What is this Time server you speak of and how can i incorporate this in my isolated cam network...thx
NTP or Network Time Protocol allows for synchronized clocks on data networks that either connect to the internet to get time data from servers like pool.ntp.org or 0.north-america.pool.ntp.org or time.windows.com, for greater precision or non-internet accessible locations you can use a special GPS receiver to introduce a time signal. NTP sources will range from Stratum 0 to Stratum 3, a Stratum 0 server is an atomic clock or GPS receiver and will be the highest precision time keeping devices while a Stratum 3 indicates a time source synchronize from a Stratum 2 source. Stratum ranks above 0 do not denote quality or accuracy of the time signal but rather a tiered hierarchical system designed to prevent loops and conflicting data.
In my own network I use a pfSense firewall which is, among other things, running an NTP server. It synchronizes to various internet time sources and is commonly either a Stratum 2 or Stratum 1 service. The pfSense firewall is a FreeBSD Unix based system and not all devices, including my Dahua cameras, seem to be happy with using it as such I have a Microsoft Windows 2012 R2 server that is also running as an NTP time server. My Cameras synchronize to my 2012 R2 server which in turn synchronizes to my pfSense which in turn synchronizes to authoritative internet time sources in pool.ntp.org. The result is my network devices capable of utilizing NTP are all within a few milliseconds of each other and official US time. I have considered setting my cameras, servers, computers, etc to UTC or Universal Time Coordinated instead of my local time zone but I find it too hard to think in UTC so I have stayed with my local time zone for convenience. UTC is basically Greenwich Mean Time without daylight saying time so it is the same consistent time throughout the whole year. I have found that because of different camera models I have, all are Dahua but not all the same model, even with NTP enabled in the cameras web interface and directed to a Stratum 2-3 time source the time stamp on my various feeds can be as much as a whole 1 second out of sync with each other. Despite this "grinding my gears" it is a perfectly acceptable margin of error for my home network that I haven't been able to correct.
I have my cameras isolated from the internet by assigning them static IPv4 addresses (e.g. 192.168.1.112) and then giving them the wrong default gateway address (e.g. my pfSense is 192.168.1.1 but I assign 192.168.1.254 to the cameras) which results in them being able to talk on my local network but not out to the internet. I also have the extra, and probably unnecessary step, or having a firewall rule specifically blocking outbound traffic from the block of IPv4 addresses my cameras have. From here I can log into the web interface of my cameras, enable NTP, give it the IP address of my 2012 R2 server (192.168.1.220) and set the query interval at 1 minute. Now every minute my cameras will sync their time with the 2012 R2 server.
I have to say that the time keeping circuitry in the Dahua cameras is abysmal as I originally tried to have them sync every hour and they would drift several seconds out of sync in that time, I then went to every 10 minutes and they were still drifting noticeably so I finally dropped it to 1 minute and now it is barely a second of variance between models of cameras. I have 3 different model of Dahua camera and within the same model the time sync is perfect.
Additionally you can further enable devices on your network to utilize NTP by setting a DHCP option. DHCP or Dynamic Host Configurable Protocol is the service that gives out IPv4 addresses to devices on your network automatically instead of you having to manually/statically assign them to each device. Fully featured DHCP servers, which not all are, have various options beyond pool of address, Default Gateway, DNS server that can be set. One of these additional DHCP options will specify the NTP configuration DHCP clients are to use. I have mine set to my 2012 R2 server so my desktops, laptops, smartphones etc etc will synchronize their clocks to my server if they are able.
I find timekeeping to be a fascinating subject and one of both interesting history as well as astonishing scientific advancement and capability. For example did you know that the definition of a second was changed in 1964 from 1/86,400th of a mean solar day to the unperturbed ground-state hyperfine transition frequency of the Cesium-133 atom which equals 9,192.631,770. Compare and contrast why there are 24 hours in a day, 60 minutes in an hour and 60 seconds in a minute...because the ancient Sumerians hated fractions more than anything else.
Edit: corrected a mistake I made in the 5th digit of the definition of a second from a 4 to a 3.
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