Subject: Re: assymmetric links

From: Sanket S Nesargi <[email-masked]>
Date: Mon, 17 Apr 2000 15:10:40 -0500 (CDT)

Hi,

The assumption of symmetric links is not limited to AODV, few other
protocols also make this assumption (eg., TORA). A solution to this
problem has been addressed in the paper by Prakash presented
at DIALM last year. The approach proposed here works on each node
maintaining a list nodes which it can reach directly, as well as the nodes
from which it can be reached directly. This information is propagated in
the routing messages. The topology information is maintained as a matrix
and unidirectional links are easily identified. This enables nodes to make
use of the unidirectional links correctly. However a N * N matrix needs
to be maintained and exchanged, where N is the number of nodes in the
system. When the system size is large, the overhead can be
significant. This needs to be reduced.

Currently, we are working on an approach based on tunneling link layer
ACKs and routing updates in a strongly connected ad hoc network,
containing unidirectional links. Tunneling is done by encapsulating the 
link layer packets and routing updates in IP packets and using standard
routing for them (based on paths established by the routing protocol 
,neglecting the presence of unidirectional links). This
allows the node at the head of the unidirectional link to make use of
it. This should enable routing protocols that assume symmetric links, to
work across unidirectional links effectively. This work is nearing
completion, and I shall be posting a write up of it in the next couple of
weeks.

Thanks,
- Sanket

Sanket Nesargi
University of Texas at Dallas
Richardson, TX 75080