TN577 packet gateway (PGATE) provides 4 RS-423 physical ports
for X.25 protocol interfaces between the system and adjuncts.
this application, PGATE functions as the data communications interface
unit providing protocol conversion between the X.25 protocol and
the mode 3 protocol carried across the LAN Bus.
X.25 protocol (Levels 1 and 2) is terminated and the data reformatted
into the ISDN packet mode protocol for transport across the LAN
adjuncts include AUDIX, CMS, and Message Server Adjunct (MSA).
TN577 also supports the Distributed Communications System (DCS)
environment by providing X.25 signaling through 1 of the RS-423
physical ports, or back through the system using the TDM Bus to
the appropriate DS1 or tie trunk circuit pack.