> But now I don't see what's to stop a home user from buying a more
> general-purpose router which happens to have a ZigBee port or something,
> and plugging it in such a way that it *should* behave as a stub router.
> How does it discover that and configure itself accordingly?
Disclaimer: I know nothing about ZigBee.
My first reaction is that we'll cross that bridge when we come to it.
My second reaction is that in a properly functioning network, the ordinary
mechanisms of the routing protocol will effectively treat the link as
a stub. If the topology is just
Homenet --- A ........
(ZigBee)
then obviously the ZigBee link will not be used for transit. If the
topology is redundant:
Homenet --- A ------ B
| |
| |
C ...... D
(ZigBee)
then the routing protocol should assign a sufficiently high metric to the
ZigBee link, so that in effect it will be treated as a stub link.
(Disclaimer: the current implementation of Babel doesn't do that yet, it
currently only has a taxonomy of wired/wireless/bridged/BATMAN, I'm quite
willing to implement it if somebody has a suitable device to test on.)
Where you run into trouble is when the Homenet topology is not redundant
enough, and there is a fault on the Homenet side:
Homenet --- A B
| |
| |
C ...... D
(ZigBee)
Here, no matter how high the metric of the ZigBee link, Homenet traffic
from A to B will want to go through it. If A is your NAS and B is your
TV, then an attempt to start a streaming session may bring the ZigBee link
to its knees.
My third reaction is that this should be avoided by proper AQM on the
ZigBee link, but I don't know anything about AQM for ZigBee, so I'll shut
up.
So in summary, the stub functionality is only necessary when (1) the
topology is redundant, (2) the ZigBee link doesn't have adequate AQM, and
(3) the ZigBee link needs to remain functional even when the Homenet gets
otherwise partitioned. While I agree that there are useful use cases for
that (you certainly want your thermostat to keep functioning even when
somebody unplugged the Ethernet from your television), frankly, I'm not
going to loose too much sleep over that.
-- Juliusz
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