A Highly Adaptive Distributed Routing Algorithm for Mobile Wireless Networks

1. A Highly Adaptive Distributed Routing Algorithm for Mobile Wireless Networks Research Paper By V. D. Park and M. S. Corson

2. 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)

3. 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

4. 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

5. Routing in Mobile Networks AP N1 N3 N2 N1 N3 N4 N5 N2

6. Routing in Mobile Networks AP N1 N3 N2 N1 N3 N4 N5 N2

7. 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

8. 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

9. 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

10. 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

11. Foundation and Basic Structure • Protocol uses three distinct control packets • Query (QRY) • Creating routes • Update (UPD) • Creating and maintaining routes • Clear (CLR) • Erasing routes

12. 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

13. 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

14. 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

15. 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

16. Route Creation

17. Maintaining Routes • Performed only for nodes having a height other than NULL • Any neighbor having a NULL height is not used

18. Maintaining Routes

19. Maintaining Routes

20. Maintaining Routes

21. Erasing Routes • A propagation of CLR packet erases routes • CLR is broadcasted upon the detection of a partition in the network

22. Erasing Routes

23. 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

24. Complexity Comparison

25. Conclusion • A highly adaptive distributed routing algorithm is proposed • Suited for operation in mobile wireless networks • Maintains loop free multipath routing to destinations for which routing is required • Transmits three type of control messages for creation, updation and deletion of routes