[e2e] Ressource Fairness or Througput Fairness, was Re: Opportunistic Scheduling.
detlef.bosau at web.de
Wed Jul 18 10:15:18 PDT 2007
Dave Eckhardt wrote:
>> Do we talk about ressource fairness?
>> Or do we talk about throughput fairness?
> It is possible to do both, in a balanced way. Some time back
> we did some initial thinking about that.
> D. Eckhardt, P. Steenkiste.
> Effort-limited Fair (ELF) Scheduling for Wireless Networks.
> (erratum: In Section VI, the crossover error rate is 55%, not 50%)
> Dave Eckhardt
I just read your paper and get somewhat lost in the use of
- capacity loss,
It is just an observation of mine, that these terms are somewhat
polymorphic, particularly when they are used by CS and EE people. And I
personaly think, this is a very serious issue as it is often hardly
possible to communicate at all between these disciplines...
Just a very premature observation.
And now for something completely different: Scheduling.
Sometimes, I get the impression they were three kinds of engineers
dealing with networks.
1.: CS / packet switching guys, which basically don´t know about
scheduling in communication networks.
Packets are stored in a FIFO queue and that´s it.
2.: EE/ telco / line swichting guys, which basically can´t imagine
anything else than scheduling,
they have congenital schedulers inside.
3.: Multimedia / DiffServ / IntServ/ QoS guys, who are something in
O.k. I belong to the first category. (And I strongly don´t belong to the
third, even more after having got in touch with multimedia over wireless
So, just for my understanding I raise a perhaps stupid question:
Let´s assume a cellular network. Why do we need a scheduler then in the
base station? (I once asked this an EE guy and got no answer...)
Basically, I see exactly one reason: In networks which require a link
layer recovery mechanism and where the BS-Terminal links suffer from
very different error rates, we need a mechanism which prevents
starvation problems and head of line blocking.
Particularly the link layer recovery may insert traffic which must be
served before any other traffic for flow control reasons: Unacknowledged
data occupies memory at the sender. In addition incomplete L3 packets
occupy memory at the receiver, particularly becaause incomplete packets
cannot be handed to the application. The worst case is that a receiver
cannot receive additional data in order to have packets completed and
cannot pass packets to the application, so there is a dead lock
situation. Therefore, retransmissions are given higher priority then
first / new transmissions.
Is this correct?
Perhaps, I´m a bit nitpicking here. But when I introduce a scheduler at
the base station at all, there must be a convincing reason to do so. And
I only found the aforementioned one...
Back to the cellular network.
So, how do we integrate such a cell with a base station with a scheduler
and a number of terminals into the big picture of
- best effort
- in many cases self clocked
- end to end traffic ?
At the moment, I think a ressource fair scheduler at the base station
would be the best solution to do this.
What do you think?
Detlef Bosau Mail: detlef.bosau at web.de
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