Time synchronization is an often overlooked concept in computer networking. The Network Time Protocol, also just shortened to NTP, is a network protocol and standard that allows distributed computers to synchronize their time.
Why is this important? Keeping proper time on computers, particularly when dealing with several computers communicating with each other, is important for things such as logging data and tracing of activity. On an NVR, perhaps the most important aspect is that of file system accuracy. Knowing when files were written or read is important to verify the when the activities in recorded video took place, as well as to perform forensic searches. Computer systems also need to know which version of files are most current for syncing files and performing file recovery. Time is also used by operating systems for many security and management controls, such as when using Active Directory/LDAP.
NTP consists of different tiers, originating from extremely accurate atomic clocks. These tiers are referred to as “stratum,” and measure the distance between systems in each tier and the atomic clocks in the top-most tier, deemed to be officially accurate. As the stratum number increases, the confidence of being synched to the most official time decreases. Primary time servers, such as time.nist.gov, pool.ntp.org, time.windows.com, time.google.com, and many others, are in Stratum 1.
When enabled, an NTP client like the NVR running your ExacqVision Server, begins a request from the NTP server.
Your system then automatically calculates the delay in the network link and uses the offset time (the offset time is based on the time zone setting you choose) and adjusts its own clock to the correct time and date.
If your system time is much different from the NTP source when this begins, it may take 5-10 minutes and several of these exchanges with the NTP source to initially bring the system clock into alignment with the NTP source. Once your system is synchronized it will continue checking for updates about every 10 minutes.
If you are experiencing problems communicating with an NTP source on the internet, you may need to investigate your firewall or antivirus settings. The exchanges made by the NTP protocol utilize UDP on Port 123.
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How to check the Stratum level used on Windows
- Open a CMD window to reveal a CLI prompt.
- Enter the following command:
C:\Windows\System32\w32tm.exe /query /status
- The stratum level can be seen on the second line of the results. The following example:
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How to check the Stratum level used on Linux (Ubuntu)
- Open a Terminal window to reveal a CLI prompt.
- Enter the following command:
ntpq -c rv
- The stratum level can be seen on row three of the results, as pictured in the example below:
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