An Approach to Primary NTP by Using the LINUX Kernel

The popularity of NTP is unmatched by any other network timing protocol. A complete NTP implementation is usually realized in user space, but the nature of primary NTP makes it possible, even favorable from a performance point of view, to implement primary NTP within the kernel of a UNIX like operating system. Primary NTP is simply a time stamping interface between the physical clock and a network description in form of NTP-packets. This paper introduces the concept of KNTPD, a Kernel NTP Daemon for use as a Stratum 1 only NTP server. It suggests a light weighted implementation using Linux netfilter hooks. KNTPD and its PPS-API is particularly suitable for small specialized devices, such as system on chip (SOC) solutions that integrate into timing products to provide high performance NTP capability. Examples could be industry atomic frequency standards used in the telecom industry, timescale devices, such as phase steppers, or GPS receivers.