Symmetricom Time Server user manual Stratum

NTP V 3.0 Data Format per RFC-1305 Appendix A: NTP Version 3, NTPQ, and NTPDC

Stratum

The stratum is an eight bit integer providing the stratum level of the time source. TimeVault operates in stratum 1, denoting a primary reference.

Poll Interval

The poll interval is a signed eight bit integer used as the exponent of two to yield in seconds the minimum interval between consecutive messages. For example, a poll interval value of six implies a minimum interval of 64 seconds. TimeVault does not alter the setting of this field.

Precision

The precision is a signed eight bit integer used as the exponent of two to yield in seconds the precision of the local time source and any other hardware affecting the base level “jitter” of the time server. This field is set to approximate TimeVault’s time stamping resolution, which is 10 µs. So the precision byte is set to –16, which is equivalent to a precision of 15.26 µs.

Synchronizing Distance (Root Delay Version 3)

The root delay is a signed 32 bit fixed point number representing the predicted round-trip delay in seconds to the primary synchronizing source. The fraction point is between bits 15 and 16. This value is set to 0 seconds in TimeVault.

Synchronizing Dispersion (Root Dispersion Version 3)

The root dispersion is a signed 32 bit fixed point number representing the maximum error in seconds relative to the primary synchronizing source. This value is a function of the precision and the quality of the synchronization input option.

When the synchronization input option is GPS, then TimeVault self determines the accuracy. Once the accuracy has been determined, then TimeVault sets the root dispersion equal to ten times the square root of the sum of the squares of the precision and the accuracy, except for the ACTS synchronization option, where the root dispersion is set equal to the accuracy (see Appendix E for details about ACTS).

Reference Clock Identifier

The reference clock identifier is a 32 bit code identifying the particular type of timing source. Strata 0 and 1 use a four-octet, left justified, zero-padded ASCII string. TimeVault operates as Stratum 1 and uses this four-octet string based on the local time source input as shown in Table A-2below. This setting is determined based on TimeVault’s synchronization input option.

6000-100AppA.fm Rev. C TimeVault™ User’s Manual A-93