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

• O if the terminating PBX fails to obtain the calling name (for example, the originating PBX end does

not send it)

The FXS voice subscriber line sends the calling identity information to the called telephone. The calling

identity information is sent to the called telephone through frequency shift keying (FSK) modulation

between first and second rings. Therefore, the called user must pick up the telephone 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 sh

ows 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.