3Com MSR 50 Series Configuration Manual page 2321

sends back a seizure acknowledgement signal after it recognizes the seizure
signal. At this time, the circuits of the both sides are seized, and they start
interregister signaling exchange. When the called party picks up the phone, the
terminating point sends a backward answer signal. After the originating point
recognizes the received signal, it establishes the call.
Figure 672 R2 digital line signaling - call establishment
Originating point Originating point Originating point Originating point
Seized Seized Seized Seized
Seizure -ACK Seizure -ACK
Register signaling exchange Register signaling exchange Register signaling exchange Register signaling exchange
Ringback Ringback
Answer Answer Answer Answer
tone tone tone tone
---Talk --- ---Talk --- ---Talk --- ---Talk ---
Originating point releases the call: The originating point sends a clear-forward
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signal 10. When the terminating point recognizes the clear-forward signal, it
sends a backward signal 10 (release guard signal or clear-forward
acknowledgement signal). After the originating point recognizes the backward
signal 10, it releases the trunk circuit.
Figure 673 R2 digital line signaling - originating point releases the call
Originating Point Originating Point Originating Point Originating Point
--- Talk --- --- Talk --- --- Talk --- --- Talk ---
Clear-forward Clear-forward
Clear-back Clear-back
Release-guard Release-guard
Terminating point releases the call: The terminating point sends a clear-back
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signal 11. After the originating point receives the clear-back signal, it sends a
clear-forward signal 10. After the terminating point recognizes the forward
signal 10 sent by the originating point, it sends a backward signal 10. After the
originating point recognizes the backward signal 10, it releases the trunk
circuit.
Terminating point Terminating point Terminating point Terminating point
-ACK -ACK
Ringing Ringing Ringing Ringing
Off-hook Off-hook
Terminating point Terminating point Terminating point Terminating point
Configuring R2 Signaling 2321