[e2e] Why Buffering?
detlef.bosau at web.de
Sun Jun 21 02:33:50 PDT 2009
David P. Reed wrote:
> Dave - This is variously known as Little's Theorem or Little's Lemma.
> The general pattern is true for many stochastic arrival processes
> into queues. It precedes Kleinrock, and belongs to queueing theory.
Little's Theorem can be easily applied in wired networks where a link's
capacity is easily expressed as "latency throghput product", often
referred to as "latency bandwidth product" which is in fact a bit sloppy.
The situation becomes a bit more complicated in wireless networks,
particularly WWAN, where the preconditions for Little's Theorem may not
hold, particularly the service time may not be stationary or stable.
I sometimes wonder about papers who claim quite impressive "latency
bandwidth products" for wireless networks - and actually the authors
simply miss the fact that the transportation system is highly occupied
by local retransmissions and that we have a relationship between average
service, average throughput and the average amount of data being in flight.
I even remember a paper which claims latency bandwidth products for GPRS
in the range of MBytes IIRC.
At a first glance, I wondered where this huge amount of data would fit
onto the air interface ;-)
So, we should be extremely careful in applying Little's Theorem on WWAN.
As a consequence, we should even reconsider approaches like packet pair,
packet train and the like and whether they really hold in WWAN or
similar networks with highly volatile line conditions.
Detlef Bosau Galileistraße 30 70565 Stuttgart
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