Can somebody please explain me how the broadcasts work in multihop wireless networks. Are the packets unicast forwarded or broadcast forwarded. For e.g. A,B,C,D are four nodes, (A&B) in each other's range & (B,C & D) in the other range. When A broadcasts a packet, how will B forward the packet to C & D ? Unicast forwarding or it too will broadcast? If it will be broadcasted, it creates a broadcast storm, How will that be handled? Thanks in advance.
It depends on the mesh network wireless bridge implimentation. Most early versions were your worst nightmare, where any packet without a destination MAC address is treated like a broadcast and is sprayed all over the network. STP (spanning tree) will eliminate loops, but there's still quite a bit of broadcast (and sometimes multicast) traffic.
Monitoring one local municipal mesh network, all I saw were continuous ARP requests from all over the internet. This is one of the first things that mesh software and firmware has to fix. I don't know how it's done without looking at the code, but my guess(tm) is that they might cheat and insert the destination MAC address in the IP header, thus preventing the broadcast from propogating more than one hop. The routers might also cache ARP requests. Dive into some of the open source mesh networking code and see what (if anything) they do about the problem. (Meraki based) More code:
Thank you sir, I tried to find some info for some protocols: While BATMAN keeps on forwarding the broadcasts "OGMs are send and repeated as UDP broadcasts, therefore OGMs are flooded until every node has received it at least once, or until they got lost due to packet loss of communication links, or until their TTL (time to live) value has expired. " OLSR anyways has its MPR's which take the responsibility of doing so. Though i am still pondering over how the opportunistic protocols handles them. The broadcast information is overheard, so whether the broadcasts should be forwarded or not. I think i should read a little more. Thanks again.
OGM's (Originator Messages) are just one type of broadcast packet. The simply announce that the node is alive and well, which is picked up by neighboring nodes in order to establish a (dynamic) route. Section 5 deals with "Flooding Mechanism" which doesn't mean generating a broadcast storm, but instead has something to do with announcing the arrival of a new node.
If you drop down to Section 8, there is a list of value ranges. Doesn't look like TTL is used to restrict broadcast repropagation. Otherwise, there's nothing in the BATMAN spec that talks about other types of broacasts.
Sorry, I don't have an instant answer. How it handles broadcasts has to be in the code somewhere. However, if you don't find a specific mechanism to limit broadcast retransmission (other than STP to prevent loops), I think it may default to handling broadcasts exactly as in the wired ethernet model, where each packet goes to ALL nodes on the network.
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