Unicast Routing in obile d oc etworks Routing problem 1 2 Responsibility of a routing protocol etermining an optimal way to find optimal routes etermining a feasible path to a destination based on a certain criterion iscovering, storing, and exchanging routing information athering information about a path break and updating the information accordingly Why traditional routing is not suitable for obile d hoc etworks (Ts)? 3 4 (1) Periodic updates in Wired etwork is unnecessary in wireless ad hoc networks Periodic route advertisement as in V may be unnecessary ould conserve battery power when little or no movement. Put in sleep mode whenever possible. how routing table of, and 5 6 1
Traditional network has few links (2) Traditional network has small number of paths 7 8 Wireless channel is inherently broadcast any links many path ost of the paths are redundant Redundant paths increase unnecessary routing updates 17 nodes 17 entries in the routing table of each node (although all are within 1 one hop) (3) obile environment in Wireless ad hoc networks demands new link characteristics 9 10 ost mobility is a new phenomenon ig challenge link failure/repair due to mobility may have different characteristics than those due to other causes n conventional routing Routers occasionally goes down and up ost may change due to congestion ut routers in wired network never move rate of link failure/repair may be high when nodes move fast (4) n wired networks, usually there exists symmetric environment 11 12 2
ully ymmetric nvironment all nodes have identical capabilities and responsibilities symmetric apabilities transmission ranges and radios may differ battery life at different nodes may differ processing capacity may be different at different nodes (5) ew performance metrics for wireless ad hoc networks are needed 13 14 ew performance criteria may be needed route stability despite mobility energy consumption esirable characteristics of routing protocol in T 15 16 esirable characteristics of routing protocol in T istributed vs entralized algorithm inimum ontrol Overhead onsumes W, resources, power inimal processing overhead eavy-weight protocols a big O istributed protocol ast responsiveness to topology changes ocalized reaction to topology changes oop avoidance calability 17 18 3
ast Responsiveness to Topology changes ast Responsiveness to Topology changes 19 20 ocalized reaction to topology changes ocalized reaction to topology changes 21 22 calability hould be invariant with network size. looding-based routing protocols nonscalable lobalized reaction to topology changes non-scalable eader contains complete route info nonscalable Overview of Unicast Routing Protocols 23 24 4
Possible approaches looding warm ntelligence Routing table based looding for ata elivery ender broadcasts data packet P to all its neighbors ach node receiving P forwards P to its neighbors equence numbers used to avoid the possibility of forwarding the same packet more than once Packet P reaches destination provided that is reachable from sender ode does not forward the packet 25 26 looding for ata elivery looding for ata elivery roadcast transmission Represents a node that has received packet P Represents that connected nodes are within each other s transmission range 27 Represents a node that receives packet P for the first time Represents transmission of packet P 28 looding for ata elivery looding for ata elivery ode receives packet P from two neighbors: potential for collision ode receives packet P from and, but does not forward it again, because node has already forwarded packet P once 29 30 5
looding for ata elivery looding for ata elivery odes and both broadcast packet P to node ince nodes and are hidden from each other, their transmissions may collide => Packet P may not be delivered to node at all, despite the use of flooding 31 ode does not forward packet P, because node is the intended destination of packet P 32 looding for ata elivery looding for ata elivery looding completed odes unreachable from do not receive packet P (e.g., node ) odes for which all paths from go through the destination also do not receive packet P (example: node ) (difference with flooding for broadcast and flooding unicast 33 looding may deliver packets to too many nodes (in the worst case, all nodes reachable from sender may receive the packet) 34 looding for ata elivery: dvantages looding for ata elivery: dvantages implicity lmost memory-less Potentially higher possibility of data delivery ecause packets may be delivered to the destination on multiple paths 35 ay be more efficient than other protocols when rate of information transmission is low enough that the overhead of explicit route discovery/maintenance incurred by other protocols is relatively higher this scenario may occur, for instance, when nodes transmit small data packets relatively infrequently, and many topology changes occur between consecutive packet transmissions 36 6
looding for ata elivery: isadvantages Potentially, very high overhead ata packets may be delivered to too many nodes who do not need to receive them Potentially lower reliability of data delivery looding uses broadcasting -- hard to implement reliable broadcast delivery without significantly increasing overhead roadcasting in 802.11 is unreliable looding for ata elivery: isadvantages n our example, nodes and may transmit to node simultaneously, resulting in loss of the packet in this case, destination would not receive the packet at all 37 38 looding of ontrol Packets Possible approaches any protocols perform (potentially limited) flooding of control packets, instead of data packets The control packets are used to discover routes iscovered routes are subsequently used to send data packet (s) Overhead of control packet flooding is amortized over data packets transmitted between consecutive control packet floods 39 looding warm ntelligence Routing table based 40 nt colony based routing The emergent collective intelligence of groups of simple agents onabeau et al. 1999 Why are ants interesting? ants solve complex tasks by simple local means single ants are dumb ant colonies are intelligent ants are grand masters in search and exploitation 41 42 7
ood search behavior nt colony in action nts do search for food by walking randomly ifferent from human approach uman beings are more organized ow can an ant, upon discovering food, find its way back to the nest? ven if an ant makes it back to the nest, how can it inform the other ants about the food's location? 43 44 nt colony in action nt colony in action 45 46 nt colony in action nt colony in action 47 48 8
Rough dea Possible approaches looding warm ntelligence Routing table based 49 50 Routing table based Protocols any protocols have been proposed ome have been invented specifically for T Others are adapted from previously proposed protocols for wired networks o single protocol works well in all environments some attempts made to develop adaptive protocols Types of routing in T lat Proactive Routing Table driven: estination-equenced istance Vector (V), WRP) Routing ink state ish-ye Routing, R, OR. On-emand or Reactive Routing d hoc On-demand istance Vector (OV) Routing ynamic ource Routing (R) Routing ybrid chemes one Routing RP, RP (proactive near, reactive long distance) afari (reactive near, proactive long distance) eographical Routing 51 52 Proactive routing in T Reactive routing in T Proactive: maintain routing information regardless of need for communication Update messages sent throughout the network periodically or when network topology changes. ow latency, suitable for real-time traffic andwidth might get wasted due to periodic updates They maintain O() state per node, = #nodes Reactive: discover route only when you need it aves energy and bandwidth during inactivity ignificant delay might occur as a result of route discovery ood for light loads, collapse in large loads 53 54 9
Trade-off atency of route discovery Proactive protocols may have lower latency since routes are maintained at all times Reactive protocols may have higher latency because a route from X to will be found only when X attempts to send to Overhead of route discovery/maintenance Reactive protocols may have lower overhead since routes are determined only if needed Proactive protocols can (but not necessarily) result in higher overhead due to continuous route updating Which approach achieves a better trade-off depends on the traffic and mobility patterns 55 10