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ANOTHER PART OF YOUR LIFE IS ABOUT TO go digital. This time it's data communica- tion?transferring files, connecting to re- mote networks, and other "talking" a computer does on the phone with fellow computers. By going digital, you don't need to use error-prone analog modems; instead you get nearly error-free data communication at speeds modems can only dream of. Telephone companies in the United States, Canada, Japan, and Western Europe offer digital services that cost about the same to use per call as high- speed modems. These services are called switched digital services because they take advantage of switched phone lines to keep costs down. Placing a call switches on a connection to a phone line, and ending a call switches off the connection, freeing the line for another call. You pay only for calls you make, not for full-time use of a dedi- cated phone line. MacWorld started using switched digi- tal services last summer to transmit scanned-image files and Aldus PageMaker files of magazine pages to and from Digi- tal Pre-Press International (DPI), a San Francisco prepress service bureau. The files, which range in size from several hundred kilobytes to over 100 megabytes, used to be copied onto disk cartridges and carried to DPI by bike messenger. In ad- dition, MacWorld's San Francisco office keeps stories and artwork on a file server that sister magazines in other countries can quickly access using switched digital ser- vices. Previewing and copying those files by modem takes forever, and transfers too often fail due to noisy phone lines. What You Get U.S. TELEPHONE COMPANIES OFFER two types of switched digital services, switched 56-kbps service and ISDN (In- tegrated Services Digital Network). With switched 56 service you get a single phone line that can transfer digital data at speeds up to 56,000 bits per second. You can't use the line to make voice calls or send Group 3 faxes. ISDN service gives you more than one communication channel on a single line. You get two or more 64,000-bps channels for digitized voice, digital data, or Group 4 (high-speed digital) fax calls. These are called B (Bearer) channels. You can use B channels independently or combine the channels for higher data- transmission rates. For example, you might talk on one B channel while your computer communicates on another, or you might combine two B channels for video teleconferencing. The B channels only carry content. Another channel, called the D (Delta) channel, carries signaling information that makes and controls B-channel con- nections. The D channel operates at 16,000 bps or 64,000 bps depending on the type of ISDN service. Signaling doesn't keep the D channel busy, so it can also be used for data transfer at rates equivalent to those of a 9600-bps modem or for X.2 5 packet switching. In addition to data-transfer capabili- ties, ISDN can improve the sound qual- ity of voice calls. ISDN also offers fea- tures such as the ability to display a caller's phone number before you answer a call, add that number to a list of unan- swered calls, or use it to look up infor- mation about the caller in your database. (Access to the caller's number may be re- stricted or blocked in some states.) Several newly announced applications can use ISDN voice features, including Northern Telecom's Meridien TeleCenter, and Cvpress Research's PhonePro. Where It Goes ALTHROGH SWITCHED 56 AND ISDN are switched services, you can't use them to call just anywhere. You can call other switched digital lines served by the same central office. Calling beyond your local telephone company's central office be- comes more complicated, especially for ISDN. The transmission rate drops to 56,000 bps because that's the maximum for the trunk lines that carry calls outside a central office. Likewise, calls outside your service area (as depicted in your telephone book), state, or country run at 56,000 bps. For example, MacWorld and DPI are served by the same central office in San Francisco and can transfer files at 64,000 bps over an ISDN line. But when Mac- World Japan places an ISDN call to Mac- World in San Francisco, the two commu- nicate at 56,000 bps. Still, that transfer speed is many times faster than a high- speed modem. Where It Is YOU MAY HAVE TROUBLE OBTAINING ISDN or switched 56 service from your local phone company. Neither service is available everywhere. Right now ISDN service is concentrated in the business districts of major metropolitan areas (see "ISDN Lines in the U.S."). Switched 56 service is more widely available but is not universal. Even in areas where switched digital services are available, phone com- pany representatives may not know ISDN and switched 56 exist, or they may not know them by those generic names. Each phone company has its own names for these services. Pacific Bell, for ex- ample, has an ISDN service named Centrex IS and a switched 56 service named CenPath. Fortunately this picture should improve during the next year as telephone companies install more ISDN and switched 56 services and promote them more aggressively. Like names, charges for switched digital services vary among phone com- panies. Your local phone company may compound the cost of getting ISDN or switched 56 by requiring that you also have an unrelated service such as Centrex, which gives business customers PBX capabilities from the phone-com- pany central office. Pacific Bell charges $540 to $650 to establish Centrex service and install two Centrex lines (its mini- mum) with a switched digital service on one of them. In addition to paying the phone company's installation costs, you must buy special equipment to attach to the phone lines (the type of equipment varies depending on the type of service the phone company offers). Pacific Bell charges $30 to $40 monthly per switched digital line and $15 per conventional voice Centrex line. You also pay connect charges at standard voice-call rates. Lower-cost switched digital services are available in some parts of the United States and should become more wide- spread this year. If vou plan to make ISDN or switched 56 calls outside your state or service area, vou must choose a long-distance company and pay it for those calls. Switched digi- tal calls cost the same as ordinary voice calls on AT&T, MCI, and Sprint. To get ISDN at your building, you must be located within about 2 miles of a phone company central office that has switching equipment for routing ISDN calls. This distance will in- crease to about 3.5 miles as telephone companies install new switching equipment over the next few years. For switched 56 service vou must be within about 3.5 miles of a central office with switched 56 switching equipment. The geographical areas served by central offices vary widely; they are roughly the size of? but by no means coincide with ? zip code areas. If you are farther away than the maximum distance, the phone company must run a high- speed dedicated line from a switched digital central office to your phone company cen- tral office or directly to your building. You pay a monthly fee for full-time use of that line and also pay by the call for calls that must be routed beyond the central office. A dedicated line is generally not economical unless you install at least six ISDN or switched 56 lines on it. Inside Your Building NEITHER BASIC-RATE ISDN (TWO B channels and one D channel) nor switched 56 service requires special wiring inside your building. Basic-rate ISDN service, like ordinary voice service, uses two of the four wires routed to common RJ- 11 modular jacks. Switched 56 service re- quires either two wires or four, depending on the specific type of service your phone company offers. You can usually replace an existing voice line with basic-rate ISDN or switched 56 service without any wiring change inside the building. To use an ISDN line, you must install a terminator, called an NTl, to maintain signal quality on the phone-company lines. The NTl terminator usually con- nects to your RJ-l 1 wall jack. It costs $100 to $300, and you must buy one that has been made for the switching equipment installed in your phone company's central office. As the switching equipment mi- grates to new standards over the next few years, you should have a wider choice of vendors. Switched 56 service does not need a terminator. Connecting to a Mac ALTHOUGH ISDN AND SWITCHED 56 services transfer data digitally, you can't connect them directly to a com- puter. You don't need an ordinary mo- dem to convert digital data from the computer to analog data (sounds) or the reverse. Instead you need a device that prepares the digital data from a com- puter for transmission on digital phone lines. Think of it as a digital modem. The ISDN digital modem is called a terminal adapter (TA). You can buy a freestanding TA from Northern Tele- com, Fujitsu, Hayes, UDS/Motorola, and other companies for $750 to $2000. You can also install a TA inside any Macintosh with a spare NuBus slot. Apple should already be shipping its $1099 ISDN NB Card. Apple's NuBus board and some of the freestanding TAs convert a second B channel to let you plug in a standard telephone, answering machine, or Group 3 fax machine. Alter- natively, you can buy an ISDN telephone with an integral TA and data port for $500 to $1000 from AT&T or Fujitsu, or for $700 to $1100 from Telrad. Digital modems for switched 56 go under two names, depending on the type of switched 56 service your phone com- pany offers. One is called a DSU/CSU (Digital Service Unit/Channel Service Unit) and the other is called a Data Unit. AT&T, Northern Telecom, UDS/ Motorola, and others sell them. Some ISDN terminal adapters can also be used as switched 56 digital modems. To further complicate the situation, digital modems are not all compatible with each other, nor is every digital mo- dem compatible with all types of switch- ing equipment used in phone-company central offices. You may be unable to call someone else who has switched digital service because your digital modems are incompatible. And if you're not careful, you could buy a digital modem that won't work with the switching equip- ment at your phone-company central of- fice or with the switching equipment at your new central office after you move across town. Using a Digital Modem DIGITAL MODELS WITH SWITCHED digital services can speed up file transfer, screen sharing, and remote network ac- cess. For simple file transfer between two Macs, you can use Microphone II, WhiteKnight, VersaTerm Pro, or an- other terminal program. To remotely operate (and exchange files with) another Macintosh, you can use screen-sharing software like Timbuktu/Remote. Prod- ucts like Farallon's PhoneNet Liaison and Shiva's TeleBridge let you access E-mail, file servers, and other network services from a remote Mac. When used with a freestanding digi- tal modem connected to the Mac's mo- dem or printer port, none of these appli- cations can take full advantage of switched digital speed. The Mac serial ports can run at 57,600 bps asynchro- nously, but today's system software, which handles serial communications for appli- cation programs, can't sustain that rate. The serial port can usually sustain a throughput rate of 19,200 bps?the exact speed depends on factors such as the speed of your Mac, the communications proto- col, and the design of the application program. Some programs can achieve full switched digital speed if they are used with an ISDN NuBus board. These pro- grams use the Communications Toolbox part of system software to transfer data synchronously at 56,000 bps or 64,000 bps through the ISDN board. At this writing, VersaTerm Pro and Timbuktu/Remote are compatible with the Communications Toolbox, and compatible versions of the other products mentioned above are in progress. (The Communications Toolbox is built into System 7 and can be added as an INIT to Systems 6.0.4 through 6.0.8.) On Your Network WITH SWITCHED DIGITAL SER- vices you can go beyond connecting Mac to a distant network. You can interconnect multiple AppleTalk networks and share network ser- vices. For instance, MacWorld af- filiates in different countries can link networks to access each other's file servers and exchange E-mail by placing ISDN phone calls. After linking networks, a MacWorld editor uses Timbuktu (Remote Acess Software)to preview large illustrations (by opening them on the distant network's file server) and to trans- fer files. Timbuktu or a new prod- uct, Aspects, let several users work on the same document simulta- neously from separate Macs. You can also access a distant network with the Chooser and connect to file servers, items shared with System 7's file shar- ing, and printers. If you use the Chooser to mount a distant file server or shared item on your desktop, you can copy files to or from the server with the Finder. With applications that take advan- tage of System 7's publish and subscribe technology, you can in- clude live copies of material from a distant file server or shared disk. If someone changes the original material, your documents are au- tomaticaliy updated across the switched digital network link. Ap- plications that use System 7's pro- gram-linking capability to share services, such as MacProject II 2.5 and Claris Resolve, could be lo- cated on remote networks. To set up a switched digital link between AppleTalk networks, you connect each network to a router, each router to a modem, and each digital modem to a switched digital phone line. The router examines packets of data traveling on the local network and routes packets headed for the distant network across the phone line. Some routers, such as Farallon's - $395 PhoneNet Liaison, are software that run on any Macintosh connected to the network. Hardware routers connect independently to the LocalTalk cabling. They include Engage Communication's $1895 SyncRouter, Shiva's $599 Tele- Bridge, Solana Electronics' $2195 H-Server, and International Transware's $899 TransTalk. Although the Phone- Net Liaison and the TeleBridge routers cost less, they communicate asynchro- nously at only 19,200 bps to 38,400 bps. The other routers communicate syn- chronouslv at the switched digital service's full 64,000 bps or 56,000 bps. Routers made by different companies are incompatible, and more compatibil- ity problems exist between routers, digi- tal modems, and phone-company central- office switching equipment. In setting up its international file server, for ex- ample, MacWorld first tried H-Servers, found them to be incompatible with something in Tokyo, switched to Synch- Routers, and is currently evaluating TransTalk routers for its enhanced net- work-security options. Other people in Tokyo, New York, and Paris, however, have used H-Servers without any trou- ble whatsoever. To make your network more secure, some routers let vou restrict access bv users on linked networks to specific zones in your network. Without this zone- blocking control someone at MacWorld could accidentally print a docu- ment on DPI's imagesetter?a costly mistake. Some routers offer other security provisions that help keep hackers out of your network. Experienced users say network performance across a switched digital link rivals that of a direct connection to a LocalTalk net- work with five to ten active users. Apparently a private 56,000-bps or 64,000-bps connection using a hardware router approximately matches an individual's share of a 232,000-bps LocalTalk or Phone- Net-type connection. Of course performance declines when several people actively use an ISDN or switched 56 network connection simultaneously. Your choice of digital modem and router may also give you lower performance. Not only are switched digital services fast, they are also ex- tremely reliable. You can't transfer multimegabyte files frequently us- ing ordinary modems and voice phone lines without failures due to line noise. But MacWorld editors routinely use ISDN to transfer tens of megabytes across town and across the Pacific without any fail- ure. Other ISDN and switched 56 users report the same reliability? no errors, period. ISDN Today SWITCHED 56 AND ISDN PROMISE a lot and deliver it to some Macin- tosh users, but don't hang up your modem just yet. You'll still need it to connect to commercial informa- tion services, national E-mail ser- vices, and electronic bulletin boards. And if vou sometimes ac- cess files and E-mail on your office network or your office Macintosh from home or a hotel room, you'll want a mo- dem for that too. Switched digital ser- vices can't help you with those connec- tions today. Right now those most able to take advantage of ISDN or switched 56 ser- vices are businesses needing to link loca- tions and transfer lots of data regularly but not constantly. The rest of us must anx- iously wait while switched digital services come to our telephone prefixes.