From mboxrd@z Thu Jan 1 00:00:00 1970 Content-Type: text/plain; charset="iso-8859-1" Date: Thu, 07 Aug 2008 11:45:18 +0200 From: "Elektra Elektra" In-Reply-To: <200808061520.59927.axel@open-mesh.net> Message-ID: <20080807094518.56620@gmx.net> MIME-Version: 1.0 References: <7itzdzzero.fsf@lanthane.pps.jussieu.fr> <200808061520.59927.axel@open-mesh.net> Subject: Re: [B.A.T.M.A.N.] Re: A few comments on the BATMAN routing protocol Content-Transfer-Encoding: quoted-printable Reply-To: The list for a Better Approach To Mobile Ad-hoc Networking List-Id: The list for a Better Approach To Mobile Ad-hoc Networking List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: The list for a Better Approach To Mobile Ad-hoc Networking , Juliusz.Chroboczek@pps.jussieu.fr Cc: b.a.t.m.a.n@open-mesh.net, elektra@open-mesh.net, siwu@hrz.tu-chemnitz.de, olsr-users@lists.olsr.org, babel-users@lists.alioth.debian.org, lindner_marek@yahoo.de, roman@steinerweb.at Hello Juliusz! Axel and Simon are right, in the situation you have described the protocol= wouldn't loop. It is a broken route. > > S crashes, and A switches to B as its next hop for S. At this point, > > B is still using A as its next hop, so we have a temporary routing loop. If S crashes A and B are not going to change their routing tables anymore -= since S doesn't send any OGMs anymore which could trigger a change in the = routing tables of A and B. So A and B stay put until the garbage collector = purges the broken route. The assumption that A switches to B is false.=20 The reason why I believe that Batman is loop free is, that routes are updat= ed upon receiving OGMs from the best ranking next hop. The best ranking nex= t hop knows the best route better than me, because its likelihood of receiv= ing OGMs is greater than the local likelihood. If a locally received OGM - = received via the best ranking neighbor - triggers an update it is granted t= hat the best ranking next hop is already informed - naturally,,, So the cha= in of potential forwarders is loop free until the destination.=20 This is particularly so because the current implementations are sequence nu= mber based, rather than using timers. This is granting that temporary loops= can't occur - which could happen if timers could occasionally trigger purg= es that are not synced. =20 This is consistent with the test results of Batman-Experimental at Meraka i= n a physical 49-node grid. I did some inital tests there on the 4 longest p= ossible routes in the grid (from each corner to each opposite corner, from = each center of side to center of opposite side) at -30 dBm transmit power, = -30dbm receive attenuation. 4 simultaneous traffic streams were saturating = the capacity of these routes, all colliding in the center of the grid. Link= s were very weak, with high packet loss to single hop neighbors even when t= he whole network was idle. So a round trip from corner to corner often took= 12 - 15 hops.=20 Under no circumstances did the protocol loop. Also we did run a long series= of tests with Batman-EXP and OLSR with ETX and Fisheye enabled, that David= Johnson had previously used to compare mesh routing protocols, like AODV, = DART, OLSR-RFC, OLSR with ETX . http://wirelessafrica.meraka.org.za/wiki/images/9/98/Batman_ifip.pdf cu elektra --=20 Psssst! Schon das coole Video vom GMX MultiMessenger gesehen? Der Eine f=FCr Alle: http://www.gmx.net/de/go/messenger03