There are many higher end features of access control systems that are often misunderstood. This month, I have been asked about a couple of these…

What is the difference between logical and timed anti-passback?

Anti-passback is a feature designed to stop a valid user entering into a secure area and then passing their token back to somebody else so they can use it.

On a normal door it doesn’t often make sense to employ this feature as, if the valid user wanted to let somebody else in, they would hold the door open for them.

When using turnstiles, however, it can be useful. Employing anti-passback in the right way helps to ensure the access control event log is correct.

Also, if you are tracking which users are currently on site, it means that the access control system can monitor this accurately. This is vital when using the access control system for recording who is present in the event of a fire.

There are two established methods of anti-passback: logical and timed.

Logical anti-passback - This method works by tracking where the user is in the building and only allowing them to make logical transactions.

A logical transaction in this case means entering an area that adjoins the one you’re in. For example, a user enters a building via the main entrance which leads into the Reception area.

From there, the system will only allow them access to areas that adjoin the Reception area. The system understands that they have gone from the ‘Outside world’ area to the ‘Reception’ area.

Once in Reception, the user will only be permitted access to areas adjoining Reception. If the user passes their token back so that somebody else can get access to Reception then the token will be denied access.

Logical anti-passback relies on doors being grouped into areas and the relationship between these areas being defined.

Timed anti-passback – This method is a simpler approach to the problem and does not require any concept of areas.

Timed anti-pass back means that a user will not be allowed through a door twice in a particular time period. A turnstile into a library, for example, may only permit access if the user has not already been through in the last five minutes. This stops users handing their tokens back to other people.

What is image verification and how can it be used?

Image verification is a useful feature that allows the identification of a user to be verified (by a real person) before access is granted.

This is best illustrated by an example. A user presents their token at the main entrance of a high security building.

A security guard at a PC somewhere will be alerted to the fact that somebody has requested entry. The access control software will display the user’s photo, from their record on the system, next to a CCTV image of the user at the main entrance.

The security guard compares the images and must verify that the person at the door is the genuine owner of the token.

Once verified, the security guard presses a button to allow the user access.

Of course, all of this happens in real time so it’s important that the security guard is on their toes!