network synchronization

Network Synchronization

DESCRIPTION

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Copyright

Copyright Ericsson AB 20072009. All rights reserved.

Disclaimer

No part of this document might be reproduced in any form without the writtenpermission of the copyright owner.

The contents of this document are subject to revision without notice due tocontinued progress in methodology, design and manufacturing. Ericsson shallhave no liability for any error or damage of any kind resulting from the useof this document.

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Contents

Contents

1 Introduction 11.1 Target Groups 11.2 Prerequisites 1

2 Functions and Concepts 32.1 Network Views 32.2 Equipment View 92.3 Duplication of Synchronization 12

3 Managed Object Model 153.1 Managed Object Overview 153.2 Managed Objects 174 Configuration Management 194.1 The Synchronization Reference Lists 194.2 Adding and Reconfiguring a Network Synchronization

Reference 194.3 The IP Synchronization Reference 204.4 The IP Time Server 204.5 Minimizing the Start-Up Time for Synchronization over IP

by Locking Temporarily to a Local Clock 21

5 Fault Management 235.1 Configuration of Fault Management 235.2 State of the Node Clock 235.3 Fault Scenarios 235.4 Preparation for Replacing a PIU 28

6 Performance Management 31

7 Security Management 33

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Introduction

1 Introduction

This document describes the management model and concepts for themanaged objects that belong to Network Synchronization.The document provides an understanding of how the area is modelled,including the functions related to the area and how they are managed.

A managed area represents a group of functions and Managed Objects (MO)within the node, where each area is relatively independent of other areas.

The Network Synchronization function deals with the selection of networksynchronization references and the distribution of synchronization within thenode.

1.1 Target GroupsThe target groups for this document are personnel working in the followingareas:

General Operation and Maintenance activities, where a detailedunderstanding of a specific area is required

Network planning

Troubleshooting

1.2 PrerequisitesPrevious knowledge of the following is beneficial:

The standards and concepts applicable to this area.

The Managed Object Model (MOM) concept, see Managed Object Model(MOM) User Guide.

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Functions and Concepts

2 Functions and Concepts

2.1 Network ViewsThe purpose of the function, Network Synchronization is to synchronize allnodes in a network to a Primary Reference Clock (PRC). The PRC is usually acesium beam clock but the Global Positioning System (GPS) is also used insome networks.

The networks can be either PDH/SDH networks or IP/Ethernet networks. In aPDH/SDH network, synchronization is distributed on the physical PDH/SDHlinks. In an IP/Ethernet network, packets are used and they have no relationshipto the phase and frequency of the physical links.

Section 2.1.2 on page 7 describes the network view of synchronization in aPDH/SDH network. Section 2.1.3 on page 8 describes the network view ofsynchronization in an IP/Ethernet network.

2.1.1 General Synchronization Networks

The PRC is distributed over transmission links or dedicated synchronizationlinks in the network. The PRC(s) synchronize(s) the next level of clocks, thatis, the Synchronization Supply Units (SSU). They in their turn synchronize theSynchronous Digital Hierarchy (SDH) Equipment Clocks (SEC). One or morelinks are used as synchronization references. The Network SynchronizationPlan specifies which links are used for synchronization and which links eachnode uses.

In normal operation, SSU and SEC clocks are synchronized to a PRC. Thisstate is called Locked mode.

A clock that has lost its connection to the PRC attempts to keep the frequencyof the PRC. This state is called Holdover mode.

Free-running mode is when the clock has never been in Locked mode andthus has never compared its oscillator with the PRC frequency, or when themaximum holdover time has elapsed.

Figure 1 shows a synchronization chain from a PRC to an SEC. Thisrepresentation focuses on the synchronization characteristics in termsof frequency, jitter, wander and Maximum Time Interval Error (MTIE). Ifthe number of SECs becomes too high, it might be necessary to insert aSynchronization Supply Unit (SSU) to improve the synchronization quality.

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PRC level

SSU level

SEC level

L=Locked

L L

L

LLLLLL

L

L L

Figure 1 Synchronization Chain

If a fault occurs, the chain in Figure 1 breaks. In Figure 2, an example is given.After the failure, only the two left-most SECs are synchronized to the PRC. Thethird SEC is in Holdover mode and synchronizes the fourth SEC. The SSUdetects a low clock quality in the Synchronization Status Message (SSM) sentby the fourth SEC or it detects a frequency deviation in the incoming clock. Itdiscards the synchronization reference coming from the SEC, enters Holdovermode and synchronizes the remaining part of the chain to the right.

fault

PRC synchronization network connection

SSU synchronization network connection

SEC synchronization network connection

L L H L

H

L L L L

L

L L

H=HoldoverL=Locked

Figure 2 Failure of a Synchronization Connection

The lines between the clocks in Figure 1 are Synchronization Distribution (SD)trails and the whole path between the master clock (PRC) and a slave clock is a

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Network Synchronization (NS) network connection. This is further described inFigure 3. The selection of a particular synchronization input SD trail is donewith an NS connection in the NS connection function (the ovals on the topin Figure 3).

SDSD

SD

NS

NE 2

SDSD

SD

NS

SDSD

SD

NS

SD

PR C

SD

SD link con n 1-2 SD link c onn 2-3 SD link c onn 3-4

SD trail 1- 2 S D trail 2-3 SD trail 3-4

NS network connec tion

NS link conn 2-3 NS link conn 3-4

transportlayers

NE 1 N E 3 N E 4

Figure 3 SD Trails and NS Network Connections

The purpose of network synchronization is to synchronize all clocks in thenetwork to a common frequency, that is, to have the same long-term frequencyaccuracy everywhere. It is highly recommended that the source for thelong-term frequency accuracy is a PRC. To secure PRC availability at any time,the synchronization network must be implemented in redundant structures.This prevents individual clocks from entering holdover mode if a single networkfailure occurs.

A representation of the redundancy of the synchronization network is shown inFigure 4. The two SSUs are connected to the top PRC. The SSU on the lefthas only one route to the top PRC and therefore has a backup PRC. Exceptfor the lowest level, all nodes have (at least) two independent routes to besynchronized on. This reflects the situation in a typical core network. If a faultoccurs, the node selects another synchronization reference instead of enteringHoldover mode. On the lowest level, the SEC nodes have only one route to besynchronized on. This reflects the situation in a typical access network. If afault occurs on a link to the nodes on the lowest level, the nodes enter Holdovermode. In the figure, all the arrows are SD trails.

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PRC

SSU

SEC

SSUPRC

SEC SEC SEC SEC

SEC SEC SEC SEC SEC

SEC SEC SEC SEC SEC

Figure 4 Redundancy in Synchronization Networks

On node level, network synchronization is simply a matter of selecting asynchronization reference.

Figure 5 gives an overview of the network synchronization of a node. Thesynchronization references connected to the node are to the left. There is aselector that chooses the synchronization reference that the node should use.This is a more detailed view of the selection of a synchronization reference,where the selector makes the NS connections in the model in Figure 3.

The selection is based on a strict priority order. The selected synchronizationreference is supervised and filtered by the SEC and is then distributed to alloutputs of the node that carry synchronization.

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Selector

SEC

Figure 5 Node View of Network Synchronization

The network synchronization plan describes how network synchronizationshould be done in a particular network. The plan describes which nodes thereare in the network and which clock types they are equipped with. It details thelinks that are used for conveying information on network synchronization, andfinally on node level, the inputs that are used as the network synchronizationreferences and their priorities.

Thus the network synchronization plan is the main input for configuration ofthe network synchronization in a node. Based on that, the synchronizationreferences and the priority between them are defined in the node.

2.1.2 PDH and SDH Networks

The following applies to most nodes in a network and it is valid for allCPP-based nodes.

In ATM networks with PDH and SDH transmission and in SDH networks,all the outputs from the SDH or ATM nodes are synchronized to the nodeclock. Classical PDH Network Elements such as digital multiplexers aretiming-transparent and can in this context be regarded as cables, that is, partof the SD trails.

There are also some SDH add/drop multiplexers, in particular the NorthAmerican region, whose east interfaces are synchronized to the west interfacesand vice versa.

In some nodes, particularly in data-communication equipment, there is theconcept of loop timing. This means that the output from all ports of thatnode are individually synchronized to the input of the same port. Specialconsideration must be given to these nodes in the network synchronization plan.

Figure 6 shows an example network. There is an NS network connection fromthe master clock to all slave clocks but only one clock is shown in the figure.All outgoing SD trails are synchronized to the node clock. Several NS networkconnections share the same SD trails meaning that a node located after anothercannot be synchronized to any other master clock.

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All the node clocks along an NS network connection are in effect cascaded.

GPS(PRC)

= SD trail= NS network connection

Figure 6 Example of a Synchronization Network (PDH/SDH-based Networks)

2.1.3 IP Networks

Network synchronization in an IP-based network is performed using timestamps inserted in IP packets.

The IP Synchronization Reference consists of a Time Client in the node and anassociated Time Server in another node.

On request from the Time Client, a Time Server generates packets carrying thetime stamps, and the client receives this synchronization information. The TimeClient uses the time stamps to generate and control the clocks.

An example of an IP network is shown in Figure 7. Synchronization Distributiontrails are transparent to the nodes, meaning that cascading in the classicalsense is not applicable. The timestamp packets passing along SynchronizationDistribution trails are subject to delay variation by the IP network. This variationmight seriously affect the characteristics of the network synchronization.

The Network Synchronization network connections consist of only one SDtrail. Two nodes connected to the same node can also be synchronized todifferent Time Servers, as shown by the upper two nodes to the right that arenot synchronized to the same Time Server, although they are connected tothe same intermediate nodes.

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C

C

C

C

C

C

GPS(PRC)

S

S

S

S

Stand aloneTime Server

= SD trail= NS network connection

= Ti me Server= Ti me ClientC

S

Figure 7 Example of a Synchronization Network for IP-based Networks

The Time Server can either be a stand-alone Time Server node , or a TimeServer integrated within a CPP-based node. An IpAccessHostEt MO actsas a Time Server in the CPP-based node. The server reacts to incomingtime stamp IP packets (from the client), adds the current time to the relevantfields and returns them to the source IP address, that is, the address of theTime Client.

A CPP-based node acting as Time Server for IP synchronization cannot besynchronized to an IP synchronization reference (that is, a node cannot be aTime Server and a Time Client at the same time).In the Time Client, the required synchronization information from the IP packetsis extracted using a Differential Time Method algorithm. Differential TimeMethods are based on the time differences between a Time Server and a TimeClient. The IP packet delays computed from the time stamps for the server andfor the client allow the client to calculate its oscillator frequency drift comparedto the Time Server frequency and to tune the client clock to the Time Server.

For more information on the generation and termination of IP packets and onthe IP host, see the description of IP Transport.

2.2 Equipment ViewThe internal implementation of the network synchronization function isdivided into two parts: the synchronization selection with filtering, and thesynchronization distribution.

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There are three implementations of the Network Synchronization function:TUB-based, CBU-based and DU-based corresponding to the Timing UnitBoard, the Control Base Unit and the Digital Unit.

Figure 8 shows the full equipment view of the network synchronization for aTUB-based node. There are A and B planes marked with suffixes.

ET

SXU SCU TU SCU SXU

User

SXU SCU TU SCU SXU

One ISL link per plane and per extension subrack

ref 2

1.5/2/10 MHzand/or 1PPS

ref 3

ref 1

ET

SCU SCU

User

SCU SCU

ref 4

AlternativeISL pathsPlane A

Plane B

1..4

Main Subrack

Extension Subrack

a

a

aa

a

a

bb

b

b

b

bb b

b

b

bb

aa

a aaa

1..4 1..4

1..4

ET Exchange TerminalSCU Switch Core UnitSXU Switch Extension UnitISL Inter Subrack Link

TU Timing UnitUser A Plug In Unit, could be an ET or other

unit using the network synchronization1PPS 1 Pulse Per Second

AlternativeISL paths

RedundancyTermination

Figure 8 Equipment View in the TUB case

The SCUs and SXUs are present both in the selection direction (toward TU)and in the distribution direction (toward the clock users) in the figure but it isthe same unit in both directions. The ET represents any Exchange Terminal.The clock users in the egress direction to the right are PIUs other than TUs,SCUs and SXUs.

There are two types of references: dedicated synchronization ports and trafficports. The dedicated ports are located on the TUs (ref 1 and ref 2) and thetraffic ports are located on ETs. The references on ETs might be in the mainsubrack (ref 3) or in an extension subrack (ref 4). Ref 4 is sent to the SCUs forboth A and B planes in the extension subrack and is then sent over ISLs to the

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SCUs in the main subrack, either directly or over SXUs. Ref 3 is sent directlyto the SCUs of both A and B planes. References are selected on the SCUsin the main and extension subracks.

The SCUs in the main subracks send the reference to the TU in their plane. TheTU filters the reference and generates the node clock for the A and B planesrespectively. The TUs send the filtered clock to the SCUs in the main subrack.

The SCUs distribute the node clock to all clock users (including ETs). For theextension subrack, the distribution might go over ISLs directly from the SCU inthe main subrack to the SCU in the extension subrack, or the distribution mightpass through an SXU. The clock users get the clocks from both the A and Bplanes, and the final selection of which plane the clock user is synchronizedto, is made there.

In a node with CBU boards, there are no SCUs in the main subrack, and thereare no extension subracks. So compared to Figure 8, the SCUs (and SXUs)are not present, see Figure 9.

ET Exchange TerminalCBU Control Base Unit

TU Timing UnitUser A Plug In Unit, could be an ETs or units using

the network synchronization1PPS 1 Pulse Per Second

CBU subrack

1,5/2/10 MHzor 1PPS

1,5/2/10 MHzor 1PPS

ETa

b

RedundancyTerminationRef 1

Ref 2

Ref 3

TUb(CBUb)

Usera

b

ET

b

a

TUa(CBUa)

Figure 9 Equipment View in the CBU Case

A DU-based node has only one or two DU boards. Both the TU and the clockUser are located on the same DU. If there are two DUs, the clock User in onecan only get clock from the TU in the same DU.

See Figure 10.

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ET Exchange TerminalDU Digital Unit

TU Timing UnitUser ETs or other units using network synchronization1PPS 1 Pulse Per Second

Secondary DU

2/10 MHzor 1PPS

2/10 MHzor 1PPS

User

Ref 1

Ref 2

Ref 3 TUa

User

ET

Primary DU

Ref 4ET

TUa

Figure 10 Equipment View in the DU Case

2.3 Duplication of SynchronizationDue to the different architectures of the TUB-, CBU- and DU-based nodes, theduplication has different characteristics.

2.3.1 TUB and CBU nodes

A node might have duplicated (redundant) or not duplicated (non-redundant)synchronization. If synchronization is duplicated, all clocks and selection aswell as distribution functions are duplicated in an A and a B plane to givetolerance to single hardware faults. The A and B planes are marked withsuffixes in Figure 8 and Figure 9. If synchronization is not duplicated, there isonly an A plane and the node is not single-fault tolerant.

2.3.2 DU nodes

A node might be a single-DU configuration or a dual-DU configuration. Ina dual-DU node, there are two TimingUnit MOs: one master and theother slave. The master TimingUnit is in the DU that has the ACTIVEsynchronization reference and the slave is the TimingUnit in the DU thatdoes not have the ACTIVE synchronization reference. If there is only oneTimingUnit in a node, it is master even if it does not have any availablesynchronization references. The slave TimingUnit is synchronized to themaster. Figure 10 shows a dual-DU node. The upper DU is the primary DU andthe other is the secondary DU. These identities are permanent once the node isconfigured. Assuming that Ref 3 is active, the TimingUnit in the primary DU

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is the master. The slave TimingUnit is synchronized to the master with theinter-PIU cable that carries the synchronization signals shown with the crossedarrows between the TUs in Figure 10.

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Managed Object Model

3 Managed Object Model

This section describes the management model defined for this area.

3.1 Managed Object OverviewThe Managed Area, Network Synchronization represents a subset of the MOM.The following illustration shows the MOs for this area.

The Managed Objects within Network Synchronization MA are: Synchronization

TimingUnit

TuSyncRef

There are also a number of other MOs that support the Network Synchronizationfunction. The most important MOs are the SwitchCoreUnit (SCU) andSwitchExtensionUnit (SXU) where the selection and distribution of networksynchronization are located. Also the SwitchInternalLink (ISL) andPlugInUnit (PIU) are used.The Time Server is controlled by the IpAccessHostEt MO.

The MOs in Network Synchronization are shown in Figure 11.

The MOs for Equipment are shown in Figure 12.

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Figure 11 Functional View of the MOs in Network Synchronization

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Managed Object Model

Figure 12 Equipment View of the MOs in Network Synchronization

The TUB, the CBU and the DU boards are of type PlugInUnit. The TUB, theCBU and the DU boards contain a TimingUnit. The TimingUnit on a TUBor DU board is a child to the PlugInUnit.

3.2 Managed ObjectsThis section gives an overview of the MOs within a part of the area and theirrelationships to other MOs.

3.2.1 Synchronization

This MO models the network synchronization function, that is, the definitionand selection of synchronization references. The MO also reports the statusin the nodeSystemClock.

The MO has links to up to eight network synchronization references.The references are represented by the MOs: E1PhysPathTerm,E3PhysPathTerm, J1PhysPathTerm, Os155SpiTtp, T1PhysPathTerm,T3PhysPathTerm, IpSyncRef and TuSyncRef.

The MO is automatically created when the node starts.

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3.2.2 TimingUnit

This MO models the implementation entities of the network synchronizationfunction. It represents the hardware of the network synchronization oscillators.Its purpose is to report the state and the status of the clock in a plane.

A TimingUnit MO is created for each TUB, CBU or DU board in the node.

3.2.3 TuSyncRef

This MO models the network synchronization reference directly connected tothe Timing Unit board, CBU or DU. It represents the dedicated synchronizationreferences supported by the board. The input is located in the TimingUnitMO.

It reports the operational state and availability status of the networksynchronization reference.

The TUSyncRef MOs are manually created under the TimingUnit MO.

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Configuration Management

4 Configuration Management

No network synchronization references are defined by default.

4.1 The Synchronization Reference ListsThe Local Distinguished Name (LDN) of the registered synchronizationreferences is kept in a list in the Synchronization MO. The list has exactlyeight positions or items. This list is the syncReference attribute. If a positionin the list does not have a defined reference, the list position has the valueNULL.

Besides the syncReference attribute, or list, there are also thesyncRefPriority, syncRefStatus and syncRefActivity attributes.They are also lists with exactly eight positions each. For a position withsyncReference equal to NULL, the syncRefPriority is zero. The valuesof the attributes, syncRefStatus and syncRefActivity are not validin their list positions that coincide with the NULL, and zero positions in thesyncReference and syncRefPriority lists.

An example with four registered references is as follows, where the letters A toF represent user-defined value components:

syncReference:ManagedElement=1, Equipment=1, Subrack=A, Slot=5, PlugInUnit=1,TimingUnit=1, TuSyncRef=F;ManagedElement=1, Equipment=1, Subrack=B, Slot=20, PlugInUnit=1,ExchangeTerminal =1, Os155SpiTtp=4;ManagedElement=1, Equipment=1, Subrack=C, Slot=7, PlugInUnit=1,ExchangeTerminal =1, E1PhysPathTerm=1;NULL; NULL; NULL;ManagedElement=1, IpSystem=1, IpAccessHostEt=D, IpSyncRef =E;NULL

syncRefPriority: 4; 3; 5; 0; 0; 0; 6; 0

syncRefStatus: OK; FAILED; OK; FAILED; FAILED; FAILED; OK; FAILED

syncRefActivity: ACTIVE; INACTIVE; INACTIVE; INACTIVE; INACTIVE;INACTIVE; INACTIVE; INACTIVE

4.2 Adding and Reconfiguring a Network SynchronizationReferenceA network synchronization reference is registered with the actionaddSyncRefResource that associates the MO representing the reference to

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the Synchronization MO. At the same time, the priority of the reference isset.

A maximum of eight synchronization references can be defined. The priority isa number between 1 and 8, ordering the references in a strict priority order.The reference with the highest priority (lowest number) that is available, isselected as synchronization source.

The priority of a network synchronization reference is changed with the actionchangeSyncRefPriority on the MO Synchronization.

A network synchronization reference is deregistered with the actionremoveSyncRefResource that associates the MO representing the referenceto the Synchronization MO.

4.3 The IP Synchronization ReferenceThe IpSyncRef MO needs to be configured. All other synchronizationreference MOs represent a physical port of the node and the synchronizationsource that is determined by the network. The IpSyncRef represents a logicaltermination point. It has to be connected with its synchronization source byassigning the IP address of the Time Server to the IpSyncRef.

Before the IP address is changed, the administrativeState should be setto LOCKED to prevent transients during the change. The administrative statemust not be set to UNLOCKED in the same transaction as it is set to LOCKED.

It is not possible to create any IpSyncRef MOs, if the node is a Time Server.

4.4 The IP Time ServerIn order to be able to act as an IP synchronization source, one or more TimeServers must be enabled. That is done by enabling a Time Server on theIpAccessHostEt MO. By doing so, the IpAccessHostEt starts to answerrequests from Time Clients. See the description of IP Transport.

A node cannot have any IpAccessHostEt with Time Servers enabled, if thereare any IpSyncRef MOs in the node.

The IP Time Server should be located as close to the external Ethernetinterface as possible. Avoid using IpAccessHostEt MOs located behind anEthernet Subrack Link (ESL) or Ethernet switch board. See the description ofEthernet Switching for information about Ethernet links in the node.

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Configuration Management

4.5 Minimizing the Start-Up Time for Synchronization overIP by Locking Temporarily to a Local ClockIn order for a node to lock to an IpSyncRef within 16 minutes, the IP networkmust have sufficiently low delay variations. In some IP networks, the delayvariation between the node and the Time Server is low enough to be able tolock the node to the Time Server but so high that it takes several hours to lockthe node. To avoid such a long start-up time, it is possible to first synchronizethe node to a stable clock and then change to an IpSyncRef. The followingdescribes that procedure.

The stable clock must have a frequency of 2048 kHz or 10 MHz. The accuracymust be better than 1 ppb relative to International Atomic Time (TAI) orCoordinated Universal Time (UTC).1. Connect the stable clock to a dedicated reference input.

2. If more than seven synchronization references are registered, remove theone with lowest priority.

3. Create a TuSyncRef for the input to which the stable clock is connected.

4. With the action addSyncRefResource, register the TuSyncRef assynchronization reference.

5. Set administrativeState for all IpSyncRef MOs to LOCKED.

6. Verify that the attribute syncRefActivity for the TuSyncRef becomesACTIVE.

7. Wait 16 minutes and then verify that the nodeSystemClock attribute hasvalue LOCKED_MODE.

It is recommended to leave the node synchronized to the stable clock aslong as possible.

8. Set administrativeState for all IpSyncRef MOs to UNLOCKED.

9. With the action removeSyncRefResource, deregister the TuSyncRef assynchronization reference.

10. Delete the TuSyncRef MO.

11. If a reference was removed in Step 2, add it again.

12. Disconnect the stable clock from the node.

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Fault Management

5 Fault Management

See the separate lists of alarms and events.

5.1 Configuration of Fault ManagementThe node can be configured so that a degradation fault on the transmissionlink is considered as a reason to disqualify the reference as a networksynchronization reference in the MO Synchronization. The configuration isvalid for all PDH and SDH references, that is, it is not possible to have differentconfigurations for different references.

5.2 State of the Node ClockThe state of the node clock is given by the attribute, nodeSystemClock in theMO, Synchronization. The state of the system clocks for each plane isgiven by the attribute, tuSystemClock in the MO, TimingUnit. The valuesof nodeSystemClock and tuSystemClock can differ only in a node withduplicated network synchronization.

5.3 Fault Scenarios

5.3.1 Fault on a Synchronization Reference

The consequences of a fault that occurs on a synchronization reference aredescribed in the following sections, depending on the type of synchronizationreference.

5.3.1.1 PDH and SDH Synchronization References

If a fault occurs on a PDH or an SDH port that is a synchronization reference,the port MO, see Figure 11, issues an alarm. The synchronization referencestatus (syncRefStatus) is FAILED or DEGRADED.This normally indicates a fault in the network.

5.3.1.2 Dedicated Synchronization References

If a fault occurs on a dedicated synchronization reference, the TuSyncRefMO issues the TU Synch Reference Loss of Signal alarm. Thesynchronization reference status (syncRefStatus) is FAILED.

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This normally indicates a fault in the equipment in the same building as wherethe node is situated.

5.3.1.3 GPS Synchronization References

The following applies only to GPS references on a DU-based node that isconfigured in time-locking mode. For all other cases, the information in Section5.3.1.2 on page 23 applies.

If the connected GPS receiver is of an unsupported type or if several nodesshare the same GPS receiver in a non-functional way, the data receivedfrom the GPS might be missing or unusable, resulting in no valid timinginformation. The frequency information is still received from the reference,thus the TU Synch Reference Loss of Signal alarm is not issued. TheNetwork Synch Time from GPS Missing alarm is issued instead. Thesynchronization reference status (syncRefStatus) is FAILED.This normally indicates a fault in the equipment in the same building as wherethe node is situated.

5.3.1.4 IP Synchronization References

There is constant surveillance of the connections to the Time Servers. If thesurveillance indicates loss of connection to a Time Server, the alarm SynchReference Not Reliable is raised by the IpSyncRef MO. See thedescription of IP Transport.

The synchronization reference status (syncRefStatus) is FAILED. Thisnormally indicates a fault in the network.

The header of the IP time stamp packets contains information put there bythe Time Server, giving information about the server. The contents of theheaders of the NTP packets are supervised for two possible problems. Theyare the Stratum level and the Leap Indicator (LI) fields. A Stratum leveldifferent from one indicates that the NTP server is not controlled by PRCor possibly not synchronized at all. A Leap Indication (LI) equal to threeindicates that the server has an alarm condition. If any of these conditionsoccurs, the Time Server is considered to be unreliable, the alarm SynchReference Not Reliable is issued and the synchronization referencestatus (syncRefStatus) is NOT_RELIABLE.The delay variation of the Time Stamp packets is also monitored for theACTIVE reference. If it exceeds the limits for a synchronization reference, thealarm Synch Reference Not Reliable is issued also in this case and thesynchronization reference status (syncRefStatus) is LOW_QUALITY.In the first case, this normally indicates that a Time Server is not synchronized.In the second case, this normally indicates some sort of overload situationin the IP network.

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Fault Management

5.3.1.5 General Consequences of Synchronization Reference Faults

If the reference was active, the fault-free reference with the highest priority isselected and an event, A new reference has been selected as theactive reference is issued.

If the synchronization reference was the last one available, the node entersHOLD_OVER_MODE. The alarm, System Clock in Holdover Mode and theevent, The state of the system clock has changed are issued.

Several defined references

If the synchronization reference was the next to last one, a Loss of SynchReference Redundancy alarm is issued.

If the alarm Loss of Synch Reference Redundancy was active, it isceased.

5.3.2 Absence of Synchronization References for a Longer Period of Time

If all synchronization references are unavailable, nodeSystemClock is inHOLD_OVER_MODE and the alarm, System Clock in Holdover Mode andthe event, The state of the system clock has changed are issued.

If none of the synchronization references recovers, the node will after a whilenot be able to maintain Holdover mode. If that happens, the alarm, SystemClock Quality Degradation is issued together with the event, Thestate of the system clock has changed. The alarm, System Clockin Holdover Mode is ceased.

5.3.3 Frequency Deviation of Some but Not All SynchronizationReferences

If the active synchronization reference has an excessive frequency deviation,it is detected as Loss of Tracking. A Loss of Tracking alarm isissued and the nodeSystemClock enters LOSS_OF_TRACKING_MODE.The active synchronization reference status (syncRefStatus) will beLOSS_OF_TRACKING.

If the synchronization reference was the second but last one, a Loss ofSynch Reference Redundancy alarm is issued.

The fault-free reference with the highest priority is selected and an event, A newreference has been selected as the active reference is issued.

It might be discovered that the new active synchronization referencealso has a frequency deviation that will be detected as Loss of Tracking.The Synchronization reference status (syncRefStatus) will beLOSS_OF_TRACKING for this reference as well.

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Finally, a synchronization reference that does not have a frequency deviationis selected and an event, A new reference has been selected asthe active reference is issued. The nodeSystemClock leavesLOSS_OF_TRACKING_MODE and enters LOCKED_MODE and the node isworking normally.

When the synchronization references do not have any frequency deviationany longer, the LOSS_OF_TRACKING of the synchronization references(syncRefStatus) can be reset. That is done manually for each reference.Inactive synchronization references are not supervised for frequency deviation.

5.3.4 Frequency Deviation of All Synchronization References

When all synchronization references (syncRefStatus) are inLOSS_OF_TRACKING, the nodeSystemClock also remains inLOSS_OF_TRACKING_MODE.

An automatic recovery procedure is started. The node attempts to lock to thesynchronization reference with the highest priority.

When the synchronization reference has been repaired, the node manages tolock to the reference and the nodeSystemClock leaves LOSS_OF_TRACKINGmode and enters LOCKED_MODE. The node is now working normally. TheLOSS_OF_TRACKING status is cleared for the attribute, syncRefStatus forthe active reference and for all other references with lower priority.

5.3.5 Aging or Frequency Faults of a Node Clock

TUB- or CBU-based node without Duplicated Synchronization, orDU-based node

If the single clock gets a hardware fault so that it cannot track thereferences, nodeSystemClock enters LOSS_OF_TRACKING_MODE.The active synchronization reference (syncRefStatus) gets the statusLOSS_OF_TRACKING and all the other references follow when they becomeactive. A Loss of Synch Reference Redundancy alarm might be issuedand later ceased, if the node had several synchronization references. Thealarms, Loss of Tracking and Loss of System Clock are issued.

The automatic recovery procedure will not be successful. The PIU with thefailed Timing Unit must be replaced.

The TimingUnit MO in the single A plane will have its tuSystemClockidentical to the nodeSystemClock.

Note: The alarm situation is identical to that in Section 5.3.4 on page 26.

TUB- or CBU-based node with Duplicated Synchronization

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Fault Management

If the clock in one of the planes gets faults so that it cannot track thereferences, tuSystemClock in the MO, TimingUnit for that planeenters LOSS_OF_TRACKING_MODE. The node uses the other plane andtuSystemClock in the MO, TimingUnit remains in LOCKED_MODE. Thealarm, Loss of System Clock Redundancy is issued.

The value of nodeSystemClock is not changed.

5.3.6 Faults of Synchronization Reference Path

If a hardware fault occurs along the synchronization reference path, the alarm,Synch Reference Path HW Fault is issued.

TUB- or CBU-based node without Duplicated Synchronization

The synchronization reference status for the active reference (syncRefStatus)becomes FAILED. The active synchronization reference is changed, asdescribed in Section 5.3.1.5 on page 25. The fault is somewhere in the ET,SCU, ISL, SXU, SCU, CBU or TU in the A plane, see Figure 8. The faulty unitneeds to be changed.

TUB- or CBU-based node with Duplicated Synchronization

The synchronization reference status for the active reference (syncRefStatus)becomes REF_PATH_FAILED_A or REF_PATH_FAILED_B in the plane wherethe fault occurred, see Figure 8. If the active synchronization referencepaths have failed in both planes, the reference becomes FAILED. The activesynchronization reference is changed, as described in Section 5.3.1.5 on page25. The fault is somewhere in the ET, SCU, ISL, SXU, SCU, CBU or TU in theplane of the fault. The faulty unit needs to be changed.

DU-based node

The synchronization reference status (syncRefStatus) becomesREF_PATH_FAILED_A if the reference is located on the primary DU, orREF_PATH_FAILED_B if the reference is located on the secondary DU, seeFigure 10. If the synchronization reference is ACTIVE, another synchronizationreference is selected, as described in Section 5.3.1.5 on page 25. The faultyDU needs to be changed.

The fault localization principle is in all cases to replace units until the alarmceases.

5.3.7 Transients on a Synchronization Reference

There might be transients on a Synchronization reference that are not detectedby the port and do not cause any alarms to be raised by the port MOs in Figure11. If those transients are too severe, the Synchronization MO detectsthem and issues the alarm Synch Reference Path HW Fault. Thesynchronization reference status for the active reference (syncRefStatus)

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becomes REF_PATH_FAILED_A or REF_PATH_FAILED_B in the plane wherethe transients were first detected. If the transients were detected in both planesor in a DU, the reference becomes FAILED.

5.3.8 Faults in System Clock Distribution

In the case of a hardware fault in the system clock distribution, any of thealarms: Plug-In Unit Synch Hardware Fault, TU System ClockPath HW Fault, SCB System Clock Path HW Fault or SXB SystemClock Path HW Fault is issued.

The alarm indicates where the fault has been detected but that is notnecessarily where the fault is located. The fault might in general be located onthe unit generating the signal, the unit detecting the absence of the signal orthe unit connecting them. Figure 8 gives a view of how the units are related toeach other.

The fault localization principle is to replace the most likely faulty unit first andcontinue in descending order of likelihood until the fault is found.

5.3.9 Hardware faults in TimingUnit

If a hardware fault occurs on the PIU with a TimingUnit, an alarm is issued.If it is on a TUB, the alarm Plug-In Unit HW Failure is issued by thePlugInUnit MO. If the fault is on a CBU or DU, the TU Hardware Faultalarm is issued by the TimingUnit MO.

5.3.10 Faults on the Inter-PIU Link

The following applies only to DU-based nodes. If a hardware fault occurson the inter-PIU link between the two DUs in a dual-DU configuration thatonly affects TimingUnit network synchronization, the Slave TU Out ofSynchronization alarm is issued by the slave TimingUnit MO. If the faultsaffects the whole link, the Inter-PIU Link Fault alarm is issued by theinterPiuLink MO.

The consequence of this fault is that the DU with the slave TimingUnitwill not be able to keep its clock within specification and will be inFREE_RUNNING_MODE.

5.4 Preparation for Replacing a PIU

5.4.1 TUB- or CBU-based Node

See the instruction for replacing Timing Unit Board or a Control Base Unit.

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Fault Management

The network synchronization function might be duplicated in a node with twoplanes (A and B) with duplicated Timing Units, Switch Core Units, SwitchExtension Units and Switch Internal Links, see Figure 8. The following assumesthat none of the Network Synchronization units has a fault or is locked in anyway.

Before removing any of those units, ensure that they are locked with theadministrativeState of the MO PlugInUnit they are located on,see the instructions Lock Board, or for the SwitchInternalLink with theadministrativeState directly on the MO. By doing so, within 20s the PIUsin the affected subracks select synchronization from the other plane, minimizingthe impact of the maintenance action.

Locking of the PlugInUnit for the SwitchCoreUnit or TimingUnit(including CBU) in the main subrack causes all the PIUs in the node to takesynchronization from the other plane.

Locking of the PlugInUnit for the SwitchExtensionUnit in the mainsubrack causes all the PIUs in all extension subracks connected to thatSwitchExtensionUnit to take synchronization from the other plane.

Locking of the SwitchCoreUnit PlugInUnit in an extension subrackcauses all the PIUs in that extension subrack to take synchronization from theother plane. Administrative locking of the SwitchInternalLink causes thatextension subrack to take synchronization from another link.

If the active synchronization reference is a TuSyncRef, that is, a dedicatedreference on the TimingUnit or CBU, the administrative locking of the PIU forthe TimingUnit causes the reference to be discarded, as the TuSyncRef isDEPENDENCY_LOCKED.

If any other active synchronization reference passes any locked PIUs, it isnot affected by the locking. The reference is discarded only when the PIU isphysically removed from the subrack.

If the Timing Unit is located on a CBU, it is not possible to control the networksynchronization redundancy separately from the other functions on the CBU.

If the node does not have duplicated Network Synchronization or if any of theNetwork Synchronization units has faults or is locked in any way, replacing theboard will cause disturbances. If the PIU with the TimingUnit is replaced,the historical frequency data used for fast restart is lost, and in particular in thecase of IP synchronization references, the start-up time might be longer.

5.4.2 DU-based Node

See the instruction for replacing a Digital Unit.

Before removing a DU, ensure that the DU is locked with theadministrativeState of the MO PlugInUnit where the DU is located,see the instruction Lock Board.

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If the node is a dual-DU configuration and if both DUs are unlocked andfault-free, locking of a DU causes the other DU to take over the role of masterclock, if this is not already the case. If the ACTIVE reference is located on theDU being locked, a new reference is selected on the other DU, if any. If noreference is available on the other DU, disturbances might occur if replacingthe board takes a longer time than the holdover period. The consequencesof not having any synchronization references are described in Section 5.3.2on page 25.

If the node is a single-DU configuration, the whole node is non-operationalwhen the board is being replaced. The historical frequency data used for fastrestart is lost ,and in particular in the case of IP synchronization references, thestart-up time might be longer.

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Performance Management

6 Performance Management

See the specifications of the PM counters in the MOM.

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Security Management

7 Security Management

Not applicable.

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toc1 Introduction1.1 Target Groups1.2 Prerequisites

2 Functions and Concepts2.1 Network Views2.1.1 General Synchronization Networks2.1.2 PDH and SDH Networks2.1.3 IP Networks

2.2 Equipment View2.3 Duplication of Synchronization2.3.1 TUB and CBU nodes2.3.2 DU nodes

3 Managed Object Model3.1 Managed Object Overview3.2 Managed Objects3.2.1 Synchronization3.2.2 TimingUnit3.2.3 TuSyncRef

4 Configuration Management4.1 The Synchronization Reference Lists4.2 Adding and Reconfiguring a Network Synchronization Reference4.3 The IP Synchronization Reference4.4 The IP Time Server4.5 Minimizing the Start-Up Time for Synchronization over IP by

5 Fault Management5.1 Configuration of Fault Management 5.2 State of the Node Clock5.3 Fault Scenarios5.3.1 Fault on a Synchronization Reference5.3.1.1 PDH and SDH Synchronization References5.3.1.2 Dedicated Synchronization References5.3.1.3 GPS Synchronization References5.3.1.4 IP Synchronization References5.3.1.5 General Consequences of Synchronization Reference Faults

5.3.2 Absence of Synchronization References for a Longer Period 5.3.3 Frequency Deviation of Some but Not All Synchronization Re5.3.4 Frequency Deviation of All Synchronization References5.3.5 Aging or Frequency Faults of a Node Clock5.3.6 Faults of Synchronization Reference Path5.3.7 Transients on a Synchronization Reference5.3.8 Faults in System Clock Distribution5.3.9 Hardware faults in TimingUnit5.3.10 Faults on the Inter-PIU Link

5.4 Preparation for Replacing a PIU5.4.1 TUB- or CBU-based Node5.4.2 DU-based Node

6 Performance Management7 Security Management

network synchronization

Documents

apdhsdh network

network synchronization2

managed area

network view ofsynchronization

network viewsthe purpose

duplication of synchronization

ip synchronization reference

management model