Chapter: 05-Mobile Computing Mobile Adhoc Networks By: Mr. Abdul Haseeb Khan

Outline Routing Protocol MANETS Definition Ad hoc vs. cellular networks MANETS Applications MANETS Challenges Routing Protocol Expected Properties of Ad-hoc Routing Protocols A taxonomy for routing protocols in Mobile ad common protocols(DSDV, AODV, DSR, ZRP, TORA)

Infrastructure-based wireless networks Typical wireless network: Based on infrastructure E.g., GSM, UMTS, … Base stations connected to a wired backbone network Mobile entities communicate wirelessly to these base stations Traffic between different mobile entities is relayed by base stations and wired backbone Mobility is supported by switching from one base station to another Backbone infrastructure required for administrative tasks IP backbone Further networks Gateways Server Router

Infrastructure-based wireless networks – Limits? What if … No infrastructure is available? – E.g., in disaster areas It is too expensive/inconvenient to set up? – E.g., in remote, large construction sites There is no time to set it up? – E.g., in military operations

Possible applications for infrastructure-free networks Factory floor automation Disaster recovery Car-to-car communication Military networking: Tanks, soldiers, … Finding out empty parking lots in a city, without asking a server Search-and-rescue in an avalanche Personal area networking (watch, glasses, PDA, medical appliance, …) …

Factory floor automation

Disaster recovery

Car-to-car communication

Solution: (Wireless) ad hoc networks Try to construct a network without infrastructure, using networking abilities of the participants This is an ad hoc network – a network constructed “for a special purpose” Simplest example: Laptops in a conference room – a single-hop ad hoc network

Problems/challenges for ad hoc networks Without a central infrastructure, things become much more difficult Problems are due to Lack of central entity for organization available Limited range of wireless communication Mobility of participants Battery-operated entities

No central entity ! self-organization Without a central entity (like a base station), participants must organize themselves into a network (self-organization) Pertains to (among others): Medium access control – no base station can assign transmission resources, must be decided in a distributed fashion Finding a route from one participant to another

Limited range ! multi-hopping ? For many scenarios, communication with peers outside immediate communication range is required Direct communication limited because of distance, obstacles, … Solution: multi-hop network

Mobility ! Suitable, adaptive protocols In many (not all!) ad hoc network applications, participants move around In cellular network: simply hand over to another base station In mobile ad hoc networks (MANET): Mobility changes neighborhood relationship Must be compensated for E.g., routes in the network have to be changed Complicated by scale Large number of such nodes difficult to support

Battery-operated devices ! energy-efficient operation Often (not always!), participants in an ad hoc network draw energy from batteries Desirable: long run time for Individual devices Network as a whole ! Energy-efficient networking protocols E.g., use multi-hop routes with low energy consumption (energy/bit) E.g., take available battery capacity of devices into account How to resolve conflicts between different optimizations?

MANETs characteristics Heterogeneous nodes Do not need backbone infrastructure support Self-creating not rely on a pre-existing fixed infrastructure Self-organizing no predetermined topology Self-administering no central control creating a network “on the fly” Are easy to deploy Useful when infrastructure is absent, destroyed or impractical Infrastructure may not be present in a disaster area or war zone because there is no dependence on infrastructure, the network is robust and low-cost. Finally, MANETs form the basis of all pervasive and ubiquitous computing.

MANETs Applications Military environments Emergency operations Soldiers, tanks, planes Emergency operations Search-and-rescue Policing and fire fighting Civilian environments Taxi cab network Meeting rooms Sports stadiums

Ad hoc networks & Cellular networks Infrastructure less Multiple hop Radio power limitation, channel utilization, and power-saving concerns DCF(distributed coordination function) Cellular networks Infrastructure-based one hop(uplink or downlink) PCF(pointed coordination function)

MANETs Challenges Spectrum allocation Self-configuration Medium access control (MAC) Energy efficiency TCP Performance Mobility management Security & privacy Routing protocols Multicasting QoS Service Location, Provision, Access

Routing in MANET In general, MANET routing protocols are expected to satisfy the following essential principles: Tolerance of unexpected network faults (e.g. device and link failures) Flexibility to increasing traffic loads Minimal energy consumption (especially for smaller clients) Mobile IP needs infrastructure Home Agent/Foreign Agent in the fixed network DNS, routing etc. are not designed for mobility MANET No default router available “every” node also needs to be a router

Properties of good routing protocol in MANET Must be distributed Adaptive to frequent topology changes Must be localized, since global state maintenance involves a huge state propagation control overhead Loop free and free from stale routes Convergence should be quick

Issues in Routing in MANET Mobility Topology highly dynamic due to movement of nodes Ongoing sessions suffer frequent path breaks Even though wired network protocol find alternate paths when a path breaks, the convergence is slow Bandwidth constraint Limited bandwidth imposes constraint on routing protocols to maintain topological information Due to frequent changes in topology the control overhead of keeping the topology current could be very high

MANET routing protocols Proactive or Table-driven protocols Traditional distributed shortest-path protocols Example: DSDV (destination sequenced distance vector) Reactive or On-demand routing protocols Determine route if and when needed Example: DSR (dynamic source routing) Hybrid protocols Adaptive; Combination of proactive and reactive Example : ZRP (zone routing protocol) Hierarchical Geographical

Expected Properties of Routing Ideally an ad hoc network routing protocol should be distributed in order to increase reliability assume routes as unidirectional links be power efficient. consider its security be hybrid protocols be aware of Quality of Service

Proactive routing protocols-DSDV Is based on the idea of Bellman-Ford routing algorithm Every mobile station maintains a routing table that lists all available destinations the number of hops to reach the destination the sequence number assigned by the destination node A station transmits its routing table periodically if a significant change has occurred in its table from the last update sent The routing table updates can be sent in two ways full dump incremental update

Example DSDV MH3 MH5 MH4 MH8 MH2 MH6 MH7 MH1 MH1

Example DSDV Destination Next hop Metric Sequence number MH1 MH2 2 Routing table at MH4 Destination Next hop Metric Sequence number MH1 MH2 2 S406_MH1 1 S128_MH2 MH3 S564_MH3 MH4 S710_MH4 MH5 MH6 S392_MH5 S076_MH6 MH7 S128_MH7 MH8 3 S050_MH8

Example DSDV Destination Metric Sequence number MH1 2 S406_MH1 MH2 1 Advertisement from MH4 Destination Metric Sequence number MH1 2 S406_MH1 MH2 1 S128_MH2 MH3 S564_MH3 MH4 S710_MH4 MH5 S392_MH5 MH6 S076_MH6 MH7 S128_MH7 MH8 3 S050_MH8

Routing table at MH4 (after MH1 moves) Example DSDV Routing table at MH4 (after MH1 moves) Destination Next hop Metric Sequence number MH1 MH6 3 S516_MH1 MH2 1 S128_MH2 MH3 2 S564_MH3 MH4 S710_MH4 MH5 S392_MH5 S076_MH6 MH7 S128_MH7 MH8 S050_MH8

Advertisement from MH4 (after MH1 moves) Example DSDV Advertisement from MH4 (after MH1 moves) Destination Metric Sequence number MH4 S710_MH4 MH1 3 S516_MH1 MH2 1 S128_MH2 MH3 2 S564_MH3 MH5 S392_MH5 MH6 S076_MH6 MH7 S128_MH7 MH8 S050_MH8

DSDV: Advantages & Disadvantages Routes available to all destinations Less latency in route set up Disadvantages Updates are propagated throughout the network Updates due to broken link (due to mobility) can lead to heavy control traffic Even a small network with high mobility or large network with low mobility can choke the network In order to get information about a particular destination node, a node has to wait for a table update message initiated by the same destination node This delay would result in stale routing information

Reactive routing protocols- DSR Reactive routing protocols are intended to maintain routing information about ‘active’ routes only. Routes are created when desired by the source node. Hence, the protocols are known as on-demand routing protocols. However, no periodic routing advertisement messages are sent, thereby reducing network bandwidth overhead, particularly during periods when little or no significant host movement is taking place.

DSR A node maintains route caches containing the source routes that it is aware of The node updates entries in the route cache as and when it learns about new routes route discovery route request packet contains the address of the source the destination a unique identification number route reply is generated by an intermediate node with current information about the destination route maintenance Route error packets are generated at a node when the data link layer encounters a fatal transmission problem Acknowledgements, including passive acknowledgments

Dynamic Source Routing (DSR) Source S initiates a route discovery by flooding Route Request (RREQ) Each node appends its own identifier when forwarding RREQ Destination D on receiving the first RREQ, sends a Route Reply (RREP) RREP sent on route obtained by reversing the route appended in RREQ RREP includes the route from S to D, on which RREQ was received by D S routes data using “source route” mechanism

Dynamic Source Routing (DSR) Routing Discovery Example: A H I B C J Destination G Source D E F K Source: http://www.ics.uci.edu/~atm/adhoc/paper-collection/johnson-dsr.pdf The following series of slides illustrates the behavior of the DSR’s Route Discovery algorithm Advantages: Adapts quickly to frequent node movement resulting in need to change packet routes Does not require significant overhead in periods when node movement is low Tests show algorithm performs well in conditions with large host density and high movement Route lengths have been shown to be within factor of 1.01 of optimal path

Dynamic Source Routing (DSR)

Represents a node that has received RREQ for D from S Route Discovery in DSR Y Z S E F B C M L J A G H D K I N Represents a node that has received RREQ for D from S Source: Vaidya

Route Discovery in DSR Y Broadcast transmission Z [S] S E F B C M L J G H D K I N Represents transmission of RREQ [X,Y] Represents list of identifiers appended to RREQ

Route Discovery in DSR Y Z S [S,E] E F B C M L J A G [S,C] H D K I N Node H receives packet RREQ from two neighbors: potential for collision

Route Discovery in DSR Y Z S E F B [S,E,F] C M L J A G H D K [S,C,G] I Node C receives RREQ from G and H, but does not forward it again, because node C has already forwarded RREQ once

Route Discovery in DSR Y Z S E F [S,E,F,J] B C M L J A G H D K I N [S,C,G,K] Nodes J and K both broadcast RREQ to node D Since nodes J and K are hidden from each other, their transmissions may collide

Route Discovery in DSR Y Z S E [S,E,F,J,M] F B C M L J A G H D K I N Node D does not forward RREQ, because node D is the intended target of the route discovery

Represents RREP control message Route Reply in DSR Y Z S RREP [S,E,F,J,D] E F B C M L J A G H D K I N Represents RREP control message

Packet header size grows with route length Data Delivery in DSR Y Z DATA [S,E,F,J,D] S E F B C M L J A G H D K I N Packet header size grows with route length

Route Error (RERR) Y Z RERR [J-D] S E F B C M L J A G H D K I N J sends a route error to S along route J-F-E-S when its attempt to forward the data packet S (with route SEFJD) on J-D fails (an ACK mechanism has to be there in packet forwarding)

Route caching Uses: Problems: Finding alternate routes in case original route breaks Route reply from intermediate nodes Problems: Cached routes may become invalid over time and due to host mobility Stale caches can adversely affect performance

DSR: Route caching Each node caches a new route it learns by any means When node S finds route [S,E,F,J,D] to node D, node S also learns route [S,E,F] to node F When node K receives Route Request [S,C,G] destined for node, node K learns route [K,G,C,S] to node S

Route caching When node F forwards Route Reply RREP [S,E,F,J,D], node F learns route [F,J,D] to node D When node E forwards Data [S,E,F,J,D] it learns route [E,F,J,D] to node D A node may also overhear Data to learn routes

Use of route caching [S,E,F,J,D] [E,F,J,D] S E [F,J,D],[F,E,S] F B [J,F,E,S] C M L [G,C,S] J A G [C,S] H D K [K,G,C,S] I N RREP RREQ Z When Z sends a route request for C, node K sends back a route reply [Z,K,G,C] to Z using a locally cached route Source: Vaidya

DSR: Advantages Routes maintained only between nodes who need to communicate reduces overhead of route maintenance Route caching can further reduce route discovery overhead A single route discovery may yield many routes to the destination, due to intermediate nodes replying from local caches

DSR: Disadvantages Packet header size grows with route length due to source routing Latency to discover a route before data can be sent Flood of route requests may potentially reach all nodes in the network An intermediate node may send Route Reply using a stale cached route, thus polluting other caches Inconsistency during route reconstruction phase

MANET Routing Algorithms FLOODING TABLE-DRIVEN ON-DEMAND HYBRID + Simplicity + Multiple path to the destination - High Overhead - Lower reliability of data delivery : Because of broadcast behavior of flooding ? Network properties : + Rate of topology changes increase - Number of communications increases - Number of nodes in the network increases + Delay of route determination decreases -Communication overhead increases -Storage requirements increases + Number of communication increases - Rate of topology changes increases + Communication overhead decreases but it is subject to number of communications in the network - Not optimal bandwidth utilization - Delay of route determination increases + Rate of topology changes increases o Better trade-off between communication overhead and delay ? Network properties :o Rate of topology changes increases o Number of communications increases o Number of nodes in the network increases