In-depth Comparison between NTP and PTP Servers for Your GPS Time Source

Time stamping and client synchronization are vital for any network. While you can synchronize with public network clocks, they come with the risk of compromising the security of your business network. Luckily, GPS time servers can synchronize with a GPS time source to provide precise time intervals to a nanosecond’s accuracy.

The 31 satellites of the Global Position System have inbuilt high-accuracy atomic clocks that relay time signals to a GPS receiver. The receiver is synchronized to your GPS time server, which distributes the received time packets to your network system, either NTP or PTP. The network linked to the GPS time source depends on your time resolution needs. Here is an in-depth look into NTP and PTP networks and how they affect time synchronization.

Network Time Protocol (NTP)

NTP servers use one of the oldest internet protocols still widely used today. Currently, in its fourth major version, the server is directly linked to a highly accurate time source, i.e., the GPS satellites. The NTP receives time information from the GPS satellites through a hierarchical system known as strata. The information is then processed through algorithms that remove latency, and the accurate time is broadcast to all devices on the network.

Stata-0 are accurate GPS time sources such as atomic time clocks. Below them are primary time servers in strata-1 that conduct quick sanity test and data backup. Strata-1 act as servers to clients in Strata-2, and so on. An NTP network can hold up fifteen strata, but every stratum slightly decreases synchronization leading to lower accuracy. NTP accuracy is tens of milliseconds, which is more than enough for most commercial and industrial applications.

Synchronization selection in NTP occurs on the client’s side. The client receives multiple timestamps from different sources and filters out ‘false tickers.’ The client utilizes algorithms to process time sent by the servers and the maximum expected error. The measurements, combined with adjustments to the local clock, provide accurate time results.

Precise Time Protocol (PTP)

PTP servers are time-based synchronization standards that offer nanosecond to picosecond accuracy. The tight synchronization bases on the fact that it uses hardware time stamping as compared to NTP, which utilizes software networks. PTP devices synchronize the amount of time the sync messages spend in each device, eliminating device latency.

The servers are arranged in a master/slave hierarchical system. The grandmaster in the system connects to the GPS time source and relays the time information periodically to masters connected to the network. Each master then relays information to slaves in the network through a series of four messages. The sequence produces four different timestamps:

  • Time-1: The master sends the initial sync information.
  • Time-2: The slave receives the initial sync message.
  • Time-3: The slave sends a delay request to the master.
  • Time-4: The master receives the delay request.

The master sends all the four timestamps to the slave, and the slave can calculate the network latency in both directions providing high time resolution. High time accuracy is vital in scientific and financial institutions.

NTP Vs. PTP

The time server chosen depends on your business network demand on time accuracy. A dedicated NTP server will provide secure and accurate time stamping. For higher time synchronization, a PTP server is preferable.

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