batman-adv: improved client announcement mechanism

The client announcement mechanism informs every mesh node in the network
of any connected non-mesh client, in order to find the path towards that
client from any given point in the mesh.

The old implementation was based on the simple idea of appending a data
buffer to each OGM containing all the client MAC addresses the node is
serving. All other nodes can populate their global translation tables
(table which links client MAC addresses to node addresses) using this
MAC address buffer and linking it to the node's address contained in the
OGM. A node that wants to contact a client has to lookup the node the
client is connected to and its address in the global translation table.

It is easy to understand that this implementation suffers from several
issues:
 - big overhead (each and every OGM contains the entire list of
   connected clients)
 - high latencies for client route updates due to long OGM trip time and
   OGM losses

The new implementation addresses these issues by appending client
changes (new client joined or a client left) to the OGM instead of
filling it with all the client addresses each time. In this way nodes
can modify their global tables by means of "updates", thus reducing the
overhead within the OGMs.

To keep the entire network in sync each node maintains a translation
table version number (ttvn) and a translation table checksum. These
values are spread with the OGM to allow all the network participants to
determine whether or not they need to update their translation table
information.

When a translation table lookup is performed in order to send a packet
to a client attached to another node, the destination's ttvn is added to
the payload packet. Forwarding nodes can compare the packet's ttvn with
their destination's ttvn (this node could have a fresher information
than the source) and re-route the packet if necessary. This greatly
reduces the packet loss of clients roaming from one AP to the next.

Signed-off-by: Antonio Quartulli <ordex@autistici.org>
Signed-off-by: Marek Lindner <lindner_marek@yahoo.de>
Signed-off-by: Sven Eckelmann <sven@narfation.org>

1 files changed, 6 insertions, 1 deletions

diff --git a/net/batman-adv/main.h b/net/batman-adv/main.h
index 714a2414d913..6f53a1de778c 100644
--- a/net/batman-adv/main.h
+++ b/net/batman-adv/main.h
@@ -46,11 +46,15 @@
 /* sliding packet range of received originator messages in squence numbers
  * (should be a multiple of our word size) */
 #define TQ_LOCAL_WINDOW_SIZE 64
+#define TT_REQUEST_TIMEOUT 3 /* seconds we have to keep pending tt_req */
+
 #define TQ_GLOBAL_WINDOW_SIZE 5
 #define TQ_LOCAL_BIDRECT_SEND_MINIMUM 1
 #define TQ_LOCAL_BIDRECT_RECV_MINIMUM 1
 #define TQ_TOTAL_BIDRECT_LIMIT 1
 
+#define TT_OGM_APPEND_MAX 3 /* number of OGMs sent with the last tt diff */
+
 #define NO_FLAGS 0
 
 #define NUM_WORDS (TQ_LOCAL_WINDOW_SIZE / WORD_BIT_SIZE)
@@ -96,7 +100,8 @@ enum mesh_state {
 enum dbg_level {
 	DBG_BATMAN = 1 << 0,
 	DBG_ROUTES = 1 << 1, /* route added / changed / deleted */
-	DBG_ALL    = 3
+	DBG_TT	   = 1 << 2, /* translation table operations */
+	DBG_ALL    = 7
 };