1. Mobile and Wireless Computing Institute for Computer Science, University of Freiburg Western Australian Interactive Virtual Environments Centre (IVEC) Lecture 3 : The Dynamic Source Routing Protocol  Lecture 3.1 : An Overview of the DSR Protocol.  Lecture 3.2 : Routing Details and Performance of the DSR Protocol

2. Mobile and Wireless Computing Institute for Computer Science, University of Freiburg Western Australian Interactive Virtual Environments Centre (IVEC) Dynamic Source Routing (DSR) Protocol  The DSR is a simple and efficient protocol for routing in mobile, ad hoc and wireless networks.  DSR is suitable for routing in multi-hop networks.  A mobile, ad hoc network is completely self- organizing while using the DSR protocol. All nodes cooperate to forward packets.

3. Mobile and Wireless Computing Institute for Computer Science, University of Freiburg Western Australian Interactive Virtual Environments Centre (IVEC) The DSR Protocol (I)  Nodes in the network may move about, join or leave.  All routing is automatically determined by the protocol.  The number and sequence of intermediate hops needed to reach any destination may change dynamically. Hence the network topology may be quite complex.

4. Mobile and Wireless Computing Institute for Computer Science, University of Freiburg Western Australian Interactive Virtual Environments Centre (IVEC) The DSR Protocol (II)  DSR is an on-demand or reactive routing protocol.  When a source node S wants to send a message to a destination node D, the process starts with a route discovery phase.  The message is sent once a route has been discovered and S knows about the discovered route.

5. Mobile and Wireless Computing Institute for Computer Science, University of Freiburg Western Australian Interactive Virtual Environments Centre (IVEC) The DSR Protocol (III)  However, DSR extensively takes advantage of existing knowledge of the network topology.  Each node gathers information about the network topology by overhearing other nodes’ transmissions.  This is known as promiscuous mode of operation and most wireless cards support this (IEEE 802.11 standard).

6. Mobile and Wireless Computing Institute for Computer Science, University of Freiburg Western Australian Interactive Virtual Environments Centre (IVEC) The DSR Protocol (IV)  Each node maintains a route cache to remember routes that it has learnt about.  One of the main advantages of DSR as opposed to a table driven protocol like DSDV is that the number of control messages is much smaller.  Hence DSR is more energy-efficient and does not congest the network with too many control messages.

7. Mobile and Wireless Computing Institute for Computer Science, University of Freiburg Western Australian Interactive Virtual Environments Centre (IVEC) An Example when a Route is Discovered Completely B D A A AB C ABC E ABCD  A is trying to find a route to E  Each intermediate node appends its ID at the end.  E knows the reverse route and sends a route reply.

8. Mobile and Wireless Computing Institute for Computer Science, University of Freiburg Western Australian Interactive Virtual Environments Centre (IVEC) An Example when a Route is Discovered Partially A A B AB C D E  A is trying to find a route to E  C already has a route to E in its route cache.  C sends back the complete route to A.

9. Mobile and Wireless Computing Institute for Computer Science, University of Freiburg Western Australian Interactive Virtual Environments Centre (IVEC) Assumptions  All nodes wishing to communicate with other nodes in the ad hoc network participate fully in running the DSR protocol.  The diameter of the network is more than 1, but usually a small number.  In other words, a message usually goes through only a small number of hops.

10. Mobile and Wireless Computing Institute for Computer Science, University of Freiburg Western Australian Interactive Virtual Environments Centre (IVEC) Assumptions  The nodes may move at any time without notice and may even move continuously.  However, we assume that the speed with which the nodes move is moderate with respect to the packet transmission latency or wireless transmission range of the network.  If the nodes move extremely fast, the only possible protocol is flooding.

11. Mobile and Wireless Computing Institute for Computer Science, University of Freiburg Western Australian Interactive Virtual Environments Centre (IVEC) Assumptions  Each node selects a single IP address by which it is known in the network.  This is necessary for assigning a unique ID for each node.  Each node may or may not work in the promiscuous mode. However, most wireless interface cards support this.

12. Mobile and Wireless Computing Institute for Computer Science, University of Freiburg Western Australian Interactive Virtual Environments Centre (IVEC) Overview and Important Properties  The DSR protocol has two important mechanisms through which the protocol operates. – Route Discovery : A node S wishing to send a packet to node D obtains a route to D – Route Maintenance : When S is using a discovered route to D, S may detect that the route is broken. In such cases, S may use an alternate route to D (if it is known), or start another route discovery phase to D.

13. Mobile and Wireless Computing Institute for Computer Science, University of Freiburg Western Australian Interactive Virtual Environments Centre (IVEC) Overview of the DSR Protocol  Route discovery and route maintenance operate entirely on-demand.  There is no need to broadcast periodically to update routing information in individual nodes. DSDV requires such periodic broadcasts.  The number of overhead packets is much smaller in DSR. The number of overhead packets drop to zero when the nodes are static and all routes have been discovered.

14. Mobile and Wireless Computing Institute for Computer Science, University of Freiburg Western Australian Interactive Virtual Environments Centre (IVEC) Overview of the DSR Protocol  When nodes are mobile and/or communication pattern changes, the number of overhead packets increase proportionately.  It is necessary to discover new routes in these situations and hence the new route discovery packets are the overhead packets.  Note that, a node may receive multiple routes to a destination in response to a route discovery request.

15. Mobile and Wireless Computing Institute for Computer Science, University of Freiburg Western Australian Interactive Virtual Environments Centre (IVEC) Overview of the DSR Protocol  A node may store multiple routes to a destination in its route cache.  A node can react to changes in network topology much more rapidly by taking advantage of cached routes.  For example, if one route to a destination is broken, the source node can choose another route to the destination from its route cache.

16. Mobile and Wireless Computing Institute for Computer Science, University of Freiburg Western Australian Interactive Virtual Environments Centre (IVEC) DSR Route Discovery  Consider the case when a source node S wants to send a packet to a destination node D.  In a ‘good situation’, S already knows a route to D from its route cache.  In this case, S will add the sequence of hops to D in the header of the packet. Then S will send the packet to the first node in this sequence.

17. Mobile and Wireless Computing Institute for Computer Science, University of Freiburg Western Australian Interactive Virtual Environments Centre (IVEC) DSR Route Discovery  In the ‘bad case’ S will not find any route to D in its route cache.  S will initiate the route discovery protocol. In this case, we call S the initiator and D the target of this protocol.

18. Mobile and Wireless Computing Institute for Computer Science, University of Freiburg Western Australian Interactive Virtual Environments Centre (IVEC) DSR Route Discovery  Node S is trying to discover a route to node D.  S broadcasts a route request message to its neighbours. This message is received by all nodes within the transmission range of S.  Each route request message contains the initiator and target of the route discovery.  Also, each route request is stamped with a unique ID assigned by the initiator.

19. Mobile and Wireless Computing Institute for Computer Science, University of Freiburg Western Australian Interactive Virtual Environments Centre (IVEC) An Example Route Discovery A B C D A AB ABC E ABCD

20. Mobile and Wireless Computing Institute for Computer Science, University of Freiburg Western Australian Interactive Virtual Environments Centre (IVEC) DSR Route Discovery  Every node that receives a route request message, does one of the following : – A node like B first searches its route cache to see whether it has a stored route to D. If it has such a route, B sends that route to S. – If there is no such route in its route cache, B broadcasts the route request message to its neighbours. B attaches its own ID to the route request message