Re: [e2e] Ressource Fairness or Througput Fairness, was Re: Opportunistic Scheduling.

> Let's assume a cellular network.

We more or less anti-assumed that, but I'll try to answer the question anyway.

> Why do we need a scheduler then in the base station?

You probably don't *need* one. But if an error-sensitive scheduler would let you undetectably degrade the quality experienced by a user in a good spot in exchange for enabling a user in a bad spot to "unfairly" (in an air-time sense) get enough quality to keep paying you by the minute for his call, you might *want* one. That's a possible monetary answer; for LANs one might imagine a sense of community supporting the idea of spending a little extra air time to help out somebody temporarily in a bad spot (maybe next to a microwave oven which will shut off soon).

> 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.

You could do that by abandoning transmission of the head-of-line packet after some amount of time (arguing it is "resource fair" to starve the station having trouble to keep the link going).

Or you could fragment packets into link-level frames with different sizes and codings for each station depending on its error environment, and then round-robin sub-packet frames to stations (you'd need to have N head-of-line packets instead of 1, but that should be ok).

> 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.

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An alternative perspective is that if other people have already firmly decided to introduce schedulers at base stations we might want to make suggestions about better schedulers :-)

> 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
> - asynchronous
> - in many cases self clocked
> - end to end traffic ?

I'm not sure I understand the question... in CDMA networks (coming soon to a GSM phone near you!) soft handoff already means there is a level of coordination above the "base station".

> At the moment, I think a ressource fair scheduler at the base station
> would be the best solution to do this.

We hope the paper argues that effort-fair (== "resource fair") is "fair" but undesirable in some situations, that outcome-fair is "fair" but undesirable in other situations, and that a hybrid notion of fairness is both desirable and achievable.

Dave Eckhardt

P.S. There is further material in my dissertation, including a warning about the difficulty of measuring per-station conditions when trying to do scheduling. Received on Wed Jul 18 15:31:32 2007