Conforming to the Mazeof Network Standards

ITU-T Recommendationsand Practical Applicationsin PDH/SDH Networks

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Recommendations Description Page

G.783 SDH equipment functional blocks 1

G.783 Section 10 Jitter and wander parameters at MUX and DEMUX ports 3

G.823 Jitter and wander parameters at PDH interfaces 5

G.825 Jitter parameters at SDH interfaces contained in a SDH network 6

G.958 Jitter parameters at SDH regenerator ports 8

G.813 Jitter and wander parameters of SDH equipment slave clocks 9

G.826 Error performance in SDH/PDH networks 12

M.2100 Performance levels for BIS of international PDH paths. 14

G.841 Types and characteristics of SDH network protection architecture 15

G.841 Linear Multiplex section protection (MSP) protocol, commands and operation 16(G.783 Annex A)

If the switch-over time is exceeded or communi-cation between the network elements is not reliable, we must find the reason. With its bytecapture function, the ANT-20 enables detailed analysis of the SOH bytes. Up to 265 changes inthe K1/K2 combination are recorded. The ANT-20can be configured to measure in monitor mode or in through mode in the protection channel of the SDH ring.

The ANT-20Õs solution is flexible and lets you se-lect different events as your measurement criterion:� SDH: MS-AIS, AU-AIS, TU-AIS, TSE � SONET: AIS-L, AIS-P, AIS-V, TSEThe switchover time is specified as 50 ms. TheANT-20 measures the duration of the event on the tributary with a resolution of 1 ms, even if thesignal has bit error ratios up to 2u10-4. A secondANT-20 can be used to generate the APS. In through mode, the instrument generates the alarm types SF (B2 >1u10-3) and SD (B2 >1u10-6), and in OOS mode also LOS, LOF,MS-AIS (AIS-L). The procedure is as follows: 1. Set the signal structure using the ANT-20Õs

signal structure editor. Start the APS timemeasurement.

2. Activate APS by manually interrupting the working channel, by generating an event with a second ANT-20 in through mode, or using a network management setting.

3. Measure the interruption time. Compare it withthe expected value. Result interpretation is simple: ÒpassedÓ or ÒfailedÓ. SOH/TOH

byte capture

working channel

protection channel

APS timemeasurement.Event: AIS, TSE

PDHNetwork

G.823

G.958

G.841

G.825G.813

G.821G.826

M.2100

Jitter TestWander

Jitter Test

Cross Connect TestError

Performance

Author

Ben Di-Lorenzo, Stephan Schultz,Frank Coenning, Wolfgang MillerState: December 1998

Why Do Recommendations Exist for SDH/PDH Networks?

Telecommunications networks are not built fromtechnologies that are individually specified by eachservice provider. If they were, imagine how hard itwould be to connect from one service provider tothe next! The logical solution is to have a universalorganization (or organizations) specifying trans-mission methods that are universally applicable toall service providers. One of these bodies is theInternational Telecommunication Union � Tele-communication Standardization Sector (ITU-T)formally known as CCITT. The ITU-T is responsible

for studying technical, operating and tariff questionsand issuing Recommendations on them with a view tostandardizing telecommunications on a worldwidebasis. Many telecommunication networks use network ele-ments that are specified by ITU-T Recommendations.The Advanced Network Tester (ANT-20) recognizesthese Recommendations and carries out measure-ments to qualify them. This note will directly quoteRecommendations from ITU-T and then apply themto practical applications performed on the ANT-20.

Abbreviation list :

ADM Add & Drop MultiplexerAIS Alarm Indication SignalAPS Automatic Protection SwitchingBBE Backround Block ErrorBBER Backround Block Error RatioBIP Bit Interleaved ParityBIS Bringing Into ServiceCRC Cyclic Redundancy CheckDEMUX DemultiplexerDXC Digital Cross ConnectES Errored SecondESR Errored Second RatioEFS Error Free SecondFMTJ Fast Maximum Tolerable JitterIG International GatewayISM In Service MonitoringJTF Jitter Transfer Function HP High Order PathLOF Loss Of FrameLP Low Order PathMS Multiplex SectionMSOH Multiplex Section

OverheadMSP Multiplex Section

ProtectionMST Multiplex Section Termination

FunctionMTJ Maximum Tolerable Jitter MTIE Maximum Time Interval ErrorMUX MultiplexOOS Out of ServiceOS Optical SectionPDH Plesiochronous Digital HierarchyPEP Path End PointRDI Remote Defect IndicationPRC Primary Reference ClockUI Unit IntervalREG RegeneratorRS Regenerator Section RST Regenerator Section Termination

FunctionRSOH Regenerator Section OverheadSES Severely Errored SecondSESR Severely Errored Second RatioSD Signal DegradationSDH Synchronous Digital HierarchySEC Synchronous Equipment ClockSF Signal FailureSTM Synchronous Transport ModuleTDEV Time DeviationVC Virtual Container

Figure 29: Measuring switch-over time

Figure 28: Result from the switch-over measurement

Figure 30: Byte capture shows content of K1/K2 bytes in plain text

1

Recommendation G.783: Characteristics ofSynchronous Digital Hierarchy (SDH) EquipmentFunctional Blocks

“This Recommendation defines a library of basicbuilding blocks and a set of rules by which theymay be combined in order to describe a digitaltransmission equipment. The library comprises thefunctional building blocks needed to specifycompletely the generic functional structure of theSynchronous Digital Hierarchy.”The Recommendation describes processes withinthe basic building blocks, the so called “atomicfunctions”, for example the generation andevaluation of overheads used for performancemonitoring. The regenerator section termination and

adaptation function acts as a source and sink forthe regenerator section overhead (RSOH). TheRSOH contains bytes A1, A2, B1, J0, E1, F1, D1 toD3 and bytes reserved for national use. Thissection acts as a maintenance entity between andincluding two regenerator termination functions. The multiplex section termination and adaptationfunction acts as a source and sink for the multiplexsection overhead (MSOH). The MSOH containsbytes B2, K1, K2, D4 to D12, S1, M1, E2 and bytesreserved for national use. This section acts as amaintenance entity between and including twomultiplex termination functions.

G.783 APPLICATION

MSOH Byte Functionality and BERT

RSOH Byte Functionality and BERT

In BriefPDH signals are transported over four main SDHlayers all of which play critical parts in certifyingSDH transmission. The physical layer is classifiedas the fifth layer. The section overhead (SOH) ismainly built up from the RSOH and MSOH, whichguide the payload of the STM-N signal betweenmultiplex and regenerator elements within anetwork. With this particular asset of the STM-Ntechnology, the overhead of the STM-N signal canbe tested and in turn test the MST and RSTfunctions.

Figure 1 illustrates the different layers which arepassed by a signal when it is transmitted through anetwork. The different layers are terminated depen-ding on the functions implemented in the networkelements. For example, the regenerator layerguides the signal between the MUX and REG, thena new RSOH is generated at the output of the REGto guide the signal to the ADM, and so on. Thelower path (LP) layer will come into play when thePDH tributaries are terminated at the DEMUX.

LP: Lower Order PathHP: Higher Order PathMS: Multiplex SectionRS: Regenerator SectionOS: Optical Section

Figure 1

Application

A suitable application for testing the RST and MSTfunctions lies in the Anomaly/Defect generator andanalyzer. SDH technology uses a maintenanceinteraction flow where different signals are trans-mitted through particular bytes of the overhead toindicate anomalies and defects. Messages aregenerated due to an interaction with corresponding

layer errors. For example, if a LOF is generated inthe RS layer then an AIS defect will display in thePDH layer. Test can be performed with the ANT-20by sending out defects in the different layers andlooking at the reactions in the correspondinglayers. Figure 2 a/b illustrates two general setupswhich will result in two different error alarms beinggenerated. The black line setup will generate error alarms of aHP and MS layer nature if a RS defect was firstgenerated. The red line setup will generate erroralarms of PDH layer nature due to the fact that aPDH signal is examined.

2

Recommendation G.783: Section 10 Specification of Jitter and WanderThis section of recommendation G.783 specifiesinput and output jitter/wander requirements whichdirectly refer to recommendations G.958, G.825and G.813 which will be explained later in thisnote. This recommendation also specifies wanderand combined jitter caused by PDH tributarymapping and pointer adjustments.“The combined jitter arising from tributary mappingand pointer adjustments should be specified interms of peak-to-peak amplitude over a givenfrequency band, under application of represen-

tative specified pointer adjustment test sequences,for a given measurement interval.”A major factor that must be realized in this specifi-cation of mapping and pointer jitter on PDHinterfaces is the definition of the filter character-istics. Most important is the specification of thehighpass filter characteristics due to the lowfrequency components of pointer jitter. Tables1a/1b show the filter characteristics for mappingjitter generation and combined jitter generation.

Figure 3a: The user interfacewindow for generatingdifferent anomaliesand defects.

Figure 3b: Results in graphicalformat.

Figure 3bFigure 3a

Figure 2bFigure 2a

3

G.703 Maximum(PDH) Filter characteristics pk-pk

interfaces mapping jitter

kbit/s f1 f3 f4 f1–f4 f3–f4high pass high pass low pass

1,544 10 Hz 8 kHz 40 kHz (Note 1) 0.1 UI

2,048 20 Hz 18 kHz 100 kHz (Note 1) 0.075 UI(700 Hz)

6,312 10 Hz 3 kHz 60 kHz (Note 1) 0.1 UI

34,368 100 Hz 10 kHz 800 kHz (Note 1) 0.075 UI

44,736 10 Hz 30 kHz 400 kHz 0.4 UI 0.1 UI

139,264 200 Hz 10 kHz 3,500 kHz (Note 1) (Note 2)

Notes1. These values are for further study2. A value of 0.075 UI has been proposed

Table 1a: Mapping jitter

G.703 Maximum(PDH) Filter characteristics pk-pk combined

interfaces jitter

kbit/s f1 f3 f4 f1–f4 f3–f4high pass high pass low pass

1,544 10 Hz 8 kHz 40 kHz 1.5 UI (Note 1)

2,048 20 Hz 18 kHz 100 kHz 0.4 UI 0.075 UI(700 Hz)

6,312 10 Hz 3 kHz 60 kHz 1.5 UI (Note 1)

34,368 100 Hz 10 kHz 800 kHz 0.4 UI 0.075 UI0.75 UI

44,736 10 Hz 30 kHz 400 kHz (Note 1) (Note 1)

139,264 200 Hz 10 kHz 3 500 kHz (Note 1) (Note 1)

Note 1These values are for further study

Table 1b: Combined jitter

Mapping and combined jitter occurs when PDHsignals are transported over a SDH network. PDHtributaries need to be contained in the virtualcontainer (VC) of a SDH transport module (STM).Accommodation of the PDH bit rate to the SDHclock requires a bit stuffing procedure during themapping process. These stuffing phase steps leadto additional mapping jitter. The same thing, but with higher amplitude occurs if pointer adjustments

are apparent. Both effects together result incombined jitter. The recommendation specifiesvalues to which the MUX and DEMUX must adhereto ensure as little jitter in the system as possible.The recommendation also defines pointer testsequences which are used to test the performanceof SDH equipment with regard to SDH tributaryjitter. These pointer test sequences are illustratedin Figure 4.

In Brief

4

The ANT-20 has theadvantage of generating AUand TU pointers simultan-eously. The application is set up totest the DUT’s combined andmapped jitter limits. This isperformed by inputting anSTM-N signal and moni-toring the PDH tributaries, (i.e. 2,8,34,140 Mbit/s). TheANT-20 will analyze jitter asillustrated in Recommen-dation G.783, but with thepointer test sequencesactivated simultaneously.

G.783 Section 10 APPLICATION

PDH interfaces Jitter with pointer simulation

Figure 5a: The pointer value ingraphical format with the currentvalue (shown ringed).

Figure 5b: The possible sequencesthat the ANT-20 may generate as specified by ITU-T Recom-

mendation G.783.

Figure 4: Pointer sequences acc. to G.783

Figure 5a

Figure 5c

Figure 5b

Tributaryports

2,048 kHz

Pointer actionMissing pointer action

Additional pointer action

87-3 sequence

43-44 sequence

Start of nextsequence

Start of nextsequence

4 missingpointer action

86-4 sequence

Start of nextsequence

Application

5

Recommendation G.823: Control of JITTER and WANDER within DigitalNetworks Based on the 2,048 kbit/s Hierarchy

Parameter value Network limit Measurement filter bandwidth

Digital rate B1 unit interval B2 unit interval Band-pass filter having a lower cut-off(kbit/s) peak-peak peak-peak frequency f1 or f3 and an upper cut-off

frequency f4f1 f3 f4

64 0.25 0.05 20 Hz 3 kHz 20 kHz(Note 1)2,048 1.5 0.2 20 Hz 18 khz 100 kHz

(700 Hz)8,448 1.5 0.2 20 Hz 3 kHz 400 kHz

(80 kHz)34,368 1.5 0.15 100 Hz 10 kHz 800 kHz139,264 1.5 00.75 200 Hz 10 kHz 3 500 kHz

Notes1. For the codirectional interface only.2. The frequency values shown in parenthesis only apply to certain national interfaces.3. UI = Unit Interval

for 64 kbit/s 1 UI = 15.60 nsfor 2,048 kbit/s 1 UI = 488.00 ns B1 is the permissible jitter with the band passfor 8,448 kbit/s 1 UI = 118.00 ns filter cut-off f1 and f4.for 34,368 kbit/s 1 UI = 29.10 ns B2 is the permissible jitter with the band passfor 139,264 kbit/s 1 UI = 7.18 ns filter cut-off f3 and f4.

“The scope of this Recommendation is to define the parameters and the relevant values that areable to control satisfactorily the amount of jitter and wander present at the plesiochronous digitalhierarchy (PDH) network interface.”The limits set for the maximum permissible levels of jitter at PDH interfaces within digitalnetworks are illustrated in Table 2. Therecommendation points out that the limits shouldbe met for all operating conditions regardless of

Table 2: Jitter limitsfor PDH interfacesdefining the cor-responding filterbandwidth.

Figure 6: Permissible MTIE vs.observation period s for the output

of a network node.

the amount of equipment preceding the interface. This recommendation covers also limits for wander influences that appear over the equip-ment interfaces of a PDH network. The Recommendation states that “magnitudes of wander, being largely dependent on thefundamental propagation characteristics oftransmission media and the aging of clock circuitry, can be predicted.” For PDH interfaces the following limits apply.

Figure 6 illustrates the permissible maximum timeinterval error (MTIE) vs. observation period S forthe output of a network node. MTIE is themaximum UI which was recorded at an instant ofthe period S. S can be a 10 sec observation timewhich makes up a 12 hour measuring period.

In Brief

This Recommendation focuses on networkscontaining equipment with PDH interfaces. Whennetworks are designed, service providers need totake into account the values illustrated in Table 2and Figure 6, ensuring that all network elementson line do not introduce any more jitter or wanderinto a PDH network system.

MTIE(ns)

Observation Period (S)

6

G.823 APPLICATION

PDH interface Jitter and Maximum Tolerable Jitter

PDH interface Wander (MTIE)

PDH regenerators Jitter Transfer Function

Figure 7 shows the setup to test the performanceof the DUT’s jitter capabilities for PDH signals.Jitter transfer function and maximum tolerable jittertests can also be performed under this Recommen-dation. These two measurements are explained inmore detail in the sections for RecommendationG.958 and G.825. For wander refer to G.813.The jitter result window in Figure 8 is for manualmode. In this mode the user can set jitter ampli-tudes manually and observe the reaction of theDUT through errors and alarms. Phase hits occurwhen a specific jitter threshold is exceeded. The results are recorded using a counter. Limits of the hitthreshold may be set via the SET button.The jitter generator/analyzer window allows theuser to select the application measurement formaximum tolerable jitter (MTJ) or fast MTJ (FMTJ),jitter transfer function and wander analysis.

Recommendation G.825: Control of JITTER andWANDER within Digital Networks Based on theSynchronous Digital Hierarchy (SDH)

“The scope of this Recommendation is to define the parameters and the relevant values that areable to control satisfactorily the amount of jitter andwander present at the SDH network interface.”This Recommendation specifies the jitter limits

applied to the SDH network interfaces. Networkinterfaces (e.g. international boundaries) mustmeet interface limits regardless of the individualcarrier’s choice of equipment. These limits aredisplayed in Table 3.

Figure 8: The resultswindow for jitter for a

PDH signal.

STM level f1 (Hz) f3 (kHz) f4 (MHz) B1 (UIpp) B2 (UIpp)

STM-1 optical 500 65 1.3 1.5 0.15

STM-1 electrical 500 65 1.3 1.5 0.075

STM-4 optical 1,000 250 5 1.5 0.15

STM-16 optical 5,000 under study 20 1.5 0.15(Note 2)

Notes1. UIpp = Unit interval 2. A value of 1 MHz has been suggested.

for STM-1 UI = 6.43 ns B1 is the permissable jitter with the band for STM-4 UI = 1.61 ns pass filter cut-off f1 and f4.for STM-16 UI = 0.40 ns B2 is the permissable jitter with the band

pass filter cut-off f3 and f4.

Table 3

Figure 7

PDHInterface

Application

DUT

7

G.825 APPLICATION

ALL SDH interface Jitter, Maximum Tolerable Jitter

In Brief

This Recommendation applies to SDH serviceproviders who need to test the quality of the SDHinterfaces where SDH networks span a large area.Table 3 illustrates limits which any interface in thenetwork will need to meet to ensure a quality

The setup to test the performance of maximumtolerable jitter (MTJ) at SDH network interfaces isshown in Figure 9. MTJ measurements are generally performed by increasing jitter amplitudesat certain scan frequencies and evaluating thenumber of errors that the DUT produces. The ANT-20 performs this procedure in an auto-mated way, thus generating different jitter ampli-tudes at certain frequencies and recording the jitteramplitude when the DUT failed, then comparingthese values against the Recommendation mask.

Figure 10: Differenttolerance masks andscan frequencies canbe user defined, byclicking on the “SET”button situated in thetitle bar.

Figure 9

STM-4Interface

network. Jitter and Wander limits for network ele-ments without connection to the network are morestringend to meet the network interface require-ments. Such limits are defined in RecommendationG.783 and G.958 for SDH network elements.

Application

Figure 11: MTJ resultsrecorded in tabularand graphical formatagainst tolerancemasks set by ITU-T.

DUT

8

Recommendation G.958: Digital Line Systems Based on the SynchronousDigital Hierarchy for Use on Optical Fiber Cables

Interface Measuring filter Peak-to-peak amplitude

STM-1 500 Hz to 1.3 MHz 0.30 UI

65 KHz to 1.3 MHz 0.10 UI

STM-4 1,000 Hz to 5 MHz 0.30 UI

250 kHz to 5 MHz 0.10 UI

STM-16 5,000 Hz to 20 MHz 0.30 UI

1 MHz to 20 MHz 0.10 UI

For STM-1 1 UI = 6.43 nsFor STM-4 1 UI = 1.61 nsFor STM-16 1 UI = 0.40 ns

“Jitter transfer function (JTF) is defined as the ratioof jitter on the output STM-N signal to the jitter ap-plied on the input STM-N signal vs. frequency.”This factor indicates the degree to which jitter isamplified or attenuated by a regenerator. If the jitteramplification of several regenerators is too high,the accumulated jitter amplitude at the end of theline system may exceed the network limits.

STM-N level (type) fc (kHz) P (dB)

STM-1 (A) 130 0.1STM-1 (B) 30 0.1STM-4 (A) 500 0.1STM-4 (B) 30 0.1STM-16 (A) 2,000 0.1STM-16 (B) 30 0.1

STM-M ft (kHz) fo (kHz) A1 (Uip-p) A2 (Uip-p)Level

STM-1 65 6.5 0.15 1.5

STM-4 250 25 0.15 1.5

STM-16 1,000 100 0.15 1.5

“This Recommendation specifies characteristics ofdigital synchronous line systems based on thesynchronous digital hierarchy (SDH) to providetransverse compatibility.”This Recommendation will focus on jitter gener-ation, jitter transfer and jitter tolerance of regener-ators.“Jitter generation is defined as the amount of jitterat the STM-N output of SDH regenerators.” Theamplitude of the jitter present at the output of eachregenerator should not exceed a specified limitvalue.Table 4 displays the proposed figures from therevised draft of recommendation G.958 on STM-Njitter generation for output jitter at an STM-N inter-face assuming the absence of jitter at the inputinterface, thus intrinsic jitter.

In Brief

This recommendation focuses on the limits thatSDH regenerators need to meet to be part of aquality network system. Each regenerator canintroduce jitter resulting in jitter accumulation,

“Jitter tolerance is defined as the peak-to-peakamplitude of sinusoidal jitter applied on the inputSTM-N signal that causes a 1 dB optical penalty atthe optical equipment.”Regenerators must be able to tolerate a specifiedjitter amplitude at the input without any errorsoccurring.

NOTE: Relevant parts of Recommendation G.958including the jitter requirements of regenerators willin future be moved to section 10 of a revisedversion of Recommendation G.783.

Table 4: Intrinsic jitter limits

Table 6 illustrates the jitter tolerance parameters

Table 5 illustrates the jitter transfer parameters for twoclasses of regenerators with different frequency bandwidths

affecting greatly the purity of the transportedsignal. Regenerators need to be within the required limits to reassure the performance of a network.

9

G.958 APPLICATION

SDH regenerator Intrinsic Jitter, Jitter Transfer interface Function, Jitter Tolerance

SDH regenerator Wander

Application

JTF measurements are of particular importancewhen dealing with regenerators. Checks arecarried out to demonstrate that the jitter gain of aregenerator is below the defined value of recom-mendation G.958. If this is not the case, then “jitterrunaway” occurs after several regenerators. JTF ismeasured by applying a signal with defined jittermodulation over the frequency range of the DUT.The jitter amplitude is selected so that the DUT canhandle it at any frequency. The ANT-20 meas-ures the resulting jitter amplitude at the output ofthe DUT at various TX jitter frequencies. The log ofthe ratio between input and output gives the jittergain or attenuation.Jitter transfer function measurements are im-proved by compensating for intrinsic jitter of theDUT and the ANT-20 by carrying out calibrationmeasurements first. This improves the measure-ment accuracy.

Recommendation G.813: Timing Characteristics of SDH Equipment Slave Clocks (SEC)

“This Recommendation outlines requirements fortiming devices used in synchronizing networkequipment that operates according to the principlesgoverned by the Synchronous Digital Hierarchy(SDH).”In a normal SDH system, the SDH equipment clock(SEC) is synchronized to a primary reference clock(PRC). SECs have multiple reference inputs whichthe clock can refer to however, when links betweenthe master and slave clocks fail, then the SEC’sfrequency will start to drift from that of the PRC at a rate dependent on the quality of the oscillator in the slave clock. This is referred to as “holdover”.This Recommendation specifies requirements for two options. “Option 1”, applies to SDHnetworks optimized for the 2,048 kbit/s hierarchy.“Option 2” applies to SDH network optimized for the 1,544 kbit/s hierarchy, which will not be referredto in this note.

Figure 13: The resultsare displayed ingraphical or tabularformat.

“Noise generation of a SEC represents the amountof phase noise produced at the output when thereis an ideal input reference signal or the clock is inholdover state.” This is commonly known as wan-der generation and is measured in maximum timeinterval error (MTIE) and time deviation (TDEV).Figure 14 illustrates MTIE versus observationinterval for constant and variable temperatures,

Figure 14: MTIE vs.Observation Time forconstant and variabletemperatures

Figure 12: Jitter transfer function test of regenerators.

where the menasurement needs normally a largeperiod of time. From time interval (TIE) measure-ments the time deviation TDEV can be calculated.TDEV values are a measure of the phase errorvariation versus the integration time. Put simply,the time deviation is calculated for each pointwithin a measurement time (T) for an instant thattravels through the entire measurement time TTotal.Figure 15 shows TDEV versus observation intervalfor constant temperature.

STM-16Regenerator

0.1 1.0 10 100 1,000

Observation interval τ (s)

(var. temp.)

1,000

150

100

63

40

10

0

(const. temp.)MT

IE (

ns)

10

“The noise tolerance of a SEC indicates the min-imum phase noise level at the input of the clockthat should be accommodated whilst:

– Maintaining the clock within prescribedperformance limits.

– Not causing any alarms.– Not causing the clock to switch reference.– Not causing the clock to go into holdover.”

Interface Measure filter Peak-to-peak amplitude

STM-1 500 Hz to 1.3 MHz 0.50 UI

65 kHz to 1.3 MHz 0.10 UI

STM-4 1,000 Hz to 5 MHz 0.50 UI

250 kHz to 5 MHz 0.10 UI

STM-16 5,000 Hz to 20 MHz 0.50 UI

1 MHz to 20 MHz 0.10 UI

For STM-1 1 UI = 6.43 nsFor STM-4 1 UI = 1.61 nsFor STM-16 1 UI = 0.40 ns

The noise tolerance is also commonly known aswander tolerance and is characterized by MTIEand TDEV masks illustrated in Figures 16a/16b.Jitter tolerance limits are also specified in thisrecommendation for SDH network elementsexcluding regenerators, which G.958 covers.Figure 17 shows the maximum tolerable input jitterfor 2,048 kHz and 2,048 kbits Synchronizationinterface.

Figures 16a/16b: The input wander tolerance mask (MTIE and TDEV).

Figure 17: The lower limit of the maximum tolerable inputjitter of 2,048 kHz and 2,048 kbit/s signals carryingsynchronization to a SEC.

“The noise transfer characteristics of the SECdetermines its properties with regard to the transferof excursions of the input phase relative to thecarrier phase.” In the passband the phase gain ofthe SEC should be smaller than 0.2 dB (2.3%).The Recommendation states, “The minimumbandwidth requirement for a SEC is 1 Hz and themaximum bandwidth requirement is 10 Hz.”

Figure 16a

Figure 16b

Figure 15: TDEV vs.observation time for constanttemperature

Table 7

0.1 1.0 10 20 100 1,000

0.1 1.0 7 10 100 1,000

0.1 1.0 2.5 10 20 100 400 1,000

Observation interval τ (s)

Observation interval τ (s)

Observation interval τ (s)100

106.4

3.2

1.0

0.1

1,000

170100

1210

0.1

105.5

2.0

1.0

0.25

0.1

(const. temp.)

TD

EV

(ns

)

TD

EV

(ns

)M

TIE

(ns

)

0.1 10 19 49 100 1,000 10,000 100,000

Observation interval τ (s)

250

100

Peak-to-peakjitter amplitude

(ns)

This Recommendation also specifies limits for jittergeneration on SDH output interfaces. The differ-ence between G.958 and this Recommendation isthat this recommendation defines limits for allnetwork elements, excluding regenerators. The limits defined in this part of the recommendationare less stringent than the limits defined in G.958,as Table 7 shows.

11

In Brief

SDH network elements use internal clocks (SEC)as timing sources. These clock sources should be synchronized to a PRC via the SDH line inter-face or via a 2,048 MHz clock line.

G.813 APPLICATION

SDH NE (SEC) Wander

SDH interface Jitter

ANT-20 can perform measurements on the wholerange of interfaces from PDH to SDH. Due to theinstrument’s large storage capacity, long-termmeasurements can run up to 100,000 sec orlonger. The measured values are displayed in thejitter generator/analyzer window as a graph of thetime interval error (TIE) versus time. Numericalvalues of MTIE and TIE are shown above thegraph, as illustrated in Figure 19.

Figure 20: The offline analyzerfor MTIE and TDEV.

Figure 19: Resultwindow illustratingANT-20’s wandermeasurement.

Figure 18

DUT

PRC

2,048 kHz Ref.

To check the quality of the timing signal and inter-nal clock, the phase of the reference clock (PRC)is compared with that of the transmitted data signalor clock output signal. The long-term phasevariation is referred to as wander.

Application

The wander generation setup consists of the ANT-20 connected as in Figure 18. Wandertolerance can be tested by generating wander overthe DUT and then observing the output for anyerrors and alarms. The wander that is placed overthe DUT is in the form of a sinusoidal wave, asdefined in Recommendation G.813. The results of wander generation tests which aredisplayed in Figure 19 can be imported into the ANT-20’s offline analyzer software. In this program

the MTIE and TDEV are calculated as a function of the observation interval. These results are thencompared to predefined standards and to user-defined tolerance masks which determine the clock quality.

12

Recommendation G.826: Error PerformanceParameters and Objectives for International, ConstantBit Rate Digital Paths at or above the Primary Rate:

Rate Mbit/s 1.5 to 5 >5 to 15 >15 to 55 >55 to 160 >160 to 3500

Bits/block 800–5,000 2,000–8,000 4,000–20,000 6,000–20,000 15,000–30,000

ESR 0.04 0.05 0.075 0.16

SESR 0.002 0.002 0.002 0.002 0.002

BBER 2 u 10-4 2 u 10-4 2 u 10-4 2 u 10-4 10-4

“Recommendation G.826 specifies error perform-ance events, parameters and objectives for digitalpaths operating at bit rates at or above the primaryrate. Paths are used to support services such ascircuit switched, packet switched and leased lineservices.” Specifications that refer to bit rates that are n u 64 kbit/s (n < 24 or 32 resp.) are inRecommendation G.821. “Recommendation G.826 is based upon the errorperformance measurement of blocks. A block is aset of consecutive bits associated with the path,each bit belongs to one and only one block.Consecutive bits may not be contiguous in time.” These blocks can be monitored in two differentmodes. In-service monitoring or out-of-servicemonitoring. In-service monitoring allows measure-ment while the system is operational. Errordetection codes e.g. BIP or CRC are evaluated toassess performance parameters. Out-of-servicemeasurements are mainly used for aligning newlysetup communications equipment. The parametersmonitored are errored second, severely erroredsecond and background block error.

Events

OErrored Second (ES): A one second periodwith one or more errored blocks or at least onedefect.

OSeverely Errored Second (SES): A one-second period which contains M 30% erroredblocks or least one defect. SES is a subset of ES.

OBackground Block Error (BBE): An erroredblock not occurring as part of an SES.

Parameters

OErrored Second Ratio (ESR): The ratio of ESto total seconds in available time during fixedmeasurement interval.

OSeverely Errored Second Ratio (SESR): Theratio of SES to total seconds in available timeduring a fixed measurement interval.

OBackground Block Error Ratio (BBER): Theratio of Background Block Errors (BBE) to totalblocks in available time during a fixed measure-ment interval. The count of total blocks exclu-des all blocks during SESs.

G.821 G.826 M.2100

Purpose Error Error BISPerformance Performance Limits

OOS ISM/OOS ISM/OOS

Technology N-ISDN PDH/SDH/Cell-based PDH

Min. bit rate 64 kbit/s 1.5 Mbit/s 64 kbit/s

Max. bit rate <primary rate SDH rates 140 Mbit/s

Evaluation 30 days 30 days specified in period M.2110

Measurement Bit error based Block error based Bit/Block error based

Table 8: End-to-enderror performanceobjectives for 27,500 kminternational digitalHRP.

Table 9: ErrorperformanceRecommendation

13

In Brief

Every SDH path has an embedded error perform-ance monitoring capability from which a number ofstandard parameters are calculated within thenetwork element. The management needs theseparameters for several reasons, as follows:– Verification of contracted performance of paths

with clients;– Verification of the performance of manufac-

turer’s equipment over its lifetime;

Application

The G.826 measurement interface allows the userto view the EB at the near and far end of the trans-mission path. ES, EFS SES are also included asthe parameters for the overall transmission perfor-mance results. The “VERDICT” box gives a directindication as to whether the communications pathmeets the requirements of the recommendationdepending on the path allocation.

IG is the international gateway that connects thenational portion to the international portion whichusually corresponds to a DXC, higher order MUXor a switch. The international portion of an end-to-

Out-of-Service In-Service

Figure 23a: Near end measurements (A to C) B1, B2,BIP2 are included.

Figure 21: The hypothetical reference path (HRP) for which error performance objectives are defined

Figure 22: Result display ANT-20 G.826 performance analysis

Figure 23b: Far end measurements (C to A ) RDI,RDI are included.

SDH network

Terminatingcountry Terminating

country

PEP IG

Nationalportion

Nationalportion

International portion

Hypothetical reference path

27,500 km

Intermediatecountries

Intercountry(e. g. path

carried overa submarine

cableIG IG IG IG PEP

Input signal Output signal

end path begins in one terminating country andends in the second terminating country. It is notpossible to have less than or more than twoterminating countries for an international path.

– Identification of performance degradations inorder to prompt remedial maintenance action;

– Provision of black spot analysis information fornetwork quality improvement programs.

The ANT-20 carries out a performance analysis forthree recommendations: G.821, G.826 andM.2100. The ANT-20 can perform the G.826 test in out-of-service or in-service mode.

14

Recommendation M.2100: Performance Limits forBringing-into-Service and Maintenance of InternationalPDH Paths, Sections and Transmission Systems

“Recommendation M.2100 provides limits for bring-ing-into-service and maintenance of internationalsections, paths and transmission systems at everylevel of the plesiochronous digital hierarchy from64 kbit/s. Error timing and availability performanceare considered.

“This recommendation uses certain principleswhich are the basis of the maintenance of a digitalnetwork:

– It is desirable to do in-service, continuous meas-urements. In some cases (e.g. bringing-into-service), out-of-service measurements may benecessary.

– A single set of parameters must be used formaintenance of every level of the hierarchy (this principle does not apply to limits).

– Error performance limits of transmissionsystems are dependent on the medium used.However, due to the many possible networkstructures, error performance limits on paths are independent of the medium.”

Parameter (Note) End-to-end PRO(maximum % of time)

Errored Seconds (ES) 4.0

Severly Errored Seconds (SES) 0.1

Network level Maximum Errored Maximum Severely Errored Seconds (ES) % of time Seconds (SES) % of time

Primary 2 0.1

Secondary 2.5 0.1

Tertiary 3.75 0.1

Quaternary 8 0.1

Table 10 displays the values which are specified for 64 kbit/s. The RPO is based on 40 % of theend-to-end RPO taken from RecommendationG.821. RPO stands for the reference performanceobjective, upon which other performance objectivevalues are based.

Primary, secondary, tertiary and quaternary standfor the relevant levels in the Plesiochronous DigitalHierarchy. The PRO figures given in the table areequal to 50% of the performance objectives given inRecommendation G.826.

In Brief

This Recommendation indicates the limits toquantify an international digital network and its

Application

The same setup can be used as illustrated in thefigure below for out-of-service in RecommendationG.826.The analysis in general, including all G.826 meas-urements, provides separate results for the “NEAR END” and the “FAR END”. This simplymeans that errors occurring directly in the path areanalyzed as well as errors occurring in the returnpath which are indicated by a remote errorindicator message (e.g. E-bit at 2,048 Mbit/s) orremote defect indication. This allows bothdirections to be monitored at one end of a path.

Table 10: End-to-enderror reference per-formance objectives at64 kbit/s

Figure 24: Result display ANT-20, M.2100 performance analysis

Table 11: End-to-enderror performanceobjectives at or abovethe primary rate

elements. These limits are to be used to indicatethe need for actions during maintenance andbringing-into-service of network paths.

15

Recommendation G.841: Types and Characteristics ofSDH Network Protection Architectures

Keeping the downtimes of SDH paths to an abso-lute minimum is extremely important for networkoperators, since the quality of the services theyoffer is the main feature that distinguishes themany different providers.

1. MS dedicated protection ringAn MS dedicated protection ring consists of two counter-rotating rings, each transmitting inopposite directions relative to each other. In thiscase, only one ring carries normal traffic to beprotected while to other is reserved for protectionof this normal traffic (see Figure 26a). The normaltraffic for example is carried only in the clockwisedirection. It is protected by beeing simultaneouslytransported in the opposite direction. If the normaltraffic is interrupted, the terminating networkelement switches to the protection channel (in theexample shown here: failure between B and C ->network element E switches over to the protectionchannel). MS dedicated protection ring would alsorequire using the APS bytes, K1 and K2, forprotection switching.

2. MS shared protection ringMS shared protection rings can be categorized into twotypes: two-fiber and four-fiber. The ring APS protocolaccommodates both types. For MS shared protection rings, the working channelscarry the normal traffic signals to be protected while theprotection channels are reserved for protection of thisservice. Normal traffic signals are transportedbidirectionally over spans: an incoming tributary travelsin one direction of the working channels while itsassociated outgoing tributary travels in the oppositedirection but over the same spans.– Two-fiber shared protection ringThis protection architecture requires only two fibers foreach span of the ring. Each fiber carries both workingchannels and protection channels. On each fiber, halfthe channels are defined as working channels and halfare defined as protection channels. The normal trafficcarried on working channels in one fiber are protectedby the protection channels traveling in the oppositedirection around the ring (see Figure 25a). This permitsthe bidirectional transport of normal traffic.

Figure 26a

Figure 26b

Figure 25a

Figure 25b

Traffic from A to E

Traffic from A to E

Traffic from E to A

Traffic from E to A__ working channel__ protection channel

“This recommendation provides the necessaryequipment-level specifications to implementdifferent choices of protection architectures forSynchronous Digital Hierarchy (SDH) networks. ...Physical implementations of these protectionarchitectures may include rings, or linear chains ofnodes. Each protection classification includesguidelines on network objectives, architecture,application functionality, switching criteria, proto-cols, and algorithms.”A series of mechanisms, designed to prevent pro-longed transmission path downtimes in the eventof a defect, is defined for SDH networks.

The generic term for these mechanisms is APS(Automatic Protection Switching). Systemresources which during normal operation are eithernot used at all or only for very low-priority traffic aremade available for this purpose. If a defect occurs,the “normal” traffic is then diverted automatically tothese spare paths. In addition to the correctsequence of this switchover procedure, which mayinvolve more than 10 different network elements,the time from the interruption of traffic to when theconnection is restored is a critical factor. Accordingto ITU-T Recommendation G.841, this time shouldbe less than 50 ms .

In Brief

16

In the event of a cable cut, normal traffic transmit-ted toward the failed span is switched at one nodeto the protection channels trasmitted in the oppo-site direction (away from the failure). This bridgedtraffic travels the long way around the ring on theprotection channels to the other node where thenormal traffic from the protection channels isswitched back onto the working channels. In theother direction, the normal traffic ist bridged andswitched in the same manner. Figure 25b illustra-tes a ring switch in response to a cable cut.– Four-fiber shared protection ringTwo out of the four glass fibers transport the work-ing channels and two the protection channels. Onefiber pair (working + protection) travels clockwise

around the ring, while the other pair travels aroundit in the counterclockwise direction. Thus, bidirec-tional connections can be operated. There are two possible mechanisms if a defectoccurs. One of them functions in the same way aswith the two-fiber shared protection ring. The trafficis switched over in the network elements locatedclosest to the fault and transported via the protectionfiber for the opposite direction (“ring switching”).The second mechanism is known as “span switch-ing.” In the event of a defect the traffic is trans-ported via the protection fiber that operates in thesame direction as the faulty working fiber. Conse-quently, only the link segment that is actually faultyis switched over to standby.

Section 7.1 of the revised Recommendation G.841contains the protocol for the switchover procedure ofthe APS mechanisms compatible with 1: n operation.

1+1 operation:The traffic is transported simultaneously via theworking path and the protection path. The receiv-ing end then decides which of the two paths is tobe used.

1:1 operation:The spare path can only be used if a switchovertakes place at both the transmitting end and thereceiving end.

1:N operation:A 1:N configuration represents a more cost-effect-ive solution than the other two mechanisms de-scribed above. N working channels are protectedby one protection channel. If there are no defectsin the network, this protection channel can be usedto transport low-priority traffic.

Application

Proper interworking of the network elements re-quires the proper response on the part of the APS

Recommendation G.841 Section 7.1 (G.783 Annex A):Linear Multiplex Section Protection (MSP)

Annex B of G.841 describes the MSP protocoloptimized for 1+1 operation. Linear MSP wasspecified in Annex A of G.783 which is now includedin the new revised Recommendation G.841.

In Brief

signaling to changes in the signal status or to theappropriate switching commands from networkmanagement. The ANT-20 makes this testsimple and reliable by interpreting the protocolelements in plain text. APS commands can alsobe generated in the descriptor directly from themenu, without complicated bit manipulations.The ANT-20 understands the K1/K2 codes forlinear MSP conforming to ITU-T G.783 as wellas those for MS SPRING to ITU-T G.841. We measure the switchover time out-of-service(OOS) on the PDH or SDH/SONET tributaries ofthe ADMs (add-drop multiplexers). Depending onthe configuration, alarms and bit errors (Test Sequence Errors, TSE) appear on the tributaryports for the duration of the switchoverprocedure. What customers are interested in isthe interruption time on the tributary and not justthe K1/K2 switchover according to the APSprotocol.

Figure 27: ANT-20 interpreter for ring switching

Recommendations Description Page

G.783 SDH equipment functional blocks 1

G.783 Section 10 Jitter and wander parameters at MUX and DEMUX ports 3

G.823 Jitter and wander parameters at PDH interfaces 5

G.825 Jitter parameters at SDH interfaces contained in a SDH network 6

G.958 Jitter parameters at SDH regenerator ports 8

G.813 Jitter and wander parameters of SDH equipment slave clocks 9

G.826 Error performance in SDH/PDH networks 12

M.2100 Performance levels for BIS of international PDH paths. 14

G.841 Types and characteristics of SDH network protection architecture 15

G.841 Linear Multiplex section protection (MSP) protocol, commands and operation 16(G.783 Annex A)

If the switch-over time is exceeded or communi-cation between the network elements is not reliable, we must find the reason. With its bytecapture function, the ANT-20 enables detailed analysis of the SOH bytes. Up to 265 changes inthe K1/K2 combination are recorded. The ANT-20can be configured to measure in monitor mode or in through mode in the protection channel of the SDH ring.

The ANT-20Õs solution is flexible and lets you se-lect different events as your measurement criterion:� SDH: MS-AIS, AU-AIS, TU-AIS, TSE � SONET: AIS-L, AIS-P, AIS-V, TSEThe switchover time is specified as 50 ms. TheANT-20 measures the duration of the event on the tributary with a resolution of 1 ms, even if thesignal has bit error ratios up to 2u10-4. A secondANT-20 can be used to generate the APS. In through mode, the instrument generates the alarm types SF (B2 >1u10-3) and SD (B2 >1u10-6), and in OOS mode also LOS, LOF,MS-AIS (AIS-L). The procedure is as follows: 1. Set the signal structure using the ANT-20Õs

signal structure editor. Start the APS timemeasurement.

2. Activate APS by manually interrupting the working channel, by generating an event with a second ANT-20 in through mode, or using a network management setting.

3. Measure the interruption time. Compare it withthe expected value. Result interpretation is simple: ÒpassedÓ or ÒfailedÓ. SOH/TOH

byte capture

working channel

protection channel

APS timemeasurement.Event: AIS, TSE

PDHNetwork

G.823

G.958

G.841

G.825G.813

G.821G.826

M.2100

Jitter TestWander

Jitter Test

Cross Connect TestError

Performance

Author

Ben Di-Lorenzo, Stephan Schultz,Frank Coenning, Wolfgang MillerState: December 1998

Why Do Recommendations Exist for SDH/PDH Networks?

Telecommunications networks are not built fromtechnologies that are individually specified by eachservice provider. If they were, imagine how hard itwould be to connect from one service provider tothe next! The logical solution is to have a universalorganization (or organizations) specifying trans-mission methods that are universally applicable toall service providers. One of these bodies is theInternational Telecommunication Union � Tele-communication Standardization Sector (ITU-T)formally known as CCITT. The ITU-T is responsible

for studying technical, operating and tariff questionsand issuing Recommendations on them with a view tostandardizing telecommunications on a worldwidebasis. Many telecommunication networks use network ele-ments that are specified by ITU-T Recommendations.The Advanced Network Tester (ANT-20) recognizesthese Recommendations and carries out measure-ments to qualify them. This note will directly quoteRecommendations from ITU-T and then apply themto practical applications performed on the ANT-20.

Abbreviation list :

ADM Add & Drop MultiplexerAIS Alarm Indication SignalAPS Automatic Protection SwitchingBBE Backround Block ErrorBBER Backround Block Error RatioBIP Bit Interleaved ParityBIS Bringing Into ServiceCRC Cyclic Redundancy CheckDEMUX DemultiplexerDXC Digital Cross ConnectES Errored SecondESR Errored Second RatioEFS Error Free SecondFMTJ Fast Maximum Tolerable JitterIG International GatewayISM In Service MonitoringJTF Jitter Transfer Function HP High Order PathLOF Loss Of FrameLP Low Order PathMS Multiplex SectionMSOH Multiplex Section

OverheadMSP Multiplex Section

ProtectionMST Multiplex Section Termination

FunctionMTJ Maximum Tolerable Jitter MTIE Maximum Time Interval ErrorMUX MultiplexOOS Out of ServiceOS Optical SectionPDH Plesiochronous Digital HierarchyPEP Path End PointRDI Remote Defect IndicationPRC Primary Reference ClockUI Unit IntervalREG RegeneratorRS Regenerator Section RST Regenerator Section Termination

FunctionRSOH Regenerator Section OverheadSES Severely Errored SecondSESR Severely Errored Second RatioSD Signal DegradationSDH Synchronous Digital HierarchySEC Synchronous Equipment ClockSF Signal FailureSTM Synchronous Transport ModuleTDEV Time DeviationVC Virtual Container

Figure 29: Measuring switch-over time

Figure 28: Result from the switch-over measurement

Figure 30: Byte capture shows content of K1/K2 bytes in plain text

Conforming to the Mazeof Network Standards

ITU-T Recommendationsand Practical Applicationsin PDH/SDH Networks

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