NEC NEAX 2400 IPX Programming Manual page 300

IS-11572 (LAYER 3 SPECIFICATIONS FOR INTER-PBX SIGNALING PROTOCOL)
(c) The connection patterns for the UUS transmission are shown in the figure below.
Pattern 1: The ISDN tandem connection
Note:
Pattern 2: The interface used in the terminating office is Q-sig/IS-11572.
Pattern 3: The interface used in the originating office is Q-sig/IS-11572.
CHAPTER 6
Page 282
Revision 1.0
Either ISDN(a) or ISDN(b) is Q-sig/IS-11572 interface.
PBX
ISDN(a)
ISDN
message
(UUS)
ISDN
ISDN
message
terminal
(UUS)
PBX
Q-sig/
IS-11572
ISDN
message
(UUS)
NDA-24305
PBX
ISDN(b)
ISDN
message
(UUS)
PBX
Q-sig/
IS-11572
ISDN
message
(UUS)
PBX
ISDN
message
(UUS)
PBX
PBX
ISDN
terminal