[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...
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"
Let's go make home routers and wifi faster! With better software!
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