1、ITU-T RECMN*G=73b 93 4862573 0583365 Lb4 = INTERNATIONAL TELECOMMUNICATION UNION ITU-T TELECOMMUNICATION STANDARDIZATION SECTOR OF ITU G.736 (03/93) GENERAL ASPECTS OF DIGITAL TRANSMISSION CHARACTERISTICS OF A SYNCHRONOUS DIGITAL MULTIPLEX EQUIPMENT OPERATING AT 2048 kbits ITU-T Recommendation G.736
2、 (Previously “CCITT Recommendation”) ITU-T RECMN*G*736 93 m 4862591 0583366 OTO FOREWORD The Telecommunication Standardization Sector (IT-T) is a permanent organ of the International Telecom- munication Union. The IT-T is responsible for studying technical, operating and tariff questions and issuing
3、 Recommendations on them with a view to standardizing telecommunications on a worldwide basis. The World Telecommunication Standardization Conference (WTSC), which meets every four years, established the topics for study by the Il7J-T Study Groups which, in their turn, produce Recommendations on the
4、se topics. IT-T Recommendation G.736 was revised by the ITU-T Study Group XV (1988-1993) and was approved by the WTSC Ielsinki, March 1-12, 1993). NOTES 1 As a consequence of a reform process within the International Telecommunication Union (ITU), the CCITT ceased to exist as of 28 February 1993. In
5、 its place, the ITU Telecommunication Standardization Sector (ITU-T) was created as of 1 March 1993. Similarly, in this reform process, the CCIR and the IFRB have been replaced by the Radiocommunication Sector. In order not to delay publication of this Recommendation, no change has been made in the
6、text to references containing the acronyms “CCIIT, CCIR or IFRB” or their associated entities such as Plenary Assembly, Secretariat, etc. Future editions of this Recommendation will contain the proper terminology related to the new ITU structure. 2 telecommunication administration and a recognized o
7、perating agency. in this Recommendation, the expression “Administration” is used for conciseness to indicate both a O ITU 1994 AU rights reserved. No part of this publication may be reproduced or utilized in any form or by any means, electronic or mechanical, including photocopying and microfilm, wi
8、thout permission in writing from the ITU. CONTENTS Page . 1 1 General characteristics 1 1 1.1 Bit rate 1.2 Timing signai 2 Frame structure . 3 Frame alignment and CRC procedures 3.1 3.2 Recovery of frame alignment . 3.3 3.4 CRC bit monitoring Fault conditions and consequent actions 4.1 Fault conditi
9、ons Loss of frame alignment . CRC multiframe alignment in time slot O . 4 4.2 Consequent actions . 4 5 Interfaces 6 Jitter 4 Jitter at 2048 kbit/s output 6.2 Jitter at tributary outputs 4 . 5 4 6.1 6.3 Jitter transfer functions . Recommendation 6.736 (03/93) i ITU-T RECNN*G-736 93 W 4862573 05833b8
10、973 Recommendation G.736 CHARACTERISTICS OF A SYNCHRONOUS DIGITAL MULTIPLEX EQUIPMENT OPERATING AT 2048 kbih (Melbourne, 1988; revised at Helsinki, 1993) This Recommendation gives the characteristics of a synchronous digital multiplex equipment, to combine up to 3 1 tributary channels at 64 kbit/s o
11、r n x 64 kbit/s in a 2048 kbit/s digital stream. 1 General characteristics 1.1 Bit rate The nominal bit rate is 2048 kbit/s. The tolerance on this rate is f 50 parts per million (ppm). 1.2 Timing signal It should be possible to derive the transmit timing signal from any of the following: a) b) c) fr
12、om an internai oscillator. NOTES 1 2 from the received 2048 kbits signal; from an external source at 2048 kHz (see 5); The possibility of also deriving the transmit timing signai from a 64 kbit/s or n x 64 kbit/s tributary is under study. The provision of a timing signal output, available for the pu
13、rpose of synchronizing other equipments, is an option that might be required depending upon national synchronization arrangements. 2 Frame structure Refer to 2.3 and 5 of Recommendation G.704 for the basic frame structure and Characteristics of the frame structure carrying channels at various bit ra
14、tes in 2048 kbit/s. Bit 1 of the frame should be used in accordance with 2.2.3 of G.704, i.e. for a CRC check bit procedure. NOTE - In case of interconnection with multiplex equipment using time slot 16 for internal purposes, the use of this time slot for a 64 kbit/s tributary could be excluded. It
15、could also be used for internal purposes according to Recommendation G.704. 3 Frame alignment and CRC procedures (An illustration of the procedure is given in Figure 2/G.706.) 3.1 Loss of frame alignment Refer to 4.1. UG.706. 3.2 Recovery of frame alignment Refer to 4.1.2/G.706. 3.3 Refer to 4.2/G.7
16、06. CRC multiframe alignment in time slot O 3.4 CRC bit monitoring Refer to 4.3/G.706. Recommendation G.736 (03193) 1 ITU-T RECHNaG.73b 73 = 48b259L 0583367 BOT w 4 Fault conditions and consequent actions 4.1 Fault conditions The digital muldex should detect the following fault conditions. 4.1.1 Fai
17、lure of power supply 4.1.2 Failure of the incoming signal at the 64 kbih tributary input port NOTE - This detection is not mandatory when contradirectional interfaces are used. 4.1.3 Loss of the incoming signai at 2048 kbih NOTES 1 2 The detection of this fault condition is required only when it doe
18、s not result in an indication of loss of fiame Where separate circuits are used for the digital signal and the timing signal, the loss of either or both should constitute alignment. the loss of the incoming signal. 4.1.4 Loss of frame alignment at 2048 kbis 4.1.5 4.1.5.1 seconds should be less than
19、10-6. With a random bit error ratio of 2 1.10-3, the probability of activating the indication of fault condition in a few seconds should be higher than 0.95. 4.1.5.2 few seconds should be almost O. With a random bit error ratio I 1.104, the probability of deactivating the indication of fault conditi
20、on in a few seconds should be higher than 0.95. NOTE - The activating and deactivating period specified as “a few seconds” is intended to be in the order of 4 to 5 seconds. Excessive bit error ratio detected by monitoring the frame alignment signal With a random bit error ratio of I 1. lo4, the prob
21、ability of activating the indication of fault condition in a few With a random bit error ratio of 2-1-10-3, the probability of deactivating the indication of fault condition in a 4.1.6 Loss of timing signai The internal oscillator is not locked to the timing signals defined in items a) and b) of 1.2
22、 and in Note 1 of 1.2. The detection criteria for this fault condition are under study. 4.1.7 See 4.2. Alarm condition received from the remote digitai muidex 4.2 Consequent actions Further to the detection of a fault condition, appropriate actions should be taken as specified in Table 1. The conseq
23、uent actions are as follows. 4.2.1 Prompt maintenance alarm indication generated to signify that performance is below acceptable standards and maintenance attention is required locally. When the AIS (see General Note below to4.2) at a 2048 kbit/s input is detected, the prompt maintenance alarm indic
24、ation association with loss of frame alignment (see 4.1.4) and excessive error ratio (see4.1.5) should be inhibited, while the rest of the consequent actions are in accordance with those associated in Table 1 with the two fault conditions. NOTE - The location and provision of any visual andor audibl
25、e alarm activated by the alarm indications given in 4.2.1 is left to the discretion of each Administration. 4.2.2 Alarm indication to the remote end transmitted by changing bit 3 of channel time slot O from the state O to the state 1 in those frames not containing the frame alignment signal. This sh
26、ould be effected as soon as possible. 4.2.3 AIS applied to all 64 kbit/s or n x 64 kbit/s outputs and state “1” to corresponding abcd bits in time slot 16 if used (see General Note below to4.2). This action should be taken as soon as possible and not later than 2 ms after detection of the fault cond
27、ition. 2 Recommendation 6.736 (03193) ITU-T RECMN*G-736 73 m 4862593 0583370 523 m Prompt maintenance alarm indication generated Equipment part Alarm indication to the remote end tratlsmitted Backward Forward alarm alarm Multiplexer and demultiplexer Yes (see 4.2.1) Yes (see 4.2.1) Multiplexer only
28、Yes Yes Demultiplexer only TABLE VG.736 Fault conditions and consequent actions for the 2048 kbit/s synchronous digitai multiplex equipment Fault conditions (see 4.1) Failure of power supply Loss of timing signal _ Loss of incoming signal at a 64 kbits or n x 64 kbis input (see Note under 4.1.2) Los
29、s of incoming signal at 2048 kbits Loss of frame alignment (see Note 2 of 4.2 of Rec. G.706) Error ratio 1.10-3 alignment signal Alarm indication received from the remote end Consequent actions (see 4.2) I Yes 1 Yes 1 Yes (if practicable) (if practicable) Yes I Yes I Yes (Note 2) (Note 2) AIS applie
30、d to all 64 kbits and n x 64 kbit/s outputs State I in time slot 16 (Note 1) Yes (if practicable) Yes Yes Yes AIS applied to the relevant time slots of the 2048 kbit/s composite signal State 1 in time slot 16 (Note i) Yes (if practicable) Yes NOTES 1 Applicable if time slot 16 is used for channel as
31、sociated signalling or channel associated supervisiodmaintenace only. 2 In order to enable appropriate actions at the remote end, the indication of loss of timing signai should not be transmitted in bit 3 of time slot O. The transmission of this indication is under study. 3 A Yes in the table signif
32、ies 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 the condition is the only one present. If more than one fault condition is simul
33、taneously present, the relevant action should be taken if, for at least one of the conditions, a Yes is defined in relation to this action. Recommendation 6.736 (03/93) 3 ITU-T RECMN*G.736 93 W 486259L 0583373 468 4.2.4 64 kbis signal is provided). binary 1s. AIS applied to relevant time slots in th
34、e composite 2048 kbis output signal (if supervision of incoming GENERAL NOTE to 4.2 - The equivalent binary content of the alarm indication signal (AIS) is a continuous stream of The strategy for detecting the presence of the AIS should be such that with a high probability the AIS is detectable even
35、 in the presence of random errors having a mean error ratio I l.lP3. Nevertheless, a signal in which all the binary elements, with the exception of the frame alignment signal, are in the state 1, should not be taken as an AIS. NOTE - All timing requirements quoted apply equally to restoration, subse
36、quent to the fault condition clearing. 5 Interfaces The digital interfaces at 2048 kbit/s should be in accordance with Recommendation G.703. This interface should be used for both n x 64 kbit/s tributaries and 2048 kbit/s multiplexed signal. The digital interfaces at 64 kbit/s should be of either th
37、e codirectional or the contradirectional type specified in Recommendation G.703. The interface for external synchronization of the transmit timing signal should be in accordance with G.703. NOTE - In the case of the 64 kbis codirectional interface, the design of the input ports should take account o
38、f the need to provide octet alignment, 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. In the case of the n X 64 kbis interface, the design of the input p
39、orts should similarly take account of the need to provide frame alignment to allow controlled slips. 6 Jitter 6.1 Jitter at 2048 kbit/s output 6.1.1 In the case where the transmitting timing signal is derived from an internal oscillator, the peak-to-peak jitter at the 2048 kbit/s output should not e
40、xceed 0.05 U1 when it is measured within the frequency range fromfl= 20 Hz to f4 = 100 kHz. See Figure ZG.823. 6.1.2 In the case where the transmitting timing signal is derived from an external source having no jitter, the peak- to-peak jitter at the 2048 kbis output should not exceed 0.05 UI when i
41、t is measured within the frequency range from fi = 20 HZ t0f4 = 100 kHz. 6.1.3 In the case where the transmitting timing signal is derived from the incoming 2048 kbit/s signal having no jitter, the peak-to-peak jitter at the 2048 kbis output should not exceed 0.10 U1 when it is measured within the f
42、requency range from fi = 20 Hz to f4 = 100 kHz. The equivalent binary content of the test signal applied at the 2048 kbit/s input shall be a pseudo-random bit sequence of length 215 - 1 as specified in Recommendation 0.151. NOTE - It may be necessary to include a frame alignment signal in the test s
43、ignal to enable the measurement to be carried out. 6.2 Jitter at tributary outputs 6.2.1 In the case where the incoming 2048 kbis signal has no jitter, the peak-to-peak jitter at the 64 kbis output should not exceed 0.025 U1 when it is measured within the range fromfl= 20 Hz t0f4 = 10 kHz. The equiv
44、alent binary content of the test signal applied to the 2048 kbit/s input shall be a pseudo-random bit sequence of length 215 - 1 as specified in Recommendation O. 15 1. 6.2.2 signal should not exceed 0.10 UI when measured within the range fromfl= 20 Hz t0f4 = 10 kHz. be necessary to include a frame
45、alignment signal in the test signal. The peak-to-peak jitter value for the 2048 kbit/s tributary signal when there is no jitter at the 2048 kbis input NOTE - In order to carry out these measurements without invoking AIS at the 64 and n x 64 kbis outputs it will nonnally 4 Recommendation 6.7% (0-3) I
46、TU-T RECMN*G*736 73 D 4862573 0583372 3T4 D 6.3 Jitter transfer functions 6.3.1 The jitter transfer function between the 2048 kHz external synchronization signal and the 2048 kbit/s output signai should not exceed the gaidfrequency limits given in Figure 1. The 2048 kHz signal shall be modulated wit
47、h sinusoidal jitter. This may also be applicable to the n x 64 kbih tributary output. dB 0.5 - 8 R -1 9.5 NOTES kHz -8.4 dB f0 T1514170-93dO1 1 The ftequencyfo should be less than 20 Hz, and as low as possible (e.g. 10 Hz), taking into account the limitations of measuring equipment. 2 To achieve acc
48、urate measurements, the use of a selective method is recommended with a bandwidth sufficiently small referred to the relevant measurement frequency but not wider than 40 Hz. 3 For interfaces within national boundaries, this characteristic may be used. FIGURE UG.736 Jitter transfer function without j
49、itter reduction Some Administrations require that equipment is fitted with jitter reducers. In this case, the jitter transfer function should not exceed the gaidfrequency limits given in Figure 2. - 8 O N -19.5 ,., 9; /, 5 , . , 5, ,i T1514180-93d02 NOTES 1 into account the limitations of measuring equipment. 2 a bandwidth sufficiently small referred to the relevant measurement frequency but not wider than 40 Hz. The frequencyfoshould be less than 20 Hz, and as low as possible (e.g. 10 Hz), taking To achieve accurate measurements, the use of a se
