ISDN Connectivity by Jeff Newman and David Willis ISDN Applications ISDN can be used to enable many different applications, including single-user remote access, remote LAN connectivity, Internet access, disaster recovery for leased lines and videoconferencing. Additionally, many computer-telephony applications could take advantage of ISDN's infrastructure and services. Single-User ISDN Remote Access ISDN can support up to eight different chained devices, whether they are analog our digital, including computers transmitting data much the way that a modem does, voice or digital telephones, fax machines or entire LANs with printers, servers, workstations and so on. This makes ISDN ideal for home office connections using terminal adapters (TAs) or bridges. An entire home office can operate over a single BRI conn ection. Voice calls can be maintained, faxes can be sent and received, data can be transferred and print jobs can be submitted all at the same time--completely transparent to the user. ISDN has a full set of advanced call-handling features (another task of the D channel), such as call line ID (CLI) that eliminates the need for call-back security. The incoming call identifies the source's call address so that equipment at the central site can accept or reject that call automatically, adding security to the remote access solution. ISDN also has call waiting, forwarding and conferencing up to eight levels deep. ISDN's digital nature coupled with CLI allows smart applications to tie incoming calls to databases that can automatically bring up information about the incoming caller before the phone is even answered. There are many possibilities for clever applications to be implemented using ISDN in this way. ISDN TAs, which are the most common devices for single user/home office connections, function similar to modems and can use popular protocols such as PPP/SLIP or other remote access packages that modems traditionally are intended. Remote LAN Connectivity ISDN can connect entire LANs between individual remote offices and central sites, sharing all of the resources such as file servers, printers and Internet gateways contained at each. Small office or branch office LANs can be connected to central sites cheaply using ISDN, allowing them to share all of the resources of the central site at up to 512 Kbps using the TAs, bridges or routers. All of this equipment is available today, and you have many vendors to choose from. Internet Access The rise in popularity of the Internet is one of the biggest driving factors for telephone companies to further their ISDN deployment. The graphic nature of the World Wide Web and the Internet's vast resources have created a demand for faster transfer rates from businesses right down to the average hous ehold. Seeing the possibilities, telephone companies, Internet service providers and operating systems vendors alike are supporting ISDN. Most but not all ISPs offer ISDN, so make sure that you have a local phone call to a provider that offers ISDN BRI service before you buy an ISDN circuit with the intentions for using it for Internet access. Also, investigate thoroughly the ISDN offering from your local provider, noting the access charges for the entire BRI connection, whether it is per B channel usage, general time usage, compression tax or based on the type of data offered over those channels. A typical ISP will charge around $2.50 per hour per 2B call. Some providers offer cheaper voice connections using BRI to save on usage charges, but this will most likely come at a sacrifice to reliability for the connection, so be wary of those kinds of deals. It is important to find out what equipment that the ISP has on their side of the link. Many vendors' devices either do not work well together, or offer proprietary solutions to channel management, protocols or compression algorithms that can hinder your connection. You will want to buy equipment that you can afford and that will give you full advantage of the services and bandwidth that BRI ISDN has to offer. Remember that you are going to be paying the telephone company usage charges for the BRI calls to the ISP and also paying the ISP for the Internet usage charges according to that higher-speed connection. Establish exactly what you need from the ISP and what you can afford, then ask many questions before you even buy your ISDN connection and equipment. Leased Line Fallback ISDN is a good solution for leased line fallback for critical connections. Since it is typically tariffed according to usage and carries a comparable monthly charge to POTS connections, ISDN is idea for serving as an active residual connection to sites that can temporarily survive on a lower but still relatively high and reliab le bandwidth, when normal high-speed dedicated circuits or equipment has failed or are under routine maintenance. Several vendors offer fallback switches that integrate with ISDN, offering this degree of network availability by constantly monitoring the leads of the normal circuits. Companies such as HT Communications [ www.htcomm.com ] and Hadax Electronics [ www.linnet.com/~hadax/ ] are good places to start for more information. Videoconferencing via ISDN Technologies that normally would normally be unavailable to most people dialing in remotely are now possible using ISDN. Videoconferencing is a prime example. The higher bandwidth required for smoother frame animation at higher resolutions with real time audio is now available to remote users. Several vendors offer affordable videoconferencing solutions that will allow desktop-to-desktop videoconference via ISDN as well as desktop-to-room-based units. For more information on videoconference, see "Bytes, Camera, Action!" (Network Computing, March 1, 1996). May 16, 1996 Print This Page E-mail this URL