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 -+15 ppm, 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 signal in one of the two following frames. Note - As it is not strictly necessary to specify the detailed frame alignment strategy, any suitable frame alignment strategy may be used provided 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 justification 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 signal 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 旼컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컫컴컴컴컴컴커 � Nominal tributary bit rate (kbit/s) �44736 � � Number of tributaries �3 � 쳐컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컵컴컴컴컴컴캑 � � � � Frame structure 쿍it number � 쳐컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컵컴컴컴컴컴캑 � � � � 쿞et I � � Frame alignment signal (111110100000) �1 to 12 � � Bits from tributaries �13 to 159 � � 쿞et II � � Justification control bits Cj1 (Note 6) �1 to 3 � � Bits from tributaries �4 to 159 � � 쿞et III � � Justification control bits Cj2 (Note 6) �1 to 3 � � Bits from tributaries �4 to 159 � � 쿞et 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 � � 쿞et V � � Justification control bits Cj4 (Note 6) �1 to 3 � � Bits from tributaries �4 to 159 � � 쿞et 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 � 쳐컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컵컴컴컴컴컴캑 � 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 � 읕컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컨컴컴컴컴컴켸 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 including 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 tributary 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 characteristic 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 10 Hz. 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 jitter 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 having 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. 旼컴컴컴컴컴컴컴컴컴컴컴컴쩡컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴커 � � � 쿛eak-to-peak sinusoidal � Frequency � � jitter amplitude � � 쳐컴컴컴컴컴컫컴컴컴컴컴컴탠컴컴컴컴쩡컴컴컴컴쩡컴컴컴컴쩡컴컴컴캑 � � � � � � � � A1 [UI] � A2 [UI] � f1 [Hz] � f2 [Hz] � f3 [Hz] � f4 [Hz]� 쳐컴컴컴컴컴컵컴컴컴컴컴컴탠컴컴컴컴탠컴컴컴컴탠컴컴컴컴탠컴컴컴캑 � � � � � � � � 5.0 � 0.1 � 10 � 2.3 k � 60 k � 400 k � � � � � � � � 읕컴컴컴컴컴컨컴컴컴컴컴컴좔컴컴컴컴좔컴컴컴컴좔컴컴컴컴좔컴컴컴켸 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 jittered 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 demultiplexer 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 Recommendation M.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 indication is given in Recommendation M.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 multiplexer, 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 旼컴컴컴컴쩡컴컴컴컴컴컫컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴� � � � Consequent actions (see  10.2) � � � 쳐컴컴컴컴컴쩡컴컴컴컴컫컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴캑 � � � � � AIS applied � � � � � 쳐컴컴컴컴컴쩡컴컴컴컴쩡컴컴컴컴� 쿐quipment쿑ault 쿛rompt 쿌larm � � 쿟o the � 쿾art 쿬ondition 쿺aintenance쿶ndication� � 퀁elevant � � �(see  10.1)쿪larm 퀃o the 쿟o all the 쿟o the 퀃ime � � � 쿶ndication 퀁emote 퀃ributaries쿬omposite퀂lots of � � � 쿲enerated 쿺ultiplex � 퀂ignal 퀃he � � � � 쿮quipment � � 쿬omposite� � � � 쿲enerated � � 퀂ignal � 쳐컴컴컴컴탠컴컴컴컴컴컵컴컴컴컴컴컵컴컴컴컴컴탠컴컴컴컴컴탠컴컴컴컴탠컴컴컴컴� 쿘ulti- 쿑ailure of � Yes � 쿧es, if 쿧es, if � � 쿾lexer 쿾ower � � 쿾racticable쿾racti- � � 쿪nd 퀂upply � � � 쿬able � � 쿭emulti- � � � � � � � 쿾lexer � � � � � � � 쳐컴컴컴컴탠컴컴컴컴컴컵컴컴컴컴컴컵컴컴컴컴컴탠컴컴컴컴컴탠컴컴컴컴탠컴컴컴컴� 쿘ulti- 쿗oss of in- � Yes � � � � Yes � 쿾lexer 쿬oming � � � � � � 쿽nly 퀂ignal on a � � � � � � � 퀃ributary � � � � � � 쳐컴컴컴컴탠컴컴컴컴컴컵컴컴컴컴컴컵컴컴컴컴컴탠컴컴컴컴컴탠컴컴컴컴탠컴컴컴컴� � 쿗oss of in- � Yes � Yes � Yes � � � � 쿬oming � � � � � � � 퀂ignal � � � � � � � 쳐컴컴컴컴컴컵컴컴컴컴컴컵컴컴컴컴컴탠컴컴컴컴컴탠컴컴컴컴탠컴컴컴컴� 쿏emulti- 쿗oss of � Yes � Yes � Yes � � � 쿾lexer 쿯rame � � � � � � 쿽nly 쿪lignment � � � � � � � 쳐컴컴컴컴컴컵컴컴컴컴컴컵컴컴컴컴컴탠컴컴컴컴컴탠컴컴컴컴탠컴컴컴컴� � 쿌larm � � � � � � � 쿶ndication � � � � � � � 퀁eceived � � � � � � � 쿯rom the � � � � � � � 퀁emote � � � � � � � 쿺ultiplex � � � � � � � 쿮quipment � � � � � � 읕컴컴컴컴좔컴컴컴컴컴컨컴컴컴컴컴컨컴컴컴컴컴좔컴컴컴컴컴좔컴컴컴컴좔컴컴컴컴� 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. 컴컴컴컴