Conference irocz::terminal_servers

3444.0. "flow control back across Lan?" by CHEFS::KERRISON_G (Let the skunk drink the Martini!) Thu Feb 20 1997 07:35

    Hi
    
    I've some printing problems that I'm experiencing that I just cannot
    easily isolate. They seem flow control-ish but i've open mind as to
    what the cause and fix is.
    
    The printers are connected to DS90TL, and are serviced by a Digital
    UNIX LAT connection.(DS900TM controlled printers appear to also have
    this problem)
    
    The printers are set up to do DTR flow control (and some have both
    XON/Xoff and DTR) - and the DS90TL is set up for DSR/DTR flow control
    and signal control disabled.
    
    in addition the port is set to output flow control enabled (and input
    curiously).
    
    In standard operation the files are put on the queue that then puts to
    the terminal server. The terminal server port lights up and then the
    terminal server sends to the printer.
    
    If the printer buffer is too full then it "flow controls off" the
    terminal server port until such time as the printer can cope again and
    "flow controls on" the TS port. This "seems" to work a treat -
    particularly from our testing in house it doesn't fail.
    
    However, we still have problems. The printers are appearing as offline
    on the UNIX sytem as so no data is sent to the TS.
    
    It is presumably possible that while the ts port is "flowed
    off" that data is still being sent from Digital UNIX across the LAN. 
    Presumably possible also that there is a limited size buffer in the 
    TS so this would have to "flow control off" and later "on" the data 
    flow from the UNIX system across the lan (and this could happen even 
    if the TS port wasn't "output flow control offed").
    
    What if any flow control mechanisms exists here between the TS and the
    Digital UNIX and its print queues? (sorry if this is a really dumb
    question)
    
    The problem here occurred on a printer with both xon/xoff and dtr flow
    set and also a dtr only printer - where the print queues were set to
    recognise xon/xoff flow control.
    
    Normally it all just works fine, but sometimes (once here) and MANY MANY
    times on customer site the queues just say printer offline. And they're
    not offline. And no lights appear on the TS ports..
    
    help!
    
    any ideas? there are no "known" bugs with the LAT, line printer daemons
    or anything else related on UNIX...  
    
    
    regards
    
    Gary
    
             

RE: .0
    
>    What if any flow control mechanisms exists here between the TS and the
>    Digital UNIX and its print queues? (sorry if this is a really dumb
>    question)
 
For LAT connetions, this is accomplished by the exchange of LAT "credits".

Regards,

Dave

    re: -1
    
    Aha.
    
    are these "credits" monitorable? tunable? configurable? on both the 
    TS and on Digital UNIX?
     
    
    Can I see if one end is waiting for a credit? If LAt on UNIX is waiting
    for a wake-up credit from the TS, can I determine whether the TS should
    have issued one (buffer below n% full) ? Can I force the TS to issue
    a credit?
    
    So in this scenario the LAT and not the print queues is stalled
    - which in turn stalls the data flow from printer queue to LAT...?
    
    Gary
             

  Hi,

  The credits are not tuneable from the TS side.  I don't know about the 
  UNIX end. 

  There's no command to monitor credits or buffer usage on TS or to determine
  if the TS is waiting for credits. You could use a LAN analyzer such as IRIS
  or a Data General Sniffer to monitor the credit exchange on the net.  It 
  would take some time and effort to walk through the trace and account for 
  all the credits.

  Have you used the SHOW PORT n STATUS command to verify that it's not a simple
  matter of the port being XOFF'd?  

  bob richard