What is ISDN?

ISDN stands for Integrated Services for Digital Network and is basically a way for two parties to connect to each other over phone lines but at a much better quality than a phone.

It uses technology that requires each party to have an 'ISDN Box' in order to code and decode (a codec) the signal to and from a studio (i.e. someone's microphone). These boxes can extremely expensive and have to be installed by specialists. It's also not always available in the area which can be a serious down side.

In the voice over industry they are used frequently to connect to voice over talent that may not be present at the studio recording them. For example, if the studio that is producing an advert is in New York but the client wants a voice that is based in LA, they will usually connect via ISDN. Depending on the codec this will use two telephone lines to spread the bandwidth over them both resulting in a high quality connection. This comes at a price of around $1 per minute per line. So an hour session would cost whoever dialled out around $120 in line charges alone! 

Whilst this technology has been around since the 80's, it is still used often. However, with internet speeds getting quicker it is getting forced out by products such as ipDTL and Source-Connect. These are far cheaper to initially buy and only requires a fairly decent internet connection.