Kyle Fitzpatrick Konstantin Zak Wireless Routing Kyle Fitzpatrick Konstantin Zak

Outline Background Routing problem Protocols Comparisons Conclusion Table driven On-demand driven Comparisons Conclusion References

Background 1970s – Wireless networks first appeared 1980s – First mobile networks Present – Two variations of mobile wireless networks Infrastructured Infrastructureless

Infrastructured Fixed access points Mobile units only communicate with AP Handoff between APs as mobile unit moves Typical applications include office wireless networks

Infrastructureless Ad-hoc network No fixed routers Every node responsible for routing

Ad-hoc Networks Dynamic topology Self organizing High bandwidth Spatial reuse Wireless

Wireless Routing Problem Discover routes between nodes Avoid loops Avoid high power consumption Low bandwidth High error rates Limited memory

Table driven vs. On-demand Maintain routing information for all nodes Broadcasts network changes Creates routes only when needed Recent routes cached

Existing Protocols

Table Driven Protocols

Destination-Sequenced Distance-Vector Routing (DSDV) Based on Bellman-Ford routing mechanism Nodes maintain table for of all possible destinations with number of hops to each Freedom from loops

Bellman-Ford Columns of table represent the directly attached neighbors Rows represent all destinations in the network Contains the path for sending packets to each destination in the network and distance/or time to transmit on that path (we call this "cost"). The measurements in this algorithm are the number of hops, latency, the number of outgoing packets, etc.

Problems with BF Counting to infinity Routing loops

DSDV Solution Tag each route table entry with a sequence number Distinguish stale routes from new ones, thus avoid loops

New Route Broadcasts Destination address Number of hops Sequence number from destination, as originally stamped by destination Unique sequence number for broadcast

Route update Routing table updates transmitted throughout network for consistency To avoid network congestion, two kinds of packets are sent “full dump,” carries all available routing information Smaller packets used to relay routing changes since last dump

Proof of Loop-free Property

Clusterhead Gateway Switch Routing (CGSR) Uses DSDV as underlying routing scheme Instead of “flat” network, CGSR is a clustered multi-hop Cluster head selection algorithm Gateway nodes within communication of two cluster heads

Routing from Node 1 to Node 8

Wireless Routing Protocol (WRP) Each node maintains four tables Distance table Routing table Link-cost table Message retransmission Update messages inform each other of link changes “hello” messages sent periodically

Loop Freedom Communicate the distance and second-to-last hop info for each destination Avoids “count-to-infinity” nodes perform consistency checks of predecessor information from neighbors

On-Demand Protocols

Dynamic Source Routing (DSR) Mobile nodes maintain route caches with complete routes to destinations. Multiple routes per destination allowed Route caches updated continually Two phase protocol: Route discovery Route maintenance

Route Discovery Route request packet Destination address Source node address Unique identification number Route record

Route Request

Route Discovery, cont. Route reply returns route record to initiator Obtain return route from: Route cache Reverse route record Route discovery packet

Route Reply

Route Maintenance Route error packets Acknowledgments Cache entries for lost node removed Other routes truncated at lost node Acknowledgments Active Passive

Signal Stability Routing (SSR) Two cooperative protocols Dynamic Routing Protocol (DRP) Static Routing Protocol (SRP) Routes chosen based on signal strength and location stabilty.

Dynamic Routing Protocol Signal Stability Table (SST) Periodic beacons Signal strength (strong or weak) Routing Table (RT) Stores path to destinations Only route requests from strong channels are processed

Static Routing Protocol Passes packets up stack Forwards packets Initiates route search

Temporally-Ordered Routing Algorithm (TORA) Designed for highly dynamic topologies Provides multiple routes Utilizes a time based height metric Requires synchronized clocks

Ad-hoc On-Demand Distance Vector Routing (AODV) Routes as needed Periodic advertisements optional Scales to large topologies Requires neighbors detect each others’ broadcasts

AODV Goals Broadcast discovery packets only when necessary Distinguish between local connectivity and general topology Only disseminate topology changes to neighbors likely to need it

An AODV Node Two counters Route table Route request expiration timer Node sequence number Broadcast_id Route table Route request expiration timer

Route Table Destination Next hop Number of hops Destination sequence number Active neighbors Route expiration time

Path Discovery Initiated with route request (RREQ) RREQ is broadcasted < source_addr, source_seq_#, broadcast_id, dest_addr, dest_seq_#, hop_cnt > RREQ is broadcasted Nodes either satisfy RREQ or rebroadcast it RREQs are satisfied with a route reply (RREP)

Reverse Path Intermediate nodes store: Destination IP Source IP Broadcast_id Reverse path expiration time Source sequence number

Forward Path Conditionals for route reply Has route? Bi-directional link? >= dest_seq_#? If the above conditions are met then a route reply (RREP) is issued < source_addr, dest_addr, dest_seq_#, hop_cnt, lifetime>

Path Maintenance Link failure detection Periodic “hello” messages Link-layer acknowledgements Nodes issue special RREP with hop_cnt equal to ∞. RREP propagates to all active neighbors

Future Development Multicast Elimination of “hello” messages Intermediate node route rebuilding

AODV Summary Nodes store only needed routes Broadcasts minimized Quick link failure response Loop-free routes Scalable to large topologies

Comparisons

Table-Driven Comparison DSDV inefficient due to requirement of periodic updates, regardless of topology changes CSGR performance improved due to token scheduling, gateway code scheduling, and path reservation “hello” packets WRP don’t allow nodes to sleep

Table-Driven Routing Protocols

Source-Initiated On-Demand Routing Comparison DSR has more overhead then AODV since packets carry full routing information SSR paths tend to be longer lived, hence higher throughput TORA supports multiple routes Unlike AODV and DSR, intermediate routes can’t reply to route requests sent toward destination, causing delays

Source-Initiated On-Demand Routing Protocols

Conclusion Reasons for choosing AODV Small memory requirements Limits power consumption Flexible Scalable

References E.M. Royer, C-K Toh. “A Review of Current Routing Protocols for Ad Hoc Mobile Wireless Networks,” IEEE Personal Com., April 1999, pp. 46-55. C.E. Perkins, E.M. Royer. “Ad Hoc On Demand Distance Vector Routing,” Proceedings of 2nd IEEE Workshop on Mobile Computing Systems and Applications, February 1999. C.E. Perkins, P. Bhagwat. “Highly Dynamic Destination-Sequenced Distance-Vector Routing (DSDV) for Mobile Computers.” Computer Communications Review, October 1994, pp. 234-244. D.B. Johnson, D.A. Maltz, J. Broch. “DSR: The Dynamic Source Routing Protocol for Multi-Hop Wireless Ad Hoc Networks.” Ad Hoc Networking. C.E. Perkins ed., Chapter 5, pp. 139-172. A. Salam. “Mesh Networks.” School of Digital Radio Communications for Research and Training in Developing Countries. Latin American Networking School. February 2004.