• Martin Hundebøll's avatar
    batman-adv: network coding - add the initial infrastructure code · d353d8d4
    Martin Hundebøll authored
    Network coding exploits the 802.11 shared medium to allow multiple
    packets to be sent in a single transmission. In brief, a relay can XOR
    two packets, and send the coded packet to two destinations. The
    receivers can decode one of the original packets by XOR'ing the coded
    packet with the other original packet. This will lead to increased
    throughput in topologies where two packets cross one relay.
    
    In a simple topology with three nodes, it takes four transmissions
    without network coding to get one packet from Node A to Node B and one
    from Node B to Node A:
    
     1.  Node A  ---- p1 --->  Node R                Node B
     2.  Node A                Node R  <--- p2 ----  Node B
     3.  Node A  <--- p2 ----  Node R                Node B
     4.  Node A                Node R  ---- p1 --->  Node B
    
    With network coding, the relay only needs one transmission, which saves
    us one slot of valuable airtime:
    
     1.  Node A  ---- p1 --->  Node R                Node B
     2.  Node A                Node R  <--- p2 ----  Node B
     3.  Node A  <- p1 x p2 -  Node R  - p1 x p2 ->  Node B
    
    The same principle holds for a topology including five nodes. Here the
    packets from Node A and Node B are overheard by Node C and Node D,
    respectively. This allows Node R to send a network coded packet to save
    one transmission:
    
       Node A                  Node B
    
        |     \              /    |
        |      p1          p2     |
        |       \          /      |
        p1       > Node R <       p2
        |                         |
        |         /      \        |
        |    p1 x p2    p1 x p2   |
        v       /          \      v
               /            \
       Node C <              > Node D
    
    More information is available on the open-mesh.org wiki[1].
    
    This patch adds the initial code to support network coding in
    batman-adv. It sets up a worker thread to do house keeping and adds a
    sysfs file to enable/disable network coding. The feature is disabled by
    default, as it requires a wifi-driver with working promiscuous mode, and
    also because it adds a small delay at each hop.
    
    [1] http://www.open-mesh.org/projects/batman-adv/wiki/CatwomanSigned-off-by: default avatarMartin Hundebøll <martin@hundeboll.net>
    Signed-off-by: default avatarMarek Lindner <lindner_marek@yahoo.de>
    Signed-off-by: default avatarAntonio Quartulli <ordex@autistici.org>
    d353d8d4
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