[p2p-hackers] Keep Alive and network performance

[Daniel B.]

In an optimistic communications should not use pings per say. My  
preference is just to write the data. To deal with optimism, in some  
cases, you do need feedback. A couple of choices are to use checksums  
or last-heard-from in your data.

There are many complex issues here. Many of them depend on the P2P  
network and your application. Speed of notification is only sometimes  
important. If you are sending data via relayed machines, it would be  
better to stop a send soon, when the destination disappears. If the  
relays store for a later forward, the source does not care that the  
destination is up or down because the destination will eventually get  
the message.

If we assume infinite bandwidth and computers that can never be  
flooded by bandwidth, its all cool. If we assume spotty wifi and 5  
year old computers, the solutions need to be carefully implemented to  
avoid failures.

On Feb 9, 2006, at 1:34 AM, Matthew Gertner wrote:

> Daniel B. wrote:
>
>> Keep alive is both a missing component in practical P2P and a  
>> reason  why P2P is also hard to make practical.
>>
>> The trap is that the keep-alive is between two machines. Imagine   
>> hundreds of thousands of machines!!!! Even with small signatures   
>> matching each machine, we are talking about a flooded network. A   
>> secondary trap is managing reliability. Reliability in P2P is not   
>> moving bytes back and forth, but also taking into account the  
>> machine  may be a laptop or other personal computer that has a  
>> pathetic uptime.
>>
>> The better choice is online/offline signaling and optimistic   
>> communications with good error control.
>
> I assume that by "optimistic communications" you mean that we  
> should assume a connection exists and confirm this using periodic  
> pings? Isn't this basically the equivalent of KA? It seems to me  
> that the fundamental tradeoff is speed of notification vs. extra  
> network traffic (i.e. you know more quickly when someone's network  
> connection is cut if you ping more often), and this is the case  
> both for KA and for a custom optimistic approach that uses pings.  
> Am I missing something?
>
> Cheers,
> Matt
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