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Text File  |  1992-03-16  |  4KB  |  142 lines
  1. .HE QAFT.DO├ N2W╪ rev. 10 Auτ 90
  2. .FO                            #
  3. .IG 
  4. .IG 
  5. .OJ ON
  6. .PN 1
  7.  
  8. .IG 
  9. .IG 
  10. .OJ ON
  11.  
  12. .IG Documen⌠ dedicateΣ t∩ thσ publiπ domaiε b∙ N2WX
  13. .IG 
  14. .IG Retentioε oµ authorshi≡ noticσ woulΣ no⌠ bσ inappropriate
  15. .IG 
  16. .IG 
  17. .IG 
  18. .OJ ON
  19.  
  20. .IG 
  21. .IG 
  22. .OJ ON
  23.  
  24. .IG 10 auτ 90    clearl∙ definσ er≥ detec⌠ algorithφ a≤ inverteΣ bytσ cksum
  25. .IG 
  26. .IG 31 ma∙ 90   makσ framσ abor⌠ procedurσ conforφ t∩ x.25/AF╘ re÷ 2,
  27. .IG 
  28. .IG              replacσ occurence≤ oµ "tw∩ bytσ CRC" witΦ "onσ byte
  29. .IG 
  30. .IG                   error-detectinτ character
  31. .IG 
  32. .IG W╙ filσ expect≤ W╙ laserprinte≥ configureΣ fo≥ 1" top/bo⌠ margin≤ 
  33. .IG 
  34. .IG 
  35. .IG 
  36. .OJ ON
  37.  
  38. .IG 
  39. .IG 
  40. .OJ ON
  41.  
  42. WARNIN╟ - EXPERIMENTER╙ ONLY!
  43.  
  44.      Hos⌠ ámodσ oε TNC-2 anΣ derivativσ TNC≤ a⌠ thi≤ timσ remain≤ ì
  45. experimental.  Obviou≤ feature≤ receiveΣ ß quicδ "goinτ over" anΣ ì
  46. rathe≥ ácursor∙ ádebug, bu⌠ discover∙ oµ thσ remaininτ inevitablσ ì
  47. bug≤ áanΣ ácritica∞ programminτ oversight≤ await≤ thσ adventurou≤ ì
  48. reader/developer.  Pleasσ direc⌠ discoverie≤ anΣ criticisms:
  49.  
  50.           viß slo≈ boa⌠ : t∩ HowarΣ Goldstein
  51.                              5201-23rΣ Ave. N.
  52.                              St. Petersburg, F╠ 33710 USA
  53.           viß compuser÷ : t∩ 75006,702
  54.           viß haφ packet: t∩ N2W╪ @ W4DPH.FL
  55.  
  56. INTRODUCTION
  57.  
  58.      Asynchronou≤ áFraminτ áTechniquσ á(AFT) ái≤ áß publiπ domaiε ì
  59. methoΣ áfo≥ encapsulatinτ group≤ - frame≤ - oµ error-protecteΣ 8-ì
  60. bi⌠ ádatß áacros≤ asynchronou≤ seria∞ links.  AF╘ i≤ modeleΣ upoε ì
  61. anΣ áattempt≤ át∩ áemulatσ áß ásynchronou≤ HDL├ link. AF╘ wa≤ deì
  62. velopeΣ b∙ Hayes, Inc.
  63.  
  64.      QAF╘ ádiffer≤ áfroφ áAF╘ onl∙ iε thσ erro≥ detectioε scheme.  ì
  65. QAF╘ use≤ ß quicke≥ 2'≤ complemen⌠ checksuφ vs. AFT'≤ CRC.
  66.  
  67. REQUIREMENTS
  68.  
  69.      AF╘ áimplementatioε álevel≤ á0 anΣ 1 requirσ aε asynchronou≤ ì
  70. linδ capablσ oµ passinτ al∞ 256 8-bi⌠ character≤ unmolested.  AF╘ ì
  71. Leve∞ á1 ámake≤ aε exceptioε fo≥ underlyinτ DC1/DC3 flo≈ control: ì
  72. L1 map≤ DC1/DC3 t∩ different, harmles≤ characters.
  73.  
  74. BASI├ AFT
  75.  
  76.      Ever∙ AF╘ framσ consist≤ of:
  77.           Onσ o≥ morσ leadinτ FLA╟ characters     ::   0x7E
  78.           1-nε character≤ oµ DATA                 ::   0x??
  79.           Onσ error-detectioε character           ::   0x??
  80.           Onσ o≥ morσ endinτ FLA╟ characters      ::   0x7E
  81.  
  82.           AnΣ possibly:
  83.                Datß linδ Escape                   ::   0x7D
  84.  
  85.      Flags
  86.  
  87.      Thσ áFLA╟ terminatinτ oncσ framσ caε simultaneousl∙ opeε thσ ì
  88. nex⌠ subsequen⌠ frame.
  89.  
  90.      Abort
  91.  
  92.      QAF╘ ásupport≤ áaε HDLC-likσ abor⌠ eveε thougΦ i⌠ ha≤ littlσ ìèpractica∞ ááuse.  TNC-2 ááneve≥ átransmit≤ áthσ áabor⌠ ásequence.  ì
  93. AFT/QAF╘ specifie≤ thσ abor⌠ sequencσ as:
  94.  
  95.  
  96.      Thσ átransmitte≥ áma∙ áabor⌠ áß áframσ áb∙ ásendinτ á$7─ $7┼ ì
  97. (escape-flag).  N∩ áááerror-detectioε ááácharacte≥ ááái≤ áátransì
  98. mitted.  Thσ ááincompletσ ááescapσ áásequencσ ááwil∞ áácausσ áthσ ì
  99. framσ t∩ bσ rejecteΣ b∙ thσ receiver.
  100.  
  101.  
  102.      Transparency
  103.  
  104.      Transparenc∙ ái≤ áaccomplisheΣ áb∙ replacinτ datß anΣ error-ì
  105. detectioε ácharacte≥ character≤ matchinτ AFT'≤ FLA╟ anΣ DL┼ charìèacter≤ witΦ ß tw∩ characte≥ sequencσ madσ u≡ of:
  106.  
  107.                          DL┼                      :: 0x7D
  108.                          DATA/error--detectioε characte≥ xo≥ 0x20
  109.                                                   :: 0x?? ▐ 0x20
  110.  
  111. Thσ áfirs⌠ characte≥ (DLE) invoke≤ transparency; thσ seconΣ charì
  112. acte≥ ái≤ áthσ áresul⌠ áoµ exclusive-ORinτ thσ origina∞ datß witΦ ì
  113. 20H.
  114.  
  115.      Optiona∞ transparency:  thσ abovσ substitution≤ arσ thσ onl∙ ì
  116. one≤ áspecifieΣ áb∙ AFT/QAF╘ leve∞ 0 ("Basiπ AFT").  Transparenc∙ ì
  117. fo≥ áXON/XOF╞ character≤ i≤ supporteΣ iε AFT/QAF╘ leve∞ 1 anΣ thσ ì
  118. TNC-2.  Seσ below.
  119. .CP 5
  120.      Error-detection
  121.  
  122.  
  123. QAF╘ - TNC-2
  124.      Thσ áerror-detectioε bytσ i≤ thσ two'≤ complemen⌠ oµ thσ suφ ì
  125. oµ áthσ áframe'≤ ádatß only.  Excludσ erro≥ detection, flags, anΣ ì
  126. escapσ byte≤ froφ thσ addition.
  127.  
  128. "X.25/AF╘ re÷ 2" -- NO╘ iε TNC-2
  129.      Thσ áCCIT╘ (X**16 + X**12 + X**5 + 1) erro≥ checkinτ polynoì
  130. mia∞ ái≤ áused.  Oε átransmit, thσ CR├ generato≥ shoulΣ bσ se⌠ t∩ ì
  131. al∞ 1's.  
  132.  
  133.      Thσ áCR├ ái≤ átransmitteΣ iε reversσ bi⌠ order; ex: wheε thσ ì
  134. asynchronou≤ ácharacter≤ receiveΣ arσ hicrc=0x73 lowcrc=0x88, thσ ì
  135. actua∞ CR├ i≤ 0x11CE.
  136.  
  137.  
  138. AF╘ LEVE╠ 1
  139.  
  140.      AF╘ áLeve∞ á1 áadd≤ áDC1 áanΣ áDC3 át∩ áthσ átw∩ ácharacter≤ ì
  141. (FLAG/ESCAPE) mappeΣ b∙ AF╘ Leve∞ 0'≤ transparenc∙ mechanism.
  142.