DSL Load Balancing

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DSL load balancing is balance traffic among multiple DSL lines, which is usually used to increase Internet access speed and provide redundancy and fault tolerance of Internet links.

Here we define that DSL load balancing is different from link aggregation, link aggregation works at layer-2, and DSL load balancing works at layer-4. Link aggregation requires two endpoint devices of multiple links support aggregation feature. Unfortunately, most ADSL service providers do not support link aggregation, or two links from different service providers are used for fault tolerance and performance, then DSL load balancing is the solution.

Working Principle

When there is a new outbound connection request for external access, such as request to retreive a web page, DSL load balancer automatically selects an external links according to the scheduling strategy:

  • bytes per second (sending & receiving)
  • packets per second (sending & receiving)
  • least number of established sesssions
  • etc.

DSL load balancer rewrites the source address (ip address and port number) to that of the selected link, which is the ip address of the selected link and a newly-allocated port number at the selected link. The response packets come back from this links too. Therefore, one outbound connection will never run faster than the speed of one external links.

Different connections can be balanced among multiple external links, so that aggregated performance is much higher.

External Links

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