1. UNIT-V Ad-hoc Networks

2. 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”

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

4. 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

5. 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.

6. 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

7. 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

8. 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.

9. 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

10. 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

11. 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

12. 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

13. 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!

14. Intro -2

15. 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

16. Application areas Tactical military Emergencies Sensor
Meetings/conferences

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

18. Simple routing protocol example
Propagation of routing table
Routing and transmitting

19. 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

20. 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

21. Renewal of Position Notification Packet1 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

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

23. 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

24. 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.

25. 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

26. 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

27. 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

28. 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?