UNIT-V Ad-hoc Networks

Ad-hoc Networks Two types of wireless network: Infrastructured the mobile node can move while communicating the base stations are fixed as the node goes out of the range of a base station, it gets into the range of another base station Infrastructureless or ad-hoc there are no fixed base stations all the nodes in the network need to act as routers In Latin “ad-hoc” literally means “for this purpose only”. Then an ad-hoc network can be regarded as “spontaneous network”

Ad-hoc Networks Infrastructured network Infrastructure (Wired line) Radio tower Desktop computer PDA Radio tower Laptop computer Laptop computer Pen computer

Infrastructurless (ad-hoc) network or MANET (Mobile Ad-hoc NETwork) Ad-hoc Networks Infrastructurless (ad-hoc) network or MANET (Mobile Ad-hoc NETwork) PDA Pen computer Laptop computer

Ad-hoc Networks Classification of ad-hoc networks Single hop – nodes are in their reach area and can communicate directly Multi hop – some nodes are far and cannot communicate directly. The traffic has to be forwarded by other intermediate nodes.

Characteristics of an ad-hoc network Ad-hoc Networks Characteristics of an ad-hoc network Collection of mobile nodes forming a temporary network Network topology changes frequently and unpredictably No centralized administration or standard support services Each host is an independent router Hosts use wireless RF transceivers as network interface Number of nodes 10 to 100 or at most 1000

Ad-hoc Networks Why we need ad-hoc networks? Setting up of fixed access points and backbone infrastructure is not always viable Infrastructure may not be present in a disaster area or war zone Infrastructure may not be practical for short-range radios; Bluetooth (range ~ 10m) Do not need backbone infrastructure support Are easy to deploy Useful when infrastructure is absent, destroyed or impractical

Ad-hoc Networks Example applications of ad hoc networks: emergency search-and-rescue operations, meetings or conventions in which persons wish to quickly share information, data acquisition operations in inhospitable terrain, local area networks in the future.

Ad-hoc Networks Mobile Ad Hoc Networking is a multi-layer problem ! - Security - Service Discovery - Location-dependent Application Physical/Link Layer Network Layer Transport Layer Application Layer - TCP - Quality of Service - Routing - Addressing - Location Management - Power Control - Multiuser Detection - Channel Access

Problems with Routing Is it possible to use standard routing protocols? Distance-vector protocols Slow convergence due to “Count to Infinity” Problem Creates loops during node failure, network partition or congestion Link state protocols Use flooding technique and create excessive traffic and control overhead Require a lot of processor power and therefore high power consumption

Problems with Routing packet loss due to transmission errors Limitations of the Wireless Network packet loss due to transmission errors variable capacity links frequent disconnections/partitions limited communication bandwidth Broadcast nature of the communications Limitations Imposed by Mobility dynamically changing topologies/routes lack of mobility awareness by system/applications Limitations of the Mobile Computer short battery lifetime limited capacities

DSDV DSDV (Destination Sequenced Distance Vector) Each node sends and responds to routing control message the same way No hierarchical structure Avoids the resource costs involved in maintaining high-level structure Scalability may become an issue in larger networks

DSDV known also as Distributed Bellman-Ford all available destinations Basic Routing Protocol known also as Distributed Bellman-Ford Every node maintains a routing table all available destinations the next node to reach to destination the number of hops to reach the destination Periodically send table to all neighbors to maintain topology Bi-directional links are required!

Intro -2

Short introduction to wireless multihop networks Two or more nodes equipped with wireless communications and networking capability Base station is not necessary A node can communicate directly with another node that is immediately within radio range To communicate with nodes outside its own radio range an intermediate node is used to forward the packet The network is self-organizing and adaptive (autonomous distributed control is required) Nodes are able to detect the presence of other nodes and join them into the network The nodes don’t need to be of the same type (phone, PDA, laptop, sensor, etc.) This is a kind of network made without base stations. It can be made by a collection of two or more devices equipped with wireless communications and networking capability. Such devices can communicate with another node that is immediately within their radio range or one that is outside their radio range. For the latter scenario, an intermediate node is used to replay or forward the packet from the source toward the destination. Ad-hoc wireless networks are also self-organizing and adaptive. This means that a formed network can be de-formed on the fly without the need for any system administration. The term “ad-hoc” tends to imply that it can take different forms and that it can be mobile, standalone, or networked. Ad-hoc nodes or devices should be able to detect the presence of other such devices and to perform the necessary handshaking to allow communications and the sharing of information and services (joining new nodes into the network automatically). The intermediate node must know the next hop node when a destination terminal is given

Application areas Tactical military Emergencies Sensor Meetings/conferences

Challenges Dynamic topologies Bandwidth-constrained, variable capacity links Energy-constrained Limited physical security Scalability

Simple routing protocol example Propagation of routing table Routing and transmitting

Routing table Destination terminal Next node A B C E D … Each terminal has its own routing table (in proactive routing algorithms) Destination terminal Next node A B C E D … This is an example of a simple routing table

Position notification packet Used to make and update the Routing Table Broadcasted in a limited area Contents of the packet: ID of terminal which the created the packet Timestamp for the created packet ID of hop source terminal Hop count

Renewal of Position Notification Packet 1 B 2 A 1 A 1 C 3 A B D C A A A B A C B B C C t =1 t =2 t =3 t =4

Basic transmitting procedure Request to send (RTS) Clear to send (CTS) Ready to receive (RTR)

Topology problem Hidden terminal problem Exposed terminal problem Busy tones Siden dette er et meget enkelt eksempel har det mange problemer Truls vil nå utdype noen eksempler på rutings algoritmer som løser noen av disse problemene

Ad Hoc routing protocols Proactive Large overhead Reactive Delay before first packet Doesn’t scale Hybrid scheme Clusters Vi har to kategorier av rutings algoritmer. Tabell baserte, der nodene til enhver tid vet hvordan de skal videresende pakker til en viss adresse. (Eksempelet til Audun var av den typen) Rutingsinformasjon sendes periodisk og ved endringer. Liten forsinkelse (nodene har full oversikt), sanntids-trafikk. Ressurser (båndbredde, batteri) kastes bort pga unødig mye oppdatering. Samme som i Internett (her er det mer bevegelse) Reaktive, der rutingsinformasjon ikke oppdateres før det er bruk for den. Sparer de ressursene som sløses i det proaktive tilfellet. Avsender sørger for at en vei blir funnet før den sender. ‘Route discovery’ mekansimen kan gi stor forsinkelse før første pakke kan sendes. Skalerer dårlig pga Flooding. Kombinasjon gjøres ved å dele opp i clustere. En protokoll internt. En annen mellom lederne i ulike clustere.

Unicast, id-centric routing Given: a network/a graph Each node has a unique identifier (ID) Goal: Derive a mechanism that allows a packet sent from an arbitrary node to arrive at some arbitrary destination node The routing & forwarding problem Routing: Construct data structures (e.g., tables) that contain information how a given destination can be reached Forwarding: Consult these data structures to forward a given packet to its next hop Challenges Nodes may move around, neighborhood relations change Optimization metrics may be more complicated than “smallest hop count” – e.g., energy efficiency

Ad-hoc routing protocols Because of challenges, standard routing approaches not really applicable Too big an overhead, too slow in reacting to changes Examples: Dijkstra’s link state algorithm; Bellman-Ford distance vector algorithm Simple solution: Flooding Does not need any information (routing tables) – simple Packets are usually delivered to destination But: overhead is prohibitive ! Usually not acceptable, either ! Need specific, ad hoc routing protocols

Ad hoc routing protocols – classification Main question to ask: When does the routing protocol operate? Option 1: Routing protocol always tries to keep its routing data up-to-date Protocol is proactive (active before tables are actually needed) or table-driven Option 2: Route is only determined when actually needed Protocol operates on demand Option 3: Combine these behaviors Hybrid protocols

Ad hoc routing protocols – classification Is the network regarded as flat or hierarchical? Compare topology control, traditional routing Which data is used to identify nodes? An arbitrary identifier? The position of a node? Can be used to assist in geographic routing protocols because choice of next hop neighbor can be computed based on destination address Identifiers that are not arbitrary, but carry some structure? As in traditional routing Structure akin to position, on a logical level?