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

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


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.

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ITU-T G.8261/Y.1361

ITU-T G.8261/Y.1361 pdf

This Recommendation defines synchronization aspects in packet networks. It specifies the
maximum network limits of jitter and wander that shall not be exceeded. It specifies the minimum
equipment tolerance to jitter and wander that shall be provided at the boundary of these packet
networks at TDM interfaces. It also outlines the minimum requirements for the synchronization
function of network elements.

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ITU-T G.825

ITU-T  G.825 pdf

The scope of this ITU-T 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-network interfaces (NNI).
SDH network interfaces, to which this ITU-T Recommendation is applicable, are defined in terms of bit rates and frame structures in ITU-T Recommendation G.707; their electrical characteristics are described in ITU-T Recommendation G.703 and the optical characteristics in ITU-T Recommendations G.957 and G.691.
Additional information regarding the architecture of SDH networks is found in ITU-T Recommendation G.803.
Jitter and wander requirements for PDH and synchronization networks are specified in ITU-T Recommendation G.823, for networks based on the first level bit rate of 2048 kbit/s, and in ITU-T
Recommendation G.824 for networks based on the first-level bit rate of 1544 kbit/s.

The jitter and wander control philosophy is based on the need:
–- to recommend a maximum network limit that should not be exceeded at any relevant
interface;
– -to recommend a consistent framework for the specification of individual digital equipment
(i.e. jitter and wander transfer, tolerance and generation requirements);
–- to provide sufficient information and guidelines for organizations to measure and study jitter
and wander accumulation in any network configuration.

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ITU-T G.823

ITU-T G.823 PDF

The control of jitter and wander within digital networks which are based on the 2048 kbit/s hierarchy.

This ITU-T Recommendation specifies the relevant parameters and their limiting values that are able
to satisfactorily control the amount of jitter and wander present at Network Node Interfaces (NNI) of
Plesiochronous Digital Hierarchy (PDH) and synchronization networks which are based on the firstlevel
hierarchical bit rate of 2048 kbit/s.
This ITU-T Recommendation also specifies the jitter and wander requirements at PDH
User-Network Interfaces (UNI). However, particular terminals or services may have additional jitter
and wander requirements and in those cases the relevant ITU-T Recommendations shall apply.
Requirements for NNI of PDH and synchronization networks which are based on the first-level
hierarchical bit rate of 1544 kbit/s are specified in ITU-T Recommendation G.824 and requirements
for Synchronous Digital Hierarchy (SDH) NNI are specified in ITU-T Recommendation G.825.
The jitter and wander requirements specified in this ITU-T Recommendation are applicable to the
interfaces irrespective of the underlying transport mechanism (PDH, SDH or ATM networks, for
example).
The jitter and wander requirements for an interface will be different, depending on whether the
signal at the interface is used to transport traffic and/or synchronization. The requirements for both
traffic and synchronization interfaces are specified in this ITU-T Recommendation in the appropriate
clauses.
A synchronization network that conforms to the network limits for jitter and wander specified in this
ITU-T Recommendation will be suitable for the synchronization of SDH and Public Switched
Telephone Network (PSTN) networks.
This ITU-T Recommendation also specifies the jitter and wander requirements for interfaces using
the generic frame structures at PDH rates as defined in ITU-T Recommendation G.832.
The electrical characteristics of the relevant PDH network interfaces are defined in ITU-T
Recommendation G.703.
The jitter and wander control philosophy of this ITU-T Recommendation is based on the need:
a) to specify a maximum network limit of jitter and wander that shall not be exceeded at any
relevant interface;
b) to specify a minimum equipment tolerance to jitter and wander that shall be provided at any
relevant interface;
c) to establish a consistent framework for the specification of individual digital equipment
types; and
d) to provide sufficient information and guidelines for organizations to measure and study jitter
and wander characteristics in any network configuration.

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ITU-T G.813

ITU-T G.813 pdf

This Recommendation outlines requirements for timing devices used in synchronizing network
equipment that operate according to the principles governed by the Synchronous Digital Hierarchy
(SDH). These requirements apply under the normal environmental conditions specified for the SDH
equipment. In normal operation, SDH equipment contains a slave clock traceable to a primary
reference clock. In general, the SDH equipment clock (SEC) will have multiple reference inputs. In
the event that all links between the master and the slave clock fail, the equipment should be capable
of maintaining operation (holdover) within prescribed performance limits.
The SEC is part of the SDH equipment, the functions of which are specified in ITU-T Rec. G.783
as the Synchronous Equipment Timing Source (SETS). Slave clocks used in SDH equipment must
meet specific requirements in order to comply with network jitter requirements for plesiochronous
tributaries.
This Recommendation contains two options for the SEC. The first option, referred to as "Option 1,"
applies to SDH networks optimized for the 2048 kbit/s hierarchy. These networks allow the
worst-case synchronization reference chain as specified in Figure 8-5/G.803. The second option,
referred to as "Option 2," applies to SDH networks optimized for the particular 1544 kbit/s
hierarchy that includes the rates 1544 kbit/s, 6312 kbit/s, and 44 736 kbit/s. The synchronization
reference chain for these networks is defined in Appendix II.
An SDH equipment slave clock should comply with all of the requirements specific to one option
and should not mix requirements between Options 1 and 2. In the clauses where one requirement is
specified, the requirements are common to both options. It is the intention that Options 1 and 2
should be harmonized in the future.
Careful consideration should be taken when interworking between networks with SECs based on
Option 1 and networks with SECs based on Option 2.
This Recommendation defines the minimum requirements for clocks in SDH NEs. However, some
SDH NEs may have a higher quality clock. This Recommendation allows for proper network
operation when a SEC (Option 1 or 2) is timed from another SEC (like option), or a higher quality
clock. Hierarchical timing distribution is recommended for SDH networks. Timing should not be
passed from a SEC in free-run/holdover mode to a higher quality clock since the higher quality
clock should not follow the SEC signal during fault conditions.

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ITU-T G.812

ITU-T G.812 pdf

Timing requirements of slave clocks suitable for use as node clocks in synchronization networks

This Recommendation outlines minimum requirements for timing devices used as node clocks in synchronization networks. The function of a node clock is to select one of the external synchronization links coming into a telecommunications station as the active synchronization reference, to attenuate its jitter and wander and subsequently to distribute the reference to the telecommunication equipment in the station. The requirements in this Recommendation apply under the normal environmental conditions specified for telecommunications equipment.

This Recommendation specifies node clocks suitable for use in SDH and PSTN network applications. They may provide acceptable performance for other applications, but that has to be investigated for each case individually.In normal operation, a node clock is operating as a slave clock, traceable to a primary reference clock. For purposes of redundancy, a node clock will in general have multiple reference inputs. In the event that all links between the master(s) and the node clock fail, the node clock should be capable of maintaining operation within prescribed performance limits (the hold-over mode of operation).

A node clock can be a separate piece of equipment called a Stand Alone Synchronization Equipment (SASE) or it can be a part of another equipment such as a telephony exchange or an SDH cross-connect.

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ITU-T G.803

 ITU-T G.803 pdf


Architecture of transport networks based on the synchronous digital hierarchy (SDH)-This ITU-T Recommendation describes the functional architecture of transport networks including
network synchronization principles for networks that are based on the SDH. This ITU-T
Recommendation uses the architectural description defined in ITU-T Recommendation G.805, the
generic functional architecture of transport networks. The application of various mappings is also
included.

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Testing Sync-E Wander to ITU-T G.8262

Testing Sync-E Wander to ITU-T G.8262 pdf

This document outlines the test process for testing Wander of FE and 1GbE SyncE network elements to
G.8262 using the Calnex Paragon Sync.
Covered in this document is;
1. Wander Generation – G.8262 Section 8
2. Wander Tolerance – G.8262 Section 9
3. Wander Transfer – G.8262 Section 10

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SDH_Pocket_Guide

sdh_Pocket_Guide PDF

Contents
-Introduction 1
-What is the situation in the ªsynchronousº market? 4
-Why SDH? 6
-The synchronous digital hierarchie in terms of a layer model 10
-What are the components of a synchronous network? 12
-The STM-1 frame format 16
-How are PDH and ATM signals transported by SDH? 20
-What is the difference between SDH and SONET? 23
-Pointer procedures 26
-AU-4 contiguous concatenation 30
-AU-4 virtual concatenation 32
-Transmission at higher hierarchy levels 33
-Error and alarm monitoring 34
-Automatic protection switching 39
-Synchronization 44
-TMN in the SDH network 47
-SDH measurement tasks 50
-Sensor tests 52
--APS time measurement 53
Performance analysis 55
-Tandem Connection Monitoring 58
-Jitter measurements 59
-Overview of current ITU-T Recommendations 64
-Abbreviations 67

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