5. ISDN or IP?

There are two different technologies for video communication: IP (internet protocol), which uses the internet; and ISDN (integrated services digital network), which uses the phone lines. Each technology has its own benefits and drawbacks.

Overview of the two technologies

ISDN technology has existed for over 20 years, and until broadband IP connections became widespread, most video conferences were held using ISDN communication.

Each ISDN phone line consists of 2 so called B-channels, each of which gives a bandwidth of 64 kbit/s. That is: each ISDN phone line gives a total bandwidth of 128 kbit/s.

When you make a video call by ISDN, you dial a standard telephone number, e.g. +47 222 333 444.

Broadband IP connections are becoming more and more widespread, and the bandwidth is ever increasing. IP connections uses the TCP/IP protocol to transfer data, for instance in an IP video conference.

To make a video call using IP, your codec (and the far end codec) needs to have a public IP address, which is in the form 158.36.21.99 (fours number in the range 0-255, separated by a dot). You call the other participant by entering the far end IP address.

Costs

The great advantage of IP communication is that it’s cheap. You usually pay a flat monthly or annual subscription cost, in proportion to the bandwidth you want.

For ISDN communication, on the other hand, you’re charged by the minute, in addition to subscription costs. ISDN communication uses a number of data channels, each channel giving a bandwidth of 64 kbit/s, and you have to pay for each data channel you’re using. For instance: if you need to make a video call at 256 kbit/s using ISDN, you need 2 lines (128 * 2 = 256). The fact that the by-the-minute-costs are directly proportional to your bandwidth requirements, multipart conferences by ISDN can be very expensive.

For instance: If you’re holding a multipart conference with 3 external parties (+ yourself), and each party has a 256 kbit/s connection (that is, 2 * 128 kbit/s connections), you’ll have to pay for 3 * 2 ISDN lines. Assuming that the call rate is 0,10 euro per minute, the hourly costs add up to 3 * 2 * 0,10 euro/min * 60 min/hour= 36 euro/hour . If this conference lasts a day (6-7 hours), the costs can be formidable.

The installation costs associated with ISDN (getting the phone lines installed) are usually somewhat higher than with a broadband IP connection.

Stability

ISDN is, on the whole, more robust and less susceptible to network congestion and broken connections. If you’re using IP communication, you’re typically sharing network capacity with many other users, and if the bandwidth of the network is exceeded, you will experience packet loss and consequently poor video/audio quality.

Video quality

Video quality is related to the call rate (or bandwidth), and not to the particular technology used to transfer the data. In other words, IP and ISDN will (in theory) give exactly the same video quality at a given bandwidth (say a video call at 256 kbit/s).

But as discussed above, IP is more susceptible to network congestion and bandwidth fluctuations, compared to ISDN. Therefore ISDN can be expected to give a more consistent video quality.

On the other hand, IP connections enable you to use extremely high bandwidths (some codecs can handle call rates up to 6 Mbit/s), which in theory gives almost broadcast quality. It’s usually not practical to use such extreme call rates, however, because most networks have bottlenecks that will cause very high packet loss at such call rates.

It’s better to choose a moderate, but consistent call rate that gives minimal packet loss.

Firewalls

ISDN has one great advantage over IP: it bypasses firewalls. If you’re going to hold a video conference with someone who’s behind a restrictive (e.g. corporate) firewall, you may find it impossible to make a connection through the firewall. In such cases, ISDN is a good option.

So what should I choose? The different pros and cons of IP and ISDN are summarized in the table below:

If you do a lot of video conferences, and your budget can handle it, it’s a great asset to have both ISDN and IP connections available. If either one fails, the other can be used as a backup.