Synchronization

Network Synchronization

DESCRIPTION

1551-CXA 110 3292 Uen J

Copyright

© Ericsson AB 2007–2012. All rights reserved. No part of this document may bereproduced in any form without the written permission of the copyright owner.

Disclaimer

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.

1551-CXA 110 3292 Uen J | 2012-07-23

Contents

Contents

1 Introduction 1

1.1 Target Groups 1

1.2 Prerequisites 1

2 Functions and Concepts 3

2.1 Product View 3

2.2 Network Views 3

2.3 Equipment View 13

2.4 Redundancy of Synchronization 18

3 Managed Object Model 19

3.1 Managed Object Overview 19

3.2 Managed Objects 21

4 Configuration Management 25

4.1 Synchronization Reference Lists 25

4.2 Adding and Reconfiguring a Network SynchronizationReference 26

4.3 Frequency Synchronization using NTP 26

4.4 Frequency Synchronization using PTP 27

4.5 Time Synchronization using PTP 27

4.6 IP Time Servers (NTP) 27

5 Fault Management 29

5.1 Configuration of Fault Management 29

5.2 State of the Node Clock 29

5.3 Fault Scenarios 29

5.4 Preparation for Replacing a PIU 35

6 Performance Management 39

7 Security Management 41

8 License Management 43

8.1 PTP Licenses 43

9 Files 45

1551-CXA 110 3292 Uen J | 2012-07-23


1551-CXA 110 3292 Uen J | 2012-07-23

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 modeled includingthe 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 Groups

The 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 Prerequisites

Previous 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.

11551-CXA 110 3292 Uen J | 2012-07-23


2 1551-CXA 110 3292 Uen J | 2012-07-23

Functions and Concepts

2 Functions and Concepts

2.1 Product View

This section describes general aspects of network synchronization andconcepts that apply to any equipment involved in network synchronization. Thissection also describes management functions applicable to Ericsson nodes inthe WCDMA and the LTE RAN as well as Ericsson's Mobile Media Gateway.

However in some RBS configurations, the Ericsson product TransportConnectivity Unit (TCU) is used to provide IP connectivity and synchronizationsupport for an RBS node. Although the management of network synchronizationaspects of the TCU is similar to the description below, the managementfunctions of the TCU are described in the product documentation for the TCU.

Note: When an Ericsson RBS includes a TCU, from a network synchronizationcharacteristics perspective, the two nodes are regarded as one entity.That is, the characteristics at the interface between the TCU and theRBS should not be expected to meet general synchronization standardrequirements. This also applies to the Site Integration Unit (SIU) whichis a similar legacy product.

2.2 Network Views

The 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.

Note: Do not confuse Network synchronization with database synchronization,where the latter deals with aligning the content of databases.

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 can be used, which then have norelationship to the phase and frequency of the physical links.

Time synchronization of nodes is sometimes needed. If so, a directly connectedGPS receiver, a box providing a discrete time synchronization interface(HPTSI), or a time server supporting time distribution through a packet protocolis used.

Section 2.2.4 on page 8 describes the network view of synchronization in aPDH/SDH network. Section 2.2.5 on page 9 describes the network view ofsynchronization in a Packet network.

31551-CXA 110 3292 Uen J | 2012-07-23


2.2.1 General Aspects of Frequency Synchronization Networks

The PRC is distributed over transmission links, by packets, or dedicatedsynchronization links in the network. The PRC(s) optionally synchronize(s) thenext level of clocks, that is, the Synchronization Supply Units (SSU). Theyin turn synchronize the integrated clocks in the telecom equipment, such asSynchronous Digital Hierarchy (SDH) Equipment Clocks (SEC), EthernetEquipment Clocks (EEC), or for PTP: Grand Master Clock, Boundary Clock, orOrdinary Clock. In the context of Ericsson's solution for network synchronizationusing NTP, the NTP server and slave are a part of the Network Synchronizationconnection. One or more links or Packet communication associations are usedas synchronization references. The Network Synchronization Plan specifieswhich links or associations are used for synchronization and which links eachnode uses.

In normal operation, clocks are synchronized to a PRC. This state is calledLocked 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 period has elapsed.

Figure 1 shows an example of a synchronization chain from a PRC to an SEC.This representation focuses on the synchronization characteristics in terms offrequency, jitter, wander and Maximum Time Interval Error (MTIE). If the numberof SECs becomes too high, it might be necessary to insert a SynchronizationSupply Unit (SSU) to improve the synchronization quality. If a packet method isused, not all nodes may be Network Synchronization nodes. That is, routers orEthernet switches, may just forward the synchronization packets.

4 1551-CXA 110 3292 Uen J | 2012-07-23


PRC level

SSU level

SEC/EEC 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

51551-CXA 110 3292 Uen J | 2012-07-23


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 frequency synchronization is to synchronize all clocksin the network to a common frequency, that is, to have the same long-termfrequency accuracy everywhere. It is highly recommended that the sourcefor the long-term frequency accuracy is a PRC. To secure PRC availabilityat any time, the synchronization network must be implemented in redundantstructures. This prevents individual clocks from entering holdover mode if asingle network failure 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.

6 1551-CXA 110 3292 Uen J | 2012-07-23


PRC

SSU

SEC

SSUPRC

SEC SEC SEC SEC

SEC SEC SEC SEC SEC

SEC SEC SEC SEC SEC

Figure 4 Redundancy in Synchronization Networks

2.2.2 General Aspects of Time Synchronization Networks

The purpose of network time synchronization is to synchronize all clocks in thenetwork to a common time, that is, to have the same long-term time accuracyeverywhere. The source for the long-term time accuracy must be a PRC ofhigh accuracy (Hydrogen maser technology). To secure PRC availability atany time, the synchronization network must be implemented in redundantstructures. This prevents individual clocks from entering holdover mode if asingle network failure occurs.

The PRC time is distributed either from a Global Navigation Satellite System(GNSS) such as GPS, by time distribution over packets such as PTP, or throughdiscrete timing interfaces such as the High Precision Time SynchronizationInterface (HPTSI). These methods may also be combined to form a timesynchronization trail.

In the GNSS case, a satellite receiver is connected directly to the node thatneeds to be high-precision time synchronized. For time distribution over apacket network, the Time PRC is connected to a time server, which generatespackets containing time stamps of high accuracy. The discrete time interfaceuses dedicated equipment and interfaces to build up an end-to-end or a partof the synchronization trail.

71551-CXA 110 3292 Uen J | 2012-07-23


2.2.3 Node View of Network Synchronization and the NetworkSynchronization Plan

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 equipment clock and is thendistributed to all outputs of the node that carry synchronization.

Selector

Clock

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 detailsthe links and associations that are used for conveying information on networksynchronization, and finally on node level, the inputs that are used as thenetwork synchronization references 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.

2.2.4 PDH and SDH Networks

The following applies to most nodes in a network and it is valid for allCPP-based nodes with SDH or PDH interfaces.

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 are

8 1551-CXA 110 3292 Uen J | 2012-07-23


timing-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 in 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.

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)

2.2.5 Packet Networks

Network synchronization in a packet-based network is performed using timestamps inserted in IP packets or in Ethernet frames.

There are two protocols supporting network synchronization over Packets: NTPand PTP (also called IEEE 1588). NTP is used for frequency synchronizationonly, whereas PTP supports both frequency synchronization and timesynchronization.

91551-CXA 110 3292 Uen J | 2012-07-23


(Setting the real-time clock of the node, for example for time stamping ofalarms, is not a network synchronization function. Also for the real-time clock,an NTP protocol is used, but this function uses an association separate fromthe network synchronization associations.)

2.2.5.1 Network Synchronization using NTP 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 NTP packets carryingthe time stamps, and the client receives this synchronization information. Thetime client 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.

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 the NTP Method

The time server can either be a stand-alone time server node, or a time serverintegrated within a node. An IpAccessHostEt MO acts as a time server inthe node. The server reacts to incoming timestamp IP packets (from the client),

10 1551-CXA 110 3292 Uen J | 2012-07-23


adds the current time to the relevant fields and returns them to the source IPaddress, that is, the address of the time client.

A CPP-based node acting as time server for IP-NTP synchronization cannotbe synchronized to an IP synchronization reference (that is, a node cannot bea time 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.

2.2.5.2 Network Synchronization using PTP Packets

PTP can be used both for frequency synchronization and for timesynchronization. PTP packets can be carried by UDP/IP packets, or byEthernet frames directly. The definition of PTP relies on the concept of masterand slave clocks, where an SD trail goes from a master to a slave. A PTPnetwork may contain the following elements:

• Grand Master. This is the time server for PTP. It serves the PTP networkwith high-precision time stamps. The Grand Master is compulsory in aPTP network.

• Boundary Clock. This element is a both PTP slave clock and a masterclock that regenerates the time of the Grand Master. It has multiple inputsand outputs. In the same manner as the Grand Master, it can send outlocally generated PTP packets to slaves. Thus, a chain of Boundary Clockscan be built. The Boundary Clock is optional in a PTP network.

• Transparent Clock. The task of this element is to remove the delay variationof a transiting PTP packet. This is achieved by subtracting the transit timeof the PTP packet from the time stamp. The transit time is calculated fromthe time the PTP packet is received at the ingress port of the router orswitch until it leaves the egress port. The transit time of all transparentclocks between a master and a slave are added up and communicated bythe protocol to the slave clock. As it does not regain time, the TransparentClock is not a slave clock. The Transparent Clock is optional in a PTPnetwork.

• Ordinary Slave Clock. This is the time client for PTP, and is the end-nodeslave clock in the PTP synchronization trail. It may regain time or frequencydepending on the requirement of the end node it is serving. The OrdinarySlave Clock is compulsory in a PTP network.

An example of a PTP network is shown in Figure 8.

111551-CXA 110 3292 Uen J | 2012-07-23


L0000540A

Ordinary clock- Slave

RBS

Ordinary clock- Slave

RBS

Masterport

Master

te

Transport Network

L2 Switch

L2 Switch L2 Switch

port

Slaveport

Boundary clock

E to E TransparentClock

E to E TransparentClock

Ordinary clock- Master

IEEE 1588Time Server

Figure 8 IEEE 1588 Network View

A PTP network can operate in two modes: Multicast or Unicast. In the multicastmode, PTP packets are sent from the master clock to all slave clocks in themulticast domain. In the unicast mode, a slave clock in the PTP network setsup a subscription for PTP packets in a master clock.

A PTP network may use two time stamp methods: one-step or two-step. In thetwo-step method, first a time stamp packet with a imprecise time is sent, but itis followed by a packet correcting the time of the first packet. The latter packetis called a follow-up message. In the one-step method, no follow-up messageis sent. Thus, the first packet must have a time stamp of sufficient precision.

In the context of PTP, there is a concept called domain. There is a domainnumber that must be configured in master and slave clocks. However, thedomain concept has different interpretations if unicast or multicast is used.These interpretations are elaborated under the respective headings below.

The PTP Ordinary Slave Clock for both frequency synchronization and timesynchronization is supported. Up to eight Ordinary Slave Clocks can be createdin a node.

12 1551-CXA 110 3292 Uen J | 2012-07-23


The PTP standard defines a ‘‘Best Master Clock Algorithm’’ that finds themaster clock with the precision in the PTP network by exchanging informationbetween clocks in the network. However, this method is not supported. Instead,as is common practice in telecom networks, an Alternative Best Master methodis adopted.

PTP Frequency Synchronization

For frequency synchronization, the ‘‘telecom profile’’ is adopted, whichprescribes the use of UDP over IP and unicast. Boundary and TransparentClocks are not required. It is recommended that at least two Master clocks areused in the network. In a node with the Ordinary Clock support, one instanceof the MO PacketFrequencySyncRef is created for each master clock. Inthe context of the telecom profile, the PTP domain is recognized by the IPaddress of the master clock. The domain number configured in the slave clockmust be the same as the domain number of the master clock. If master clockredundancy is required, two domains must be created, each with a master andslave clock pair. The same principle applies regardless of whether BoundaryClocks are used in the network. The task of network planning becomes morecomplicated in the case of Boundary clocks.

Both IPv4 and IPv6 are supported.

PTP Time Synchronization

For Time synchronization, PTP mapping to Ethernet and Multicast is thesupported method. The use of Boundary and or Transparent Clocks throughoutthe whole network is recommended, to achieve sufficient time accuracy. Forthe Ordinary slave clock, one instance of the MO PacketTimeSyncRef iscreated for each master to which the node is connected. In the context of PTPtime synchronization over Ethernet, the PTP domain is defined by the PTPdomain number solely. It is thus important that the network is planned so thateach master has a unique domain number, so that each PacketTimeSyncRefMO can be associated with a unique master clock.

2.3 Equipment View

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

There are four implementations of the Network Synchronization function:TUB-based, CBU-based, DU- based and SCXB-based corresponding to theTiming Unit Board, the Control Base Unit, the Digital Unit and the SystemControl Switch Board respectively.

Synchronization references can either be a port on a TU or a traffic-carryingport. The TuSyncRef, the GpsSyncRef and the HptsiSyncRef referencesare located on the TUs and the traffic ports are located on ETs. The traffic portreferences can be further distinguished by the format in which they carry the

131551-CXA 110 3292 Uen J | 2012-07-23


timing information. For the PDH/SDH traffic ports, the framing carries the timinginformation whereas the packet Synchronization references, represented by theMOs: IpSyncRef, PacketFrequencySyncRef and PacketTimeSyncRef,carry the timing information as time-stamped packets in time protocols.

2.3.1 Equipment View, TUB Nodes

Figure 9 shows the full equipment view of the network synchronization for aTUB-based node. The A and B planes are marked as suffixes.

ET

SXU SCU TU SCU SXU

User

SXU SCU TU SCU SXU

One ISL link per plane and per extension subrack

ref 2

TuSyncRef

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 synchronization

AlternativeISL paths

RedundancyTermination

TuSyncRef

Figure 9 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.

14 1551-CXA 110 3292 Uen J | 2012-07-23


The TuSyncRef ports are located on the TUs (reference 1 and reference 2)and the traffic ports are located on ETs. The references on ETs might be in themain subrack (reference 3) or in an extension subrack (reference 4). Reference4 is sent to the SCUs for both A and B planes in the extension subrack and isthen sent over ISLs to the SCUs in the main subrack, either directly or overSXUs. Reference 3 is sent directly to the SCUs of both A and B planes.References are selected on the SCUs in 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 system 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 SCUin the main subrack to the SCU in the extension subrack, or the distributionmight pass through an SXU. The clock users get the clocks from both the Aand B planes, and the final selection of the plane to which the clock user issynchronized, is made there.

2.3.2 Equipment View, CBU Nodes

In a node with CBU boards, there are no SCUs in the main subrack, and thereare no extension subracks.

Configurations with more than one CBU are not supported.

Compared to Figure 9, the SCUs (and SXUs) are not present, see Figure 10.

ET Exchange TerminalCBU Control Base Unit

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

the network synchronization

CBU subrack

TuSyncRef orGpsSyncRef

ETa

RedundancyTerminationRef 1

Ref 3

Usera

ETTUa

(CBUa)

Figure 10 Equipment View in the CBU Case

151551-CXA 110 3292 Uen J | 2012-07-23


2.3.3 Equipment View, DU Nodes

A DU-based node has one to three DU boards. In a 2-DU node, the two TUscan switch between the master and the slave role, and all synchronizationinputs can be used as references. In a 3-DU node, only one TU can be themaster, and only the synchronization inputs on the master DU can be used asreferences. The two other TUs are slaves connected to the master TU.

Both the TU and the clock user are located on the same DU. If there is morethan one DU, the clock user in each DU can only get the clock from the TUin the same DU.

See Figure 11.

ET Exchange TerminalDU Digital Unit

TU Timing UnitUser ETs or other units using network synchronization

Secondary DU

TuSyncRef,GpsSyncRef orHptsiSyncRef

User

Ref 1

Ref 2

Ref 3 TUa

User

ET

Primary DU

Ref 4ET

TUa

TuSyncRef,GpsSyncRef orHptsiSyncRef

Figure 11 Equipment View in the DU Case

2.3.4 Equipment View, SCXB Nodes

Figure 12 shows the full equipment view of the network synchronization for aSCXB-based node. The A and B planes are marked as suffixes.

16 1551-CXA 110 3292 Uen J | 2012-07-23


TU SCD

User

TU SCD

One cISL per plane and per extension subrack

ref 2

TuSyncRef

ref 1

SCD

User

SCD

Main Subrack

Extension Subrack

a

aa

b

b b

b

b

aa

1..41..4

cISL Control Inter Switch LinkSCD System Clock DistributionSCXB System Control Switch Board

TU Timing UnitUser A Plug In Unit with users of the system clock

RedundancyTermination

TuSyncRef

(SCXB )b

(SCXB )a

(SCXB )

(SCXB )

a

b

Figure 12 Equipment View in the SCXB Case

TuSyncRef is the only type of synchronization reference supported in anSCXB-based node.

Each SCXB has a SystemClockDistribution MO. If the SCXB is locatedin the main subrack, the SCXB also has a TimingUnit MO.

The TuSyncRef ports are connected to the TUs (reference 1 and reference 2).Therefore synchronization references are available only on the SCXBs in themain subrack. The TU filters the reference and generates the system clock,which is distributed within the node.

The system clock in the main subrack distributes the system clock forthe A and B planes respectively, to the other TU and to the system clockusers in the main subrack. The SystemClockDistribution in the mainsubrack also distributes the system clock for their respective plane, over theControlInterSwitchLink to the SCXBs in the extension subracks.

171551-CXA 110 3292 Uen J | 2012-07-23


The SystemClockDistribution in the extension subracks distributes thesystem clock for the A and B plane respectively to the system clock users inthe extension subrack.

2.4 Redundancy of Synchronization

Due to the different architectures of the TUB-, CBU-, DU- and SCXB-basednodes, the redundancy has different characteristics.

Redundancy of CBU nodes is not supported.

2.4.1 Redundancy of TUB

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 9 and Figure 10. If synchronization is not duplicated, there isonly an A plane and the node is not single-fault tolerant.

2.4.2 Redundancy of DU Nodes

There is no redundancy for synchronization in DU-based nodes.

2.4.3 Redundancy of SCXB Nodes

An SCXB-based node is always duplicated. All clocks, reference selectionas well 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 12.

18 1551-CXA 110 3292 Uen J | 2012-07-23

Managed Object Model

3 Managed Object Model

This section describes the management model defined for this area.

3.1 Managed Object Overview

The Managed Area, Network Synchronization represents a subset of the MOM.

The Managed Objects within the Network Synchronization MA are:

• Synchronization

• TimingUnit

• SystemClockDistribution

• TuSyncRef

• GpsSyncRef

• HptsiSyncRef

• PacketFrequencySyncRef

• PacketTimeSyncRef

There are also a number of other MOs that support the Network Synchronizationfunction. In TUB-based nodes, the most important supporting MOs are theSwitchCoreUnit (SCU) and the SwitchExtensionUnit (SXU) wherethe selection and distribution of network synchronization are located. Alsothe SwitchInternalLink (ISL) and PlugInUnit (PIU) are used. InSCXB-based nodes, also the ControlSwitch, the ControlSwitchPort,ControlInterSwitchLink the PlugInUnit MOs support the NetworkSynchronization function.

The NTP Time Server is controlled by the IpAccessHostEt MO.

The MOs in Network Synchronization are shown in Figure 13.

The MOs for Equipment are shown in Figure 14.

191551-CXA 110 3292 Uen J | 2012-07-23


Figure 13 Functional View of the MOs in Network Synchronization

20 1551-CXA 110 3292 Uen J | 2012-07-23


Figure 14 Equipment View of the MOs in Network Synchronization

The TUB, the CBU, the DU and the SCXB boards are of type PlugInUnitcontaining the TimingUnit. The TimingUnit on a TUB, a DU or an SCXBboard is a child of the PlugInUnit MO.

The SCXB PlugInUnit is also the parent of the SystemClockDistributionMO.

3.2 Managed Objects

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

211551-CXA 110 3292 Uen J | 2012-07-23


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 attribute.

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, GpsSyncRef, TuSyncRef, HptsiSyncRef,PacketFrequencySyncRef and PacketTimeSyncRef.

The Synchronization MO is automatically created when the node starts.

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. Itis also created for each SCXB located in the main subrack.

Note: In an SCXB-based node with autoconfiguration, the MO TimingUnitis created when the MO PlugInUnit is created, under the conditionthat the SCXB is located in the main subrack. In this case, the MOTimingUnit is created at the same time as the MOs PlugInUnitand SystemClockDistribution are created.

The attributes gpsOutEnabled or hptsiOutEnabled can be set inDU-based nodes, making it possible to configure GPS or HPTSI ports to output1PPS and time information. It is not possible to set gpsOutEnabled orhptsiOutEnabled to true if there exists a GpsSyncRef, HptsiSyncRefor a TuSyncRef child of the sameTimingUnit MO. It is not possible to setthe attribute hptsiOutEnabled to true if the attribute gpsOutEnabledis set to true, or vice versa.

3.2.3 SystemClockDistribution

This MO models the distribution of system clock signals from an SCXB tosystem clock users in the same subrack or to other subracks.

The MO SystemClockDistribution is created on all SCXBs whenthe PlugInUnit MO is created, under the condition that the node usesautoconfiguration.

The system clock distribution between subracks uses the Control Inter SwitchLink (CISL), represented by the MO ControlInterSwitchLink. The CISLis connected in each end to a Control Switch Port, represented by the MO

22 1551-CXA 110 3292 Uen J | 2012-07-23


ControlSwitchPort, and further to the Ethernet Switch represented by theMO ControlSwitch.

3.2.4 TuSyncRef

This MO models a frequency network synchronization reference directlyconnected to the Timing Unit board, CBU, DU or SCXB. It represents thesynchronization references supported by the board without providing any phaseor time information.

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

The TuSyncRef MOs are created manually under the TimingUnit MO.

The MO TuSyncRef cannot be created if the gpsOutEnabled or thehptsiOutEnabled attributes of the parent TimingUnit are set to true or ifa GpsSyncRef or an HptsiSyncRef MO is created.

3.2.5 GpsSyncRef

This MO models the GPS time synchronization reference directly connected tothe CBU or the DU. It represents the synchronization references that providesGPS time information.


In addition, the MO models a number of other GPS features representedin attributes for the antenna position, the dilution of precision, the status ofreceived data and satellite data. The attribute gpsCompensationDelaymakes it possible to compensate for delays in cables and intermediateequipment. The attribute observationPoint shows when the estimationof the node position (of a node that is not moving) is considered accurate. Ifthe estimation of the node position is found to be accurate, that informationtogether with the delay compensation is used to provide more accurate timeinformation to the node.

The GpsSyncRef MOs are created manually under the TimingUnit MO.

The MO GpsSyncRef cannot be created if the gpsOutEnabled or thehptsiOutEnabled attributes of the parent TimingUnit are set to true, or ifa TuSyncRef or an HptsiSyncRef MO is created.

3.2.6 HptsiSyncRef

This MO models the discrete time synchronization reference directly connectedto the DU. It represents the synchronization references that provide HPTSItime information.

231551-CXA 110 3292 Uen J | 2012-07-23



In addition, the MO models a number of other HPTSI features represented inattributes for the type of clock source (Beidou, GPS, 1588 or other), the HPTSIsynchronization status (accuracy), and source status, as well as the jitter leveland the number of leap seconds. The attribute hptsiCompensationDelaymakes it possible to compensate for delays in cables and intermediateequipment.

The HptsiSyncRef MOs are created manually under the TimingUnit MO.

The MO HptsiSyncRef cannot be created if the gpsOutEnabled orhptsiOutEnabled attributes of the parent TimingUnit are set to true, orif a TuSyncRef or a GpsSyncRef MO is created.

3.2.7 PacketFrequencySyncRef

This MO models the network synchronization over packets reference forfrequency synchronization of the node using PTP.

For this MO, it is possible to configure the DSCP value for the PTP packets,PTP domain, the PTP server address (PTP master or boundary clock), and thereference to the IpAccessHostEt MO used for the PTP communication.

It reports the operational state and availability status of the networksynchronization reference, as well as attributes for packet synchronizationstatus, PTP grandmaster identity, PTP own and parent port identity and masterclock quality.

The PacketFrequencySyncRef MOs are created manually under theSynchronization MO.

3.2.8 PacketTimeSyncRef

For this MO, it is possible to configure pBit for the Ethernet frames carrying PTPpackets, PTP domain, and the reference to the GigaBitEthernet MO usedfor the PTP communication.

It reports the operational state and availability status of the networksynchronization reference, as well as attributes for packet synchronizationstatus, PTP grandmaster identity, PTP own and parent port identity and masterclock quality.

The PacketFrequencySyncRef MOs are created manually under theSynchronization MO.

24 1551-CXA 110 3292 Uen J | 2012-07-23

Configuration Management

4 Configuration Management

No network synchronization references are defined by default.

4.1 Synchronization Reference Lists

The 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 value NULL.

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.

The synchronization reference with the value ACTIVE in the syncRefActivityattribute represents the selected synchronization reference. Only onesynchronization reference can be ACTIVE at a time.

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

251551-CXA 110 3292 Uen J | 2012-07-23


4.2 Adding and Reconfiguring a Network SynchronizationReference

A network synchronization reference is registered with the actionaddSyncRefResource that associates the MO representing the reference tothe 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 Frequency Synchronization using NTP

The IpSyncRef MO needs to be configured. Most other synchronizationreference MOs represent a physical port of the node and the synchronizationsource that is determined by the network. The IpSyncRef MO represents alogical termination point. It has to be connected with its synchronization sourceby assigning the IP address of the time server to the IpSyncRef MO.

The time server can be specified either as a numeric IP address or as a domainname. If it is a domain name, DNS resolve attempts are made repeatedly untilthe domain name is resolved.

A resolved IP address is used permanently except in the following two cases:

• A domain name is resolved when the IpSyncRef MO has changedadministrative state.

• If the time server is unreachable, DNS resolves are made until anIP address to a reachable time server is received. If the existingcachedIpAddress becomes reachable, the DNS resolve attempt stops.

To prevent transients during a change of IP address, set the administrativestate of the IpSyncRef MO to LOCKED. The administrative state must not beset 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.

26 1551-CXA 110 3292 Uen J | 2012-07-23

Configuration Management

4.4 Frequency Synchronization using PTP

The MO PacketFrequencySyncRef needs to be configured. There mustbe one MO created for each master to which the node can synchronize. Theattribute ptpDomain must be set to the same value as in the master clock.The master clock is identified by its IP address, which is set in the attributeserverAddress.

4.5 Time Synchronization using PTP

The MO PacketTimeSyncRef needs to be configured. There must be oneMO created for each master to which the node can synchronize. Each masterhas a unique domain number. The corresponding domain number is configuredin the attribute ptpDomain.

4.6 IP Time Servers (NTP)

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 Ttme server should be located as close to the external Ethernet interfaceas possible. Avoid using IpAccessHostEt MOs located behind an EthernetSubrack Link (ESL) or Ethernet switch board. See the description of EthernetSwitching for information about Ethernet links in the node.

271551-CXA 110 3292 Uen J | 2012-07-23


28 1551-CXA 110 3292 Uen J | 2012-07-23

Fault Management

5 Fault Management

See the separate lists of alarms and events.

5.1 Configuration of Fault Management

The node can be configured so that a degradation fault based onhigh Bit Error Rate on the transmission link is considered as a reasonto disqualify the reference as a network synchronization reference inthe MO Synchronization. This configuration is set by the attributedegradationIsFault. The configuration is valid for all PDH and SDHreferences. The configuration is applicable for the node, that is, it is not possibleto have different configurations for different references.

5.2 State of the Node Clock

The 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 withredundant 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 synchronizationreference, the port MO issues an alarm. The synchronization reference status(syncRefStatus) is FAILED or DEGRADED.

This normally indicates a fault in the network.

5.3.1.2 Timing Unit Synchronization References

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

291551-CXA 110 3292 Uen J | 2012-07-23


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

5.3.1.3 GPS Synchronization References

Fault management of a GPS Synchronization reference is handled by theGpsSyncRef MO.

GPS synchronization references are applicable for CBU-based nodes andDU-based nodes.

If there are failures detected on a GpsSyncRef, the alarm Network SynchTime from GPS Missing is issued.

Depending on the fault, the alarm Network Synch Time from GPSMissing contains further information and provides status information in theattribute gpsRefState.

5.3.1.4 HPTSI Synchronization References

The HptsiSyncRef MO has no alarms. The status of the interface can beviewed through the attributes hptsiMonitorAlarm,hptsiPpsState andhptsiStateOfClockSource. Status information is also provided in theattribute gpsRefState.

5.3.1.5 IP-NTP 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 NTPServer Reachability Fault is issued 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 timestamp packets contains information put there by thetime server, giving information about the server. The contents of the headersof the NTP packets are supervised for two possible problems. They are theStratum level and the Leap Indicator (LI) fields. A Stratum level different fromone indicates that the NTP server is not controlled by PRC or possibly notsynchronized at all. A Leap Indication (LI) equal to 3 indicates that the serverhas an alarm condition. If any of these conditions occurs, the time server isconsidered to be unreliable, the alarm Synch Reference Not Reliableis issued and the synchronization reference status (syncRefStatus) isNOT_RELIABLE.

The delay variation of the timestamp packets is also monitored for the ACTIVEreference. If it exceeds the limits for a synchronization reference, the alarmSync Reference PDV Problem is issued, and the syncRefStatus isset to PDV_PROBLEM.

30 1551-CXA 110 3292 Uen J | 2012-07-23

Fault Management

5.3.1.6 PTP Synchronization References

There is constant surveillance of the connections to the master clock. If a failureis detected, the alarm Packet Server Availability Fault is issued bythe PacketFrequencySyncRef or the PacketTimeSyncRef MOs. Theattribute packetSyncStatus gives further information on the status of theconnection to the master. The status information mostly gives indications ofproblems in the master clock, but can also indicate some network problemssuch as loss of packets. Several states can be indicated simultaneously asa sum of fault codes.

The delay variation of the PTP packets is also monitored for the ACTIVEreference. If it exceeds the limits for a synchronization reference, the alarmSync Reference PDV Problem is issued. If the synchronization sourcesignals a state indicating that it cannot be used for synchronization, the clientnode issues a Packet Server Availability Fault alarm, and thesynchronization reference status (syncRefStatus) is set toFAILED.

5.3.1.7 General Consequences of Synchronization Reference Faults

If the reference was active, the fault-free reference with the highest priorityis selected.

If the synchronization reference was the last one available, the node entersHOLD_OVER_MODE. In a DU-based node, if the state HOLD_OVER_MODEpersists and is close to the maximum holdover time, the alarm ClockCalibration Expiry Soon is 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 ofTime for TUB, SCXB and CBU nodes

If all synchronization references are unavailable, nodeSystemClock is inHOLD_OVER_MODE and the alarm, System Clock in Holdover Modeis 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 and the alarm System Clock inHoldover Mode is ceased.

311551-CXA 110 3292 Uen J | 2012-07-23


5.3.3 Absence of Synchronization References for a Longer Period ofTime for DU nodes

If all synchronization references are unavailable, nodeSystemClock is inHOLD_OVER_MODE. The node can operate for a substantial time in holdovermode if no other faults are detected. If none of the synchronization referencesrecovers, the node will after a while not be able to maintain holdover mode andinstead go into FREE_RUNNING_MODE. If that happens, the alarm SystemClock Quality Degradation is issued. To inform that there is a large riskthat the node will go into the free-running mode soon if no actions are taken,the alarm Clock Calibration Expiry Soon is issued. An estimation ofthe remaining time is included in the alarm.

5.3.4 Frequency Deviation of Some but Not All SynchronizationReferences

If the active synchronization reference has an excessive frequency deviation, itis detected as ‘‘Loss of Tracking’’. A Loss of Tracking alarm is issued andthe attribute nodeSystemClock takes the value LOSS_OF_TRACKING_MODE.The active synchronization reference status (syncRefStatus) isLOSS_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.

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.

Finally, a synchronization reference that does not have a frequency deviationis selected. The node system clock leaves LOSS_OF_TRACKING_MODE andenters LOCKED_MODE and the node is working 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 bythe action ResetLossOfTracking.

Inactive synchronization references are not supervised for frequency deviation.

5.3.5 Frequency Deviation of All Synchronization References

When all synchronization references (syncRefStatus) are inLOSS_OF_TRACKING, the node system clock also remains inLOSS_OF_TRACKING_MODE.

32 1551-CXA 110 3292 Uen J | 2012-07-23

Fault Management

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 node system clock 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.

5.3.6 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 the references,the attribute nodeSystemClock takes the value 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 5.3.5 on page 32.

TUB-, CBU- or SCXB-based node with Duplicated Synchronization

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.

5.3.7 Faults of Synchronization Reference Path

If a hardware fault occurs along the synchronization reference path, the alarmSynch 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_MODE. The active synchronization reference is changed, asdescribed in Section 5.3.1.7 on page 31. The fault is somewhere in the ET,

331551-CXA 110 3292 Uen J | 2012-07-23


SCU, ISL, SXU, SCU, CBU or TU in the A plane, see Figure 9. The faulty unitneeds to be changed.

TUB- or SCXB-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 9. If the active synchronization reference pathshave failed in both planes, the reference becomes FAILED_MODE. The activesynchronization reference is changed, as described in Section 5.3.1.7 on page31. The fault is somewhere in the ET, SCU, ISL, SXU, SCU, CBU, SCD or TUin the plane of the fault. The faulty unit needs to be changed.

DU-based node

For a dual-DU node, the following applies:

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 11. If the synchronization reference is ACTIVE, another synchronizationreference is selected, as described in Section 5.3.1.7 on page 31. The faultyDU or IDL cable needs to be changed.

For a triple-DU node, the following applies:

The alarm Slave TU Out of Synchronization is issued, andthe synchronization reference status (syncRefStatus) becomesREF_PATH_FAILED_A. The faulty DU or IDL cable needs to be changed.

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

5.3.8 Transients on a Synchronization Reference

There might be transients on a Synchronization reference that are notdetected by the port and do not cause any alarms to be issued by the portMOs. 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)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.

5.3.9 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. If the node is SCXB-based, these alarms,

34 1551-CXA 110 3292 Uen J | 2012-07-23

Fault Management

except the Plug-In Unit Synch Hardware Fault alarm, are replaced bythe System Clock Distribution HW Fault alarm.

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 or theunit connecting them. Figure 9, Figure 10, Figure 11 or Figure 12 give a view ofhow the units are related to each 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.

5.3.10 Hardware faults in TimingUnit

If a hardware fault occurs on the PIU with a TimingUnit, an alarm is issued. Ifit is on a TUB or an SCXB, the alarm Plug-In Unit HW Failure is issuedby the PlugInUnit MO. If the fault is on a CBU or DU, the TU HardwareFault alarm is issued by the TimingUnit MO. A TimingUnit of a DU mightalso issue the alarm TU Oscillator Temperature Fault which eitherindicates a fault in the climate control of the RBS, or a hardware fault on theTiming Unit.

5.3.11 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 multi-DU configuration thatonly affects TimingUnit network synchronization, the Slave TU Out ofSynchronization alarm is issued by the slave TimingUnit MO. If the faultsaffect 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-, CBU- or SCXB-based Node

See the instruction for replacing a Timing Unit Board, a Control Base Unit, aSwitch Core Board, a Switch Extension Board or a System Control SwitchBoard.

In TUB-based nodes, the network synchronization function might be duplicatedin a node with two planes (A and B) with duplicated Timing Units, Switch CoreUnits, Switch Extension Units and Switch Internal Links, see Figure 9. AlsoCBU-based nodes, see Figure 10 may be duplicated with two planes (A and

351551-CXA 110 3292 Uen J | 2012-07-23


B) with duplicated Timing Units. SCXB- based nodes, see Figure 12, arealways duplicated with two planes (A and B) with duplicated Timing Units.The following assumes that none of the Network Synchronization units has afault or is locked in any way.

Before removing any of those units, ensure that they are locked with theadministrativeState of the MO PlugInUnit they are located on,see the instruction Lock Board, or for the SwitchInternalLink with theadministrativeState directly on the MO. By doing so, within 20 secondsthe PIUs in the affected subracks select synchronization from the other plane,minimizing the 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 PlugInUnit for the SwitchCoreUnit 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.

Locking of the PlugInUnit for the ControlSwitch in the main subrackcauses all the PIUs in the node to take synchronization from the other plane.

Locking of the PlugInUnit for the ControlSwitch in the extension subrackcauses all the PIUs in that extension subrack to take synchronization fromthe other plane.

Administrative locking of the ControlInterSwitchLink causes theextension subrack to take synchronization from another link.

If the active synchronization reference is a TuSyncRef or a GpsSyncRef onthe TimingUnit, the administrative locking of the PIU for the TimingUnitcauses the reference to be discarded, as the TuSyncRef MO or theGpsSyncRef MO is DEPENDENCY_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 node does not have duplicated Network Synchronization or if any of theNetwork Synchronization units has faults or is locked in any way, replacing theboard causes disturbances. If the PIU with the TimingUnit is replaced, thehistorical frequency data used for fast restart are lost, and in particular in thecase of IP synchronization references, the start-up time might be longer.

36 1551-CXA 110 3292 Uen J | 2012-07-23

Fault Management

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.

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 available. If noreference is available on the DU acting as slave and if the DU acting as masteris being replaced, the slave enters holdover mode. As the holdover periodspecified for the node does not apply for the slave, the board must be replacedwithin 15 minutes. The consequences of not having any synchronizationreferences are described in Section 5.3.2 on page 31.

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 are lost, and in particular in the case of IP synchronization references,the start-up time might be longer.

If the node is a triple-DU configuration, the whole node is non-operational whenthe board with the master TU is being replaced. If any of the slave DUs arereplaced, the node will be re-synchronized automatically.

371551-CXA 110 3292 Uen J | 2012-07-23


38 1551-CXA 110 3292 Uen J | 2012-07-23

Performance Management

6 Performance Management

See the specifications of the PM counters in the MOM.

391551-CXA 110 3292 Uen J | 2012-07-23


40 1551-CXA 110 3292 Uen J | 2012-07-23

Security Management

7 Security Management

Not applicable.

411551-CXA 110 3292 Uen J | 2012-07-23


42 1551-CXA 110 3292 Uen J | 2012-07-23

License Management

8 License Management

To use a licensed feature, a license key file for the feature must exist inthe node. Each licensed feature has its own MO containing the attributeslicenseState and featureState. The attribute licenseState has thevalue ENABLED if a license exists. A licensed feature is activated by settingthe attribute featureState to ACTIVATED. General license management isdescribed in the description of Licensing.

8.1 PTP Licenses

PTP is a licensed feature managed by the PacketFrequencySyncRef andthe PacketTimeSyncRef MO respectively. There is one license in each MO.If no license has been installed, if the installed license has expired, or if theattribute featureState is set to DEACTIVATED, it is possible to configurePTP, but the PTP packet flow will be disabled. That is, no PTP packets arereceived by or transmitted from the node.

431551-CXA 110 3292 Uen J | 2012-07-23


44 1551-CXA 110 3292 Uen J | 2012-07-23

Files

9 Files

Not applicable.

451551-CXA 110 3292 Uen J | 2012-07-23

Synchronization

Documents

Transcript of Synchronization