[e2e] Why Buffering?

[Detlef Bosau]

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

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