A form of switching in which the individual packets, or cells, have a fixed length and a fixed internal structure; in many cases the cells are also deliberately kept to a small size, typically a few tens of bytes. Once the initial decision on cell routing has been made, typically at the time of creating a virtual circuit, it is possible to realize the actual switching activity almost entirely in table-driven hardware, rather than invoking a software implementation, allowing very short switching times. The large number of cells into which even a short message is subdivided increases the ratio of overheads to useful payload. See also ATM, frame relay.