Project

General

Profile

This page is OUTDATED!

This page was superseded with an update for the feature, documentered here

Multi-link Optimizations

batman-adv is able to work on different interfaces - multiple WiFi interfaces, but also Ethernet interfaces. If two or more nodes are interconnected through batman-adv on multiple interfaces, they may leverage some features to increase throughput, which are explained here.

For more technical information, please see our technical multi-link documentation

Interface alternating

With Interface alternating, batman-adv forwards frames on a different interface than on which the frame was received. The purpose of this alternation is to reduce interference (we can either send or receive on a WiFi interface at one time) and to balance the network load better on the available interfaces, and eventually increases throughput. The mechanism is illustrated below for a chain of nodes with two interfaces.

Interface alternating is only performed if the two candidate links to the next hop have a similar quality. This feature is enabled by default and does not have to be enabled manually.

Interface bonding

When multiple links (with similar transmit quality) are available to the same neighbor, batman-adv may distribute the frames to be sent over these available links. The individual frames are sent over the links in a round robin fashion as illustrated below. Using this technique, the throughput may be increased by the number of links involved in the bonding. In practical tests over two WiFi links, we have seen more than 50% of throughput gain.

However, if the links have different speeds (batman-adv won't detect that), the throughput may even decrease due to the slower link slowing down the whole bonding. Therefore, this feature must be explicitly enabled. One may enable it for certain nodes in a known environment, the same setting does not have to be applied mesh wide.

To enable bonding, use batctl:

batctl bonding enable

Throughput gain

At the WirelessBattleMesh v3 we performed throughput tests to measure the gain of the various modes:

This graph shows a 3 node setup each with 2 802.11abg wifi interfaces connected to the mesh network (1x 2.4GHz and 1x 5.8GHz). As you can see the alternating mode is able to maintain the performance. The old default behavior sometimes manages to maintain a similar level of performance but is rather unstable.

alternation_chain.dia (1.78 KB) Simon Wunderlich, 03/06/2012 08:36 PM

bonding_roundrobin.dia (1.76 KB) Simon Wunderlich, 03/06/2012 08:36 PM

alternation_chain.dia.jpg View (19.6 KB) Simon Wunderlich, 03/06/2012 08:36 PM

bonding_roundrobin.dia.jpg View (15.7 KB) Simon Wunderlich, 03/06/2012 08:36 PM

bonding_2hops.png View (10.2 KB) Marek Lindner, 03/07/2012 08:27 AM