A Wavefront arbiter is a circuit used to make decisions which control the crossbar of a high capacity switch fabric in parallel. It was commercialized in the TT1 chip set made by Abrizio and sold by PMC-Sierra.

A crossbar is the centre portion of a switch fabric which connects the inputs (on the left) which the outputs (on the bottom). A set of decisions of which inputs are connected to which outputs must be made at each arbitration period.

An arbiter is the circuit that makes the decision as to which of the crossbar's many switches should be closed.

A wavefront aribiter is a particular type of arbiter that is optimized for high-speed operation. For a unicast switch, the algorithm is as follows: The decision starts at a single point in the matrix which represents a single physical switch, for example the upper left hand corner. A decision is made whether to close that switch, connecting the corresponding input and output. The result of this decision is then fed to the right along the matrix axis representing the input, and down along the matrix axis representing the output. The results of the first computation then enable the next computation at the point to the right and at the point below. The results of these subsequent two calculations then are then fed to the points below and to the right of them. These results then enable the decisions at the next three points which are to the right and below. These results are again fed to the right and below. This calculation continues until all of the decisions have been made. In the case where the calculation did not start in the upper left hand corner, the results wrap around the right back to the first left column and around the bottom to the top row.

The benefit of this type of calculation is that it can be implemented in a combinatorial manner, allowing the wavefront to propagate across much or all of the matrix in one or a few clock periods.

There are numerous variants of this method including randomizing the order in the which the rows and columns are considered. Additionally, there are multicast variants of this method.

Switches