Talkdown/Talkoff Testing
“Calling Identity Delivery on Call Waiting” (CIDCW) is the standardized name for the
telephone service that allows customers to see the number of a third party calling during
an ongoing telephone call. CIDCW is also called “Caller ID on Call Waiting” and “Type
2 Caller ID,” and is defined in Telecordia SR-TSV-002476 and SR-3004 guidelines.
The CIDCW is sent from Stored Program Control Switching System (SPCS), also called
the “switch” or the “central office,” the normal location of the SPCS. The signaling
protocol for CIDCW is as follows:
1) The customer line is already in the “off-hook” condition, and connected to the
SPCS (central office switch).
2) The SPCS sends a CPE Alerting Signal (CAS) comprising two simultaneous
tones with frequencies of 2130 Hz and 2750 Hz for a duration of 75 to 85 mS.
3) The SPCS mutes all outgoing speech (called “far-end” speech).
4) The Customer Premise Equipment (CPE) verifies that there are no extensions offhook at the customer premise. If off-hook extensions are detected, then no
acknowledgment of the CAS to the SPCS is made.
5) If no off-hook extensions are detected, then within 100 mS the CPE sends and
Acknowledgment (ACK) signal for 55 to 65 mS. The ACK signal is either a
DTMF “D” or “A” tone, depending if the CPE is Type 2 or Type 3, respectively.
6) The CPE mutes the handset and keypad to prevent customer speech (called “nearend” speech) from interfering with the CIDCW data.
7) Within 500 mS of receipt of the ACK signal, the SPCS sends the CIDCW data.
The data is transmitted at 1200 Baud using Frequency Shift Keying (FSK).
8) Within 50 mS of receipt of the data, the CPE will unmute the handset and keypad
to allow near-end speech and digit transmission.
SPCS Unmutes
SPCS & CPE Mutes
CAS
75-85 mS 0-100 mS
ACK
//
55-65 mS
0-500 mS
CPE
Unmute
FSK
0-50 mS
Figure 1: CIDCW Timing
CIDCW signals are further defined in the recommendations as follows:
Signal
CAS
DTMF-D
DTMF-A
Frequency
Level
2130 Hz + 0.5%
-32 to -14 dBm
2750 Hz + 0.5%
-32 to -14 dBm
941 Hz + 1.5%
-10.5 to - 8.5 dBm
1633 Hz + 1.5%
-8.5 to - 6.5 dBm
697 Hz + 1.5%
-10.5 to - 8.5 dBm
1633 Hz + 1.5%
-8.5 to - 6.5 dBm
Table 1: CIDCW Signals
1
Caller ID on Call Waiting Testing
The Telecordia SR-3004 guideline requires the following conformance tests (in addition
to the tests required for Caller ID Type 2 CPE):
•
•
•
•
•
•
CAS Detector Performance
DTMF Acknowledgment Signal Measurements
CAS Reception to ACK Generation Timing
CPE Handset and Receiver Muter Timings and Verification
On-Hook FSK Reception
Variations in Timing from ACK to FSK
CAS Detector Performance tests
A test plan (and references) for CAS detector performance is provided in the appendices
to the SR-TSV-002476 standard. The plan lists three types of tests:
1) Signal recognition tests without speech present
2) Talkdown tests – missed signals in the presence of speech
3) Talkoff tests -- false detections caused by speech
Test connections for the three sets of tests are summarized in Table 2.
Test
Recognition
Talkdown
Far-end Talkoff
Near-end
Talkoff
Detector
Location
All Locations
No Hybrid
CAS Source
Connection
Tip & Ring
Tip & Ring
Tip & Ring of
Hybrid
Tip & Ring
Receive Side
of Hybrid
Tip & Ring
through worstcase Loop
All Locations
Tip & Ring of
Hybrid
Receive Side
of Hybrid
Far-End Speech
Connection
Near-End Speech
Connection
Tip & Ring
with Pre-Emphasis
Electrical on Receive
Side of Hybrid (with
Pre-Emphasis)
Acoustic on Receive
Side of Hybrid (no
Pre-Emphasis r)
Electrical on Receive
Side of Hybrid (Use
Pre-Emphasis if
electrical connection)
Tip & Ring
No Source Connection, but worstcase Loop connected to Tip and
Ring, terminated on far-end with
900 Ohms
Electrical on Receive
Side of Hybrid (Use
Pre-Emphasis if
electrical connection)
Electrical on Receive
Side of Hybrid (Use
Pre-Emphasis if
electrical connection)
Table 2: Summary of Test Connections
2
If the CAS detector is connected to the tip and ring side of a hybrid (e.g. an adjunct), then
SR-3004 specifies that all signals are applied and measured at the tip and ring interface.
If the CAS detector is on the receive side of a hybrid, then SR-3004 first requires the
determination of the test loop at the tip-ring side of the hybrid which causes the lowest
transhybrid loss from the transmit side to the tip-ring side of the hybrid.
Tip
Tx
Ring
Rx
Figure 2: Hybrid
SR-3004 describes the following procedure to determine the worst-case loop:
1) Determine the threshold of the CAS Detector by transmitting CAS tones on tip
and ring while lowering the level of the signal until the detector cannot accurately
detect 20 simultaneous CAS signals. Call the dB level the T_and_R_threshold.
2) Transmit CAS tones acoustically into the transmitter while measuring the signal
level on tip and ring. Lower the signal level until the detector cannot accurately
detect 20 simultaneous CAS signals. Call the dB level the Near_End_threshold.
3) Calculate the transhybrid loss as Near_End_threshold - T_and_R_threshold.
4) Repeat for each of the following eight loops:
A
11 kft
22 AWG
B
3 kft
22 AWG
H88
Load
6 kft
22 AWG
H88
Load
C
3 kft
22 AWG
H88
Load
6 kft
22 AWG
H88
Load
3 kft
24 AWG
H88
Load
6 kft
22 AWG
H88
Load
9 kft
22 AWG
D
6 kft
22 AWG
4 kft
24 AWG
6 kft
26 AWG
6 kft
22 AWG
E
H88
Load
9 kft
22 AWG
3 kft
22 AWG
9 kft
26 AWG
5 kft
24 AWG
1 kft
24 AWG
3
F
19 kft
26 AWG
3 kft
26 AWG
G
1 kft
24 AWG
H
3 kft
22 AWG
1 kft
24 AWG
1 kft
24 AWG
H88
Load
6 kft
22 AWG
H88
Load
6 kft
22 AWG
6 kft
22 AWG
H88
Load
6 kft
22 AWG
H88
Load
H88
Load
6 kft
22 AWG
H88
Load
6 kft
22 AWG
H88
Load
6 kft
22 AWG
1 kft
24 AWG
Figure 3: Test Loops
1) Signal recognition tests
The following tests are made on a received CAS signal with no speech present. The loop
determination test is not needed. The detector can be either at tip and ring or at the
receive side of the hybrid. The connections to the CAS source are shown in Figure 2.
Tip
CAS
Tones
Tx
DET
Ring
Rx
DET
Figure 2: Signal Recognition test Connections
The signal parameter limits are measured across the 600 Ohm tip and ring interface and
are shown in table 2:
Frequency
Level
Twist
2130 Hz + 0.5% -32 to -14 dBm 0 to 6 dB
2750 Hz + 0.5% -32 to -14 dBm 0 to 6 dB
Table 2: CAS parameters
Duration
75 to 85 mS
75 to 85 mS
4
The guidelines also note that signals less than –45 dBm should always be rejected.
The test plan lists three groups of signal recognition tests. For each group of tests, 1000
CAS signals are sent (at a rate of <2/Sec) for each combination of signals within the
group. All signals must be correctly received.
Group 1: All parameters are to measured across the 600 Ohm tip and ring interface and
are set to the nominal values shown in the table 3:
Frequency
2130 Hz + 2 Hz
2750 Hz + 2 Hz
Level
Twist
-22 dBm + 1 dB
0 to 2 dB
-22 dBm + 1 dB
0 to 2 dB
Table 3: CAS nominal values
Duration
79 to 81 mS
79 to 81 mS
This produces only one combination for Group 1 tests, as shown in table 2.
Group 2: Each parameter is sequentially set to its extreme value as given in table 2,
while all other parameters are set to their nominal values as given in table 3. All levels
are measured across the 600 Ohm tip and ring interface. The set of combinations is
summarized in the TIA/EIA-777 standard and is shown in table 4:
Test
2
3
4
5
6
7
8
9
10
11
12
13
Lower Tone
2119.4 Hz
2140.7 Hz
2130 Hz
2130 Hz
2130 Hz
2130 Hz
2130 Hz
2130 Hz
2130 Hz
2130 Hz
2130 Hz
2130 Hz
Level
Upper Tone
Level
-22 dBm
2750 Hz
-22 dBm
-22 dBm
2750 Hz
-22 dBm
-22 dBm
2736.3 Hz
-22 dBm
-22 dBm
2763.8 Hz
-22 dBm
-32 dBm
2750 Hz
-32 dBm
-14 dBm
2750 Hz
-14 dBm
-32 dBm
2750 Hz
-26 dBm
-26 dBm
2750 Hz
-32 dBm
-14 dBm
2750 Hz
-20 dBm
-20 dBm
2750 Hz
-14 dBm
-22 dBm
2750 Hz
-22 dBm
-22 dBm
2750 Hz
-22 dBm
Table 4: CAS group 2 combinations
Duration
80 mS
80 mS
80 mS
80 mS
80 mS
80 mS
80 mS
80 mS
80 mS
80 mS
75 mS
80 mS
Group 3: Each parameter is sequentially set to 90% of the value from nominal to extreme.
All levels are measured across the 600 Ohm tip and ring interface. The set of
combinations is also summarized in TIA/EIA-777 and is shown in brief in table 5:
Test
14
...
62
Lower Tone
2120.4 Hz
2130 Hz
Level
-31 dBm
Upper Tone
2737.6 Hz
Level
-31 dBm
-46 dBm
2750 Hz
-46 dBm
Table 5: CAS group 3 combinations
Duration
75.5 mS
80 mS
5
2) Talkdown tests
Talkdown is defined as a missed CAS detection due to interfering speech. Since the
SPCS far-end speech is muted during the time the CAS tone is sent, only near-end speech
from the CPE can cause a missed CAS detection.
The CAS signal source is always connected to tip and ring.
For CAS detectors without a hybrid, the equalized near-end speech (see below) is mixed
with the CAS signal at the tip and ring interface to the device under test. The loop
determination test is not needed.
The near-end speech signals first pass though a pre-emphasis equalizer that simulates the
frequency response of the transmitter acoustics and electrical circuits. SR-TSV-002476
defines the equalizer as linear on a logarithmic scale from 300 Hz to 3000 Hz, with the
response at 300 Hz down 5 dB relative to 1000 Hz, and the response at 3000 Hz up 5 dB
relative to 1000 Hz.
For CAS detectors without a hybrid, the near-end speech is connected at the tip and ring
interface to the device under test. The loop determination test is not needed.
Connections are shown in Figure 3:
CAS
Tones
Near-end
Speech
Tip
Mixer
DET
Equalizer
Ring
Figure 3: Talkdown Test Connections for Detectors without a Hybrid
For CAS detectors that are connected at tip and ring, the near-end speech source should
be connected at the transmit side of the hybrid either electrically or by acoustic coupling.
The loop determination test is needed. Connections are shown in Figure 4:
Tip
CAS
Tones
Tx
DET
Equalizer
Or
Coupler
Near-end
Speech
Rx
Ring
Figure 4: Talkdown Test Connections for Detectors Connected to Tip and Ring
If the source is electrically coupled, then the near-end speech signals must first be passed
though a pre-emphasis equalizer that simulates the frequency response of the transmitter
acoustics and electrical circuits. SR-TSV-002476 defines the equalizer as linear on a
logarithmic scale from 300 Hz to 3000 Hz, with the response at 300 Hz down 5 dB
relative to 1000 Hz, and the response at 3000 Hz up 5 dB relative to 1000 Hz.
6
If the source is acoustically coupled to a device under test, then the speaker used in the
acoustic coupler must have a flat frequency response.
For CAS detectors that are connected at receive side of a hybrid transformer, the near-end
speech source should be connected at the transmit side of the hybrid either electrically or
by acoustic coupling. The loop determination test is required, and the worse case loop is
connected to the tip and ring interface of the hybrid. Connections are shown in Figure 5.
Tip
CAS
Tones
Tx
Equalizer
Or
Coupler
Rx
DET
Worse-case
Loop
Ring
Near-end
Speech
Figure 5: Talkdown Connections with the Detector Connected to the Receive Port
If the source is electrically coupled, then the near-end speech signals must first be passed
though a pre-emphasis equalizer that simulates the frequency response of the transmitter
acoustics and electrical circuits. SR-TSV-002476 defines the equalizer as linear on a
logarithmic scale from 300 Hz to 3000 Hz, with the response at 300 Hz down 5 dB
relative to 1000 Hz, and the response at 3000 Hz up 5 dB relative to 1000 Hz.
If the source is acoustically coupled to a device under test, then the speaker used in the
acoustic coupler must have a flat frequency response.
The talkdown test proceeds by sending CAS tones of different levels on tip and ring
while simultaneously sending speech of different levels on the near-end speech
connection. All levels are measured across the 600 Ohm tip and ring interface. SR-TSV002476 specifies testing at seven different CAS-to-Speech ratios, as given in table 6:
Signal/Speech Ratio CAS Level
Speech Level
-19 dB
-26 dBm
-7 dBm
-15 dB
-28 dBm
-13 dBm
-12 dB
-22 dBm
-10 dBm
-10 dB
-26 dBm
-16 dBm
-6 dB
-28 dBm
-22 dBm
-3 dB
-22 dBm
-19 dBm
0 dB
-28 dBm
-28 dBm
Table 6: Talkdown Test Levels
For each signal/speech ratio in Table 6, the “number of misses per signal sent” should be
recorded. This is the talkdown rate.
7
The Talkdown test is performed with continuous speech applied at the near-end. In real
world conversations, near-end speech would only be present for 50% of the time. The
Talkdown rates can, therefore, be divided by two. This is the “derated talkdown rate.”
Using the results of the derated talkdown rate and straight-line interpolation, construct the
matrix of interpolated results shown in table 7, and record the derated talkdown rate in
each of the positions in the matrix.
Note that for any signal/speech ratios >0 dB, it is assumed that Talkdown will be
negligible, and the corresponding positions in the matrix can be assigned a value of zero
(see the very lightly colored cells in the matrix in Table 7).
DTR: Derated Talkdown rate
Speech
Level
dBm
-7
-10
-13
-16
-19
-22
-25
-28
-31
CAS Signal Level in dBm (probability)
-30
DTR
-23
(0.000129)
DTR
-20
(0.000774)
DTR
-17
(0.000129)
DTR
-14
(0.000129)
DTR
-11
(0.000129)
DTR
-8
(0.000129)
DTR
-23
(0.000129)
DTR
-23
(0.000129)
DTR
-23
(0.000129)
-28
DTR
-21
(0.000172)
DTR
-18
(0.001032)
DTR
-15
(0.000129)
DTR
-12
(0.000129)
DTR
-9
(0.000129)
DTR
-6
(0.000129)
DTR
-23
(0.000129)
DTR
-23
(0.000129)
DTR
-23
(0.000129)
-26
DTR
-19
(0.000344)
DTR
-16
(0.002064)
DTR
-13
(0.000129)
DTR
-10
(0.000129)
DTR
-7
(0.000129)
DTR
-4
(0.000129)
DTR
-23
(0.000129)
DTR
-23
(0.000129)
DTR
-23
(0.000129)
-24
DTR
-17
(0.000731)
DTR
-14
(0.004386)
DTR
-11
(0.000129)
DTR
-8
(0.000129)
DTR
-5
(0.000129)
DTR
-2
(0.000129)
DTR
-23
(0.000129)
DTR
-23
(0.000129)
DTR
-23
(0.000129)
-22
DTR
-15
(0.000731)
DTR
-12
(0.004386)
DTR
-9
(0.000129)
DTR
-6
(0.000129)
DTR
-3
(0.000129)
DTR
0
(0.000129)
DTR
-23
(0.000129)
DTR
-23
(0.000129)
DTR
-23
(0.000129)
-20
DTR
-13
(0.000731)
DTR
-10
(0.004386)
DTR
-7
(0.000129)
DTR
-4
(0.000129)
DTR
-1
(0.000129)
DTR
-23
(0.000129)
DTR
-23
(0.000129)
DTR
-23
(0.000129)
DTR
-23
(0.000129)
-18
DTR
-11
(0.000731)
DTR
-8
(0.004386)
DTR
-5
(0.000129)
DTR
-2
(0.000129)
DTR
1
(0.000129)
DTR
-23
(0.000129)
DTR
-23
(0.000129)
DTR
-23
(0.000129)
DTR
-23
(0.000129)
-18
DTR
-9
(0.000731)
DTR
-6
(0.004386)
DTR
-3
(0.000129)
DTR
0
(0.000129)
DTR
3
(0.000129)
DTR
-23
(0.000129)
DTR
-23
(0.000129)
DTR
-23
(0.000129)
DTR
-23
(0.000129)
Table 7: Talkdown Test Matrix
Once the talkdown matrix is filled in, there are three test conditions that must be met:
a) Condition 1: 99.5% of the signals set should correctly received when the CAS
signal is –22 dBm/tone, and the speech level is –19 dBm (see the darkly shaded
cell in the Table 7 matrix.)
8
b) Condition 2: At least 93% of the signals should be correctly received for the CAS
and speech levels in the weighted average of the worse 1.22% of all conditions
(see the lightly shaded cells in the Table 7 matrix.)
c) Condition 3: At least 99.5% of the signals should be correctly received for the
CAS and speech levels in the weighted average of all conditions.
3) Talkoff tests
Talkoff is defined as a false CAS detection due to interfering speech when no legitimate
CAS tone is being sent from the SPCS. Talkoff can be caused by both near-end or farend speech. The SR-3004 guidelines recommend two separate sets of talkoff tests:
a) Talkoff tests with far-end speech: The far-end speech sources is connected at the
tip and ring interface to the device under test. The loop determination test is not
needed. The detector can be either at tip and ring or at the receive side of the hybrid.
The connections to the speech source are shown in Figure 6.
Tip
Near-end
Speech
Equalizer
DET
Ring
Figure 6: Far-end Talkoff Test Connections
b) Talkoff tests with near-end speech: For CAS detectors without a hybrid, the near
end speech source is connected at the tip and ring interface to the device under test.
The loop determination test is not needed.
The near-end speech signals must first pass though a pre-emphasis equalizer that
simulates the frequency response of the transmitter acoustics and electrical circuits.
SR-TSV-002476 defines the equalizer as linear on a logarithmic scale from 300 Hz to
3000 Hz, with the response at 300 Hz down 5 dB relative to 1000 Hz, and the
response at 3000 Hz up 5 dB relative to 1000 Hz. The connections to the speech
source are shown in Figure 7.
Tip
Near-end
Speech
Equalizer
DET
Ring
Figure 7: Near-end Talkoff Test Connections for Detectors with no Hybrid
For CAS detectors that are connected at the tip and ring side of a hybrid transformer,
the near-end speech source should be connected at the transmit side of the hybrid
either electrically or by acoustic coupling. The loop determination test is not required.
9
If the source is electrically coupled, then the near-end speech signals must first be
passed though a pre-emphasis equalizer that simulates the frequency response of the
transmitter acoustics and electrical circuits. The equalizer is defined as linear on a
logarithmic scale from 300 Hz to 3000 Hz, with the response at 300 Hz down 5 dB
relative to 1000 Hz, and the response at 3000 Hz up 5 dB relative to 1000 Hz.
If the source is acoustically coupled to a device under test, then the speaker used in
the acoustic coupler must have a flat frequency response.
Connections are shown in Figure 7.
Tip
Tx
DET
Equalizer
Or
Coupler
Near-end
Speech
Rx
Ring
Figure 7: Near-End Talkoff Test Connections with Detector at Tip and Ring
For CAS detectors that are connected at the receive side of a hybrid transformer, the
near-end speech source should be connected at the transmit side of the hybrid either
electrically or by acoustic coupling. The loop determination test is required, and the
worse case loop is connected to the tip and ring interface of the hybrid.
If the source is electrically coupled, then the near-end speech signals must first be
passed though a pre-emphasis equalizer that simulates the frequency response of the
transmitter acoustics and electrical circuits. The equalizer is defined as linear on a
logarithmic scale from 300 Hz to 3000 Hz, with the response at 300 Hz down 5 dB
relative to 1000 Hz, and the response at 3000 Hz up 5 dB relative to 1000 Hz.
If the source is acoustically coupled to a device under test, then the speaker used in
the acoustic coupler must have a flat frequency response.
Connections are shown in Figure 8.
Tip
.
900
Ohms
Tx
Equalizer
Or
Coupler
Rx
DET
Worse-case
Loop
Ring
Near-end
Speech
Figure 8: Near-End Talkoff Test Connections with Detector at the Receive Port
Both the near-end and far-end talkoff tests proceed by sending and measuring speech of
different levels across the 600-Ohm tip and ring interface. SR-TSV-002476 specifies
testing at nine different speech levels of near-end speech and eight different levels of
near-end speech, as given in table 8:
10
Near-end Speech & DTR
Far-end speech & DTR
-7 dBm
-13 dBm
-10 dBm
-16 dBm
-13 dBm
-19 dBm
-16 dBm
-22 dBm
-19 dBm
-25 dBm
-22 dBm
-28 dBm
-25 dBm
-31 dBm
-28 dBm
-31 dBm
Table 8: Talkoff Test Levels
For each speech level in Table 8, record the rate of talkoffs per hour for both near-end
and far-end speech. In real world conversations, near-end speech would only be present
for 50% of the time. The talkoff rate can, therefore, be divided by two. The new rate is
called the “Derated talkdown rate (DTR).
The above derated talkdown rates for near-end and far-end speech can be combined into a
single 8x9 matrix as give in Table 9. Since the two talkoff rates are uncorrelated, for
each position in the matrix, combine the results for the near-end derated talkdown rate
and the far-end derated talkdown rate into a single “Combined Talkdown Rate.”
Near
End
dBm
-7
-10
-13
-16
-19
-22
-25
-28
-31
-13
(0.03)
CTR
(0.000129)
CTR
(0.000129)
CTR
(0.000129)
CTR
(0.000129)
CTR
(0.000129)
CTR
(0.000129)
CTR
(0.000129)
CTR
(0.000129)
CTR
(0.000129)
-16
(0.03)
CTR
(0.000129)
CTR
(0.000129)
CTR
(0.000129)
CTR
(0.000129)
CTR
(0.000129)
CTR
000129)
CTR
(0.000129)
CTR
(0.000129)
CTR
(0.000129)
Near End Speech in dBm (probability)
-19
-22
-25
(0.03)
(0.03)
(0.03)
CTR
CTR
CTR
(0.000129) (0.000129) (0.000129)
CTR
CTR
CTR
(0.000129) (0.000129) (0.000129)
CTR
CTR
CTR
(0.000129) (0.000129) (0.000129)
CTR
CTR
CTR
(0.000129) (0.000129) (0.000129)
CTR
CTR
CTR
(0.000129) (0.000129) (0.000129)
CTR
CTR
CTR
(0.000129) (0.000129) (0.000129)
CTR
CTR
CTR
(0.000129) (0.000129) (0.000129)
CTR
CTR
CTR
(0.000129) (0.000129) (0.000129)
CTR
CTR
CTR
(0.000129) (0.000129) (0.000129)
Table 10: Talkoff Test Matrix
-28
(0.03)
CTR
(0.000129)
CTR
CTR
(0.000129)
CTR
(0.000129)
CTR
(0.000129)
CTR
(0.000129)
CTR
(0.000129)
CTR
(0.000129)
CTR
(0.000129)
-31
(0.03)
CTR
(0.000129)
CTR
(0.000129)
CTR
(0.000129)
CTR
(0.000129)
CTR
(0.000129)
CTR
(0.000129)
CTR
(0.000129)
CTR
(0.000129)
CTR
(0.000129)
CTR: Combined Talkdown rate
The guidelines state that the talkdown and talkoff tests may be interleaved to save test
time. This implies that a simplified subset of the 63 total results can be used for the
11
talkoff tests, as with the talkdown tests. The matrix in Table 10 above could, therefore,
be constructed using interpolated readings based on the readings in Table 11:
Far-end Speech
Near-end Speech
-7 dBm
-7 dBm
-13 dBm
-13 dBm
-10 dBm
-10 dBm
-16 dBm
-16 dBm
-22 dBm
-22 dBm
-19 dBm
-19 dBm
-28 dBm
-28 dBm
Table 11: Talkoff Test Levels
This non-sequential set of levels corresponds to the set of near-end speech levels used in
the talkdown test (See figure 6).
Once the talkoff matrix is filled in, there are three test conditions that must be met:
a) Condition 1: The talkoff rate should be less than 1 in 45 hours for the nearend speech level of –19 dBm and the far-end speech level 0f –28 dBm (see the
darkly shaded cell in the Table 10 matrix.)
b) Condition 2: The talkoff rate should be less than 1 in 10 hours for the worst
1.14% of all combinations (see the lightly shaded cell in the Table 10 matrix.)
c) The talkoff rate should be less than 1 in 35 hours for weighted average of all
combinations.
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