Routing data packets through optical backplane routers

A communication system comprises an optical backplane 8 which is arranged to feed a plurality of disparate data router 6, each router 6 having ingress ports 7 fed from a plurality of lines, one for each ingress port 7, each of which lines utilises a plurality of TDM data slots, data packages being fed from the router via router egress ports 9 some of which egress ports 9 route data back to the backplane 8, and others of which feed data to other routes 10, each data package being labeled in accordance with the line in which it traveled to the router and the TDM slot which it occupied whereby the labels define for each package an address, each router 6 comprising a lookup table 11 which cross-correlates these addresses with egress ports 9, whereby each data package is routed to an appropriate egress port 9 as indicated by the lookup table in dependence upon its label.