3Com MSR 50 Series Configuration Manual page 2320

2320 C 134: E1
HAPTER AND
T1 C
ONFIGURATION
Figure 671 R2 signaling elements
Originating PBX
Originating side
Telephone
1 ITU-T digital line signaling
Digital line signaling is responsible for changing call statuses and conditions of a
line. It functions to identify and detect these four states: calling party goes
off-hook and seizes the line, called party goes 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 respectively
have four bits (A, B, C and D) as flag bits, with C and D bits fixed to 01. Therefore,
the forward line signaling adopts a
adopts a and b bits, as shown in the following table:
b b
Table 82 Line signaling bit description
Bit Description
a Identifies working state of device at the
f
originating point and indicates state of
the calling party line
b Indicates fault state from the originating
f
point to the terminating point
a Indicates state of the called party line
b
(on-hook or off-hook)
b Indicates state of device at the
b
terminating point (idle or seized)
Table 83 State code of line signaling
State of the circuit
Idle
Seized
Seizure-ack
Answer
Clear-back
Clear-forward
Blocked
Unblocked
The following are typical R2 digital line signaling interaction procedures:
Call establishment: When the trunk circuit is idle, the originating point sends a
■
forward seizure signal to the terminating point. The terminating point then
Forward signaling
PSTN
Terminating side
Backward signaling
and b bits and the backward line signaling
f f
Vale = 0
Off-hook, seized
Normal
Off-hook by
called party
Idle
Signaling code
Forward
a b
f f
1 0
0 0
0 0
0 0
0 0
0 0
1 0
1 0
Terminating PBX
Telephone
Value = 1
On-hook (idle)
Faulty
On-hook by
called party
Seized or
blocked
Backward
a b
b b
1 0
1 0
1 1
0 1
1 1
0/1 1
1 1
1 0