SIST ETS 300 417-6-1 E1:2003

SLOVENSKI STANDARD
01-december-2003
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Transmission and Multiplexing (TM); Generic requirements of transport functionality of
equipment; Part 6-1: Synchronization layer functions
Ta slovenski standard je istoveten z: ETS 300 417-6-1 Edition 1
ICS:
33.040.20 Prenosni sistem Transmission systems
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

EUROPEAN ETS 300 417-6-1
TELECOMMUNICATION August 1998
STANDARD
Source: TM Reference: DE/TM-01015-6-1
ICS: 33.020
Key words: transmission, SDH, synchronization
Transmission and Multiplexing (TM);
Generic requirements of transport functionality of equipment;
Part 6-1: Synchronization layer functions
ETSI
European Telecommunications Standards Institute
ETSI Secretariat
Postal address: F-06921 Sophia Antipolis CEDEX - FRANCE
Office address: 650 Route des Lucioles - Sophia Antipolis - Valbonne - FRANCE
Internet: secretariat@etsi.fr - http://www.etsi.fr - http://www.etsi.org
Tel.: +33 4 92 94 42 00 - Fax: +33 4 93 65 47 16
Copyright Notification: No part may be reproduced except as authorized by written permission. The copyright and the
foregoing restriction extend to reproduction in all media.
© European Telecommunications Standards Institute 1998. All rights reserved.

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ETS 300 417-6-1: August 1998
Whilst every care has been taken in the preparation and publication of this document, errors in content,
typographical or otherwise, may occur. If you have comments concerning its accuracy, please write to
"ETSI Standards Making Support Dept." at the address shown on the title page.

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ETS 300 417-6-1: August 1998
Contents
Foreword .7
1 Scope .9
2 Normative references.9
3 Definitions, abbreviations and symbols.10
3.1 Definitions .10
3.2 Abbreviations .11
3.3 Symbols and diagrammatic conventions .12
3.4 Introduction .12
4 Synchronization principles.12
4.1 Network synchronization.12
4.2 Synchronization distribution trails.14
4.3 Synchronization interfaces.14
4.3.1 Synchronous Transport Module, level N (STM-N) .15
4.3.2 2 Mbit/s.15
4.3.3 2 MHz .15
4.3.4 34 Mbit/s and 140 Mbit/s with 125 ms frame structure.15
4.4 Clock-Source Quality-Level .15
4.4.1 Clock-Source Quality- Level Definitions .15
4.4.2 Hierarchy of Clock-Sources Quality Level or (CS_QL) .16
4.4.3 Forcing of Clock-Source Quality-Levels.16
4.5 SSM and TM channels.16
4.5.1 SSM and TM message sets .17
4.5.2 SSM and TM code word generation.17
4.5.3 SSM and TM code word interpretation.18
4.6 Selection process.19
4.7 Signal fail .19
4.8 Hold-off time .20
4.9 WTR time.20
4.10 Synchronization source priorities .20
4.11 External commands (EXTCMD) .21
4.11.1 EXTCMDs per nominated synchronization source.21
4.11.1.1 Set_Lockout#p command.21
4.11.1.2 Clear_Lockout#p command .21
4.11.2 EXTCMDs per selection process .21
4.11.2.1 CLR command.21
4.11.2.2 Forced switch #p command.22
4.11.2.3 Manual switch #p command.22
4.12 Automatic reference selection process.22
4.12.1 QL-enabled mode.22
4.12.2 QL-disabled mode.23
4.13 Timing loop prevention.23
4.13.1 Station clock input used as a source for station clock output.23
4.13.2 Between NEs with SEC type clocks .23
4.13.3 Between NEs with a SEC clock and a NE or SASE with a SSU clock and
only one link.24
4.13.3.1 QL/SSM processing supported between SASE and NE.24
4.13.3.2 QL/SSM processing not supported between SASE and
NE.26
4.13.4 Between NEs with a SEC clock and a NE or SASE with a SSU clock and
several links.28
4.14 Delay times for NEs with SEC .28
4.15 Delay times for NEs with SSU or for SASE .29
4.16 Synchronization layer functions .29

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4.17 Overview of the processes performed within the atomic functions. 30
5 Synchronization distribution layer atomic functions . 31
5.1 SD Connection function (SD_C) . 32
5.2 SD Trail Termination (TT) functions. 33
5.2.1 SD TT source function (SD_TT_So) . 33
5.2.2 SD TT sink function (SD_TT_Sk). 34
5.3 SD adaptation functions . 36
5.3.1 SD layer to NS layer SEC quality adaptation source function (SD/NS-
SEC-A_So) . 36
5.3.2 SD layer to NS layer SEC quality adaptation sink function (SD/NS-
SEC_A_Sk). 39
5.3.3 SD layer to NS layer SSU quality adaptation source function (SD/NS-
SSU-A_So) . 40
5.3.4 SD layer to NS layer SSU quality adaptation sink function (SD/NS-
SSU_A_Sk). 40
5.3.5 SD layer to NS layer PRC quality adaptation source function (SD/NS-
PRC-A_So) . 40
5.3.6 SD layer to NS layer adaptation source function (SD/NS_A_So). 40
6 NS layer atomic functions. 41
6.1 NS_connection functions (NS_C) . 42
7 TL to SD layer atomic function. 44
7.1 STM-1 multiplex section adaptation functions. 44
7.1.1 STM-1 multiplex section to sd adaptation source (MS1/SD_A_So) . 44
7.1.2 STM-1 multiplex section to SD adaptation sink (MS1/SD_A_Sk). 45
7.2 STM-4 multiplex section adaptation functions. 46
7.2.1 STM-4 multiplex section to SD adaptation source (MS4/SD_A_So) . 46
7.2.2 STM-4 multiplex section to SD adaptation sink (MS4/SD_A_Sk). 48
7.3 STM-16 multiplex section adaptation functions. 49
7.3.1 STM-16 multiplex section to SD adaptation source (MS16/SD_A_So) . 49
7.3.2 STM-16 multiplex section to SD adaptation sink (MS16/SD_A_Sk). 50
7.4 P31s adaptation functions. 51
7.4.1 P31s to SD adaptation source (P31s/SD_A_So). 51
7.4.2 P31s to SD adaptation sink (P31s/SD_A_Sk) . 53
7.5 P4s adaptation functions. 55
7.5.1 P4s to SD adaptation source (P4s/SD_A_So). 55
7.5.2 P4s to SD adaptation sink (P4s/SD_A_Sk) . 57
7.6 P12s layer adaptation functions . 58
7.6.1 P12s layer adaptation source functions. 58
7.6.1.1 Type 1 P12s to SD adaptation source for station clock
output supporting SSM (P12s/SD-sc-1_A_So) . 58
7.6.1.2 Type 2 P12s to SD adaptation source for station clock
output port not supporting SSM (P12s/SD-sc-2_A_So). 60
7.6.2 P12s layer adaptation sink functions . 61
7.6.2.1 Type 1 P12s to SD adaptation sink for traffic input port
(P12s/SD-tf_A_Sk). 62
7.6.2.2 Type 2 P12s to SD adaptation sink for station clock input
port (P12s/SD-sc_A_Sk). 63
7.7 T12 layer adaptation functions . 64
7.7.1 T12 to SD adaptation source (T12/SD_A_So) . 64
7.7.2 T12 to SD adaptation sink (T12/SD_A_Sk). 66
8 Equipment clock to TLs clock adaptation functions. 67
8.1 STM-N layer . 67
8.1.1 STM-1 Layer Clock (LC) adaptation source (MS1-LC_A_So). 67
8.1.2 STM-4 LC adaptation source (MS4-LC_A_So) . 68
8.1.3 STM-16 LC adaptation source (MS16-LC_A_So) . 69
8.2 VC layers. 70
8.2.1 VC-4 LC adaptation source (S4-LC_A_So). 70
8.2.2 VC-3 LC adaptation source (S3-LC_A_So). 71
8.2.3 VC-2 LC adaptation source (S2-LC_A_So). 72

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ETS 300 417-6-1: August 1998
8.2.4 VC-12 LC adaptation source (S12-LC_A_So).73
8.2.5 VC-11 LC adaptation source (S11-LC_A_So).74
8.3 Pxx layers .75
8.3.1 P4s LC adaptation source (P4s-LC_A_So).75
8.3.2 P31s LC adaptation source (P31s-LC_A_So).76
8.3.3 P12s LC adaptation source (P12s-LC_A_So).77
8.4 T12 layer .78
8.4.1 T12 LC adaptation source (T12-LC_A_So).78
Annex A (normative): Synchronization selection process .79
Annex B (informative): TL models for synchronization information.90
Annex C (informative): Examples of synchronization functionality in the NE .93
Annex D (informative): Delay time allocation .96
D.1 Delay and processing times for the synchronization selection process .96
D.2 Non switching message delay T .97
NSM
D.3 Switching message delay T .97
SM
D.4 Holdover message delay T .98
HM
D.5 Wait to restore time T .99
WTR
Annex E (informative): Overview of inputs/outputs to the atomic functions.100
History.101

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Foreword
This European Telecommunication Standard (ETS) has been produced by the Transmission and
Multiplexing (TM) Technical Committee of the European Telecommunications Standards Institute (ETSI).
This ETS has been produced in order to provide inter-vendor and inter-operator compatibility of
Synchronous Digital Hierarchy (SDH) equipment.
This ETS consists of 8 parts as follows:
Part 1: "Generic processes and performance" (ETS 300 417-1-1 [1]);
Part 2: "SDH and PDH physical section layer functions" (ETS 300 417-2-1 [6]);
Part 3: "STM-N regenerator and multiplex section layer functions" (ETS 300 417-3-1 [7]);
Part 4: "SDH path layer functions" (ETS 300 417-4-1 [8]);
Part 5: "PDH path layer functions" (ETS 300 417-5-1 [9]);
Part 6: "Synchronization layer functions" (ETS 300 417-6-1);
Part 7: "Auxiliary layer functions" (ETS 300 417-7-1);
Part 8: "Compound and major compound functions" (ETS 300 417-8-1).
Transposition dates
Date of adoption of this ETS: 24 July 1998
Date of latest announcement of this ETS (doa): 30 November 1998
Date of latest publication of new National Standard
or endorsement of this ETS (dop/e): 31 May 1999
Date of withdrawal of any conflicting National Standard (dow): 31 May 1999

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1 Scope
This ETS specifies a library of basic Synchronization Distribution (SD) building blocks, referred to as
"atomic functions" and a set of rules by which they are combined in order to describe a digital transmission
equipment. The library defined in this ETS forms part of the set of libraries defined in ETS 300 417 series.
The library comprises the functional building blocks needed to completely specify the generic functional
structure of the European digital transmission hierarchy. Equipment that is compliant with this ETS should
be describable as an interconnection of a subset of these functional blocks contained within this ETS. The
interconnection of these blocks should obey the combination rules given in ETS 300 417. The generic
functionality is described in ETS 300 417-1-1 [1].
This ETS assumes that there are only two types of Synchronization Supply Units (SSUs), transit and local,
as currently defined in ITU-T Recommendation G.812 [18]. However, STC TM3 has approved in
September 1996 a new SSU with enhanced characteristics. The inclusion of such an SSU in this ETS is
for further study.
This ETS does not specify the atomic functions that are specific to SSU and Primary Reference Clock
(PRC); the Synchronization Status Message (SSM) selection algorithm specified in the present document
applies only to SEC’s.
2 Normative references
This ETS incorporates by dated or undated reference, provisions from other publications. These
normative references are cited at the appropriate places in the text and the publications are listed
hereafter. For dated references subsequent amendments to, or revisions of, any of these publications
apply to this ETS only when incorporated in it by amendments or revisions. For undated references the
latest edition of the publication referred to applies.
[1] ETS 300 417-1-1 (1996): "Transmission and Multiplexing (TM); Generic
functional requirements for Synchronous Digital Hierarchy (SDH) equipment;
Part 1-1: Generic processes and performance".
[2] ETS 300 147: "Transmission and Multiplexing (TM); Synchronous Digital
Hierarchy (SDH); Multiplexing structure".
[3] ETS 300 166 (1993): "Transmission and Multiplexing (TM); Physical and
electrical characteristics of hierarchical digital interfaces for equipment using the
2 048 kbit/s - based plesiochronous or synchronous digital hierarchies".
[4] ITU-T Recommendation G.707 (1996): "Network node interface for the
synchronous digital hierarchy (SDH)".
[5] ITU-T Recommendation G.783: "Characteristics of synchronous digital hierarchy
(SDH) equipment functional blocks".
[6] ETS 300 417-2-1: "Transmission and Multiplexing (TM); Generic requirements
of transport functionality of equipment; Part 2-1: Synchronous Digital Hierarchy
(SDH) and Plesiochronous Digital Hierarchy (PDH) physical section layer
functions".
[7] ETS 300 417-3-1: "Transmission and Multiplexing (TM); Generic requirements
of transport functionality of equipment; Part 3-1: Synchronous Transport
Module-N (STM-N) regenerator and multiplex section layer functions".
[8] ETS 300 417-4-1: "Transmission and Multiplexing (TM); Generic requirements
of transport functionality of equipment; Part 4-1: Synchronous Digital Hierarchy
(SDH) path layer functions".
[9] ETS 300 417-5-1: "Transmission and Multiplexing (TM); Generic requirements
of transport functionality of equipment; Part 5-1: Plesiochronous Digital
Hierarchy (PDH) path layer functions".

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ETS 300 417-6-1: August 1998
[10] ETS 300 462-2: "Transmission and Multiplexing (TM); Generic requirements for
synchronization networks; Part 2: Synchronization network architecture".
[11] ETS 300 462-4: "Transmission and Multiplexing (TM); Generic requirements for
synchronization networks; Part 4: Timing characteristics of slave clocks suitable
for synchronization supply to Synchronous Digital Hierarchy (SDH) and
Plesiochronous Digital Hierarchy (PDH) equipment".
[12] ETS 300 462-5: "Transmission and Multiplexing (TM); Generic requirements for
synchronization networks; Part 5: Timing characteristics of slave clocks suitable
for operation in Synchronous Digital Hierarchy (SDH) equipment".
[13] ETS 300 462-6: "Transmission and Multiplexing (TM); Generic requirements for
synchronization networks; Part 6: Timing characteristics of primary reference
clocks".
[14] ITU-T Recommendation G.704 (1995): "Synchronous frame structures used at
1 544, 6 312, 2 048, 8 488 and 44 736 kbit/s hierarchical levels".
[15] ETS 300 337 (1996): "Transmission and Multiplexing (TM); Generic frame
structures for the transport of various signals (including Asynchronous Transfer
Mode (ATM) cells and Synchronous Digital Hierarchy (SDH) elements) at the
ITU-T Recommendation G.702 hierarchical rates of 2 048 kbit/s, 34 368 kbit/s
and 139 264 kbit/s".
[16] ETS 300 337 (1995): "Transmission and Multiplexing (TM); Generic frame
structures for the transport of various signals (including Asynchronous Transfer
Mode (ATM) cells and Synchronous Digital Hierarchy (SDH) elements) at the
ITU-T Recommendation G.702 hierarchical rates of 2 048 kbit/s, 34 368 kbit/s
and 139 264 kbit/s".
[17] ITU-T Recommendation G.811 (1988): "Timing requirements at the outputs of
primary reference clocks suitable for plesiochronous operation of international
digital links".
[18] ITU-T Recommendation G.812 (1988.): "Timing requirements at the outputs of
slave clocks suitable for plesiochronous operation of international digital links".
[19] ITU-T Recommendation G.813 (1996): "Timing characteristics of SDH
equipment slave clocks (SEC)".
[20] ETS 300 167: "Transmission and Multiplexing (TM); Functional characteristics of
2 048 kbit/s interfaces".
[21] ETS 300 462-1: "Transmission and Multiplexing (TM); Generic requirements for
synchronization networks; Part 1: Definitions and terminology for
synchronization networks".
3 Definitions, abbreviations and symbols
3.1 Definitions
For the purposes of this ETS, the following definition applies:
timing loop: This is a network condition where a slave clock providing synchronization becomes locked to
its own timing signal. It is generally created when the slave clock Timing Information (TI) is looped back to
its own input, either directly or via other network equipments. Timing loops should be prevented in
networks by careful network design.
QL minimum: QL_minimum is a configurable parameter used in the squelching of clock output signals. If
the Quality Level (QL) of the signal used to derive the output falls below QL_Minimum then the output will
be squelched (cut-off or set to Alarm Indication Signal (AIS)).

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ETS 300 417-6-1: August 1998
Clock-Source Quality-Level: The clock-source quality-level of a SDH Equipment Clock (SEC) or Stand
Alone Synchronization Equipment (SASE) is defined as the grade of clock to which it is ultimately
traceable; i.e. the grade-of-clock to which it is synchronized directly or indirectly via a chain of SEC’s, and
SASE’s however long this chain of clocks is. For example, the clock-source quality-level may be a PRC
complying with ETS 300 462-6 [13], or it may be a Slave Clock in holdover-mode, complying with
ETS 300 462-4 [11], or a ETS 300 462-5 [12] Clock in holdover or free-run.
The clock-source quality-level is essentially, therefore, an indication only of the long-term accuracy of the
Network Element (NE) Clock.
Station Clock: This is a node clock as defined in ETS 300 462-1 [21].
The functional definitions are given in ETS 300 417-1-1 [1].
3.2 Abbreviations
For the purposes of this ETS, the following abbreviations apply:
AI Adaptation Information
AIS Alarm Indication Signal
AP Access Point
CI Characteristic Information
CK timing information - Clock signal
CLR Clear
CP Connection Point
CS timing information - Clock Source
CSid Clock Source identifier
DNU Do Not Use
ES1 STM-1 Electrical Section layer
EXTCMD External Command
FS timing information - Frame Start
FSw Forced Switch
HO Hold Over mode
HO Hold Off time
ID IDentifier
INVx INValid x
LC Layer Clock
LO Lock Out
LO Locked mode
LOS Loss Of Signal
LSB Least Significant Bit
LTI Loss of Timing Information
MA Maintenance and Adaptation
MI Management Information
MON MONitored
MFP MultiFrame Present
MFS MultiFrame Start
MS Multiplex Section
MSB Most Significant Bit
MSw Manual Switch
MTIE Maximum Time Interval Error
NE Network Element
NS Network Synchronization
NSUPP Not supported
OSn STM-N Optical Section layer
P12s 2 048 kbit/s PDH path layer with synchronous 125 ms frame structure according
to ETS 300 167 [20]
P31s 34 368 kbit/s PDH path layer with synchronous 125 ms frame structure
according to ETS 300 337 [15]
P4s 139 264 kbit/s PDH path layer with synchronous 125 ms frame structure
according to ETS 300 337 [15]
PDH Plesiochronous Digital Hierarchy
PRC Primary Reference Clock
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QL Quality Level
RI Remote Information
RSn STM-N Regenerator Section layer
SASE Stand Alone Synchronization Equipment
SD Synchronization Distribution
SDH Synchronous Digital Hierarchy
SDL Specification and Description Language
SEC SDH Equipment Clock
SF Signal Fail
SQLCH Squelch
SSF Server Signal Fail
SSM Synchronization Status Message
SSU Synchronization Supply Unit
SSUL Local SSU
SSUT Transit SSU
STM-N Synchronous Transport Module, level N
Sk Sink
So Source
TCP Termination Connection Point
TDEV Time DEViation
TI Timing Information
TL Transport Layer
TM Timing Marker
TT Trail Termination
TSF Trail Signal Fail
UNC UNConnected
VC-n Virtual Container, level n
WTR Wait to Restore
3.3 Symbols and diagrammatic conventions
The symbols and diagrammatic conventions are given in ETS 300 417-1-1 [1].
3.4 Introduction
This subclause defines the atomic functions that are part of the 2 synchronization layers, the SD layer and
the Network Synchronization (NS) layer. It also defines some atomic functions, part of the Transport Layer
(TL), which are related with synchronization.
These functions describe the synchronization of SDH NEs and how SDH NEs are involved in NS.
4 Synchronization principles
4.1 Network synchronization
Synchronization network architecture is specified in ETS 300 462-2 [10].
Synchronization information is transmitted through the network via synchronization network connections.
These synchronization network connections can transport different synchronization levels. Each
synchronization network connection is provided by one or more synchronization link connections, each
supported by a synchronized primary or secondary rate Plesiochronous Digital Hierarchy (PDH) trail or
SDH multiplex section trail (see clause 5 of ETS 300 462-2 [10]).
Some of these synchronized primary or secondary rate PDH trail or SDH multiplex section trail signals
contain a communication channel, the SSM or the Timing Marker (TM) transporting a quality Identifier
(ID). This QL ID can be used to select the highest synchronization level incoming reference signal from a
set of nominated synchronization references available at the NE.
Synchronization network connections are uni-directional and generally point to multipoint.
ETS 300 462-2 [10] specifies a master-slave synchronization technique for synchronizing SDH networks
(see subclause 4.1 of ETS 300 462-2 [10]). Figures 1 to 4 illustrate the synchronization network
connection model.
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ETS 300 417-6-1: August 1998
PRC level
SSU level
SEC level
Figure 1: General representation of a synchronization network
PRC synchronization network connection
Figure 2: Representation of the PRC network connection
fault
PRC synchronization network connection
SSU synchronization network connection
SEC synchronization network connection
Figure 3: Representation of the synchronization network connection in case of failure
fault
PRC synchronization network connection
SSU synchronization network connection
Figure 4: Example of restoration of the synchronization (see figure 7 of ETS 300 462-2 [10])

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4.2 Synchronization distribution trails
SD trails transport timing between two adjacent equipments.
From a synchronization view point, adjacent NEs are those NEs that are interconnected via section
signals. Between two such adjacent NEs a uni-directional SD trail exists.
A SD trail starts at the input of the SD_TT_So function and ends at the output of the SD_TT_Sk function.
A SD link connection transports synchronization TI between two adjacent Connection Points (CP) of the
NS_C function.
A NS network connection transports synchronization TI over a series of synchronization link connection.
NE 1 NE 2 NE 3 NE 4
NS network connection
NS NS NS
NS link conn 2-3 NS link conn 3-4
PRC
SD trail 2-3 SD trail 3-4
SD trail 1-2
SD SD SD SD SD SD SD
SD SD SD SD
transport
layers
SD link conn 1-2 SD link conn 2-3 SD link conn 3-4
Figure 5: Example of series of SD network connection transporting PRC quality timing
reference information
4.3 Synchronization interfaces
Synchronization trails can be carried through the network by a number of interfaces. Currently, the
following signals are defined for such transport (refer also to figures B.1 to B.4):
- without traffic:
- 2 048 kHz (T12);
- 2 048 kbit/s (E12+P12s);
- with traffic:
- 2 488 320 kbit/s (OS16+RS16+MS16);
- 622 080 kbit/s (OS4+RS4+MS4);
- 155 520 kbit/s (OS1 (or ES1)+RS1+MS1);
- 139 264 kbit/s (E4+P4s);
- 34 368 kbit/s (E31+P31s);
- 2 048 kbit/s (E12+P12s).
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4.3.1 Synchronous Transport Module, level N (STM-N)
The STM-N transport signals carry (in addition to the payload) reference TI and an indication of the QL of
the source generating this TI, via the SSM as defined in ETS 300 147 [2].
NOTE: Old equipment may not be able to support SSM via their STM-N interfaces.
4.3.2 2 Mbit/s
The 2 Mbit/s transport signals may carry (in addition to the payload) reference TI.
The 2 Mbit/s timing reference signals (without payload) carry reference TI to specific synchronization
ports.
Both signals can carry an indication of the QL of the source generating the TI via the SSM as specified in
ITU-T Recommendation G.704 [14].
NOTE: Old equipment may not be able to support SSM on their 2 Mbit/s interfaces.
4.3.3 2 MHz
Synchronization can be carried through 2 MHz signals to specific synchronization ports (so called station
clock ports). This signal does not carry an indication of the QL of the source generating the TI.
4.3.4 34 Mbit/s and 140 Mbit/s with 125 ms frame structure
34 Mbit/s and 140 Mbit/s signals with 125 ms frame structure as defined in ETS 300 337 [15] carry a full
4 bit SSM code.
NOTE: For interworking with equipments compliant with the initial edition of ETS 300 337 [15],
new equipments should be able to be configured to recognize and generate the TM
which is located in bit 8 of the Maintenance and Adaptation (MA) byte: the TM is set to
"0" to indicate that the timing source is traceable to a PRC, and is otherwise set to "1".
4.4 Clock-Source Quality-Level
4.4.1 Clock-Source Quality- Level Definitions
The following Clock Source (CS) QLs are defined in the synchronization process of SDH network
corresponding to 4 levels of synchronization quality (ETS 300 462-2 [10]).
QL-PRC: This synchronization trail transports a timing quality generated by a PRC that is
defined in ETS 300 462-6 [13].
QL-SSU T: This synchronization trail transports a timing quality generated by either a transit
slave clock that is defined in ITU-T Recommendation G.812 [18] or a SSU that is
defined in ETS 300 462-4 [11].
QL-SSU L: This synchronization trail transports a timing quality generated by a local
slave clock that is defined in ITU-T Recommendation G.812 [18].
QL-SEC: This synchronization trail transports a timing quality generated by a SEC that is
defined in ETS 300 462-5 [12].
QL-DNU: This signal should not be used for synchronization.
NOTE: The QL-unknown QL was defined to characterize the quality of existing network. This
QL is no longer supported by the SSM algorithm.

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4.4.2 Hierarchy of Clock-Sources Quality Level or (CS_QL)
The following table defines the QL hierarchy.
Table 1: Hierarchy of quality levels
Quality Level (QL) Order
QL-PRC highest
QL-SSU T |
QL-SSU L |
QL-SEC |
QL-DNU |
QL-INVx, -FAILED, -UNC, -NSUPP lowest
The QLs QL-INVx, QL-FAILED, QL- UNC and QL-NSUPP are internal QLs inside the NE and are never
generated at an output port.
QL-INVx is generated by the XX/SD_A_Sk function if an unallocated SSM value is received, where x
represents the binary value of this SSM.
QL-NSUPP is generated by the XX/SD_A_Sk function when the function is not supporting the SSM TM
processing.
QL-FAILED is generated by the SD_TT_Sk function when the terminated SD trail is in the Signal Fail (SF)
state.
QL-UNC is generated by the SD_C or NS_C function when the output signal is not connected to an input,
but instead to the internal unconnected signal generator.
4.4.3 Forcing of Clock-Source Quality-Levels
For synchronization source signals/interfaces not supporting SSM transport/processing, it is possible to
force the QL to a fixed provisioned value. This allows to use these signals/interfaces as synchronization
sources in an automatic reference selection process operating in QL-enabled mode.
Forcing of QLs is used for new equipment operating in QL-enabled mode in order to:
- interwork with old equipment not supporting SSM/TM generation;
- interwork with new equipment operating in QL-disabled mode;
- select interfaces not supporting SSM/TM processing;
- select signals for which SSM/TM is not defined in (2 MHz).
4.5 SSM and TM channels
The following signals have a four bit SSM channel defined:
- STM-N (N = 1, 4, 16): bits 5 to 8 of the byte S1 (called SSMB, SSM Byte) of the multiplex section
overhead as defined in ITU-T Recommendation G.707 [4].
- 2 Mbit/s octet structured according to ITU-T Recommendation G.704 [14]: bits S to S
ax1 ax4
(x = 4, 5, 6, 7, or 8) of TS0.
- 34 Mbit/s as defined in ETS 300 337 [15]: bit 8 of MA byte with a 4 frame multiframe.
- 140 Mbit/s as defined in ETS 300 337 [15]: bit 8 of MA byte with a 4 frame multiframe.

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ETS 300 417-6-1: August 1998
The following signals may have a one bit TM channel:
- 34 Mbit/s with a 125 ms frame structure as defined in ETS 300 337 [16]: bit 8 of byte MA.
- 140 Mbit/s with a 125 ms frame structure as defined in ETS 300 337 [16]: bit 8 of byte MA.
4.5.1 SSM and TM message sets
Five SSM codes are defined to represent CS QL as listed below:
- code 0010 (Quality PRC) means that the source of the trail is a PRC clock (ETS 300 462-6 [13],
ITU-T Recommendation G.811 [17]);
- code 0100 (Quality SSU-T), means that the source of the trail is a transit SSU clock
(ITU-T Recommendation G.812-T [18]) or a SSU that is defined in ETS 300 462-4 [11];
- code 1000 (Quality SSU-L), means that the source of the trail is a SSU clock
(ITU-T Recommendation G.812-L [18]);
- code 1011 (Quality SEC), means that the source of the trail is a SEC clock (ETS 300 462-5 [12],
option 1 of ITU-T Recommendation G.813 [19]);
- code 1111 (quality DNU), means that the signal carrying this SSM shall not be used for
synchronization because a timing loop situation could result if it is used.
Two TM codes were defined in ETS 300 337 [15] and [16]:
- code 0 (Quality PRC), means that the source of the trail is a PRC clock (ETS 300 462-6 [13],
ITU-T Recommendation G.811 [17]);
- code 1 (Quality less_than_PRC), means that the source of the trail is not a PRC clock.
4.5.2 SSM and TM code word generation
The SSM can be viewed as an application specific data communication channel with a limited message
set. The message that shall be generated and inserted depends on the applied QL indication that is input
to the adaptation source function. The following table presents the relation between the existing set of QLs
and SSM codes.
Table 2: Quality level set and coding in SSM
Quality Level (QL) SSM usage SSM coding [MSB.LSB]
QL-PRC enabled 0010
QL-SSUT enabled 0100
QL-SSUL enabled 1000
QL-SEC enabled 1011
QL-DNU enabled 1111
- disabled 1111
The TM can be viewed as an application specific data communication channel with a limited message set.
The message that shall be generated and inserted depends on the applied QL indication that is input to
the adaptation source function. The following table presents the relation between the existing set of QLs
and TM codes.
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ETS 300 417-6-1: August 1998
Table 3: Quality level set and coding in TM
Quality Level (QL) TM usage TM coding
QL-PRC enabled 0
QL-SSUT enabled 1
QL-SSUL enabled 1
QL-SEC enabled 1
QL-DNU enabled 1
- disabled 1
At network boundaries, it should be possible to prevent synchronization information passing the interface.
This can be achieved by disabling the SSM (TM) usage.
4.5.3 SSM and TM code word interpretation
At the receive side, the received SSM bits are to be validated by a persistency check and then interpreted
to determine the QL.
Table 4: Interpretation of SSM codes
SSM code [MSB.LSB] QL interpretation
0000 QL-INV0
0001 QL-INV1
0010 QL-PRC
0011 QL-INV3
0100 QL-SSUT
0101 QL-INV5
0110 QL-INV6
0111 QL-INV7
1000 QL-SSUL
1001 QL-INV9
1010 QL-INV10
1011 QL-SEC
1100 QL-INV12
1101 QL-INV13
1110 QL-INV14
1111 QL-DNU
Table 5: Interpretation of TM codes
TM code QL interpretation
0 QL-PRC
1 QL-DNU
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ETS 300 417-6-1: August 1998
4.6 Selection process
The process of selecting a synchronization source from the set of physical ports is performed in three
steps.
nominated
automatic selected
assigned
automatic selected
physical
sync sources
synchronization
synchronization
synchronization
ports
selection process 1 source
sources
source
for station
clock output
(e.g. for internal
4 clock)
6 8
: 13
: 1
: 8
N 13
(e.g. for station
clock output)
nominated
sync sources
selection process 2
Figure 6: Visualization of the synchronization source selection process(es)
1) Assignment of a physical port to be a synchronization source: Select a (limited) set of interface
signals (from the total set of interfaces) to act as synchronization sources.
This is performed in the SD_C function by means of adding matrix connections between a group of
inputs (connected to the server layer) and outputs (connected to the SD_TT_Sk functions).
2) Nomination of a synchronization source for an automatic selection process: Select a (sub)set of the
synchronization sources to contribute to a selection process.
This is performed in the NS_C function by means of assigning a priority to the synchronization
source (see subclause 4.10).
3) Automatic Selection Process. Selects the "best" synchronization source of the set from nominated
sources according to the selection algorithm (see subclause 4.12).
NOTE: The specifications in this ETS allow a selection to be made between any set of
synchronization interface signals input to a NE, independent of the actual
synchronization network architecture deployed in the network. It is the network
operator’s responsibility to ensure that timing loops are not created.
4.7 Signal fail
SF for a synchronization source is activated in case of defects detected in the server layers. In addition an
unconnected synchronization signal has also SF active in order to allow correct processing in the QL
disabled mode. Inclusion of specific synchronization failures (e.g. exceeded frequency deviation,
exceeded wander limits) as SF criteria for SSU are for further study.
In order to avoid reactions on short pulses or intermittent SF information, the SF information is passed
through a hold-off and Wait to Restore (WTR) processes before it is considered by the selection process.
NOTE 1: The delay of the SF information is only performed for the information passed to the
selection process. The SF information for the main data path to the output of the NS_C
function is not delayed.
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ETS 300 417-6-1: August 1998
In QL enabled mode the QL of a synchronization source with active SF is set to QL-FAILED. The selection
process will react to this QL value instead of the SF signal in this mode.
NOTE 2: Due to different persistence times for defect detection and the SSM acceptance
process, a defect leading to SF could also result in a change of the QL value shortly
before SF is activated. The implementation has to ensure that the selection process
does not select a new synchronization source based on this intermediate QL value.
4.8 Hold-off time
The hold-off time ensures that short activation of SF are not passed to the selection process.
In QL-disabled mode SF shall be active for the hold-off time before it is passed to the selection process.
In QL-enabled mode a QL value of QL-FAILED shall exist for the hold-off time before it is passed to the
selection process. In the mean time the previous QL value is passed to the selection process.
NOTE: Other QL values than QL-FAILED will be passed to the selection process immediately.
Separate hold-off timers are used for each input to a selection process (nominated source).
The hold-off time is fixed in the range of 300 ms to 1 800 ms.
4.9 WTR time
The WTR time ensures that a previous failed synchronization source is only again considered as available
by the selection process if it is fault free for a certain time.
In QL-disabled mode after deactivation of SF, it shall be false for the WTR time before SF false is passed
to the selection process. In the mean time SF true is passed to the selection process.
In QL-enabled mode after a change of the QL from QL-FAILED to any other value, the quality value s
...