Traffic shaping

Traffic shaping works by debursting traffic flows. The result are smooth traffic flow rates.

Simple and crude traffic shaping example:

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

When many traffic flows passes a packet bottleneck (logical or physical) the benefit of traffic shaping are:

• Less jitter.
• Less dropped packets.

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.

Traffic shaping are 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-dropss and this lowers the likelihood of TCP global synchronization.
• A number of port queue bufferss.
• VLAN IEEE 802.1p and IEEE 802.1D.

See also:

• Network congestion avoidance
• Quality of Service
• Multilayer switch

External Links

• IT-world.com, Traffic Shaping 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 Quote: "...Control the rate at which packets are sent (not just how many)..."
• Network World, 03/05/01: Where should traffic shaping occur?
• Network World, 03/07/01: WAN-side traffic shaping
• Traffic Shaping with Linux v2.4 and HTB qdisc
• Linux Advanced Routing and Traffic Control HOWTO