Q.931 messages
[ ] Layer 3
C CONNECT
CA CONNECT ACKNOWLEDGE
CP CALL PROCEEDING
D DISCONNECT
R RELEASE
RC RELEASE COMPLETE
S SETUP
X.25 layer 3 messages
Any layer 3 message preceded by X.25indicates an X.25 layer 3 packet (e.g. X.25 CR means X.25 call request).
CA Call accepted
CC Call connected
CLC Clear confirmation
CLI Clear indication
CLR Clear request
CR Call request
IC Incoming call
SQ Restart request
SF Restart confirmation
SI Restart indication
Layer 2 frames
( ) Layer 2
GTEI Group TEI (127)
A.B X.25 layer 2 addresses(includes command and response)
SABM Set asynchronous balance mode
SABME Set asynchronous balance mode extended
UA Unnumbered acknowledgement frame
UI Unnumbered information frame(i.e. using unacknowledged information transfer at layer 2)
I Information frame
DISC Disconnect frame
Layer 2 addresses marked (x, p) indicates that the SAPI element of the frame address is coded for packet type (SAPI = 16) information as described in Recommendation Q.921. Layer 2 addresses marked (x, s) refer to signalling type (SAPI = 0) information.