VNC Viewer freezing? Or is it the server?

[Chris Jaecker]

Hi Jason,

I'm sure the rest of the list will have at this from the VNC side, but I'd 
like to review from the routing point of view. You say 128K ISDN, 
presumably a Basic Rate Interface.

The topology looks something like this, I think

<VNC Server> 
<----Ethernet---><Router><---ISDN----><PC><-------Ethernet---><VNC Client>

Correct me if this is off.

So the remote pc makes a call, then the client connects to the server, with 
the remote pc acting as a router. There are a number of things that could 
cause a problem here, and they're to do with the routing function. The most 
likely is that the remote pc could decide the call is over due to some 
timer and drop it. Generally devices that make isdn calls have a default 
period of "no interesting traffic" after which a call will be disconnected 
to save on the telephone bill. From your description, the call is being 
dropped without regard to the in-progress vnc session.

So you need to convince the calling pc that the vnc is "interesting traffic".

A quick test for this would be to ping constantly from the calling pc to 
the VNC server or another device on the server side, as it would keep the 
call up. Usually pings are "interesting" because they are used for 
troubleshooting. While the pings are going through establish a vnc session 
from client to server and see if it stays alive past the 5 minute cut-off. 
If it does, you need to configure the calling device to make the VNC tcp 
traffic "interesting", which will make the problem go away. I can't 
remember what port it is, but all TCP traffic would probably work.

Other possibility: If you are using both B channels (the full 128K), then 
you are probably using multilink PPP, which fragments and reassembles 
packets. If the "routers" are not properly implementing MPPP, then they 
could lose the plot on the fragmentation and reassembly, causing the 
interfaces to hang. Try using only 1 B channel, or toggling configurable 
options to find a work around. I don't know what the devices are, so this 
is hard to call, but compression and other PPP options may not be 
implemented equally.

The fact that ping doesn't work once the connection fails suggests that the 
call is dropped rather than there's a VNC connection problem.

By the way, the web client isn't any different from the regular VNC client, 
it is simply a java app downloaded to the client from the server as opposed 
to a local client program. Once it is downloaded and running, it works the 
same way as the regular client.

Hope this gives you something to go on. Let me know more about the topology 
if you can, as it sounds like it's the intervening devices that are making 
the problem occur than VNC.

Best wishes

Chris Jaecker

At 06:00  3/04/02 +0100, you wrote:
>Date: Tue, 2 Apr 2002 16:05:32 +0100
>From: Jason McClean <Jason "at" listawood.co.uk>
>Subject: VNC Viewer freezing? Or is it the server?
>
>I have the following problem (3.3.3r7)
>
>two machines (win2k SP2) one has the VNC Server running.  The remote machine
>dials into our network over ISDN (dual channel 128k).  Once the connection
>is made, the other Win2k machine on the network connects to the VNC server.
>I'm sure there are nicer ways of doing that bit, but that's not the problem.
>
>After a certain amount of time (not always the same but around the 5 minute
>mark), the viewer seems to freeze.  The remote pointer doesn't move about
>etc.  This seems to affect the whole ppp connection.  I can no longer ping
>the remote machine.  If the remote machine disconnects from the network and
>then reconnects, the viewer can be used again until it freezes. The VNC
>server is not restarted.
>
>I don't have any problems using VNC on the local network - I can have
>connections for hours.  I can dial into the network from a win98 machine and
>connect to a VNC server on a Win2k machine with no problems.
>
>Any ideas anyone.  It may be the connection, but I'm not convinced yet.  I
>trawled throught the mailing list archives and found an almost similar
>problem, but closing the viewer and reconnecting solved that - the whole
>connection disappears in this case so the viewer can't find anything to
>connect to.  If I don't use VNC, I can keep the connection alive for as long
>as I need and transfer data to and from with no probs.
>
>==========================
>Jason McClean
>IT Manager
>Listawood Limited
>Tel: +44 (0) 1485 529100
>Fax: +44 (0) 1485 529200
>http://www.listawood.co.uk
>Enquiries: magic "at" listawood.co.uk
>==========================
>
>------------------------------
>
>Date: Tue, 2 Apr 2002 16:54:19 +0100
>From: Jason McClean <Jason "at" listawood.co.uk>
>Subject: RE: VNC Viewer freezing? Or is it the server?
>
>Update:
>Don't seem to have any problems using the java viewer! Just been using that
>for a fair while - slower but if the connection to the vnc server is more
>reliable then such is life.
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