ACC X.25 Protocol User's Guide

X.25 Application Programming
X.25 Link Initialization
Chapter 4 73
In addition, the ACC X.25 subsystem also generates an unsolicited
status message to indicate that X.25 at level 3 is up. At this point the
X.25 link is in a normal operational state and can be used to establish
calls and transfer data across virtual circuits. However, note that VC
ZLUs must also be enabled and activated before they can be used.