Com.X Administrator Guide
Page 94
The Com.X product range incorporates state of the art, innovative, embedded on-
DSP-chip echo cancellation that off-loads resources from the system server.
Echo cancellation can how-ever affect fax and modem signaling and data. It is
therefore important to understand the impact of echo cancellation on fax and modem
negotiation and configure devices correctly for fax use.
Echo cancellation is performed at the source device, where 'source' here indicates a
network endpoint that introduces a signal into the PBX system. In the Com.X
systems echo cancellation takes place on FXO, BRI and PRI ports/channels
terminating traffic from the PSTN for routing in the system, as well as FXS ports
originating calls via the PBX.
If not configured properly for fax support, faxes and modems may fail or higher baud
rate operation might not be possible.
At these sources, if a fax start “CNG” tone is detected and the port / channels are
correctly configured for fax, the echo cancelers are automatically disabled, and a
clear channel is offered for fax service.
In the case of PRI and BRI channels, channels may serve both voice and fax traffic,
and detection of the fax tone is required before echo cancellation can be switched
off. This detection is configurable from the Hardware panel for BRI trunk groups and
PRI ports.
Since fax devices are usually affixed to individual ports, and specific incoming DIDs
reserved for fax use, in the case of FXS and FXO, ports need to be deliberately
reserved for fax use by disabling echo cancellation. This is done for FXO ports by
enabling the “Detect Fax” option, and for FXS ports by enabling the “Fax channel”
option in the hardware panel, which disables echo cancellation and configures
additional jitter buffering for the port.
3.6.8.2 Telco issues
Telco FXO connectivity, cable distance and environment, etc. introduces additional
signal to noise ratio and impedance elements into the equation and may not support
high baud rates.
3.6.8.3 Timing
Timing in the system is very important to ensure successful fax / modem
communication. The iTA device (e.g. the internal BRI / PRI enabled iTA MPC card in
the Com.X1 case or the BRI / PRI iTA in the Com.X2 case) connected to the telco
interface should have the highest timing priority (line N), and other iTAs connected
should derive timing from this device (system). Please see section 3.4.5.1 for detail
on configuring the timing source on an iTA device.
In scenarios where multiple PRI links are configured to the same telco, setting the
first PRI as PRI Line 1 is recommended (i.e. deriving clocking from the telco line) and
setting all other PRIs to System (i.e. sharing the clocking of the first PRI in the
transmit direction and honoring the telco's clocking on each PRI in the receive
direction.
In gateway scenarios, where one or more PRIs face the telco and one or more PRIs
face a 3
rd
party device, the telco-facing PRIs should be configured as above, and the
PRIs facing the 3
rd
party device should be configured to use System timing. In this
scenario the “transmit clocking” setting should be enabled the relevant PRI ports in
the GUI hardware panel.
©2010 –
2016
Far South Networks
Содержание Com.X
Страница 34: ...Com X Administrator Guide Page 34 Figure 26 Global Settings 2010 2016 Far South Networks ...
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Страница 110: ...Com X Administrator Guide Page 110 Figure 92 SIP trunk basic configuration options 2010 2016 Far South Networks ...
