Banyan switch

A Banyan Switch is a complex crossover switch used in electrical or optical switches.It is named for its resemblance to the roots of the Banyan tree which crossover in complex patterns. Logical banyan switches are used in logic or signal pathways to crossover switching of signals onto new pathways.

They can be mechanical MEMS, electrical or optical NLO. Their complexity depends on the topology of the individual switches in a switch matrix (how wide it is by how many 'plies' or layers of switches it takes), to implement a desired crossover logic.

Design

Typical crossover matrices follow this formula: an N×N Banyan switch uses (N/2) log₂ N elements.Other formulas are used for differing number of crossover layers and scaling is possible, but becomes very large and complex with large NxN arrays. CAD and AI can be used to take the drudgery out of creating these designs.

The switches are measured by how many stages, and how many up/down sorters and crosspoints. Switches often have buffers built-in to speed up switching speeds.

A typical switch may have:
# A 2x2 and 4x4 down sorter
# Followed by an 8x8 up sorter
# Followed by a 2x2 crosspoint Banyan switch network

This results in 3 level sorting for a 3 stage banyan network switch.

A Simple Example

Consider a 2x2 Banyan switch, which requires (2/2) log₂ 2 = 1 switching element. This switch takes two inputs, numbered 0 and 1, and two outputs, numbered 0 and 1. Every packet that comes in has a header that contains one bit indicating what its destination is (either 0 or 1). If the switch reads the bit and it has value 0, it sends the packet to its higher output (which is 0 in this case), and to its lower output if the routing bit is one. By connecting these switching elements in series and parallel it is possible therefore, to route packets in more complicated ways depending on the desired routes to establish.

Future Directions and Further Information

The future is moving to larger arrays of inputs and outputs needed in a very small space. See wafer fabrication and VLAs.

ee also

*crossover switches
*Crossbar switches
*Clos network a non blocking crossover switch that needs fewer than N^2 switches
*Nonblocking minimal spanning switch and signal switching.
*optical computers use crossover switches