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

Introduction to Ad Hoc Mobile Wireless Networks

電機學院電信研究所曾志成

[email protected]

Jan 10, 2000

電信研究所曾志成

2

Outline

Introduction Features Network architectures MAC protocols Routing protocols Conclusions

Jan 10, 2000


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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

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4

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

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Network ArchitecturesHierarchical

Nodes are partitioned into clusters Some nodes are chosen as cluster

heads Properties:

easy to manage mobility sub-optimal routing

tie r- 2 ne tw o rk

tie r- 1 ne tw o rk

tie r- 1 ne tw o rk

tie r- 1 ne tw o rk

tie r- 1 ne tw o rk

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Network ArchitecturesFlat 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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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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8MAC ProtocolsTo Sense Or Not To Sense?

Hidden terminal problem1. A transmits to B

2. C wants to transmit to B. It does not hear A’s transmission, accesses the channel and collides.

A B C

r a d i oh o r i z o n

Exposed terminal problem1. B transmits to A2. C wants to transmits to D. It hears B’s transmission and unnecessarily defers.

A B C D

radiohoriz on

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MAC ProtocolsMACA Protocol

RTS(Request To Send), CTS(Clear To Send) Transmitter driven Three-way handshake Hidden terminal problem still exists

A B

C

R T S

ra d io ho rizo n

A B

C

C T S

ra d io ho rizo n

A B

C

D A T A

ra d io ho rizo n

b lo c k e d fro m T x b lo c k e d fro m T x

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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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Characterization of Ad Hoc Routing Protocols

CGSR

DSDV WRP

Table-driven

AODV DSR

TORA

L M R

SSR

ABR

Source-initiated on-Demand

Ad hoc Routing Porotocols

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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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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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14Distance Vector Routing Counting-to-Infinity

Router A is “down”A B C D E

1335577..

2244668..

3335577..

4444668..

Router A is “up”

A B C D E

1111

222

33

4

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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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16Destination-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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8

7

6

543

2

1

1

Destination-Sequenced Distance-Vector Routing (2)

87654321

66664222

32120212 S406_MH1

S128_MH2S564_MH3S710_MH4S392_MH5S076_MH6S128_MH7S050_MH8

SEQ NO.MetricNextDes

87654321

66664226

32120213 S516_MH1

S238_MH2S674_MH3S820_MH4S502_MH5S186_MH6S238_MH7S160_MH8

SEQ NO.MetricNextDes

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18Clusterhead Gateway Switch Routing (CGSR) (1)

1

2

34

5

6

7

8

NodeGatewayCluster Head

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19Clusterhead 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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The Wireless Routing Protocol (WRP) (1)

J

IB

K

(0,J)

(2,K)

(2,K)

(1,K)

J

IB

K

(0,J)

(2,K)

(2,K)

(infinity,-)

J

IB

K

(0,J)

(10,I)

(10,B)

(infinity,-)

J

IB

K

(0,J)

(10,I)

(11,B)

1010

1

1 5

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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.

Comparison (Table-Driven)

PARAMETERS DSDV CGSR WRP

Time Complexity O(d) O(d) O(h)

CommunicationComplexity

O(x=N) O(x=N) O(x=N)

Routing philosophy Flat Hierarchical Flat*

Loop free Yes Yes Yes ,but notinstantaenous

Multicast capability No No** No

Number of required tables Two Two Four

Frequency of updatetransmissions

Periodicallyand asneeded

Periodically Periodicallyand as needed

Update transmitted to Neighbors Neighborsand clusterhead

Neighbors

Utilizes sequence numbers Yes Yes Yes

Utilizes hello message Yes No Yes

Critical nodes No Yes No

Routing Metric ShortestPath

ShortestPath

Shortest Path

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.

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23Source-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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24Ad Hoc On-Demand Distance Vector Routing (1)

N1

N2

N3

N4

N5

N6

N7

N8

N1

N2

N3

N4

N5

N6

N7

N8

source

source

destinationdestination

Propagation of RREQ Path of the RREP to the source

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25Ad Hoc On-DemandDistance 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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Dynamic Source Routing (DSR) (1)

N1

N2

N3

N4

N5

N6

N7

N8

N1

N2

N3

N4

N5

N1

N7

N8source

N1

N1

N1-N2

N1-N3

N1-N3-N4

N1-N3-N4

N1-N2-N5

N1-N3-N4-N6

N1-N3-N4-N7

destination

N1-N2-N5-N8

N1-N2-N5-N8

N1-N2-N5-N8N1-N3-N4

source

destination

Building of the route record during route discovery

Propagation of the route reply with the route record

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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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28Temporally Ordered Routing Algorithm (TORA) (1)

AB C

D

EF

G

AB C

D

E

AB C

D

E

AB C

D

E

F

F F

G

G G

Assume G is the destination

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29Temporally 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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Associativity-Based Routing (ABR) (1)

SRC

SRC

RN[1]

BQDEST

RN[0]

LQ[H]DEST

SRC

DEST

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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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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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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.

PERFORMANCE PARAMETERS AODV DSR TORA ABR SSR

Time complexity(initialization) O(2d) O(2d) O(2d) O(d+z) O(d+z)

Time complexity(Postfailure) O(2d) O(2d) or 0* O(2d) O(l+z) O(l+z)

Communication complexity(initialization)

O(2N) O(2N) O(2N) O(N+y) O(N+y)

Communication complexity(postfailure)

O(2N) O(2N) O(2x) O(x+y) O(x+y)

Routing philosophy Flat Flat Flat Flat Flat

Loop-free Yes Yes Yes Yes Yes

Multicast capbility Yes No No** No No

Beaconing requirements No No No Yes Yes

Multiple route possibilities No Yes Yes No No

Routes maintained in Route Table Route Table Route Table

Route Table

Route Table

Utilizes route cache/table expiration timers

Yes No No No No

Route reconfiguration methodology Erase route, notify source

Erase route, notify source

Link reversal, route repair

Localized broadcast query

Erase route, notify source

Routing metric Freshest and shortest path

Shortest Path

Shortest path

Associativity and shortest path and others***

Associativity and stability

Comparison of Source-Initiated On-Demand Routing Protocols

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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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36Proactive/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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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

A

B

C

D

E

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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

FE

C

A

G

SB

D

H

Jan 10, 2000


39Signal Stability-Based Adaptive Routing

Dynamic Routing Protocol (DRP) Forwarding Protocol (FP) Signal Stability Table (SST) Routing Table (RT)

Applicationsand

network layerprotocols

FP

Extended interface

Device driver

DRP

SSA

Host Signal strength Last Clicks Set

Y

Z

Signal Stability Table

Destination Next hopYZ

Routing Table

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Cluster-Based Routing Dividing the topology into a

number of overlapping clusters. Using broadcast routing and

connectionless packet forwarding approach.

tier-2 network

tier-1 network

tier-1 network

tier-1 network

tier-1 network

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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.

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

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

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

Documents

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

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

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