WPCL 2BJ|x ` H   x|@  @8'@8' 13.HRecommendation G.747    h$SECOND ORDER DIGITAL MULTIPLEX EQUIPMENT OPERATING AT 6312 KBIT/S AND h1MULTIPLEXING THREE TRIBUTARIES AT 2048KBIT/S 1.HGeneral  8 HThe 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.HBit rate HThe bit rates of the tributary and multiplex signals should be 2048kbit/s + 50 ppm and 6312 kbit/s + 30 ppm, respectively, as specified in Recommendation G.703. 3.HFrame structure HTable l/G.747 gives the recommended 6312 kbit/s multiplexing frame structure. 4.HLoss and recovery of frame alignment and consequent action  X HLoss of frame alignment should be assumed to have taken place when four consecutive frame alignment signals have been incorrectly received in their predicted positions. HWhen 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. HThe 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.HMultiplexing and justification methods HCyclic bit interleaving in the tributary numbering order and positive justification are recommended. HThe justification control signal should be distributed and use the Cjiĩbits (j=1,2,3; i=1,2,3) (see Note 5 to Table 1/G.747). HPositive justification should be indicated by the justification control signal 111 and no justification by the signal 000. Majority decision is recommended. HTable l/G.747 gives the maximum justification rate per tributary and the nominal justification ratio. JTABLE 1/G.747 P <6312 kbit/s multiplexing frame structureă P +   +  Nominal tributary bit rate (kbit/s)  2048  +  Number of tributaries  3  + +  Frame structure  Bit number  + +   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  + +  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  +   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 timeslots 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 timeslots 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.HJitter 6.1HMuldex jitter transfer characteristic HA 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.  w.Ԍ 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. HThe selective measurement method should be used. IFIGURE 1/G.747 P >Muldex jitter transfer characteristică 6.2HOutput jitter 6.2.1HTributary output jitter HWith no jitter applied to the input ports of the multiplexer and with the multiplexer directly connected to the demultiplexer, the peaktopeak jitter at the tributary output port should not exceed 0.2 UI over a measurement interval of one minute in the frequency range from f0 to 100 kHz (see Note 1). HWhen measured with an instrument incorporating a bandpass filter having a lower cutoff frequency of 18 kHz, a rolloff of 20 dB/decade and an upper limit of 100 kHz, the peaktopeak 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 measurement should be 700 Hz. 6.2.2HMultiplexer output jitter HThe peaktopeak 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 frequency range from f1 = 10 Hz to f4 = 60 Hz. 6.3HInput jitter 6.3.1HTributary input jitter HThe 2048 kbit/s input port should be capable of accommodating levels of input jitter up to the limits given in G.823. 6.3.2HDemultiplexer input jitter HThe 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 having any value of jitter allowed for the 2048 kbit/s. .   . Peaktopeak sinusoidal  Frequency  .  jitter amplitude   . .  A1 [UI]  A2 [UI]  f1 [Hz]  f2 [Hz]  f3 [Hz]  f4 [Hz]  . .  5.0  0.15  10  120  4 k  60 k  .   IFIGURE 2/G.747 P :Lower limit of maximum tolerable sinusoidal ă Cinput jitter at 6312 kbit/să 7.HDigital interfaces HThe digital interfaces at 2048 kbit/s and 6312 kbit/s should be in accordance with Recommendation G.703. 8.HTiming signal HIf 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.HService digits HThree 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.HFault conditions and consequent actions 10.1HFault conditions 10.1.1 The digital multiplex equipment should detect the following fault conditions: HH1)h  failure of power supply;  `    HH2)h  loss of an incoming 2048 kbit/s tributary signal at a multiplexer input port;  `  w.ԌHH3)h  loss of an incoming 6312 kbit/s multiplex signal at a demultiplexer input port;  ( HH4)h  loss of frame alignment signal at a demultiplexer input port;  `    HH5)h  detection of an alarm indication received from the remote multiplex equipment at a demultiplexer input port;  `    HH6)h  detection of alarm indication signal (AIS) at a demultiplexer input port.  `   h 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 447366312 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.10é3. 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 endtoend error performance monitoring of the 6312kbit/s digital block as well as the procedure for detecting such degradation are for further study. 10.2HConsequent actions HFurther 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 indication 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:  8 HH© all three 2048 kbit/s tributary outputs from the demultiplexer;  `  H 6312 kbit/s output of the multiplexer;   HH© 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 A .Fault conditions and consequent actionsă         Consequent actions (see  10.2)          AIS applied       Equipment Fault Prompt Alarm   To the  part condition maintenance indication   relevant   (see  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   Multi Failure of  Yes  Yes, if Yes, if   plexer power   practicable practi   and supply    cable   demulti        plexer         Multi Loss of in  Yes     Yes  plexer coming       only signal on a        tributary         Loss of in  Yes  Yes  Yes     coming        signal         Demulti Loss of  Yes  Yes  Yes    plexer frame       only alignment          Alarm        indication        received        from the        remote        multiplex        equipment         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.