Mobile Adhoc Network MANET full report

[seminar class]

PRESENTED BY:
P. Mahesh Naik

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Wireless Networks
 Need: Access computing and communication services, on the move
 Infrastructure-based Networks
– traditional cellular systems (base station infrastructure)
 Wireless LANs
– Infrared (IrDA) or radio links (Wavelan)
– very flexible within the reception area; ad-hoc networks possible
– low bandwidth compared to wired networks (1-10 Mbit/s)
 Ad hoc Networks
– useful when infrastructure not available, impractical, or expensive
– military applications, rescue, home networking
Cellular Wireless
 Single hop wireless connectivity to the wired world
– Space divided into cells
– A base station is responsible to communicate with hosts in its cell
– Mobile hosts can change cells while communicating
– Hand-off occurs when a mobile host starts communicating via a new base station
Multi-Hop Wireless
 May need to traverse multiple links to reach destination
 Mobility causes route changes
Mobile Ad Hoc Networks (MANET)
 Host movement frequent
 Topology change frequent
 No cellular infrastructure. Multi-hop wireless links.
 Data must be routed via intermediate nodes.
Why 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)
 Ad hoc networks:
– Do not need backbone infrastructure support
– Are easy to deploy
– Useful when infrastructure is absent, destroyed or impractical
Many Applications
 Personal area networking
– cell phone, laptop, ear phone, wrist watch
 Military environments
– soldiers, tanks, planes
 Civilian environments
– taxi cab network
– meeting rooms
– sports stadiums
– boats, small aircraft
 Emergency operations
– search-and-rescue
– policing and fire fighting
Challenges in Mobile Environments
• 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
Effect of mobility on the protocol stack
 Application
– new applications and adaptations
 Transport
– congestion and flow control
 Network
– addressing and routing
 Link
– media access and handoff
 Physical
– transmission errors and interference
Medium Access Control in MANET Motivation
 Can we apply media access methods from fixed networks?
 Example CSMA/CD
– Carrier Sense Multiple Access with Collision Detection
– send as soon as the medium is free, listen into the medium if a collision occurs (original method in IEEE 802.3)
 Medium access problems in wireless networks
– signal strength decreases proportional to the square of the distance
– sender would apply CS and CD, but the collisions happen at the receiver
– sender may not “hear” the collision, i.e., CD does not work
– CS might not work, e.g. if a terminal is “hidden”
Hidden and Exposed Terminals
 Hidden terminals
– A sends to B, C cannot receive A
– C wants to send to B, C senses a “free” medium (CS fails)
– collision at B, A cannot receive the collision (CD fails)
– A is “hidden” for C
 Exposed terminals
– B sends to A, C wants to send to another terminal (not A or B)
– C senses carrier, finds medium in use and has to wait
– A is outside the radio range of C, therefore waiting is not necessary
– C is “exposed” to B