Dynamic Source Routing in ad hoc wireless networks

Transcription

1 Dynamic Source Routing in ad hoc wireless networks David B. Johnson David A. Maltz Computer Science Department Carnegie Mellon University In Mobile Computing, vol. 353, chapter 5, T. Imielinski and H. Korth(ed.), Kluwer Academic Publishers,

2 Outline Introduction Assumptions Basic Operation Route Discovery Route Maintenance Optimizations Performance Evaluation Conclusion 2

3 Introduction (1/3) Ad hoc network A collection of mobile hosts with wireless network interfaces may form a temporary network Without the aid of any established infrastructure or centralized administration 3

4 Introduction (2/2) Dynamic Source Routing The sender of a packet determines the complete sequence of nodes through which to forward the packet The sender explicitly lists this route in the packet s header DSR offers a number of advantages Uses no periodic routing advertisement messages Network bandwidth overhead Battery power 4

5 Assumptions Each host should be willing to forward packets for other hosts The diameter of the ad hoc network may be greater than one Hosts move at any time without notice, but the speed with which hosts move is moderate Hosts can enable a promiscuous receive mode on their wireless network interface hardware 5

6 Basic Operation The sender constructs a source route in the packet s header Each host in the ad hoc network maintains a route cache When a host sends a packet to another host A route is found Use this route to transmit the packet No route is found Use the route discovery The route should fail The correct operation of a route in use we call route maintenance 6

7 Basic Operation Route Discovery (1/3) A host initiating a route discovery Broadcasts a route request packet Each route request packet contains Route record Initiator address Request id If the route discovery is successful The Initiating host receives a route reply packet 7

8 Basic Operation Route Discovery (2/3) When any host receives a route request packet, it processes the request according to the following steps: If <initiator address, request id> is found in this host Discard the route request packet If this host s address is already listed in the route record Discard the route request packet If the target of the request matches this host s address Return a copy of this route in a route reply packet to the initiator Otherwise, append this host s address to the route record, and re-broadcast the request 8

9 Basic Operation Route Discovery (3/3) N1-N2-N5-N8 N1 N1 N1 N3 N2 N1-N2-N5-N8 N1-N2 N1-N3 N4 N5 N1-N3-N4 N1-N2-N5-N8 N1-N3-N4 N7 N1-N3-N4 N6 N1-N2-N5 N8 9

10 Basic Operation Route Maintenance (1/2) Conventional routing protocols integrate route discovery with route maintenance by continuously sending periodic routing updates There are no periodic message of any kind from any of the mobile hosts It monitors the operation of the route and inform the sender of any routing errors The host sends a route error packet to the original sender 10

11 Basic Operation Route Maintenance (2/2) route error N2 route error N5 N8 N1 N4 N7 N3 N6 11

12 Optimizations Full Use of the Route Cache (1/2) A host can add entries to its route cache any time it learns a new route A host may use its route cache to avoid propagating a route request packet received from another host 12

13 Optimizations Full Use of the Route Cache (2/2) There are two problems can occur Collision Delay for a period of d d = H x ( h 1 + r ) h : the length of network hops for the route to be returned r : a random number between 0 and 1 H : a small constant delay to be introduced per hop (4 msec) Loop The host instead discards the request if the route in its reply would contain a loop 13

14 Optimizations Reflecting Shorter Routes While two hosts are communicating with each other using cached routes it is desirable for the hosts to begin using shorter routes if the hosts move sufficiently closer together Network interfaces operate in promiscuous receive mode Use an unsolicited route reply packet It has not yet added this method to simulator 14

15 Optimizations Improved Handling of Errors Use promiscuous receive mode 15

16 Performance Evaluation (1/3) The Simulation The area in which the host move is square, 9 meters on a side Each host moves with a velocity between 0.3 ~ 0.7 meters / s Each transceiver has a range of 3 meters Packet lengths 70% of the packets are long packets (1000 bytes) The remainder are short packets (32 bytes) Transmissions to a host that is out of range always fail while transmissions to a host in range fail with a probability of 5% The bandwidth for transmitting data is 100 Kbytes / s 16

17 Performance Evaluation (2/3) 17

18 Performance Evaluation (3/3) 18

19 Conclusion This paper has presented a protocol for routing packets between wireless mobile hosts in an ad hoc network. Future work Security 19