[OLSR-users] Regular data broadcasting in ad hoc networks

lolo (spam-protected)
Sat Dec 18 17:20:39 CET 2004

Hi Sven-Ola

Sven-Ola Tuecke wrote:

>long answers may be found in RFC 922 (google for rfc-922). The relevant 
>statement is: <cite>The primary rule for avoiding loops is "never broadcast 
>a datagram on the hardware network it was received on"</cite>.
Ok that is where comes from the rule adopted for simple data broadcast.

> Because every 
>routing protocol (such as OLSR) only configure the underlying network 
>layers, the RFC 922 rules are still valid.
As i said before it's a bit weird since every Ad Hoc Routing Protocols 
this basic rule every time in order to flood their control packets like 
TC or
RREQ messages through the network. What differentiate the broadcasting
of those routing protocols packets from other regular data packets is that
routers scrutiny them before transmitting them again on the same interface
they came from, whereas regular data packets are simply discarded.

>Moreover: ETH/Wlan-bridged devices may have broadcasting loops, if you 
>connect them with an ethernet cable. A broadcast packet will loop through 
>WLAN->eth->eth->WLAN->WLAN->eth->eth etc. until the TTL is used up. TTL is 
>ususally above 30.
As Andreas suggested, in a wireless environment, a local service should
intercept those regular data broadcast packet in order to choose between
following the RFC-922 rule of thumb (discard them) or giving them a
second chance (forward them)

For what I understand, in wireless networks, nowadays, the RFC-922 rule
way is is still choosen because there is no other practical solution



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