16-05-2014, 02:05 PM
PROJECT REPORT ON Distributed Cache Update for a Dynamic Source Routing Protocol
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ABSTRACT
On-demand routing protocols use route caches to make routing decisions. Due to
mobility,cached routes easily become stale. To address the cache staleness issue,
prior work in DSR used heuristics with ad hoc parameters to predict the lifetime of a link
or a route.
The goal of our project is to proactively disseminating the broken link information to the
nodes that have that link in their caches. We define a new cache structure called a cache
table and present a distributed cache update algorithm. Each node maintains in its cache
table the information necessary for cache updates. When a link failure is detected, the
algorithm notifies all reachable nodes that have cached the link in a distributed manner.
We show that the algorithm outperforms DSR with path caches and with Link-MaxLife,
an adaptive timeout mechanism for link caches. We conclude that proactive cache
updating is key to the adaptation of on-demand routing protocols to mobility.
Introduction
Aim the Project
Routing protocols for ad hoc networks can be classified into two major types: proactive
and on-demand. Proactive protocols attempt to maintain up-to-date routing information to
all nodes by periodically disseminating topology updates throughout the network. In
contrast, on demand protocols attempt to discover a route only when a route is needed.
To reduce the overhead and the latency of initiating a route discovery for each packet, on-
demand routing protocols use route Caches. Due to mobility, cached routes easily
become stale. Using stale routes causes packet losses, and increases latency and
overhead. In this paper, we investigate how to make on-demand routing Protocols adapt
quickly to topology changes. This problem is important because such protocols use route
caches to make routing decisions; it is challenging because topology changes are
frequent.
To address the cache staleness issue in DSR (the Dynamic Source Routing protocol)
priorwork used adaptive timeout mechanisms. Such mechanisms use heuristics with ad
hoc parameters to predict the lifetime of a link or a route. However, a predetermined
choice of ad hoc parameters for certain scenarios may not work well for others, and
scenarios in the real world are different from those used in simulations. Moreover,
heuristics cannot accurately estimate timeouts because topology changes are
unpredictable. As a result, either valid routes will be removed or stale routes will be kept
in caches.
Existing System
TCP performance degrades significantly in Mobile Ad hoc Networks due to the packet
losses. Most of these packet losses result from the Route failures due to network mobility.
TCP assumes such losses occur because of congestion, thus invokes congestion control
mechanisms such as decreasing congestion windows, raising timeout, etc, thus greatly
reduce TCP throughput.
However, after a link failure is detected, several packets will be dropped from the
network interface queue; TCP will time out because of these packet losses, as well as for
Acknowledgement losses caused by route failures.
There is no intimation information regarding about to the failure links to the Node from
its neighboring Node’s. So that the Source Node cannot able to make the Route
Decision’s at the time of data transfer.
Proposed System
Prior work in DSR used heuristics with ad hoc parameters to predict the lifetime of a
linkor a route. However, heuristics cannot accurately estimate timeouts because topology
changes are unpredictable.
Prior researches have proposed to provide link failure feedback to TCP so that TCP can
avoid responding to route failures as if congestion had occurred.
We propose proactively disseminating the broken link information to the nodes that have
that link in their caches. We define a new cache structure called a cache table and present
a distributed cache update algorithm. Each node maintains in its cache table the
Information necessary for cache updates.
The Source Node has the information regarding about the Destination and the
Intermediate Node links failure, So that it is useful from Packet loss and reduce the
latency time while data transfer throughout the Network.