CS 672 Paper Presentation

1. CS 672 Paper Presentation “CarNet: A Scalable Ad Hoc Wireless Network System” Robert Morris, John Jannotti, Frans Kaashoek, Jinyang Li, Douglas Decouto MIT Proceedings of the 9th ACM SIGOPS European Workshop, September 2000 Presented By Saif Iqbal

2. Introduction • CarNet is an application for a large ad hoc mobile network • Radio nodes in cars which communicate using a Grid routing system • Grid uses geographic forwarding and a distributed location service • Applications – Internet, congestion monitoring, fleet tracking • Most of CarNet is speculative • Focus is on scalable ad hoc routing

3. Grid - Key Design Drivers • Main goal: provide dynamisms without sacrificing scalability • Automatic configuration • No reliance on fixed infrastructure • Mobile nodes • Interaction between applications and changing resources • Underlying protocols should provide the APIs and use algorithms to • take advantage of changing network topologies

4. Grid Design & Architecture • MANET idea: network nodes use radio to talk to immediate neighbors, • and reach destinations by forwarding each other’s packets • Assumption: nodes that are physically close are likely to be close in the • network topology – connected by a small number of radio hops • Foundation: geographic forwarding – a source node annotates each • packet with the location of the destination

5. Grid Location Service (GLS) • Need a database that maps each node’s permanent id to its current • geographic location • The location database should be distributed, robust, and efficient • GLS fulfills these requirements • Algorithm • Distributed algorithm f(i): maps each node identifier to a location list • Locations produced by f(i) act as node-i’s location servers • When node-i moves, it uses geographic forwarding to send position • updates to the locations specified by the hash function • Nodes close to these locations remember node-i’s position • When node-j wants to find node-i, it sends queries to locations in f(i) • Nodes close to these locations will know node-i’s location and respond

6. Grid Scalability • Scales well – per-node cost in storage/messages forwarded is • proportional to the log of total number of nodes • Number of Grid protocol packets forwarded/node/sec as function of the total # nodes

7. Grid Scalability Fraction of data packets that are successfully delivered by Grid as a function of the total #nodes

8. Grid Density • Low • Geographic forwarding fails when the network is insufficiently dense • A node which has to forward a packet may not find any neighbor within • its radio range which are closer to the destination • Grid will route around holes using GPSR or other techniques • High • If a network is too dense then radios that lie within the radio range of • each other must share the limited spectrum • As node density increases the available bandwidth to each node • decreases • Use variable power radios to vary transmit power to keep an • approximately constant number of nodes within radio range

9. Applications • Building the CarNet system around Grid • CarNet car will have a node consisting of – embedded Linux computer, • IEEE 802.11 radio, GPS recevier, displays • Resource Location • In ad hoc networks need to locate resources dynamically • Associate a standard name to a resource, which is hashed to obtain an • ID • The resource then participates in the GLS protocol using that ID • When performing a location look up the nodes will get the resource • closest to them

10. Applications • IP Connectivity • IP connectivity to the Internet is an important goal of CarNet • Each Grid node is given an IP address, a subnet mask, and the IP • address of the default router – the Grid-to-Internet gateway • Wireless nodes use a hash of their IP address as their Grid ID • Grid node to Grid node – a simple location query can get the destination • node’s location • Grid node to Internet – determine the location of the gateway and • forward packets to it • Internet to Grid node – packets to the closest gateway to the source • Redundant gateways for better connectivity

11. Applications • CarNet Specific • Location directed multicast to query/advertise services • Traffic congestion monitoring • Over-the-horizon radar detection • Information exchange through voice chat • Marine applications • Privacy • Using GLS any node may locate any other whose ID is well-known • Privacy of user’s location and movements is an issue • Nodes can share a pool of IP addresses – opening connections to a node • will be impossible as its current ID is unknown • Nodes can employ proxies to prevent contacted nodes from learning the • connector node’s location

12. Conclusion • CarNet is a test bed to explore protocols for large ad hoc networks – has • not yet been deployed • Potential new problems and solutions • Number of other ad hoc routing algorithms – DSR, AODV, DSDV – • do not scale as well as Grid • Grid does not use global flooding of queries or topology information • Problem of varying node density requires adaptive algorithms • Creation of new applications suited to geographically aware networks