Mobile Ad-Hoc Networks Part I. Based on presentation from Matthias Hollick (Technische Universität Darmstadt)

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1 Mobile Ad-Hoc Networks Part I Thomas Plagemann Based on presentation from Matthias Hollick (Technische Universität Darmstadt) Outline Part I: Introduction and Motivation Terminology, Basics and Applications Ad Hoc vs. the Internet Model Understanding Ad Hoc Routing Characteristics of Ad Hoc Communication Ad Hoc Routing Paradigms Part II: Selected Ad Hoc Routing Protocols The Ad Hoc On-demand Distance Vector Protocol (AODV) Dynamic Source Routing (DSR) Location Aided Routing (LAR) Optimized Links-State Routing (OLSR) Current Research Optimized forwarding in MANETs Problem and Solution Space 3 1

2 Goal & Contents Goals Identify and highlight application requirements for Mobile Ad Hoc Networks (MANET) Understand the MANET ecosystem : mobility, user density, etc. Derive requirements for MANET routing Contents (1) Terminology and Definitions (2) Basic Operation of MANETs (3) Application scenarios for MANETs (4) Mobility characteristics and feasibility of MANETs (5) Requirements for MANET routing 4 The Promise of Ad Hoc Networks Networking without infrastructure [Source: [Source: 5 2

3 Terminology and Paradigms Ad hoc often improvised or impromptu; an ad hoc committee meeting Wordnet formed or used for specific or immediate problems or needs; ad hoc solutions fashioned from whatever is immediately available: improvised; large ad hoc parades and demonstrations Encyclopædia Britannica Spontaneous arising from a momentary impulse controlled and directed internally; self-acting produced without being planted or without human labor; indigenous developing without apparent external influence, force, cause, or treatment Encyclopædia Britannica 6 Basics (Mobile) Ad Hoc Communication Networks - MANET Historical successor of packet radio networks Self-organizing, mobile and wireless nodes Absence of infrastructure, multi-hop routing necessary Systems are both, terminals (end-systems) and routers (nodes) Constraints (dynamics, energy, bandwidth, link asymmetry 7 3

4 Traditional Wired Networks endsystem (source) router endsystem (destination) separation between endsystems and routers routers responsible for finding stable path 8 [M. Ammar, Co-Next 2005] Mobile Ad-hoc Wireless Networks node (source) node (destination) node = endsystem + router no separation between endsystems and routers nodes responsible for finding stable path 9 [M. Ammar, Co-Next 2005] 4

5 Mobile Ad-hoc Wireless Networks node (source) node (destination) nodes may move routing layer responsible for reconstructing (repairing) stable paths when movement occurs 10 [M. Ammar, Co-Next 2005] The MANET Wireless Paradigm The Network is Connected There exists a (possibly multi-hop) path from any source to any destination The path exists for a long-enough period of time to allow meaningful communication If the path is disrupted it can be repaired in short order Looks like the Internet above the network layer 11 [M. Ammar, Co-Next 2005] 5

6 Wireless Mesh Network 12 Ad Hoc vs. The Internet Model User Demands Spontaneous App. Behavior P2P App. Characteristics Service Discovery Disconnected Operations Ad Hoc Routing Distributed Medium Access Wireless Communication WWW IPtel IMS..." SMTP HTTP RTP..." TCP UDP " " IP" " ethernet" CSMA sonet..." copper fiber radio..." New Apps. Name Resolution Gateway Discovery Addressing Power Control User / Device Mobility Absence of Infrastructure 13 6

7 Peer to Peer vs. Ad Hoc 14 Peer to Peer vs. Ad Hoc P2P Relevant resources located at nodes at the edges ("peers") Variable connectivity is the norm e.g. does it support dial-up users with variable IP addresses Combined Client and Server functionality for all end system nodes also for intermediate nodes Peers with significant autonomy e.g. storage / processing done by autonomous end-systems Direct data transfer between peers e.g. more-or-less no central control Content locations widely distributed and most often replicated 15 7

8 Peer to Peer vs. Ad Hoc (cont.) Ad Hoc and P2P share paradigms Ad Hoc focuses on network level and below P2P focuses on application level Coexistence of Ad Hoc and P2P is possible / synergetic 16 Applications Military applications Battlefield communication (soldiers, tanks, planes, ) Smart dust (sensor networks to detect chemical, biological threats) Civilian applications Vehicular environment (telematics, car to car communication, taxi cab network, ) Entertainment (filesharing, gaming,... in train, car, plane, school, ) Event support (conferences, sport-events, exhibitions, meetings, lectures) Home networking / Personal Area Networking (VCR, DVD, home entertainment, remote control, cell phone, laptop, watch, ) Disaster recovery (emergency services, ambulance, police, ) Smart dust (sensor networks for civilian applications) Ubiquitous computers with short-range interactions (embedded systems, smart buildings/artefacts, ) Cellular range extension, moveable base stations (UMTS, WLAN, 17 WMAN, ) 8

9 Applications (cont.) 18 (Source: Daimler Chrysler) [ 19 9

10 Outline Part I: Introduction and Motivation Terminology, Basics and Applications Ad Hoc vs. the Internet Model Understanding Ad Hoc Routing Characteristics of Ad Hoc Communication Ad Hoc Routing Paradigms Part II: Selected Ad Hoc Routing Protocols The Ad Hoc On-demand Distance Vector Protocol (AODV) Dynamic Source Routing (DSR) Location Aided Routing (LAR) Optimized Links-State Routing (OLSR) Current Research Optimized forwarding in MANETs Problem and Solution Space 20 Characteristics of Ad Hoc Communications Characteristics are dominated by heterogeneity and variability Mobility characteristics (speed, predictability, uniformity, synthetic vs. empirical models, ) Wireless characteristics (broadcast nature of the net, packet losses due to transmission errors, limited range, hidden and exposed terminals, partitioning) Application / traffic characteristics and patterns (P2P, real time, unicast, multicast, geocast, CBR, VBR, self-similar, ) System characteristics (distribution, absence of infrastructure, (unpredictable) high dynamics, (a)symmetry ) Inherent heterogeneity Do nodes have identical capabilities, responsibilities, and constraints? Transmission ranges and radios may differ, battery life may differ, processing capacity may differ, (asymmetric capabilities) Only some nodes may route packets, some nodes may act as leaders of nearby nodes, e.g. cluster head (asymmetric responsibilities) 21 Adaptation is crucial 10

11 Mobility Characteristics Synthetic Random waypoint Select a random destination (within the specified area) Select a random speed (0 < v max_speed) Move After reaching the destination, pause a random time (0 < p max_pause_time) 22 Example User Mobility: What is Realistic? 10 nodes? 100 nodes? 1000 nodes? nodes? 4000m x 3000m 1000m 1 m/s à 1000s 5 m/s à 200s 20m/s à 50s 1000m x 1000m, 333 nodes 11

12 Macroscopic Workload / Mobility Model Synthetic mobility models (see demo) Easy to use Strict separation from traffic models Unrealistic for large scenarios (e.g. random waypoint) Empirical workload / mobility models Data is hard to obtain Can often not be separated in mobility vs. traffic Available for past scenarios (may not be generalized easily) Hybrid workload / mobility model (synthetic traffic, empirical mobility) (see demo) Pros: flexibility, realism Cons: lots of parameters, data is hard to obtain Trade-off 24 Demo of Mobility Models Synthetic mobility model e.g. random walk, random waypoint Demo: ANSim, see

13 Wireless Characteristics Wireless signal strength Transmit power Loss over distance (falls off by d 2 ) Shadowing (e.g. absorption by walls) Multi-path (e.g. bouncing off of metal objects) 26 Wireless Characteristics (cont.) Figure 4-26.(a)The hidden terminal problem. (b) The exposed station problem 27 [Source: A. Tanenbaum Computer Networks] 13

14 Why specialized Ad Hoc Routing Within MANETs Some nodes may be out of range of others Must use other peer nodes as routers to forward packets Need to find new routes as nodes move or conditions change (highly dynamic and unpredictable) Routing protocol captures and distributes state of network Routing strategy (algorithm) computes shortest paths 28 Requirements for Ad Hoc Routing The routing protocol needs to Converge fast Minimize signaling overhead The routing strategy (algorithm) may include Shortest distance Minimum delay Minimum loss Minimum congestion (load-balancing) Minimal interference Maximum stability of routes or maximal signal strength Minimum energy (power aware routing) Standard Internet routing cannot fulfill these requirements Assumes infrastructure, assumes symmetrical conditions, assumes plenty of resources, to slow, misses metrics, 29 14

15 Ad Hoc Routing Paradigms Flooding of Data Packets Simple approach, extremely high overhead Many protocols perform (limited) flooding of control packets To discover routes Overhead of control packet flooding is amortized over data packets transmitted between consecutive control packet floods Uniform Protocols Topology-based (e.g. source routing) Destination-based (usually distance vector paradigm) Proactive (table-driven) vs. reactive (on-demand) paradigms Trade-off latency vs. overhead Non-Uniform Protocols Hierarchical protocols, Cluster-based, flat protocols Geographical protocols Hybrid protocols (e.g. combination of proactive and reactive) There is no silver bullet to ad hoc routing 30 Taxonomy of Routing Protocols Based on [Feeney 99] 31 15

16 Some Routing Protocols / Frameworks AODV - Ad Hoc On Demand Distance Vector (Perkins, NOKIA; Belding-Royer, UCSB; Das, UC) CEDAR - Core-Extraction Distributed Ad Hoc Routing DREAM - Distance Routing Effect Algorithm for Mobility DSDV - Destination-Sequenced Distance Vector DSR - Dynamic Source Routing (Johnson, CMU) FSR - Fisheye State Routing LANMAR - Landmark Ad Hoc Routing LAR - Location Aided Routing OLSR - Optimized Link State Routing (Clausen, Jacquet, INRIA) TBRPF - Topology Broadcast based on Reverse-Path Forwarding (Ogier,Templin, SRI) Tora / IMEP - Temporally-Ordered Routing Algorithm / Internet Manet Encapsulation Protocol ZRP - Zone Routing Protocol (Haas, Cornell) see also 32 Mobile Ad-Hoc Networks Part II Thomas Plagemann Based on presentation from Matthias Hollick (Technische Universität Darmstadt) 16

17 Outline Part I: Introduction and Motivation Terminology, Basics and Applications Ad Hoc vs. the Internet Model Understanding Ad Hoc Routing Characteristics of Ad Hoc Communication Ad Hoc Routing Paradigms Part II: Selected Ad Hoc Routing Protocols The Ad Hoc On-demand Distance Vector Protocol (AODV) Dynamic Source Routing (DSR) Location Aided Routing (LAR) Optimized Links-State Routing (OLSR) Current Research Optimized forwarding in MANETs Problem and Solution Space 34 Goal of this Lecture & Contents of this Module Goals Discuss working of selected MANET routing protocols/paradigms Explain the detailed working of the discussed routing protocols Understand trade-offs in choosing appropriate routing protocols Contents (1) The Ad Hoc On-demand Distance Vector Protocol (AODV) (2) Dynamic Source Routing (DSR) (3) Location Aided Routing (LAR) (4) Optimized Links-State Routing (OLSR) 35 17

18 Ad hoc On-demand Distance Vector Protocol (AODV) Reactive routing protocol All nodes are treated equal Based on distance vector principle Route discovery cycle for route finding Flooded / Broadcast Route Request (RREQ) Unicast Route Reply (RREP) along reverse path of RREQ Unicast Route Error (RERR) No overhead on data packets Loop freedom is achieved through sequence numbers, also solves count to infinity problem Status Implementations available (IPv4, IPv6) Interoperability testing (successful) 36 Experimental RFC status issued (July 2003) Routing Table Fields Destination IP address Destination Sequence Number Valid Destination Sequence Number Flag Other state and routing flags Network Interface Hop Count (needed to reach destination) Next Hop Precursor List Lifetime (route expiration or deletion time) 37 18

19 AODV Route Discovery Overview Route discovery Broadcast flood acquisition using Route Request (RREQ) A RREQ must never be broadcast more than once by any node Nodes sets up a reverse path pointing towards the source Route Reply (RREP) propagation D S 38 Route Request (RREQ) Message When node S wants to send a message to node D, S searches its route table for a route to D. If there is no route, S initiates a RREQ message with the following components : The IP addresses of S and D The current sequence number of S and the last known sequence number of D A broadcast ID from S. This broadcast ID is incremented each time S sends a RREQ message. [Source: Dr. R. B. Patel CSE 302-manet-aodv] 39 19

20 Processing a RREQ Message The <broadcast ID, IP address> pair of the source S forms a unique identifier for the RREQ. Suppose a node P receives the RREQ from S. P first checks whether it has received this RREQ before. Each node stores the <broadcast ID, IPaddress> pairs for all the recent RREQs it has received. [Source: Dr. R. B. Patel CSE 302-manet-aodv] 40 Processing a RREQ Message (cont.) S Q P D If P has seen this RREQ from S already, P discards the RREQ. Otherwise, P processes the RREQ : P sets up a reverse route entry in its route table for the source S. This entry contains the IP address and current sequence number of S, number of hops to S and the address of the neighbour from whom P got the RREQ. [Source: Dr. R. B. Patel CSE 302-manet-aodv] 41 20

21 Lifetime of a Route-Table Entry A lifetime is associated with the entry in the route table. This is an important feature of AODV. If a route entry is not used within the specified lifetime, it is deleted. A route is maintained only when it is used. A route that is unused for a long time is assumed to be stale. [Source: Dr. R. B. Patel CSE 302-manet-aodv] 42 Route Requests in AODV Y S E Z A B H C I G F K J M D N L Represents a node that has received RREQ for D from S [Source: Dr. R. B. Patel CSE 302-manet-aodv] 43 21

22 Route Requests in AODV (cont.) Broadcast transmission Y Z A B H S C I E G F K J M D N L Represents transmission of RREQ 44 [Source: Dr. R. B. Patel CSE 302-manet-aodv] Route Requests in AODV (cont.) Y Z A B H S C I E G F K J M D N L Represents links on Reverse Path [Source: Dr. R. B. Patel CSE 302-manet-aodv] 45 22

23 Route Requests in AODV (cont.) Y Z A B H S C I E G F K J M D N L Node C receives RREQ from G and H, but does not forward it again, because node C has already forwarded RREQ once [Source: Dr. R. B. Patel CSE 302-manet-aodv] 46 Reverse Path Setup in AODV Y Z A B H S C I E G F K J M D N L [Source: Dr. R. B. Patel CSE 302-manet-aodv] 47 23

24 Reverse Path Setup in AODV A nodes replies to a RREQ with RREP if there is a route to D with sequence number sequence number in RREQ If D responds it includes in RREP IP address of S and D Current sequence number Hop count := 0 Length of time the route is valid If any other node responds it includes in RREP IP address of S and D Record of destination s sequence number Hop count := distance from destination Calculated length of time route to destination will be valid 48 Reverse Path Setup in AODV Y Z S E A B H C I G F K J D M N L Node D does not forward RREQ, because node D is the intended target of the RREQ [Source: Dr. R. B. Patel CSE 302-manet-aodv] 49 24

25 Forward Path Setup in AODV Intermediate nodes set-up up a forwarding path entry when they receive RREP IP address of destination IP address of neighbor the RREP arrived from Hop count to destination Lifetime := lifetime in RREP Forward RREP towards S If multiple RREPs for one destination are received Process and forward the first one Handle later RREPs only if it contains a greater destination sequence number or a smaller hop count 50 Forward Path Setup in AODV Y Z S E A B H C I G F K J D M N L Forward links are setup when RREP travels along the reverse path Represents a link on the forward path [Source: Dr. R. B. Patel CSE 302-manet-aodv] 51 25

26 AODV Route Maintenance Timers to keep route alive A routing table entry maintaining a reverse path is purged after a timeout interval Timeout should be long enough to allow RREP to come back A routing table entry maintaining a forward path is purged if not used for a active_route_timeout interval If no data is being sent using a particular routing table entry, that entry will be deleted from the routing table (even if the route may actually still be valid) Destination Sequence numbers to determine fresh routes To avoid using old/broken routes To prevent formation of loops B E C D A 52 AODV Route Error Link failure reporting / repairing routes When node X is unable to forward packet P (from node S to node D) on link (X,Y), it generates a Route Error (RERR) message Node X increments the destination sequence number for D cached at node X The incremented sequence number N is included in the RERR, which is sent out based upon precursor lists When node S receives the RERR, it initiates a new route discovery for D using destination sequence number at least as large as N S X Y D 53 26

27 Additional Features of AODV Target networks Where routing churn is high enough that proactively maintaining routes is unproductive, and that can absorb a network wide broadcast rate The authors claim scalability up to 10,000 nodes (performance suffers, simulation results) Multiple optimizations AODV-LR - Local Repair AODV-ESP - Expanding-Ring Search Multi-path extension proposed (AODVM, AOMDV) Multiple open issues Security QoS Protocol needs operational experience to discover further issues 54 Concluding Quiz Why MANETs? Principles of MANETs? Difference between P2P & MANETs? How to evaluate MANETs? Which classes of routing protocols? What are the key ideas of AODV? How does the ring search work? 55 27