Re: [DNA] Definition of "Link Up" and "Link Down" events?

[James Kempf <kempf@docomolabs-usa.com>]

Bernard,

> > I interpret "Link Going Down" to mean that the mobile node and base
station
> > have begun some procedure to initiate handover.
>
> It is one thing to have an "idle timeout" feature that will cause a given
> interface to be brought down to due to lack of traffic.  This signal
> presumably is sent from upper layers to the lower layer.  It is another
> thing to have the lower layer predict its future link quality.  Existing
> data shows that link quality can be highly variable so that these
> predictions are not necessarily very accurate.
>

In CDMA, the link quality predictions are very accurate. The host and base
station do closed loop and open loop power control to keep the signal
strength within range so that the signal quality is acceptable. The
standards typically have a minimum power level defined at which the base
station and mobile node initiate handover. After a handover, the power level
for handover is lower to avoid hystersis and ping ponging.

In 802.16 (which is a TDMA protocol), the base station and terminal exchange
link quality information periodically. Also, the terminal can initiate
periodic ranging, in which it starts transmitting at the lowest power and
steps up the power level until it reaches a level at which the signal
quality is optimal to the base station.

I also have heard that 802.11k is supposed to help provide similar
functionality to 802.11, though I have not looked into it.

That said, I think it makes sense to keep the worst case in mind when
designing DNA, and current 802.11 is certainly a candidate for that, as
you've indicated.


            jak