NEC NEAX 2400 IPX Programming Manual page 304

Q-SIG (CIRCUIT SWITCHED BASIC CALL - ETSI VERSION)
1. Q reference point
The Q reference point is not expected to be a physical interface but is shown in conceptual terms in the figure
below.
The Q-Sig protocol creates Layer 3 messages for inter-PTN (PBX) signaling.
Protocol
Control
Data Link
Layer
Physical
Layer
Note: Conforming to Q921-a (PBX-PBX Interface)
CHAPTER 6
Page 286
Revision 1.0
PBX
Call
Control
Q
DTI
Control Plane Protocol Model
Q
Protocol defined
in this standard
DTI
Layer 2 Note
Layer 3
PBX to PBX
NDA-24305
PBX
Call
Control
Protocol
Control
Data Link
Layer
Physical
Layer