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Traffic Shaping - WAN Optimization

Traffic shaping manages the volume of data sent to the network. The smaller the volumes, the better overall network performance – something all ISPs like. Traffic shaping can work in one of three ways:

  • Controlling volume of traffic during a specific time period – this is known as bandwidth throttling
  • Controlling the maximum rate at which traffic can be sent – this is called rate limiting
  • A complex algorithm called GCRA (Generic Cell Rate Algorithm) - this algorithm for traffic shaping is particularly useful in ATM (Asynchronous Transfer Mode) networks. It measures the timing of cells on virtual paths or channels and judges them against bandwidth and jitter limits in the desired traffic profile for that virtual path or channel. If the cells do not conform. Cells that do not conform can either be delayed or dropped to meet the desired profile.

Traffic shaping is usually applied at the edges of networks to control traffic coming into the network. Sometimes it may be applied at a source such as a computer or network card or by some element in the network. Policing of traffic is the related but distinct practice of dropping packets or marking them.

Traffic Shaping – Uses

Traffic shaping is very widely used for engineering network traffic and is resorted to by several ISPs as one of many Internet Traffic Management Practices (ITMPs). Some nodes in an IP network have the capability of buffering. In such instances, when the link is at capacity, and the node buffers traffic, it is considered a form of traffic shaping.

Traffic Shaping – Implementation

Traffic shaping is implemented around the concept of delaying metered traffic. This is done in such a way that each and every packet complies with the desirable traffic profile or contract. Metering of traffic is implemented with either the leaky bucket or token bucket algorithm. The leaky bucket algorithm finds favor in ATM networks whiles the latter in IP networks. Metered packets are cached in a buffer on a first in first out basis (FIFO) until they can be sent in compliance with the desired traffic profile or contract. If arriving traffic already meets desired profile compliance, they may be transmitted immediately or after some delay in the buffer till its scheduled transmission time or never when buffer overflow happens.

Traffic shaping is limited by the finiteness of its buffer. When the buffer is full, packets will be dropped. An approached that is commonly used to handle this to drop any traffic that arrives after the buffer is full or the use of a dropping algorithm such as Random Early Discard (RED) or just allowing traffic to bypass without traffic shaping.

Traffic Shaping – Classification of Traffic

Traffic classification is a method of categorizing traffic on things such as port number or protocol. Each class can be shaped differently and separately to match the desired traffic profile.

Traffic Management

Unfortunately, the word traffic shaping is confused and often interchanged and confused with the traffic management. Traffic shaping is a specific technique and is one of many that comprise the gamete of traffic management. Anything that an ISP does to limit of manage traffic entering their networks is tagged by most users as traffic management.

Internet Service Providers (ISPs) – Traffic Management

ISPs love traffic shaping because it reduces the loads on their network. ISPs have high traffic expensive networks and limiting loads by any user assists them in keeping moderate users happy by making as much of bandwidth as possible available. ISPs either intelligently shape traffic by importance and sometimes in a rather harsh manner by discouraging use of certain applications.

Classification of traffic allows ISPs to intelligently shape traffic which allows them to profile desirable customers and their traffic habits while denying or penalizing the undesirable ones. Many object to this because they believe and hold the position that the ISP should not be the one who decides desirable andf important traffic and all traffic should flow unimpeded.

Traffic Shaping in the Corporate Environment

Traffic shaping is being increasingly practiced by corporations. Corporations usually have wide area networks and increasingly applications and data is centrally located. As more and more bandwidth hungry applications are deployed and coupling this with the high cost of dedicated circuits has made corporate rethink their network strategy. A part of this revaluation is the trend towards traffic shaping. Traffic shaping is a means of reducing the need for increasing bandwidth.