Traffic Shaping - Definition and Overview

In computer networking traffic shaping works by debursting traffic flows, that is smoothing the peaks and troughs of data transmission.

Simple traffic shaping example

• Before traffic shaping: 10 packets in one second, 0 packets in the next second, 10 packets in the next second, 0 packets the next second.
• After traffic shaping: 1 packet/0.2 seconds.

Benefits of traffic shaping

When much traffic flows past a packet bottleneck (logical or physical) the benefits of traffic shaping are:

• Less jitter.
• Less dropped packets.
• Smaller Lag

Additionally off-site networks queues, such as often found on the provider side of dial-in connections, don't get filled up. That way smaller pingtimes can be achieved if Traffic shaping is combined with some sort of Quality of Service classification system.

On/off behavior, especially with hysteresis, promotes packet-bursts:

• half duplex - link collisions make delay variations (jitter), because the packets are delayed with each collision by the backoff-time.
• Port queue buffer IEEE 802.3x "flow"-control.

Technologies commonly using traffic shaping

Traffic shaping is often used in combination with:

• Differentiated services, Integrated services - incl. traffic classification and prioritization.
• weighted round robin, WRR.
• RED, WRED - Lessens the possibility of port queue buffer tail-drops and this lowers the likelihood of TCP global synchronization.
• A number of port queue buffers.
• VLAN IEEE 802.1p and IEEE 802.1D.

See also

• Network congestion avoidance
• Quality of Service
• Bandwidth throttling
• Multilayer switch
• Rate limiting
• Token bucket
• Leaky bucket

External Links

• IT-world.com, Traffic Shaping (http://www.itworld.com/nl/sup_mgr/05142001/) Quote: "...Traffic shaping aims to decrease the burstiness of UDP and TCP traffic, thereby decreasing the load on the router and switch buffers as well as the latency jitter caused by long queues...."
• Traffic Shaping (http://www.cs.panam.edu/~meng/Course/CS6345/Notes/chpt-5/node23.html) Quote: "...Control the rate at which packets are sent (not just how many)..."
• Network World, 03/05/01: Where should traffic shaping occur? (http://www.nwfusion.com/newsletters/frame/2001/00477507.html)
• Network World, 03/07/01: WAN-side traffic shaping (http://www.nwfusion.com/newsletters/frame/2001/00477508.html)
• A Practical Guide to Linux Traffic Control (http://talk.trekweb.com/~jasonb/articles/traffic_shaping/)
• Traffic Shaping with Linux v2.4 and HTB qdisc (http://www.trekweb.com/~jasonb/articles/linux_tc_minihowto.shtml)
• Linux Advanced Routing and Traffic Control HOWTO (http://lartc.org/howto/index.html)
• cFosSpeed driver for Windows (http://www.cfos.com/techinfo/shape_e.htm)