9,600-Bpsmodems

I • COMMUNICA TlONS • HOW ARD MARKS AND M. DA VID STONE :De.. : G)I'A-S rCAIIC- , f-c. ~ o for . 1 • 9,600-bpsMODEMS ,. u n .ve t ,eo ood dec io to somewhat more than 15 minutes~ 2.4QO. e sions require ·n bps rnodems to around 8 minutes. good ioforma· Wilhin lhe lasl 18 months. manufaclu r· tion-data th at ers have broughl 9,6OO·bps modems lo c a n be s peed· markel. This is nol equiprnent la be used il y galhered , simply 10 conneCI to CompuServe ar to plugged iOl o a chal wilh friends on a local bullelio board. repon. aod delivered lo lhe boss's desk . It is high·speed, high,cosl equ ipment. ahle \ Like desklop messeogers, PCs relrieve da· 10 send messages at four times lhe speed af 13-from hani disks and, wilh lhe help a 2,400·bps modem and bearing price tags frum a modem, fro m olher PCs. Ihal can lop$2,OOO . 1t is ideal forcorporale 15 PC-lO-PC communications pUI olher use, where people need lO send lruly large High-speed nwd.ems people's data with in our reach. minutes files-budgelary analyses, perhaps, or ali ;~ can transmit your files four away . They eliminate lhe inconveni ence oflasl year's fi gures on sales acti vily in lhe of producing repons lO be messengered 10 Wesl and Soulh. They are a1so good vehi· ,nd or even eight times olher locations, bUI-if lhe files you need eles for remate access to distaol comput are long-they a1so cao lie up lelephooe ers . minicomputer gateways and LAN lO faster than the modem lines and resuh in exorbitant telephone LAN bridges. you may now be using. bills. The 13 high-speed modems Ihal we re· Technology has broughl us a long way viewed-Ihe Cermetek 96OOE , lhe Codex frum lhe days of 300-bil·per·second mo 2260, Dala Race's PC-Race 24/96, lhe dems wheo seodiog a IOOK file woul d tie Faslcomm 2496-T, lhe Gandalf Access up lhe phone lioe for more Ihan 50 mio· Series V.32. lhe Hayes V-Series Sman 02 ules. The 1, 200-bps modems CUI Ihal time modem 9600, lhe Microcom AX/9624c, ig,~ __________________________________________________~ P C M A G A Z I N E • A P R I L 2 b. I 9 8 8 105 ,. IflGH-SPEED MODEMS lhe Racal-Vadic 9600VP, ',elebil's Trail a technical and scientific standards group dem, Ihey mUSI be echoed back along lhe Blazer Plus. lhe Telenelics 96OOE, Uni based in Europe. sarne line 50 Ihal lhe modem will recagnize ve=i Data Syslems' UDS V. 32, U.S. Ihat lhe data arrived safely. However, lhe RobOlics' Courier HST .•nd Ven-Tel's WEIGHfOFLAW Although CCITT V.32 modem musl be able lo recagnize Palhfinder 18K-were .11 compalible aetivities are technicaJly called "recam Ihal lhe echoes are echoes and nOl incom enough 10 be used wilh PC lelecommuni mendations" rather than "slandards," ing data. For Ihis reason, lhe V.32 mo calions software Ihal supports lhe Hayes Ihey often have lhe impact of law. Mem dems require special echo-cancellation cir A T command seI. The produclS range in bers of lhe cem are national govern cuilS Ihal leI lhe modem keep tmck of price from $795 to $2,095. ments; in most European countries tele what's been sem, compare it wilh what's phone syslems are governrnent cornlng in. screen DUl lhe echo. and re· IN TIIE BEGINNING Codex made lhe monopolies, and il is aClually illegal in ceive only lhe data Ihat was inlended for fLJ'S19.600-bps modem. 1I appeared in lhe some countries to use modems lhat don '( Ü-nOl a copy ofwhal iljusl sento This cir early 1980s, sold for abouI $10,000, and f ollow cem recommendations. cuitry adds about $500 lO lhe cosI. was designed for mainframe communica r- In an effon lO produce affordable high tions. 1I is wilhin lhe lasl year and a half speed prodUClS for lhe PC mmel, modem Ihal high-speed, 9,600-bps modems have manufaclurers have developed several in become affordable and pracrical for PC • Within the last year genious-and incompatible--approaches communic3tions. BUI attempling 10 lhat use less-expensive modulation choose lhe righl one certainly can be a dif and a half, 9,60ü· schemes lo emulale full-<luplex operation. ficult proposilion. In general Ihese are lermed pseudo-full Until recently. buying a modem was bps modems have duplex modems, sometimes misleadingly relalively easy because you didn'l have lo called "asymmetrical. " worry much abouI compatibilily. Ali mo become affordable dems of a given speed used lhe sarne mod PING-PONG PROBLEMS The mOSI ulation scheme. Regardless of whal make and practical for popular approach, represemed here by lhe or model of modem was aI lhe olher end of Faslcornm 2496-T and Dala Race's PC lhe line, your modem could talk to il. The PC communications, Race 24/96's BMX mode, has been to standards Ihal established Ihis compatibil combine lhe widely available V.29 lech ity evolved from the exclusive hold AT&T nology and lhe Rockwell V.29 modem haq Qver telecommunications in lhe days The recommendations Ihal resulted in chip seI wilh a microproces5Or and memo before deregulation. For a long time, lhe slandards on 2,400-pps modems were ry for buffers. This allows you to make a only modems you could legally use were straightforward and widely adopled. BUI half-duplex modem Ihal would aUlomati made and rented lo you. jusI as lelephones unfonunalely, in lhe area of high-speed cally rum lhe line around when Ihere was were. by AT&T. In facI, AT&T didn'l modems, lechnology has moved fasler data in the receiving modern ' s transmit even use lhe word modem. The devices Ihan lhe cem. And lhe technical com buffer. This so-caIled "ping-pong" melh were called "dataphones." plexity of performing high-speed commu od works fine for file transfers where lhe An FCC ruling in lhe mid-1970s, how nication has confused lhe issue. The line needn'l be rumed around often. How ever, broughl competirion into lhe markel ccm has acrually issued IWO recommen ever, it can cause problems in more-imer and made il legal for people to connecl dations on 9,600-bps modems. Neilher is aClive applications because standard V.29 non-AT&T devices lo lhe phone lines. Jusl complelely satisfaclory for general PC devices take 253 milliseconds-<>ver \4 of as new telephone manufacturers arose to communications. a second-to rum lhe liDe and rrain to the challenge AT&T's Weslem Electric, olher The V.29 standard, which is used in aI line conditions. Training allows two mer vendors began getting ioto lhe modem most ali fax machines, defines a half-<lu dems to delermine lhe condition of lhe business. The modulalion schemes of lhe plex 9,600-bps modem, and lhe V.32 stan lelephone line so Ihal Ihey can use lhe ap dataphone becarne lhe standards, and mo dard defines a full-<luplex device. propriale frequencies and prolacaIs to dem manufacturers made their products AlmoSI ali standard PC communica transfer data. compatible wilh lhe Bell 103 (300 bps) and lions software requires full-duplex mo Modem manufacrurers looking for bel Bell 212 (1 ,200 bps) dataphones. Those dems. BUI V.32 modems tend lo be much ter performance in interactive appli cations standards on 300- and I ,200-bps modems more pricey: Ihey average abouI $2,500 developed fasler-training half-<luplex mo remain in place. BUI by lhe time 9,600-bps each. The reason? The bandwidlh of a tele dems. These are represented in Ihis review modems appeared on lhe scene in lhe early phone network is lirniled. Wbere standard by lhe Microcom AX/9624c, in which Mi I 980s, many vendors were in lhe business. 1,200-bps modems can send and receive crocom designed lhe modem lO drop down WilhoUI a single induslIy leader lO dictale data 00 a telephone line ai the same time, a in speed to 1,200- or2,400-bps fuJl-<luplex lhe new slandards, lhe role becarne Ihal of 9,600-bps modem consumes ali avaiJable when Ihere is data in bolh modems' buff the Consultative Commillee for lnlema bandwidlh to send data in one direction. ers. This is al50 lhe approach taken in lhe rional Telegraph and Telephone (CCm), After data tones are senl by a V.32 mo- RacaI-Vadic 96OOVP. Bolh are developed P C M A G A Z 1 N E • A P R 1 L 2 6, I 9 8 8 106 ~ • • GLOSSARY~·OFXERMS ASYMMETRICAL MODULATION OIECKSVM·A method of describing ,then transmit An example wou1d be a The process. through which a modem ,;8 block of·data~calculatedby,adding ali two-way nulio system, in which the op. working in a full-duplex environment -~the bytes in the block together and taking ~r says ~~ver't 10 signal theother op. willsimul~eously transmit data in1Wo 1he low-order'(right-side) :16 bits. This eratorto speak. ·directi~ aí aifferent:speeds. An uym-.: ':.method will.detect-,single-bit errorsarid metrical modem:.mayoffer bigh-speed: ·~memultiple-bit. '.':~:':. UNE ·I1JRNAROUND . On 'a:.half-du- qansmission in one direction, low-speed c, plex connection, 1he process ofchanging in the other. -CPS Characters ':per ·secand. '1Another the direction in which data is being trans- ,measure of.:the.speed -of a communica- .

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