Subject: RE: [manet] AODV : receiving and forwarding route replies

From: [email-masked]
Date: Tue, 5 Oct 2004 08:21:33 +0200

Hi,

The destination sequence number of station D is only updated when :
- the station D itself sends a RREQ
- a route to the D is broken. In that case, the node whose link to the D is
broken increments the destination sequence number of D. Later, this node
sends AODV messages with updated sequence number for destination D.

In the example below, the sequence number of S4 is never updated. It is the
reason why S3 never propagates the RREP message corresponding to the RREQ
originated at S1.

Anyhow, it is the way I have understood RFC 3561. If I am wrong, I would
like somebody to tell me what is not correct in my understanding.

	Raphaël

-----Message d'origine-----
De : Yann -EADS- [mailto:[email-masked]]
Envoyé : lundi 4 octobre 2004 18:02
À : [email-masked]
Objet : RE: [manet] AODV : receiving and forwarding route replies

Hello,

I guess that the forward route is actually updated upon receiving the RREP. 
In my mind, the sequence number received by S2 is greater than the one which

created its route to S4. And if this route is updated, it fowards the RREP 
to S1.

Am I wrong ?

>From: [email-masked]
>To: [email-masked]
>Subject: [manet] AODV : receiving and forwarding route replies
>Date: Mon, 4 Oct 2004 17:18:18 +0200
>
>Hi all,
>
>As it is described in RFC 3561, AODV incorrectly handles RREP forwarding
>when route reply by intermediate nodes is not activated.
>Let's consider the following network :
>
>S1 --- S2 --- S3 --- S4
>
>First, S2 establishes a route to S4.
>Then S1 wants to do the same thing. If intermediate node reply is not
>activated, the route research reaches S4, that sends a RREP back to S1.
>Nevertheless, in section 6.7 of RFC 3561 a node forwards a RREP only if a
>forward route (to the destination) has been updated (or created). As this 
>is
>not the case here, the RREP is not forwarded and the route to S4 is never
>established on S1.
>
>Any comment ?
>
>	Raphaël
>
>
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>manet mailing list
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---

From: "John Mullen" <[email-masked]>
Date: Tue, 5 Oct 2004 12:05:59 -0600

Hi Raphael,

>From Section 2 on p. 3,

   As long as the endpoints of a communication connection have valid
   routes to each other, AODV does not play any role.  When a route to a
   new destination is needed, the node broadcasts a RREQ to find a route
   to the destination.  A route can be determined when the RREQ reaches
   either the destination itself, or an intermediate node with a 'fresh
   enough' route to the destination.  A 'fresh enough' route is a valid
   route entry for the destination whose associated sequence number is
   at least as great as that contained in the RREQ.

>From the last line, if the route is fresh enough, S2 sends a RREP back
to S1.  If not, when the RREQ propagation continues to S4, the
destination sequence number will be higher (otherwise the route is fresh
enough).  From p. 12, one of the cases in which a node increments its
sequence number is:

   -  Immediately before a destination node originates a RREP in
      response to a RREQ, it MUST update its own sequence number to the
      maximum of its current sequence number and the destination
      sequence number in the RREQ packet.

So, if the route is not "fresh enough," the destination will increment
its own sequence number.  (Otherwise it won't see the RREQ).  This means
that by the time you get to Section 6.7, either the RREP is simply
confirming the known route, in which case S2 need not reply to S1
because it already did so earlier, or it is indicating some sort of
better route from S2 to S4, in which case S2 will forward the RREP to S1
to correct its earlier misinformation.  

At least, that is how I understand it.

John Mullen

-----Original Message-----
From: [email-masked] [mailto:[email-masked]] On Behalf
Of [email-masked]
Sent: Monday, October 04, 2004 11:22 PM
To: [email-masked]; [email-masked]
Subject: RE: [manet] AODV : receiving and forwarding route replies

Hi,

The destination sequence number of station D is only updated when :
- the station D itself sends a RREQ
- a route to the D is broken. In that case, the node whose link to the D
is broken increments the destination sequence number of D. Later, this
node sends AODV messages with updated sequence number for destination D.

In the example below, the sequence number of S4 is never updated. It is
the reason why S3 never propagates the RREP message corresponding to the
RREQ originated at S1.

	Raphaël

-----Message d'origine-----
De : Yann -EADS- [mailto:[email-masked]]
Envoyé : lundi 4 octobre 2004 18:02
À : [email-masked]
Objet : RE: [manet] AODV : receiving and forwarding route replies

Hello,

I guess that the forward route is actually updated upon receiving the
RREP. 
In my mind, the sequence number received by S2 is greater than the one
which

created its route to S4. And if this route is updated, it fowards the
RREP 
to S1.

Am I wrong ?

>As it is described in RFC 3561, AODV incorrectly handles RREP 
>forwarding when route reply by intermediate nodes is not activated. 

>Nevertheless, in section 6.7 of RFC 3561 a node forwards a RREP only if

>a forward route (to the destination) has been updated (or created). As 
>this is not the case here, the RREP is not forwarded and the route to 
>S4 is never established on S1.
>
>Any comment ?
>
>	Raphaël
>
>