Appendix
A-29
4.5 Major Signals Used for Channel B Layer 2
SABME (Set Asynchronous Balanced Mode Extend)
It is the first signal sent by the calling side to the called side when setting layer 2.
UA (Unnumbered Acknowledge)
It is a signal used to acknowledge response to SAMBE or DISC.
DISC (Disconnect)
It is used to instruct disconnection of layer 2.
4.6 Major Signals Used for Channel B Layer 3
SQ (Restart Request)
It is a signal transmitted before layer 3 is connected
SI (Restart Indication)
It is a signal received before layer 3 is connected.
SF (Restart Confirmation)
It is a signal used to acknowledge response to SQ or SI.
CR (Call Request)
It is a signal transmitted when layer 3 is connected.
CN (Incoming Call)
It is a signal received when layer 3 is connected.
CA (Cal Accepted)
It is a signal used to acknowledge response to CN.
CC (Call Connected)
It is a signal used to acknowledge response to CR.
CQ (Clear Request)
It is a signal transmitted when layer 3 is disconnected.
CI (Clear Indication)
It is a signal received when layer 3 is disconnected.
CF (Clear Confirmation)
It is a signal used to acknowledge response to CQ or CI.
4.7 Major Signals Used for Channel B Layer 4
TCR (Transport Connection Request)
It is a signal transmitted when layer 4 is connected. It checks the maker code and negoti-
ates data size.
TCA (Transport Connection Accept)
It is a signal transmitted when TCR has been received and layer 4 may be connected.
TCC (Transport Connection Clear)
It is a signal transmitted when TCR has been received and layer 4 cannot be connected.
TBR (Transport Block Reject)
It is a signal transmitted when an error has been discovered in the information of layer 4.
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