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8. Recommendation G.738
CHARACTERISTICS OF PRIMARY PCM MULTIPLEX EQUIP-
MENT
OPERATING AT 2048 KBIT/S AND OFFERING SYNCHRONOUS
DIGITAL ACCESS AT 320 KBIT/S AND/OR 64 KBIT/S
(Melbourne, 1988)
This Recommendation gives the characteristics of a PCM multiplex
equipment operating at 2048kbit/s and providing one or several of the
following internal digital access options:
- bidirectional synchronous 64 kbit/s channels (see Figure1a/G.738;
- unidirectional synchronous 320 kbit/s channels (see Figure1b/
G.738.
The 320 kbit/s channel is based on the allocation of 5x64kbit/s time
slots, e.g., for setting up sound-programme circuits according to
RecommendationsJ.43 and J.44.
Because these circuits are specified as unidirectional, the equipment for
insertion/extraction has to be separated as shown in Figures1b/G.738.
1. General characteristics
1.1 Fundamental characteristics for voice channel encoding
The encoding law used is the A-law as specified in
RecommendationG.711. The sampling rate, load capacity and the code
are also specified in that Recommendation.
The number of quantized values is 256.
Note - The inversion of bits 2, 4, 6 and 8 is covered by the encoding law
and is applicable only to voice channel time slots.
1.2 Bit rate
The nominal bit rate is 2048 kbit/s. The tolerance on this rate is +50
parts per million (ppm).
1.3 Timing signal
It should be possible to derive the transmit timing signal from any of the
following:
a) from the received 2084 kbit/s signal;
b) from an external source at 2048 kHz (see º5);
c) from an internal oscillator.
Note - The provision of a timing signal output, available for the purpose
of synchronizing other equipments, is an option that might be required
depending upon national synchronization arrangements.
1.4 Types of access
a) access for bidirectional synchronous 64 kbit/s channels (see
Figure1a/G.738);
b) access for unidirectional synchronous 320 kbit/s channels (see Fig-
ure 1b/G.738).
Note - The synchronous insertion of a digital sound programme signal
into a 320 kbit/s channel requires the internal regeneration of a timing
signal T synchronized by the 2048 kbit/s signal I1. the timing signal is
used for synchronizing the sampling frequency of the analogue/digital
converters producing the digital sound programme signal.
2. Frame structure and use of derived channel time slot
2.1 Frame structure of 2048 kbit/s signal
Refer to º2.3 of Recommendation G.704. Bit 1 of the frame should be
used in accordance with º2.3.3/6.706, i.e., for a CRC check bit proce-
dure.
2.2 Use of derived channel time slots
2.2.1 Telephone channels
It should be possible to assign channel time slots 1 to 15 and 17 to 31 to
30 telephone channels numbered from 1 to 30.
2.2.2 64 kbit/s access
The number of accessible channel time slots should be at least four and
the equipment shall allow access to any of channel time slots 1 to 15 and
17 to 31.
Note - Equipment exists which provides access to at least four channel
time slots in the following order to priority:
6 - 22 - 14 - 30 - 2 - 18 - 10 - 26 - 4 - 20 - 12 - 28 - 8 - 24 - 5 -21 - 13
- 29 - 1 - 17 - 9 - 25 - 3 - 19 - 11 - 27 - 7 - 23 - 15 - 31.
2.2.3 320 kbit/s access
The time slot allocation for digital channels with bit rate at 320kbit/s is
given in the following table:
+ûûûûûûûûûûûûûûûûûûûûûûûûûûûûûûûûûûûûûûûûûûûûûûûûûûûûûûûûû
ûû+ûûûûûûûûûûû+
_ 320 kbit/s channels (Note 1) _ DSP _
+ûûûûûûûûû+ûûûûûûûûû+ûûûûûûûûû+ûûûûûûûûû+ûûûûûûûûû+ûûûûûû
ûûû+ ACCESS _
_ A _ B _ C _ D _ E _ F _ POINTS _
+ûûûûûûûûû+ûûûûûûûûû+ûûûûûûûûû+ûûûûûûûûû+ûûûûûûûûû+ûûûûûû
ûûû+ûûûûûûûûûûû+
_ 1 - 2 - _ 6 - 7 - _ 11 - 12 _ 17 - 18 _ 22 - 23 _ 27 - 28 _ I3, T, E3 _
_ 3 - 4 - _ 8 - 9 - _ - 13 - _ - 19 - _ - 24 - _ - 29 - _ Figure _
_ 5 _ 10 _ 14 - 15 _ 20 - 21 _ 25 - 26 _ 30 - 31 _ 1b/G.738 _
+ûûûûûûûûû+ûûûûûûûûû+ûûûûûûûûû+ûûûûûûûûû+ûûûûûûûûû+ûûûûûû
ûûû+ûûûûûûûûûûû+
Note 1 - The six possible 320 kbit/s channels in a 2048 kbit/s stream are
numbered A to F. Preferably the channel pairs A-B, C-D, and E-F should
be used for stereophonic transmission.
Note 2 - If the channel time slot 16 which is assigned to signalling as cov-
ered in º5 below is not needed for signalling, it may be used for purposes
other thana voice channel encoded within the PCM multiplex equipment.
a) Bidirectional synchronous insertion/extraction of 64 kbit/s data
channels
b) Unidirectional synchronous insertion and extraction of digital
sound-programme (DSP) into/out of a 320 kbit/s channel
I,E: insertion side; extraction side
I1,E1: 2048 kbit/s interface
I2,E2 64 kbit/s interface
I3,E3: synchronous; digital sound programme signal access
T: timing signal
FIGURE 1/G.738
PCM multiplex equipment operating at 2048 kbit/s
and offering access to digital sound-programme signals
and/or to synchronous 64 kbit/s data channels
3. Frame alignment and CRC procedures
(An illustration of the procedure is given in Figure2/G.706.)
3.1 Loss of frame alignment
Refer to º4.1.1. of Recommendation G.706.
3.2 Recovery of frame alignment
Refer to º4.1.2 of Recommendation G.706.
3.3 CRC multiframe alignment in TSO
Refer to º4.2 of Recommendation G.706.
3.4 CRC bit monitoring
Refer to º4.3 of Recommendation G.706.
4. Fault conditions and consequent actions
4.1 Fault conditions
The PMC multiplex equipment should detect the following conditions:
4.1.1 Failure of power supply.
4.1.2 Failure of codec (except when using single channel codecs).
As a minimum requirement, this fault condition should be recognized
when for at least one signal level in the range -21 to -6dBmO, the signal-
to-quantizing noise ration performance of the local codec is 18 dB or
more below the level recommended in RecommendationG.712.
4.1.3 Loss of incoming signals at the 64 kbit/s and 320 kbit/s tributary
input ports.
Note 1 - This detection is not mandatory when contradirectional inter-
faces are used.
Note 2 - The detection of this fault condition is not mandatory for chan-
nel time slot 16 when channel associated signalling is used and the sig-
nalling multiplex equipment is situated within a few metres of the PCM
multiplex equipment.
4.1.4 Loss of the incoming signal at 2048 kbit/s.
Note 1 - The detection of this fault condition is required only when it
does not result in an indication of loss of frame alignment.
Note 2 - Where separate circuits are used for the digital signal and the
timing signal, the loss of either or both should constitute loss of the
incoming signal.
4.1.5 Loss of frame alignment.
4.1.6 Excessive bit error ratio detected by monitoring the frame alignment
signal.
4.1.6.1 With a random bit error ratio of < 10-4, the probability of activat-
ing the indication of fault condition in a few seconds should be less than
10-6.
With a random bit error ratio of > 10-3, the probability of activating the
indication of fault condition in a few seconds should be higher than 0.95.
4.1.6.2 With a random bit error ratio of > 10-3, the probability of deacti-
vating the indication of fault condition in a few seconds should be
almost0.
With a random bit error ratio of < 10-4, the probability of deactivating
theindication of fault condition in a few seconds should be higher than
0.95.
Note - The activating and deactivating period specified as "a few sec-
onds" is intended to be in the order of 4 to 5 seconds.
4.1.7 Alarm indication received from the remote PCM multiplex equip-
ment (see º4.2.3).
4.2 Consequent actions
Further to the detection of a fault condition, appropriate actions should be
taken as specified in Table1/G.738. The consequent actions are as fol-
lows:
4.2.1 Service alarm indication generated to signify that the service pro-
vided by the PCM multiplex is no longer available. This indication
should be forwarded at least to the switching and/or signalling multiplex
equipment depending upon the arrangements provided. The indication
should be given as soon as possible and not later than 2ms after detection
of the relevant fault condition.
This specification, taking into account the specification given in º2.5, is
equivalent to recommending that the average time to detect a loss of
frame alignment or a loss of the incoming 2048kbit/s signal and to give
the relevant indication should not be greater than 3ms.
When using common channel signalling the indication should be for-
warded to the switching equipment by means of a separate interface on
the PCM multiplex equipment.
4.2.2 Prompt maintenance alarm indication generated to signify that per-
formance is below acceptable standards and maintenance attention is
required locally. When the AIS (see general note below to º4.2) at
2048kbit/s input is detected the prompt maintenance alarm indication,
associated with loss of frame alignment (see º4.1.5) and excessive error
rate (see º4.1.6), should be inhibited, while the rest of the consequent
actions are in accordance with those associated in Table1/G.738 with the
two fault conditions.
Note - The location and provision of any visual and/or audible alarm acti-
vated by the alarm indications given in º4.2.1 and º4.2.2, is left to the
discretion of each administration.
4.2.3 Alarm indication to the remote end transmitted by changing bit 3 of
channel time slot 0 from the state 0 to the state 1 in those frames not con-
taining the frame alignment signal. This should be effected as soon as
possible.
4.2.4 Transmission suppressed at the analogue voice-frequency outputs
4.2.5 AIS applied to all 64 kbit/s and 320 kbit/s outputs (see general note
below to º4.2). For 64 kbit/s outputs this action should be taken as soon
as possible and not later than 2ms after the detection of the fault condi-
tion.
4.2.6 AIS applied to relevant time slots in the composite 2048kbit/s out-
put signal (if suspension of incoming 64 kbit/s and 320 kbit/s signals is
provided).
Notes to º4.2
Note 1 - The equivalent binary content of the alarm indication signal
(AIS) is a continuous stream of binary 1s. The strategy for detecting the
presence of the AIS should be such that with a high probability the AIS is
detectable even in the presence of random errors having a mean error rate
of 1 in 103. Nevertheless, a signal in which all the binary elements, with
the exception of the frame alignment signal, are in the state 1, should not
be taken as an AIS.
Note 2 - All timing requirements quoted apply equally to restoration,
subsequent to the fault condition clearing.
5. Signalling
Text as in Recommendation G.732.
6. Interfaces
6.1 Audio frequency interface
The analogue audio frequency interfaces should be in accordance with
RecommendationsG.712, G.713, G.714 and G.715.
6.2 Digital interfaces
The digital interfaces at 2048 kbit/s should be in accordance with Recom-
mendation G.703.
The digital interfaces at 64 kbit/s should be of either the codirectional or
the contradirectional type specified in RecommendationG.703. The
specification for 64 kbit/s interfaces are not mandatory for channel asso-
ciated signalling. The interface for external synchronization of the trans-
mitting timing signal should be in accordance with
RecommendationG.703.
The need to define a digital interface operating at 320 kbit/s is under
study.
Note 1 - It should be noted that, according to the principle of minimizing
the number of different types of interfaces, the information rate of
320kbit/s will be offered to customers at the user/network interface level
using the 2048kbit/s interface as defined in Recommendation I.431 and
RecommendationG.703.
Note 2 - In the case of the 64 kbit/s codirectional interface, the design of
the input ports should take into account the need to provide octet align-
ment, to allow controlled slips when the tributary timing and that of the
multiplexer timing source are plesiochronous, and to absorb jitter and
wander up to the limits given in RecommendationG.823.
TABLE 1/G.738
Fault conditions and consequent actions for the PCM multiplex equip-
ment
+ûûûûûûûûûûûûûûû+ûûûûûûûûûûûûûûû+ûûûûûûûûûûûûûûûûûûûûûûûû
ûûûûûûûûûûûûûûûûûûûûûûûûûûûûûûûûûûûûûûûûûûûûûûûûûûûûûûûûûû
ûûûûûûûûûûûûû+
_Equipment _Fault _ Consequent actions (see
º3.2) _
_ part _ conditions +ûûûûûûûûûûûûûûû+ûûûûûûûûûûûûûûû+ûûû
ûûûûûûûûûûûû+ûûûûûûûûûûûûûûû+ûûûûûûûûûûûûûûû+ûûûûûûûûûûûûû
ûû+
_ _ (see º4.1) _ Service _ Prompt _ Alarm _ Trans-
mission _ AIS applied _ AIS applied _
_ _ _ alarm _ maintenance _ indication _ sup-
pressed at _ to 64 kbit/s _ to the _
_ _ _ indication _ alarm _ remote end _ the
analogue _ and 320 kbit/s_ relevant time _
_ _ _ generated _ indication _ transmitted _ voice-
_ outputs _ slot of the _
_ _ _ _ _ _ frequency _
_ 2048 kbit/s _
_ _ _ _ _ _ outputs _
_ composite _
_ _ _ _ _ _ _ _
signal _
+ûûûûûûûûûûûûûûû+ûûûûûûûûûûûûûûû+ûûûûûûûûûûûûûûû+ûûûûûûûû
ûûûûûûû+ûûûûûûûûûûûûûûû+ûûûûûûûûûûûûûûû+ûûûûûûûûûûûûûûû+ûû
ûûûûûûûûûûûûû+
_ _ Failure of _ Yes _ Yes _ Yes (if _ Yes (if
_ Yes (if _ Yes (if _
_ Multiplexer _ power supply _ _ _ practicable) _
practicable) _ practicable) _ practicable) _
_ and +ûûûûûûûûûûûûûûû+ûûûûûûûûûûûûûûû+ûûûûûûûûûûûûûûû
+ûûûûûûûûûûûûûûû+ûûûûûûûûûûûûûûû+ûûûûûûûûûûûûûûû+ûûûûûûûûû
ûûûûûû+
_ demultiplexer _ Failure of _ Yes _ Yes _ Yes _ Yes
_ _ _
_ _ codec _ _ _ _ _
_ _
+ûûûûûûûûûûûûûûû+ûûûûûûûûûûûûûûû+ûûûûûûûûûûûûûûû+ûûûûûûûû
ûûûûûûû+ûûûûûûûûûûûûûûû+ûûûûûûûûûûûûûûû+ûûûûûûûûûûûûûûû+ûû
ûûûûûûûûûûûûû+
_ Multiplexer _ Loss of _ _ Yes _ _ _
_ Yes _
_ only _ incoming _ _ _ _ _
_ _
_ _ signal at _ _ _ _ _
_ _
_ _ 64 kbit/s _ _ _ _ _
_ _
_ _ and/or _ _ _ _ _
_ _
_ _ 320 kbit/s _ _ _ _ _
_ _
_ _ inputs (see _ _ _ _ _
_ _
_ _ note under _ _ _ _ _
_ _
_ _ º4.1.3) _ _ _ _ _
_ _
+ûûûûûûûûûûûûûûû+ûûûûûûûûûûûûûûû+ûûûûûûûûûûûûûûû+ûûûûûûûû
ûûûûûûû+ûûûûûûûûûûûûûûû+ûûûûûûûûûûûûûûû+ûûûûûûûûûûûûûûû+ûû
ûûûûûûûûûûûûû+
TABLE 1/G.738 (continued)
+ûûûûûûûûûûûûûûû+ûûûûûûûûûûûûûûû+ûûûûûûûûûûûûûûûûûûûûûûûû
ûûûûûûûûûûûûûûûûûûûûûûûûûûûûûûûûûûûûûûûûûûûûûûûûûûûûûûûûûû
ûûûûûûûûûûûûû+
_Equipment _Fault _ Consequent actions (see
º3.2) _
_ part _ conditions +ûûûûûûûûûûûûûûû+ûûûûûûûûûûûûûûû+ûûû
ûûûûûûûûûûûû+ûûûûûûûûûûûûûûû+ûûûûûûûûûûûûûûû+ûûûûûûûûûûûûû
ûû+
_ _ (see º 4.1) _ Service _ Prompt _ Alarm _ Trans-
mission _ AIS applied _ AIS applied _
_ _ _ alarm _ maintenance _ indication _ sup-
pressed at _ to 64 kbit/s _ to the _
_ _ _ indication _ alarm _ remote end _ the
analogue _ and 320 kbit/s_ relevant time _
_ _ _ generated _ indication _ transmitted _ voice-
_ outputs _ slot of the _
_ _ _ _ _ _ frequency _
_ 2048 kbit/s _
_ _ _ _ _ _ outputs _
_ composite _
_ _ _ _ _ _ _ _
signal _
+ûûûûûûûûûûûûûûû+ûûûûûûûûûûûûûûû+ûûûûûûûûûûûûûûû+ûûûûûûûû
ûûûûûûû+ûûûûûûûûûûûûûûû+ûûûûûûûûûûûûûûû+ûûûûûûûûûûûûûûû+ûû
ûûûûûûûûûûûûû+
_ _ Loss of _ Yes _ Yes _ Yes _ Yes _
Yes _ _
_ _ incoming _ _ _ _ _
_ _
_ _ signal at _ _ _ _ _
_ _
_ _ 2048 kbit/s _ _ _ _ _
_ _
_ +ûûûûûûûûûûûûûûû+ûûûûûûûûûûûûûûû+ûûûûûûûûûûûûûûû
+ûûûûûûûûûûûûûûû+ûûûûûûûûûûûûûûû+ûûûûûûûûûûûûûûû+ûûûûûûûûû
ûûûûûû+
_ _ Loss of frame _ Yes _ Yes (see _ Yes _ Yes
_ Yes _ _
_ _ alignment _ _ º 4.2.2) _ _ _
_ _
_ _ (see Note 2 _ _ _ _ _
_ _
_ _ 4.2/G.706) _ _ _ _ _
_ _
_ Demultiplexer +ûûûûûûûûûûûûûûû+ûûûûûûûûûûûûûûû+ûûûûûûûûûûû
ûûûû+ûûûûûûûûûûûûûûû+ûûûûûûûûûûûûûûû+ûûûûûûûûûûûûûûû+ûûûûû
ûûûûûûûûûû+
_ only _ Error ratio _ Yes _ Yes (see _ Yes _ Yes
_ Yes _ _
_ _ 1 10-3 _ _ º4.2.2) _ _ _
_ _
_ _ alignment _ _ _ _ _
_ _
_ _ signal _ _ _ _ _ _
_
_ +ûûûûûûûûûûûûûûû+ûûûûûûûûûûûûûûû+ûûûûûûûûûûûûûûû
+ûûûûûûûûûûûûûûû+ûûûûûûûûûûûûûûû+ûûûûûûûûûûûûûûû+ûûûûûûûûû
ûûûûûû+
_ _ Alarm _ Yes _ _ _ _
_ _
_ _ indication _ _ _ _ _
_ _
_ _ received from _ _ _ _ _
_ _
_ _ the remote end_ _ _ _ _
_ _
+ûûûûûûûûûûûûûûû+ûûûûûûûûûûûûûûû+ûûûûûûûûûûûûûûû+ûûûûûûûû
ûûûûûûû+ûûûûûûûûûûûûûûû+ûûûûûûûûûûûûûûû+ûûûûûûûûûûûûûûû+ûû
ûûûûûûûûûûûûû+
Note to Table 1/G.738 - A "Yes" in the table signifies that an action
should be taken as a consequence of the relevant fault condition. An open
space in the table signifies that the relevant action should not be taken as
a consequence of the relevant fault condition, if this condition is the only
one present. If more than one fault condition is simultaneously present,
the relevant action should be taken if, for at least one of the conditions, a
"Yes" is defined in relation to this action.
7. Jitter
7.1 Jitter at 2048 kbit/s output (see Figure 2/G.823)
7.1.1 In the case where the transmitting timing signal is derived from an
internal oscillator, the peak-to-peak jitter at the 2048 kbit/s output should
not exceed 0.05 UI when it is measured within the frequency range from
f1=20Hz to f4 = 100 kHz.
7.1.2 In the case where the transmitting timing signal is derived from an
external source having no jitter, the peak-to-peak jitter at the 2048kbit/s
output should not exceed 0.05UI when it is measured within the fre-
quency range from f1=20Hz to f4=100kHz.
7.1.3 In the case where the transmitting timing signal is derived from the
incoming 2048kbit/s signal having no jitter, the peak-to-peak jitter at the
2048kbit/s output should not exceed 0.10UI when it is measured within
the frequency range from f1=20Hz to f4 = 100 kHz. The equivalent
binary content of the test signal applied at the 2048kbit/s input shall be a
pseudo-random bit sequence of length 215-1 as specified in
Recommendation0.151.
Note - It may be necessary to include a frame alignment signal in the test
signal to enable the measurement to be carried out.
7.2 Jitter at tributary outputs
7.2.1 Jitter at 64 kbit/s output
In the case where the incoming 2048 kbit/s signal has no jitter, the peak-
to-peak jitter at the 64 kbit/s output should not exceed 0.025UI when it is
measured within the frequency range from f1 = 20Hz to f4=10kHz.
The equivalent binary content of the test signal applied to the 2048kbit/s
input shall be a pseudo-random bit sequence of length 215-1 as specified
in Recommendation0.151.
Note - In order to carry out this measurement without invoking AIS at the
64kbit/s output it will normally be necessary to include a frame align-
ment signal in the test signal.
7.2.2 Jitter at 320 kbit/s output
Since the physical and electrical characteristics of a 320 kbit/s interface
are identical to those of the 2048 kbit/s interface, the specification of this
parameter is the same as that given in º7.1.3 above.
7.3 Jitter transfer functions
7.3.1 The jitter transfer function between the 2048 kbit/s external syn-
chronization signal and the 2048kbit/s output signal should not exceed
the gain/frequency limits given in Figure2/G.738. The 2048kHz signal
shall be modulated with sinusoidal jitter.
Some administrations require that equipment is fitted with jitter reducers.
In this case, the jitter transfer function should not exceed the gain/fre-
quency limits given in Figure3/G.738.
7.3.2 In the case where the transmitting timing is derived from the incom-
ing signal the jitter transfer function between the 2048kbit/s input and
the 2048kbit/s output shall be as specified in º7.3.1.
Note 1 - The 2048kbit/s test signal shall be modulated by sinusoidal jit-
ter. The equivalent binary content of the test signal shall be 1000.
Note 2 - It may be necessary to include a frame alignment signal in the
test signal to enable the measurement to be carried out.
Note 1 - The frequency f0 should be less than 20Hz and as low as possi-
ble (e.g., 10Hz), taking into account the limitations of measuring equip-
ment.
Note 2 - To achieve accurate measurements, the use of a selective method
is recommended with a bandwidth sufficiently small referred to the rele-
vant measurement frequency but not wider that 40Hz.
Note 3 - For interfaces within national boundaries, this characteristic may
be used.
FIGURE 2/G.738
Note 1 - The frequency f0 should be less than 20 Hz and as low as possi-
ble (e.g., 10Hz), taking into account the limitations of measuring equip-
ment.
Note 2 - To achieve accurate measurement, the use of a selective method
is recommended with a bandwidth sufficiently small referred to the rele-
vant measurement frequency but not wider than 40Hz.
FIGURE 3/G.738
7.3.3 The jitter transfer function between the 2048kbit/s input and
the64kbit/s output should not exceed -29.6dB when measured over the
frequency range f0 to 10kHz. The frequency f0 should be less than
20Hz and as low as possible (e.g., 10Hz), taking into account the limita-
tions of measuring equipment.
Note 1 - The 2048 kbit/s test signal shall be modulated by sinusoidal jit-
ter. The equivalent binary content of the test signal shall be 1000.
Note 2 - In order to carry out this measurement without invoking AIS at
the 64kbit/s output it will normally be necessary to include a frame
alignment signal in the test signal.
Note 3 - The jitter reduction of 1/32 due to demultiplexing is equivalent
to -30.1dB.
7.3.4 Since the physical and electrical characteristics of a 320kbit/s inter-
face are identical to those of 2048kbit/s interface, the jitter transfer func-
tion between 2048kbit/s input and 320kbit/s output is the same as that
given in 7.3.1 and 7.3.2 above.
