"CCITT X.25 recommendation" . "X.25 protocol" . . . . . "X.25 packet-switching" . . . "Packet Assembler/Disassembler Protocol" . . "X.25" . . "X.25 Packet Switching Network" . . "x25" . "international digital connections" . "correspond to OSI layers 1 to 3" . "X.25" . . . "X.25 \u00A7 History" . "X.25 data network" . . . . . . . "ISO/IEC 8208" . . . . . . "X.25 Recommendation" . . . "x.25" . . . . . . "X25 network" . . "CCITT X.25" .