Videophones always seem to be on the verge of taking off when something causes a problem: poor quality, lack of bandwidth, cost, firewalls, network address translation (NAT), the need to prearrange calls, and so on.

I came across another one last week. A keen user who is deaf and uses the videophone for sign language wanted to change his ISP and found he couldn’t take his IP address with him. His friends could no longer contact him.

The system was never supposed to work like that. Videophones allow you to enter the IP address of your correspondent but you’re really supposed to put in some other string that is translated to an IP address. It’s rather like the way web browsers work.

There are several of these look-up systems, using the internet Domain Name System (DNS) as the mechanism. The string you enter is the Uniform Resource Identifier (URI), which can take a bewildering variety of forms. You can use URIs based on domain names, email addresses or telephone numbers, and probably some others as well. These have to be entered into the DNS before they can be used. People or organisations with their own domain names should be able to set up their DNS entries to do the job, but for everyone else it is probably the responsibility of the ISP.

The DNS may return information about the destination videophone or it may be about the remote gatekeeper, the device which controls a group of videophones. In either case, the calling videophone should be able to make the connection. But what if you want to make a call to someone in a large company? Your correspondent probably has a private IP address, rather than a public one, so you can’t make the connection, as when a phone call can’t be made directly but has to go through the switchboard.

Tandberg has just announced a product called the Entrypoint that is set up to intercept video calls coming in to a company. The caller sees a screen with a set of menu options, such as employees with videophones, the receptionist, customer service or canned videos, selects the required destination and is connected. This neat idea makes it possible to put in video calls to large companies without having to phone or email beforehand. So, another video problem bites the dust.

However, the problem with IP addresses still remains. As videophones and videophone applications on PCs become more common, ISPs will have to help out by configuring their DNS entries for video. There is a business opportunity here for third parties to offer gatekeeper and DNS services if ISPs duck out of it. Linking up with a third party could also solve the firewall/NAT problem.

I wonder what the next problem will be.