R2511-HP MSR Router Series Voice Configuration Guide(V5)

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off-hook and answers the call, calling party releases the call, and called party releases the call.
Accordingly, it sets the line to be idle or seized. This signaling is transmitted in the 16th multiframe
timeslot of PCM system. The two transmission directions of each line have 4 bits (A, B, C and D) as flag
bits, with C and D bits fixed to 01. Therefore, the forward line signaling adopts a
f
and b
f
bits and the
backward line signaling adopts a
b
and b
b
bits, as shown in the following table:
Table 5 Line signaling bit description
Bit Description Vale = 0 Value = 1
a
f
Identifies working state of device at the
originating side and indicates state of the calling
party line.
Off-hook, seized On-hook (idle)
b
f
Indicates fault state from the originating side to
the terminating side.
Normal Faulty
a
b
Indicates state of the called party line (on-hook or
off-hook).
Off-hook by called
party
On-hook by called party
b
b
Indicates state of device at the terminating side
(idle or seized).
Idle Seized or blocked
Table 6 State code of line signaling
State of the circuit
Signaling code
Forward Backward
a
f
b
f
a
b
b
b
Idle 1 0 1 0
Seized 0 0 1 0
Seizure-ack 0 0 1 1
Answer 0 0 0 1
Clear-back 0 0 1 1
Clear-forward 0 0 0/1 1
Blocked 1 0 1 1
Unblocked 1 0 1 0
The following are typical R2 digital line signaling interaction procedures:
1. Call establishment.
When the circuit is idle, the originating side sends a forward seizure signal to the terminating side.
The terminating side then 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 side sends a
backward answer signal. After the originating side recognizes the received signal, it establishes
the call.