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Major Issues (Cont’d.)
n MAC protocols*
n Contention vs. contention-free
n Applications and middleware
n Measurement and experimentation
n Security*
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Ad Hoc Wireless Networks
(Infrastructureless networks)
n Manet (mobile ad hoc networks)
n Mobile distributed multihop wireless networks
n Temporary in nature n No base station and rapidly deployable n Neighborhood awareness n Multiple-hop communication n Unit disk graph: host connection based
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Wireless MAC: Major Issues
Distributed operations
Synchronization Hidden terminals
Real-time traffic Resource reservation Ability to measure
n Receiver-initiated
• MACA-BI (By Invitation)
n Other extensions
• March and PAMAS
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MACA (P. Khan)
No carrier-sensing for channel
Two special signals
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Table of Contents (cont’d.)
n Infrastructureless networks
Wireless MAC (IEEE 802.11 and Bluetooth) Ad Hoc Routing Protocols Multicasting and Broadcasting Security Network Coding
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Wireless MAC
n A MAC (Media Access Protocol) is a set of rules or procedures to allow the efficient use of a shared medium.
• Contention vs. contention-free • Sender-initiated vs. receiver-initiated
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2020/11/24
移动自组织网络
Table of Contents
n Introduction n Infrastructured networks
n Handoff n location management (mobile IP) n channel assignment
n Resource management
n Networks resource allocation and energy efficiency
n QoS management*
n Dynamic advance reservation and adaptive error control techniques
•
five wireless mobile hosts.
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A•Appplilciacatitoionnss
n Defense industry (battlefield) n Law enforcement n Academic institutions (conference and
n Pure: transmitted at arbitrary time n Slotted: transmitted at start of a time
slot n p-persistent: slotted and transmitted
with a probability p
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• MACA (Multiple Access with Collision Avoidance) (RTS-CTS-data)
• MACAW (MACA with Acknowledgement) • BTMA (Busy Tone Multiple Access) • DBTMA (Dual BTMA)
n Binary countdown: use binary station address in bidding.
Hybrid n Mixed contention-free with contention
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Wireless MAC
n Hidden Terminal Problem
resource availability
Exposed terminals Power and rate
Throughput
control
Access delay
Directional antennas
Fairness
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Wireless MAC
Contention-based n ALOHA: no collision avoidance
Pervasive computing Social networks
n Sample on-going projects
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Ad Hoc Wireless Networks
(Infrastructureless networks)
n An ad hoc network is a collection of wireless mobile host forming a temporary network without the aid of any centralized administration or standard support services regularly available on the wide area network to which the hosts may normally be connected (Johnson and Maltz)
n Network coding
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n Reduce number of transmissions 移动自组织网络
Issues to be Covered
n Wireless Media Access Protocols (MAC) n Ad Hoc Routing Protocols n Multicasting and Broadcasting n Power Optimization n Security n Network Coding
on geographical distance
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Sample Ad Hoc Networks
n Sensor networks n Indoor wireless applications n Mesh no nodes, hidden from one another (out of transmission range), attempt to send information to the same receiving node.
• Packet collisions.
n Exposed Node Problem
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Major Issues
n Mobility management
n Addressing and routing*
n Location tracking
n Absolute vs. Relative, GPS
n Network management
n Merge and split
meeting) n Personal area networks and Bluetooth n Home networking n Embedding computing applications n Health facilities n Disaster recovery (search-and-rescue)
n RTS-CTS problem 1
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n Authentication, encryption, anonymity, and intrusion detection
n Error control and failure
n Error correction and retransmission, deployment of back-up systems
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Table of Contents (cont’d.)
n Infrastructureless networks (cont’d.)
Power Optimization
n Applications
Sensor networks and indoor wireless environments
n “small world” that are very large graphs that tend to be sparse, clustered, and have a small diameter.
n “six degree of separation”
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•Characteristics
• A node is inhibited from transmitting to other nodes on overhearing a packet transmission.
• Wasted bandwidth.
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Wireless MAC
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n Sender-initiated
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Wireless MAC
n Carrier Sense Multiple Access (CSMA): listen to determine whether
there is activity on the channel n Persistent: continuously listens n Nonpersistent: waits a random amount
n Self-organizing: without centralized control
n Scarce resources: bandwidth and batteries
n Dynamic network topology
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Unit Disk Graph
•Figure 1: A simple ad hoc wireless network of
• RTS: request-to-send • CTS: clear-to-send
Packet lost
• Binary exponential back-up
Overcomes the hidden terminal issue
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Sample collision
of time before re-testing n p-persistent: slotted and transmit when
idle with a probability of p
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Wireless MAC
Contention-free protocols
n Bit-map protocol: each contention period consists of N slots.