Developing Low-Cost NTP Stratum 1 Servers with Linux PTP and GPS

For the past two decades, the design of high-performance stratum-1 NTP servers, those with internal means of synchronization to hardware clocks, have involved the use of specialized bus interface cards often utilizing proprietary device drivers. Those commercially available bus clocks provide memory-mappable time registers synchronized to GPS or Master Clock time code (such as IRIG-B and, more recently, IEEE 1588). Providing an essentially global NTP service has proven costly for timing labs as at the U.S. Naval Observatory. In 2007 a trio of Hewlett-Packard Unix servers, each with two bus clocks, and fronted by a redundant pair of IP load balancers cost over $53 thousand in 2014 dollars. A growing number of LAN-on-Motherboard (LoM) and bus card Ethernet adapters are now providing support for IEEE 1588 Precise Time Protocol, perhaps obviating the need for costly synchronized bus clocks. Open-source development projects at ntp.org, linuxptp.org, and kernel.org have resulted in widespread access to PPS and PTP hosted on low-cost platforms. To investigate the utility of inexpensive network timing a pair of Supermicro SYS-5015A-EHF-D525 servers with Intel® Atom processors were integrated with PTP-enabled NICs, GPS, and NTP and Linux PTP to test network timing in a PTP Grandmaster/Slave configuration. Results of long-term tests show quite satisfactory timing stability, well within the range of NTP timing requirements.