Current terabit routers are based on multi-stage switching networks developed in the early 1980's. These switching networks consist of switching modules which buffer and routes the packets; a topology which determines how the modules are connected; and a routing algorithm which determines how the packets are routed between the modules;

The Banyan and Butterfly networks are two of the better known multi-stage switching networks.

  • Switching Module: A Banyan or Butterfly's switching module consists of buffers, a 2x2 crossbar, and decision logic which analyzes the header and controls the crossbar.

  • Topology: The topology of a Banyan and Butterfly network is based on parallel sorting networks. They achieve complete connectivity in log 2 N rows.

  • Routing Algorithm: The path-based routing algorithm used by Banyan and Butterfly network is similar to the digit-by-digit routing used by the telephone network. The first row of switching modules use the most significant bit of the destination address; the second row of modules use the second most significant bit, etc. This algorithm is simple in terms of hardware and only requires a packet's destination address to make a routing decision.


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