[Olsr-users] General question about ad hoc routing

[Robert Keyes]

On Wed, 8 Sep 2010, ZioPRoTo (Saverio Proto) wrote:

>> For example, the MPR of A in this scenario is B, then it will be the next
>> hop in OLSR internal routing table but in kernel routing table we just know
>> that we have to send this message for the interface X.
>
> this is not correct.
>
> from the routing table you know the IP address of your next hop, not
> just the interface to send the packet out.
>
> you then use the ARP protocol to discover the Mac address of the next
> hop, and you will send a 802.11 frame that is unicast for your next
> hop and will be discarded from other station that overhear the frame
> from the radio channel.

This is of course true. But, in the original question was the idea that 
packets are broadcast. This is true in the radio [level 0 and level 
1] sense, but not in the Ethernet [level 2] sense. OLSR uses just 
unicast, but there have been attempts to make use of packets which are 
'accidently overheard'. I designed such a system eight years ago. I can't 
find the document on it now, so I can't share it with you. A few years 
later, Sanjit Biswas proposed his 
ExOR routing protocol which is similar in some ways. Because of widely 
varying latencies across the network, this protocol isn't very useful in 
modern, 'low latency' networks. However it can be useful in a 'batch' type 
of delivery system, such as that used for email or UseNet news.

I'd describe it more, but I don't want to post too much that is off the 
OLSR topic!