hi koojana
thanks for ur reply and time...
>2. The RFC says: "Once created, the
RREP is unicast to the next hop toward the originator of the RREQ, as
>indicated by the route table entry for that originator. As the RREP is
forwarded back towards the node >>>>which originated the RREQ
message, the Hop Count field is incremented by one at each hop. Thus, when
>>>the RREP reaches the originator, the Hop Count represents the
distance, in hops, of the destination from >the originator." Is the Hop
Count field in the RREP not supposed to contain the number of hops from the
>>>source to the destination, rather than from the destination to the
source ?
Why do you think this way? Anyway, Hop
counts from source to the destination is known while processing the
RREQ.
Section 5.2 of the RFC: the Hop Count field in the RREP is supposed
to contain "The number of hops from the Originator IP Address to the
Destination IP Address.".
Section 6.6 (also quoted above as Point 2): "Thus, when the RREP reaches
the originator, the Hop Count represents the distance, in hops, of the
destination from the originator."
Are these two statements not mutually contradictory ? This is because the
processing of the RREP (as mentioned in Section 6.6 and quoted above) seems to
be such that the Hop Count field of the RREP, when it will finally
reach the Originator, will contain the number of hops from the
Destination to the Originator, and not vice-versa. This is in direct
contradiction with what is specified about the Hop Count field in the
format of the RREP in Section 5.2.
Also, as you rightly said, when a RREQ reaches the node which issues the
RREP (whether the final Destination or an intermediate node), its Hop Count
field contains the number of hops from the Originator to the Destination. This
is precisely the information that the Source (and not the Destination) needs,
so as to enter it in the Hop Count field of its Route Entry for the
particular Destination. However, if the RREP contains the number of hops from
the Destination to the Source (and not vice-versa), the Originator will never
learn of this information. This is why I think that the Hop Count field of the
RREP MUST contain the number of hops from the Originator to the Destination,
and not vice-versa. Please correct me if I am wrong with this.
thanks for ur time
varnit
----- Original Message -----
Sent: Monday, July 12,
2004 1:01 PM
Subject: RE: [manet] RREP
generation in AODV
Hi Varnit,
>This is a query regarding the
RREP generation in AODV, from Section 6.6 of its Internet Draft, >RFC
3561. >1. The RFC says: "When generating a RREP message, a node copies
the Destination IP >>Address and the Originator Sequence Number from
the RREQ message into the corresponding fields >in the RREP message."
>To which field in the RREP
does the Originator Sequence Number from the RREQ go ? There is only
>Destination Sequence Number field in the RREP.
This was discussed in the ML. This
should read Orginator IP address instead of orginator Sequence
number.
>2. The RFC says: "Once created, the
RREP is unicast to the next hop toward the originator of the RREQ, as
>indicated by the route table entry for that originator. As the RREP is
forwarded back towards the node >>>>which originated the RREQ
message, the Hop Count field is incremented by one at each hop. Thus, when
>>>the RREP reaches the originator, the Hop Count represents the
distance, in hops, of the destination from >the originator." Is the Hop
Count field in the RREP not supposed to contain the number of hops from the
>>>source to the destination, rather than from the destination to
the source ?
Why do you think this way? Anyway, Hop
counts from source to the destination is known while processing the
RREQ.
>3. The RREP is supposed to be Route
Reply, ie it is supposed to carry routing information that the source
>can use to send packets to the destibation. However it does not have any
field that tells the source about >such a route or the next-hop it should
choose for a route to the destination. Is it that the source will
>>simply take the node from which it first received the RREP as the
next-hop for a route to the destination >?
When propagating RREQ, each node
creates (source and intermediate) the route towards the source. AODV works
to find a minimum hops path between the S (Source) and D (Destination).
Therefore, D will only process the RREQ with minimum hops in case if it gets
more than one RREQs for an unique discovery. Then D will send RREP over this
minimum hops paths that are found during the route discovery process. When
receiving RREP over minimum hops path, S will create a route towards the D
over this path via next hop. In this way, RREP does not require any other
fields. What you asked is needed for DSR (I guess).
Regards
Koojana
Koojana Kuladinithi BSc, MSc
University of Bremen, FB 1 - IKOM/ComNets
Otto-Hahn-Allee NW 1, 28359 Bremen -
Germany
Tel.: +49 421 218 8264, Fax:
+49 421 218 3601,
Email:
koo at comnets.uni-bremen.de
WWW:
http://www.comnets.uni-bremen.de/~koo