Be (back) on Time!

PTP Protocol

If we want to synchronize our (Windows) network/hosts, then PTP is the ways to go. What you can achieve with dedicated hardware such as the ExaNIC devices, was presented very well in thorough detail at a STAC conference [4]. So a quick reminder what PTP is: PTP works by using a two-way exchange of timing messages, known as “event messages”.

  1. Hardware based timestamping
  2. Boundary / Transparent clocks

Software based Timestamping:

When looking at software based timestamping we see the following criteria:

PTP with software timestamp approach [derived from [2]]

Hardware Timestamping

PTP with hardware timestamp approach [derived from [2]]

PTP Grandmaster functionality

While locked to GPS, the Grandmaster clock can provide precise nanosecond timestamp resolution and accuracy better than 30 nanoseconds referenced to GPS. A Grandmaster clock incorporates a local reference oscillator that is disciplined to GPS. See the screenshot of the command prompt for stat details of the Grandmaster. In our setup we are using the ExaNIC X10-GM [7] with an OCXO oscillator. This oscillator is the reference clock used with dedicated hardware for the precise timestamp of the incoming delay request and outgoing sync packets. The dedicated hardware approach is unaffected by operating system or network traffic latency.

ExaNIC X10-GM [7] and ExaNIC X10-GM Windows PTP status

PTP Slave with Hardware Timestamping, in general and as part of the ExaNIC on Windows solution

Hardware timestamps with a PTP software daemon provide precise nanosecond timestamp resolution with dedicated hardware. In our solution we use the PCIe Gen3 compliant ExaNIC X25 NICs (formerly Exablaze, now Cisco SmartNIC) with an TCXO oscillator offering a resolution of 4.2ns. As such, the hardware timestamp enabled slave solution has many advantages over the software slave, such as an improved oscillator, a 1PPS output for measurements compared to the master, and dedicated hardware that is unaffected by the operating system latency. Synchronization of better than 100 nanoseconds is achievable, even in a larger network with a transparent or IEEE 1588 compliant (boundary) Ethernet switch. Ideally ExaLINK Fusion et al.

Comparison HW versus SW based timestamps

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NEIO Systems, Ltd.

NEIO Systems, Ltd.

http://fastsockets.com || low latency, networking experts, 10GbE++, FPGA trading, Linux and Windows internals gurus