Everything over IP

Carriers have found that it makes commercial sense to put voice on packet-switched IP networks. And the same should be true for corporates, says Bill Pechey

Most IT managers will be familiar with voice over IP (VoIP), fax over IP (FoIP), and other methods of carrying specific types of analogue data over IP networks. This XoIP stuff goes back to when people realised that the Internet could carry digitised speech. But it doesn't really work very well because of the way the Internet is built, rather than because of IP itself.

Carriers soon realised that if they could get VoIP to work they could take advantage of the lower cost of IP equipment compared with the Asynchronous Transfer Mode (ATM) kit they had been working with. Many of the ideas that had been developed for ATM could be adapted for IP. We're not really talking about the Internet here but about new, high-quality IP networks designed specifically with voice in mind.

ATM and IP are packet-based technologies that make better use of long-distance connections than the old circuit-switching methods of telephone networks. Packet networks also make it more efficient to carry data and voice traffic simultaneously.

There has been a recent flurry of activity from standards bodies to define how IP networks should carry different types of traffic. Fax over IP is defined by ITU Recommendation T.38. It decodes fax modem information at the boundary of the IP network and sends it digitally to the other side of the IP cloud where it is converted back to a conventional fax signal. The gateways that do the conversion are the subjects of several standards: H.248, G.799.1, etc. These cover other types of traffic as well, such as video conferencing and audio-graphic conferencing.

This is where modem over IP (MoIP) comes in. There's a lot of dial-up modem traffic on the telephone networks and it's very important to be able to carry it efficiently over IP networks. The MoIP gateways will usually demodulate the modem signals and send the data and control signals to the gateway at the other end. One of the problems is that there are many different types of modems. The gateways will either have to recognise all of these or simply transmit the modem signal as if it were voice. The chances are that MoIP gateways will also have to handle ISDN data calls.

The ITU is working on a standard called G.IPCME (IP Circuit Multiplication Equipment), which will reduce the bandwidth needed for voice calls by sending data only when someone is speaking. The basic technique has been used for years on intercontinental connections and works very well; it should work even better on IP networks. G.IPCME devices will probably include FoIP and MoIP facilities as well.

Carriers are now building high-performance IP networks that will increasingly take traffic away from traditional networks. Corporate users should enjoy low tariffs if they encode their external traffic so that it can be carried directly on IP networks. Many large companies have their own private IP networks already in place and can adapt them to carry internal traffic using the same equipment. This ought to make life simpler for the IT manager.

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