[Make-wifi-fast] half the transmission time?

dpreed at reed.com dpreed at reed.com
Thu Dec 15 08:40:54 EST 2016

The citation for the "fact" in the first paragraph is a theory paper, not a measurement paper.

My experience with theory papers in this space is that they are incredibly sensitive to assumptions, and such assumptions are often wildly wrong compared to the real world of radio, often in the pessimistic direction!

Theorists are terrible at inventing models unless their models are tested by measuring.

Thus, it is important for the measurement community to adopt the attitude of experimental physics... Measure all predicted behaviors, even if you'd like to believe the beautiful theory. This is how the diameter of the proton was discovered to be off in the second significant digit, way off. Yet we are repeatedly told by the theoretical physicists that the Standard Model is accurate to 15 significant digits at minimum.

Theory is great, and I use it a lot, even doing my own theory work. But I also check predictions about engineered systems by measuring. Even such claims as "widely known facts", which, by the way should been challenged by peer review!

Do we know any measurements that challenge this claim? Of course... 

-----Original Message-----
From: "Dave Taht" <dave.taht at gmail.com>
Sent: Wed, Dec 14, 2016 at 6:55 pm
To: make-wifi-fast at lists.bufferbloat.net
Subject: [Make-wifi-fast] half the transmission time?

H/T to Bruno Moraes:

"Over   half   of   the   transmission   time   in   WiFi networks  is
 dedicated  to  ensuring  that  errors  are  corrected  or detected.
 Despite    these    mechanisms,    many    studies    have concluded
  that    frame    error    rates    vary.    An    increased
understanding of why frames are lost is a pragmatic approach to
improving    real    world    802.11    throughput.    The
potential beneficiaries  of  this research,  include  rate  control
algorithms, Modulation  and  Coding  Schemes,  simulation  models,
frame  size selection    and    802.11    configuration    guidelines.
   This    paper presents a measurement study of the factors which
correlate with packet  loss  in  802.11  WiFi.  Both  passive  and
active  approaches were  used  to  investigate  how  the  frame  size,
 modulation  and coding  scheme  and  airtime  effect  the  loss
rate.  Overall,  packet errors  were  high,  but  the  size  of
frames  were  not  a  major determinant  of  the  loss  rate.  The
loss  rate  decreased  with  the airtime  but  at  substantially
lower  rates  than  those  suggested  in simple  packet  error
models.  Future  work  will  further  try  to isolate  and investigate
 specific  errors,  such  as  head  on  collisions in the preamble"

Dave Täht
Let's go make home routers and wifi faster! With better software!
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