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: "Govind Krishnamurthi" <[email-masked]>
Date: Mon, 25 Mar 2002 17:11:58 -0500

James,

>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.
[Govind] Well this information can be kept as part of the MN's profile. But 
I am sure there are other ways to do it. As I explained in the previous 
mail, I don't see why the MN's forgetting to power on a interface card or 
forget inserting is such a big deal. Again, I am not
advocating that this is the way to do it. All I am saying is that
we shouldn't say that this isn't possible at this stage when we are just
considering requirements.

>
>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?

[Govind] Ofcourse, the MN will do the waking, but the AR can help it wake up 
selectively as opposed to the MN periodically waking up as you seem to 
suggest  as the only way to go.

>
>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.

[Govind] Maybe, but that is quite out of scope for the current discussion. 
The point is whether the network can help or not. I believe
that it can.

>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.

[Govind]Frankly, I don't know about this i.e., if it is a part of the spec..

But theoretically at least it should be possible to operate in the same 
frequency. Even if the spreading codes are the same. Yes, this will cause 
packet collisions but CSMA/CA can handle it is it not? All we have
to make sure is we backoff properly and make sure that the MN receives 
beacons. My previous discussions however were under the assumptions
that multiple APs of WLANs are found.

>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.

[Govind] I agree that we should keep the actual solution simple.
But in the process we shouldn't compromise on getting to the best solution.

Regards,
Govind.

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