Application Note 243

Synchronization has been a fundamental requirement in digital networks since the introduction of PDH systems in the 1980s, through the rollout of SDH/SONET in the 1990s to today’s optical transport networks (OTNs). Synchronization distribution has been widely available through the physical layer of all of these technologies, and equipment vendors and network operators alike have had the luxury of utilizing this to transmit time and timing information from the core to the edge.

The increasing demands on network operators to supply richer service offerings at more competitive rates has forced a convergence of network technologies to packet-based methods. This has caused a paradigm shift in the availability of physical-layer synchronization—moving away from the circuit-switched world to that of connectionless operation. The requirements for stable time and timing still exist for many applications and nodes within the packet-switched network, and new technologies have been devised to accommodate transport synchronization over higher layers through packet networks. Therefore, not only is testing and monitoring of synchronization performance carried out at the physical layer, now the packet-layer performance has to be tested and monitored too.

Even as service providers move towards an all-packet network, the footprint of time-division multiplexing (TDM) services and circuits is still a major part of the network. TDM transport continues to represent signifi cant revenue for service providers and carriers and must still be supported during the transition phase. Therefore, synchronization must be maintained in the TDM portion of the network and essentially implemented in the packet portion of the network to ensure smooth operations and interoperability between both domains.

The growth of wireless services is driving the push for Ethernet as a replacement technology in backhaul networks. However, synchronization is a must for cellular and wireless operation, as base stations must be synchronized in order to hand off calls between base stations, to minimize dropped calls and ensure proper billing—all refl ected in customer satisfaction.

This application note explores the current state of synchronization standards for the synchronization over packet implementations, as well as methods of deployment and the tools and techniques required to assure the successful implementation and ongoing support of such systems. It also introduces EXFO’s upcoming test solution for network synchronization and examines the various aspects and advantages of this solution.

Measuring the Pulse of your network with Syncwatch-110Thierno Diallo, Product Specialist, Transport and Datacom Business Unit

Digital network SDh transport Broadband Services

application Voice Voice + Data Voice + Data + Multimedia Voice + Data + Multimedia

Signaling R2 (PSTN)

SS7/IN (ISDN/B-ISDN)

SIGTRAN/MEGACO (ISDN/B-ISDN)

AII-IP signalling (MEGACO/SIP/H.323)

transport TDM Switching

TDM/ATM Switching

IP/ATM Routing

IP/MPLS (Routin LDP)

transmission SDH SDH SDH/WDM/OXC/GbE WDM/OXC/NgSDH

access link 2W loop 2W loop/dial-up FLC

2E loop/xDSL Cable/Ethernet/PON/FLC

All kinds of access types

› Central primary reference clock (PRC)

› Distribution over copper E1 trunks

› Local node clock phase following oscillators

› Non-redundant

› Protection 1:N

› Distributed primary reference sources (PRS)

› G.812 type I, II, V or VI filtering/holdover oscillators

› Remote management

› Distrubution impaired by SDH payload pointers/created timing islands

› New requirements:

- Protection 1+1

- Time of day NTP/PTP/UTI

- Remote management

› NGN transport technologies create even more timing islands

› Network monitoring, management, security

1980 1990 2000 2010

Synchronization Profile

Figure 1. Network and synchronization evolution

© 2010 EXFO Inc. All rights reserved.

Application Note 243

Synchronization BaSicSSynchronization can be defined as the coordinated and simultaneous relationship between time-keeping among multiple devices. For people outside of the telecom world, synchronization typically refers to time synchronization where one or more devices have the same time as a reference clock, typically the universal time clock (UTC); when synchronized, two devices will have the proper time of day (ToD) in reference to the universal time reference, regardless of their geographical location.

However for network engineers, synchronization has a very precise and critical use. Telecom networks, such as SONET and SDH networks, are based on a synchronous architecture, meaning that all data signals are synchronized and clocked using virtually the same clock throughout. This ensures that all ports that carry data do so at the same frequency or with very little offset, and therefore, network throughput is deterministic and fixed for a specific transport rate.

Ethernet on the other hand is an asynchronous technology where each Ethernet port has its own independent clock circuit and oscillator. Because each port is clock independent, frequency offsets between interconnected ports can be relatively high. To solve this issue, Ethernet devices typically implement buffers that can store traffic and then mitigate the effect of offsets between two ports. Therefore, telecom networks require two other types of synchronization in addition to time synchronization, that is, frequency synchronization and phase synchronization.

Frequency synchronization is typically a physical synchronization where the output clocks between devices is synchronized. When two devices are frequency synchronized, they basically generate the same number of bits over an integration period (typically 1 second). When they are not frequency synchronized, one device will generate more bits per second than the other, which can cause overflow and eventually bit errors or traffic loss.

Phase synchronization refers to the simultaneous variation of clocks between devices. When phase-synchronized, the two devices will shift at exactly the same time from one clock pulse to the other. A real-world example would be to compare two watches side-by-side. When synchronized, these two watches will increment at exactly the same time. When unsynchronized, one device will count faster than the other, and in the network world, these variations are the equivalent of phase offset.

Synchronization technologieS in the network

legacy Frequency SynchronizationModern telecom networks, such as SONET and SDH, are synchronous networks where all transmission is based on a common clock source. These technologies implement hierarchical levels of clock accuracy where a highly precise clock feeds other clocks—each node connects and synchronizes itself to the clock with the highest accuracy.

In SDH, a highly precise, cesium-based master clock, referred to as the “primary reference clock” (PRC), is distributed all over the networks through data signals by synchronizing the output bit clocks via each node’s equipment clocks (SECs). As the clock accuracy degrades with each hop, network nodes known as synchronization supply units (SSUs) are dedicated to regenerating the clock signal, thus ensuring that all nodes remain synchronized to a primary rate. SONET employs the same synchronization mechanism but uses a different terminology: from stratum 1 (highest accuracy) to stratum 4 (lowest accuracy).

Packet SynchronizationAs the network moves towards Ethernet as the transport technology of choice, synchronization remains a major issue. As Ethernet and TDM technologies continue to coexist, technologies like circuit-emulation services (CES) provide capabilities to map TDM traffic on Ethernet infrastructure and vice versa, enabling a smooth changeover for network operators transitioning to an all-packet network.

To interconnect these two technologies, frequency synchronization is key since the TDM technologies have frequency offset tolerances that are much more restrictive than the asynchronous Ethernet technologies. Ethernet relies on inexpensive holdover oscillators and can stop transmitting traffic or buffer data, while TDM technologies rely on the continuous transmission and presence of synchronization reference. Synchronous Ethernet solves these issues by ensuring frequency synchronization at the physical level. Ethernet SyncE achieves frequency by timing the output bit clocks from a highly accurate stratum 1 traceable clock signals in a fashion similar to traditional TDM and SONET/SDH synchronization. SyncE supports the exchange of synchronization status messages (SSM) and now includes a newly introduced Ethernet synchronization messaging channel (ESMC), which ensures that the Ethernet node with SyncE enabled always derives its timing from the most reliable source.

However, since SyncE is a synchronization technology based on layer 1, it requires that all ports on the synchronized path be enabled for SyncE. Any node that is non SyncE-enabled on the path will automatically break the synchronization from this node. This is an issue for network providers that have a multitude of Ethernet ports between the primary synchronization unit and the edge device that needs synchronization, as all the ports must be SyncE enabled to synchronize to the edge. Such requirements can increase the cost of deployments as hardware and software upgrades can dramatically increase the total cost of ownership. SyncE also only focuses on frequency synchronization and does not guarantee phase synchronization—although the phase requirements can be somewhat assessed via SyncE.

© 2010 EXFO Inc. All rights reserved.

Application Note 243

The next packet synchronization technology, the Precise Time Protocol (PTP) is specifically designed to provide high clock accuracy through a packet network via a continuous exchange of packets with appropriate timestamps. In this protocol, a highly precise clock source, referred to as the “grand-master clock” generates timestamp announcements and responds to timestamp requests from boundary clocks, thus ensuring that the boundary clocks and the slave clocks are precisely aligned to the grand-master clocks. By relying on the holdover capability and the precision of the integrated clocks in combination with the continuous exchange of timestamps between PTP-enabled devices, frequency and phase accuracy can be maintained at a sub-microsecond range thus ensuring synchronization within the network. In addition to frequency and phase synchronization, ToD synchronization can also ensure that all PTP-enabled devices are synchronized with the proper time, based on coordinated universal time (UTC).

The advantage of PTP is that as a packed-based technology, only boundary and slave clock needs to be aware of the nature of the packets and therefore, synchronization packets are forwarded as any other data packets within the network. This flexibility reduces the cost of ownership as the main upgrade to the networks are limited to synchronization equipment contrarily to the SyncE approach that requires both synchronization equipment and upgrade of all Ethernet ports on the link to SyncE specifications.

The major weakness of PTP is also due to its packet nature. As the synchronization packets used by PTP are forwarded in the network between grand master and hosts, they are subject to all network events such as frame delay (latency), frame-delay variation (packet jitter) and frame loss. Even with the best practice of applying high priority to synchronization flows, these synchronization packets will still experience congestion and possible routing and forwarding issues such as out-of-sequence and route flaps. The host clock’s holdover circuit must be stable enough to maintain synchronization where the synchronization packets experienced network events.

As for ToD synchronization, protocols such as Network Time Protocol (NTP) ensure that customers are correctly updated with the time-of-day information based on a standard universal time source. NTP and its different versions distribute time and day information periodically to customers, such as personal computers and network devices while ensuring corrections for geographic locations. ToD synchronization is typically achieved via a connection to internet time servers, over the air through radio signals or via GPS synchronization.

PurPoSe oF Synchronization teSting/Monitoring

Testing and monitoring are fundamental to qualifying both network nodes and the networks as a whole. Also, synchronization testing and monitoring is important in helping to identify general transmission and/or switching failures/errors. Synchronization generally degrades as it traverses each and every piece of the transmission equipment that transports or regenerates the synchronization signal. Poor synchronization can be the result of a synchronization system failure, but it can also be the result of changes (improvements or reductions) to the underlying performance of the transport infrastructure.

› “Sync testing” is generally used to indicate short-term (hours/days) measurement of synchronization signals. These measurements are often taken in the lab or in the field as the result of network problems; performance is compared to the agreed standard performance measures.

› “Sync monitoring” is a synchronization measurement taken over the long term (weeks/months). The collected results are compared to an agreed standard or the network-specific performance metrics; synchronization monitoring is typically undertaken as a proactive network activity.

Synchronization MetricsMeasuring synchronization accuracy almost entirely rests on the offset between the significant events of the tested signal compared to the same significant event of the reference clock. This significant event, typically the rising edge of a clock pulse, serves as the trigger value, and any deviation between the two clocks provides the timing difference. From the perspective of the synchronization metrics, the wander of the clock or the phase variation of the clock with a frequency content of less than 10 Hz is the main parameter of interest for multiple reasons:

› As modern clock circuitry, PLLs are designed to eliminate jitter (when frequency content of the phase variation is greater than 10 Hz). Wander, on the other hand, slowly accumulates in the network as nodes synchronized in a daisy chain. Offsets from one node will have repercussions on the clock accuracy of the node that synchronize to it and so on, until incorrect or total loss of synchronization occurs.

› Clock circuitry accuracy decays over time with the aging of the clock oscillator, and temperature variations physically affect the clock circuitry over time. Therefore, it is important for network operators to periodically perform tests to ensure the accuracy and stability of the synchronization and clocking mechanisms in the network.

technology Frequency Synchronization

Phase Synchronization

time of Day

Legacy frequency (TDM) Yes Yes No

Synchronous Ethernet Yes Yes No

IEEE 1588v2 Precise Time Protocol Yes Yes Yes

Network Time Protocol (NTP) No No Yes

© 2010 EXFO Inc. All rights reserved.

Application Note 243

As clock wander typically occurs over a long period of test time, synchronization metrics also must be adapted for long periods of testing in conjunction with a stable and highly accurate clock source as reference. Synchronization metrics typically consist of three key measurements, the time interval error (TIE), maximum time interval error (MTIE) and time deviation (TDEV).

› TIE is a basic measurement of the phase difference between the reference clock and the clock under test, based on the time difference between significant events. This basic measurement, performed over many hours or days of tests, provide immediate offsets between the clocks. Because of its instantaneous nature, this measurement is not ideal for the long-term but provides an assessment of the peak offsets of phase variations, which typically lead to failures.

› MTIE is a measurement based on TIE data designed to provide the maximum deviation of the peak-to-peak value of the TIE within, by widening the observation window. Typically produced after processing the TIE data, the MTIE provides the worst-possible TIE change within different observation windows and can be used to predict the stability of the clock frequency over time.

› TDEV is another measurement derived from TIE data and provides the average phase variations of the clock by expressing the root mean square (RMS) of the variations of the MTIE for specific measurement windows. As MTIE is focused on the worst case, any peak variation will limit the visibility of small variations. TDEV on the other hand averages the worst peak variations and provides a good indication of the periodicities or TIE offsets. TDEV provides information about the short-term stability of the clock and the random noise in the clock accuracy.

Newer metrics are now being introduced to provide better visibility of the accuracy of the clock. Metrics such as the modified allan deviation (MDEV), although useful, are typically used in lab applications for specific frequency stability measurements and are not typically used in field scenarios. The shift to packet-based synchronization has also led the industry to define new metrics, maximum average time interval error (MATIE) and maximum average frequency error (MAFE), to better characterize the frequency and phase errors due to packet events such as packet-delay variation. Note that these metrics are still under study by the various synchronization committees.

In addition to these metrics, international standards committees have released guidelines that describe the acceptable levels of performance for synchronization in telecommunications network. These guidelines aim to define the acceptable performance limits of network equipment with the final aim to help ensure trouble-free synchronization when the network is in full service with this equipment deployed. Synchronization testing using performance masks is therefore a key step in the deployment of maintenance of the network and must ensure that metrics are within these ranges in order to ensure trouble-free transmission.

additional Packet MetricsWith the introduction of PTP, network operators must now qualify new packet metrics based on the PTP architecture. In PTP, since packet synchronization is performed via an exchange of messages, the synchronization flow is therefore sensitive to the presence or absence of messages due to frame-delay variation and frame loss. The PTP flow will be affected by congestion, link failures and queuing due to high traffic flow, just like any other service which in turn can affect the accuracy of the synchronization between the boundary or slave clocks and higher-quality clocks.

Moreover, messages are exchanged unidirectionally, meaning that nodes will exchange and terminate the synchronization packets. This induces the concept of unidirectional performance as a direction can experience more network events than the other directions. Asymmetrical behavior may cause synchronization packets to experience more delays, congestion and possible loss in one direction, while the other direction remains trouble-free.

For such reasons, PTP testing involves not only testing the phase and frequency characteristic of the timing, but also the performance of the synchronization packet flow due to network resources and network events. The key performance indicators PTP’s flow direction must be independently assessed for performance to produce reliable results as well as to understand the relationship between time synchronization and packet events.

Various standards have been defined as the network evolved from TDM to a packet solution. From the test and metrics perspective, the standards committees are also studying new metrics specifically for packet-based synchronization technologies. The ITU-T Study Group 15 Question 13 are working on new series of standards and metrics such as the G.826x series, which define frequency distribution and performance, and the G.827x series, which define phase/time distribution and performance over packet-based synchronization technologies.

introDucing the eXFo Syncwatch-110The new EXFO SyncWatch-110 is an all-in-one synchronization test tool that provides precise, accurate and flexible synchronization testing tool within a single package. This new test unit enables powerful synchronization testing with the flexibility of different operation modes to help customers find and solve network synchronization issues.

The SyncWatch-110 unit’s main testing features make it a complete synchronization tool. As the network completes its evolution to Ethernet and Packet, synchronization will eventually transition to a packet-based solution such as PTP. In the meantime, operators still face testing synchronization while preparing for PTP, which necessitates a tool that will support both legacy and Ethernet synchronization tools.

SyncWatch-110 provides a complete solution with support for legacy synchronization as well as new Ethernet-based synchronization—in a single, compact package. Designed as an all-in-one test tool for network synchronization issues, SyncWatch-110 enables users with all relevant interface from legacy frequency inputs to packet inputs, including:

› Legacy frequency testing via T1/E1 interfaces

› General frequency inputs providing the capability to measure any Frequency signal from 64 Khz to 200 Mhz (in increments of 8 kHz)

› 1 pulse per second test input for frequency assessment of GPS-synched devices

› Ethernet test port for packet synchronization technologies (PTP and SyncE)

© 2010 EXFO Inc. All rights reserved.

Application Note 243

accurate referenceA key aspect of testing synchronization is the accuracy of the reference clock—since the measurement can only be as precise as the reference clock. SyncWatch-110 can be equipped with extremely precise references, either a highly accurate Rubidium reference clock or an internal GPS receiver both with primary reference clock quality that exceeds the performance of PRC as specifi ed by G.811. Each reference clock can provide accurate holdover capabilities in the event of GPS signal outage or provide measurement stability when testing in the fi eld.

The EXFO SyncWatch-110 unit can also use any external reference provided by the customer, thus leveraging the existing synchronization infrastructure and ensuring that the measurements are referenced to the same source as the location.

Powerful analysisSyncWatch-110 provides live measurement of the TIE and can calculate and display at any point the MTIE and TDEV measurements via the SyncWatch-110 measurement application. All results can be saved for post processing using Symmetricom’s industry-standard, time-monitor analyzer application, included with a SyncWatch-110 Stand-Alone license, providing extensive and scientifi c quality results and precision.

Modes of operationSyncWatch-110 can function in three specifi c modes:

Stand-Alone mode is the typical test mode where a user is directly connected to a single SyncWatch-110 unit for testing, either through a direct Ethernet connection or through a network. The Stand-Alone mode provides real-time data analysis with live reporting of results for immediate interpretation via a simple tool; this mode is ideal for evaluating synchronization in the fi eld, lab trials or fi eld commissioning.

Since access to a synchronization expert can sometimes be diffi cult, network operators will enjoy the flexibility of the SyncWatch-110 USB mode and therefore, better manage expertise resources. The USB mode is a simplifi ed mode where a SyncWatch-110 fi nds its confi guration from a USB key, automatically launches the test with the predefined configuration and stores results on the USB key. Using this mode, tier-1 personnel can be dispatched with a unit and a preconfi gured USB key for testing. Once testing is complete, the USB key can be analyzed by a synchronization expert, thus saving time and money and ensuring that expertise is properly used.

As previously mentioned, synchronization can gradually decay over long periods of time; therefore, testing over long periods of time may be necessary to better qualify the stability and accuracy of clocks. With packet synchronization, timestamp packets are subject to network events, and the stability of the clock may be variable over the course of time as the network load varies. Managed mode provides the capability to perform network synchronization testing, where multiple SyncWatch-110 units collect and dump data on servers for continuous 24/7 monitoring of the synchronization health. Once synchronization failure is detected, network operators can quickly determine which link is failing or what metric has been crossed, as well as on which synchronization unit, thereby providing a global view of synchronization over the network.GPS

SyncWatch-110

GPS

SyncWatch-110

STEP 1: USB Configurator

STEP 2: Data Acquisition

STEP 3: Post-Processing and Data Analysis

STEP 2:STEP 2:

© 2010 EXFO Inc. All rights reserved.

Application Note 243

The combination of the Brix network monitoring system and SyncWatch-110 provides a powerful monitoring solution where network operators have complete visibility over the health of data fl ows and synchronization fl ows.

Syncwatch-110 anD the network Synchronization liFecycleThe EXFO lifecycle proposes four distinct stages to constructing and operating a network. These stages cover the entire lifecycle of the network—from the initial construction phase to the fi nal monitoring and troubleshooting phases.

SyncWatch-110 complements the network lifecycle by providing comprehensive testing capabilities for all phases. As synchronization is being deployed or maintained, the SyncWatch-110 unit enables operators to conceptualize, introduce, benchmark and monitor network synchronization effi ciently and with confi dence.

From the perspective of network synchronization, the network lifecycle is modified to focus specifically on synchronization testing. The network lifecycle adapted to network synchronization can therefore be segmented in different phases similar to the following lifecycle:

laboratory trial and equipment BenchmarkThe first phase of any synchronization deployment consists of proving the synchronization design in laboratory trials with a mock network that simulates the production setup. This critical phase gives the opportunity to network planners and engineers to test different synchronization scenario such as migration to different synchronization technologies such as SyncE or simulate network loading and view the effect on packet synchronization.

SyncWatch-110 provides a complete and accurate test solution to measure synchronization in lab trials and the equipment benchmark. In a lab-trial scenario, SyncWatch-110 can be used in long-term measurements and qualify synchronization at different key points of the lab network to measure the effect of changes and network events on the quality of synchronization. Using the advanced reporting capabilities, network engineers can compare multiple results and properly plan network flows and routes to ensure accurate synchronization before deployment on a production network.

equipment Benchmark Equipment benchmarking is a critical phase for device manufacturers and network planners especially when integrating new equipment or upgrading existing equipment with network synchronization capability. Benchmarking allows engineers to make an informed decision on the equipment selection or to qualify the performance of the network synchronization devices, based on precise and factual data.

A typical equipment benchmark can be performed using the two input capabilities of SyncWatch-110 coupled to a single highly precise reference, such as a Rubidium interface. SyncWatch-110 can simultaneously measure performance on two inputs and accurately provide a benchmark of two devices compared to the reference.

Server

Results Alerts

SyncWatch-110

SyncWatch-110

SyncWatch-110

Server

SyncWatch-110SyncWatch-110

GPS

Test Signal

SyncWatch-110SyncWatch-110SyncWatch-110SyncWatch-110SyncWatch-110SyncWatch-110SyncWatch-110

GPS

1laboratory

trial/equipment benchmark

2Synch testing/synch service

turn-up and burn-inturn-up and burn-in

construction Service turn-up/ Monitoring troubleshooting Burn-in

3network

synchronization monitoring

4troubleshooting of synchronization

issues

© 2010 EXFO Inc. All rights reserved.

Application Note 243

lab trialBefore putting a network in service, the synchronization testing phase allows network operators to test and qualify synchronization for short-term and long-term periods, as well as to ensure the stability of the synchronization mechanism and resiliency of the synchronization path.

Whether in a central location or in the fi eld, a SyncWatch-110 unit in Stand-Alone mode provides synchronization experts with powerful testing capabilities to perform extensive testing for stability and frequency synchronization—either in exchange centers or in field locations, such as remote cabinets at wireless towers.

Synchronization Service turn-up and Burn-inWhen using PTP, synchronization packets are classifi ed as a service and are typically with the highest priority within the network. Although serviced with priority, synchronization traffi c is still subject to network events and are sensitive to congestion and queuing.

The synchronization service turn-up and burn-in phase allows network engineers to qualify the ability of the network to properly service the synchronization traffi c according to its confi gured priority, and to verify the performance of the network synchronization fl ow under simulated or real-life loading conditions. As a service, typical testing should focus on the key performance indicators of frame delay variation, frame delay and frame loss and the infl uence of other streams on the synchronization stream during congestion or high network utilization conditions.

The burn-in phase is an essential testing phase where the fl ow is soaked for a longer test period to assess its stability under various loading conditions. This phase provides an assessment of the stability of the network synchronization fl ow over a longer test period and provides a good indication of the capability of the network to effi ciently transport multiple services while maintaining the performance of the synchronization fl ow.

SyncWatch-110 provides support for testing PTP synchronization services by enabling network operators the capability to establish connectivity to a grand master clock and monitor both the performance of the key performance indicators of the network synchronization fl ow and simultaneously measure the phase and associated synchronization metrics. These dual capabilities enable synchronization experts to accurately determine if there are any packet performance issues that can affect synchronization or if there are any issues with the stability of the clock under test—from a frequency and phase perspective.

As a versatile testing unit, SyncWatch-110 enables network engineers to perform complete testing using any available frequency input, enabling the use of the SyncWatch-110 in a variety of situations with a variety of end points. For both of the testing legacy synchronization systems—SyncE interfaces from a cell backhaul path or a PTP stability from a eNodeB—SyncWatch-110 accurately measures synchronization performance and packet performance from a single device.

10 GigE

10 GigE

10 GigE

T1/E1

TDMFrequency

Data Center

T1/E1T1/E1T1/E1T1/E1T1/E1T1/E1

TDMTDMTDMTDMFrequency

T1

SSU

TDM

TDM Frequency

SyncE

TDMTDM

T1T1T1T1T1

10 GigE

10 GigESONET/SDH

GigE Metro

Core

TDM FrequencyTDM FrequencyTDM FrequencyTDM Frequency

TDMTDMFrequencyFrequencyFrequency

SyncWatch-110SyncWatch-110SyncWatch-110SyncWatch-110SyncWatch-110

SyncWatch-110

SyncWatch-110

1588v2

GigE

1588v2

1588 andFrequency

SONET/SDH

SONET/SDH

CoreCore

GrandMaster (GM)

Application Note 243

EXFO Corporate Headquarters > 400 Godin Avenue, Quebec City (Quebec) G1M 2K2 CANADA | Tel.: +1 418 683-0211 | Fax: +1 418 683-2170 | info@EXFO.com

Toll-free: +1 800 663-3936 (USA and Canada) | www.EXFO.com

EXFO America 3701 Plano Parkway, Suite 160 Plano, TX 75075 USA Tel.: +1 800 663-3936 Fax: +1 972 836-0164 EXFO Asia 151 Chin Swee Road, #03-29 Manhattan House SINGAPORE 169876 Tel.: +65 6333 8241 Fax: +65 6333 8242EXFO China 36 North, 3rd Ring Road East, Dongcheng District Beijing 100013 P. R. CHINA Tel.: + 86 10 5825 7755 Fax: +86 10 5825 7722 Room 1207, Tower C, Global Trade CenterEXFO Europe Omega Enterprise Park, Electron Way Chandlers Ford, Hampshire S053 4SE ENGLAND Tel.: +44 2380 246810 Fax: +44 2380 246801EXFO NetHawk Elektroniikkatie 2 FI-90590 Oulu, FINLAND Tel.: +358 (0)403 010 300 Fax: +358 (0)8 564 5203EXFO Service Assurance 270 Billerica Road Chelmsford, MA 01824 USA Tel.: +1 978 367-5600 Fax: +1 978 367-5700

Synchronization Monitoring and troubleshootingAs synchronization is deployed in the network, continuous monitoring is required since network synchronization stability decays over time. Synchronization monitoring is necessary in order to monitor the health of synchronization mechanism over the network and to ensure quick and effi cient reaction to synch failures within the network.

By using the Managed mode, a number of SyncWatch-110 units can continuously monitor synchronization accuracy at key points of the network and dump all data to a centralized server for data correlation. This Managed mode ensures that complex network synchronization issues can be correlated and traced to specific segments. The EXFO SyncWatch-110 can be configured with thresholds that automatically send alarms to network management systems (NMS). This powerful capability ensures that network operators can react quickly to synchronization degradation before errors or failures occur and maintain synchronization throughout the network. In the troubleshooting phase, network operators can perform troubleshooting of network synchronization failures.

troubleshootingIn the event of synchronization issues, network engineers can be tasked to diagnose and correct synchronization issues. The EXFO SyncWatch-110 is the complete troubleshooting tool through its versatility and the fl exibility of having multiple inputs. Whether qualifying legacy or packet-based synchronization issues, the SyncWatch provides powerful and complete testing capabilities from a single device.

concluSionThe increasing demand on network operators to provide more services at competitive rates has resulted in a paradigm shift in the availability of physical-layer synchronization, requiring not only testing and monitoring of synchronization performance carried out at the physical layer, but the packet-layer performance has to be tested and monitored too. EXFO’s SyncWatch-110 Synchronization Testing Unit is the tool of choice to qualify and monitor next-gen network synchronization, while assessing synchronization health throughout the network lifecycle.

APNOTE234.1AN © 2010 EXFO Inc. All rights reserved. 2008

Printed in Canada 10/07

SyncWatch-110

SyncWatch-110OK

ThresholdCrossing, Warning

Fail

Ordinary Clock

SyncWatch-110

Ordinary ClockOrdinary Clock

Ordinary ClockOrdinary ClockOrdinary Clock

Ordinary ClockOrdinary ClockSyncWatch-110SyncWatch-110

SyncWatch-110SyncWatch-110

SyncWatch-110

Grand Master (GM)