[Info-vax] Timeout in a write using QUIW.

[Jan-Erik Söderholm]

Den 2023-06-22 kl. 14:24, skrev Simon Clubley:
> On 2023-06-21, Jan-Erik Söderholm <jan-erik.soderholm at telia.com> wrote:
>>
>> Now, we are having issues with an application when *writing*
>> to a terminal (TNA) device using QUIW that points to a small
>> label printer. If the printer is offline or not accessable on
>> the network, the application just hangs.
>>
> 
> [snip]
> 
>>
>> These are new printers where they decided to use Wifi
>> instead of wired connection. We do not see these issues
>> on our older label printers which are all hard wired...
>>
>> I will of course again suggest that they do take the cost to
>> ask for wired network connections instead of using Wifi...
>>
>> I also fixed a COM file that pings these 7 printers once each
>> 10 seconds, and it clearly shows that the connections comes
>> and goes more or less all the time. And when that happens to
>> be the same time as they try to print a label, it just hangs...
>>
> 
> Others have given you some excellent workarounds, but I am more
> interested in _why_ you have the problem in the first place.
> 
> First off, it's not fully clear, but are these label printers
> directly on the network, with their own IP address, instead of
> via a terminal server ? I am assuming they are directly on the
> network for the rest of this post.

Sure, there own IP addresses (on one of the Wifi subnets).

> 
> It sounds like you have a permanent TCP/IP connection to the
> printers via reverse telnet. In that case, do you have keepalive
> packets from VMS enabled on the connection ?

We use the "reconnect" options when creating the TNA device. So that
(at least normally) any activity from VMS will init an automatic
re-connect, should the link have been disconnected.
But that of course depends on that the other end is available
at that point in time.

> 
> If you do, but the keepalive interval is 75 seconds or greater,
> try reducing it to 30 seconds in case the printers are going into
> some wireless low-power mode after a short period of time of network
> inactivity.


I do not think it is that kind of issues. We have a ping routine
that is pinging these addresses in a loop each 10 seconds.
And that shows that they sometimes gets anavailable. No specific
pattern, just that it happens all over the day.

> 
> (30 seconds is what I tell ssh to use for keepalive packets when
> I use WAN connections, and it seems like a reasonable value to me.)
> 
> If that works, look to see if the printers have some low-power settings
> that can be adjusted or disabled.
> 
> The keepalives should end up with the telnet connection being dropped
> by VMS on failure, so that you can reconnect.
> 
> Is there anyway you can do the telnet connection on demand and then
> tear it down again immediately afterwards, instead of keeping it open
> all the time, even when you are not printing labels ?

The TCP connection as such is opened when VMS has anything to send and
disconnected aftarwards. So each label printout involves a full
connect/print/disconnect on the TCP level (as can be seen in OPERATOR.LOG).

The issue seems to be if one of the (short) Wifi outages happens to
be at the same time as VMS tries to print a label. Then it looks up.

Anyway, it seems as hard wiring these printers seems to be the
route forward right now.

Thanks for you points!

And as I said before, after Friday next week, this is not my problem
anymore... :-) And again, VMS was never replaced with anything, that
is not why I'm leaving. My contract was simply not renewed.

Jan-Erik.




> 
> Simon.
>