sDlC、wAs invEntED By iBm to rEplACE thE olDErBisynChronous protoCol For wiDE ArEA ConnECtions BEtwEEn iBm EquipmEnt.
A、vAriEtion oF thE (71) protoCol CAllED nrm is EssEntiAlly thE sAmE As sDlC、
sDlC、is (72) protoCol likE hDlC, FrAmE rElAy or x.25.An sDlC、nEtwork is mADE up oF (73) thAt Controls All CommuniCAtions, AnD (74) .it is CApABlE oF (75) .opErAtion, But Almost All prACtiCAl AppliCAtions ArE striCtly hAlF DuplEx.
A、hDlC
B．FrAmE rElAy
C．x.25
D．x.21