From: becka@rz.uni-duesseldorf.de
  To  : ggi-develop@eskimo.com
  Date: Sun, 18 Apr 1999 13:18:31 +0200 (MEST)

Re: New ggi program released (and network programming question)

Hi !

> More information, screenshot, and downloads are available at 
> http://e.x0r.ml.org/phere .

Downloads don't work. Server tells file doesn't exist.

> My question: I understand it's better to have updating done
> using UDP (because there's less overhead, no retransmission,
> etc).  Currently, when a person joins, the server sends a UDP 
> message to all of the clients.  What has occurred to me, 
> though, is that UDP isn't reliable.  This means it is possible
> that the message will be lost.  Losing any important message
> (ie "change map") wouldn't be good.

Yes.

> I can see two possible solutions:
> - Establish a TCP connection and a UDP "connection" 

That's pretty awkward I'd say ...

> - Require clients to respond with an "I got it" message to 
> important messages over UDP.  Problems: extra complexity, 
> bandwidth overhead (which seems unavoidable no matter what).

Yes - I'd do that. It's basically what TCP does "under the hood".

The server keeps track of all clients anyway - right ?
Well - it has to so it knows where to distribute updates.

So I'd just add a "waiting for ACK" queue to the array (?) that holds the
data for the clients. You add all packets that need an ACK to that queue
together with a timestamp and a retransmission count. If you get an ACK from
a client, you delete the record from the queue.

Other than that, you regularly check the queues and see if a packet has been
there for too long. If so, retransmit, and if the retransmission count
becomes too high, consider the client dead and remove it from the list.

I think that's the simplest solution. Maybe someone proves me wrong ? :-)

CU, ANdy

-- 
= Andreas Beck                    |  Email :  <andreas.beck@ggi-project.org> =