Traffic shaping

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Traffic shaping, is an attempt to control computer network traffic in order to optimize or guarantee performance, low latency, and/or bandwidth. Traffic shaping deals with concepts of classification, queue disciplines, enforcing policies, congestion management, quality of service (QoS), and fairness. Recent BW needs from Internet users have led ISPs to also shape their traffic by blocking certain ports.

1 Summary
2 Benefits
3 BitTorrent
4 Rogers Communications
5 Uses
6 See also
7 References
8 External links

[edit] Summary

Traffic shaping provides a mechanism to control the 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 predominant 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.

[edit] Benefits

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

Less jitter.
Reduced packet loss.
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.

[edit] BitTorrent

In the last year many ISPs have begun using Traffic Shaping software to curb the usage of BitTorrent and other Peer-to-Peer filesharing protocols, such as DC and Soulseek. Nominally their reasoning behind these actions would be to decrease jitter and packet loss, but the truth of the matter is that many of them offer unlimited bandwidth at a certain speed and filesharing systems swallow a greater than anticipated amount of that bandwidth. Many have opted for traffic shaping (also referred to as "throttling") to manage the usage of this bandwidth, prioritizing web browsing and on-line gaming over Peer-to-Peer traffic and ftp downloads, either because they are unable to upgrade their bandwidth fast enough, or as an alternative to upgrading their bandwidth. The unfortunate side-effect to this system is it comes across as ISPs attempting to attack and stop Peer-to-Peer connections, a perfectly legal system of data transfer which many corporations use for their own purposes; for example, MAIET entertainment uses BitTorrent for GunZ The Duel updates and Blizzard Entertainment use BitTorrent for World of Warcraft updates. Note that these statements do not hold true for all ISPs, but it is entirely likely that many use traffic shaping specifically for the purposes of curbing Peer-to-Peer usage. Depending on the country and the copyright laws in question this could represent an infringement on certain freedoms.^{[citation needed]}

[edit] Rogers Communications

Canadian based Rogers Communications is currently being investigated by the CRTC due to their recent implementation of Traffic Shaping policies for their 2.3 million customers. A decision is expected in early 2008.

[edit] Uses

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.

[edit] See also

[edit] References

"Deploying IP and MPLS QoS for Multiservice Networks: Theory and Practice" by John Evans, Clarence Filsfils (Morgan Kaufmann, 2007, ISBN 0-123-70549-5)

^ 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.