for the TDM bus and packet bus and fiber optic links interconnecting
in a Port Network (PN) between a PN and another PN in a direct-connect
system and between a PN and an SNI in a switch node carrier in
a CSS-connected system.
control channel applications and time-slot interchanging between
the PPN and EPNs.\
circuit switched data, packet-switched data, network control,
timing control, and DS1 control.