[nos-bbs] Collision avoidance

[Steven Stimpson]

  ----- Original Message ----- 
  From: George (Skip) VerDuin 
  To: TAPR xNOS Mailing List 
  Sent: Sunday, August 13, 2006 1:21 PM
  Subject: Re: [nos-bbs] Collision avoidance


  Hey Steve - I need to be very accurate in this and can not take the chance of mis-interpreting your input...

  >SNIP< 

   HI skip. Here is a snippet from my autoexec.nos The parm is AX25 IRTT, Initial Round Trip Timer.
  These are VHF parms.

  #
  ax25 timertype orig
  # Initial rtt for ax25 (FRACK) is 4 secs. (Works out to abt 4-8 sec actually)
  ax25 irtt 4000
  # RespTime in ms
  ax25 t2 5
  # Check Time in ms (450 secs 1/2 of No-Activity)
  ax25 t3 950000
  # No-Activity Time in Secs
  ax25 t4 180000

  Note my t3 and t4 settings are absurd, this was to hold a link with
  a packetcluster around the clock some time ago. Check the docs
  for setting on those, or do what ka1nnn says here and start with 450 for t3,
  and double that for t4. Also, since we owned the freq, my
  Resp timer is rude. ax25 timertype is a method of backing
  off the frack timer with each missed frame. Never tried
  it with VHF but on H.F. it can reach epic proportions
  and is no good.


  In addition, can you confirm that entering kiss mode locks out the TNC frack timer so there is no timer-race?

   Sure. The frack timer is a function of the Level2 firmware that resides in
  the tnc. This is all disabled when entering KISS. Level 2 is run
  in the computer, and is sent with each frame as a KISS header.
  TXD, RESP, DWAIT, FRACK and I believe TXTAIL are all
  handled by your KISS app. Note I said believe. I have
  experimented with all these from the MSYS command
  console and they can be changed on a per packet basis.
   But I bet some of the programmers could tell you for sure which ones
  are and aren't. I'm not entirely sure what you mean by timer race?




  >From your experience, could you pass on the set of all (TNC and software) parameters that work well together at 300B HF kiss
   >SNIP< 

   On some of the extremely busy nets, a frack timer of 11 seconds...Yes, eleven seconds, would
  keep frames from backing up in the tnc. You also need to add the time it takes to
  transmit the frame into account, since the frack timer starts counting
  in the computer the moment the frame leaves the computer. If it takes
  5 seconds to TX the frame but frack is only 4, there is going to be problems.
  If you have to wait 4 seconds for the frequency to clear
  and then another five while you TX, there is going to be bigger problems.

   Another parm to watchout for is PTHRESH. Poll threshold. If your paclen
  is 64, and pthresh is not set, each time the frack timer expires
  the whole 64 length frame will be sent over and over. much better
  to send a poll then the entire frame. A friend of mine
  solved this by setting paclen to 64 and pthresh to 62.

   If you want to see all this in action set your frack to 1/2 second,
  TXD to one second, paclen to 255, disable pthresh, set your retry
  to 10, and connect to a  buddy on a clear freq. send a big
  frame and it should crash and burn :-)

   I went to wa8ded firmware some time ago. It like half-kiss, and half-TNC.
  level2 resides in the tnc, and all the timers know the state of the DCD.

  GL, hope this isn't TMI but it's raining out and there is nothing to do :-)


  Steven
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