batman-adv: network coding - add the initial infrastructure code
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/Catwoman
Signed-off-by: Martin Hundebøll <martin@hundeboll.net>
Signed-off-by: Marek Lindner <lindner_marek@yahoo.de>
Signed-off-by: Antonio Quartulli <ordex@autistici.org>
diff --git a/Documentation/ABI/testing/sysfs-class-net-mesh b/Documentation/ABI/testing/sysfs-class-net-mesh
index bc41da6..bdcd8b4 100644
--- a/Documentation/ABI/testing/sysfs-class-net-mesh
+++ b/Documentation/ABI/testing/sysfs-class-net-mesh
@@ -67,6 +67,14 @@
Defines the penalty which will be applied to an
originator message's tq-field on every hop.
+What: /sys/class/net/<mesh_iface>/mesh/network_coding
+Date: Nov 2012
+Contact: Martin Hundeboll <martin@hundeboll.net>
+Description:
+ Controls whether Network Coding (using some magic
+ to send fewer wifi packets but still the same
+ content) is enabled or not.
+
What: /sys/class/net/<mesh_iface>/mesh/orig_interval
Date: May 2010
Contact: Marek Lindner <lindner_marek@yahoo.de>