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A Highly Adaptive Distributed Routing
Algorithm for Mobile Wireless Networks
Research Paper
By
V. D. Park and M. S. Corson
Introduction A distributed routing protocol for mobile,
multihop, wireless networks is presented Protocol is a type of “link reversal” algorithms The protocol is highly adaptive, efficient and
scalable Best suited for dense networks
Protocol uses a synchronized physical or logical clock
Temporally Ordered Routing Algorithm (TORA)
Introduction A mobile adhoc network is a collection of
mobile routers Mobility requires fast protocol adaptation for
routing purposes Existing shortest path algorithms and
adaptive shortest path algorithms are not well suited in a dense and highly dynamic environment These algorithm maintain only one path
Routing in Mobile Networks Access Point Configuration
The access point does the routing Everyone node is at one hop distance No routing
Adhoc Network Every node is a router Nodes can be at 1 – N hops
MANET The complete network becomes mobile
Existing Protocols Some Existing algorithms include
Gafini Bertsekas (GB) algorithm Lightweight Mobile Routing (LMR) protocol Destination Sequenced Distance Vector (DSDV) Wireless Routing Protocol (WRP) Dynamic Source Routing (DSR) protocol
All these algorithms have stability problem in dense networks or are limited by discovery of only one path
Efficient Routing in Dense Mobile Networks
Efficient routing in dense networks require Distributed execution Loop free routing Provision of multiple routes Quick route establishment Less communication overhead
Routing optimality is of less significance sine mobility changes the shortest path
TORA Protocol Assumptions
Each node N has a unique identifier (ID) Each link L allows two-way communication A node failure occurs if all links incident to that node are severed Each node is always aware of its neighbors All transmission are broadcasted and transmissions are received in order All nodes have synchronized clocks
Notations Network is modeled as directed acyclic graph
N is a finite set of nodes L is a set of initially undirected links
Each link L maybe assigned one of the following states Undirected Directed from node i to j - upstream Directed from node j to i - downstream
),( LNG
Foundation and Basic Structure Creating routes
Establishment of a sequence of directed links leading from node to destination
Only initiated when a node with no directed links require a route through query/reply messages
Assigning direction to links in n undirected network or portion Maintaining routes
Reacting to topological changes in a network in a manner such that routes to the destination are established within a finite time
The directed portions returned to a destination oriented DAG Erasing routes
Upon detection of a network partition all links must be undirected to erase invalid routes
Foundation and Basic Structure Protocol uses three distinct control packets
Query (QRY) Creating routes
Update (UPD) Creating and maintaining routes
Clear (CLR) Erasing routes
Algorithm Description At any given time an ordered quintuple is associated
with each node
First value is a time tag set to the time of link failure Second value is a unique originator ID (unique ID of the node
which defined the new reference level) Reference levels can be ordered lexicographically
Third value is a single bit used to divide each of the unique reference levels into two unique sub-level
Fourth value is an integer used to order nodes with respect to a common reference level
last value is the unique ID of the node itself
),,,,( iroidH iiiii
Ni
Algorithm Description Conceptually the quintuple represents the
height of the node with respect to A reference level represented by the first three
values in the quintuple A new reference level is defined each time a node
loses its last downstream link due to a link failure A delta value instrumental in propagation of a
reference level
Route Creation Routes are created using QRY and UPD
packets QRY consists of a destination ID (did) UPD consists of a did and the height of the node
i which is broadcasting the packet H Each node other than destination maintains a
Route-Required (RR) flag which is initially un-set and the time at which last UPD packet was broadcast and the time at which each link became active
Route Creation When QRY is Received If the receiving node has no downstream links and RR is
un-set it re-broadcasts the QRY and sets the RR If the receiving node has no downstream links and its RR
is set it discard the QRY packet If receiving node has atleast one downstream link and its
height is NULL it sets its height and broadcasts a UPD (delta value is incremented)
If the receiving node has atleast one downstream link and its height is non-NULL
It first compares the time last UPD was broadcasted to the time the link over which the QRY packet was received became active
If UPD has been broadcast since the link became active it discards QRY otherwise, broadcasts UPD packet. If a node has the RR flag set when new link is established it broadcasts a QRY packet
Maintaining Routes Performed only for nodes having a height
other than NULL Any neighbor having a NULL height is not used
Maintaining RoutesNode i loses its last
downstream link
Was the linklost due to a
failure?Case 1
Generate newreference level
Case 2Propagate the
highest neighbor’sreference level
Do all the neighbors havethe same reference level?
Is the reflection bit inthat reference set to 1?
Did this node originallydefine that reference level?
Case 3Reflect back a
higher sub level
Case 4Partition detected,
erase invalid routes
Case 5Generate newreference level
YES NO
NO
YES
NOYES
YESNO
Erasing Routes A propagation of CLR packet erases routes
CLR is broadcasted upon the detection of a partition in the network
Performance No comparative simulation results are
available (at the time of writing of the paper)
Complexity comparison with other protocols show that TORA has linear complexity