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Fiber OpticsKnowledge SharingIsaac Mwesigwa

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Synchronous Digital Hierarchy (SDH)

• Introduction• SDH advantages• Bit Rates• Standard Frame representation• Frame structure• SDH Multiplexing• Concatenation• Architecture• SDH Equipment• Network topologies• Network protection 2

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Introduction

SONET(Synchronous Optical Network) or SDH(Synchronous Digital Hierarchy) as it's known in Europe, is the transmission of high speed, high capacity optical telecommunication systems.

SONET is the protocol for North America and Japan while SDH is the definition for Europe. The differences between SONET and SDH are slight.Digital signals in all the network elements in a SDH network are controlled by a master clock. The signal are aligned to each other which is why they are termed synchronous…explain with diagram….

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SDH- Characteristics

• SDH defines the rate, the frame and the multiplexing process• First standards were approved by the ITU-T in 11/1988 (G.7xx)• The SDH is an international, high-rate telecommunication

network standard • The SDH is defined as an assembly for normalized digital

transport structures• SDH provides centralized network management

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SDH Advantages versus PDHPDH principle

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SDH Advantages versus PDHSDH principle

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SDH Advantages versus PDH• SDH is based on the principal of direct synchronous

multiplexing.• Essentially, separate, slower signals can be multiplexed directly

onto higher speed SDH signals without intermediate stages of multiplexing.

• SDH is more flexible than PDH and provides advanced network management and maintenance features.

• Can be used in the three traditional telecommunications areas: long-haul networks, local networks and loop carriers. It can also be used to carry CATV video traffic.

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Bit Rates

International organization defined standardized bit rates :

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SDH: Standard Frame Representation

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SDH frame structure

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SDH frame structure

All SDH frames have the same structure :

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SDH Multiplexing

E.g: 2Mbps mapping

E1: 2.048Mb/s

STM-1 AU-4 VC-4

C-12VC-12

TUG-3

TUG-2

TU-12

x3

x7

x3

VC-n

AU-n

AUG

STM-n Synchronous Transport Module

Administrative Unit Group: One or more AU(s)

Administrative Unit: VC + pointers

Virtual Container: payload + path overhead

AUG

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The following are the different steps in the mapping of 2Mbps stream• Formation of container C12• Formation of virtual container VC12• Formation of tributary unit TU12• Multiplexing of TU12 ‘s to form TUG3• Multiplexing of TUG3‘s to form VC4• Formation of administrative unit AU4• Formation of administrative unit group AUG• Adding SOH to form STM1

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The SDH Multiplexing map

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What is the « concatenation » ?

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What are the different « concatenation »possibilities?

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What is the « Justification » ?

But in practical, the E4 speed can be a little bit faster or slower than the theoretical speed.

If you want to adapt the speed variation, you need a special system called « justification » each time you want to map atributary.

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SDH architecture basics

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SDH architecture basics : Regenerator section

Regenerator section is the basic segment of SDH network.It is the smallest entity which can managed by the system.

Each repeater monitors defects such as Loss Of Signal, Loss OfFrame etBy passing through a repeater, the R-SOH is fullyrecalculated.

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SDH architecture basics : Multiplexing section

The multiplexing section is the entity delimitated by 2 equipment which process the payload of an STM-N.Detects defects and errored blocks and generated special alarm in the forward and backward direction.Manage the Automatic Protection Switching with K1 and K2 bytes.Regenerated a complete SOH.

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SDH architecture basics : VC4 high path

The VC4 High Path is an entity which transport a C4 container from end to another end of a network.A VC4 can be affected to one customer.

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SDH equipments : Terminal Multiplexer• Input: Low Bit Rate and PDH/T-Carrier Tributaries• Output: High Bit Rate SDH Signals

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SDH equipments : Regenerator

• Input: STM-N Synchronous Signal• Output: STM-N Synchronous Signal• Reconditions Transmission To Minimize Jitter, Dispersion, Etc.

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SDH equipments : Transponder ( Converter)λ• Input: STM-N Synchronous Signal at λ1• Output: STM-N Synchronous Signal at λ2• Changes the Wavelength of the Transmission Signal

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SDH equipments : Add/Drop Multiplexer• Input: STM-N Synchronous Signal• Output: STM-N Synchronous Signal• Allows the Extraction and Injection of Synchronous Tributaries

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SDH equipments : Digital Cross Connect• Input: Many STM-N Optical Signals• Output: Many STM-N Optical Signals• Allows Routing of STM-N Signals at High Data Rates

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Network Topology

Point to Point• Large Capacity (with DWDM)• Few Links• Example: Intercontinental Submarine Links

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Network Topology

Ring, Bus, Tree and Star• Differing Capacity• Many Links• Example: Access Networks

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Network Topology

Mesh• Many Links• High Capacity• Example: Transport Networks

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Network protection

• 1+1 Protection• Most Redundant• Most Expensive

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Network protection

1:N Protection• Least Redundant• Most Efficient

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Network protection

• During an Automatic Protection Switching, the network loses

traffic (= the operator loses money!!!).

• That ’s the reason why it ’s very important for an operator to

check the correct working of APS.

• The main parameter is the switch duration. The

recommendation give 50 ms (max) to recover a correct signal.

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Quality standards

• ITU-T G.826 – Quality parameters, objectives and calculations

for bit rates at or above the primary rate

• ITU-T G.821 – Error performance of a digital connection

operating below the primary rate

• ITU-T M.2100 – Performance limits for system turn-up and

maintenance

• ITU-T G.783 – Recommendation for automatic protection

switching and standardized pointer movements42

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Quality parameters

• Errored Seconds (ES) – Seconds during which there is at least

one error per block or frame

• Severely Errored Seconds (SES) – Length of time during which

a major alarm (LOS, LOF, AIS, Etc.) is recorded or when 30% of

the frames received in one second contain errors

• Unavailability – Length of time where SONET equipment is not

available (beginning after 10 consecutive SES)

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