[p2p-hackers] UDP Behavior in the Real World

David Barrett dbarrett at quinthar.com
Fri Oct 20 19:50:52 EDT 2006


Thanks.  By "does happen" do you mean "it happens for everyone every once
and a while" or "it happens frequently for some users and not at all for
others"?  

 

I realize the internet is a big place and there will always be some user
that has any networking property in unusually high or unusually low
frequency.  But I'm curious what the "usual" frequency is for this sort of
thing, if you have any data on this.

 

-david

 

  _____  

From: p2p-hackers-bounces at lists.zooko.com
[mailto:p2p-hackers-bounces at lists.zooko.com] On Behalf Of Alex Pankratov
Sent: Friday, October 20, 2006 4:30 PM
To: 'theory and practice of decentralized computer networks'
Subject: RE: [p2p-hackers] UDP Behavior in the Real World

 

Regarding (1) - reordering does happen. 

 

First of all it happens in L2 load-balanced scenarios, ie when the traffic 

goes through virtualized servers or server clusters. It also happens when 

the traffic goes through multi-CPU routers and finally It happens (though 

less frequently) due to route flips.

 

There is an anecdotal evidence that reordering also happens more

frequently over Gigabit links, but I suspect that this is hardware specific

and it has something to do with NIC drivers flipping between interrupt and

poll-based modes.

 

Alex

 

  _____  

From: p2p-hackers-bounces at lists.zooko.com
[mailto:p2p-hackers-bounces at lists.zooko.com] On Behalf Of David Barrett
Sent: Friday, October 20, 2006 4:14 PM
To: 'theory and practice of decentralized computer networks'
Subject: [p2p-hackers] UDP Behavior in the Real World

So I'm working on a TCP over UDP layer and I'm wondering about the
following; what have you seen?

 

1)       How often does out-of-order packet delivery happen in the real
world?  My reading and experience indicates it's actually very rare, but I'm
curious if you concur.

2)       How often does duplicate packet delivery happen in the real world?
Again, I'm of the impression it's even more rare than out-of-order, but I'd
like your thoughts.

Clearly, these happen and need to be accounted for.  But I'm curious to what
degree they happen, as this affects performance characteristics of the
implementation.

 

-david

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