Subject: Re: [Seamoby] Re: Regarding CAR Discovery - Sleeping WLAN interface case

From: "Govind Krishnamurthi" <[email-masked]>
Date: Mon, 25 Mar 2002 12:27:40 -0500

James,
[snip]
>
>So the key is "expressed the requirement." What does this mean? Does the
>MN periodically poll the AR for this information, or does it send a
>subscription to receive a notification that then gets passed along as
>part of the MN's context transfer when the MN moves?
>

[Govind] I agree this is an optimization that the network can help
the MN to wake up the interface only when necessary. Clearly power control
is an obvious case and if the AR knows that the MN has two interfaces it
should be enough... Unless the MN indicates that such
a help is not needed (as the case when it is using both interfaces)
the network can generally assume that only one will be turned on.
Also, it needn't wake the MN up for every AR representing the sleeping
interface, it can do  so only for those which the MN is authorized to roam 
in, together with AR being able to satisfy the MN's requirements.
Also, there is more power saving in waking up selectively than in
waking up periodically.

[snip]
>
>I had in mind primarily the latter. If the MN brings up the WLAN
>interface, there is no need for CAR discovery because it just needs to
>Neighbor Discovery (in IPv6). CAR discovery is only of interest if the
>MN wants to find out about other media options prior to bringing up the
>interface.

[Govind] What if it wants to move from one WLAN network to another...
essentially to save cost for eg?, and it has just one interface.
Clearly, CAR discovery is needed for FMIPv6 and context transfer and
they do talk about WLAN -> WLAN handovers.
[snip]
>
>Sure, but the issue is whether the MN periodically polls or there is
>some kind of subscription/notification protocol that gets passed along
>with context transfer. The former is simpler, the latter more bandwidth
>efficient.

[Govind] I don't see any great loss of simplicity in the latter. I do see 
the bandwidth/power/time efficiency in the latter though.

Regards,
Govind.

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From: "James Kempf" <[email-masked]>
Date: Mon, 25 Mar 2002 13:53:35 -0800

> the network can generally assume that only one will be turned on.

I can't see how the AR can know how many interfaces the MN has. On any
particular day, there may be two or only one, or maybe even none if the
user forgot all her interface cards.

> Also, there is more power saving in waking up selectively than in

The AR won't do the waking, the MN will. That is, if the MN is getting
traffic on one interface, it will get the CAR information on that
interface, then the MN will make the decision about whether to power up
the other interface.
How can the AR wake the MN on an interface that doesn't have any power,
much less IP service?

More specifically, the software on the MN will probably ask the user
about whether they want to switch it on, or perhaps some kind of user
agent.

> they do talk about WLAN -> WLAN handovers.

To my knowledge, it is not possible to deploy two different 802.11b
networks in the same area. It would be possible to deploy an 802.11a and
802.11b network because they operate in different frequency ranges, but
I view that as essentially two different media. Not sure about 802.11g.

> the bandwidth/power/time efficiency in the latter though.

Well, the other alternative is that the AR could simply pass the CAR
information along when the MN arrives. No need for the AR to know
anything more than that the MN arrives, i.e. keep it reeeaaal simple.

            jak

---

From: "James Kempf" <[email-masked]>
Date: Mon, 25 Mar 2002 13:53:35 -0800

jak