[e2e] Spurious Timeouts in mobile wireless networks, was: Re: Retransmission Timouts revisited

[Filipe Abrantes]

Hi Francesco,

Francesco Vacirca wrote:
>> The "spurious timeout" problem often claimed in mobile wireless 
>> networks thus should be basically a problem with extreme delay spikes.
> 
> 
> This is correct: delay spikes that are not "seen" in the first and 
> second order moments of rtt distributions and that are used for the RTO 
> setting.
> 
>>
>> As to my understanding, we can exclude other problems, the only 
>> problem with TCP in mobile wireless networks are unexpected, or 
>> unforeseeable respectively, delay spikes or a sudden increase of delays.
> 
> 
> Well, packet losses are the main problem... and they should be hidden to 
> TCP with wireless link layer protocol and persistant retransmissions...
> 

Well, if packet loss is hidden by L2 retransmissions, then, packet loss 
would become delay, which can become spurious timeouts (depending on the 
delay increase) right? Then spurious timeouts won't be that marginal...

Best regards

Filipe

> 
> Spurious timeouts are a second (marginal) problem that in my opinion 
> (and in my research) are not frequent events in a well engineered 
> GPRS/UMTS network.

> 
> Francesco
> 
>>
>> This can be due to
>> - scheduling (voice is priorized over data)
>> - route change (I don´t know whether this is that important, because 
>> much of this is micromobility)
>> - changes in physical path properties.
>>
> 
> 

-- 
Filipe Lameiro Abrantes
INESC Porto
Campus da FEUP
Rua Dr. Roberto Frias, 378
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Portugal

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E-mail: fla at inescporto.pt