Fxo Voice Subscriber Line; Fxo Interface; Cid; Busy Tone Detection - HP FlexNetwork MSR Series Configuration Manual

after the second ring to make sure that the calling identity information is sent and received correctly.
Otherwise, the calling identity information might fail to be displayed.

FXO voice subscriber line

FXO interface

A foreign exchange office (FXO) interface, that is, a two-port loop trunk interface, uses an RJ-11
connector and a telephone cable to connect local calls to a PSTN or PBX. Like an FXS interface, an
FXO interface accomplishes signaling exchange based on the level changes on the Tip/Ring line. An
FXO interface can be connected only to an FXS interface.

CID

The FXO voice subscriber line receives the calling identity information from the PBX. The FXO
interface receives the modulation information of the calling identity information from the PBX
between the first and second rings. (This is the default situation. Use the cid ring command to
configure the time for CID check.) Then, the calling identity information undergoes FSK
demodulation and parity check. The function of sending calling identity information is checked after
the parity check succeeds. If the function is enabled, the calling identity information is sent to the IP
network. If the function is disabled, the identity information is empty.

Busy tone detection

Signaling standards and busy tone characteristics might vary with devices. Therefore, busy tones
cannot be recognized by a fixed threshold value.
The automatic busy tone recognition technology can solve this issue. This technology uses software
to sample and analyze busy tones to produce a set of parameters that represent the most common
patterns of busy tones. After configured with these parameters, the FXO ports can recognize
different types of busy tones.
Busy tone recognition includes the following elements:
•
Busy tone frequency—Most busy tones have one or two frequencies.
•
Duty ratio—Duration ratio of high/low levels composing a busy tone signal, which is also
referred to as make-break ratio. The specifications of the duty ratio of a busy tone vary with
countries and regions. The national standard of China is 350 milliseconds/350 milliseconds (10%
error allowed).
•
Detection threshold—Threshold used to determine whether a level is a high level or low level.
If the level higher than the threshold, it is regarded as a high level. Otherwise, it is regarded as
a low level.
Figure 8
shows the typical network diagram for automatic busy tone detection. Telephone A is
connected to PBX A, which connects to the FXO interface of Router A through an ordinary telephone
line. The connection of the peer end is similar.
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