Subject: [pilc] RE: Link-layer Triggers Protocol draft

From: Ali Mohammed-MALI1 <[email-masked]>
Date: Tue, 2 Jul 2002 18:16:10 -0500

Hi Alper,

>The generator of the L2 trigger cannot assess whether this is interesting
>or not. It's up-to the consumer of the trigger to assess this. You are
>right,
>not all L2 events result in a L3 event. But this is not up-to the servers
>to decide...

The only information that the clients get as part of the triggers is the l2 address of the "other end". How can they use this information to make sure it is an L3 event?. The host would probably need some mapping(l2-l3) or protocol to find out if this is a l3 event.

>In either case, L2 address is the address of the "other end" of the link.
>For example, if trigger is received by the access router, the "other end"
>of the link is "access device" of the wireless client.

I understand the client aspect, how about the server?. How is it supposed to know it is servicing a host client or access router client?. This would entail that we have a version of host server and access router server since the servers need to provide different information in the trigger data.

Mohammed 

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From: "Alper E. YEGIN" <[email-masked]>
Date: Tue, 2 Jul 2002 18:42:10 -0700

Hello Mohammed,

> The only information that the clients get as part of the triggers is the l2 address of the "other end". How can they use this information to make sure it is an L3 event?. The host would probably ne…

For example, upon receiving a link-up, a mobile node can send
a router solicitation and receive a router advertisement. Whether
this change in link-connectivity warrants a change in network-layer
connectivity depends on the content of the received router advertisement.
IP stack of the mobile node needs to make this decision. The link-up
trigger was used as a "hint" by the IP stack of the mobile node.

Or, in the case of fast Mobile IPv6 handovers, if mobile node receives
link-up for an access point that it was anticipating to handover to (i.e.,
there is some state already), then it can conclude that it moved there
and continue the FMIPv6 exchange by sending an unsolicited
neighbor advertisement.

So, you are right, no single L2 event warrants a L3 event on its own.
This information is used along with some other action/information.

> I understand the client aspect, how about the server?. How is it supposed to know it is servicing a host client or access router client?. This would entail that we have a version of host server and…

It's not different, really. A L2-triggers server always provides the L2 address
of the remote end point when a link goes up or down. That means, the mobile
host will learn the L2 address of the access point (i.e., the remote end of mobile
host's wireless link), and the access router will learn the L2 address of the
access device of the mobile node (i.e., the remote end of the access point's
wireless link) when the wireless link goes down. 

                        ~~~~~..    ..~~~~~ 
                     \|/                  \|/ 
          link        | MAC1           MAC2|       link  
+------+  down   +----+---+            +---+----+  down   +--------+ 
|      | <------ | access |            | access | ------> |        | 
| host +---------+ device |            | point  +---------+ access | 
|      |         |(bridge)|            |(bridge)|         | router | 
+------+         +--------+            +--------+         +--------+ 

In this above scenario, host will be notified about MAC2,
as this is the remote end point's L2 address from access
device's perspective. Access router will be notified about MAC1, 
as this is the remote end point's L2 address from 
access point's perspective.

alper