France Telecom has announced that, from this summer, users will be able to use the ISDN D channel in order to access its Transpac national X25 packet-switched network. Basic-rate ISDN provides two circuit-switched 64Kbps Bearer channels and one 16Kbps packet-switched data channel, used for network signalling, but which can also be used for carrying user data. The French approach provides users with 9.6Kbps of this channel for their data. The actual announcement was made in November, but was so low-key that it escaped our – and almost everybody else’s – attention at the time. France Telecom says that the service will go live this summer. When pursued, no-one at the French PTT was able to confirm the tariffs that would be levied for D-channel connection, so we are indebted to Didier Mithouard, who heads up the Cap Gemini Sogeti SA Telecommunications team in Paris. Mithouard says that the company is charging 400 francs – $74 – per month for interconnection for the service and 0.06 centimes per Kilobyte of data – a charge that sounds very reasonable. The attractive thing about D channel services is that call set-up times are very fast, helping speed the transfer of small amounts of data. On top of that, devices such as personal computers attached to the public network should each have a unique address, which means that theoretically software could be written to enable them to receive data as a background task, and let electronic mail, for example, trickle in as and when. Apart from this, the most obvious application is for those involved in electronic funds transfer at point of sale: the D-channel is uniquely suited to shuttling small amounts of data such as credit verification very quickly. In fact, says Mithouard, both the Banque National de Paris and the Credit Lyonnais have run experimental pilots looking at ISDN usage, with one concentrating on D-channel access, while the other used more conventional B-channel dial-up. The study discovered however that the D-channel access was not sufficiently error-free to be used in the world of high finance, without some form of error checking or acknowledgement, which the French implementation does not include. In the UK, British Telecommunications Plc is still keeping quiet about when we can expect to see a UK D-channel service. However the ISDN marketing department has let on that two trials will be taking place later this year. No details were available about either the sector from which the companies will be although rumour has it, not surprisingly, that they will be telecommunications manufacturers – perhaps testing D-channel interface cards before the service is launched. Similar mutterings suggest that the company is not just looking at D-channel as a method of access to its public data network, but also enabling transparent and direct D-channel-to-D-channel working.
