Re: [tlug] Skype windows vs linux again

[Jim <jep200404@example.com>]

Steve S wrote:

> I don't understand how skype uses the network, but the time between 
> going offline with one and online with the other was only a few seconds.

Even if they were simultaneous, 
the network connections could be drastically different. 

If at least one of the computers is not firewalled, 
then it can directly receive incoming connections, 
so after the two parties have met at Skype's servers, 
the firewalled computer can initiate a connection from 
behind the firewall to the non-firewalled computer. 
This provides minimal latency and so is desirable. 

If both computers are behind firewalls, then incoming 
connections from each other will be blocked by the their 
firewalls. So a bit of a trick is use. Neither can receive 
connections, but both can initiate connections. So Skype 
arranges for a third computer (that is not behind a firewall) 
to accept connections from you and your friend's computer, 
and pass the traffic between those two connections. 
The data has to go through another computer and double 
the network connections, so latency increases. It is a 
necessary evil. 

> >It would not surprise me if the Linux box had its own firewalling 
> >by default, 
> >
> It does.  And the linksys router I use does ip forwarding I think, 

Unless you have intentionally poked holes in the "router", 
it is almost certainly behaving the same for Linux and XP. 

What does "IP forwarding" mean to you? 

> Actually XP has a built in firewall now too I think.  

Perhaps the tight integration of stuff in XP could allow an 
application (such as Skype) to open a hole in that firewall. 

> I don't understand how echoing can 
> occur in the digital domain though.

I would not expect echoing to happen in the digital domain, 
but since you raised networking as an issue, I addressed that. 

> Also I need to google and check out the skype site 
> to see if they have any ideas.

   http://www.google.com/search?q=skype+echo+linux