WAN: ATM-2
End to end, cells walks through Virtual Circuits
Inside the network, cells are switched by high performances hardware switches
Between switches, cells are carried into SDH (Synchronous Digital Hierarchy) frames
SDH is the low level protocol for data transmission through optical links at 155, 466, 622,… Mbits/s (the equivalent in the US is SONET (Synchronous Optical NETwork))