ad hoc networks-mscsp.ppt - technische universität ilmenau · ad hoc networks summer semester...

Integrated Communication Systems GroupIlmenau University of Technology

Ad Hoc Networks

Summer Semester 2012

Integrated Communication Systems Group

Outline

• Introduction

• Medium Access Control (MAC)

• Routing

• Interworking with Infrastructure

• Conclusions

• References

Advanced Networking, Master Program 2



Introduction


Basics

• Short-lived networks

• Standards– 802.11 a/b/g– 802.15 (Bluetooth)– 802.15a (UWB)– 802.15.5 (Zigbee)– HIPERLAN/2

• Two main tasks in each node– Local task, i.e. message is processed in the node– Routing, i.e. message is routed to another node



Characteristics

• No fixed infrastructure

• Dynamic topology (due to nodes mobility)

• Multi-hopping

• Self-organized networks: addressing, routing, clustering, locationmanagement, power control, etc.

• Limited security

• Bandwidth constraints: congestion is a norm

• ……..



Applications


Automotive networks

Military communications

Interactive lectures


Scenarios


Vehicular Ad Hoc NETworks (VANETs)

Wireless Sensor Networks (WSNs)

Wireless Mesh Networks (WMNs)


Scenarios


Multi-hop communication(Ad Hoc mode)

Infrastructuremode

Mobile gateway (works in two modes) Mobile in

infrastructure mode

High bit rate data coverage

Low bit rate data coverage

Border region (no coverage)



Medium Access Control (MAC)


Basics

• Multiple users compete for access to a common, shared medium.Thus, suitable MAC mechanisms are required see Medium Access Schemes Lecture for details

• Problems– Hidden and exposed terminals– Problems related to the use of multiple channels

- Node has a single interface- Node has multiple interfaces

– Problems related to broadcast- Redundancy: all nodes forward broadcast packets same packet is

received from many nodes- Contention: nodes compete to access the medium if the medium is free,

broadcast packet will be sent- Collision: no RTS/CTS dialog hidden terminal problem



Hidden and Exposed Terminals

• Hidden terminals– A sends to B, C cannot receive A signal– C wants to send to B, C senses a “free” medium– Collision at B, A cannot receive C signal– A is “hidden” for C

• Exposed terminals– B sends to A, C wants to send to D– C has to wait (it is inside the radio range of B).– however, A is outside the radio range of C. Therefore, waiting is not

necessary– C is “exposed” to B


A B C

A B C D


Problems Related to the Use of Multiple Channels

• Node has a single interface– Fixed at a particular channel (traditional solution)

- Problems: how to synchronize with others using the same channel, etc.– May be switched among different channels

- Problems: how to select the suitable channel to switch to, how long willthis switch take, how long can you use this channel, etc.

• Node has multiple interfaces– Each interface may be fixed at a particular channel or switched

dynamically among different channels– A combination between fixed and dynamically switching interfaces,

i.e. some are fixed at certain channels, while others are switcheddynamically

– Problems: how to select suitable channels for each interface(depends on neighbors information), when to switch, how tosynchronize with other nodes in the network, broadcasting, etc.



Problems Related to the Use of Multiple Channels


CBA

Interface1

Interface2

Interface1

Interface2

Interface1

Interface2Interface3

Ch1

Ch11

Ch6

Ch6

Ch11Ch1 Ch6

Ch6


Multi-Channel MAC Approaches

• Dedicated control channel– One channel for control messages and others for data traffic– Needs two or more interfaces

• Split phase– Communication in two phases

- Channel negotiation phase (a default channel is used by all nodes)- Data transfer phase (all channels are used to transmit data during this phase

including the default one)– Works with one interfaces

• Common hopping sequence– All nodes follow the same channel hopping sequence– Works with one interfaces

• Multiple rendezvous– Each node follows its own channel hopping sequence– Works with one interface



Dedicated Control Channel


A B

RTS CTS DATA

Ch0 (control)Ch1Ch2Ch3

RTS1 CTS1Data (A B)

RTS2 CTS2

Data (C D)

AB

D

2 C

1 3

24

AB

D

1 C AB

D

3 C

C D

Ch0

Ch1

Ch0

AB

D

4 CCh2

Ch1

Ch1


Dedicated Control Channel

• A wants to send data to B (AB)1. Selection of communication channel

A exchanges RTS/CTS with B to determine the channel to be used C and D receive RTS/CTS due to using a common single channel for signaling

2. After the channel has been selected, A sends data to B

• After some time, C wants to send data to D (CD)3. Selection of communication channel

- A exchanges RTS/CTS with D to determine the channel to be used4. After that, C sends data to D as well.



Split Phase


Control phase

Wai

t for

dat

a ph

ase

Data phase

Ch0Ch1Ch2Ch3

RTS1 CTS1 RTS2 CTS2

Data (C D)

RTS CTS DATA

1 2

3

AB

D

1 C

Ch0

AB

D2 C

C D

Ch0

A B

AB

D3 C

A B and C D

Ch1

Ch2

Data (A B)


Split Phase

• Control phase1. A wants to send data to B (AB)

A exchanges RTS/CTS with B to determine the channel to be used (Ch0 in thisexample)

2. After a while, C wants to send data to D as well (CD) A exchanges RTS/CTS with D to determine the channel that should be used (ch2 in

this example)Notice that there are no data exchanged between nodes yet. They have to waitfor the start of the following data phase

• Data phase3. A begins sending data to B and C begins sending data to DNotice that the channel (Ch0) is used to send data as well. Moreover, no controlmessages are allowed to be exchanged during a data phase



Common Hopping Sequence

A B C D

No

com

mun

icat

e

3 6

RTS CTS DATA

x y

Ch0Ch1Ch2Ch3

RTS1 CTS1 Data (A B)

RTS2 CTS2 Data (C D)Data (A D)RTS3 CTS3Idle

Idle

Idle

Idle

1

4

72

3 5

6

8

Idle

AB

DC

Ch0

1

AB

DC

Ch0

2

No

com

mun

icat

e

AB

DC

Ch2

4

AB

DC

Ch2

5

Ch0

Ch0


Common Hopping Sequence

• All nodes follow the same hopping sequence. In our example, the hopping sequence is as follows: Ch0Ch1Ch2Ch3Ch0 ....

• A wants to send data to B (AB)1. Node A checks the hopping sequence, i.e. (Ch0 in the example) and

exchanges RTS/CTS with B2. A sends data to B3. There is no communications between nodes(x)

• C wants to send data to D as well (CD)4. Node C checks the hopping sequence, i.e. (Ch2 in the example) and

exchanges RTS/CTS with D5. C sends data to D .6. There is no communications between nodes(x(y)



Multiple Rendezvous

A B1

A and B are Idle A communicates with B A and B are Idle

A B2

3

Ch3Ch0

Ch2Ch3

A BCh0Ch2

4 A BCh1Ch1

A BCh1Ch1

5

A B

A BCh1Ch2

Ch0Ch0

A BCh2Ch3

10

11

12

13

Ch0Ch1Ch2Ch3

RTS/CTS Data exchange Hopping sequenceActual hopping sequence of AActual hopping sequence of B

Default hopping sequence of ADefault hopping sequence of B

1 2 3 4 5 6 7 8 9 10 11 12 13

A switches to the channel of B to

communicate with it


Multiple Rendezvous

• Each node has a special hopping sequence generated by applying anequation on a certain seed. Notice that the equation is known to all nodes

– Example equation: new channel = (old channel + seed) mod (number ofchannels)

– Seed varies between 1 and (number of channels) -1– When two neighbors meet at any time (switch to the same channel), seeds of

both are exchanged

• When a node A wants to communicate with another node B– Node A uses the current channel as well as the seed of B and calculates the

next channel of B– As soon as B switches to the next channel, A switches to the same channel

too and exchanges RTS/CTS with B followed by data exchange (steps 4 N)

• After finishing data communication, each node retains its hoppingsequence



Use of Multiple Channels - Discussion

Dedicated control channel and split phase (referred to as singlerendezvous protocols as well)• Advantages

– No synchronization required to determine the control channel– Efficient for networks with less density

• Disadvantages– Using single control channel can become the bottleneck under some

operating conditions, e.g. high number of nodes, etc.

Common hopping sequence and multiple rendezvous (referred to asmultiple rendezvous protocols as well)• Advantages

– Allow nodes to use several channels in parallel– Alleviate the rendezvous channel congestion problem

• Disadvantages– Essential challenge is the ensuring that the idle transmitter and

receiver will visit the same rendezvous channel



Routing


Routing-Challenges

• Classical approaches from fixed networks fail– Very slow convergence– large overhead

• Dynamic of the topology– frequent changes of connections, connection quality

• Limited performance of mobile systems– periodic updates of routing tables need energy without contributing to

the transmission of user data, sleep modes difficult to realize– limited bandwidth of the system is reduced even more due to the

exchange of routing information



Classification of Routing Protocols in MANET

• Proactive (table-driven): A centralized node to assign the IP addresses

– Routes are calculated before needed – Keep routing information to all nodes up-to-dateExamples: DSDV, GSR, WRP, OLSR

• Reactive (on-demand): – Routes are only calculated, when needed – Does not keep routing information to all node up-to-dateExamples: AODV, DSR, LMR, ABR

• Hybrid:– Reactive and Proactive at the same timeExamples: ZRP, SHARP, Safari



Ad Hoc On-Demand Distance Vector Routing (AODV)


Defintion

• Reactive routing protocol• Routes created on a demand basis

AODV contains 2 phases

• Path Discovery• Path Maintenance


Path Discovery (find a path)

Path Discovery consists of:• Route Request (RREQ)

• Route Reply (RREP)– Each neighbor either satisfies the RREQ by sending– A route reply RREP back to the source : if it has a route to the

destination– Rebroadcasts the RREQ to its own neighbors : if it has no route to

destination



Path Discovery (find a path)

• N1 wants to send a packet to N8 • Is the path from N1 to N8 in the Routing table?• N1 generates RREQ and sends it to its neighbour nodes• If a node receives a packet twice, it will discard it• The node sends a RREP to N1 if it knows a route to the destination N8• If not, the node broadcasts RREQ to its neighbour nodes• A route can be determined when the RREQ reaches a node that offers

reachability to the destination. (e.g., the destination itself).

Advanced Networking, Master Program 29AODV route discovery


Path Maintenance

Path Maintenance is needed when:• The topology of the network has changed• If the source node moves during an active session

– it can reinitiate the route discovery procedure to establish a newroute to the destination

• When either the destination or some intermediate node moves– a special RREP is sent to the affected source nodes– Periodic hello messages can be used to ensure symmetric links as

well as to detect link failures



AODV Advantages and Disadvantages

Advantages

• Nodes store only the routes that are needed• Need for broadcast is minimized• Reduces memory requirements• Quick response to link breakage in active routes• Scalable to large populations of nodes

Disadvantages

• Delay caused by route discovery process• Bidirectional connection needed




Interworking with Infrastructure


Problem Statements

• Two different mechanisms for mobility management• Two addressing schemes (hierarchical in the Internet, flat in Ad Hoc

networks)


N1

N2N3

N4N5

N6

MH

HAInternet

AP1 AP2

MHMH

CN

FA

MANETsMobility

management

e.g. MIP, HMIPv6, etc.

e.g. DSR, AODV, etc.

CN

WLAN

Flat addressing

Hierarchical addressing

FA


Solution Principles


N1N2

N3

N4N5

N6

MH with global address

HAInternet

AP1 AP2

GWGW

CN

FA

FA

Mobility management

e.g. MIP, HMIPv6, etc.

e.g. DSR, AODV, etc.


Solution Principles

• At least one node in a MANET should act as a gateway enablingcommunication with the rest of the world

• Interworking between mobility protocols operating ininfrastructured networks (e.g. MIP, HMIPv6, etc.) and MANETrouting protocols (e.g. DSR, AODV, etc.)

• Preferably each node aiming at accessing the Internet is assigneda global IP address



Research Issues and Challenges

• Gateway discovery and selection• Address auto-configuration• Routing


N1N2

N3

N7 N5

N6

MH

Internet

AP1 AP2

GWGW

CN

FA

N4

Flat routing

Hierarchical routing

HA


37

Ad hoc network layers and research challenges


Conclusions

• Lots of challenges to be solved in Ad Hoc networks• The application field determines which are more important• Research mainly focuses on

– Self-organizing and self-healing capabilities- Route selection and maintenance- Resources usage optimization- Gateway selection- Location update- Rapid initial configuration and dynamic reconfiguration- ….

– Continued operation and connectivity during mobility- Multi-hop handover dealing

– High reliability, availability and security



References


Introduction• S. Basagni, M. Conti, S. Giordano, I. Stomjmenovec: “Mobile Ad hoc Networking”, A John Wiley & Sons,

Publication, 2004Medium Access Control• J. Mo, H. W. So and J. Walrand: “Comparison of Multi-Channel MAC Protocols,” in Proc. of International

Workshop on Modeling Analysis and Simulation of Wireless and Mobile Systems (MSWiM), pp. 209 –218, Montréal, Quebec, Canada , October 2005.

• Y. Tseng, S. Ni, Y. Chen, and J. Sheu: “The broadcast storm problem in a mobile ad hoc network,”WINET Wireless Networks, vol. 8, no. 2–3, pp. 153–167, march–may 2002

• D. Kouvatsos, I. Mkwawa: “Broadcasting Methods in Mobile Ad Hoc Networks: An Overview,”Proceeding of the HetNet, UK, 2005.

Routing• AODV-http://www.ietf.org/rfc/rfc3561.txtInterworking with Infrastructure• J. Xi & C. Bettstetter: “Wireless multihop Internet access: Gateway discovery, routing, and addressing,”

Proc. Int. Conf. on 3rd Generation Wireless and Beyond, San Francisco, USA, 2002.


Visitors address:Technische Universität IlmenauHelmholtzplatzZuse BuildingRoom 1032D-98693 Ilmenau

fon: +49 (0)3677 69 2819e-mail: [email protected]

www.tu-ilmenau.de/ics


Univ.-Prof. Dr.-Ing. Andreas Mitschele-Thiel

Contact

ad hoc networks-mscsp.ppt - technische universität ilmenau · ad hoc networks summer semester...

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