One problem with buying a basic rate ISDN line for data transmission is that you can talk only to other ISDN data devices, and not to modems attached to the analogue public switched telephone network. One way to get around this problem would be to produce an ISDN device that is able to mimic a modem when required. This is what St Albans, Hertfordshire-based Jaguar Communications Ltd has come up with, in a box that it was previewing at the Telecommunication Managers Association convention in Brighton recently. The Digidial ISDN modem has two data ports which can be configured either as synchronous X21 or asynchronous V.24 devices; more interestingly, when working as a V.24 serial device, the port can be used either as a straight ISDN terminal adaptor, or be set up to look like a modem. To achieve this, Jaguar uses a standard Rockwell International Corp modem chip set to take the data stream and modulate it into the same analogue wave-form used by conventional modems. This wave-form is then digitised before being sent to the ISDN network as a standard speech call. At the other end of the line, the network operator’s local exchange converts the signal back to analogue so that it appears to the remote telephone as a standard modem call. The chip set used supports all standards between V.32 and V.21, so really perverse users can use their ISDN line to carry data at 300bps if the mood takes them. On the other hand, both MNP 5 and V.42bis compression standards are supported to help boost throughputs. For good measure, Group 3 facsimile protocols are also thrown in. Both V.110 and V.120 rate adaptation are also implemented, the former providing up to 19.2Kbps for asynchronous traffic, the latter up to the full 64Kbps for synchronous. While the user needs to configure the box manually for outgoing calls, it is intelligent enough to route incoming ones automatically; so if one port is set for modem traffic and the other for ISDN calls, received data will be routed appropriately. Moreover, the box includes support for a standard analogue voice telephone. The company says that it is expecting interim British Approvals Board for Telecommunications approval for the UK market in January and should ship in the first quarter next year at around UKP1,600. Europe-wide approval procedures will begin immediately afterwards. Marketing manager John Early said its use of the Mitel ISDN dialling chip should help along the US approvals procedure.
