Repository : ssh://git@open-mesh.org/doc
On branches: backup-redmine/2017-07-13,master
commit ce06183b19a7c4db1df9f21b200ff65273555014 Author: Antonio Quartulli a@unstable.cc Date: Fri Feb 10 01:36:07 2012 +0000
doc: batman-adv/DistributedArpTable
ce06183b19a7c4db1df9f21b200ff65273555014 batman-adv/DistributedArpTable.textile | 19 +++++++++++++++++-- 1 file changed, 17 insertions(+), 2 deletions(-)
diff --git a/batman-adv/DistributedArpTable.textile b/batman-adv/DistributedArpTable.textile index d857f344..44b38302 100644 --- a/batman-adv/DistributedArpTable.textile +++ b/batman-adv/DistributedArpTable.textile @@ -1,5 +1,20 @@ h1. Distributed ARP Table
-TODO +D.A.T. (Distributed ARP Table) is a feature aimed to solve the unreliability problem of the ARP mechanism +which uses a simple broadcast flooding technique in order to retrieve the the data in the network.
-this page will contain all the details related to the implementation of DAT, how it works and why it improves the performance of the network. \ No newline at end of file +h2. The Problem + +In each and every subnet the ARP protocol is extremely important: it gives the hosts the possibility to send IP datagram to each other +by retrieving their MAC-layer address. The first step in an ARP dialogue is to issue a broadcast ARP request containing the IP address of the +desidered node which will flood the whole subnet. Once the node using such IP receives the packet, a unicast ARP Reply is sent back +in order to communicate its own MAC-layer address and so becoming reachable for the node that issued the request. + +The mechanism is pretty simple and works well until the probability of losing packets in the network is low enough. For this reason Ethernet or +wireless-infrastructured LANcan use such protocol as is without getting in troubles. Unluckily it is not possible to state the same for a wireless +mesh network, where the probability of losing a packet increase with the number of links the packet has to traverse. In particular, this probability +gets higher if the packet to send is of type broadcast (this is due to the MAC layer limitations which do not provide ARQ mechanism for this packet type) +like the ARP Request. Assuming to be in a fairly sparse wireless mesh network, an ARP Request could get lost several times before being able to find +its destination, thus dramatically increasing the latency of establishing an IP connection. + +h2. How DAT \ No newline at end of file