Repository : ssh://git@open-mesh.org/doc

On branches: batman-adv-doc,master

commit dbc0c083ce4b1a9639ba7b075f49da89df1694bf Author: Marek Lindner lindner_marek@yahoo.de Date: Sat Apr 11 08:12:48 2009 +0800

remove deprecated hop penalty section

dbc0c083ce4b1a9639ba7b075f49da89df1694bf batman_iv.docbook | 47 ----------------------------------------------- 1 file changed, 47 deletions(-)

diff --git a/batman_iv.docbook b/batman_iv.docbook index 4b9afe04..d98f5cbb 100644 --- a/batman_iv.docbook +++ b/batman_iv.docbook @@ -324,53 +324,6 @@ <para> Even in more sophisticated scenarios with more nodes/hops this concept successfully reduces the packets. It ensures that packet only travels paths which did not see this OGM before. </para> -<para> - In certain cases B.A.T.M.A.N. IV is unable to detect the 'real' source of an OGM which may lead to temporary routing loops. The following section is going to illustrate the issue and how the echo cancellation addresses it using an Ethernet network as example for the sake of simplicity. WiFi and other mediums are less susceptible as Ethernet but still affected. -</para> -<para> - Example: The node S (source) has a WiFi connection towards node A but no link to node B at all. Node A and node B are connected via Ethernet. We assume the Ethernet connection to be perfect (no packet loss) whereas the WiFi connection suffers from occasional collisions and interferences. -</para> -<para> - <inlinemediaobject> - <imageobject> <imagedata fileref="images/hop_penalty3.eps" format="EPS" scale="50" /> </imageobject> - <imageobject> <imagedata fileref="images/hop_penalty3.png" format="PNG" /> </imageobject> - <textobject> <phrase>example topology</phrase> </textobject> - </inlinemediaobject> -</para> -<para> - Whenever node A receives a packet via the WiFi connection it will rebroadcast the information on the Ethernet to inform neighbor nodes about the existance of the source node. Node B receives the broadcast and parses the packet before rebroadcasting it. At that point node A will receive that very packet again. -</para> -<para> - <inlinemediaobject> - <imageobject> <imagedata fileref="images/hop_penalty4.eps" format="EPS" scale="50" /> </imageobject> - <imageobject> <imagedata fileref="images/hop_penalty4.png" format="PNG" /> </imageobject> - <textobject> <phrase>packet hops</phrase> </textobject> - </inlinemediaobject> -</para> -<para> - B.A.T.M.A.N. III would have dropped the packet at this point. It has a duplicate packet detection based on sequence numbers only. The sequence number is known, hence the packet dropped (the fastest packet wins). In asymetric environments this may lead to suboptimal routing decisions. Therefore B.A.T.M.A.N. IV interprets the arrival of this packet as second path towards the originator. This path transmits the packet slower (due to more hops for example) but but may offer a better transmit quality. Duplicate sequence numbers are dropped if they arrive via the same neighbor. -</para> -<para> - On a lossy medium the TQ value is decreased while travelling from hop to hop (see asymetric link handling). The Ethernet connection does not suffer from packet loss which results in not decreasing the TQ value at all. Node A has 2 possible routes towards the originator: The node S itself and node B (both will advertise the same TQ value). -</para> -<para> - <inlinemediaobject> - <imageobject> <imagedata fileref="images/hop_penalty5.eps" format="EPS" scale="50" /> </imageobject> - <imageobject> <imagedata fileref="images/hop_penalty5.png" format="PNG" /> </imageobject> - <textobject> <phrase>route candidates</phrase> </textobject> - </inlinemediaobject> -</para> -<para> - As B.A.T.M.A.N. IV values TQ and fastest packet the node A's route will point towards the node S. Once the WiFi link quality drops (for a few moments due to some collisions) the TQ value from the node S will drop. At that point the B.A.T.M.A.N. IV node A will change its route towards node B which offers a better TQ value. Node A and node B will send packets forth and back in a loop. -</para> -<para> - <inlinemediaobject> - <imageobject> <imagedata fileref="images/hop_penalty6.eps" format="EPS" scale="50" /> </imageobject> - <imageobject> <imagedata fileref="images/hop_penalty6.png" format="PNG" /> </imageobject> - <textobject> <phrase>applied hop penalty</phrase> </textobject> - </inlinemediaobject> - -</para> </sect2>

<sect2 id="batman4_tq_hop_penalty">