Itu Errorperf an Ae

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Application Note

WEBSITE:www.jdsu.com

Understanding ITU-T Error Performance RecommendationsBy Andreas Alpert

ITU-T Recommendations on Physical Layer Error Performance in Digital Transmission Systems

Introduction

Error perormance at the physical layer o digital communications equipment is a major actor in determining transmissionquality. Measurements o error perormance orm the basis o operation o a number o test sets rom JDSU.Since error perormance is a critical component o transmission quality in digital networks, the IU- has published anumber o recommendations laying down error perormance parameters and objectives. Important examples include rec-ommendations G.821, G.826, G.828, G.829, G.8201, I.356 and the M.21xx series. his paper describes the meanings othese recommendations using G.821/G.826 on the one hand and M.2100 on the other. It also considers the relationshipbetween G.826, G.828 and the other M-series recommendations mentioned. Brie reerence is also made to recommen-dation G.829 and the new recommendation G.8201 or optical transport networks and to a set o new recommendations

addressing the perormance o packet-based networks (Y.1540, Y.1541, Y.1560 and Y.1561).

History

In 1980, the irst version o IU- recommendation G.821 was adopted. It deined the bit error perormance o interna-tional ISDN connections with a bit rate o 64 kb/s [5]. By 1996, G.821 had reached its ourth version. he technical contentremained unchanged as the bit rate range was extended to N 64 kb/s. Here, N is chosen such that the bit rate is below therate o the PDH primary systems. Annex D was deleted and with it any reerence to higher bit rates. In addition, the degrad-ed minute (DM) error perormance parameter was suppressed.

For a good while, G.821 was the standard or planning, installing and operating digital networks.

Over the years, however, diiculties in practical use o G.821 came to light. here are two main issues:a) he error perormance requirements in G.821 are based exclusively on 64 kb/s connections. Real-lie error monitoring

is generally perormed on transmission systems operating at signiicantly higher bit rates. he results obtained were

normalized to a 64 kb/s channel. Annex D to G.821 speciied a method or doing this. However, the method wasdisputed rom its inception, and Annex D has now been deleted. With the introduction o new broadband services, itmakes little sense to normalize results to 64 kb/s anyway.

(Annex D to recommendation G.821 stipulated proportional conversion of the error count measured at a higher bit rate and allocation to a

64 kb/s channel. For instance, when measuring at a bit rate of 2048 kb/s, one divides by a factor of 2048 : 64 = 32 to obtain the error count for

64 kb/s. This method is no longer recommended. However, some JDSU test sets still allow users to exploit this technique for investigating older

test objects.)

b) he deinitions o the error perormance parameters in G.821 are based on measurement o errored bits and thus onmeasurement o the bit error ratio. However, errored bits can be clearly recognized only i the bit sequence being moni-tored is known. his highly complicates measurements during operation o a system (in-service measurements).


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Application Note: ITU-T Error Performance Recommendations 2

Recommendation G.826

As these problems came to light, work was eventually taken

up on a new recommendation, which later came to beknown as G.826 with the title: Error perormance parame-ters and objectives or international, constant bit rate digitalpaths at or above the primary rate. Ater much preliminarywork, G.826 was approved in July 19831, thus complement-ing G.821 issued in 1980. he new recommendation had tomeet the ollowing requirements:

Suitable or higher bit rates ( 1.5 Mb/s) withoutnormalization

In-service measurement o error perormanceparameters

Non-transmission-medium dependent

Non-transmission-system dependent (to supportPDH, SDH, cell-based systems)

More demanding objectives than G.821 in view oadvances in newer transmission systems

(1)A new version of recommendation G.826 was published in 2002. This

article takes into account this latest version.

How these requirements were met in recommendationG.826 is shown below.

Range of applications of recommendation G.826

he recommendation was conceived or international con-stant bit rate digital paths or above the primary rate (1544 or2048 kb/s). he term digital path is deined in IU- rec-ommendation M.60 [14]. ransmission systems belongingto a path are connected between digital distribution ramesor terminal equipment. he path end points can thus lieon the premises o end users i the overhead inormation isavailable there. In this case, G.826 also covers the custom-er access. Digital paths conorming to recommendationG.826 can be transported over any type o transmission sys-tem, whether plesiochronous, synchronous or cell-based.he inluence o the asynchronous transer mode (AM)layer is not taken into account. For AM, recommendation

I.356 applies [11].he new version o G.826 rom 2002 extends the applicabil-ity to all digital paths/connections also below the primaryrate ater this date. he applicability o G.821 is thereorelimited to connections based on equipment designedbeore 2002.he speciications in G.826 apply end-to-end to a hypo-thetical reerence path or connection having a length o27,500 km. here are no speciic provisions or dierenttransmission media (e.g. optical iber, digital radio relay,metallic cable and satellite transmission systems).

Important error performance

recommendations

Recommendation G.821:Error perormance o an inter-national digital connection operating at a bit rate belowthe primary rate and orming part o an integrated servicedigital network (ISDN)Recommendation G.826:End-to-end error perormanceparameters and objectives or international, constant bitrate digital paths and connectionsRecommendation G.828: Error perormance parametersand objectives or international, constant bit rate syn-chronous digital pathsRecommendation G.829:Error perormance events orSDH multiplex and regenerator sectionsRecommendation G.8201: Error perormance parame-ters and objectives or multi-operator international pathswithin the optical transport network (ON)Recommendation I.356:AM cell transer perormanceRecommendation M.2100: Perormance limits orbringing-into-service and maintenance o internationalmulti-operator PDH paths and connectionsRecommendations M.2101: Perormance limits orbringing-into-service and maintenance o internationalmulti-operator SDH paths and multiplex sectionsRecommendation M.2110:Bringing-into-service o inter-national multi-operator paths, sections and transmissionsystems

Recommendation M.2120: International multi-operatorpaths, sections and transmission systems ault detectionand localization proceduresRecommendation Y.1540: Internet protocol data com-munication service IP packet transer and availabilityperormance parameters (2002)Recommendation Y.1541: Network perormance objec-tives or IP-based services (2002)Recommendation Y.1560:Parameters or CP connec-tion perormance in the presence o middle boxes (2003)Recommendation Y.1561: Perormance and availabilityparameters or MPLS networks (2004)


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Figures 1 and 2 illustrate the applications o G.826. Points Aand B in igure 1 are physical interaces, e.g. to IU- rec-ommendation G.703 [6]. It is clear rom igure 2 that G.826applies only to the physical layer and not the AM layers.

Figure 1: Application of recommendation G.826 for a non-ATM end-

to-end transmission path

Figure 2: Application of recommendation G.826 for ATM networks

Block error measurement

During work on G.826, the aim rom the very start was toacilitate in-service error perormance assessment, mak-ing use o error monitoring equipment included in theactual transmission systems. his required a shit awayrom the prevailing technique o bit error measurement inG.821 and towards block error measurement.

Block monitoring takes advantage o the error monitoringequipment built into todays transmission systems. hecyclic redundancy check (CRC) technique and bit paritymonitoring are employed. In G.826, errors must be detect-ed with at least 90% probability. his requirement is metby the CRC-4 and bit interleaved parity (BIP) BIP-8 tech-niques, but not by BIP-2.

Definitions for error events and parameters

Recommendation G.826 is based on monitoring o ourerror events. hese events are deined or digital pathsin accordance with the block error evaluation principledescribed above. Deinitions o these our events are givenon the side. Regarding SEP/SEPI see section New errorevent, new error parameter, page 7.

For digital connections error events errored seconds (ES)and severely errored seconds (SES) are based on bit errorsinstead o block errors.

o simpliy testing, a deect is included in the deinitiono the SES. Deects are deined or various transmission

systems (PDH, SDH, cell-based) (see section Error peror-mance criteria used in actual practice, page 5). It should berecalled that there are error structures that do not generatea deect but still cause signiicant transmission impairment.No SES would occur even though a major impairment ispresent.It should also be noted that one older error event (thedegraded minute) was not included in G.826. his eventhas proven impractical and was also deleted rom recom-mendation G.821. Measurement o the events deinedabove provides absolute counts. For practical reasons, it ispreerred to work with ratios. Recommendation G.826 usesthree relative parameters (error parameters) listed below.In accordance with the deinition o error events, blocksoccurring within SES are not considered when computing

the background block error ratio (BBER).Note that or all three deinitions when orming the ratios,only the time during which the transmission system isavailable is considered (see section Availability o the trans-mission system, page 4).

What is a block?

A block is a set o consecutive bits associated with thepath; each bit belongs to one and only one block. Con-secutive bits may not be contiguous in time.The error events for paths

Errored block (EB)

A block in which one ore more bits are in error.Errored Seconds (ES)

A one-second period with one ore more errored blocksor at least one deect.Severely errored second (SES)

A sequence o between 3 and 9 consecutive SES.Background block error (BBE)

An errored block not occurring as part o an SES.Severely errored period (SEP)

A sequence o between 3 and 9 consecutive SESs.The error parameters

Errored second ratio (ESR)

he ratio o ES to total seconds in available time during a

ixed measurement interval.Severely errored second ratio (SESR)

he ratio o SES to total seconds in available time duringa ixed measurement interval.Background block error ratio (BBER)

he ratio o BBE to total blocks in available time during aixed measurement interval.Severely errored period intensity (SEPI)

he number o SEP events in available time, divided bythe total available time in seconds.

A BNetwork fabric, e.g. PDH, SDH

Application of G.826

ATM

P L PL

AAL

ATM

PL PL

ATM

AAL

I.356

G.826 G.826

AAL = ATM adaptation layerATM = ATM layerPL = Physical layer


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Availability of the transmission system

It was mentioned in the previous section that variousparameters are computed only when the transmissionsystem is available. For the purposes o recommendationG.826, availability ends at the start o a time interval con-taining at least ten consecutive SES in at least one directiono transmission.

he system becomes available again at the start o a timeinterval consisting o at least ten seconds that are not severe-ly errored. Figure 3 shows an example o how to determineavailability.

Figure 3: Example of unavailability determination

Objectives for error performance

he most important part o recommendation G.826 isthe speciication o the required objectives or error per-

ormance. A table (partly reproduced in table 1) gives theend-to-end objectives or the 27,500 km reerence path. Adigital path must simultaneously meet all o the objectivesgiven in the table or its bit rate. he proposed observationinterval is one month. able 1 has a number o qualiica-tions: For VC-4c concatenated containers in a 601 Mb/spath, the block length is 75,168 bits/block. his is outsidethe range in the table. he associated BBER igure is 4 10-4. It is also mentioned that ESR error objectives are notrealistically applicable at high bit rates since even i the errorratio is low, the probability o observing block errors andthus errored seconds is high. here are thus no ESR specii-cations or the bit rate range 160 to 3500 Mb/s(2).

Bit

rate

Mb/s

64 kb/s to

primary

rate

1.5 to 5 >5

to 15

>15

to 55

>55

to 160

>160

to 3500

Bits/

block

n.a. 800 to

5000

2000 to

8000

4000 to

20000

6000 to

20000

15000 to

30000

ESR 0.04 0.04 0.05 0.075 0.16 not

specified

SESR 0.002 0.002 0.002 0.002 0.002 0.002

BBER n.a. 210-4 210-4 210-4 210-4 10-4

Table 1: End-to-end error performance objectives for a 27,500 km

digital HRP or HRX

One disadvantage when it comes to using the objectives arethe variable block lengths or the dierent bit rates. Futureimprovements here would help to improve accuracy omeasurement results.Both directions o transmission on a path or connectionare monitored independently and must ulil the objectivessimultaneously. I this is not the case, then the recommen-dation is unulilled.

(2)At a transmission rate of 160 Mb/s an assumed bit error ratio of 10-8

would result in about 1.6 errors per second, if the errors are equally

distributed vs. time. Under these conditions, only errored seconds would

occur.

Allocating error objectives to the reference path or con-

nectionhe objectives rom table 1 are allocated by recommen-dation G.826 to individual portions o the reerence pathconnection. he reerence path connection is divided intotwo national portions at the end o the path connection andan international portion (igure 4).

Figure 4: Allocation of the objectives to the reference connection

path

Each national portion is allocated a block allowance o17.5% o the end-to-end objective. Each national por-tion also receives 0.2% per 100 km covered. I a satellitehop is used in the national portion, it can take up 42% o

the tolerable errors. his 42% replaces the distance-basedallowance.he international portion is allocated a block allowanceo the overall objective o 2% or each intermediate coun-try and 1% per terminating country. A maximum o ourintermediate countries is assumed. Moreover, in the inter-national portion there is a distance-based allowance o0.2% per 100 km system length. Here, a satellite hop is allo-cated 35% o the allowable overall errors.When computing the system lengths, the actual routelength is used. I it is unknown, the air route distance is used

Time

10 sec


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and multiplied by a actor o 1.25 or 1.5 respectively.he values obtained in this manner are rounded up to thenearest 500 km. I the computation or the internationalportion produces an allowance o


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real lie, however, or the purposes o G.826 a conversionactor o one was chosen or the sake o simplicity.

A detected BIP violation is thus directly interpreted as anerrored block (and thus an errored second). When it comesto SES, recommendation G.826 is very precise. Under theabove conditions, the chosen thresholds correspond to30% errored blocks, as speciied in the SES deinition. InSDH systems too, a time interval in which a deect occurs isconsidered a SES. he criteria or deects are the path-layerdeects in IU- recommendations G.707 and G.783 [2][4]. here is a distinction between deects at the near andar ends and also between lower-order and higher-orderpaths (see tables 1 and 2).

Criteria for cell-based systems

In cell-based systems, the cells are transmitted as a purestream o cells without any raming (e.g. SDH rame). heRecommendations in the I.432 series [12] describe inter-aces or such systems.

Anomalies and deects are also deined or cell-based sys-tems. Here, a block is a sequence o cells between two OAMcells.

Note: Operation and maintenance cells (OAM) are used for error perfor-

mance monitoring in ATM systems. F3 cells monitor the digital path.

Occurrence o at least one anomaly or deect results in anerrored block. Severely errored seconds are counted i 30%

errored blocks are counted, or a deect.

Flow chart

aking into account the deinitions o anomalies, deectsand availability, the (simpliied) low chart in igure 5 isobtained.

Error monitoring detects anomalies (e.g. due to blockerrors ) and deects. Anomalies and deects result in erroredblocks or severely errored time segments.aking into account the boundary conditions as deined,ES and SES are then derived.

he quantities cES, cSES and cBBE are the counter results

or ES, SES and BBE. he counters are reset at the start oa measurement. % EB means the ratio o errored blockswithin an errored second tot the total number or blocks persecond. I 30% errored blocks are counted in a second, thenSES is triggered. At the end o measurement period P, therecommendation G.826 parameters can be computed asollows, taking into account unavailable seconds (UAS):

ESR =cES

P - UAS

SESR = cSESP - UAS

BBER =cBBE

(P - UAS - cSES) blocks per second

In the simpliied low chart, the transition between Avail-ability and Unavailability is not handled properly. Allthat the low chart shows is that error events are countedonly i the system is available.

Note: In this figure the letter c stands for count

Figure 5: Flow chart illustrating the recognition of anomalies,

defects, errored blocks, ES, SES and BBE

End

cBBE = cBBE + EB(s)

cES = cES +1 cES = cES +1

cSES = cSES +1

N

Y

N

NES

(but not a SES)

Pathin available

state?

Pathin available

state?

%EB 3 0?Y

Y

SES

(and thereforean ES)

Anomalies?N

N

Defects? Y

Monitoredseconds

Y


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Presenting measurement results

Many JDSU error test sets can evaluate errors as speciied inRecommendation G.826.he screenshot on page 10 (igure 6) shows how in-servicemeasurement results captured by JDSUs advanced net-work tester AN-20.

he ollowing were evaluated: EB, BBE, ES, Error-FreeSeconds (EFS), SES and UAS. Figures 10 and 11 show theconditions or obtaining such measurement results.

Tighter error limits for modern SDH systems

Although recommendation G.826 ound broad use inthe speciication o PDH systems, very soon it was mainlyapplied to SDH systems. It became apparent that the target

values in G.826, which to a large extent were inluenced

by PDH technology and older communications media,did not match the capabilities o modern SDH systemsbased on iber optics technology. Doubts were also cast onwhether the target values in G.826 were suicient to ensureadequate transmission o AM cells over SDH installations.As a result, work started in 1997 on the development o thenew recommendation G.828(3), with the aim o speciy-ing tighter target values or error perormance applying tomodern SDH systems.

As the title Error perormance parameters and objec-tives or international, constant bit rate synchronousdigital paths indicates, G.828 also describes the error

perormance o digital paths, but is restricted exclusivelyto SDH. Recommendation G.828 has basically the samestructure as G.826. Here, too, great emphasis is placedon the ability to make in-service measurements using theblock-based measurement concept.As well as the closer error limits, the ollowing points standout rom a comparison with G.826.

(3) Approved by ITU-T study group 13 in March 2000.

Precise path definitions

During work on recommendation G.828, it was discov-

ered that no precise deinitions or SDH path and reerencepath exist in the IU literature. hese have thereore beendeined in G.828 as ollows:

Hypothetical reference path (HRP)

An HRP is deined as the whole means o digital trans-mission o a digital signal o a speciied rate, including thepath overhead, between equipment at which the signaloriginates and terminates. An end-to-end HRP spans adistance o 27,500 km.

SDH digital path

An SDH digital path is a trail carrying an SDH payload

and associated overhead through the layered transportnetwork between the path terminating equipment. Adigital path may be bi-directional or unidirectional andmay comprise both customer owned portions and net-work operator owned portions.

New error event, new error parameter

he proposal to introduce a new error event and a newerror parameter led to long and diicult discussions. hesuggestion to include the error event Severely ErroredPeriod (SEP) in G.828 was based on the results o practi-cal measurements. An SEP is deined as a period o timeduring which at least three but not more than 9 consecutiveSES occur. A period o consecutive SES can have the sameeect as a micro-interruption and may lead to a severeimpairment o the service supported by the SDH path.he parameter corresponding to SEP is called SeverelyErrored Period Intensity (SEPI) and has the dimension 1/time. Although a very conservative target value o 0.0002/swas suggested or this parameter (this would have per-mitted about 518 micro-interruptions per month), it wasnot possible to ix this target value in G.828. Based ontheir measurement results, some network operators elt itunnecessary to monitor this new error parameter. Otheroperators deended the monitoring o SEPI just as vigor-

ously. Recommendation G.828 thereore contains only thedeinitions o SEP and SEPI in a separate section, termingthem optional speciications, stating that their use requiresurther study.Such studies must particularly also take the customeraccess to the communications network (the last mile)into account. Since the error limits stipulated in G.828 areindependent o the transmission medium, the path in thecustomer access segment could be a radio link or xDSLlink, or example. In such cases, the avorable measurementresults claimed by those opposing implementation o SEPmay not be achievable.

Tandem connection monitoring

he new recommendation G.828 also takes account otandem connection monitoring, a eature o modern SDHsystems that was unknown when G.826 was being devel-oped. he list o deects leading to the triggering o an SESare much longer as a result. his is shown by the ollowingtables, which are taken rom recommendation G.828.


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Near end defects (Notes 5, 6, 7) Kind of path

Path termination Non-intrusive monitor Tandem connection

LP UNEQ (Note 3) LP UNEQ (Notes 3, 4) LPTC UNEQ (Note 3) Applicable to lower-orderpaths and lower-order tan-

dem connectionsLP TIM LP TIM LPTC TIM

LPTC LTC

LP VC AIS (Note 2)

TU LOP TU LOP TU LOP

TU AIS TU AIS TU AS

HP LOM (Note 1) HP LOM (Note 1) HP LOM (Note 1)

HP PLM HP PLM HP PLM

HP UNEQ (Note 3) HP UNEQ (Notes 3, 4) HPTC UNEQ (Note 3) Applicable to higher-order

paths and higher-order tan-

dem connectionsHP TIM HP TIM HPTC TIM

HPTC LTC

HP VC AIS (Note 2)

AU LOP AU LOP AU LOP

AU AIS AU AIS AU AISNote 1: This defect is not related to VC-3.

Note 2: VC AIS defect applies to monitoring a path at an intermediate point by means of non-intrusive monitoring.

Note 3: Paths not actually completed, e.g. during path setup, will contain the unequipped VC-n signal.

Note 4: Two types of non-intrusive monitor functions are defined in recommendation G.783. The original (version 1)

type detects the UNEQ defect when an unequipped or a supervisory-unequipped VC signal is received. The advanced

(version 2) type detects the UNEQ condition as type 1 but validates this condition by means of checking the content of

the trace identifier; the receipt of a supervisory-unequipped VC signal will not result in an UNEQ defect. Neither will the

receipt of a supervisory-unequipped VC signal result in the contribution of UNEQ condition to performance monitor-

ing; if the supervisory-unequipped VC signal was not the expected signal, TIM defect will contribute to performance

monitoring instead.

Note 5: The above defects are path defects only. Section defects such as MS AIS, RS RIM, STM LOF and STM LOS give rise

to an AIS defect in the path layers.

Note 6: When a near-end SES is caused by a near-end defect as defined above, the far-end performance event counters

are not incremented, i.e., an error-free period is assumed. When a near-end SES results from 30% errored blocks, the

far-end performance evaluation continues during the near-end SES. This approach does not allow reliable evaluation

of far-end data if the near-end SES is caused by a defect. It should be noted in particular, that the evaluation of far-end

events (such as SES or unavailability) can be inaccurate in the case where far-end SESs occur in coincidence with near-

end SESs caused by a defect. Such inaccuracies cannot be avoided, but are negligible in practice because of the low

probability of the occurrence of such phenomena.

Note 7: Refer to recommendation G.783 for defects contributing to performance monitoring in each trail termination

sink function.

Table 3: Near-end defects leading to SES

Near end defects Kind of path

Path

termination

Non-intrusive

monitor

Tandem

connection

LP RDI LP RDI LPTC TC RDI Applicable to lower-order paths and lower-order tandem connections

HP RDI HP TDI HPTC TC RDI Applicable to higher-order paths and higher-order tandem connections

Table 4: Far-end defects leading to SES


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Comparison of target error limit values in recommenda-

tions G.828 and G.826

As well as deining the new speciications SEP and SEPI,and taking tandem connection monitoring into account,the new recommendation deines tighter target values orerror perormance. his particularly aects the parametersESR and BBER. able 5 shows table 1/G.828 together withthe target values that it includes. he corresponding valuesrom G.826 or ESR and BBER are shown in brackets orcomparison.

Note 2 regarding BBER is o interest: his mentions that,or increasing block size, the BBER values cannot be keptconstant or even improved. (Also reer to next section.)

Problems in error detection with increasing block size

One uncertainty in the target value deinitions o recom-mendation G.826 was given by the ailure to provide exactinormation about the size o the blocks to be evaluated.his disadvantage has been corrected in G.828, a preciseblock length being deined or each bit rate as shown intable 5.

able 6 shows that the number o blocks monitored persecond or bit rates rom VC-3 up to VC-4-4c remainsconstant at 8,000. his means that the block size increaseswith increasing bit rate. At the same time, BIP-8 is retainedor error detection. his increasing block size results in asteady reduction in the eectiveness o error monitoringas the bit rate increases. Larger bit error rates can not bedetected accurately in this way. As a result o wide-rangingtheoretical considerations, it was suggested that the num-ber o blocks to be monitored per second should increasealong with the bit rate so as to achieve an approximatelyconstant block size. Each VC-4 virtual container shouldbe evaluated separately, so this would have meant evaluat-ing 4 8,000, 16 8,000 or 64 8,000 blocks per secondor VC-4-4c, VC-4-16c and VC-4-64c respectively. his

would mean that the block size above VC-4 would remainconstant at 18,792 bits.Regardless o the correctness o the theory behind suchconsiderations, it was not possible to implement this in therecommendation, because it could have meant changingthe corresponding hardware recommendations that werealready at a late stage o development. he considerationswere, however, relected in the new recommendationG.829.

Bit rate kb/s Path type Blocks/s ESR SESR BBER SEPI (Note 3)

1664 VC-11, TC-11 2000 0.01 (0.04) 0.002 5 10-5(2 10-4)

2240 VC-12, TC-12 2000 0.01 (0.04) 0.002 5 10-5(2 10-4)

6848 VC-2, TC-2 2000 0.01 (0.05) 0.002 5 10-5(2 10-4)

48960 VC-3, TC-3 8000 0.02 (0.075) 0.002 5 10-5(2 10-4)

150336 VC-4, TC-4 8000 0.04 (0.16) 0.002 1 10-4(1 10-4)

601344 VC-4-4c, TC-4-4c 8000 (Note 1) 0.002 1 10-4(1 10-4)

245376 VC-4-16c, TC-4-16c 8000 (Note 1 0.002 1 10-4(1 10-4)

9621504 VC-4-64c, TC-4-64c 8000 (Note 1 0.002 1 10-3(Note 2)

Note 1: ESR objectives tend to lose significance for applications at high bit rates and are therefore not specified for

paths operating at bit rates above 160 Mb/s. Nevertheless, it is recognized that the observed performance of synchro-

nous digital paths is error-free for long periods of time even at Gb/s rates; and that significant ESR indicates a degraded

transmission system. Therefore, for maintenance purposes ES monitoring should be implemented within any error per-

formance measuring devices operating at these rates.

Note 2: This BBER objective corresponds to an equivalent bit error ratio of 8.3 10-10, an improvement over the bit error

rate of 5.3 10-9for the VC-4 rate. Equivalent bit error ratio is valuable as a rate-independent indication of error perfor-

mance, as BBER objectives cannot remain constant as block sizes increase.

Note 3: SEPI objectives require further study.

Table 5: End-to-end target values for the error performance of a 27,500 km SDH-HRP


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Bit rate (kb/s) Path type Blocks/s SDH block size in

G.828

EDC

1664 VC-11, TC-11 2000 832 bits BIP-22240 VC-12, TC-12 2000 1120 bits BIP-2

6848 VC-2, TC-2 2000 3424 bits BIP-2

48960 VC-3, TC-3 8000 6120 bits BIP-8

150336 VC-4, TC-4 8000 18792 bits BIP-8

601344 VC-4-4c, TC-4-4c 8000 75168 bits BIP-8

2405376 VC-4-16c, TC-4-16c 8000 300672 bits BIP-8

9621504 VC-4-64c, TC-4-64c 8000 1202688 bits BIP-8

Table 6: Block sizes in error monitoring of SDH paths

Figure 6: Error evaluation to recommendation G.826 using the ANT-20 analyzer

Differences between recommendationsG.821, G.826 and G.828

Differences in the basic concept

Section History already pointed out some dierencesbetween the three recommendations. he main points areas ollows:

G.821 deals with connections operating at bit ratesbelow the bit rates o primary systems

G.821 is based on measuring bit errors

Since there are no overheads at these bit rates, in-service-measurements (ISM) are either impossibleor very difficult

G.821 is only applicable to connections which useequipment designed prior to the adoption o revisedG.826 (2002)

G.826 deals with connections operating at bit ratesbelow the primary rate using equipment designedafer the adoption o revised G.826 (2002) and pathsoperating at or above the primary rate

G.826 is based on measuring bit errors orconnections and block errors or paths

G.828 deals exclusively with SDH paths G.828 is based on measuring block errors

By using inherent detection schemes, in-service-measurements (ISM) are possible

Due to the potential or in-service-measurements in par-ticular, G.826 has superseded the older G.821. G.826 andG.828 are saying that they are currently the only recom-mendations required or designing the error perormanceo digital paths at or above the primary rate.

Now that G.828 has been approved, this new recommen-dation will gain in importance with regard to modern SDHsystems, and will itsel supplant G.826 and particularly

G.821.Comparing requirements for error performance

According to recommendation G.826 and also, later on,G.828 was to bolster the objectives or error perormancecompared to the older G.821. A direct comparison is notpossible due to the dierences in deining the error events.o enable comparison, we must know how the bit errorratio relates to the errored block. his relationship is a unc-tion o the error distribution vs. time. For example, i errorsoccur in a burst, recommendation G.821 would counta number o bit errors, while G.826/G.828 might countonly one errored block. On the other hand, i the errors are

equally distributed vs. time, then each bit error can producea block error. However, it can be veriied that dependingon the error model, the requirements o recommendationG.826 and G.828 can be much tougher than G.821.It should also be noted that in terms o the deined errorlimits, recommendations G.821 and G.826 are not ullycompatible. An appendix to G.826 deals with merits andlimitations o bit errors versus block errors.

Recommendation G.829

Along with G.828, the new recommendation G.829Error perormance events or SDH multiplex and regen-

erator sections was approved in March 2000 and revisedin December 2002. In contrast with the recommendationsin the G-series already mentioned, G.829 does not deineany target values. It merely describes the error events orSDH multiplex and regenerator sections. One reason orthe omission o objectives lies with the skepticism, airedby several network operators, towards accepting regula-tions governing network components that are oten theresponsibility o national authorities. Regardless o this,the deinition o the error events is important in connec-tion with bringing-into-service and maintaining SDH


11/20


sections, because measurement results will only be compa-rable i the same deinitions o events are used. G.829, too,is based on the principle o monitoring block errors, allow-ing measurements to be made in-service. Accordingly,the recommendation deines block size, number o blocksper SDH rame, number o blocks transmitted per secondand the error detection code (EDC) to be used or the vari-ous SDH bit rates up to SM-64. he deinition o the SESthresholds, i.e. the number o errored blocks that triggers anSES, is a major part o recommendation G.829. his thresh-old is set at 30% errored blocks or both recommendationsG.826 and G.828. his threshold could not be used or mul-tiplex and regenerator sections, however. Because the errordetection mechanisms at path and section level are dier-ent, identical thresholds would mean that there would be

no compatibility between the two levels. his would resultin an SES being triggered at the section level by a certainnumber o errored blocks without a corresponding SESbeing detected at the path level. he reverse situation couldalso occur. he thresholds were ixed ater comprehensivetheoretical investigation to give the best possible compat-ibility between the two levels.

able 7 shows the threshold values that were determined orSDH multiplex sections or bit rates rom SM-0 to SM-64. he abbreviation EBS stands or errored blocks. Asmentioned, recommendation G.829 covers multiplex andregenerator sections. he deinitions or regenerator sec-

tions are limited to radio link and satellite systems, however.

he principle o a ixed block length is applied in the caseo regenerator sections. Since these regulations are media-speciic, it was possible to arrive at the desired deinition interms o ixed block lengths. his is shown in table 8.

STM-N Block size Blocks

per frame

Blocks/s EDC

STM-0 6480 bits 1 8000 BIP-8

STM-1 19440 bits 1 8000 BIP-8

STM-4 19440 bits 4 4 8000 4 BIP-8

STM-16 19440 bits 16 16 8000 16 BIP-8

Table 8: Block sizes, blocks per second and EDC for regenerator sec-

tions

Applicability of error performance recom-mendations G.821, G.826, G.828 and G.829

An overview on the history and applicability o IU- phys-ical layer error perormance recommendations is shown intable 9. For systems based on new equipment designed aterthe adoption o the revised version o G.826 in December2002, the set G.826, G.828 and G.829 is covering the com-plete range o bit rates.

Bit rate STM-0 STM-1 STM-4 STM-16 STM-64

SES threshold 15% EBs 15% EBs 25% EBs 30% EBs 30% EBs

Table 7: SES thresholds for SDH multiplex sections as per recommendation G.829

Application

Digital connec-

tions operating

below the pri-

mary rate

Digital paths

operating at and

above the pri-

mary rate (PDH)

Digital paths

operating at

and above the

primary rate

(PDH, SDH, cell-

based)

Digital paths

operating at

and above the

primary rate

(PDH, cell-

based)

Digital paths

operating at

and above the

primary rate

(SDH)

SDH digital sec-

tions

Validity period


12/20


The new recommendation G.8201 for opti-cal transport networks

In 2003, recommendation G.8201 (G.optper) [9] Errorperormance parameters and objectives or multi-operatorinternational paths within the optical transport networkhas been approved. It deines error perormance param-eters and objectives or ODUk paths transported by theON as described in recommendation G.709 [3].he structure o G.8201 is very similar to the G.82x-se-ries recommendations. It is also based on the block errormeasurement concept using error detection code (EDC)inherent to the path under test and as such is useul or in-service measurements. Events, parameters and objectivesare deined accordingly. In addition to path perormance

assessment, tandem connection monitoring is also cov-ered. he SES threshold is deined to 15% errored blocksin one second and results in threshold values as shown intable 10.

Nominal bit rate (kb/s) Path type (1, 2) Blocks/s (3) SESR BBER

239/238 2488320 ODU1 20421 0.002 4 10-5

239/237 9953280 ODU2 82026 0.002 10-5

239/236 39813120 ODU3 329492 0.002 2.5 10-6

All values are provisional and they need not be met by networks until they are revised (up or down) based on real opera-

tional experience.

(1) The block size for ODUk, k = 1, 2, 3 is equal to the ODUk frame size, which is 4 3824 8 = 122368 bits.

(2) The EDC is BIP-8, and is computed over the OPUk payload (4 3808 8 bits) plus OPUk overhead (4 2 8 bits), for a

total of 4 3810 8 = 121920 bits. The EDC usage is 1 BIP-8-(3) These values are rounded to the nearest upper unit.

Table 11: End-to-end objectives for the error performance of a 27,500 km ODUk HROP

Figure 7: Hypothetical reference optical path (HROP)

Path type Bit rate (kb/s) SES threshold

ODU1 2489775 3046 EBs

ODU2 10037273 12304 EBs

ODU3 40319218 49424 EBs

Table 10: SES thresholds for ODUk paths

End-to-end error perormance objectives are providedonly or SESR and BBER. Due to the high bit rates ESRobjectives lose signiicance and are thereore not deined.able 11 shows able 8/G.8201 with the target values orerror perormance. With regard to the lack o experienceon ON systems the target values are provisional and needrevision where necessary. It should be noted that the givenobjectives assume that the standardized orward errorcorrection (FEC) scheme is used as deined in recommen-

dation G.709.

Backboneoperator domains (4 max.)

27,500 km

LODRODBOD

OGOGOGOGOGOG

BODRODLOD

OG: Operator gatewayBOD: Backbone operator domainLOD: Local operator domainROD: Regional operator domain


13/20


he 27,5000 km long hypothetical reerence optical path(HROP) uses the notion o operator domains rather thannational and international portions. hree types o domainsare identiied, the local operator domain (LOD), theregional operator domain (ROD), and the backbone opera-tor domain (BOD). he boundary between the domains iscalled an operator gateway (OG). For correspondence withG.826 and G.828, the LOD and ROD are associated withthe national portion, while the BODs are associated withthe international portion. For continued consistency withG.826 and G.828, our BODs (one or each transit country)and two pairs o LOD-ROD are used or a total o eight (8)operator domains. he HROP thereore originates and ter-minates in the domain o a local operator; it traverses thedomains o regional operators and backbone operators.

he allocation principles can be applied also to the designo error perormance or national or private ODUk paths.

he hypothetical reerence optical path is illustrated in theigure 7 above.

New Recommendations for packet-basednetworks

Y.1540: Internet protocol data communication service

IP packet transfer and availability performance param-

eters (2002)

his Recommendation deines parameters that maybe used in speciying and assessing the speed, accuracy,dependability, and availability o Internet Protocol (IP)packet transer o international IP data communicationservice. Connectionless transport is a distinguishing aspecto the IP service that is considered in IU- Rec. Y.1540.he deined parameters apply to end-to-end, point to pointIP service and to the network portions that provide, or con-tribute to the provision o, such service.

he key parameters include IP packet transer delay(IPD), IP packet delay variation (IPDV), IP packet errorratio (IPER), IP packet loss ratio (IPLR), spurious IP packetrate, and per cent IP service availability.

Y.1541: Network performance objectives for IP-based

services (2002)

his Recommendation deines six classes o network Qual-ity o Service (QoS), and speciies provisional objectives orInternet Protocol network perormance parameters. heseclasses are intended to be the basis or agreements amongnetwork providers, and between end users and their net-work providers.

Y.1560: Parameters for TCP connection performance in

the presence of middle boxes (2003)

his Recommendation describes end-to-end ransmis-sion Control Protocol (CP) perormance in terms ospeed, accuracy, and dependability in an IP-based networkwith middle boxes, which are network nodes terminatingCP connections.

Y.1561: Performance and availability parameters for

MPLS networks (2004)

his Recommendation deines parameters that may beused in speciying and assessing the perormance o speed,accuracy, dependability, and availability o packet trans-er over a Label Switched Path on a Multi-Protocol LabelSwitching (MPLS) network. he deined parameters applyto end-to-end, point-to-point and multipoint-to-point LSPand to any MPLS domain that provides, or contributes tothe provision o, packet transer services.

Network

performance

parameter

Nature of network performance

objective

QoS Classes

Class 0 Class 1 Class 2 Class 3 Class 4 Class 5

IPTD Upper bound on the mean IPTD 100 ms 400 ms 100 ms 400 ms 1 s U

IPDV Upper bound on the 1 103

quantile of IPTD minus the mini-

mum IPTD

50 ms 50 ms U U U U

IPLR Upper bound on the packet loss

probability

1 103 1 103 1 103 1 103 1 103 U

IPER Upper bound 1 104 U

U=UnspeciiedTable 12: Provisional IP network QoS class definitions and network performance objectives


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Comparison of error objectives in M.2100 and G.826

Reerence perormance objectives (RPO) are an importantparameter in recommendation M.2100. he values arechosen to assure that the requirements o G.826 are meton the long-term. his is done by setting the base values inM.2100 to only 50% o the limits in G.826. able 13 com-pares these values.

he table shows the values or the hypothetical reerencepath with a length o 27,500 km. For bit rates at or abovethe primary rate, recommendation M.2100 takes only intoaccount the international portion o a path. hereore, only63% o the objectives in able 13 may be used or this por-tion, as stipulated by G.826 or the international portion.

Note: 63% is the difference between the overall 100% allowance for a

27,500 km reference path minus 37% for the national portion. For the

national portion, G.826 defines a block allowance of 2 17.5% and a

distance-based allowance of 2% corresponding to an assumed minimum

length of 2 500 km. The result is as stated: 37%. See also table 2.

Recommendation M.2100 in the real world

Recommendation M.2100 is intended to enable dimen-sioning o portions o a transmission path (the M.2100term is path core element, PCE) so that all requirementsrom able 13 are met. A practical application o this or theerrored seconds (ES) parameter, based on the example obringing a system into service, will now be considered.

As a general rule, paths are composed o sub elements odierent length. Reerence perormance objectives (RPOs)

must be assigned to each o them. As an aid, M.2100includes tables showing the acceptable RPO allocations.able 14 gives an excerpt rom one o these tables speciyingdistance-based objectives or intermediate countries at theend o a path. here are similar tables or submarine cablesand satellites. he percent igures on the second columno the table reer to the objectives valid or M.2100 romtable 13.For example, to determine the ES objective or a portion oa path operating at the primary bit rate and having a lengtho 4000 km, one must take 6% o 0.02. his objective is thenthe starting point or measurements during bringing-into-

service and maintenance o transmission equipment.

The M.21xx-series recommendations

Differences in purpose for G and M-series recommenda-

tions

Dierences in purpose between recommendations G.821,G.826 and G.828 and the M.21xx-series start with theirdierent origins: he G-series recommendations are romIU- study group 13 (multi-protocol and IP-based net-works and their internetworking), while the M-series arerom study group 4 (telecommunication management,including MN). he main dierences in purpose or thesetwo series o recommendations are as ollows:

G.821, G.826 and G.828 define long-termperormance objectives to be met

G.821, G.826 and G.828 require very long testintervals (one month)

Te M-series recommendations are particularlyuseul when bringing-into-service new transmissionequipment. Tey are intended to assure that therequirements o the G-series are met in every case(e.g. taking into account aging o components)

As a general rule, the requirements o the M-seriesare tougher than those o the G-series consideredhere

For practical reasons, the M.21xx-seriesrecommendations allow short test intervals

Recommendation M.2100

Recommendation M.2100 (Perormance limits orbringing-into-service and maintenance o internationalmulti-operator PDH paths and connections) in its revised

version rom 2003 introduces a new more eicient bring-ing-into-service (BIS) procedure and takes into accountthe revised recommendations G.826, M.2110 and M.2120.It describes how to bring into service PDH systems andtheir components and what objectives must be met in thisprocess [14]. Here, in terms o error perormance, the basisis recommendations G.821 and G.826 in terms o timingperormance (synchronization, jitter and wander), recom-

mendations G.822 and G.823/G.824.

System level Primary Secondary Tertiary Quartenary

Rec. G.826 M.2100 G.826 M.2100 G.826 M.2100 G.826 M.2100

ESR 0.04 0.02 0.05 0.025 0.0765 0.03756 0.16 0.08

SESR 0.002 0.001 0.002 0.001 0.002 0.001 0.002 0.001

Table 13: Performance objectives in recommendations G.826 and M.2100


15/20


Unlike the case o recommendation G.826 (whose objec-tives require long-term measurements over a one-monthinterval), the real world does not look kindly on bringing-into-service and maintenance measurements that require

very long test intervals.hus, M.2100 also allows shorter test intervals, e.g. 15 min-utes. O course, with shorter tests the measurementuncertainty increases, which must be taken into accountwhen interpreting results.

Path core element Allocation (%of end-to-endobjective)

Distance 500 km 2.0 %

500 km < distance 1000 km 3.0 %

1000 km < distance 2500 km 4.0 %

2500 km < distance 5000 km 6.0 %5000 km < distance 7500 km 8.0 %

Distance > 7500 km 10.0 %

Table 14: Allocation of performance objectives to path core ele-

ments

Recommendation M.2100 describes how to derive theperormance limit S or bringing-into-service. I the per-ormance is better than the limit S, the entity can be broughtinto service with some conidence. Corrective action isrequired i perormance is worse than the limit S as shownin igure 10. he calculation is done with the ollowingsteps:

Step 1:Identiy the perormance objectives or the appropriate bitrate or ES and SES

Step 2:

Determine the path allocation A%

Step 3:

o calculate the allocated perormance objective (APO)determine the required test period (P) expressed in sec-onds and calculate the APO:APO = A PO P

Step 4:

Calculate the bringing-into-service perormance objective(BISPO):BISPO = APO/2

Step 5:

Determine the threshold value S:D = 2 BISPOS = BISPO - Dhe S values are rounded to the nearest integer value ( 0)As an example the ES limit SES is calculated or the primarylevel (e.g. bit rate 2048 kb/s) with a path allocation o 12%and a test time o one day (86400 s).

APOES= 12% 0.02 86400 = 207.36BISPOES= 2 103.68 = 20.36

SES= 103.68 - 20.36 = 83.32 (rounded to83)For test lengths o 15 minutes, 2 hours and 24 hours, recom-mendation M.2100 contains tables with numerical valuesor the limit S with path allocations in the range o 0.2% to63% or ES and SES) able 14 shows an excerpt rom oneo these tables. he 12% path allocation row contains thenumber rom the above example.

hese tables save M.2100 users the trouble o doing manycalculations. Once the percent allocation or the path ele-ment is known, the igures or bringing a system intoservice can be read o.

Figure 8: Bringing-into-service (BIS) limit

15 min 2 hours 24 hours

ES SES ES SES ES SES

Path allocation S15

S15

S2

S2

S24

S24

0.2 % 0 0 0 0 0 0

0.5 % 0 0 0 0 0 0

1.0 % 0 0 0 0 3 0

2.0 % 0 0 0 0 9 0

3.0 % 0 0 0 0 16 0

4.0 % 0 0 0 0 23 0

5.0 % 0 0 0 0 30 0

6.0 & 0 0 0 0 37 0

7.0 % 0 0 1 0 45 0

8.0 % 0 0 1 0 52 0

9.0 % 0 0 1 0 60 0

10.0 % 0 0 2 0 68 0

11.0 % 0 0 2 0 76 0

12.0 % 0 0 3 0 83 1

13.0 % 0 0 3 0 91 1

14.0 % 0 0 4 0 99 1

63.0 % 0 0 32 0 498 17

Table 15: Br inging-into-service limits for primary systems

Number of events

BISPO(APO/2)

Corrective actionrequired

Bringing-into-servicewith confidence

The objective islikely to be satisfied

The objective isunlikely to be satisfied

D

S


16/20



Recommendation M.2100 (Perormance limits orbringing-into-service and maintenance o internationalmulti-operator SDH paths and connections) [15] is veryclose to M.2100 in terms o purpose and ormat, but dealsexclusively with SDH systems. M.2101 include useul tables

as described above, and the computational techniques ordetermining parameters are essentially the same. his rec-ommendation or SDH systems according to G.820, G.828and G.829 (see also able 16) can thus be considered as theequivalent o recommendation M.2100 or PDH systems.

Application of G-series and M-series recommendations

able 16 summarizes the applications o the G-series rec-ommendations discussed here. It includes all our o theG-series recommendations and the corresponding M-se-ries recommendations.

Other recommendations in the M.21xx Series

As well as recommendations M.2100 and M.2101, there area number o other recommendations in the M.21xx series,which are o importance in describing the error peror-mance o digital communications equipment.


Recommendation M.2102 (Maintenance thresholdsand procedures or recovery mechanisms (protectionand restoration) o international SDH VC trails (paths)and multiplex sections) [17] deals with spare circuits oruse when aults occur, when transmission perormancedrops or during maintenance work. his recommendation

deines thresholds or switchover to spare circuits or SDHVC paths.


Recommendation M.2110 (Bringing-into-service inter-national multi-operator paths, sections and transmission

systems) [18] is also clearly related to M.2100 and M.2101rom its name. M.2110 takes an in-depth look at the pro-cedures used or bringing transmission equipment intoservice. One major distinction is between in-service andout-o-service measurements. For out-o-service measure-ments, this recommendation reers to the test equipmentrecommendations (O.150 [20], O.151 [21] and O.181[25]), which are covered by instruments rom JDSU. Initialmeasurements are to be perormed during bringing-into-service using pseudo-random bit sequences generated byexternal test sets.For bringing-into-service o a path the irst step is a con-tinuity test carried out over a 15-minute interval. hecontinuity test consists o sending bit errors with a test set.he test is considered passed i the path termination pointreceives the bit errors. I the test ails, ault localization andcorrection must be carried out. he procedure should berepeated until the test is successul.I the irst step is passed, as second step a 24-hour test is per-ormed o each perormance event (e.g. ES, SES). he test isconsidered passed, i the number o occurrences or all per-ormance events is less or equal to the limit S24. In this casethe path is ready or service (RFS). he test is consideredailed i unavailability occurs or the number o occurrences

Recommendation G.821 G.826 G.828 G.829 G.8201 M.2100 M.2101

Application Long-term

error perfor-

mance (OOS)

Long-term

error perfor-

mance (ISM/OOS)

Long-term

error perfor-

mance (ISM/OOS)

Error event

definition

Long-term

error perfor-

mance (ISM/OOS)

BIS limits

ISM/OOS

(PDH)

BIS limits

ISM/OOS

(SDH)

Monitored element N x 64 kb/s

connections

PDH/SDH

cell-based

paths/

n x 64 kb/s

connections

SDH paths SDH sections ODUk paths PDH paths,

sections,

systems

SDH paths,

sections

Minimum bit rate 64 kb/s 64 kb/s VC-11 Sub-STM-0 ODU1 64 kb/s VC-11,

STM-0

Maximum bit rate 31 (24) x 64

kb/s

3500 Mb/s

BC-4-4x

BC-4-64c STM-64 ODU3 140 Mb/s VC-4-64c,

STM-64

Evaluation period 30 days 30 days 30 days 30 days 24 h, 2 h,

15 min

24 h, 2 h,

7 days

(15 min)

Error detectionmechanism

Bit error Block error Block error Block error Block error Bit error,block error

Block error

Error event ES, SES ES, SES1), BBE ES, SES1), BBE ES, SES1), BBE SES1), BBE as G.821 and

G.826

as G.826,

G.828, G.829

(1) Severely errored seconds (SES) are also derived from detected defects

Table 16: Application of the G-series and M-series recommendations


17/20


o at least one perormance event is greater than S24. In thiscase, ault localization and correction must be carried out(FL).

he bringing-into-service test procedure o a path is illus-trated as low diagram in igure 9. Further procedures aredescribed or bringing-into-service more than one path atthe same time with identical and not identical routing.he measurement mentioned above as step two (24 hours)can be included in the 7-day interval.

Figure 9: Bringing-into-service procedure for a path


Recommendation M.2120 is entitled International multi-operator paths, sections and transmission systems aultdetection and localization procedures [19]. It is the orthin the series o important recommendations on bringing asystem into service and maintaining it. he latest revisiono M.2120 in 2002 provides procedures or ault detectionand localization with and without in-service monitoring.Filtering o perormance inormation are described orreporting to the telecommunication management net-work (MN). Returning into service and long-term trendanalysis are considered as well. In the context o externaltest sets, section 4.1/M.2120 dealing with out-o-servicemeasurements is important. I the transmission systemunder test can transport any traic at all, it is recommendedto use rame analyzers as described in recommendationsO.161 [22], O.162 [23] and O.163 [24]. I traic is com-pletely interrupted, then pseudo-random bit sequences arepreerred or troubleshooting (test sets rom recommenda-tions O.159, O.151 and O.181). Here, ramed signals arepreerred once more.

Figure 10: Out-of-service measurements from A to C using ANT-20

Further M-series recommendations

Also worth mentioning is M.2201, which covers AMtransmission equipment and M.2301 which deals with IP-

based networks.Recommendation M.2201

Perormance objectives, allocations and limits or bringing-into-service and maintenance o international AM virtualpath and virtual channel connections.

Figure 11: Far-end in-service measurements (from C to A) evaluating

REI (remote error indication) and RDI (remote defect indication)


Perormance objectives and procedures or provisioningand maintenance o IP-based networks.

M.2401: Error performance limits and procedures for

bringing-into-service and maintenance of multi-oper-

ator international paths and sections within an optical

transport network

his Recommendation gives error perormance objec-tives, limits and procedures or bringing into service (BIS)and maintenance o multi-operator international ODUkpaths and OUk sections in an Optical ransport Network(ON).

SDH network

STM-N

with VC-n

STM-N

with VC-n

Tx Rx

B

C

D

A

Input signal Output signal

SDHnetwork

A

B

C

Step 1

Step 2

failed

passed

Test 24 h

failed

passed

FL

RFS

Continuity test


18/20


Recommendations in the I-series

In regard to transmission perormance o digital transmis-

sion systems, two recommendations in the I-series shouldalso be mentioned:

I.356: B-ISDN AM layer cell transer perormance[11]

I.610: B-ISDN operation and maintenance principlesand unctions [13]

Both recommendations deal with the AM layer and thusgo beyond the scope o this paper on the physical layer.However, these recommendations are important to the testand measurement industry since recommendation O.191or AM test equipment [26] is based signiicantly on I.356and I.610.

I.351: Relationship among ISDN, internet protocoland physical layer perormance recommendations

Provides an overview on IU- perormance recom-mendations or dierent telecommunications systems.Furthermore, some background on the history o G-seriesperormance recommendations is given (see also table 9).


19/20


Bibliography

[1] IU- Recommendation G.703 Physical/electrical characteristics o hierarchical digitalinteraces

[2] IU- Recommendation G.707 Networknode interace or the synchronous digital hier-archy (SDH)

[3] IU- Recommendation G.709 Interaces orthe optical transport network (ON)

[4] IU- Recommendation G.783 Character-istics o synchronous digital hierarchy (SDH)equipment unctional blocks

[5] IU- Recommendation G.821 Error per-ormance o an international digital connection

operating at a bit rate below the primary rate andorming part o an integrated services digital net-work

[6] IU- Recommendation G.826 End-to-enderror perormance parameters and objectives orinternational, constant bit rate digital paths andconnections

[7] IU- Recommendation G.828 Errorperormance parameters and objectives orinternational, constant bit rate synchronous digi-tal paths

[8] IU- Recommendation G.829 Error

perormance events or SDH multiplex andregenerator sections

[9] IU- Recommendation G.8201 Errorperormance parameters and objectives ormulti-operator international paths within theoptical transport network (ON)

[10] I.351: Relationships among ISDN, IP-basednetwork and physical layer perormance Recom-mendations

[11] IU- Recommendation I.356 B-ISDN AMcell transer perormance

[12] IU- Recommendation I.432 B-ISDN User-

Network interace Physical layer speciication[13] IU- Recommendation I.610 B/ISDN opera-tion and maintenance principles and unctions

[14] IU- Recommendation M.60 Maintenanceo terminology and deinitions

[15] IU- Recommendation M.2100 Peror-mance limits or bringing-into-service andmaintenance o international multi-operatorPDH paths and connections

[16] IU- Recommendation M.2101 Peror-mance limits or bringing-into-service andmaintenance o international multi-operatorSDH paths and multiplex sections

[17] IU- Recommendation M.2102 Mainte-nance thresholds and procedures or recoverymechanisms (Protection and restoration) ointernational SDH VC trails (paths) and multi-plex sections

[18] IU- Recommendation M.2110 Bringing-into-service international multi-operator paths,sections and transmission systems

[19] IU- Recommendation M.2120 Inter-national multi-operator paths, sections andtransmission systems ault detection and local-

ization procedures[20] IU- Recommendation O.150 General

requirements or instrumentation or peror-mance measurements on digital transmissionequipment

[21] IU- Recommendation O.151 Error peror-mance measuring equipment operating at theprimary rate and above

[22] IU- Recommendation O.161 In-servicecode violation monitors or digital systems

[23] IU- Recommendation O.162 Equipment toperorm in-service monitoring on 2048, 8448,34368 and 139264 kb/s signals

[24] IU- Recommendation O.163 Equipmentto perorm in-service monitoring on 1544 kb/ssignals

[25] IU- Recommendation O.181 Equipment toassess error perormance on SM-N interaces

[26] IU- Recommendation O.191 Equipment tomeasure the cell transer perormance o AMconnections


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List of abbreviations

AIS Alarm indication signal

AM Asynchronous transer modeBBE Background block error

BBER Background block error ratio

BIP Bit interleaved parityBIS Bringing-into-service

CRC Cyclic redundancy check

DSL Digital subscriber lineEB Errored block

EDC Error detection code

ES Errored secondESR Errored second ratio

FEC Forward error correction

HP Higher-order pathHROP Hypothetical reerence optical path

HRP Hypothetical reerence path

HRX Hypothetical reerence connectionIG International gateway

ISDN Integrated services digital network

ISM In-service monitoringIU International telecommunication union

LOM Loss o multi-rameLOP Loss o pointer

LP Lower-order path

OAM Operation and maintenanceODUk Optical channel data unit-k

ON Optical transport network

PDH Plesiochronous digital hierarchyPLM Payload label mismatch

RDI Remote deect indication

SDH Synchronous digital hierarchySEP Severely errored period

SEPI Severely errored period intensitySES Severely errored secondSESR Severely errored second ratio

SM Synchronous transport module

CM andem connection monitoringIM race identiier mismatch

MN elecommunication management network

U ributary unitUNEQ Unequipped

Itu Errorperf an Ae

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