Desktop computers, PC and others, are notoriously inaccurate time keepers, varying as much as plus or minus 15 seconds per day. Moreover, web sites that reportedly provide accurate UTC time are often choked with too many users, open your system up to hackers, and are fraught with propagation delays.
For true accurate time keeping an NTP server is required. NTP servers at all network nodes provides synchronized timing for accelerated information transfers.
WHO NEEDS ACCURATE TIME
If you operate under the auspices of any of the following, you need accurate and traceable time on your network:
- Code of Federal Regulations (FDA) guidelines for the manufacturing, sales and distribution of food and drug products, 21 CFR, Part 11.1(e).
- Sarbannes-Oxley requirements of public companies to certify accuracy of financial procedures.
- NASD’s Order Audit Trail System requires that all equities trading be accurately time stamped.
- The Health Insurance Portability and Accountability Act (HIPAA).
- Gramm-Leach-Bliley Act requires accurate time synchronization of networks exchanging financial records that might allow identity theft.
- ATM banking systems.
- Corporations that require internal time stamping of critical records.
- Scientific data systems requiring time synchronization.
STRATUM LEVELS DEFINED
There are two Stratum level definitions: Network Time Protocol (NTP) and International Telecommunications Union/American National Standards Institute (ITU/ANSI).
NTP simply defines the strata level of the clock. Stratum 0 is the clock source. In the case of GPS, the clock reference used by the NTP-SSTx, it is one or more of the 24 active GPS satellites in orbit at all times. Each satellite has a cesium oscillator based clock as the Primary Reference Source from which Universal Coordinated Time (UTC) is calculated. There is propagation delay in the signal from the satellite to the ground receiver. However, after approximately 24 hours of burn-in and satellite data accumulation, propagation delay of the time signal is calculated and compensated for.
The GPS receiver in the NTP-SSTx will then, by definition, be declared a Stratum 0 source and the NTP-SSTx becomes a Stratum 1 device. So, again by definition, Stratum 0 is the source; the next level is Stratum 1 (NTP-SSTx), the next level is Stratum 2 (your server, switch, computer), Stratum 3 is other computing devices connected to Stratum 2. Stratum 4 will be those devices connected to Stratum 3, etc.
ITU/ANSI defines Strata levels by accuracy beginning with Stratum 1 as shown in the table below.
Stratum Accuracy/Adjust Range Pull In range Stability Time to Frame Slip
1 1 x 10-11 72 days
2 1 x 10-8 Capable of synchronizing to a clock with accuracy of +/-1.6 x 10-8 1 x 10-10/day 7 days
3E 1 x 10-6 Capable of synchronizing to a clock with accuracy of +/-4.6 x 10-6 1 x 10-8/day 3.5 hours
3 4.5 x 10-6 Capable of synchronizing to a clock with accuracy of +/-4.6 x 10-6 3.7 x 10-7/day 23 minutes
4E 32 x 10-6 Capable of synchronizing to a clock with accuracy of +/-32 x 10-6 32 x 10-6/day Not yet specified
4 32 x 10-6 Capable of synchronizing to a clock with accuracy of +/-32 x 10-6 32 x 10-6/day N/A
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