Subject: Re: ZRP and Parallel Packet Flooding

From: Bora Akyol <[email-masked]>
Date: Mon, 01 Dec 1997 09:41:05 -0500

Zygmunt Haas wrote:
> 
> Hi Bora,
> 
> I think that I understand your question in the case of "directional"
> transmissions. I am not sure about the case of "hidden terminal" nodes;
> i.e., I am not sure how hidden terminals present a problem for the flood
> termination process - you may want to explain this a bit more.
> 
> So, my answer here concentrates on the effect of "directional" transmission
> only. First let me state that I believe that one of the salient advantages
> that the wireless communication environment offers is the *broadcasting*
> feature. By taking advantage of this feature (such is the case in ZRP's
> eavesdropping) does simplify the algorithms and *saves bandwidth*. Thus,
> my claim would be that one should not use directional transmission in this
> environment at least not for the control traffic (i.e., route discovery
> process). Note, that this does not mean that you cannot use directional
> transmission for the actual data transmission (but you may need to have
> two antennas or a more complex antenna design).
> 

Zygmunt

I understand the benefits of the broadcast nature of radio channels,
however as Chip Elliot pointed out on spread spectrum systems
broadcast mode transmission may not be possible at all, Metricom's
system being an example.

About the hidden terminal problem:

There may be two nodes A & B that can act as a gateway between
C & D. However, nodes A & B can not hear each other's transmissions
to the environment in between. Hence there is excess routing queries due
to the hidden nature of the transmission. 

Overall, given the diverse nature of radio technologies and propagation
environments, I believe a protocol that does not rely on
broadcast and that does NOT waste radio resources as well as power
is more desirable. I believe that ZRP can be modified to function in
such a manner and be as reliable using some sort of border node
concept.

I hope this explains the hidden terminal problem somewhat more.

Regards

Bora