ITIS 6010/8010 Wireless Network Security Dr. Weichao Wang

2 AODV (Ad hoc On-demand Distance Vector) –On-demand protocol: routes are established when needed, nodes not on active paths do not have to maintain any information, routes will expire if not used –Using hello messages to discover local topology (why DSDV does not need this) –Routes have lifetime –Using sequence numbers to prevent loop –Still a table driven protocol

3 Three kinds of packets: –Route request (RREQ) –Route reply (RREP) –Route error (RERR) Path discovery –Every node has two value: sequence number and broadcast id –Broadcast RREQ:

4 The pair uniquely identifies the RREQ. Broad_s will be incremented every time a RREQ is sent. Processing of RREQ –Remembers reverse path to s: s, seq_s, hop count, previous node, route lifetime –If it has an active route, will reply with RREP –Otherwise, rebroadcast RREQ and increase hop by 1 Expanding ring search for destination

5 Sending a RREP –The RREP must have a fresher sequence number of destination –The RREP is unicast back to the source: –How can the intermediate nodes figure out hops to destination? –The nodes along the path can setup forward routes to the destination –The fresher route is preferred over short route

6 Routing entry contains –Destination, next hop, hop count, seq_d, lifetime of the path, neighbors have used this route Link failure response –RERR is sent back with incremented sequence number and infinity hop count –All active routes using this next hop will get a copy of this RERR and the information will be propagated –New RREQ or local repair can be adopted Does AODV support multiple paths b/w a source and a destination?

7

8 DSR (Dynamic Source Routing) –An on-demand routing protocol –Nodes gather topology information by overhearing network traffic –Achieves much less control traffic compared to DSDV (attention here) –Source routing is used in every data packet –Achieve loop-free –Support unidirectional routes

9 Route discovery –A node may discover and cache multiple routes to a destination –Route request packet: –The neighbor will If knows a route to d: send back a reply with the full route Otherwise, add its own node id and broadcast again –The node IDs show the accumulated path from the source and can be used to send route reply

10 Route cache by overhearing –May get multiple routes to the same destination –Accelerate route discovery –Cut unnecessary intermediate nodes Ensuring packet delivery –Active acknowledgement –Passive acknowledgement Preventing route reply storms Route error discovery and propagation –Attach the broken link in new RREQ to prevent it from being reused

11 Advantages and disadvantages –Simple routing protocol with low overhead –High latency in finding routes –Not scalable

12

13 Zone Routing Protocol (ZRP) –Reactive and proactive protocol each has advantages and disadvantages –Can we combine them? –For nearby nodes, use proactive approach; for faraway nodes, use reactive approach –ZRP has a flat view of the network. It is not a hierarchical protocol

14 Concept of zone –Every node has its own zone with a radius of r hops –Zones of different nodes will overlap –Peripheral nodes and interior nodes Routing: –Within the zone, use proactive (intrazone) –Outside of the zone, use reactive (interzone) –Each can be a family of routing protocols

15 Discovery of local topology –Hello beacons to detect active neighbors –Zone notification messages to determine nodes in zone Intrazone routing

16 Interzone routing –Instead of broadcast, the RREQ is sent to peripheral nodes through bordercast Can be achieved through multicast or multiple unicast If the peripheral node knows the route, sends back a reply (source routing or previous hop of the peripheral nodes) Otherwise, bordercast again –Sharply reduce overhead compared to broadcast

17 The size of a zone –If r = 1, it goes back to pure reactive –If r = ∞, it goes back to proactive Route maintenance –When a link breaks, the node can find an alternative route based on its zone knowledge Overhead control –Since zones overlap, a node may receive the same RREQ multiple times –How to guarantee the RREQ only propagate to outer areas?

18 Overhead control –Query detection If a node has forwarded or overheard a RREQ, it does not transfer in the reverse direction –Early termination If a node knows that the target of bordercast already gets the RREQ, it discards the packet –Random delay of bordercast