Accurate time essential for video surveillance applications

By Tim Klimasewski  July 24, 2007  

As video surveillance hardware becomes IP-based, systems are able to take advantage of the network to improve efficiency and performance. Time synchronization, in which all the clocks in cameras, recording equipment, and computers have the same time, is simple to implement on the network. It utilizes a standard protocol and a network appliance known as a time server. What’s more, the time server can be legally traceable to a time authority. The result is low-cost investment protection for the video system deployment.

Security professionals thrive in a “What if?” world, always a step ahead of the threat, constantly pushing to leverage the latest technology for today’s security issues. Understanding threats not yet contemplated. What if a security system deployment is not synchronized? An employee in a major corporation clearly compromises corporate security, but the legal department declines to prosecute. Why? Because the physical security system shows him entering the area several minutes after a particular event was logged on the computer network. Time synchronization could have preempted this problem.

The risk of manually setting time at infrequent intervals, in separate systems, with different times based on normal clock drift is unnecessary and is a legal liability. A municipality came under public scrutiny and threat of lawsuit for inadequate response to a medical emergency.

The time stamp on video shows a man collapsing at one time, but the 9-1-1 call was made much later. It was determined subsequently that the video recorder was set incorrectly. A few years ago, 9-1-1 call centers were facing these types of lawsuits for allegedly not responding to emergencies in reasonable amounts of time. Timestamped records, especially those logged on voice recorders, are often subpoenaed in court cases. It is imperative that these time records be legally traceable to a national standard authority.

Synchronized, traceable time has proven to be a successful defense of time stamped evidence. Best practices for the use of video surveillance have been published by The Scientific Working Group for Imaging Technology (SWGIT) as recommendations and guidelines for the use of CCTV in security systems for commercial Institutions. For security system data to hold up in a court of law, one must demonstrate the ability to accurately re-create the events surrounding a particular action. Accurate time stamping is essential for event reconstruction. The SWGIT recommendations specify the use of Network Time Protocol (NTP) for IP-based systems and GPS-based timing equipment as an industry-standard time synchronization method.

Legal issues aside, synchronizing clocks greatly improves the efficiency of operations for both the end-user and the system integrator. Applications work as expected, interoperability is ensured, and costs of troubleshooting and manually re-setting clocks are eliminated. Unsynchronized clocks lead to finger-pointing. A better way is to implement time synchronization for every IP video deployment.

Synchronization to Legally Traceable Time
Time, as measured by the second, is one of the seven legally-defined units of measure. Since the Treaty of the Meter in 1875, time has been coordinated worldwide.
Today, official time, known as Coordinated Universal Time (UTC), is measured by vibrations of the cesium atom, an extremely accurate time constant. (UTC replaced Greenwich Mean Time [GMT] in 1972.) UTC is kept by national metrology institutes like the National Research Council (NRC) in Ottawa and the National Institute of Standards and Technology (NIST) in Boulder, Colorado. In order to synchronize clocks to accurate time, traceability to UTC is required.

Implementing a UTC-traceable time synchronization system is a simple process for IP-based security systems. Network Time Protocol (NTP) is an “open source” time synchronization distribution standard sponsored by the Internet Engineering Task Force (IETF) and is defined by RFC1305. Client software for NTP is widely available for virtually any operating system and is typically preinstalled in IP-cameras,
DVRs, computers, etc. Configuring an NTP client is straightforward once the network has a governing source of time — a master clock, also known as a time server.

Time servers are available for general use on the Internet and can be found through the NTP Public Services Project. Their primary liability is that their use requires continuous Internet connectivity and an open port in the firewall so they cannot be used for closed security systems. What’s more problematic, however, is that the accuracy of these free sources cannot be verified.

GPS Time: Within the Firewall
The Global Positioning System (GPS) provides a cost-effective way to provide a traceable time synchronization source from inside a facility. The GPS system includes 24 satellites carrying onboard atomic clocks. The U.S. Naval Observatory monitors the satellites’ clocks and locks them to UTC for accuracy and traceability to NRC and NIST time. We are all familiar with the use of GPS to provide driving directions. These systems use accurate time and the principle of triangulation to calculate the three-dimensional position anywhere on Earth. The same GPS signal can also be used to time-synchronize devices and networks.

A GPS time server provides an integrated solution that enables accurate time stamps for video surveillance systems as well as access systems, time and attendance systems, alarms, and other elements of the network infrastructure (routers, firewalls, etc). Legally traceable timestamps provide necessary evidence and validation of events for legal proceedings. For reliability and security, the time server synchronizes to the precision time code from GPS satellites. They operate behind the firewall to synchronize all elements of network hardware and software (including system logs) down to the millisecond over LANs or
WANs, anywhere on the planet.

Tim Klimasewski is marketing manager for Spectracom in Rochester, N.Y.