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.

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[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 are commonly implemented at the network edges to control traffic entering the network. This control can be accomplished in many ways for many reasons.

Simple traffic shaping schemes like leaky bucket and token bucket rely on shaping all traffic uniformly by rate. More sophisticated techniques identify traffic using various means (matching bit patterns of data to those of known protocols is a simple, yet widely-used technique. An example to match the BitTorrent Protocol Handshaking would be a simple check to see if a packet began with character 19 which was then followed by the 19-byte string 'BitTorrent protocol'.[1]) and, upon identifying a traffic flow using a particular protocol, applies a policy on it and other flows to either guarantee a certain quality (as with VoIP) or to provide best-effort delivery. This may be applied 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].

[edit] ISPs

Traffic shaping is of interest especially to Internet Service Providers (ISPs). Their high-cost, high-traffic networks are their major assets, and as such, are the focus of all their attentions. They often use traffic shaping as a method to optimize the use of their network (sometimes by intelligently shaping traffic according to importance, other times by discouraging uses of applications by harsh means).

[edit] Benefits

To ISPs, mere protocol identification (a large part of modern traffic shaping mechanisms) gives the intangible yet significant benefit of seeing what internet traffic is flowing through the network. From this they can see which subscribers are doing what on their network and can target services to the subscriber base they have attracted.

In addition, intelligent shaping schemes can guarantee a particular Quality of Service (often measured in jitter, packet loss, and latency) for an application or a user while still allowing other traffic to use all remaining bandwidth. This allows ISPs to offer Differentiated services and to upsell existing services to subscribers (such as offering minimum-latency computer gaming for an additional fee on top of basic internet).

[edit] Three Types of Traffic

Internet traffic as viewed by ISPs can be thought of as placed into three categories: Sensitive, Best-Effort, and Undesired.

[edit] Sensitive Traffic

Sensitive traffic is traffic whose Quality of Service ISPs care about. This usually includes VoIP, online gaming, video streaming, and web surfing, but basically any application or protocol could fall under this umbrella. Shaping schemes are generally tailored in such a way that the Quality of Service of these selected uses is guaranteed, or at least prioritized over other classes of traffic. This can be accomplished by the absence of shaping schemes on these, or by positive shaping (prioritization over others).

[edit] Best-Effort Traffic

Best effort traffic is, in most western countries, all other kinds of non-detrimental traffic. This is traffic that is either not sensitive to Quality of Service metrics (jitter, packet loss, latency) or traffic that is, and the ISP is not concerned about its Quality of Service. A typical example of the former would be peer-to-peer traffic, the latter: online gaming (though there are exceptions such as [2]). Shaping schemes are generally tailored in such a way that this traffic gets 'what is left' of the bandwidth after sensitive traffic has 'taken its share'.

[edit] Undesired Traffic

In western countries, this category is generally limited to the delivery of spam and traffic created by worms, botnets, and other malicious attacks. In other countries, this definition can (and does) expand to such traffic as non-local VoIP (Skype) or video streaming services, which are squelched to create a market for the 'in-house' services of the same type. Shaping schemes usually involve identifying and blocking this traffic entirely, or just by severely hampering its operation. Rogers Communications in Canada has been accused of applying this type of shaping to peer-to-peer traffic in violation of CRTC regulations.[citation needed]

[edit] Peer-To-Peer

Peer-to-peer (P2P) traffic is particularly troublesome for traffic shaping efforts for ISPs because it is designed to use any and all available bandwidth which impacts QoS-sensitive applications (like online gaming) that use comparatively small amounts of bandwidth. That most (Gnutella, BitTorrent), if not all, popular P2P applications are location-agnostic (they care not/little if they download from a user halfway around the world or one next door) makes them even more problematic, as transfer costs as flows travel outside of a network will increase.

This has given P2P a bad reputation with internet service providers trying to roll out quality-dependent services (again, like VoIP). Some may even view P2P as an 'attack' on their networks (speculative, but not unreasonable).

However, P2P is often listed as the reason subscribers choose broadband internet. Recent figures show that the usage of one-fifth of the highest-usage subscribers must be added together to make up only close to 80% of P2P traffic on ISP networks. [3] Sandvine Incorporated, a company that provides intelligent network solutions, has also determined through traffic analysis that P2P traffic accounts for up to 60% of traffic on most networks. This shows, in contrast to previous studies and forecasts, that P2P has become more mainstream than just the four or five script kiddies on the network: there is over 20% of P2P bandwidth spread out over the entire lower-usage subscriber base.

These figures have influenced forward-thinking service providers to consider subscriber experience when implementing traffic shaping. If P2P is being used by more than the top fifth of an ISP's subscriber base, implementing a harsh anti-P2P policy will have disastrous consequences on subscriber numbers, increasing the subscriber Churn rate. In some extreme cases (like that of Rogers Communications and ihaterogers.ca) this may damage the ISPs reputation permanently.

That P2P protocols are designed specifically to avoid being identified and with enough robustness that it is agnostic to standard QoS metrics (out-of-order packets (jitter) just increase buffering, packet loss and latency just increase the download time) means that it is best classified as Best-Effort traffic. At peak times when sensitive traffic is at its height, download speeds will decrease. However, since P2P downloads are often background activities, it affects the subscriber experience little, so long as the download speeds increase to their full potential when all other subscribers hang up their VoIP phones.

[edit] Uses

Traffic shaping is often used in combination with:

[edit] See also

[edit] Companies With Products Employing Traffic Shaping

[edit] Major Internet Service Providers Using Traffic Shaping

[edit] References

  • "Deploying IP and MPLS QoS for Multiservice Networks: Theory and Practice" by John Evans, Clarence Filsfils (Morgan Kaufmann, 2007, ISBN 0-12-370549-5)
  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.
  • "Peer-to-Peer File Sharing: The Impact of File Sharing on Service Provider Networks", Sandvine Incorporated, copyright 2002

[edit] External links

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