[e2e] How many TCP flows fit in the Internet?

Detlef Bosau detlef.bosau at web.de
Tue Apr 2 03:07:33 PDT 2013

I would like refer to mobile networks in this discussion. Particularly 
in mobile networks it may be the case that the throughput on the air 
interface drops below 1 MSS/RTT, whatever the meaning of "RTT" would 
mean here. However, when we encounter a throughput of, say, 300 bit/s 
this would certainly be a "low throughtput" in this sense.

When we have a constant, stationary throughput of 300 bit/s then the 
timer back off would be sufficient: Perhaps, it takes some time outs to 
sufficiently increase RTO and afterwards, a stationary RTT (say 1 
second) and variance (say 0.5 seconds) can well be treated. 
Unfortunately, a mobile network's throughput is hardly constant or 
stationary. This may have several reasons, we recently talked about GPRS 
and I was pointed to implementation deficiencies there - however, a user 
wouldn't be more comfortable with a huge RTT if he knew, that this is 
due to the implementation ;-)

However, from recent discussions I think we can identify at least three 
reasons for huge RTT:
1. Low throughput on a link, e.g. a mobile link with noise on its air 
2. Network overload
3. Buffer bloat.

Would you agree here?

I'm curious whether these three cases could, or should, be treated using 
the same mechanism.


Detlef Bosau
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