[Olsr-dev] Seeking comments: OLSR+ETX v/s DSR+ETX

Sudheendra Murthy (spam-protected)
Wed Dec 12 21:02:19 CET 2007

Hi all,

This is more of a design question. I was wondering how OLSR with ETX
extension compares up to DSR with ETX extension.

For a detailed description of DSR+ETX, please refer to SrcRR: A High
Throughput Routing Protocol for 802.11 Mesh Networks

In brief, DSR+ETX uses periodic probe packets to maintain link quality
of neighbors. When source wants to discover a route, it broadcasts a
(modified) RREQ route request packet. Upon receiving the RREQ for the
first time, a node appends the link quality of the link on which the
packet was received and rebroadcasts it. Subsequent RREQ packets seen
by an intermediate node are forwarded only if the accumulated route
metric is better than the best metric it has forwarded so far. The
destination node upon receiving route request replies along the
accumulated route in the packet. When a SrcRR node forwards a
source-routed data packet, it updates its entry in the source route to
contain the latest ETX metric for the link on which it received the
packet. This allows the source and destination to maintain up-to-date
link caches, and discover when a route's quality has declined enough
that an alternate route would be better.

Further, the SrcRR paper introduces some minor improvements to DSR+ETX
 to resist triggering of route changes upon transient packet losses,
MAC rate control based on ETX values, route dampening and a few more.
Most of these optimizations can be incorporated into OLSR+ETX protocol

It is clear that OLSR+ETX has additional overhead of sending TC
messages when compared with DSR+ETX. Does this overhead provide
significant benefits? I am interested in knowing the pros and cons of
the OLSR+ETX and DSR+ETX protocols.

- Sudhi.

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