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Practice Section 814119/814119S
1.4 As previously stated, the 4119/S is a split-type echo canceller, meaning that the 4119/S,
used at one end of a 4-wire circuit, protects the opposite end of the circuit from echo. There-
fore, when the 4119/S (or equivalent) is used at each end of a 4-wire circuit, the parties at
both ends are protected from echo.
1.5 Unlike
an
echo suppressor, which inserts a high impedance into the return path to attenuate
echo, the 4119/S digitally computes a highly accurate echo estimate based
on
the incoming
speech signal from the far end. This estimate is then subtracted from the transmit channel
(return path) signal. When the transmit signal consists of only echo, the echo is removed,
leaving
no
signal to be returned to the speaker. When the transmit signal consists of both
echo (from the far end speaker) and near end speech, only the echo
is
removed, leaving the
near end speech signal intact for transmission to the distant end. The 4119/S allows parties
at both ends to talk simultaneously. This is known as full duplex speech or "doubletalk".
1.6 Due to its completely adaptive nature, the 4119/S cancels echo
in
any circuit whose end
path (the path between the 4119/S and the near end terminating set) exhibits at least 6dB of
Echo Return Loss (ERL) and no more than 64ms of delay.
Note: End path delay consists of the round-trip propagation delay of all facilities in
the end path, fixed delays through transmission and switching equipment,
and line dispersion, which is typically 4 to 7ms with a 3400Hz bandwidth.
Reason for Change
1.7 This practice has been reissued to change the module specifications, and to incorporate
information from Addendum Section A814119S-A, dated 3/90.
4119/S Features and Options
2
1.8 Standard 4119/S features are as follows:
• Compliance with International Telegraph and Telephone Consultive Committee (CCITT)
recommendations G.164 (for tone disabler) and G.165
• Integral NLP for removing residual echo. A switch option conditions the NLP for operation
during both singletalk (only the far end party talking) and doubletalk
or,
per the above
CCITT recommendation, during singletalk only
• 3-position front panel switch that selects any of three operating modes:
-Normal (norm),
in
which all echo control circuits are active and the module is fully
operational
-Canceller Only (canclr only),
in
which the integral NLP is disabled, leaving only the
cancellation section operational
-Disable (disable),
in
which both the cancellation section and the NLP are disabled,
leaving only straight-through transmit and receive transmission paths for testing
• A switch option that conditions the modules for operation
on
end paths with a maximum
propagation delay of either 32 or 64ms
• Switch selectable, soft clipping operation, which adds a small amount of noise at the
transmit output to make operation of the canceller less noticeable on noisy end paths
• Integral tone disabler that, upon detection of
21
00Hz tone (indicating forthcoming data
transmission), disables all echo control circuitry. This renders the module completely
transparent
in
both directions for the duration of the data transmission
• Transformer coupling at all four transmission ports
• Balanced, switch selectable 1200-, 600-, or 150-ohm terminating impedance at the termi-
nal side (terrestrial side) ports (transmit input and receive output)
• Fixed, balanced, 600-ohm terminating impedance at the facility side (satellite side) ports
(receive input and transmit output)
• Switch selectable interface Transmission Level Points (TLPs), with a choice of
-16
trans-
mit and +7 receive,
-4
transmit and +4 receive, or 0 transmit and 0 receive at both the fa-
cility and terminal side ports
Rev A
11
/3/95
