Laboratory work №9

System synchronization

1 Objective

The objective is to get acquainted with principles of synchronization in DSS SI2000 – insertion of switching node into the synchronization network, choosing the sync source.

2 Key positions

2.1 General points. The SI2000 synchronization subsystem provides operation with hierarchically organized system of type “master/slave” and stand-alone operation. Connection of DSS using the digital comm requires synchronization of this exchange from the environment. This is the requirement for transmission of data with minimal losses and errors. Transmission using PCM requires identical processing rate at both link terminals, otherwise the data is lost.

According to standards, all the digital telephone networks must be working in synchronous mode. However, it is allowed to set the plesiohronous operation mode on the first stages of exchange inculcation and in emergency situations.

The method of master-slave sync is used for synchronous synchronization setup. The local network structure, as well as structure of its sync net, may be of three types:

• hierarchical;

• ring-type using SDH equipment;

• hierarchical-ring;

In hierarchical method the quantity of sync levels on local networks must not exceed four, and in case of malfunctions in sync nets – not more than six.

The local digital telephone net must be synchronized from the TX generator, and in case of its absence – from of nodal or district TE generator. Lines for sync circuit must be selected on the basis of the minimum errors and faults.

You have to provide back-up master generators and back-up sync circuits in order to guarantee the faultless network operation. Moreover, there must be up to three back-up sync circuits depending on exchange type and purpose. Choosing and switching of sync outputs must be carried out automatically accordingly to set priority.

TE must operate in plesiochronous mode if all sync signals are lost.

The SI2000 sync subsystem has 10 inputs from higher level exchanges.

Accordingly to G.703 cl.6 standard, the PCM trunks (2048 kbps), carrying the telephone traffic, are used for synchronization.

The G.703 cl.10 interface is intended for connecting external sync sources. The frequency of external sources has to be 2 or 5 MHz. It is usually used for receiving synchro signals from SDH systems.

2.2 Insertion the node into sync network. In order to insert the SI2000 into the sync network, you need to set the sync sources and their priority. Use CMG table from Global->Synchronization menu.

The Priority parameter defines the sync source priority. First of all, the source with priority 1 is used, in case of its malfunction – with priority 2 and so on.

The Type parameter defines the sync source type. There are two options:

• 2 Mbit/s Link (G.703 cl. 6)

• External Source (G.703 cl. 10)

The Identity parameter defines the port number for 2048kbps link/External Source that is used for synchronization.

The Clock parameter value must be set accordingly to the sync source. This counts for external sources.

3 Control questions

3.1 Enumerate allowed sync network structures.

3.2 What physical interfaces are used for node sync organization?

3.3 How to manage the synchronization in Management system?

4 Home task

4.1 Answer the control questions in writing.

4.2 Get acquainted with synchronization principles and its management in switching nodes.

5 The lab task

5.1 Switch on the computer with Management Node software.

5.2 Take a look on existing sync configuration.

5.3 Add a new sync source for the trunk from labs #7-8.

6 Report contents

6.1 Answers on control questions 3.1-3.3.

6.2 Data about existing sync sources.

6.3 Results of actions on management of new sync source.

6.4 Conclusion.