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13. Recommendation G.747
SECOND ORDER DIGITAL MULTIPLEX EQUIPMENT OPERAT-
ING AT 6312 KBIT/S AND MULTIPLEXING THREE TRIBUTARIES
AT 2048KBIT/S
1. General
The digital multiplex equipment described in this Recommendation is
intended for use between networks using different digital hierarchies as
specified in Recommendations G.702 and G.802.
2. Bit rate
The bit rates of the tributary and multiplex signals should be 2048kbit/s
+ 50 ppm and 6312 kbit/s + 30 ppm, respectively, as specified in Recom-
mendation G.703.
3. Frame structure
Table l/G.747 gives the recommended 6312 kbit/s multiplexing frame
structure.
4. Loss and recovery of frame alignment and consequent action
Loss of frame alignment should be assumed to have taken place when
four consecutive frame alignment signals have been incorrectly received
in their predicted positions.
When frame alignment is assumed to be lost, the frame alignment device
should decide that such alignment has effectively been recovered when it
detects the presence of three consecutive correct frame alignment signals.
The frame alignment device having detected the appearance of a single
correct frame alignment signal, should begin a new search for the frame
alignment signal when it detects the absence of the frame alignment sig-
nal in one of the two following frames.
Note - As it is not strictly necessary to specify the detailed frame align-
ment strategy, any suitable frame alignment strategy may be used pro-
vided the performance achieved is at least as efficient in all respects as
that obtained by the above frame alignment strategy.
5. Multiplexing and justification methods
Cyclic bit interleaving in the tributary numbering order and positive justi-
fication are recommended.
The justification control signal should be distributed and use theCji-
bits (j=1,2,3; i=1,2,3) (see Note 5 to Table 1/G.747).
Positive justification should be indicated by the justification control sig-
nal 111 and no justification by the signal 000. Majority decision is rec-
ommended.
Table l/G.747 gives the maximum justification rate per tributary and the
nominal justification ratio.
TABLE 1/G.747
6312 kbit/s multiplexing frame structure
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_ Nominal tributary bit rate (kbit/s) _ 2048 _
_ Number of tributaries _ 3 _
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_ Frame structure _ Bit number_
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_ _ Set I _
_ Frame alignment signal (111010000) _ 1 to 9 _
_ Bits from tributaries _ 10 to 168 _
_ _ Set II _
_ Alarm indication to the remote multiplex equipment (Note 1) _ 1 _
_ Parity bit (Notes 2 and 3) _ 2 _
_ Bit reserved for future use (Note 4) _ 3 _
_ Bits from tributaries _ 4 to 168 _
_ _ Set III _
_ Justification control bits Cjl (Note 5) _ 1 to 3 _
_ Bits from tributaries _ 4 to 168 _
_ _ Set IV _
_ Justification control bits Cj2 (Note 5) _ 1 to 3 _
_ Bits from tributaries _ 4 to 168 _
_ _ Set V _
_ Justification control bits Cj3 (Note 5) _ 1 to 3 _
_ Bits from tributaries available for justification _ 4 to 6 _
_ Bits from tributaries _ 7 to 168 _
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_ Frame length (bits) _ 840 _
_ Bits per tributary in a frame (bits) _ 273 _
_ Maximum justification rate per tributary (kbit/s) _ 7.5 _
_ Nominal justification ratio _ 0.453 _
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Note l - See section 10.2.1.
Note 2 - The parity bit = 1 if the number of marks in all tributary bits
including the bits in the justifiable time-slots in the preceding frame is
odd; the parity bit = 0 if the number of marks in all tributary bits includ-
ing the bits in the justifiable time-slots in the preceding frame is even.
Note 3 - The implementation and the use of this parity bit procedure are
for further study.
Note 4 - This bit should be set to 1 when not used.
Note 5 - Cji (j=1,2,3; i=1,2,3) indicates the ith justification control bit of
the jth tributary.
6. Jitter
6.1 Muldex jitter transfer characteristic
A 2048 kbit/s signal, modulated by sinusoidal jitter, should be subject to
a muldex jitter transfer characteristic within the gain/frequency limits
given in Figure 1/G.747. The equivalent binary content of the test signal
should be 1000.
Note - In addition, the need to specify a demultiplexer tributary jitter
transfer characteristic from the 6312 kbit/s demultiplexer input to the
2048kbit/s demultiplexer output is for further study.
Note - The frequency f0 should be as low as possible, taking into account
the limitations of measuring equipment. In any case f0 should be no
greater than 10Hz.
The selective measurement method should be used.
FIGURE 1/G.747
Muldex jitter transfer characteristic
6.2 Output jitter
6.2.1 Tributary output jitter
With no jitter applied to the input ports of the multiplexer and with the
multiplexer directly connected to the demultiplexer, the peak-to-peak jit-
ter at the tributary output port should not exceed 0.2 UI over a measure-
ment interval of one minute in the frequency range from f0 to 100 kHz
(see Note 1).
When measured with an instrument incorporating a bandpass filter hav-
ing a lower cutoff frequency of 18 kHz, a roll-off of 20 dB/decade and an
upper limit of 100 kHz, the peak-to-peak output jitter should not exceed
0.05 UI when measured over a one minute interval (see Note 2).
Note 1 - The frequency f0 should be as low as possible, taking into
account the limitations of measurement equipment. In any case f0 should
be no greater than 10Hz.
Note 2 - For interfaces meeting the national high Q option, detailed in
Recommendation G.823, the lower cutoff frequency for the above mea-
surement should be 700 Hz.
6.2.2 Multiplexer output jitter
The peak-to-peak jitter at the 6312 kbit/s output port should not exceed
0.05 UI when it is measured over an interval of one minute within the fre-
quency range from f1 = 10 Hz to f4 = 60 Hz.
6.3 Input jitter
6.3.1 Tributary input jitter
The 2048 kbit/s input port should be capable of accommodating levels of
input jitter up to the limits given in G.823.
6.3.2 Demultiplexer input jitter
The 6312 kbit/s input port should be capable of accommodating levels of
input jitter up to the limits given in Figure 2/G.747.
Note 1 - Current Recommendation G.703 does not refer to the jitter to be
tolerated at the digital distribution frame at 6312 kbit/s nor at the input
port of equipment connected to this distribution frame.
Note 2 - The jitter accommodation requirement should be met when the
jittered input signal is composed of the multiplexed tributary signals hav-
ing any value of jitter allowed for the 2048 kbit/s.
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_Peak-to-peak sinusoidal _ Frequency _
_ jitter amplitude _ _
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_ A1 [UI] _ A2 [UI] _ f1 [Hz] _ f2 [Hz] _ f3 [Hz] _ f4 [Hz]_
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_ 5.0 _ 0.15 _ 10 _ 120 _ 4 k _ 60 k _
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FIGURE 2/G.747
Lower limit of maximum tolerable sinusoidal
input jitter at 6312 kbit/s
7. Digital interfaces
The digital interfaces at 2048 kbit/s and 6312 kbit/s should be in accor-
dance with Recommendation G.703.
8. Timing signal
If it is economically feasible, it may be desirable to be able to derive the
multiplexing timing signal from an external source as well as from an
internal source.
9. Service digits
Three bits per frame are available for service functions (see Table1/
G.747): bit 1 of Set II is used to transmit an alarm indication to the
remote multiplex equipment when specific fault conditions are detected
in the multiplex equipment (see section 10 below); bit 2 of Set II may be
used for parity check; bit 3 of Set II is reserved for future use.
10. Fault conditions and consequent actions
10.1 Fault conditions
10.1.1 The digital multiplex equipment should detect the following fault
conditions:
1) failure of power supply;
2) loss of an incoming 2048 kbit/s tributary signal at a multiplexer input
port;
3) loss of an incoming 6312 kbit/s multiplex signal at a demultiplexer
input port;
4) loss of frame alignment signal at a demultiplexer input port;
5) detection of an alarm indication received from the remote multiplex
equipment at a demultiplexer input port;
6) detection of alarm indication signal (AIS) at a demultiplexer input port.
Note 1 - The equivalent binary content of the AIS at 2048 and 6312 kbit/
s should be a continuous stream of binary ones (marks) as recommended
in
RecommendationM.20.
Note 2 - Some current 44736-6312 kbit/s demultiplexers do not issue a
6312kbit/s AIS. Thus no detection can take place in that case.
Note 3 - The strategy for detecting the presence of the AIS should be
such that the AIS is detectable even in the presence of an error ratio of
l.10-3. However, a signal with all bits except the frame alignment signal
in the state of 1, should not be mistaken as an AIS.
10.1.2 The need to monitor the degradation of the incoming 6312 kbit/s
signal for the purpose of end-to-end error performance monitoring of the
6312kbit/s digital block as well as the procedure for detecting such deg-
radation are for further study.
10.2 Consequent actions
Further to the detection of a fault condition, the appropriate actions
should be taken as specified in Table 2/G.747.
Note 1 - The concept and definition of prompt maintenance alarm indica-
tion is given in RecommendationM.20.
Note 2 - When the alarm indication signal (AIS) is detected at the input
of the demultiplexer, the prompt maintenance alarm indication associated
with loss of frame alignment should be inhibited, while the rest of the
consequent actions are in accordance with those associated in Table 2/
G.747 with the fault condition.
10.2.1 Alarm indication to the remote multiplex equipment should be
generated by changing bit 1 of Set II (see Table 1/G.747) from the state 0
to the state1.
10.2.2 AIS should be applied to the following as specified in Table 2/
G.747:
- all three 2048 kbit/s tributary outputs from the demultiplexer;
- 6312 kbit/s output of the multiplexer;
- the time slots of the 6312 kbit/s signal at the output of the multiplexer,
corresponding to the relevant 2048 kbit/s tributary.
TABLE 2/G.747
Fault conditions and consequent actions
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_ _ _ Consequent actions (see º 10.2) _
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_ _ _ _ _ AIS applied _
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_Equipment_Fault _Prompt _Alarm _ _ _To the _
_part _condition _maintenance_indication_ _ _relevant _
_ _(see º 10.1)_alarm _to the _To all the _To the _time _
_ _ _indication _remote _tributaries_composite_slots of _
_ _ _generated _multiplex _ _signal _the _
_ _ _ _equipment _ _ _composite_
_ _ _ _generated _ _ _signal _
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_Multi- _Failure of _ Yes _ _Yes, if _Yes, if _ _
_plexer _power _ _ _practicable_practi- _ _
_and _supply _ _ _ _cable _ _
_demulti- _ _ _ _ _ _ _
_plexer _ _ _ _ _ _ _
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_Multi- _Loss of in- _ Yes _ _ _ _ Yes _
_plexer _coming _ _ _ _ _ _
_only _signal on a _ _ _ _ _ _
_ _tributary _ _ _ _ _ _
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_ _Loss of in- _ Yes _ Yes _ Yes _ _ _
_ _coming _ _ _ _ _ _
_ _signal _ _ _ _ _ _
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_Demulti- _Loss of _ Yes _ Yes _ Yes _ _ _
_plexer _frame _ _ _ _ _ _
_only _alignment _ _ _ _ _ _
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_ _Alarm _ _ _ _ _ _
_ _indication _ _ _ _ _ _
_ _received _ _ _ _ _ _
_ _from the _ _ _ _ _ _
_ _remote _ _ _ _ _ _
_ _multiplex _ _ _ _ _ _
_ _equipment _ _ _ _ _ _
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Note - A Yes in the table signifies that a certain 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.
