[Info-vax] strange LAT problem

[Johnny Billquist]

On 2018-12-03 14:19, Bob Koehler wrote:
> In article <pu0os2$tgf$1 at gioia.aioe.org>, helbig at asclothestro.multivax.de (Phillip Helbig (undress to reply)) writes:
>> In article <pu0igt$54o$1 at Iltempo.Update.UU.SE>, Johnny Billquist
>> <bqt at softjar.se> writes:
>>
>>> On 2018-11-28 21:52, Phillip Helbig (undress to reply) wrote:
>>>> In article <ptls10$hsa$2 at Iltempo.Update.UU.SE>, Johnny Billquist
>>>> <bqt at softjar.se> writes:
>>>>
>>>>> Any WiFi in this picture?
>>>>
>>>> No.  There is WiFi on the same LAN, but nothing to do with VMS.
>>>
>>> Meaning you use LAT between VMS hosts, and all the VMS hosts are sitting
>>> on the same ethernet segment with nothing else in between?
>>
>> Right; just a switch.
> 
>     LAT is extreemly sensitive to timing, and it's possible that the
>     switch does not meet the needs of LAT.  We've seen network bridges
>     that required special firmware to hande LAT.  (Not routers, LAT is
>     not a routable protocol, one can expect it to stop at a router.)

I would sortof disagree.

Yes, LAT is local network only. And yes, you can have weird network gear 
that can cause issues.

But I am in fact bridging ethernet halfway around the world, including 
LAT, and it actually works fine. And the latency from going halfway 
around the world, and my silly bridge program to boot, is probably more 
delays than a local switch or bridge usually manage to create.

As for Philips problems, I don't see any smoking guns yet. Devices do 
learn about services available through multicasts. So WiFi could be a 
problem. But that's been ruled out. Seems to be a simple network in 
general. You might have packets dropped because of overload at some 
interfaces. Especially if there is a mix of 10 Mb/s and 100 Mb/s devices.

Bottom line is that if a device don't know about a service, the packets 
announcing that service must be getting lost somewhere.
Hmm, Philip - do you have DECnet? Do some machines maybe have several 
ethernet interfaces?

   Johnny

-- 
Johnny Billquist                  || "I'm on a bus
                                   ||  on a psychedelic trip
email: bqt at softjar.se             ||  Reading murder books
pdp is alive!                     ||  tryin' to stay hip" - B. Idol