0/3/ COMP 635: WIRELESS & MOILE COMMUNICTIONS Routing in d-hoc Networks Jasleen Kaur Fall 0 Infrastructure-less Wireless Networks Standard Mobile IP needs an infrastructure Ø Home gent/foreign gent in the fixed network Ø NS, routing etc. are not designed for mobility Sometimes there is no infrastructure! Ø Remote areas, ad-hoc meetings, disaster areas Ø Cost and time may be arguments against infrastructure! Main issue: routing Ø No default router available Ø Every node should be able to forward C
0/3/ Solution: Wireless d-hoc Networks Network without infrastructure Ø Use components of participants for networking Examples Ø Single-hop: ll partners max. one hop apart luetooth piconet, Ps in a room, gaming devices Ø Multi-hop: Cover larger distances, circumvent obstacles luetooth scatternet, police network, car-to-car networks MNET: Mobile d-hoc Networks 3 MNET: Mobile d-hoc Networking Mobile Router Mobile evices Fixed Network Manet Mobile IP, HCP Router End system Focus: Routing in d-hoc Networks
0/3/ Outline Routing in wired networks Ø istance vector routing, link-state routing Limitations in wireless networks d-hoc routing protocols: Ø SR, OV, 5 Unicast Routing in Wired Networks Given: Ø Graph: where nodes are routers and edges are links Ø Cost: associated with each link Find: Ø Lowest-cost path between any two nodes Reuirements: Ø Self-healing, traffic-sensitive, scalable Ø ynamic and distributed algorithms Two classes: distance-vector and link-state 6 3
0/3/ istance Vector Routing: asics asics: Ø Each node: Constructs a vector of distances to all other nodes istance vector istributes to immediate neighbors Ø Neighbors: Use the distributed information to update their own distance vectors This distributed exchange-update-exchange should lead to globally consistent distance vectors (and routing tables) istance Table ata Structure Each node has its own table with a Ø Row for each possible destination Ø Column for each directly-attached adjacent node (neighbor) E 8 C Each table entry gives cost to reach destination that adjacent node Ø istance = Cost E () Cost to estination 5 (,) = distance from to as first hop = c(,) + min w { (,w)} w = {neighbors of } C 6 8 9 5 8
0/3/ istance Table & Routing Table istance Table Routing Table 8 E C E () 8 5 5 E (),, 5 C 6 9 C,, The distance table gives the routing table Ø Just take the minimum cost per destination djacent Node to Use, Cost 9 istance Vector ynamic Routing Iterative, asynchronous: each local iteration caused by: Ø Local link cost change, or Ø Message from adjacent node that its least cost path to some destination has changed istributed: Ø Each node notifies adjacent nodes only when its least cost path to some destination changes Ø djacent nodes then notify their adjacent nodes if this update changes a least cost path Each node: wait for change in local link cost or message from adjacent node recompute distance table if least cost path to any destination has changed, notify adjacent nodes 0 5
0/3/ istance Vector Example Cost Cost Cost 8 3 (,) = c(,) + min w { (,w)} = + = 8 Cost (,) = c(,) + min w { (,w)} = + = 3 Time istance Vector Example Cost Cost Cost Cost 8 3 Cost 8 9 Cost Cost Cost Cost 3 9 Time 6
0/3/ Link Cost Changes When a node detects a local link cost change: The nodes updates its distance table If the least cost path changes, the node notifies its neighbors 50 How long does convergence take? Good news travels fast 6 6 6 3 50 5 50 5 50 50 c(,) changes t 0 t t lgorithm t 3 terminates 3 Link Cost Changes Good news travels fast, but ad news travels slow The count to infinity problem Routing Loop! oes it Terminate? 60 50 6 60 6 60 6 60 8 60 8 50 5 50 5 50 50 50 9 c(,) changes t 0 t t t 3 lgorithm t continues on
0/3/ Link State Routing pproach Each node: Ø Floods the latest state (cost) of each attached link to all other nodes in the network Ensures that flooding is reliable Ø Computes shortest-cost paths to every other node Using jikstra s algorithm Can suffer from route oscillations if cost is a function of load Link State: Ø Floods the state of neighbor links to everyone else Ø Everyone uses same graph to compute routes istance Vector: Ø Shares distance to everyone else with neighbors Ø Nodes build routes based on info sent by neighbors CN THESE E PPLIE TO WIRELESS -HOC NETWORKS? 8 8
0/3/ Wireless Networks: What s ifferent? Varying channel uality and dynamic conditions Ø Separation (and merging) of networks Ø symmetric links Ø Shortest hop may be worst choice Ø Redundant links routes need to converge uickly N 6 N N 6 N N N N 3 N N N 3 N N 5 N N 5 time = t time = t good link weak link 9 Wireless Networks: What s ifferent? Varying channel uality and dynamic conditions Ø Separation (and merging) of networks Ø symmetric links Ø Shortest hop often worst choice Ø Routes need to converge uickly Scarce transmission capacity Ø Overhead conspicuous; No freuent periodic updates Low compute power Ø No extensive route computations Low energy Ø Low control message overhead Ø Low control message freuency (to realize sleep mode) nd if that s not bad enough, add node mobility 0 9
0/3/ Routing in Wireless Mobile Networks Imagine hundreds of hosts moving Ø Routing algorithm needs to cope with varying wireless channel and node mobility Ø Routes may break, and reconnect later Where s RE guy Metrics for Routing? Minimal: Ø Number of nodes Ø Loss rate Ø elay Ø Congestion Ø Interference Ø Overhead Ø Maximal: Ø Stability of the logical network Ø attery run-time Ø Time of connectivity Ø 0
0/3/ HOW TO O ROUTING IN -HOC NETWORKS? 3 Routing Protocols Proactive protocols Ø etermine routes independent of traffic pattern Ø e.g., traditional link-state and distance-vector routing Reactive protocols Ø Maintain routes only if needed Hybrid protocols Ø Maintain routes to nearby nodes Ø iscover routes for far away nodes
0/3/ Trade-Off Latency of route discovery Ø Ø Proactive protocols may have lower latency Reactive protocols higher because a route discovery from to will be initiated only when attempts to send to Overhead of route discovery/maintenance Ø Reactive protocols may have lower overhead since routes are determined only if needed Ø Proactive protocols do continuous route updates / maintenance Which approach achieves a better trade-off depends on the traffic and mobility patterns 5