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9. Recommendation G.739
CHARACTERISTICS OF AN EXTERNAL ACCESS EQUIPMENT
OPERATING AT 2048 KBIT/S OFFERING SYNCHRONOUS
DIGITAL ACCESS AT 320 KBIT/S AND/OR 64 KBIT/S
This Recommendation gives the characteristics of equipment (external to
PCM muldexes) operating at 2048 kbit/s and providing one or several of
the following tributaries into/from channel time slots of a 2048kbit/s
composite signal:
- bidirectional synchronous 64 kbit/s access (Figure1a/G.739);
- unidirectional synchronous 320 kbit/s access (Figure 1b/G.739).
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 Figure1b/G.739.
1. General characteristics
1.1 Bit rate
The nominal bit rate is 2048kbit/s. The tolerance on this rate is +50
parts per million (ppm).
1.2 Types of external access
a) Bidirectional synchronous insertion/extraction of 64kbit/s data chan-
nels (see Figure 1a/G.739).
Note 1 - The timing signal for the insertion side should be derived from
the 2048kbit/s incoming signal at the insertion side (I0); the timing sig-
nal for the extraction side should be derived from the 2048kbit/s incom-
ing signal at the extraction side (E1).
Note 2 - The provision of a timing signal output, available for the pur-
pose of synchronizing other equipments, is an option that might be
required depending upon national synchronization arrangements.
Note 3 - Further study is required on the possible need for an internal
clock.
b) Unidirectional synchronous insertion and extraction of a digital
sound-programme signal into/out of 320kbit/s channel (see
Figure1b/G.739).
Note - The synchronous insertion equipment for 320kbit/s signals
requires the internal regeneration of a timing signal synchronized by the
2048 kbit/s input signal I0. This timing signal output of the synchronous
insertion equipment is used for synchronizing the sampling frequency of
the analogue/digital converter.
2. Frame structure and use of derived channel time slots
2.1 Frame structure of the 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/G.704, i.e., for a CRC check bit proce-
dure.
2.2 Use of derived channel time slots
Time slots not accessed flow transparently through the equipment.
Note - Further study is required as to whether the binary content of time
slots used at the access points should be replaced, after extraction from
the composite signal, by the AIS.
2.2.1 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 of 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
2.2.2 320 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.739 _
+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 than a voice channel encoded within the PCM multiplex equip-
ment.
3. Frame alignment and CRC procedures both at insertion (I0) and extrac-
tion (E1) sides
(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.
a) Bidirectional synchronous insertion/extraction of 64 kbit/s data
channels
b) Unidirectional synchronous insertion and extraction of digital
sound-programme (DSP) signal into and out of a 320 kbit/s channel
I0,I1:insertion side
E0,E1: extraction side
I2,E2 64 kbit/s interface
I3,E3: synchronous; digital sound programme signal access
T: timing signal
FIGURE 1/G.739
External access equipment for 64 and 320 kbit/s channels
4. Fault conditions and consequent actions
4.1 Fault conditions
The equipment should detect the following conditions:
4.1.1 Failure of power supply.
4.1.2 Loss of incoming signal.
Note - This detection is not mandatory when contra-directional interfaces
are used.
4.1.3 Loss of the incoming signal at 2048 kbit/s both at insertion (I0) and
extraction (E1) sides.
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.
4.1.4 Loss of frame alignment both at insertion (I0) and extraction (E1)
sides.
4.1.5 Excessive bit error ratio detected by monitoring the frame alignment
signal at both the insertion (I0) and extraction (E1) sides.
Note - The detection of this fault condition at insertion side (I0) depends
on the type of application of this equipment in a network and therefore is
not mandatory.
4.1.5.1 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.
4.1.5.2 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 almost
0.
With a random bit error ratio of < 10-4, the probability of deactivating the
indication of fault condition in a few seconds should be higher than 0.95.
Note - The activating and deactivating period specified as "as few sec-
onds" is intended to be in the order to 4 to 5 seconds.
4.2 Consequent actions
Further to the detection of fault condition, appropriate actions should be
taken as specified in Table1/G.739. The consequent actions are as fol-
lows:
4.2.1 Prompt maintenance alarm indication generated to signify that per-
formance is below acceptable standards and maintenance attention is
required locally. When the AIS at the 2048kbit/s inputs (I0, E1) is
detected (see general note below to º4.2) the prompt maintenance alarm
indication associated with loss of frame alignment (see º4.1.4) and
excessive error rate (see º4.1.5), should be inhibited, while the rest of
the consequent actions are in accordance with those associated in
Table1/G.739 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, is left to the discretion of
each administration.
4.2.2 AIS applied to I2, I3 outputs (see general note below to º4.2). This
action should be taken as soon as possible and not later than 2ms after
the detection of the fault condition.
4.2.3 AIS applied to relevant time slots in the composite 2048kbit/s out-
put signalat insertion side (I1) if supervision of the incoming I2, I3 signal
is provided.
4.2.4 Inhibition of I2, I3 digital information insertion
4.2.5 Both 2048 kbit/s signals are bypassed
Note - The provision of this consequent action depends on the type of
application of this equipment in a network and therefore is not manda-
tory.
4.2.6 AIS applied to the 2048 kbit/s output, extraction side (E0)
Note - The provision of this consequent action depends on the type of
application of this equipment in a network and therefore is not manda-
tory.
TABLE 1/G.739
Fault conditions and consequent actions for the external access equip-
ment
+ûûûûûûûûûûûûûûûûûûû+ûûûûûûûûûûûûûûûûûûûûûûûûûûûûûûûûûûûûû
ûûûûûûûûûûûûûûûûûûûûûûûûûû+ûûûûûûûûûûûûûûû+ûûûûûûûûûûûûûûû
+ûûûûûûûûûûûûûûû+
_ Fault conditions _ Consequent actions (see º4.2) _
Both _ AIS applied _ AIS applied _
_ (see º4.1) +ûûûûûûûûûûûûûûû+ûûûûûûûûûûûûûûû+ûûûûûûûûûûûû
ûûû+ûûûûûûûûûûûûûûû+ 2048 kbit/s _ to the _ to the _
_ _ Prompt _ AIS applied _ Inhibition of _ AIS applied
_ signal are _ 2048 kbit/s _ 2048 kbit/s _
_ _ maintenance _ to E2, E3 _ digital _ to the _
bypassed (see _ output, _ output, _
_ _ alarms _ outputs _ information _ relevant time _
Note under _ extraction _ insertion side_
_ _ indication _ _ insertion _ slot of the _ º4.2.5)
_ side (EO) _ (I1) (see note_
_ _ generated _ _ I2 , I3 _ 2048 kbit/s _
_ (see note _ under º4.2.7)_
_ _ _ _ _ composite _ _
under º 4.2.6)_ _
_ _ _ _ _ signal at _ _
_ _
_ _ _ _ _ insertion _ _
_ _
_ _ _ _ _ side (I0) _ _
_ _
+ûûûûûûûûûûûûûûûûûûû+ûûûûûûûûûûûûûûû+ûûûûûûûûûûûûûûû+ûûûûû
ûûûûûûûûûû+ûûûûûûûûûûûûûûû+ûûûûûûûûûûûûûûû+ûûûûûûûûûûûûûûû
+ûûûûûûûûûûûûûûû+
_ Failure of power _ Yes _ _ _ _ Yes
_ Yes (if _ Yes (if _
_ supply _ _ _ _ _ _
practicable) _ practicable) _
+ûûûûûûûûûûûûûûûûûûû+ûûûûûûûûûûûûûûû+ûûûûûûûûûûûûûûû+ûûûûû
ûûûûûûûûûû+ûûûûûûûûûûûûûûû+ûûûûûûûûûûûûûûû+ûûûûûûûûûûûûûûû
+ûûûûûûûûûûûûûûû+
_ Loss of incoming _ Yes _ _ _ Yes _
_ _ _
_ signal at I2, I3 _ _ _ _ _ _
_ _
_ inputs (see note _ _ _ _ _ _
_ _
_ under º4.1.2) _ _ _ _ _ _
_ _
+ûûûûûûûûûûûûûûûûûûû+ûûûûûûûûûûûûûûû+ûûûûûûûûûûûûûûû+ûûûûû
ûûûûûûûûûû+ûûûûûûûûûûûûûûû+ûûûûûûûûûûûûûûû+ûûûûûûûûûûûûûûû
+ûûûûûûûûûûûûûûû+
_ Loss of Extr.s._ Yes _ Yes _ _ _ _
Yes _ _
_ incoming (E1) _ _ _ _ _ _
_ _
_ signal +ûûûûûûûûûûûûûûû+ûûûûûûûûûûûûûûû+ûûûûûûûûûûûûû
ûû+ûûûûûûûûûûûûûûû+ûûûûûûûûûûûûûûû+ûûûûûûûûûûûûûûû+ûûûûûûû
ûûûûûûûû+
_ at 2048 Ins.s. _ Yes _ _ Yes _ _ _
_ Yes _
_ kbit/s (I0) _ _ _ _ _ _
_ _
+ûûûûûûûûûûûûûûûûûûû+ûûûûûûûûûûûûûûû+ûûûûûûûûûûûûûûû+ûûûûû
ûûûûûûûûûû+ûûûûûûûûûûûûûûû+ûûûûûûûûûûûûûûû+ûûûûûûûûûûûûûûû
+ûûûûûûûûûûûûûûû+
TABLE 1/G.739 (continued)
+ûûûûûûûûûûûûûûûûûûû+ûûûûûûûûûûûûûûûûûûûûûûûûûûûûûûûûûûûûû
ûûûûûûûûûûûûûûûûûûûûûûûûûû+ûûûûûûûûûûûûûûû+ûûûûûûûûûûûûûûû
+ûûûûûûûûûûûûûûû+
_ Fault conditions _ Consequent actions (see º4.2) _
Both _ AIS applied _ AIS applied _
_ (see º4.1) +ûûûûûûûûûûûûûûû+ûûûûûûûûûûûûûûû+ûûûûûûûûûûûû
ûûû+ûûûûûûûûûûûûûûû+ 2048 kbit/s _ to the _ to the _
_ _ Prompt _ AIS applied _ Inhibition of _ AIS applied
_ signal are _ 2048 kbit/s _ 2048 kbit/s _
_ _ maintenance _ to E2, E3 _ digital _ to the _
bypassed (see _ output, _ output, _
_ _ alarms _ outputs _ information _ relevant time _
Note under _ extraction _ insertion side_
_ _ indication _ _ insertion _ slot of the _ º4.2.5)
_ side (EO) _ (I1) (see note_
_ _ generated _ _ I2 , I3 _ 2048 kbit/s _
_ (see note _ under º4.2.7)_
_ _ _ _ _ composite _ _
under º4.2.6)_ _
_ _ _ _ _ signal at _ _
_ _
_ _ _ _ _ insertion _ _
_ _
_ _ _ _ _ side (I0) _ _
_ _
+ûûûûûûûûûûûûûûûûûûû+ûûûûûûûûûûûûûûû+ûûûûûûûûûûûûûûû+ûûûûû
ûûûûûûûûûû+ûûûûûûûûûûûûûûû+ûûûûûûûûûûûûûûû+ûûûûûûûûûûûûûûû
+ûûûûûûûûûûûûûûû+
_ Loss of Extr.s._ Yes (see _ Yes _ _ _ _
Yes _ _
_ frame (E1) _ º 4.2.1) _ _ _ _ _
_ _
_ alignment +ûûûûûûûûûûûûûûû+ûûûûûûûûûûûûûûû+ûûûûûûûûûûû
ûûûû+ûûûûûûûûûûûûûûû+ûûûûûûûûûûûûûûû+ûûûûûûûûûûûûûûû+ûûûûû
ûûûûûûûûûû+
_ (see Ins.s _ Yes (see _ _ Yes _ _ _
_ Yes _
_ Note 2 of (I0) _ º4.2.1) _ _ _ _ _
_ _
_ 4.2/G.706) _ _ _ _ _ _
_ _
+ûûûûûûûûûûûûûûûûûûû+ûûûûûûûûûûûûûûû+ûûûûûûûûûûûûûûû+ûûûûû
ûûûûûûûûûû+ûûûûûûûûûûûûûûû+ûûûûûûûûûûûûûûû+ûûûûûûûûûûûûûûû
+ûûûûûûûûûûûûûûû+
_ Error Extr.s._ Yes (see _ Yes _ _ _ _
Yes _ _
_ ratio (E1) _ º4.2.1) _ _ _ _ _
_ _
_ 1.10-3 _ _ _ _ _ _
_ _
_ on the _ _ _ _ _ _
_ _
_ frame +ûûûûûûûûûûûûûûû+ûûûûûûûûûûûûûûû+ûûûûûûûûûûûû
ûûû+ûûûûûûûûûûûûûûû+ûûûûûûûûûûûûûûû+ûûûûûûûûûûûûûûû+ûûûûûû
ûûûûûûûûû+
_ alignment Ins.s._ Yes (see _ _ Yes _ _
_ _ Yes _
_ signal (I0) _ º4.2.1) _ _ _ _ _
_ _
_ (see note _ _ _ _ _ _
_ _
_ under _ _ _ _ _ _
_ _
_ (º4.1.5) _ _ _ _ _ _
_ _
+ûûûûûûûûûûûûûûûûûûû+ûûûûûûûûûûûûûûû+ûûûûûûûûûûûûûûû+ûûûûû
ûûûûûûûûûû+ûûûûûûûûûûûûûûû+ûûûûûûûûûûûûûûû+ûûûûûûûûûûûûûûû
+ûûûûûûûûûûûûûûû+
Note - 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.
4.2.7 AIS applied to the 2048 kbit/s output, insertion side (I1)
Note - The provision of this consequent action depends on the type of this
equipment in a network and therefore is not mandatory.
General note to º 4.2 - The equivalent binary content of the alarm indica-
tion 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 ran-
dom errors having a mean error ratio 1.10-3. Nevertheless, a signal in
which all the binary elements, with the exception of the frame alignment
signal, are in the state1, should not be taken as an AIS.
Note - All timing requirements quoted apply equally to restoration, sub-
sequent to the fault condition clearing.
5. 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 either of the codirectional or
the contradirectional type specified in RecommendationG.703.
The need to define a digital interface operating at 320kbit/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 320
kbit/s will be offered to customers at the user/network interface level
using the 2048kbit/s interface as defined in Recommendations I.431 and
G.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 Recommendation G.823.
6. Jitter
6.1 Jitter at 2048 kbit/s output
When there is no jitter on the 2048 kbit/s inputs (I0, E1) the peak-to-peak
jitter at the 2048kbit/s outputs (I1, E0) should not exceed 0.10UI when
it is measured within the frequency range from f1=20Hz to
f4=100kHz. 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. See Figure2/G.823.
Note - It may be necessary to include a frame alignment signal in the test
signal to enable the measurement to be carried out.
6.2 Jitter at E2, E3 outputs
The jitter at the E2 (64 kbit/s) output when there is no jitter at the
2048kbit/s input (E1) should not exceed 0.025UI when measured within
the frequency range from f1=20Hz to f4=100kHz. 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 Recommen-
dation 0.151.
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
alignment signal in the test signal.
6.2.2 Since the physical and electrical characteristics of a 320kbit/s inter-
face are identical to those of the 2048kbit/s interface, the jitter at the E3
(synchronous 320kbit/s) output when there is no jitter at the 2048kbit/s
input (E1) is according to 6.1 above.
6.3 Jitter transfer functions
6.3.1 The jitter transfer function between the 2048kbit/s input (I0, E1)
and the output (I1, E0) should not exceed the gain/frequency limits given
in Figure2/G.739.
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.739.
Note 1 - The 2048 kHz signal shall be modulated with sinusoidal jitter.
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.
6.3.2 The jitter transfer function between the 2048kbit/s input (E1) and
the E2 (64 kbit/s) output should not exceed -29.6 dB when measured over
the frequency range f0 to 10 kHz. 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 2048kbit/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.
6.3.3 Since the physical and electrical characteristics of a 320kbit/s inter-
face are identical to those of the 2048kbit/s interface, the jitter transfer
function between the 2048kbit/s input (E1) and E3 (synchronous
320kbit/s) output is according to 6.3.1 above.
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 than 40Hz.
Note 3 - For interfaces within national boundaries, this characteristic may
be used.
FIGURE 2/G.739
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.739
Section 7.6 - Principal characteristics of transcoder and digital circuit
multiplication equipment.
