cache management of dynamic source routing for fault tolerance in mobile ad hoc networks
TRANSCRIPT
Cache Management of Dynamic Source Routing
for Fault Tolerance in Mobile Ad Hoc Networks
Outline
Review DSR Protocol Simulation Results Conclusions References
Review DSR
Route Cache A packet carries the list of routers in the
path Two main operation
Route Discovery Route Maintenance
No periodic messages
Review DSR
Source Node A
If no route in A’s Cache
Source Node B
Source Node C
Node B or C receives the RREQ packet from A , it check the route from it’s
cache
If the cache have the
route
Node reply the route
information to sender node
Else (the cache have no route about the
RREQ packet)
Add node’s address, and broadcast the RREQ to it’s
neighbors again
Simulation of DSR protocol
The performance is better without using cache. In “Analysis of TCP Performance
over Mobile Ad Hoc Networks” Because DSR has no mechanism to
immediately respond to dynamic network topology change.
Reply from cache introduces more routing error.
Improve DSR Cache
We have a idea from AODV Sending link layer beacons
periodically for get signal strengths. But the idea disobeys the protocol’s
design idea Improve Cache management
Protocol Description
Protocol Overview Signal strength “Confirm” message “Route ok” message “Link broken” message “Host needs recovery” message “Neighbor” message
Protocol Overview
Identify whether a route in the cache is correct or not.
A route marked stale is a route which is likely broken.
Neighbor links’ stability By monitoring the signal strength of
received packets from the neighbor node.
Signal Strength
Signal strength of the received packets
Threshold
“Confirm” and “Route OK”
A B C
BCX(S) CX X
A senses B’s signal strength beyond the threshold and wants to recovery the “stale” route BCX as normal
Node A sends a “confirm” message to node B to ask whether the route BCX can work or not.
B receives A’s “confirm” message
If B has route CX in its cache, then B sends “route ok” message to A with route BCX
If B does not have any match with A’s “confirm” message or the route CX is marked as stale, then B
does not do anything.
“Link Broken”
A B C
BCX CX X(s)
D
If C discards a “stale” route X, then is broadcasts a “link broken” message include node X
Link broken message (X)
Link broken message (X)
B and D receives the “link broken” message, it discard the route and tries to find a route to that destination
If found, then it stop and does nothing further.
If no found, then it broadcasts “link broken” message again
Link broken message (X)
WX
“Host needs recovery” and “Neighbor”
When a node restarts after its failure, it broadcasts “Host needs recovery” message to its neighbors.
When a node receives a “Host needs recovery”, it uses “neighbor” message to show that it is his neighbor now.
Advantages and Disadvantages
Advantage Do not send any periodic information
or signals so that we can keep the advantages of DSR.
Disadvantage We passively wait for packets and
measure their signal strength. A link may be stable but we discard it
since no packets are received form it.
Simulation Environment Network model consists of 30 nodes in
a 1500*300 meter flat rectangular area. Each node picks a random destination
and speed in the area and then travels to he destination in a straight line.
Bandwidth:2Mbps Transmission radius:250m TCP packet size:1460 bytes
Simulation Results of Link Failure
Simulation Results of Link Failure
Simulation Results of Link Failure
Simulation Results of Link Failure
Simulation Results of Host Failure
Simulation Results of Host Failure
Simulation Results of Host Failure
Simulation Results of Host Failure
Conclusions The simulations showed that we have
improved the performance of reply from the cache in DSR significantly, which is almost equivalent to that of no cache reply mechanism.
For future work we suggest that when designing a routing protocol for ad hoc networks, it is important to consider the host failures as well as the link failures.
References
G. Holland and N. Vaidya, “Analysis of TCP Performance over Mobile Ad Hoc Networks” in Proceedings of IEEE Mobicom’99, Seattle, WA, Auguest1999, pp.219~230