San Jose, Calif.In many test-and-measurement applications, ensuring high accuracy time transfer over probabilistic Ethernet networks is desirable. As such, Symmetricom, Inc. is now offering its XLi IEEE 1588 Grandmaster Clock with GPS (Global Positioning System) satellite reference.
Slated for exacting IEEE-1588 Precision Time Protocol test-and-measurement applications, the box uses the IEEE-1588 protocol to ensure accurate synchronization over Ethernet LANs.
Implementing the IEEE-1588 protocol, you can sync clocks to better than 100-ns accuracy with a network connection. In use, the XLi IEEE 1588 Grandmaster provides the precise time. It's also equipped to physically measure how well that time is transferred through your linking network, with precision down to 5-ns resolution.
A standard Time Interval function in the Grandmaster measures the interval between the Grandmaster 1-PPS Pulse/s) and the rising edge of an external IEEE-1588 slave 1-PPS. This measurement is output via a serial port or using a Telnet session every second, generated as an ASCII string. The string is of the minor time (fractional second).
The differences are indications of how well a slave clock can be synchronized to the Grandmaster. Statistical analyses of the time intervals (more on this below) reveal the slave's mean clock offset from the Grandmaster and distribution around the mean.
How Is It Working?
In short, this tool will let you know if the precision and accuracy possible with IEEE-1588-equipped products is actually working in your network. The XLi Grandmaster can measure time transfer accuracy through network elements such as switches or through custom network topologies.
The XLi Grandmaster can provide the time to a 1588 slave clock and measure the resulting accuracy. This can be useful to characterize both the slave clock and the network topology between the Grandmaster and the slave.
Dedicated Time-Stamp Processor
Operationally, the Grandmaster uses a dedicated 1588 time-stamp processor. Operating at 100Base-Tx Ethernet line speed, with deep time-stamp packet buffers, the Grandmaster can support thousands of 1588 slaves. This is made possible in part by sending periodic 1588 Sync & Follow_Up messages using multi-cast addressing, and in part by being able to quickly and accurately process 1588 slave-initiated Delay_Req and Delay_Resp messages.
The XLi Grandmaster can also measure time degradation through hubs and switches, characterizing them before deployment in an operational network. Switches, in particular, can add non-deterministic latency and jitter to packet transit times from a 1588 master to 1588 slaves. As a result, 1588 slave sync accuracy can be degraded from that of the master.
Where the XLi Grandmaster operates as a slave, remote slave 1-PPS is compared to the remote GPS receiver 1-PPS in the XLi Grandmaster using the standard Time Interval function. This enables accurate measurements to be made of the network between the GPS-referenced 1588 Grandmaster and the remote slave.
Operating as a 1588 slave also means accurate time can be transferred over Ethernet to the XLi Grandmaster and, for example, output as IRIG B (Inter-Range Instrumentation Group Time Code Format B) time code.
When an inconvenient distance separates the XLi Grandmaster from a slave, using GPS as a common and precise time reference also enables accurate one-way path latency testing. One XLi Grandmaster can operate as the source of time, and another XLi Grandmaster can measure slave accuracy at the remote end of a network.
Lastly, you can also order optional TimeMonitor Analyzer software. It collects and analyzes Time Interval data from the XLi Grandmaster, generating statistics, histograms, and mean time interval error charts. These can be computed on small to extremely large data sets.
Click here for a datasheet (in Adobe Acrobat .PDF format).
For more details, contact Symmetricom, Customer Service Center, 3750 Westwind Blvd., Santa Rosa, Calif. 95403. Phone: 707-528-1230, Fax: 707-527-6640.
Symmetricom, 707-528-1230, www.XLiOptions.symmttm.com