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

[Bernard Aboba <aboba@internaut.com>]

> 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 cellular protocols, there
> is extensive negotiation between the mobile node and base station prior to a
> handover. 802.16e also has this characteristic. An indication of "Link Going
> Down" on such a protocol would mean that negotiation has begun for handover
> and, at some short time in the future (perhaps indeterminate), packets will
> no longer be accepted for transmission.
>
> For 802.11, "Link Going Down" is
> meaningless because handover is completely controlled by the mobile node,
> and the link continues to accept packets until the AP scan interrupts packet
> transmission (and even there, I've seen some NICs that interrupt for AP scan
> then send a few packets out prior to the reassociation).

Agreed.