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Traffic shaping
Traffic shaping (also known as "packet shaping") is a computer network traffic management technique which delays some or all datagrams to bring them into compliance with a desired ''traffic profile''.〔(IETF RFC 2475 ) "An Architecture for Differentiated Services" section 2.3.3.3 - Internet standard definition of "Shaper"〕〔(ITU-T Recommendation I.371: Traffic control and congestion control in B-ISDN ) Section 7.2.7 defines traffic shaping as a ''traffic control mechanism'' which "alters the traffic characteristics of a stream of cells on a VCC or
a VPC to achieve a desired modification of those traffic characteristics, in order to achieve better network efficiency whilst meeting the QoS objectives or to ensure conformance at a subsequent interface. ... Shaping modifies traffic characteristics of a cell flow with the consequence of increasing the mean cell transfer delay."〕 Traffic shaping is used to optimize or guarantee performance, improve latency, and/or increase usable bandwidth for some kinds of packets by delaying other kinds. It is often confused with traffic policing, the distinct but related practice of packet dropping and packet marking.〔 Graphs illustrate differences in typical output〕
The most common type of traffic shaping is application-based traffic shaping.〔Detecting BitTorrent Blocking, ACM Internet Measurement Conference 2008, http://dl.acm.org/citation.cfm?id=1452523〕 In application-based traffic shaping, fingerprinting tools are first used to identify applications of interest, which are then subject to shaping policies. Some controversial cases of application-based traffic shaping include P2P bandwidth throttling. Many application protocols use encryption to circumvent application-based traffic shaping. Another type of traffic shaping is route-based traffic shaping. Route-based traffic shaping is conducted based on previous-hop or next-hop information.〔Ascertaining the Reality of Network Neutrality Violation in Backbone ISPs, ACM HotNets 2008, http://research.microsoft.com/apps/pubs/default.aspx?id=136790〕
==Functionality==
If a link becomes saturated to the point where there is a significant level of contention (either upstream or downstream) latency can rise substantially. Traffic shaping can be used to prevent this from occurring and keep latency in check. Traffic shaping provides a means to control the volume of traffic being sent into a network in a specified period (bandwidth throttling), or the maximum rate at which the traffic is sent (rate limiting), or more complex criteria such as GCRA. This control can be accomplished in many ways and for many reasons; however traffic shaping is always achieved by delaying packets. Traffic shaping is commonly applied at the network edges to control traffic entering the network, but can also be applied by the traffic source (for example, computer or network card〔IEEE INFOCOM 2001. Arsenic: a user-accessible gigabit Ethernet interface Pratt, I., Fraser, K., Computer Laboratory, Cambridge University; Twentieth Annual Joint Conference of the IEEE Computer and Communications Societies. Proceedings 2001 Volume 1, pages: 67-76 vol.1. Describes a gigabit Ethernet NIC with transmit traffic shaping.〕) or by an element in the network.
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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