't travel out of an interface, and this can cause delays in all packets or result in poor performance of mission-critical applications.

Traffic shaping enables network administrators to specify which applications are less important and, therefore, creates intelligence around which packets will drop or delay first. Overall, traffic shaping is an important traffic management technique to ensure high network performance.

Traffic shaping methods

Traffic shaping can only occur on packets leaving interface as opposed to those coming into the interface. The network device can use several different methods to identify to which application an IP packet exiting an interface belongs. Based on this information, the interface can drop or hold these specific packets inside a temporary queue until a certain bandwidth limit has been reached.

Traffic shaping uses a leaky bucket algorithm to eventually release the delayed packets for delivery. While this may increase latency, it's usually more efficient compared to dropping the packets.

Traffic shaping methods include the following:

Traffic shaping vs. traffic policing

Traffic shaping affects packets leaving an interface. The network temporarily stores packets deemed less important in a buffer queue and sends them out more slowly with a leaky bucket technique.

On the other hand, network professionals can configure traffic policing for traffic that exits and enters an interface. Policing will simply drop packets as opposed to storing them in a temporary queue, so policing is less efficient in most cases.

Traffic shaping and net neutrality

Traffic shaping is a frequent topic of debate between advocates of net neutrality and proponents of a two-tiered system. Advocates of net neutrality argue that users should treat internet data packets impartially, without regard to their content, destination or source. They also argue that it's difficult to delay some types of traffic without unintentionally hampering others.

On the other hand, proponents of a two-tiered system argue that there have always been different levels of internet service and a two-tiered system can enable more freedom of choice and promote internet-based commerce.

Editor's note: This article was republished in November 2022 to improve the reader experience.

22 Nov 2022

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