Subject: RE:

From: "wooighee" <[email-masked]>
Date: Tue, 21 Nov 2000 16:22:15 +0900

Hello

I have some questions regarding Route Reply Generation by an Intermediate
Node.

Let's imagine the situation where node S (source) tries to find a route to
node D (destination) using destination sequence number [n]. Say there are
four
other participating nodes 1, 2, 3 and 4 through which route lies.

S-->1-->2-->3-->4-->D

After the route is found the source starts transmitting, etc. Suddenly the
connection, say, between 2 and 3 breaks for whatever reason, then RERR
message is sent upstream to notify nodes of broken link. Let's also assume
that route entry for D in nodes from 3 through D did not expire yet.

S-->1-->2-x->3-->4-->D

After S gets RERR message it will try to find another route to D, and as
specification says uses [n+1] as a dest. seq. number to be sure that new
route
is established.

According to the AODV Draft page 10, it is written that:
------------------------------------------------------------
The node generates a RREP (as discussed further in section 8.4) if
   either:

      (i)       it has an active route to the destination, and the
                node's existing destination sequence number is ***greater
                than or equal to the Destination Sequence Number of the
                RREQ ***, or

.............

   When a reverse route is created or updated, the following actions are
   carried out:

    1. the Source Sequence Number from the RREQ is ***copied*** to the
       corresponding destination sequence number;

------------------------------------------------------------

This is the point I do not understand.

Since source sequence number is the sequence number of the SOURCE NODE and
Destination sequence number is the sequence number copied from the source
sequence
number,  there will be *no case* where intermediate node has a cached route
with
destination sequence number which is ***greater than or equal to the
Destination Sequence Number of the RREQ ***.

To make my question short, when is the scenario described in the
draft page 10 where:
--------------------------
The node generates a RREP (as discussed further in section 8.4) if
 either:

it has an active route to the destination, and the
node's existing destination sequence number is ***greater
than or equal to the Destination Sequence Number of the
RREQ ***, or
--------------------------

If anyone has any idea on this, please kindly comment.

Thank you

Regards
Ghee

---

From: "Samir R. Das" <[email-masked]>
Date: Tue, 21 Nov 2000 09:22:13 -0500

Hi,

I believe that I replied earlier to you explaining exactly this point!

In your scenario, you are right in that only the destination will reply to
RREQ and not any intermediate node. However, this does not mean that there
is no situation where an intermediate will reply to a RREQ. An easy example
is this. An intermediate can reply when a source starts a fresh sesssion and
may have a very old destination seq no.

You can also construct more complicated examples if you assume that the
destination seq nos along the nodes on an active route are not identical,
but increasing (could happen if parts of the route change in between). Then
even after a RERR an intermediate node can reply to a following RREQ.

Samir

>-----Original Message-----
>From: [email-masked]
>[mailto:[email-masked]]On Behalf Of wooighee
>Sent: Tuesday, November 21, 2000 2:22 AM
>To: [email-masked]
>Cc: wooighee
>Subject:
>
>
>Hello
>

---

From: Mahesh Marina <[email-masked]>
Date: Tue, 21 Nov 2000 11:07:37 -0500 (EST)

>        corresponding destination sequence number;

Note: in the above -- destination is the source itself and NOT the
destination of the RREQ. 

We are talking about two destinations - 1. dest
for the reverse route which is the source of RREQ; 2. dest for the forward
route which is the intended destination of RREQ.

> Destination Sequence Number of the RREQ ***.

Seems like you are confused with the wording. Sequence number
for one node is NEVER used to update the routing entry of another
node. If such arbitrary use of sequence numbers were done, then it is not
possible to claim the loop freedom!

> To make my question short, when is the scenario described in the

With the above clarification, you should be able to see that intermediate
RREPs are possible.

Regards,
Mahesh