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  1. .lh7
  2. .cw10
  3.                    Errors Bedevil Phone Data Transmission
  4.                                by Matt Kramer
  5.  
  6.  
  7.   WASHINGTON- Thσá breaku≡ oµ AT&╘ anΣ thσ risσ oµ alternativσá long-distancσ ì
  8. carrier≤á i≤ beinτ blameΣ fo≥ increaseΣ problem≤ witΦ transmittinτ datßá ove≥ ì
  9. thσ publiπ phonσ system.
  10.  
  11.   Thσá malad∙ ha≤ severa∞ symptoms«á  Modem≤ ma∙ no⌠ establisΦá ßá connectioε ì
  12. witΦá ß fello≈ computer¼á o≥ transmissioε qualit∙ ma∙ bσ poor¼á resultinτá iε ì
  13. garbleΣá line≤á oµá text¼á erroneou≤á number≤ o≥ lonτá string≤á oµá "garbageó ì
  14. characters.
  15.  
  16.   Explanation≤ fo≥ thσ probleφ var∙ widely¼á bu⌠ fe≈ telephonσ systems¼ data-ì
  17. communication≤ carrier≤ o≥ modeφ companie≤ arσ willinτ t∩ sa∙ wh∩ i≤ t∩ blamσ ì
  18. fo≥ erro≥ pronσ communication≤ lines.
  19.  
  20. More Calls Per Cable
  21.  
  22.   Somσá modeφ manufacturer≤ claiφ thσ phonσ service≤ arσ tryinτ t∩ pacδá morσ ì
  23. voicσá call≤ int∩ transmissioε cables«á  Telephonσ spokesmeε claiφ thσ publiπ ì
  24. telephone network was not designed to carry data traffic.
  25.  
  26.   Thσá complaint≤ oε transmissioε qualit∙ ech∩ concern≤ ove≥ thσá qualit∙á oµ ì
  27. voicσá communications«á  The∙ havσ mean⌠ ß growinτ buisnes≤ fo≥ softwarσá anΣ ì
  28. modeφá vendor≤ whosσ product≤ monito≥ transmissioε t∩ assurσ it≤ freedoφ froφ ì
  29. errors.
  30.  
  31.   Still¼á transmissioεá problem≤á arσ no⌠ ß sourcσá oµá constan⌠á irritation«  ì
  32. "It'≤á ß ver∙ spott∙ problem,ó saiΣ Ro∙ Andersen¼á vicσ presiden⌠ fo≥ produc⌠ ì
  33. developmen⌠á a⌠ Westerε Union¼á whicΦ relie≤ oε loca∞ telephonσ companie≤ fo≥ ì
  34. custome≥á acces≤ t∩ it≤ packet-switchinτ datß network«á  "Iεá certaiεá spots¼ ì
  35. tryinτá t∩ senΣ 240░ bit≤ pe≥ seconΣ i≤ ß probleφ anΣ iε othe≥ area≤ 120░ bp≤ ì
  36. i≤á ß disaster«á  We'vσ haΣ somσ area≤ witΦ s∩ mucΦ linσ noisσá anΣá constan⌠ ì
  37. garbled characters that we had to put in a dedicated line to the customer."
  38.  
  39.   Man∙á oµ thσ complaint≤ havσ occureΣ iε thσ aftermatΦ oµ thσ breaku≡ oµ thσ ì
  40. AT&╘ telephonσ monopoly«  AlthougΦ thσ resultinτ competitioε ma∙ havσ lowereΣ ì
  41. consume≥ telecommunication≤ prices¼ i⌠ als∩ mean⌠ morσ thaε onσ compan∙ woulΣ ì
  42. be responsible for the transmission network.
  43.  
  44.   "Wheε the∙ haΣ onσ compan∙ runninτ thσ system¼á al∞ line≤ werσ testeΣ ever∙ ì
  45. 1░á year≤ anΣ yo⌡ coulΣ pinpoin⌠ wherσ thσ problem≤ were,ó saiΣ Keε Krechmer¼ ì
  46. ßá communication≤ consultan⌠ iε Mountaiε View¼á Cali«á  "No≈ therσ i≤ n∩á onσ ì
  47. company testing the lines and it's hard to track down problems."
  48.  
  49.   Thσá lonτá distancσá carrier≤ havσ beeε thσ focu≤á oµá severa∞á complaints«  ì
  50. "Mos⌠á oµ thσ loca∞ loop≤ [operateΣ b∙ thσ regiona∞ telephonσ company▌ arσ n∩ ì
  51. troublσá a⌠á all,ó saiΣ Harr∙ Newton¼á publishe≥ oµ thσá Teleconnec⌠á monthl∙ ì
  52. magazinσá oε telephonσ systems«á  "The∙ havσ reall∙ improveΣ thσá qualit∙á oµ ì
  53. their service."
  54.  
  55.   Newtoεá say≤ hσ ha≤ haΣ problem≤ usinτ hi≤ portablσ compute≥ anΣ modeφ witΦ ì
  56. long-distancσ carriers«á  "Thei≥ engineer≤ wil∞ tel∞ yo⌡ therσ i≤ n∩ problem¼ ì
  57. bu⌠á wheεá I'vσ traveleΣ arounΣ thσ countr∙ witΦá ßá modem¼á nothinτá works,ó ì
  58. Newtoεá said«á  "Therσ i≤ s∩ mucΦ noisσ oε thσ voicσ linσ tha⌠ thσ modeφ doe≤ ì
  59. not pick up the connection [to the remote computer]."
  60.  
  61.   Othe≥ telephonσ official≤ claiφ somσ modem≤ ma∙ no⌠ bσ properl∙ designeΣ t∩ ì
  62. work with the telephone switching system.
  63.  
  64. .cp3è  "Wσ havσ se⌠ u≡ technica∞ specification≤ that¼ iµ met¼ wil∞ allo≈ equipmen⌠ ì
  65. t∩á transmi⌠ ove≥ thσ switchinτ network,ó saiΣ Vaughε Williams¼á aε assistan⌠ ì
  66. stafµ manage≥ a⌠ Ne≈ EnglanΣ Telephone«á  "Somσ manufacturer≤ makσá equipmen⌠ ì
  67. tha⌠á wil∞ mee⌠ mos⌠ oµ thσ genera∞ specifications¼á bu⌠ ß lo⌠ finΣ ß wa∙á t∩ ì
  68. design the modem differently to cut prices."
  69.  
  70.   Somσ phonσ companie≤ arσ usinτ ß ne≈ forφ oµ compressioε oε thσ phonσ line≤ ì
  71. calleΣá adaptivσá pulse-codσ modulation--ß methoΣ oµ doublinτ thσá numbe≥á oµ ì
  72. conversations one one wire from 32 to 64.
  73.  
  74. Compression Errors
  75.  
  76.   "Wheε the∙ d∩ that¼ the∙ reducσ thσ bandwidtΦ availablσ t∩ eacΦ line,ó saiΣ ì
  77. Mar∙ Schaller¼ vicσ presiden⌠ oµ marketinτ a⌠ Telebi⌠ Corp.¼ whicΦ market≤ aε ì
  78. erro≥á correctinτá modem«á  "Viocσá user≤á don'⌠ tenΣá t∩á notice¼á bu⌠á tha⌠ ì
  79. [compression▌ especiall∙ present≤ ß probleφ fo≥ [modem≤ a≤ fas⌠ a≤ 960░á bit≤ ì
  80. per second], which need every bit of bandwidth they can get."
  81.  
  82.   Schalle≥á saiΣ high-speeΣ modem≤ incu≥ ver∙ higΦ rate≤ oµ erro≥ wheε testeΣ ì
  83. over lines using adaptive pulse code modulation.
  84.  
  85.   Thσá prospec⌠ oµ thσ cominτ IntegrateΣ Service≤ Digita∞ Networδ (ISDN⌐á ha≤ ì
  86. man∙ user≤ hopinτ fo≥ bette≥ qualit∙ transmissions«á  ISD╬ woulΣ replacσá thσ ì
  87. curren⌠á analoτá o≥ tonσ baseΣ telephonσ systeφ witΦ aε al∞á digita∞á networδ ì
  88. morσ orienteΣ towarΣ thσ digital-baseΣ computer«  WitΦ ISDN¼ thσ digita∞ linσ ì
  89. wil∞ carr∙ multiplσ voicσ anΣ datß service≤ betweeε offices«á  Iε short¼á thσ ì
  90. phone system will become a large local area network.
  91.  
  92.   Bu⌠á somσ analyst≤ arσ worrieΣ tha⌠ thσ expansioε oµ digita∞ service≤á wil∞ ì
  93. causσá problems«á  "Noisσ wil∞ increase¼á especiall∙ fo≥ thosσ user≤ wh∩á arσ ì
  94. stil∞á usinτá analoτá line≤á wh∩ won'⌠ switcΦ t∩ digita∞á righ⌠á away,óá saiΣ ì
  95. Krechmer.