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  5. From: meregalli@cesi.it (Alberto Meregalli (DIF))
  6. Newsgroups: comp.protocols.kermit.misc
  7. Subject: Re: Random login prompt with K95
  8. Message-ID: <1996Dec4.123609.1220@cesi>
  9. Date: 4 Dec 96 12:36:09 +0100
  10. References: <1996Dec3.161932.1217@cesi> <581mdn$3lf$1@apakabar.cc.columbia.edu> <5824av$f1v$1@apakabar.cc.columbia.edu> <1996Dec4.110236.1219@cesi>
  11. Organization: Centro Elettrotecnico Sperimentale Italiano, Milano, Italy
  12. Lines: 82
  13.  
  14. In article <1996Dec4.110236.1219@cesi>, meregalli@cesi.it (Alberto Meregalli (DIF)) writes:
  15. > In article <5824av$f1v$1@apakabar.cc.columbia.edu>, fdc@watsun.cc.columbia.edu (Frank da Cruz) writes:
  16. >> This is probably happening because the terminal type is being renegotiated:
  17. >> "My terminal type is VT320", "I don't like that one, please try another",
  18. >> "OK, it's VT220", etc etc.  This is documented in section 6.2 of UPDATES.DOC.
  19. >> 
  20. >> It could be the root of all the other symptoms you have reported.
  21. > ...
  22. >> So far so good.  But VMS doesn't like the VT320 terminal type, so it sends
  23. >> a message asking us to try another one, so we drop down to VT220:
  24. >> 
  25. >> TELNET RCVD SB TERMINAL-TYPE SEND  IAC SE
  26. >> TELNET SENT SB NAWS 80 49 IAC SE
  27. >> TELNET SENT SB TERMINAL-TYPE IS VT220 IAC SE
  28. >> 
  29. >> But whenever we change terminal types we have to clear the screen.  Why?
  30. >> Because different terminal types might have different dimensions, coloration,
  31. >> attributes, etc, and we must initialize all of this when switching emulations.
  32. >> So now the user sees a blank screen.  (Scrollback would reveal the herald
  33. >> and Username: prompt on the previous screen.)  
  34. > 
  35. > That's what happens: we could see the Username: prompt by scrolling
  36. > back.
  37.  
  38.  
  39. I have to elaborate on that: in the sniffer captures of "regular"
  40. (i.e. appearing prompt) session the sequence is, considering only visible
  41. data and the Terminal Type option:
  42.  
  43. >From VAX                 From K95
  44.  
  45. ------1st example------------------
  46. SEND
  47.                          IS 'VT320'
  48. <cr><lf><cr>
  49. SEND
  50. <lf><cr><nul>Username:
  51.                          IS 'VT220'
  52. ------2nd example------------------
  53. SEND
  54. <cr><lf><cr>
  55.                          IS 'VT320'
  56. SEND
  57. <lf><cr><nul>Username:
  58.                          IS 'VT220'
  59. ------3rd example------------------
  60. SEND
  61. <cr><lf><cr>
  62.                          IS 'VT320'
  63. SEND
  64. <lf><cr><nul>Username:
  65.                          IS 'VT220'
  66.  
  67.  
  68. In the case that the prompt disappears this is what you see
  69.  
  70. ------1st example------------------
  71. SEND                                         |
  72. <cr><lf><cr>                                 |
  73. <lf><cr><nul>Username:                       |
  74.                                              |
  75.                          IS 'VT320'          |
  76. SEND                                         |
  77.                          eesposito<cr><lf>   |
  78. EESPOSITO<cr><lf>                            | all of this was seen 
  79. <cr><lf>Password:                            | on the screen!
  80.                          IS 'VT220'          |
  81. ------2nd example------------------
  82. SEND
  83. <cr><lf><cr>
  84. <lf><cr><nul>Username:
  85.                          IS 'VT320'
  86. SEND
  87.                          IS 'VT220'
  88.  
  89.  
  90. It seems that the screen clearing happens when the second SEND from
  91. the VAX is received, not when the new terminal type string is sent.
  92. ---------------------------------------------------------------------------
  93. Alberto Meregalli, DIF                                  tel. +39 2 2125 249
  94. CESI, Centro Elettrotecnico Sperimentale Italiano       fax  +39 2 2125 520
  95. Via Rubattino, 54 - I 20134 Milano                E-mail: meregalli@cesi.it