| O.1 | Scope and application of measurement equipment specifications covered in the O-series Recommendations
		 
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| O.3 | Climatic conditions and relevant tests for measuring equipment
		 
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| O.6 | 1020 Hz reference test frequency
		 
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| O.9 | Measuring arrangements to assess the degree of unbalance about earth
		 
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| O.11 | Maintenance access lines
		 
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| O.22 | CCITT automatic transmission measuring and signalling testing equipment ATME No. 2
		 
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| O.25 | 
[Withdrawn] Semiautomatic in-circuit echo suppressor testing system (ESTS)
		 Deleted after its content became technically out of date
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| O.27 | In-station echo canceller test equipment
		 
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| O.31 | 
[Withdrawn] Automatic measuring equipment for sound-programme circuits
		 Deleted after its content became technically out of date
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| O.32 | 
[Withdrawn] Automatic measuring equipment for stereophonic pairs of sound-programme circuits
		 Deleted after its content became technically out of date
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| O.33 | Automatic equipment for rapidly measuring stereophonic pairs and monophonic sound-programme circuits, links and connections
		 
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| O.41 | Psophometer for use on telephone-type circuits
		 This Recommendation is also included but not published in P series under alias number P.53
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| O.42 | Equipment to measure non-linear distortion using the 4-tone intermodulation method
		 
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| O.51 | 
[Withdrawn] Volume meters
		 O.51 was an alias name of ITU-T P.52. Only this alias name was suppressed. ITU-T P.52 remains valid
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| O.61 | Simple equipment to measure interruptions on telephone-type circuits
		 
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| O.62 | Sophisticated equipment to measure interruptions on telephone-type circuits
		 
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| O.71 | Impulsive noise measuring equipment for telephone-type circuits
		 This Recommendation is also included but not published in V series under alias number V.55
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| O.72 | 
[Withdrawn] Characteristics of an impulsive-noise measuring instrument for wideband data transmission
		 ITU-T O.72 was withdrawn on 1998-06-18.
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| O.81 | Group-delay measuring equipment for telephone-type circuits
		 
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| O.82 | Group-delay measuring equipment for the range 5 to 600 kHz
		 
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| O.91 | Phase jitter measuring equipment for telephone-type circuits
		 
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| O.95 | Phase and amplitude hit counters for telephone-type circuits
		 
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| O.111 | Frequency shift measuring equipment for use on carrier channels
		 
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| O.131 | Quantizing distortion measuring equipment using a pseudo-random noise test signal
		 
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| O.132 | Quantizing distortion measuring equipment using a sinusoidal test signal
		 
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| O.133 | Equipment for measuring the performance of PCM encoders and decoders
		 
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| O.150 | General requirements for instrumentation for performance measurements on digital transmission equipment
		 
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| O.151 | Error performance measuring equipment operating at the primary rate and above
		 
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| O.152 | Error performance measuring equipment for bit rates of 64 kbit/s and N x 64 kbit/s
		 
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| O.153 | Basic parameters for the measurement of error performance at bit rates below the primary rate
		 
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| O.161 | In-service code violation monitors for digital systems
		 
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| O.162 | Equipment to perform in-service monitoring on 2048, 8448, 34 368 and 139 264 kbit/s signals
		 
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| O.163 | Equipment to perform in-service monitoring on 1544 kbit/s signals
		 
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| O.171 | Timing jitter and wander measuring equipment for digital systems which are based on the plesiochronous digital hierarchy (PDH)
		 
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| O.172 | Jitter and wander measuring equipment for digital systems which are based on the synchronous digital hierarchy (SDH)
		 
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| O.173 | Jitter measuring equipment for digital systems which are based on the optical transport network
		 
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| O.174 | Jitter and wander measuring equipment for digital systems which are based on synchronous Ethernet technology
		 
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| O.175 | Jitter measuring equipment for digital systems based on XG-PON
		 
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| O.181 | Equipment to assess error performance on STM-N interfaces
		 
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| O.182 | Equipment to assess error performance on Optical Transport Network interfaces
		 
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| O.191 | Equipment to measure the cell transfer performance of ATM connections
		 
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| O.201 | Q-factor test equipment to estimate the transmission performance of optical channels
		 
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| O.211 | Test and measurement equipment to perform tests at the IP layer
		 
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| O.220 | Framework for end-to-end QoS measurement and supervision for leased-circuit services
		 
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| O.Sup3.1 | 
[Withdrawn] Measuring instrument requirements - Sinusoidal signal generators and level-measuring instruments
		 This Supplement was withdrawn because its content was out of date
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| O.Sup3.2 | 
[Withdrawn] Noise measuring instruments for telecommunication circuits
		 This Supplement was withdrawn because its content was out of date
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| O.Sup3.3 | 
[Withdrawn] Principal characteristics of volume indicators
		 This Supplement was withdrawn because its content was out of date
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| O.Sup3.4 | 
[Withdrawn] Consideration of interworking between different designs of apparatus for measuring quantizing distortion
		 This Supplement was withdrawn because its content was out of date
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| O.Sup3.6 | 
[Withdrawn] Crosstalk test device for carrier-transmission on coaxial systems
		 This Supplement was attached to ITU-T Rec. O.1 (05/96) as Appendix I without further modification
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| O.Sup3.7 | 
[Withdrawn] A measuring signal (multitone test signal) for fast measurement of amplitude and phase for telephone type circuits
		 This Supplement was renumbered as ITU-T Rec. O.81 Appendix I (06/98) without further modification
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| O.Sup3.8 | 
[Withdrawn] Guidelines concerning the measurement of jitter
		 This Supplement was attached to ITU-T Rec. O.171 (04/97) as Appendix I without further modification
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