ÿWPCL ûÿ2BJ|xÐ ` ÐÐÌÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿH øÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÌÐÐ °°°è ÐÑ Âx„|ü@Ž ÑÐ Åè5Ø'è5Ø'Å Ð9.ÁHÁÓÓÃÃRecommendation G.824ÄÄ Áà%ÁTHE CONTROL OF JITTER AND WANDER WITHIN DIGITAL NETWORKSƒ Áà+ÁWHICH ARE BASED ON THE 1544 kbit/s HIERARCHYƒ ÁHÁThe CCITT, ÃÃconsideringÄÄ Ð ( ÐÁHÁ(a)Á   Áthat timing jitter and alignment jitter can arise in digital networks; ÁHÁ(b)Á   Áthat, if proper control is not exercised, then under certain circumstances jitter can accumulate to such an extent that the following impairments can arise; Ð Ð ÐÁHÁi)Âh   Âan increase in the probability of introducing errors into digital signals at points of signal regeneration as a result of timing signals being displaced from their optimum position in time;ÆÆ ÂHHÂÂX  ÂÁ€ HÁÁ€Á ii)Á øÁthe introduction of uncontrolled slips into digital signals resulting from either data overflow or depletion in digital equipment incorporating buffer stores and phase comparators, such as jitter reducers and certain digital multiplex equipment;ÆÆ ÂHHÂÂX  ÂÁ€ HÁÁ€Á iii)Á øÁa degradation of digitally encoded analogue information as a result of phase modulation of the reconstructed samples in the digital©to©analogue conversion device at the end of the connection, which may have significant impact on digitally encoded video signals;ÆÆ ÁHÁ(c)Á   Áthat unlike some other network impairments, jitter can be reduced in magnitude by the use of jitter reducers, and in complex networks, it may be necessary to employ such devices; ÁHÁ(d)Á   Áthat wander can arise due to variations in transmission characteristics of the media and equipment, including disruptions in synchronization reference distribution; ÁHÁ(e)Á   Áthat it is necessary to accommodate wander at the input ports of digital equipment if controlled or uncontrolled slips are to be minimized; ÃÃrecommendsÄÄ ÁHÁthat the following guidelines and limits be applied in the planning of networks and in the design of equipment. 1.ÁHÁÃÃBasic jitter and wander control philosophyÄÄ ÁHÁThe goal of the strategy outlined in this Recommendation is to minimize impairments due to jitter and wander in digital networks. The strategy provides the following elements: ÁHÁa)Âh   Âspecification of network limits not to be exceeded at any hierarchical interface;ÆÆ ÁHÁb)Âh   Âa consistent framework for the specification of individual digital equipment;ÆÆ ÁHÁc)Âh   Âinformation and guidelines to predict and analyze jitter and wander accumulation in any network configuration, facilitate satisfactory control of the impairments due to this accumulation, and to provide insight into the jitter and wander performance of individual digital equipments;ÆÆ ÁHÁd)Âh   Âmeasurement methodology to facilitate accurate and repeatable jitter and wander measurements.ÆÆ ÁHÁSuggestions for measurement of parameters recommended below can be found in Supplement No. 3.8 of the O©Series (for jitter) and Supplement No. 35 (for wander). 2.ÂXHÂÃÃNetwork limits for maximum output at hierarchical interfaces and wanderÄÄ ÃÃat synchronous network nodesÄÄÆÆ 2.1ÁHÁÃÃNetwork limits for jitterÄÄ ÁHÁSpecification of maximum permissible values of output jitter at hierarchical network interfaces is necessary to enable the interconnection of digital network components (line section, multiplex equipment, exchanges) to form a digital path or connection. These limits should be met regardless of the number of interconnected network components preceding the interface. The limits are intended to be compatible with the minimum jitter tolerance of all equipment operating at the same hierarchical level. ÁHÁThe limits given in Table 1/G.824 represent maximum permissible output jitter limits at hierarchical interfaces of a digital network. In circumstances where the maximum permissible jitter amplitude occurs at an interface between two countries, it is left to the discretion of national administrations to take the appropriate remedial action. This situation is unlikely to occur very often. ÁàHOÁƒ ÁàHIÁTABLE 1/G.824ƒ À ÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀ À À À À À À À Maximum permissible output jitter at hierarchical interfaces À À ÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀ À À À À Network Limit À À À À À À À À À À Bandpass filter having a lower cut©off À À À À À À (UI peak©to©peak) À À frequency ÃÃfÄÄÃÃ1ÄÄ or ÃÃfÄÄÃÃ3ÄÄ and a minimum upper À À À À À À À À cut©off frequency ÃÃfÄÄÃÃ4ÄÄ À À ÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀ À À À À À À À À À À À À À À À ÀDigital rateÀ À BÃÃ1ÄÄ À À BÃÃ2ÄÄ À À fÃÃ1ÄÄ À À fÃÃ3ÄÄ À À fÃÃ4ÄÄ À À À À (kbit/s) À À À À À À (Hz) À À (kHz) À À (kHz) À À ÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀ À À À À À À À À À À À À À À À À 1544 À À 5.0 À À 0.1ÃÃa)ÄÄ À À 10 À À 8 À À 40 À À ÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀ À À À À À À À À À À À À À À À À 6312 À À 3.0 À À 0.1ÃÃa)ÄÄ À À 10 À À 3 À À 60 À À ÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀ À À À À À À À À À À À À À À À À 32064 À À 2.0 À À 0.1ÃÃa)ÄÄ À À 10 À À 8 À À 400 À À ÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀ À À À À À À À À À À À À À À À À 44736 À À 5.0 À À 0.1 À À 10 À À 30 À À 400 À À ÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÔ .,ÔŒÀ À À À À À À À À À À À À À À À 97728 À À 1.0 À À 0.05 À À 10 À À 240 À À 1000 À À À ÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀ À UIÁHÁUnit interval a)ÂXHÂThis value requires further study.ÆÆ ÁHÁFor systems in which the output signal is controlled by an autonomous clock (e.g., quartz oscillator) more stringent output jitter values may be defined in the relevant equipment specifications (e.g., for the muldex in Recommendation G.743, output jitter should not exceed 0.01 UI r.m.s). ÁHÁThe arrangements for measuring output jitter at a digital interface are illustrated in Figure 1/G.824. The specific jitter limits and values of filter cut©off frequencies are given in Table 1/G.824. ÁàHHÁFIGURE 1/G.824ƒ ÁàHOÁƒ ÁàH8ÁÃÃMeasurement arrangements for output jitter fromÄă ÁàH5ÁÃÃa hierarchical interface or an equipment output portÄă 2.2ÁHÁÃÃNetwork limits for wanderÄÄ ÁHÁNetwork output wander specifications at synchronous network nodes are necessary to ensure satisfactory network performance (e.g. slips, error bursts). For network nodes the following limits are specified, based on the assumption of a non©ideal synchronizing signal (containing jitter, wander, frequency departure, and other impairments) on the line delivering timing information. The maximum time interval error (MTIE) (see Recommendation G.811) over a period of ÃÃSÄÄ seconds shall not exceed the following: ÁHÁ(10Ãé2ÄÄÃÃSÄÄ + 10,000) ns; applicable to values of ÃÃSÄÄ greater than 10ÃÃ4ÄÄ. ÃÃNoteÄÄ © The resultant overall specification is illustrated in Figure 2/G.824. 3.ÁHÁÃÃFramework for the specification of individual digital equipmentsÄÄ 3.1ÁHÁÃÃBasic specification philosophyÄÄ ÁHÁJitter and wander control inherently depends on both network and equipment design. Network considerations are discussed in ÀÀ 2. The principal parameters of importance when considering the jitter and wander performance of digital equipment are: ÁHÁi)Âh   Âthe amount of jitter and wander that can be tolerated at the input;ÆÆ ÁHÁii)Âð   Âthe proportion of this input jitter and wander which filters through to the output; andÆÆ ÂHHÂÂX  ÂÁ€ HÁÁ€ÁÁHÁiii)Á øÁthe amount of jitter and wander generated by the equipment.ÆÆ ÁHÁThe intention of this section is to provide a foundation for the development of equipment requirements which will ensure that the various network equipments are compatible from the standpoint of jitter and wander performance. ÁàHHÁFIGURE 2/G.824ƒ ÁàHOÁƒ ÁàH8ÁÃÃPermissible maximum time interval error (MTIE)Äă ÁàH1ÁÃÃversus observation period S for the output of a network nodeÄă ÁHÁFurther study is required to quantify the difference in limits for transit and local nodes. In addition, wander accumulation in networks is closely tied to the stability specifications contained in Recommendations G.811, G.81x, Q.511. 3.1.1ÁHÁÃÃJitter and wander tolerance of input portsÄÄ ÁHÁIn order to ensure that any equipment will operate satisfactorily when connected to a hierarchical interface within the network, it is necessary that the equipment input ports be capable of accommodating levels of network output jitter up to the maximum network limits specified in Table 1/G.824. Specification of input jitter tolerance in terms of a single Recommendation applicable to all categories of digital equipment ensures that a certain minimum jitter tolerance is satisfied by all network elements. Most specifications of equipment input tolerance are in terms of the amplitude of sinusoidal jitter that can be applied at various frequencies without causing a designated degradation of error performance. The simplicity of this form of specification has great appeal, since it is easily verified with conventional test equipment. However, it is important to recognize that the test condition is not, in itself, intended to be representative of the type of jitter to be found in practice in a network. For some equipment, therefore, it may be necessary to specify supplemental jitter tolerance tests, and reference to the individual equipment Recommendation should always be made. ÁHÁAs a minimum guideline for equipment tolerance, it is recommended that all digital input ports of equipments be able to tolerate the sinusoidal jitter and wander defined by Figure 3/G.824 and Table 2/G.824. The limits are to be met in an operating environment. ÁHÁIn deriving the specifications contained in Table 2/G.824 for frequencies above fÃÃ3ÄÄ, the effects of the amount of alignment jitter of the equipment clock decision circuit are considered to be predominant. Measurements carried out to verify compliance with these specifications may provide environment dependent results, hence allowing some ambiguity in their interpretation. Account should be taken of the requirement at the design stage of the equipment; Supplement No. 3.8 (O©Series) provides guidance regarding environment independent measurements. ÁHÁIn deriving these specifications, the wander effects are considered to be predominant at frequencies below fÃÃ1ÄÄ, and many transmission equipments, such as digital line systems and asynchronous muldexes using justification techniques, are effectively transparent to these very low frequency changes in phase. However, such phase variation does need to be accommodated at the input of certain equipments (e.g. digital exchanges and synchronous muldexes). The requirement contained in Table 2/G.824 for frequencies below fÃÃ1ÄÄ is not amenable to simple practical evaluation, but account should be taken of the requirement at the design stage of the equipment. ÁHÁEquipment wander tolerance must be compatible with network output wander limits specified in Figure 2/G.824. Insufficient wander tolerance at synchronous equipment input ports may result in controlled or uncontrolled slips, depending on the specific slip control strategy employed. ÁàHOÁƒ ÁàHIÁTABLE 2/G.824ƒ ÁàHOÁƒ ÁàH:ÁÃÃJitter and wander tolerance of input portsÄă ÁàH@ÁÃÃ(Provisional values) (Note 1)ÄăÔ .,ÔŒ À ÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀ À À À Bit À À Jitter amplitude À À À À Test À À À À Rates À À (peak©to©peak) À À Frequency À À Signal À À À À(kbit/s)ÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀ À À À À À AÃÃ0ÄÄ À À AÃÃ1ÄÄ À À AÃÃ2ÄÄ À À fÃÃ0ÄÄ À À fÃÃ1ÄÄ À À fÃÃ2ÄÄ À À fÃÃ3ÄÄ À À fÃÃ4ÄÄ À À À À À À À À (ÀÀs) À À (UI) À À (UI) À À (Hz) À À(Hz)À À(Hz) À À(kHz)À À(kHz)À À À À ÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀ À À À À À À À À À À À À À À À À À À À À À À À À 1544 À À 18 À À 5.0 À À 0.1 À À1.2x10Ãé5ÄÄÀ À 10 À À 120 À À 6 À À 40À À 2ÃÃ20ÄÄ©1 À À À À À À(Note 2)À À À À(Note 2)À À À À À À À À À À À À(Note 3) À À À À 6312 À À 18 À À 5.0 À À 0.1 À À1.2x10Ãé5ÄÄÀ À 10 À À 50 À À 2.5 À À 60À À 2ÃÃ20ÄÄ©1 À À À À À À(Note 2)À À À À À À À À À À À À À À À À(Note 2) À À À À 32064 À À 18 À À 2.0 À À 0.1 À À1.2x10Ãé5ÄÄÀ À 10 À À 400 À À 8 À À 400À À 2ÃÃ20ÄÄ©1 À À À À À À(Note 2)À À À À À À À À À À À À À À À À(Note 2) À À À À 44736 À À 18 À À 5.0 À À 0.1 À À1.2x10Ãé5ÄÄÀ À 10 À À 600 À À 30 À À 400À À 2ÃÃ20ÄÄ©1 À À À À À À(Note 2)À À À À(Note 2)À À À À À À À À À À À À(Note 2) À À À À 97728 À À 18 À À 2.0 À À 0.1 À À1.2x10Ãé5ÄÄÀ À 10 À À12 000À À 240 À À1 000À À 2ÃÃ23ÄÄ©1 À À À À À À(Note 2)À À À À À À À À À À À À À À À À(Note 2) À À À ÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀ À ÃÃNote 1ÄÄ © Reference to individual equipment specifications should always be made to check if supplementary input jitter tolerance requirements are necessary. ÃÃNote 2ÄÄ © This value requires further study. ÃÃNote 3ÄÄ © It is necessary to suppress long zero strings in the test sequence in networks not supporting 64 kbit/s transparency. ÃÃNote 4ÄÄ © The value AÃÃ0ÄÄ (18 us) represents a relative phase deviation between the incoming signal and the internal local timing signal derived from the reference clock. ÁàHHÁFIGURE 3/G.824ƒ ÁàHOÁƒ ÁàH/ÁÃÃMask of peak©to©peak jitter and wander which must be accommodatedÄă ÁàH:ÁÃÃat the input of a node in a digital networkÄă ÁàH1ÁÃÃ(Measurement method © refer to Supplement No. 3.8 (O©Series)Äă ÁàHDÁÃÃand Supplement No. 35)Äă 3.1.2ÁHÁÃÃJitter and wander transfer characteristicsÄÄ ÁHÁJitter transfer characteristics define the ratio of output jitter to input jitter amplitude versus jitter frequency for a given bit rate. When jitter is present at the digital input port of digital equipment, in many cases some portion of the jitter is transmitted to the corresponding digital output port. Many types of digital equipment inherently attenuate the higher frequency jitter components present at the input. CCITT Recommendations dealing with particular equipment will ultimately define limiting values for its particular jitter transfer characteristics. To control jitter in cascaded homogeneous digital equipment situations, it is important to restrict the value of jitter gain. ÁHÁBecause the bandwidth of phase smoothing circuits in asynchronous digital equipment is generally above 10 Hz, wander on the input signal may appear virtually unattenuated on the output. However, in certain particular digital equipments (e.g. nodal clocks) it is necessary that wander be sufficiently attenuated from input to output. CCITT Recommendations dealing with synchronous equipment will ultimately define limiting values for particular wander transfer characteristics. 3.1.3ÁHÁÃÃIntrinsic jitter and wander generationÄÄ ÁHÁIntrinsic jitter and wander generation is defined as output jitter and wander in the absence of input jitter and wander. It is necessary to restrict the amount of intrinsic jitter and wander generated within individual digital equipments to provide control over network jitter and wander accumulation from cascaded network elements. Limits for output jitter and wander for individual digital equipments are defined in the specific CCITT equipment Recommendations. The actual limits applied depend upon the type of equipment. 3.2ÁHÁÃÃDigital line sectionsÄÄ ÁHÁTo ensure that the maximum network limit (ÀÀ 2.1) is not exceeded within a digital network, it is necessary to control the jitter and wander contributed by transmission systems. ÁHÁThe jitter specifications for digital line sections will ultimately be found in Recommendations G.911 to G.915. 3.3ÁHÁÃÃDigital muldexesÄÄ ÁHÁTo ensure that the maximum network limit (ÀÀ 2.1) is not exceeded within a digital network, it is necessary to control the jitter and wander contributed by transmission systems. ÁHÁThe jitter specifications for digital muldexes using positive justification are found in Recommendations G.743 and G.752. 3.4ÁHÁÃÃDigital exchangesÄÄ ÁHÁTo ensure that the maximum network limit (to be specified in ÀÀ 2.2) is not exceeded within a digital network, it is necessary to control jitter and wander transfer and generation, as appropriate, for digital exchanges. ÁHÁOutput wander specifications for primary reference clocks are addressed in Recommendation G.811. The jitter and wander specifications for digital transit exchanges and digital local exchanges are found in Recommendation Q.511. 4.ÁHÁÃÃJitter and wander accumulation in digital networksÄÄ ÁHÁThe variability of network configurations presents a multitude of connection possibilities. To analyze a particular network configuration, it is necessary to use the information about the jitter characteristics of individual equipments in conjunction with appropriate jitter accumulation models. Supplement No. 36 provides information to aid organizations in carrying out such evaluations. Ð h Ð The term digital section is used in these Recommendations as a general term to include digital line section and digital radio section. This term is defined in Recommendation G.701 (see also Figure 1/G.701 and Figure 2/G.960). Digital sections are defined as component parts of digital links operating at particular bit rates and may be regarded as "black boxes". For digital sections used in digital hierarchy (network) applications the inputs and outputs are recommended in the form ofÔ .,Ô "equipment interfaces" (i.e. in Recommendation G.703 for hierarchical bit rates or in the Recommendation G.931 for non©hierarchical bit rates). For digital sections used for ISDN customer access the "section boundaries" are at the T reference point and the appropriate V reference point. User©network interfaces which may be used at the T reference point are recommended in the I.400©Series of Recommendations and the exchange interfaces which may be used at the V reference points are recommended in the Q.500©Series of Recommendations. Digital section Recommendations contain the common network©related requirements applicable to digital radio, metallic and optical transmission systems. The performance requirements relate to network performance objectives.