03-11-2012, 01:04 PM
Mobile Ad Hoc Networks
Mobile Ad Hoc.ppt (Size: 540.5 KB / Downloads: 22)
MANET.docx (Size: 47.14 KB / Downloads: 24)
Routing Protocol.docx (Size: 91.16 KB / Downloads: 19)
PRORTOCOL.docx (Size: 263.36 KB / Downloads: 24)
Interzone.docx (Size: 16.43 KB / Downloads: 18)
manet work.docx (Size: 19.75 KB / Downloads: 20)
algorithm.docx (Size: 23.99 KB / Downloads: 18)
MANET..docx (Size: 20.89 KB / Downloads: 22)
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
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
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
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”
Multiple Access with Collision Avoidance (MACA)
MACA uses signaling packets for collision avoidance
RTS (request to send)
sender request the right to send from a receiver with a short RTS packet before it sends a data packet
CTS (clear to send)
receiver grants the right to send as soon as it is ready to receive
Signaling packets contain
sender address
receiver address
packet size
Variants of this method are used in IEEE 802.11
MAC: Reliability
Wireless links are prone to errors. High packet loss rate is detrimental to transport-layer performance.
Solution: Use of acknowledgements
When node B receives a data packet from node A, node B sends an Acknowledgement (Ack).
If node A fails to receive an Ack, it will retransmit the packet
This approach adopted in many protocols [Bharghavan94, IEEE 802.11]
IEEE 802.11 Wireless MAC
Distributed and centralized MAC components
Distributed Coordination Function (DCF)
Point Coordination Function (PCF)
DCF suitable for multi-hop ad hoc networking
MAC: Collision Avoidance
With half-duplex radios, collision detection is not possible
Collision avoidance: Once channel becomes idle, the node waits for a randomly chosen duration before attempting to transmit
IEEE 802.11 DCF
When transmitting a packet, choose a backoff interval in the range [0,cw]; cw is contention window
Count down the backoff interval when medium is idle
Count-down is suspended if medium becomes busy
When backoff interval reaches 0, transmit RTS
Time spent counting down backoff intervals is a part of MAC overhead
large cw leads to larger backoff intervals
small cw leads to larger number of collisions
MAC Protocols: Summary
Wireless medium is prone to hidden and exposed terminal problems
Protocols are typically based on CSMA/CA
RTS/CTS based signaling
Acks for reliability
Contention window is used for congestion control
IEEE 802.11 wireless LAN standard
Fairness issues are still unclear
Routing Protocols
Proactive protocols
Traditional distributed shortest-path protocols
Maintain routes between every host pair at all times
Based on periodic updates; High routing overhead
Example: DSDV (destination sequenced distance vector)
Reactive protocols
Determine route if and when needed
Source initiates route discovery
Example: DSR (dynamic source routing)
Hybrid protocols
Adaptive; Combination of proactive and reactive
Example : ZRP (zone routing protocol)
Location-Aided Routing (LAR)
Exploits location information to limit scope of route request flood
Location information may be obtained using GPS
Expected Zone is determined as a region that is expected to hold the current location of the destination
Expected region determined based on potentially old location information, and knowledge of the destination’s speed
Route requests limited to a Request Zone that contains the Expected Zone and location of the sender node
Mobile Ad Hoc.ppt (Size: 540.5 KB / Downloads: 22)
MANET.docx (Size: 47.14 KB / Downloads: 24)
Routing Protocol.docx (Size: 91.16 KB / Downloads: 19)
PRORTOCOL.docx (Size: 263.36 KB / Downloads: 24)
Interzone.docx (Size: 16.43 KB / Downloads: 18)
manet work.docx (Size: 19.75 KB / Downloads: 20)
algorithm.docx (Size: 23.99 KB / Downloads: 18)
MANET..docx (Size: 20.89 KB / Downloads: 22)
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
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
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
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”
Multiple Access with Collision Avoidance (MACA)
MACA uses signaling packets for collision avoidance
RTS (request to send)
sender request the right to send from a receiver with a short RTS packet before it sends a data packet
CTS (clear to send)
receiver grants the right to send as soon as it is ready to receive
Signaling packets contain
sender address
receiver address
packet size
Variants of this method are used in IEEE 802.11
MAC: Reliability
Wireless links are prone to errors. High packet loss rate is detrimental to transport-layer performance.
Solution: Use of acknowledgements
When node B receives a data packet from node A, node B sends an Acknowledgement (Ack).
If node A fails to receive an Ack, it will retransmit the packet
This approach adopted in many protocols [Bharghavan94, IEEE 802.11]
IEEE 802.11 Wireless MAC
Distributed and centralized MAC components
Distributed Coordination Function (DCF)
Point Coordination Function (PCF)
DCF suitable for multi-hop ad hoc networking
MAC: Collision Avoidance
With half-duplex radios, collision detection is not possible
Collision avoidance: Once channel becomes idle, the node waits for a randomly chosen duration before attempting to transmit
IEEE 802.11 DCF
When transmitting a packet, choose a backoff interval in the range [0,cw]; cw is contention window
Count down the backoff interval when medium is idle
Count-down is suspended if medium becomes busy
When backoff interval reaches 0, transmit RTS
Time spent counting down backoff intervals is a part of MAC overhead
large cw leads to larger backoff intervals
small cw leads to larger number of collisions
MAC Protocols: Summary
Wireless medium is prone to hidden and exposed terminal problems
Protocols are typically based on CSMA/CA
RTS/CTS based signaling
Acks for reliability
Contention window is used for congestion control
IEEE 802.11 wireless LAN standard
Fairness issues are still unclear
Routing Protocols
Proactive protocols
Traditional distributed shortest-path protocols
Maintain routes between every host pair at all times
Based on periodic updates; High routing overhead
Example: DSDV (destination sequenced distance vector)
Reactive protocols
Determine route if and when needed
Source initiates route discovery
Example: DSR (dynamic source routing)
Hybrid protocols
Adaptive; Combination of proactive and reactive
Example : ZRP (zone routing protocol)
Location-Aided Routing (LAR)
Exploits location information to limit scope of route request flood
Location information may be obtained using GPS
Expected Zone is determined as a region that is expected to hold the current location of the destination
Expected region determined based on potentially old location information, and knowledge of the destination’s speed
Route requests limited to a Request Zone that contains the Expected Zone and location of the sender node