Wavetek ACTERN ANT20 series/ant20-3035/english/operating manual/_start.pdf operating manual

Conforming to the Maze
of Network Standards

ITU-T Recommendations
and Practical Applications
in PDH/SDH Networks

Application Note 59

Why Do Recommendations Exist for SDH/PDH Networks?

Telecommunications networks are not built from
technologies that are individually specified by each
service provider. If they were, imagine how hard it
would be to connect from one service provider to
the next! The logical solution is to have a universal
organization (or organizations) specifying trans­mission methods that are universally applicable to
all service providers. One of these bodies is the
International Telecommunication Union  Tele­communication Standardization Sector (ITU-T)
formally known as CCITT. The ITU-T is responsible

for studying technical, operating and tariff questions
and issuing Recommendations on them with a view to
standardizing telecommunications on a worldwide
basis.
Many telecommunication networks use network ele­ments that are specified by ITU-T Recommendations.
The Advanced Network Tester (ANT-20) recognizes
these Recommendations and carries out measure­ments to qualify them. This note will directly quote
Recommendations from ITU-T and then apply them
to practical applications performed on the ANT-20.

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)

Cross Connect Test

G.823

Jitter Test

G.958

G.813

Wander

G.841

G.825

Jitter Test

Error

Performance

G.821
G.826

M.2100

PDH

Network

1

Recommendation G.783: Characteristics of
Synchronous Digital Hierarchy (SDH) Equipment
Functional Blocks

“This Recommendation defines a library of basic
building blocks and a set of rules by which they
may be combined in order to describe a digital
transmission equipment. The library comprises the
functional building blocks needed to specify
completely the generic functional structure of the
Synchronous Digital Hierarchy.”
The Recommendation describes processes within
the basic building blocks, the so called “atomic
functions”, for example the generation and
evaluation of overheads used for performance
monitoring.
The regenerator section termination and

adaptation function acts as a source and sink for
the regenerator section overhead (RSOH). The
RSOH contains bytes A1, A2, B1, J0, E1, F1, D1 to
D3 and bytes reserved for national use. This
section acts as a maintenance entity between and
including two regenerator termination functions.
The multiplex section termination and adaptation
function acts as a source and sink for the multiplex
section overhead (MSOH). The MSOH contains
bytes B2, K1, K2, D4 to D12, S1, M1, E2 and bytes
reserved for national use. This section acts as a
maintenance entity between and including two
multiplex termination functions.

G.783 APPLICATION
MSOH Byte Functionality and BERT
RSOH Byte Functionality and BERT

In Brief

PDH signals are transported over four main SDH
layers all of which play critical parts in certifying
SDH transmission. The physical layer is classified
as the fifth layer. The section overhead (SOH) is
mainly built up from the RSOH and MSOH, which
guide the payload of the STM-N signal between
multiplex and regenerator elements within a
network. With this particular asset of the STM-N
technology, the overhead of the STM-N signal can
be tested and in turn test the MST and RST
functions.

Figure 1 illustrates the different layers which are
passed by a signal when it is transmitted through a
network. The different layers are terminated depen­ding on the functions implemented in the network
elements. For example, the regenerator layer
guides the signal between the MUX and REG, then
a new RSOH is generated at the output of the REG
to guide the signal to the ADM, and so on. The
lower path (LP) layer will come into play when the
PDH tributaries are terminated at the DEMUX.

LP: Lower Order Path
HP: Higher Order Path
MS: Multiplex Section
RS: Regenerator Section
OS: Optical Section

Figure 1

Application

A suitable application for testing the RST and MST
functions lies in the Anomaly/Defect generator and
analyzer. SDH technology uses a maintenance
interaction flow where different signals are trans­mitted through particular bytes of the overhead to
indicate anomalies and defects. Messages are
generated due to an interaction with corresponding

layer errors. For example, if a LOF is generated in
the RS layer then an AIS defect will display in the
PDH layer. Test can be performed with the ANT-20
by sending out defects in the different layers and
looking at the reactions in the corresponding
layers. Figure 2 a/b illustrates two general setups
which will result in two different error alarms being
generated.
The black line setup will generate error alarms of a
HP and MS layer nature if a RS defect was first
generated. The red line setup will generate error
alarms of PDH layer nature due to the fact that a
PDH signal is examined.

2

Recommendation G.783: Section 10 Specification
of Jitter and Wander

This section of recommendation G.783 specifies
input and output jitter/wander requirements which
directly refer to recommendations G.958, G.825
and G.813 which will be explained later in this
note. This recommendation also specifies wander
and combined jitter caused by PDH tributary
mapping and pointer adjustments.
“The combined jitter arising from tributary mapping
and pointer adjustments should be specified in
terms of peak-to-peak amplitude over a given
frequency 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 specifi­cation of mapping and pointer jitter on PDH
interfaces is the definition of the filter character­istics. Most important is the specification of the
highpass filter characteristics due to the low
frequency components of pointer jitter. Tables
1a/1b show the filter characteristics for mapping
jitter generation and combined jitter generation.

Figure 3a:
The user interface
window for generating
different anomalies
and defects.

Figure 3b:
Results in graphical
format.

Figure 3b

Figure 3a

Figure 2bFigure 2a

3

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

interfaces mapping jitter

kbit/s f

1

f

3

f

4

f1–f

4

f3–f

4

high 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)
Notes

1. These values are for further study

2. Avalue of 0.075 UI has been proposed

Table 1a:
Mapping jitter

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

interfaces jitter

kbit/s f

1

f

3

f

4

f1–f

4

f3–f

4

high 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 UI

0.75 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 1

These values are for further study

Table 1b:
Combined jitter

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

are apparent. Both effects together result in
combined jitter. The recommendation specifies
values to which the MUX and DEMUX must adhere
to ensure as little jitter in the system as possible.
The recommendation also defines pointer test
sequences which are used to test the performance
of SDH equipment with regard to SDH tributary
jitter. These pointer test sequences are illustrated
in Figure 4.

In Brief

4

The ANT-20 has the
advantage of generating AU
and TU pointers simultan­eously.
The application is set up to
test the DUT’s combined and
mapped jitter limits. This is
performed by inputting an
STM-N signal and moni­toring the PDH tributaries,
(i.e. 2,8,34,140 Mbit/s). The
ANT-20 will analyze jitter as
illustrated in Recommen­dation G.783, but with the
pointer test sequences
activated simultaneously.

G.783 Section 10 APPLICATION
PDH interfaces Jitter with pointer simulation

Figure 5a: The pointer value in
graphical format with the current
value (shown ringed).

Figure 5b: The possible sequences

that 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

Tributary

ports

2,048 kHz

Pointer action

Application

Missing
pointer action

Start of next
sequence

4 missing
pointer action

Start of next
sequence

87-3 sequence

Additional
pointer action

43-44 sequence

Start of next
sequence

86-4 sequence

5

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

Parameter value Network limit Measurement filter bandwidth
Digital rate B

1

unit interval B2unit interval Band-pass filter having a lower cut-off

(kbit/s) peak-peak peak-peak frequency f

1

or f3and an upper cut-off
frequency f

4

f

1

f

3

f

4

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 kHz

139,264 1.5 00.75 200 Hz 10 kHz 3500 kHz

Notes

1. 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 ns
for 2,048 kbit/s 1 UI = 488.00 ns B

1

is the permissible jitter with the band pass

for 8,448 kbit/s 1 UI = 118.00 ns filter cut-off f

1

and f4.

for 34,368 kbit/s 1 UI = 29.10 ns B

2

is the permissible jitter with the band pass

for 139,264 kbit/s 1 UI = 7.18 ns filter cut-off f

3

and f4.

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

Table 2: Jitter limits
for PDH interfaces
defining the cor­responding filter
bandwidth.

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 equip­ment interfaces of a PDH network.
The Recommendation states that “magnitudes
of wander, being largely dependent on the
fundamental propagation characteristics of
transmission media and the aging of clock
circuitry, can be predicted.” For PDH interfaces
the following limits apply.

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

In Brief

This Recommendation focuses on networks
containing equipment with PDH interfaces. When
networks are designed, service providers need to
take into account the values illustrated in Table 2
and Figure 6, ensuring that all network elements
on line do not introduce any more jitter or wander
into 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 performance
of the DUT’s jitter capabilities for PDH signals.
Jitter transfer function and maximum tolerable jitter
tests can also be performed under this Recommen­dation. These two measurements are explained in
more detail in the sections for Recommendation
G.958 and G.825. For wander refer to G.813.
The jitter result window in Figure 8 is for manual
mode. In this mode the user can set jitter ampli­tudes manually and observe the reaction of the
DUT through errors and alarms. Phase hits occur
when
a specific jitter threshold is exceeded. The results
are recorded using a counter. Limits of the hit
threshold may be set via the SET button.
The jitter generator/analyzer window allows the
user to select the application measurement for
maximum tolerable jitter (MTJ) or fast MTJ (FMTJ),
jitter transfer function and wander analysis.

Recommendation G.825: Control of JITTER and
WANDER within Digital Networks Based on the
Synchronous Digital Hierarchy (SDH)

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

applied to the SDH network interfaces. Network
interfaces (e.g. international boundaries) must
meet interface limits regardless of the individual
carrier’s choice of equipment. These limits are
displayed in Table 3.

Figure 8: The results

window 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)

Notes

1. 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 f

1

and f4.

for STM-16 UI = 0.40 ns B2 is the permissable jitter with the band

pass filter cut-off f

3

and f4.

Table 3

Figure 7

PDH

Interface

Application

DUT

7

G.825 APPLICATION
ALL SDH interface Jitter, Maximum Tolerable Jitter

In Brief

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

The setup to test the performance of maximum
tolerable jitter (MTJ) at SDH network interfaces is
shown in Figure 9. MTJ measurements are
generally performed by increasing jitter amplitudes
at certain scan frequencies and evaluating the
number of errors that the DUT produces.
The ANT-20 performs this procedure in an auto­mated way, thus generating different jitter ampli­tudes at certain frequencies and recording the jitter
amplitude when the DUT failed, then comparing
these values against the Recommendation mask.

Figure 10: Different
tolerance masks and
scan frequencies can
be user defined, by
clicking on the “SET”
button situated in the
title bar.

Figure 9

STM-4

Interface

network. Jitter and Wander limits for network ele­ments without connection to the network are more
stringend to meet the network interface require­ments. Such limits are defined in Recommendation
G.783 and G.958 for SDH network elements.

Application

Figure 11: MTJ results
recorded in tabular
and graphical format
against tolerance
masks set by ITU-T.

DUT

8

Recommendation G.958:
Digital Line Systems Based on the Synchronous
Digital 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 ns
For STM-4 1 UI = 1.61 ns
For STM-16 1 UI = 0.40 ns

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

STM-N level (type) fc (kHz) P (dB)
STM-1 (A) 130 0.1

STM-1 (B) 30 0.1
STM-4 (A) 500 0.1
STM-4 (B) 30 0.1
STM-16 (A) 2,000 0.1
STM-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 of
digital synchronous line systems based on the
synchronous digital hierarchy (SDH) to provide
transverse compatibility.”
This Recommendation will focus on jitter gener­ation, jitter transfer and jitter tolerance of regener­ators.
“Jitter generation is defined as the amount of jitter
at the STM-N output of SDH regenerators.” The
amplitude of the jitter present at the output of each
regenerator should not exceed a specified limit
value.
Table 4 displays the proposed figures from the
revised draft of recommendation G.958 on STM-N
jitter generation for output jitter at an STM-N inter­face assuming the absence of jitter at the input
interface, thus intrinsic jitter.

In Brief

This recommendation focuses on the limits that
SDH regenerators need to meet to be part of a
quality network system. Each regenerator can
introduce jitter resulting in jitter accumulation,

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

NOTE: Relevant parts of Recommendation G.958
including the jitter requirements of regenerators will
in future be moved to section 10 of a revised
version of Recommendation G.783.

Table 4: Intrinsic
jitter limits

Table 6 illustrates the jitter tolerance parameters

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

affecting greatly the purity of the transported
signal. 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 importance
when dealing with regenerators. Checks are
carried out to demonstrate that the jitter gain of a
regenerator is below the defined value of recom­mendation G.958. If this is not the case, then “jitter
runaway” occurs after several regenerators. JTF is
measured by applying a signal with defined jitter
modulation over the frequency range of the DUT.
The jitter amplitude is selected so that the DUT can
handle it at any frequency. The ANT-20 meas­ures the resulting jitter amplitude at the output of
the DUT at various TX jitter frequencies. The log of
the ratio between input and output gives the jitter
gain or attenuation.
Jitter transfer function measurements are im­proved by compensating for intrinsic jitter of the
DUT and the ANT-20 by carrying out calibration
measurements first. This improves the measure­ment accuracy.

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

“This Recommendation outlines requirements for
timing devices used in synchronizing network
equipment that operates according to the principles
governed 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 which
the clock can refer to however, when links between
the master and slave clocks fail, then the SEC’s
frequency 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 SDH
networks 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 referred
to in this note.

Figure 13: The results
are displayed in
graphical or tabular
format.

“Noise generation of a SEC represents the amount
of phase noise produced at the output when there
is an ideal input reference signal or the clock is in
holdover state.” This is commonly known as wan­der generation and is measured in maximum time
interval error (MTIE) and time deviation (TDEV).
Figure 14 illustrates MTIE versus observation
interval for constant and variable temperatures,

Figure 14: MTIE vs.
Observation Time for
constant and variable
temperatures

Figure 12: Jitter transfer function test of regenerators.

where the menasurement needs normally a large
period of time. From time interval (TIE) measure­ments the time deviation TDEV can be calculated.
TDEV values are a measure of the phase error
variation versus the integration time. Put simply,
the time deviation is calculated for each point
within a measurement time (T) for an instant that
travels through the entire measurement time T

Total

.
Figure 15 shows TDEV versus observation interval
for constant temperature.

STM-16

Regenerator

0.1 1.0 10 100 1,000
Observation interval τ (s)

(var. temp.)

1,000

150
100

63
40

10

0

(const. temp.)

MTIE (ns)

10

“The noise tolerance of a SEC indicates the min­imum phase noise level at the input of the clock
that should be accommodated whilst:

– Maintaining the clock within prescribed

performance 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 ns
For STM-4 1 UI = 1.61 ns
For STM-16 1 UI = 0.40 ns

The noise tolerance is also commonly known as
wander tolerance and is characterized by MTIE
and TDEV masks illustrated in Figures 16a/16b.
Jitter tolerance limits are also specified in this
recommendation for SDH network elements
excluding regenerators, which G.958 covers.
Figure 17 shows the maximum tolerable input jitter
for 2,048 kHz and 2,048 kbits Synchronization
interface.

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

Figure 17: The lower limit of the maximum tolerable input
jitter of 2,048 kHz and 2,048 kbit/s signals carrying
synchronization to a SEC.

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

Figure 16a

Figure 16b

Figure 15: TDEV vs.
observation time
for constant
temperature

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

10

6.4

3.2

1.0

0.1

1,000

170
100

12
10

0.1

10

5.5

2.0

1.0

0.25

0.1

(const. temp.)

TDEV (ns)

TDEV (ns) MTIE (ns)

0.1 10 19 49 100 1,000 10,000 100,000
Observation interval τ (s)

250

100

Peak-to-peak

jitter amplitude

(ns)

This Recommendation also specifies limits for jitter
generation on SDH output interfaces. The differ­ence between G.958 and this Recommendation is
that this recommendation defines limits for all
network elements, excluding regenerators. The
limits defined in this part of the recommendation
are 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 inter­face 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 whole
range of interfaces from PDH to SDH. Due to the
instrument’s large storage capacity, long-term
measurements can run up to 100,000 sec or
longer. The measured values are displayed in the
jitter generator/analyzer window as a graph of the
time interval error (TIE) versus time. Numerical
values of MTIE and TIE are shown above the
graph, as illustrated in Figure 19.

Figure 20:
The offline analyzer
for MTIE and TDEV.

Figure 19: Result
window illustrating
ANT-20’s wander
measurement.

Figure 18

DUT

PRC

2,048 kHz Ref.

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

Application

The wander generation setup consists of the
ANT-20 connected as in Figure 18. Wander
tolerance can be tested by generating wander over
the DUT and then observing the output for any
errors and alarms. The wander that is placed over
the DUT is in the form of a sinusoidal wave, as
defined in Recommendation G.813.
The results of wander generation tests which are
displayed 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 then
compared to predefined standards and to user­defined tolerance masks which determine the
clock quality.

12

Recommendation G.826: Error Performance
Parameters and Objectives for International, Constant
Bit 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 perform­ance events, parameters and objectives for digital
paths operating at bit rates at or above the primary
rate. Paths are used to support services such as
circuit switched, packet switched and leased line
services.” Specifications that refer to bit rates
that are n u 64 kbit/s (n < 24 or 32 resp.) are in
Recommendation G.821.
“Recommendation G.826 is based upon the error
performance measurement of blocks. Ablock is a
set 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 different
modes. In-service monitoring or out-of-service
monitoring. In-service monitoring allows measure­ment while the system is operational. Error
detection codes e.g. BIP or CRC are evaluated to
assess performance parameters. Out-of-service
measurements are mainly used for aligning newly
setup communications equipment. The parameters
monitored are errored second, severely errored
second and background block error.

Events

OErrored Second (ES): A one second period

with one or more errored blocks or at least one
defect.

OSeverely Errored Second (SES): A one-

second period which contains M 30% errored
blocks or least one defect. SES is a subset
of ES.

OBackground Block Error (BBE): An errored

block not occurring as part of an SES.

Parameters

OErrored Second Ratio (ESR): The ratio of ES

to total seconds in available time during fixed
measurement interval.

OSeverely Errored Second Ratio (SESR): The

ratio of SES to total seconds in available time
during a fixed measurement interval.

OBackground Block Error Ratio (BBER): The

ratio of Background Block Errors (BBE) to total
blocks in available time during a fixed measure­ment interval. The count of total blocks exclu­des all blocks during SESs.

G.821 G.826 M.2100

Purpose Error Error BIS

Performance 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-end
error performance
objectives for 27,500 km
international digital
HRP.

Table 9: Error
performance
Recommendation

13

In Brief

Every SDH path has an embedded error perform­ance monitoring capability from which a number of
standard parameters are calculated within the
network element. The management needs these
parameters 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 user
to view the EB at the near and far end of the trans­mission path. ES, EFS SES are also included as
the parameters for the overall transmission perfor­mance results. The “VERDICT” box gives a direct
indication as to whether the communications path
meets the requirements of the recommendation
depending on the path allocation.

IG is the international gateway that connects the
national portion to the international portion which
usually corresponds to a DXC, higher order MUX
or 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

Terminating

country

Terminating

country

PEP IG

National

portion

National

portion

International portion

Hypothetical reference path

27,500 km

Intermediate

countries

Intercountry

(e.g. path

carried over

a submarine

cable

IG IG IG IG PEP

Input signal

Output signal

end path begins in one terminating country and
ends in the second terminating country. It is not
possible to have less than or more than two
terminating countries for an international path.

– Identification of performance degradations in

order to prompt remedial maintenance action;

– Provision of black spot analysis information for

network quality improvement programs.

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

14

Recommendation M.2100: Performance Limits for
Bringing-into-Service and Maintenance of International
PDH Paths, Sections and Transmission Systems

“Recommendation M.2100 provides limits for bring­ing-into-service and maintenance of international
sections, paths and transmission systems at every
level of the plesiochronous digital hierarchy from
64 kbit/s. Error timing and availability performance
are considered.

“This recommendation uses certain principles
which are the basis of the maintenance of a digital
network:

– It is desirable to do in-service, continuous meas-

urements. In some cases (e.g. bringing-into­service), out-of-service measurements may be
necessary.

– Asingle set of parameters must be used for

maintenance of every level of the hierarchy
(this principle does not apply to limits).

– Error performance limits of transmission

systems are dependent on the medium used.
However, due to the many possible network
structures, 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 the
end-to-end RPO taken from Recommendation
G.821. RPO stands for the reference performance
objective, upon which other performance objective
values are based.

Primary, secondary, tertiary and quaternary stand
for the relevant levels in the Plesiochronous Digital
Hierarchy. The PRO figures given in the table are
equal to 50% of the performance objectives given in
Recommendation G.826.

In Brief

This Recommendation indicates the limits to
quantify an international digital network and its

Application

The same setup can be used as illustrated in the
figure below for out-of-service in Recommendation
G.826.
The analysis in general, including all G.826 meas­urements, provides separate results for the
“NEAR END” and the “FAR END”. This simply
means that errors occurring directly in the path are
analyzed as well as errors occurring in the return
path which are indicated by a remote error
indicator message (e.g. E-bit at 2,048 Mbit/s) or
remote defect indication. This allows both
directions to be monitored at one end of a path.

Table 10: End-to-end
error reference per­formance objectives at
64 kbit/s

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

Table 11: End-to-end
error performance
objectives at or above
the primary rate

elements. These limits are to be used to indicate
the need for actions during maintenance and
bringing-into-service of network paths.

15

Recommendation G.841: Types and Characteristics of
SDH Network Protection Architectures

Keeping the downtimes of SDH paths to an abso­lute minimum is extremely important for network
operators, since the quality of the services they
offer is the main feature that distinguishes the
many different providers.

1. MS dedicated protection ring

An MS dedicated protection ring consists of
two counter-rotating rings, each transmitting in
opposite directions relative to each other. In this
case, only one ring carries normal traffic to be
protected while to other is reserved for protection
of this normal traffic (see Figure 26a). The normal
traffic for example is carried only in the clockwise
direction. It is protected by beeing simultaneously
transported in the opposite direction. If the normal
traffic is interrupted, the terminating network
element switches to the protection channel (in the
example shown here: failure between B and C ->
network element E switches over to the protection
channel). MS dedicated protection ring would also
require using the APS bytes, K1 and K2, for
protection switching.

2. MS shared protection ring

MS shared protection rings can be categorized into two
types: two-fiber and four-fiber. The ring APS protocol
accommodates both types.
For MS shared protection rings, the working channels
carry the normal traffic signals to be protected while the
protection channels are reserved for protection of this
service. Normal traffic signals are transported
bidirectionally over spans: an incoming tributary travels
in one direction of the working channels while its
associated outgoing tributary travels in the opposite
direction but over the same spans.
– Two-fiber shared protection ring
This protection architecture requires only two fibers for
each span of the ring. Each fiber carries both working
channels and protection channels. On each fiber, half
the channels are defined as working channels and half
are defined as protection channels. The normal traffic
carried on working channels in one fiber are protected
by the protection channels traveling in the opposite
direction around the ring (see Figure 25a). This permits
the 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 necessary
equipment-level specifications to implement
different choices of protection architectures for

Synchronous Digital Hierarchy (SDH) networks. ...

Physical implementations of these protection
architectures may include rings, or linear chains of
nodes. Each protection classification includes
guidelines on network objectives, architecture,
application functionality, switching criteria, proto­cols, and algorithms.”
A series of mechanisms, designed to prevent pro­longed transmission path downtimes in the event
of a defect, is defined for SDH networks.

The generic term for these mechanisms is APS
(Automatic Protection Switching). System
resources which during normal operation are either
not used at all or only for very low-priority traffic are
made available for this purpose. If a defect occurs,
the “normal” traffic is then diverted automatically to
these spare paths. In addition to the correct
sequence of this switchover procedure, which may
involve more than 10 different network elements,
the time from the interruption of traffic to when the
connection is restored is a critical factor. According
to ITU-T Recommendation G.841, this time should
be less than 50 ms.

In Brief

16

In the event of a cable cut, normal traffic transmit­ted toward the failed span is switched at one node
to the protection channels trasmitted in the oppo­site direction (away from the failure). This bridged
traffic travels the long way around the ring on the
protection channels to the other node where the
normal traffic from the protection channels is
switched back onto the working channels. In the
other direction, the normal traffic ist bridged and
switched in the same manner. Figure 25b illustra­tes a ring switch in response to a cable cut.
– Four-fiber shared protection ring
Two out of the four glass fibers transport the work­ing channels and two the protection channels. One
fiber pair (working + protection) travels clockwise

around the ring, while the other pair travels around
it in the counterclockwise direction. Thus, bidirec­tional connections can be operated.
There are two possible mechanisms if a defect
occurs. One of them functions in the same way as
with the two-fiber shared protection ring. The traffic
is switched over in the network elements located
closest to the fault and transported via the protection
fiber for the opposite direction (“ring switching”).
The second mechanism is known as “span switch­ing.” In the event of a defect the traffic is trans­ported via the protection fiber that operates in the
same direction as the faulty working fiber. Conse­quently, only the link segment that is actually faulty
is switched over to standby.

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

1+1 operation:

The traffic is transported simultaneously via the
working path and the protection path. The receiv­ing end then decides which of the two paths is to
be used.

1:1 operation:

The spare path can only be used if a switchover
takes place at both the transmitting end and the
receiving end.

1:N operation:

A 1:N configuration represents a more cost-effect­ive solution than the other two mechanisms de­scribed above. N working channels are protected
by one protection channel. If there are no defects
in the network, this protection channel can be used
to transport low-priority traffic.

Application

Proper interworking of the network elements re­quires 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 protocol
optimized for 1+1 operation. Linear MSP was
specified in Annex A of G.783 which is now included
in the new revised Recommendation G.841.

In Brief

signaling to changes in the signal status or to the
appropriate switching commands from network
management. The ANT-20 makes this test
simple and reliable by interpreting the protocol
elements in plain text. APS commands can also
be generated in the descriptor directly from the
menu, without complicated bit manipulations.
The ANT-20 understands the K1/K2 codes for
linear MSP conforming to ITU-T G.783 as well
as 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 of
the ADMs (add-drop multiplexers). Depending on
the configuration, alarms and bit errors (Test
Sequence Errors, TSE) appear on the tributary
ports for the duration of the switchover
procedure. What customers are interested in is
the interruption time on the tributary and not just
the K1/K2 switchover according to the APS
protocol.

Figure 27:

ANT-20 interpreter

for ring switching

The ANT-20Õs solution is flexible and lets you se­lect different events as your measurement criterion:
 SDH: MS-AIS, AU-AIS, TU-AIS, TSE
 SONET: AIS-L, AIS-P, AIS-V, TSE
The switchover time is specified as 50 ms. The
ANT-20 measures the duration of the event on
the tributary with a resolution of 1 ms, even if the

-

signal has bit error ratios up to 2u10

4

. A second
ANT-20 can be used to generate the APS.
In through mode, the instrument generates

-

the alarm types SF (B2 >1u10

-

(B2 >1u10

6

), and in OOS mode also LOS, LOF,

3

) and SD

MS-AIS (AIS-L). The procedure is as follows:

1. Set the signal structure using the ANT-20Õs

signal structure editor. Start the APS time
measurement.

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 with

the expected value. Result interpretation is
simple: ÒpassedÓ or ÒfailedÓ.

Figure 28: Result from the switch-over measurement

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

APS time
measurement.
Event: AIS, TSE

Figure 29: Measuring switch-over time

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

working channel

protection channel

SOH/TOH
byte capture

Abbreviation list :

ADM Add & Drop Multiplexer
AIS Alarm Indication Signal
APS Automatic Protection Switching
BBE Backround Block Error
BBER Backround Block Error Ratio
BIP Bit Interleaved Parity
BIS Bringing Into Service
CRC Cyclic Redundancy Check
DEMUX Demultiplexer
DXC Digital Cross Connect
ES Errored Second
ESR Errored Second Ratio
EFS Error Free Second
FMTJ Fast Maximum Tolerable Jitter
IG International Gateway
ISM In Service Monitoring
JTF Jitter Transfer Function
HP High Order Path
LOF Loss Of Frame
LP Low Order Path
MS Multiplex Section
MSOH Multiplex Section

Overhead

MSP Multiplex Section

Protection

MST Multiplex Section Termination

Function
MTJ Maximum Tolerable Jitter
MTIE Maximum Time Interval Error
MUX Multiplex
OOS Out of Service
OS Optical Section
PDH Plesiochronous Digital Hierarchy
PEP Path End Point
RDI Remote Defect Indication
PRC Primary Reference Clock
UI Unit Interval
REG Regenerator
RS Regenerator Section
RST Regenerator Section Termination

Function
RSOH Regenerator Section Overhead
SES Severely Errored Second
SESR Severely Errored Second Ratio
SD Signal Degradation
SDH Synchronous Digital Hierarchy
SEC Synchronous Equipment Clock
SF Signal Failure
STM Synchronous Transport Module
TDEV Time Deviation
VC Virtual Container

Author

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

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