A network standard designed by collaboration between the members of the CCITT and the vendors of WAN products, and intended primarily for the transport of ATM over long distances. The SONET standard is defined for operation over optical fibres at a minimum bit rate of 51.84 Mbps (OC-1 in North America) or 155.52 Mbps (SDH-1 in Europe). Both standards allow for speeds up to 159 Gbps.