H3C Technologies H3C MSR 50 - Manual (Page 744)

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One-to-one binding between FXS and FXO voice
subscriber lines
The one-to-one binding between FXS voice subscriber lines and FXO voice subscriber lines improves the
reliability of voice solutions. For industry-specific users, highly reliable communication over FXS voice
subscriber lines is required. That is, dedicated FXO voice subscriber lines can be used for communication
over PSTN when the IP network is unavailable. The one-to-one binding between FXS voice subscriber
lines and FXO voice subscriber lines can meet this requirement.
The one-to-one binding between FXS voice subscriber lines and FXO voice subscriber lines provides the
following functions:
• Dedicated FXO voice subscriber lines—The dedicated FXO voice subscriber lines can be used only
for the bound FXS voice subscriber lines and PSTN-originated calls received over dedicated FXO
voice subscriber lines are directly connected to the bound FXS voice subscriber lines.
• Consistent state between bound FXS and FXO voice subscriber lines—The on-hook/off-hook state
of the bound FXS and FXO voice subscriber lines is consistent. If an FXO subscriber line receives a
PSTN-originated call when the corresponding FXS voice subscriber line goes off-hook, the calling
party will hear busy tones.
Echo adjustment function
Echo is that the user hearing his own voice in the telephone receiver while he is talking. This is because
analog signals leak into the receiving path of the user. The echo adjustment function provided by the VoIP
gateway can cancel echoes to some extent.
You can cancel echoes in three ways: adjust echo duration, adjust echo cancellation parameters, and
enable the nonlinearity function of echo cancellation.
Adjusting echo duration
Table 272 Adjust echo duration
Symptom Reason Adjustment method
A user hears his or
her voice in
conversation.
The echo duration is so long that the convergence time
of echo cancellation on the network becomes longer. Shorten echo duration
The echo duration is so short that long-duration echoes
are not completely cancelled.
Prolong echo duration
Adjusting echo cancellation parameters
Table 273 Adjust echo cancellation parameters
Symptom Parameters adjusted Effect
A user hears his or her voice or
loud background noises from
the peer when speaking.
Speed up the convergence of
comfortable noise amplitudes Too fast convergence might make noises
uncomfortable.