This chapter is designed to provide the student with

Network Design

Chapter 3

Ericsson Transport Network Architecture - 2

This chapter is designed to provide the student with an understanding of Network Design.

OBJECTIVES:

Upon completion of this chapter, you will be able to:

Explain the Five Networks approach to network design

List the key areas of network design

Intentionally Blank3 Network Design

Table of Contents

TopicPage

11The Five-Network Approach

2The Traffic Network22.1Network Elements33Datacommunications73.1Control of the Network Element via a local controller:73.2Control of a Network Element via a Remote Login83.3Data communication Network (DCN)94Synchronisation104.1Priority Table114.2Internal Source115Auxiliary network126Management136.1Why SDH Management?136.2Network Management Layers14

Intentionally Blank1 The Five-Network Approach

The elements of the Five-Network approach to network design are Traffic, Synchronisation, Management, Datacommunications and Auxiliary.

Figure 1: Five Networks model

Traffic network carries the signal or data across the network

Synchronisation network ensures that all network elements are sending and receiving the signals at the same speed

Management of the network is done by a Network and Element Manager. Data Communications network allows both the management systems to communicate with the Network Elements.

Auxiliary network provides external alarms from the equipment / building to the management system along with Engineer Order Wire (EOW)2 The Traffic Network

The main requirements of a traffic network are:

Flexibility & Expansion

Protection Systems

Adaptation to old & new Technologies

Figure 2: Example of a layered network

2.1 Network Elements

Network Elements can be configured in different ways to suit the application required as follows:

Figure 3: Network Element types Terminal Multiplexer connects tributary lines to an optical line

Add / drop Multiplexer adds or drops tributary lines to an optical line

Cross-Connects performs switching between input ports & output ports

Single / Double Regenerator reshapes the pulses in the signal.

Figure 4: Network Topologies

A Point to Point network consists of two Terminal Multiplexers connected together.

A Bus or Line network has one or more Add-Drop Multiplexers between two Terminal Multiplexers

A Single Ring network consists of a number of Add-Drop Multiplexers connected together

A Double Ring network is as Single Ring, but with two sets of fibres

A Star or Hub has a central Network Element connected to other surrounding Network Elements.2.1.1 Network Protection

Network protection provides an alternative route in case of failure. The diagrams below are examples of the different types of protection available.

Figure 5: Line and Ring Network Protection

2.1.2 Cross Connections

Ericsson Network Elements support some or all of the following types of cross connections:

Figure 6: Cross-connection types

3 Datacommunications

3.1 Control of the Network Element via a local controller:

A Network Engineer can connect to a Network Element via the 'F' interface connection on the equipment. Figure 3-7 Local controller F interface connection.

Figure 7: Local Login to a Network Element

3.2 Control of a Network Element via a Remote Login

A Network Engineer can access a Network Element using a remote login via the Embedded Control Channel (ECC). This is a communications channel supported by Data Communications Channel (DCC) overheads in an STM-N frame. The engineer must know the Network Service Access Point (NSAP) Address of the Network Element.

Figure 8: Remote login to a Network Element

3.3 Data communication Network (DCN)

A data communication network is necessary to enable management of the network elements via an Ethernet connection. To facilitate this, the following is needed:

The connection to Network Elements and Management Systems

Open and Standardised Communication Technologies

Redundancy for Link and Equipment failure

Redundancy solution via Rings, Routers and Leased Lines

GNE - Gateway Network Element

ECC - Embedded Communication Channel OSS - Operation Support System

Figure 9: Example of a Data Communications Network

4 Synchronisation

The objectives of synchronisation are as follows:

No timing loops.

Traceability, even in case of link faults.

Each node should have a backup synchronisation source.

Short synchronisation trails.

Figure 10: Synchronisation Network

When the equipment has different synchronisation sources, in case of failure of the active one, another source will automatically be selected. The method for selecting the different sources can be based on the priority table or SSM algorithm.

4.1 Priority Table

The selection of synchronisation source is made according to a priority table defined via a software procedure by the operator.

This table includes all possible synchronisation sources and assigns each of them a priority value.

The system will use, by default, the source with the highest priority. If this fails, the system automatically selects the source with the next priority.

4.2 Internal Source

Free Running - the switch unit makes available an internal clock signal specified by ITU-T recommendation G.813

Holdover - the switch unit samples the in use source frequency and stores the average value in its memory for approximately 24 hours.

If the selected source is no longer available, the unit will synchronise its own oscillator using the stored average value.

Figure 11: Clock types

5 Auxiliary network

Spare capacity in the overhead sections of the SDH frame is used for the Engineer Order Wire; this allows engineers to communicate over the network between network elements. The auxiliary network also provides ground contacts for alarm reporting to the network and element manager.

Figure 12: Auxiliary Network

6 Management

6.1 Why SDH Management?

Management systems simplify and automate the management of telecommunications networks. They provide overall control and monitoring of an entire network, often from a single Network Management Centre. Due to standardisation, all vendors follow a common approach in the design of management networks.

The following types of management are possible:

Fault Management: Includes monitoring and reporting of equipment alarms.

Performance Management: Collects data about how well the network is operating. This data may be used for diagnostic purposes; also for Quality of Service measurements, upon which Service Level Agreements may be based.

Configuration Management: Enables remote configuration of the network.

Service Network: Allows connections to higher-order management systems. For example, Network Operators may use company-wide management systems covering activities such as alarm management and circuit provisioning.

6.2 Network Management Layers

Figure 13: Layers in management network6.2.1 Network Manager

The Network Manager is located above the Element Manager, and is used to monitor the physical aspects of the network. Below are some of the responsibilities of the Network Manager:

Management of links between Network Elements

Automatic, semi-automatic or manual routing of circuits across links

Generating link and circuit alarms based on equipment alarms received via the Element Manager

Collection and display of link and circuit performance data

6.2.2 Element Manager

The Element Manager resides between the Network Manager and the Local Controller level, it controls access to the network at local level and shares the database information with the Network Manager. Below are some of the responsibilities of the element manager:

Communications to Network Elements

Communications to Network Manager

Alarm Reporting

Performance Reporting

Configuration of Network Elements

The Q interface is the connection point to the Network Element, usually from an Ethernet. The Network and Element Manager can then monitor all Network Elements via the 'Q' interface connection and using the DCC / ECC channels.

Figure 14: Management NetworkIntentionally Blank

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EN/LZT

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Star or Hub

Double Ring

Single Ring

Bus or Line

Point to Point

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ADM

ADM

ADM

ADM

ECC

ECC

ECC

ECC

F

Local Controller

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Clock Type

Description

PRC

Primary reference Clock

Caesium Atomic Clock.

G.811.

Unknown

Timing from source incapable of supplying synchronisation status via S1.

SSU-T

Synchronisation Supply Unit

Transit Rubidium Atomic Clock.

G.812T

SSU-L

Synchronisation Supply Unit

Local Rubidium Atomic Clock.

G.812.

SEC

Synchronisation Equipment Clock

Network Element built -in clock.

G.813.

DNU

Do not use for Synchronisation

to avoid timing loops

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Physical Equipment

Representation of network in Element Manager

Representation of network in Network Manager

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Main Operations Centre

Data Communications Network

Backup Operations Centre

Regional Operations Centre

Regional Operations Centre

Regional Operations Centre

Network Elements

Network Elements

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Ethernet

Leased Line

ECC

GNE

GNE

NE

NE

NE

GNE

NE

NE

ECC

GNE

NE

NE

Router

Management System

Ethernet

Management System

Ethernet

Router

Router

Ethernet

Ethernet

Router

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Matrix

To/from

another

port

Port

Bidirectional

Matrix

To

another

port

Port

Unidirectional

Matrix

Loopback

To/from

another

port

Port

Matrix

To

other

ports

Port

Broadcast

Matrix

To/from

another

port

Port

Monitor

To Test port

Matrix

To/from

another

port

Port

Split Access

To Test Port

Any of the cross-connection types above may be concatenated. That is, a number of cross-connections are joined together, to give increased bandwidth.

Matrix

Ports

Ports

Concatenated

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ADM

ADM

ADM

ADM

F

Local Controller

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Failure

Working route

Protecting route

Protecting line

Working line

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STM-16, STM-64, DWDM

STM-4, STM-16

STM-4, STM-16

STM-1

STM-1

STM-1

= Add-Drop from ring

= Gateway between rings

National

Regional

Local

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Engineer Order Wire

External Alarm Collection

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Intermediate Regenerator

Add-Drop Multiplexer

Terminal Multiplexer

Digital Crossconnect

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External timing source (PRC) (Master)

Synchronous Equipment Clocks

~

~

~

~

~

~

STM-N links can be used to distribute synchronisation

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Traffic

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