Traffic shaping
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Traffic shaping provides a mechanism to control the amount and volume of traffic being sent into a network (bandwidth throttling), and the rate at which the traffic is being sent (rate limiting). For this reason, traffic shaping schemes need to be implemented at the network edges to control the traffic entering the network. It also may be necessary to identify traffic flows at the ingress point (the point at which traffic enters the network) with a granularity that allows the traffic-shaping control mechanism to separate traffic into individual flows and shape them differently 1 .
Two pre-dominate methods for shaping traffic exist: a leaky-bucket implementation and a token-bucket implementation. Both these schemes have distinctly different properties and are used for distinctly different purposes.
In computer networking, traffic shaping works by debursting traffic flows, i.e. smoothing the peaks and troughs of data transmission.
A before-and-after example of how traffic shaping works is as follows.
- 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 per 0.2 seconds.
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Benefits
When lots of traffic flows past a packet bottleneck (logical or physical) the benefits of traffic shaping are:
- Less jitter.
- Less dropped packets.
- Lower latency.
Additionally, off-site network queues, such as often found on the provider side of dial-up connections, tend to fill up less quickly. Lower latency 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 — including traffic classification and prioritization.
- Weighted round robin (WRR)
- Random early detection (RED), Weighted RED (WRED) and RED In/Out (RIO) — 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
- Teletraffic Engineering in Broadband Networks
- Network congestion avoidance
- Quality of Service
- Bandwidth throttling
- Multilayer switch
- Rate limiting
- Token bucket
- Leaky bucket
- Broadband Networks
References
Note 1: Ferguson P., Huston G., Quality of Service: Delivering QoS on the Internet and in Corporate Networks, John Wiley & Sons, Inc., 1998. ISBN 0-471-24358-2.
External links
- IT-world.com, Traffic Shaping (http://www.itworld.com/nl/sup_mgr/05142001/)
- Traffic Shaping (http://www.cs.panam.edu/~meng/Course/CS6345/Notes/chpt-5/node23.html)
- 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://www.edseek.com/~jasonb/articles/traffic_shaping/)
- Traffic Shaping with Linux v2.4 and HTB qdisc (http://www.edseek.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)