[e2e] Delivery Times .... was Re: Bandwidth, was: Re: Free Internet & IPv6

Detlef Bosau detlef.bosau at web.de
Wed Dec 26 14:48:55 PST 2012

Am 25.12.2012 04:19, schrieb dpreed at reed.com:
> Indeed, bandwidth is now meaningless as a term, just as "broadband" 
> is.   Once upon a time, both referred to bounds on the frequency 
> components of the physical layer signal, both in wires (twisted pair, 
> coax, etc) and in RF.   The RF bandwidth of 802.11b DSSS modulation 
> was about 10 MHz, whereas the bitrate achieved was about 2 Mb/sec.  
> Now we use OFDM modulation in 802.11n, with bandwidths of 40 MHz more 
> or less, but bitrates of >> 40 Mb/sec.   (yes, that is mostly because 
> of 64-QAM, which encodes 6 bits on each subcarrier within an OFDM 
> "symbol").
> What causes the 802.11n MAC protocol to achieve whatever bitrate it 
> achieves is incredibly complex.   Interestingly, in many cases the 
> problem is really bad due to "bufferbloat" in the 802.11n device 
> designs and drivers, which causes extreme buildup of latency, which 
> then causes the TCP control loops to be very slow in adapting to new 
> flows sharing the path.

And this refers directly to my original question.

May I put it in very simple words.

In mobile networks (let's include wifi there) a packet is either 
reliably delivered - in unpredictable time.
Or it is unreliably delivered - that is possible in predictable time.

Can we agree upon that?

I still want to write my research proposal. However, I'm tired to get it 
rejected after exactly these two lines.


Detlef Bosau
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The nonsense that passes for knowledge around wireless networking,
even taught by "professors of networking" is appalling.  It's the
blind leading the blind. (D.P. Reed, 2012/12/25)

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