1、INTERNATIONAL TELECOMMUNICATION UNION)45G134 / TELECOMMUNICATIONSTANDARDIZATION SECTOROF ITU30%#)b) detect and accumulate the counts of occurrences of loss of frame alignment;c) measure and display the error performance of 24-frame multiframe signals by monitoring the cyclicredundancy check (CRC-6)
2、bits and performing a CRC-6 procedure in accordance withRecommendation G.704 1 and as described below;d) detect and display the various alarm or fault conditions including loss of signal, loss of frame alignment,and other alarm conditions indicated by specific bit patterns.1.3 The equipment may opti
3、onally provide the following additional capabilities:a) detect and display the code violations in the 1544 kbits signal in accordance with Recommen-dation O.161;b) provide an external interface for extracting the information bits conveyed in any selected channel timeslot;c) provide an external inter
4、face for extracting the 4 kbit/s data link bits defined in the 24-frame multiframestructure;d) provide an external interface for extracting the signalling bits in the 12-frame and 24-frame structures.2 Input requirements2.1 InterfaceThe monitoring equipment shall be capable of operating with a test
5、load impedance at a 1544 kbit/s interfaceas defined in 2 of Recommendation G.703 2. It shall also be capable of operating when connected to protectedmonitoring points1)(see also Recommendation G.772 3).2.2 Input impedance2.2.1 Input impedance (resistive) 100 ohms2.2.2 Return loss (20 kHz to 1600 kHz
6、) 20 dB2.3 Input sensitivityAs a minimum, the monitoring equipment shall operate properly in the line terminating mode over the range ofbit rates, pulse shapes and signal levels defined in 2 of Recommendation G.703 2. It shall also be equipped with anadditional gain to compensate for the isolation l
7、oss incurred at protected monitoring points1)(see also Recommen-dation G.772 3). A signal level indicator, or other means, shall be provided for the proper adjustment of inputsensitivity._1)The specification of protected monitoring points is under study in SG XV and SG IV2 Fascicle IV.4 - Rec. O.163
8、2.4 Input jitter toleranceThe monitoring equipment shall be able to tolerate input jitter specified in Table 2/G.824 4 withoutdegradation of measuring accuracy.2.5 Input line codesThe monitoring equipment is intended for use with both AMI and B8ZS line codes. The instrument shall havethe capability
9、to select either AMI or B8ZS, through a switch or other appropriate means. The instrument should indicatewhen it is receiving B8ZS when switched to the AMI mode, and vice versa.3 Detection, measurement, and indication requirements3.1 Detection and indication of fault conditions3.1.1 Loss of line sig
10、nalUnder study.3.1.2 Loss of frame alignmentThe equipment shall recognize the loss of frame alignment as defined in Recommendation G.706 5, and anappropriate indication shall be given.3.1.3 Recovery of frame alignmentThe procedure for determining recovery of frame alignment shall be in accordance wi
11、thRecommendation G.706 5. When frame recovery is complete, the indication of loss of frame alignment shall cease.3.1.4 Alarm indication signal (AIS) from an upstream failureThe equipment shall recognize the presence of an alarm indication signal (AIS) indicating an upstream failure,and an appropriat
12、e indication shall be given. The binary equivalent of the AIS corresponds to an all ones signal. Thestrategy for the detection of the presence of an AIS shall be such that with a high probability, it is detected even in thepresence of a code violation ratio of 1 in 1000.3.1.5 Distant alarm indicatio
13、n signal (DAIS)The equipment shall recognize the presence of distant alarm indication signal as defined inRecommendation G.733 6, 4.2.4 for both 12-frame and 24-frame multiframe signals, and an appropriate indicationshall be given. The strategy for the detection of the presence of this distant alarm
14、 indication signal shall be such that witha high probability, it is detected even in the presence of a code violation ratio of 1 in 1000.3.2 Frame alignment signal (FAS) error performance measurements3.2.1 Count of errored secondsThe equipment shall be capable of counting the number of one second in
15、tervals in which one or more errorsoccur in the FAS bits associated with the 12-frame or 24-frame structures as defined in Recommendation G.704 1. Thenumber of errored seconds in a selectable time period (see 4.1) shall be counted and displayed. The equipment shallestablish one-second intervals inde
16、pendent of the occurrence of errors.3.2.2 Count of errorsThe equipment shall be capable of counting the number of FAS bit errors occurring in a selectable timeperiod (see 4.1).3.3 CRC-6 error performance monitoring3.3.1 Count of errored secondsThe equipment shall be capable of counting the number of
17、 one-second intervals in which one or more CRC-6violations are detected in 24-frame multiframe signals using the CRC-6 procedure defined in Recommen-dation G.704 1 and G.706 5. The number of errored seconds in a selectable time period shall be counted anddisplayed. The equipment shall establish one-
18、second intervals independent of the occurrence of errors.3.3.2 Performance indicationsAs an option the instrument shall be capable of providing performance information in accordance withRecommendation G.821 7.Fascicle IV.4 - Rec. O.163 33.3.3 Estimate of bit-error-ratioThis equipment shall optionall
19、y be capable of providing an estimate of the bit-error-ratio performanceof 24-frame multiframe signals in the range 104to 107by detecting CRC-6 violations. In performing thismeasurement, it shall be assumed that only one bit-error has occurred each time a CRC6 violation is detected. It isnoted that
20、this may not be an accurate estimate since more than one bit-error may occur within a 24-frame multiframe,due to the bursty nature of error occurrences.The time interval for each bit-error-ratio measurement that is within the required range of the equipment shallbe sufficiently long to include at le
21、ast ten CRC violations.3.3.4 Count of errorsThe equipment shall also be capable of counting the number of CRC-6 violations occurring in a selectable timeperiod (see 4.1).3.4 Loss of frame-alignment countThe equipment shall be capable of counting the occurrences of loss of frame alignment over a sele
22、ctable timeperiod (see 4.1). Error counters shall be disabled during intervals of loss of frame alignment.3.5 Measurement of code violationsIf the measurement of 1544 kbit/s code violations is included, the equipment shall meet the requirements ofRecommendation O.161.3.6 Channel time slot accessAs a
23、n option, receiving access may be provided to a selected 64 kbit/s channel at an external interface. Aninterface meeting the requirements of a co-directional interface output port defined in Recommendation G.703 2, ispreferred. In addition a centralized clock interface as defined in Recommendation G
24、.703 2 may be provided.3.7 4 kbit/s data link accessUnder study.3.8 Signaling bit accessUnder study.4 Control and display requirements4.1 Measurement timerA measurement interval timer shall be provided for the convenience of the user when counting errors. Thetimer shall be adjustable from 5 minutes
25、to 24 hours in steps of one minute or continuous. Manual “start” and “stop”controls shall also be provided.4.2 Count registersThe count registers shall have a capacity of at least 99999. A separate means for indicating overflow shall beprovided. Each of the registers shall be capable of being indepe
26、ndently reset. A separate register shall be provided foreach parameter or condition listed in 3.1 through 3.4.4.3 Selection of multiframe structureA control shall be provided to permit a user to select whether the 12-frame or 24-frame multiframe structure isbeing monitored. As an option the equipmen
27、t may automatically sense and display whether the signal being monitored isa 12-frame, 24-frame or neither multiframe structure.4.4 Lock/reset of displaysFor each of the fault condition indications given in 3.1 means shall be provided whereby the display willremain visible until a manual reset is op
28、erated.5 Monitoring equipment self diagnostics5.1 As an option, an internal self diagnostic system to check for correct functioning of the instrument, shall beprovided.4 Fascicle IV.4 - Rec. O.1636 Interface for remote control and measurement results6.1 As an option, an interface shall be provided f
29、or remote control of the frame signal monitoring equipment, andtransmission of measurement results. If provided, the interface bus shall comply with one of the following:a) ANSI/IEEE Std 488-1978 8b) IEC Publication 625 9c) ANSI/EIA-232-D-1986 10.7 Operating environmentThe electrical performance req
30、uirements shall be met when operating under climatic conditions as specified inRecommendation O.3, 2.1.References1 CCITT Recommendation Synchronous frame structures used at primary and secondary hierarchical levels,Vol. III, Rec. G.704.2 CCITT Recommendation Physical/electrical characteristics of hi
31、erarchical digital interfaces, Vol. III,Rec. G.703.3 CCITT Recommendation Digital protected monitor points, Vol. III, Rec. G.772.4 CCITT Recommendation The control of jitter and wander within digital networks which are based onthe 1544 kbit/s hierarchy, Vol. III, Rec. G.824.5 CCITT Recommendation Fr
32、ame alignment and cyclic redundancy check (RCR) procedures relating to basicframe structures defined in Recommendation G.704, Vol. III, Rec. G.706.6 CCITT Recommendation Characteristics of primary PCM multiplex equipment operating at 1544 kbit/s,Vol. III, Rec. G.733.7 CCITT Recommendation Error perf
33、ormance of an international digital connection forming part of anintegrated service digital network, Vol. III, Rec. G.821.8 ANSI/IEEE Std 488-1978, IEEE standard digital interface for programmable instrumentation.9 IEC Publication 625 An interface system for programmable measuring instruments (byte serial, bit parallel).10 ANSI/EIA-232-D-1986 Interface between data terminal equipment and data circuit terminating equipmentemploying serial binary data interexchange.
