[Csci551-talk] Re: [Cs551] Project b - Time out question

[xi wang]

> Hi, 
> (1)Now,,,in the termination codition of non-seed nodes,,,,they 
> shouldn't make any progress in downloading for 4 rounds,,,the 
> progress here does it mean recving some segments only or it could 
> mean also recving request as well from other clients?
> 
> if we are to consider recving a req as a progress , then we fall 
> into an infinite situation in high loss rate,,,,assume i have one 
> seed and 2 clients if the seed terminated because it didn't recv a 
> req(because the req are lost), then the 2 clients will never end 
> since they recv req from each other? 
>

You can do some experiments with these. A good way is to consider a node is making progress if it is receiving a segment or sending out a segment. Swapping segment information is not considered as progress, so there won't be infinite loops.

> 
> (2)Assume the following scenario, The delay is one second...and 
> the timeout is 5 second,,,,now if client  send to the seed seg req 
> and assume the seed has 10 replies waiting,,,then the seed will 
> send the client reply after 11 second....the problem here is the 
> client will timeout assuming that the packet is lost  where it 
> didn't>,.....Do we have to consider such a scenario in our project 
> or  we can safely assume that if i sent a packet and then i 
> timeout without recving a response then this packet is lost? 
> 
> In other words, can we assume that if the time out is always very 
> large comparing to the delay 
> 

If nodes cannot complete downloading due to high delay and small timeout value, and they terminate gracefully, that's not an error. We will use higher timeouts for some testcases.

-Xi