Publié le 8 février 2011
Measuring the Pulse of Your Network—Part 2
Part 1 of this article examined the causes of the paradigm shift in the availability of physical-layer synchronization and presents the network synchronization basics as well as the synchronization technologies in the network, including legacy frequency and packet synchronization, now let’s examine the solution.
The Synchronization Test Solution
SyncWatch-110 Synchronization Testing Unit is an all-in-one synchronization test tool that provides precise, accurate and flexible synchronization testing in a single package. This unit enables powerful synchronization testing with the flexibility of different operation modes to help customers find and solve network synchronization issues. Its 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.
This solution provides 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-synced devices
- Ethernet test port for packet synchronization technologies (PTP and SyncE)
A key aspect of testing synchronization is the accuracy of the reference clock—since the measurement can only be as precise as the reference clock. The SyncWatch unit 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 specified 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 field.
This solution 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.
SyncWatch-110 provides live measurement of the TIE and can calculate and display at any point the MTIE and TDEV measurements via its measurement application. All results can be saved for post processing using Symmetricom’s industry-standard, time-monitor analyzer application, included with a Stand-Alone license, providing extensive and scientific quality results and precision.
Modes of Operation
Three specific modes:
Stand-Alone mode is the typical test mode where a user is directly connected to a single 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 field, lab trials or field commissioning.
Since access to a synchronization expert can sometimes be difficult, network operators will enjoy the flexibility of USB mode and therefore, better manage expertise resources. The USB mode is a simplified mode where a unit finds its configuration 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 preconfigured 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 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, GPS thereby providing a global view of synchronization over the network.
The Network Synchronization Lifecycle
The 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 final 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, this unit enables operators to conceptualize, introduce, benchmark and monitor network synchronization efficiently and with confidence.
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 Benchmark
The 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 scenarios such as migration to different synchronization technologies like SyncE or simulate network loading and to 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, this unit 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 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.
Before 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 field, 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-In
When using PTP, synchronization packets are classified as a service and are typically with the highest priority within the network. Although serviced with priority, synchronization traffic is still subject to network events and is 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 traffic according to its configured priority, and to verify the performance of the network synchronization flow 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 influence 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 flow 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 flow over a longer test period and provides a good indication of the capability of the network to efficiently transport multiple services while maintaining the performance of the synchronization flow.
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 flow 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, this solution enables network engineers to perform complete testing using any available frequency input, enabling its use 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—this unit accurately measures synchronization performance and packet performance from a single device.
Synchronization Monitoring and Troubleshooting
As 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 efficient reaction to synch failures within the network.
By using the Managed mode, a number of synchronization test 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.
In the event of synchronization issues, network engineers can be tasked to diagnose and correct synchronization issues. SyncWatch-110 is the complete troubleshooting tool through its versatility and the flexibility of having multiple inputs. Whether qualifying legacy or packet-based synchronization issues, the SyncWatch provides powerful and complete testing capabilities from a single device.
The 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 SynchWatch-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.