home
***
CD-ROM
|
disk
|
FTP
|
other
***
search
/
Internet Standards
/
CD2.mdf
/
ccitt
/
1992
/
g
/
g755.asc
< prev
next >
Wrap
Text File
|
1993-08-15
|
17KB
|
701 lines
14. Recommendation G.755
DIGITAL MULTIPLEX EQUIPMENT OPERATING AT 139 264 KBIT/
S
AND MULTIPLEXING THREE TRIBUTARIES AT 44736 KBIT/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 44736
kbit/s -+20 ppm and 139 264 kbit/s -+15ppm, respectively, as specified
in Recommendation G.703.
3. Frame structure
Table 1/G.755 gives the recommended 139 264 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 the Cji-bits
(J=1,2,3; i=1,2,3,4,5) (see Note 6 to Table 1/G.75x).
Positive justification should be indicated by the justification control sig-
nal 11111 and no justification by the signal 00000. Majority decision is
recommended.
Table 1/G.755 gives the maximum justification rate per tributary and the
nominal justification ratio.
TABLE 1/G.755
139 264 kbit/s multiplexing frame structure
+ûûûûûûûûûûûûûûûûûûûûûûûûûûûûûûûûûûûûûûûûûûûûûûûûûûûûûûûû
ûûûûûûûû+ûûûûûûûûûûû+
_Nominal tributary bit rate (kbit/s)_44736 _
_Number of tributaries_3 _
+ûûûûûûûûûûûûûûûûûûûûûûûûûûûûûûûûûûûûûûûûûûûûûûûûûûûûûûûû
ûûûûûûûû+ûûûûûûûûûûû+
_ _ _
_Frame structure_Bit number_
+ûûûûûûûûûûûûûûûûûûûûûûûûûûûûûûûûûûûûûûûûûûûûûûûûûûûûûûûû
ûûûûûûûû+ûûûûûûûûûûû+
_ _ _
__Set I _
_Frame alignment signal (111110100000)_1 to 12 _
_Bits from tributaries_13 to 159 _
__Set II _
_Justification control bits Cj1(Note 6)_1 to 3 _
_Bits from tributaries_4 to 159 _
__Set III _
_Justification control bits Cj2(Note 6)_1 to 3 _
_Bits from tributaries_4 to 159 _
__Set IV _
_Justification control bits Cj3 (Note 6)_1 to 3 _
_Alarm indication to the remote multiplex equipment (Note
1)_4 _
_Parity bit (Notes 2, 3 and 4)_5 _
_Bits reserved for future use (Note 5)_6 to 9 _
_Bits from tributaries_10 to 159 _
__Set V _
_Justification control bits Cj4 (Note 6)_1 to 3 _
_Bits from tributaries_4 to 159 _
__Set VI _
_Justification control bits Cj5 (Note 6)_1 to 3 _
_Bits from tributaries available for justification_4 to 6 _
_Bits from tributaries_7 to 159 _
+ûûûûûûûûûûûûûûûûûûûûûûûûûûûûûûûûûûûûûûûûûûûûûûûûûûûûûûûû
ûûûûûûûû+ûûûûûûûûûûû+
_Frame length (bits)_954 _
_Bits per tributary in a frame (bits)_307 _
_Maximum justification rate per tributary (kbit/s)_146.0 _
_Nominal justification ratio_0.545 _
+ûûûûûûûûûûûûûûûûûûûûûûûûûûûûûûûûûûûûûûûûûûûûûûûûûûûûûûûû
ûûûûûûûû+ûûûûûûûûûûû+
Note 1 - 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 - It is recognized that existing multiplex equipment installed prior
to adoption of this Recommendation do not insert the parity bit.
Note 4 - The implementation and the use of this parity bit procedure are
for further study.
Note 5 - These bits should be set to 1 when not used.
Note 6 - Cji (j=1,2,3; i=1,2,3,4,5) indicates the ith justification control bit
of the jth tributary.
6. Jitter
6.1 Demultiplexer tributary jitter transfer characteristic
The demultiplexer 44736 kbit/s tributary jitter transfer characteristic
should meet the gain/frequency limits given in Figure 1/G.75x. The
equivalent binary content of the test signal used should result in a tribu-
tary output signal of 1000.
Note 1 - This characteristic is usually measured between the high speed
and low speed interfaces of the demultiplexer and the measurements are
taken in unit intervals. It is then necessary to introduce a correction factor
to account for the difference in the size of unit intervals.
Note 2 - In addition, the need to specify a muldex jitter transfer character-
istic is for further study.
Note 3 - It is recognized that the existing multiplex equipment designed
prior to the adoption of this Recommendation might need tributary test
signals incorporating the 44736 kbit/s frame structure defined in G.752.
Note - The frequency fO should be as low as possible, taking into
account the limitations of measuring equipment. In any case fO should be
no greater than 10Hz.
The selective measurement method should be used.
FIGURE 1/G.755
Demultiplexer tributary 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 0.3 UI when measured
over a one minute interval within the frequency range from f1 = 10 Hz
to f4 = 400 kHz.
When measured with an instrument incorporating a bandpass filter hav-
ing a lower cutoff frequency of f3 = 60 kHz, a roll-off of 20 dB/decade
and an upper limit of f4 = 400 kHz, the peak-to-peak output jitter should
not exceed 0.05 UI when it is measured over a one minute interval.
6.2.2 Multiplexer output jitter
The peak-to-peak jitter at the 139 264 kbit/s output port should not
exceed 0.05 UI when it is measured over a one minute interval within the
frequency range from 200 Hz to 3 500 kHz.
6.3 Input jitter
6.3.1 Tributary input jitter
The 44736 kbit/s input port should be capable of accommodating levels
of input jitter up to the limits given in Figure 2/G.755.
Note - Current Recommendation G.703 does not refer to the jitter to be
tolerated at the digital distribution frame at 44736 kbit/s nor at the input
port of equipment connected to this distribution frame.
+ûûûûûûûûûûûûûûûûûûûûûûûûû+ûûûûûûûûûûûûûûûûûûûûûûûûûû
ûûûûûûûûûûûû+
_ _ _
_Peak-to-peak sinusoidal_Frequency_
_jitter amplitude__
+ûûûûûûûûûûûû+ûûûûûûûûûûûû+ûûûûûûûûû+ûûûûûûûûû+ûûûûûû
ûûû+ûûûûûûûû+
_______
_A1 [UI]_A2 [UI]_f1 [Hz]_f2 [Hz]_f3 [Hz]_f4 [Hz]_
+ûûûûûûûûûûûû+ûûûûûûûûûûûû+ûûûûûûûûû+ûûûûûûûûû+ûûûûûû
ûûû+ûûûûûûûû+
_______
_5.0_0.1_10_2.3 k_60 k_400 k_
_______
+ûûûûûûûûûûûû+ûûûûûûûûûûûû+ûûûûûûûûû+ûûûûûûûûû+ûûûûûû
ûûû+ûûûûûûûû+
FIGURE 2/G.755
Lower limit of maximum tolerable sinusoidal input jitter
at 44736 kbit/s
6.3.2 Demultiplexer input jitter
The 139 264 kbit/s input port should be capable of accommodating levels
of input jitter up to the limits given in Recommendation G.823.
Note - The jitter accommodation requirement should be met when the jit-
tered input signal is composed of the multiplexed tributary signals having
any value of jitter allowed for the 44736 kbit/s level.
7. Digital interfaces
The digital interfaces at 44736 kbit/s and 139 264 kbit/s should be in
accordance 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
Six bits per frame are available for service functions (see Table 1/
G.755): bit 4 of Set IV 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 5 of Set IV may be
used for parity check; bits 6 to 9 of Set IV are 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 44736 kbit/s tributary signal at a multiplexer input
port;
3) loss of an incoming 139 264 kbit/s multiplex signal at a demulti-
plexer input port;
Note - The detection of this fault condition is required only when it
does not result in an indication of loss of frame alignment.
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 139 264 kbit/s
should be a continuous stream of binary ones (marks) as recommended in
RecommendationM.20.
Note 2 - 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
1.10-3. 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 139 264 kbit/
s signal for the purpose of end-to-end error performance monitoring of
the 139 264 kbit/s digital block as well as the procedure for detecting
such degradation 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.755.
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.755 with the fault condition.
10.2.1 Alarm indication to the remote multiplex equipment should be
generated by changing bit 4 of Set IV (see Table 1/G.755) from the state
0 to the state 1.
10.2.2 AIS should be applied to the following as specified in Table 2/
G.755:
- all three 44736 kbit/s tributary outputs from the demultiplexer;
- 139 264 kbit/s output of the multiplexer;
- the time slots of the 139 264 kbit/s signal at the output of the multi-
plexer, corresponding to the relevant 44736 kbit/s tributary.
Note - The equivalent binary content of the AIS at 44736 kbit/s is a signal
with a valid frame alignment signal, parity and justification control bits
as defined in Table 2/G.752, with the tributary bits being set to a 1010...
sequence, starting with a binary 1 after each frame alignment, multi-
frame alignment and justification control bit, and with all justification
control bits being set to binary 0.
TABLE 2/G.755
Fault conditions and consequent actions
+ûûûûûûûûû+ûûûûûûûûûûûû+ûûûûûûûûûûûûûûûûûûûûûûûûûûûûûûûûûû
ûûûûûûûûûûûûûûûûûûûû+
_ _ _ Consequent actions (see º 10.2) _
_ _ +ûûûûûûûûûûû+ûûûûûûûûûû+ûûûûûûûûûûûûûûûûûûûûûû
ûûûûûûûûû+
_ _ _ _ _ AIS applied _
_ _ _ _ +ûûûûûûûûûûû+ûûûûûûûûû+ûûûûûûûûû+
_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 _
+ûûûûûûûûû+ûûûûûûûûûûûû+ûûûûûûûûûûû+ûûûûûûûûûû+ûûûûûûûûûû
û+ûûûûûûûûû+ûûûûûûûûû+
_Multi- _Failure of _ Yes _ _Yes, if _Yes, if _ _
_plexer _power _ _ _practicable_practi- _ _
_and _supply _ _ _ _cable _ _
_demulti- _ _ _ _ _ _ _
_plexer _ _ _ _ _ _ _
+ûûûûûûûûû+ûûûûûûûûûûûû+ûûûûûûûûûûû+ûûûûûûûûûû+ûûûûûûûûûû
û+ûûûûûûûûû+ûûûûûûûûû+
_Multi- _Loss of in- _ Yes _ _ _ _ Yes _
_plexer _coming _ _ _ _ _ _
_only _signal on a _ _ _ _ _ _
_ _tributary _ _ _ _ _ _
+ûûûûûûûûû+ûûûûûûûûûûûû+ûûûûûûûûûûû+ûûûûûûûûûû+ûûûûûûûûûû
û+ûûûûûûûûû+ûûûûûûûûû+
_ _Loss of in- _ Yes _ Yes _ Yes _ _ _
_ _coming _ _ _ _ _ _
_ _signal _ _ _ _ _ _
_ +ûûûûûûûûûûûû+ûûûûûûûûûûû+ûûûûûûûûûû+ûûûûûûûûûûû+ûûû
ûûûûûû+ûûûûûûûûû+
_Demulti- _Loss of _ Yes _ Yes _ Yes _ _ _
_plexer _frame _ _ _ _ _ _
_only _alignment _ _ _ _ _ _
_ +ûûûûûûûûûûûû+ûûûûûûûûûûû+ûûûûûûûûûû+ûûûûûûûûûûû+ûûû
ûûûûûû+ûûûûûûûûû+
_ _Alarm _ _ _ _ _ _
_ _indication _ _ _ _ _ _
_ _received _ _ _ _ _ _
_ _from the _ _ _ _ _ _
_ _remote _ _ _ _ _ _
_ _multiplex _ _ _ _ _ _
_ _equipment _ _ _ _ _ _
+ûûûûûûûûû+ûûûûûûûûûûûû+ûûûûûûûûûûû+ûûûûûûûûûû+ûûûûûûûûûû
û+ûûûûûûûûû+ûûûûûûûûû+
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.
ûûûûûûûû
