1. Introduction to Ad Hoc Mobile Wireless Networks
電機學院電信研究所
曾志成

2. Outline Introduction Features Network architectures MAC protocols
Jan 10, 2000
Jan 10, 2000
Outline
Introduction
Features
Network architectures
MAC protocols
Routing protocols
Conclusions
電信研究所 曾志成
Chih-Cheng Tseng

3. Introduction What is Ad Hoc Network? Example:
Jan 10, 2000
Introduction
What is Ad Hoc Network?
An Ad Hoc network is a collection of wireless mobile hosts forming a temporary network without the aid of any centralized administration.
Example:
Rescue Missions
Exhibitions
Conferences
電信研究所 曾志成

4. Features Lack of a centralized entity
Jan 10, 2000
Features
Lack of a centralized entity
All the communication is carried over the wireless medium
Rapid mobile host movements
Limited wireless bandwidth
Limited battery power
Multi-hop routing
電信研究所 曾志成

5. Network Architectures Hierarchical
Jan 10, 2000
Jan 10, 2000
Network Architectures Hierarchical
Nodes are partitioned into clusters
Some nodes are chosen as cluster heads
Properties:
easy to manage mobility
sub-optimal routing
電信研究所 曾志成
Chih-Cheng Tseng

6. Network Architectures Flat Topology
Jan 10, 2000
Network Architectures Flat Topology
All nodes are equal
Each node is considered as a router
existence of multiple paths
no “single-point-failure”
flow control
congestion control
power efficiency
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7. MAC Protocols Contention-based Contention-free CSMA-family
Jan 10, 2000
MAC Protocols
Contention-based
CSMA-family
efficient under low load, unstable under heavy load
users sense the channel at the transmitter but collisions occur at the receiver
Contention-free
Reservation, Polling, Token passing
not efficient under light load, stable under heavy load
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8. MAC Protocols To Sense Or Not To Sense?
Jan 10, 2000
MAC Protocols To Sense Or Not To Sense?
Hidden terminal problem
1. A transmits to B
2. C wants to transmit to B. It does not hear A’s transmission, accesses the channel and collides.
Exposed terminal problem
1. B transmits to A
2. C wants to transmits to D.
It hears B’s transmission
and unnecessarily defers.
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9. MAC Protocols MACA Protocol
Jan 10, 2000
MAC Protocols MACA Protocol
RTS(Request To Send), CTS(Clear To Send)
Transmitter driven
Three-way handshake
Hidden terminal problem still exists
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10. Challenges of Routing Protocol
Jan 10, 2000
Challenges of Routing Protocol
The topology may changes quite often.
The router moves around dynamically.
The life time of a link decreases.
Lots of routing information are useless.
Hard to determine a route to the destination.
Network bandwidth
Power consumption
Convergence issues
Storage overhead
Computational overhead
Loop free
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11. Characterization of Ad Hoc Routing Protocols
Jan 10, 2000
Characterization of Ad Hoc Routing Protocols
電信研究所 曾志成

12. Table-Driven Routing Protocols
Jan 10, 2000
Table-Driven Routing Protocols
Each node respond to changes in network topology by propagating updates throughout the network.
Always a ready path for any O-D pair.
Low route delay, Bandwidth inefficiency
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13. Distance Vector Routing
Jan 10, 2000
Distance Vector Routing
Distributed Bellman-Ford
Each router
contains a routing table.
periodically broadcasts to each of its neighbor routers its view of the distance to all hosts.
computes the shortest path to each host based on the information advertised by each of its neighbors.
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14. Distance Vector Routing Counting-to-Infinity
Jan 10, 2000
Distance Vector Routing Counting-to-Infinity
Router A is “down”
Router A is “up” A B C D E A B C D E 1 3 5 7 .  2 4 6 8 .  3 5 7 .  4 6 8 .   1  2  3  4
電信研究所 曾志成

15. Link State Routing Who are my neighbors?
Jan 10, 2000
Link State Routing
Who are my neighbors?
HELLO packet
Computes the cost between my neighbors.
Builds up a link-state packet.
Broadcasts the link-state packet.
Flooding
Computes a new path.
Dijkstra algorithm
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16. Destination-Sequenced Distance-Vector Routing (1)
Jan 10, 2000
Destination-Sequenced Distance-Vector Routing (1)
Each entry of routing table is marked with a sequence number assigned by destination nodes.
Freedom from loops in routing table.
Two possible types of packet: full dump and incremental.
The route labeled with the most recent sequence number is used, if ties, the one with the smallest metric is used.
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17. Destination-Sequenced Distance-Vector Routing (2)
Jan 10, 2000
Jan 10, 2000
Destination-Sequenced Distance-Vector Routing (2) 8 7 6 5 4 3 2 1
S406_MH1
S128_MH2
S564_MH3
S710_MH4
S392_MH5
S076_MH6
S128_MH7
S050_MH8
SEQ NO.
Metric
Next
Des 4 5 3 2 8 6 1 7 8 7 6 5 4 3 2 1
S516_MH1
S238_MH2
S674_MH3
S820_MH4
S502_MH5
S186_MH6
S238_MH7
S160_MH8
SEQ NO.
Metric
Next
Des 1
電信研究所 曾志成
Chih-Cheng Tseng

18. Clusterhead Gateway Switch Routing (CGSR) (1)
Jan 10, 2000
Clusterhead Gateway Switch Routing (CGSR) (1) 5 4 3 6 8 1 7 2
Node
Gateway
Cluster Head
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19. Clusterhead Gateway Switch Routing (CGSR) (2)
Jan 10, 2000
Clusterhead Gateway Switch Routing (CGSR) (2)
Hierarchical architecture.
Cluster head selection algorithm.
Least Cluster Change(LCC) clustering algorithm.
Use DSDV as underlying routing scheme with heuristic cluster-head-to-gateway routing approach.
Routing table and cluster member table.
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20. The Wireless Routing Protocol (WRP) (1)
Jan 10, 2000
The Wireless Routing Protocol (WRP) (1)
(0,J)
(0,J) J 10 J
(2,K) 10
(2,K) 1 5 B I B I 1
(2,K)
(2,K) K K
(1,K)
(infinity,-)
(0,J)
(0,J) J J
(10,B) B I B I
(10,I)
(10,I) K K
(11,B)
(infinity,-)
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21. The Wireless Routing Protocol (WRP)(2)
Jan 10, 2000
The Wireless Routing Protocol (WRP)(2)
Each node responsible for maintaining four table:
Distance table (distance to each node from each neighbor and predecessor)
Routing Table (shortest distance and predecessor to each node)
Link-Cost Table
Message retransmission list(MRL) table
MRL records which updates in an update message need to be retransmitted and which neighbor should acknowledge the retransmission.
Hello Message required.
Avoid “count-to-infinity”.
Path-Finding Algorithm.
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22. Comparison (Table-Driven)
N =number or nodes in the network. D =diameter. h =height of routing tree
x =number of nodes affected by topological change
*WRP can use hierarchically. ** There is a separate protocol can support multicast.

23. Source-Initiated On-Demand Routing Protocols (1)
Jan 10, 2000
Source-Initiated On-Demand Routing Protocols (1)
Create routes only when desired by the source node.
Route discovery process.
Route maintenance process.
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24. Ad Hoc On-Demand Distance Vector Routing (1)
Jan 10, 2000
Ad Hoc On-Demand Distance Vector Routing (1) N2
destination N2
destination N5 N8 N5 N8
source N1 N1 N7 N4 N7
source N4 N3 N6 N3 N6
Propagation of RREQ
Path of the RREP to the source
電信研究所 曾志成

25. Ad Hoc On-Demand Distance Vector Routing (2)
Jan 10, 2000
Ad Hoc On-Demand Distance Vector Routing (2)
Build on DSDV.
Pure on-demand route acquisition system.
Path recovery process: broadcast RREQ packet with sequence number.
The destination or intermediate node responds by unicasting a RREP packet back to the neighbor from which it first receive RREQ.
Only supports symmetric link.
Route maintenance: link failure notification is propagated.
Hello message can be used, but not required.
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26. Dynamic Source Routing (DSR) (1)
Jan 10, 2000
Dynamic Source Routing (DSR) (1) N2
destination
N1-N2
N1-N2-N5 N1 N5 N8 N2
destination
N1-N2-N5-N8
N1-N2-N5-N8
N1-N3-N4
N1-N3-N4-N7
N1-N2-N5-N8 N5 N8
source N1
N1-N3-N4 N7 N4 N1
N1-N3-N4
N1-N3-N4-N6 N1
N1-N3 N7
source N4 N3 N6 N3 N1
Building of the route record during route discovery
Propagation of the route reply with the route record
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27. Dynamic Source Routing (DSR) (2)
Jan 10, 2000
Dynamic Source Routing (DSR) (2)
Each node maintain a route cache.
Route discovery: broadcast route request packet. Route reply is generated when reach either the destination or intermediate node.
Piggyback if no symmetric links.
Route maintenance: route error packet are generated when data link layer report, and route cache contained the hop are truncated.
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28. Temporally Ordered Routing Algorithm (TORA) (1)
Jan 10, 2000
Temporally Ordered Routing Algorithm (TORA) (1) B C B C A A D D G G E E F F
Assume G is the destination B C B C A A D D G G E E F F
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29. Temporally Ordered Routing Algorithm (TORA) (2)
Jan 10, 2000
Temporally Ordered Routing Algorithm (TORA) (2)
Provide multiple routes.
Three basic function:
Route creation
Route maintenance: concept of link reversal.
Route erasure: using clear packet.
Establish Directed Acyclic Graph (DAG) similar to Lightweight Mobile Routing (LMR).
Require synchronized clocks.
Similar to the “count-to-infinity” problem.
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30. Associativity-Based Routing (ABR) (1)
Jan 10, 2000
Associativity-Based Routing (ABR) (1)
DEST BQ
SRC
SRC
RN[1]
DEST
LQ[H]
SRC
RN[0]
DEST
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31. Associativity-Based Routing (ABR) (2)
Jan 10, 2000
Associativity-Based Routing (ABR) (2)
New routing metric: degree of association stability - connection stability of one node with respect to another node over time and space.
Three phase:
Route discovery: broadcast query and await-reply, metric by association stability.
Route reconstruction (RRC)
Route Deletion
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32. Associativity-Based Routing (ABR) (3)
Jan 10, 2000
Associativity-Based Routing (ABR) (3)
RRC in ABR:
SRC Node Movement
DEST Node Movement
Intermediate Nodes (Ins) Movement
Upper Arm IN’s Moves
Lower Arm IN’s Moves
Subnet-Bridging MH Movement
Concurrent Nodes Movement: 7 cases...
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33. Signal Stability Routing (SSR) (1)
Jan 10, 2000
Signal Stability Routing (SSR) (1)
Route base on the signal strength between nodes and a node’s location stability.
Cooperative protocols:
Dynamic Routing Protocol
Signal Stability Table
Routing Table
Static Routing Protocol: passing packet up the stack if it is receiver or looking up in RT.
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34. Comparison of Source-Initiated On-Demand Routing Protocols

35. Comparison Between AODV and DSR
Jan 10, 2000
Comparison Between AODV and DSR
The communication overhead of DSR is larger.
The memory overhead of DSR is larger.
AODV require symmetric link.
DSR not using periodic routing advertisements.
DSR allow multiple routes to destination.
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36. Proactive/Table-Driven Protocols
Jan 10, 2000
Proactive/Table-Driven Protocols
Attempts to continuously evaluate the routes within the network
Always a ready path for any O-D pair.
Distance vector: Each router maintains a table giving the distance from itself to all possible destination.
Link state: Each router maintains a complete picture of the topology of the entire network.
Low route delay, Bandwidth inefficiency
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37. Reactive/On-Demand Protocols
Jan 10, 2000
Reactive/On-Demand Protocols
Invoke a route determination procedure on demand only
Route construction/discovery
Route maintenance
Route optimization
Long route discovery delay
Not applicable for real-time communication
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38. Jan 10, 2000
Jan 10, 2000
Zone Routing Protocol
A routing zone is defined to includes the nodes whose distance is at most some predefined number rZONE.
Inside the zone: proactive
Outside the zone: reactive
Only nodes at the boundary
of zone are queried
電信研究所 曾志成
Chih-Cheng Tseng

39. Signal Stability-Based Adaptive Routing
Jan 10, 2000
Jan 10, 2000
Signal Stability-Based Adaptive Routing
Dynamic Routing Protocol (DRP)
Forwarding Protocol (FP)
Signal Stability Table (SST)
Routing Table (RT)
電信研究所 曾志成
Chih-Cheng Tseng

40. Cluster-Based Routing
Jan 10, 2000
Cluster-Based Routing
Dividing the topology into a number of overlapping clusters.
Using broadcast routing and connectionless packet forwarding approach.
電信研究所 曾志成

41. Jan 10, 2000
Conclusions
Some issues in the design of ad hoc networks are pointed out.
The MAC protocols need to solve the hidden terminal problem.
The routing protocols have to be able to adapt to the dynamic topology changes.
QoS guaranteed needs to be addressed if multimedia application is considered.
電信研究所 曾志成