ad hoc networks - technische universität ilmenau · ad hoc networks advanced mobile ... – fixed...

Integrated Communication Systems Group Ilmenau University of Technology

Ad Hoc Networks

Advanced Mobile Communication Networks

Integrated Communication Systems Group

Advanced Mobile Communication Networks, Master Program

Outline

• Introduction

• Medium Access Control (MAC) in Multi-Channel Scenario

• Routing • Example from ICS Research

• Conclusion • References

2


Advanced Mobile Communication Networks, Master Program 3

Introduction



Mobile Ad Hoc Networks (MANETs)

• Spontaneous federation of wireless devices – No infrastructure (base station / access point), no backbone – Devices can be mobile

• Packet-based forwarding – Each device must serve as a router – Routes between devices can span multiple hops

• Ad hoc networks are self organizing – No central components

4

Transmission range r

r



Advantages and Application Scenarios

• Advantages – Easy and cheap deployment

• E.g. using 802.11 in license free ISM band (2.4 GHz) – Reduced transmission power – Robust to component failures

• Application: where there is no access to infrastructure – Military applications

• Groups of soldiers, tanks, planes... – Civil applications

• Conferences, exhibitions, meetings, lectures, gaming, … – Car-to-car-communication, network for taxis, police, … – Extension of cellular networks

• Disaster recovery ( Int. Graduate School on Mobile Communications) – After crash of infrastructure (e.g. telephone network after earthquake) – Rescue

5



Applications

6

Automotive networks

Military communications

Interactive lectures



Scenarios

7

Vehicular Ad Hoc NETworks (VANETs)

Wireless Sensor Networks (WSNs)

Wireless Mesh Networks (WMNs)



Scenarios

8

Multi-hop communication (Ad Hoc mode)

Infrastructure mode

Mobile gateway (works in two modes) Mobile in

infrastructure mode

High bit rate data coverage

Low bit rate data coverage

Border region (no coverage)



MANET Properties

• Highly dynamic topology – Mobility of devices – Changing of quality of wireless channel (fading) – Partitioning and merging of ad hoc networks possible

• Asymmetric / unidirectional links – Different quality in both directions

• Wireless medium is semi-broadcast medium – Hidden and exposed terminals

• Limited battery capacity of mobile devices – Additional battery drain due to (e.g.) routing functionality

• Limited bandwidth – Additional bandwidth required for routing and MAC functionality

• Time synchronization difficult – Problem for low power modes (e.g. sleeping periodically)

• Security mechanism hard to apply – Every devices must be able to forward packets no encryption of routing

headers

9



Medium Access Control (MAC) in Multi-Channel MANET



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

11



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 will this 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 switched dynamically

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

12



Problems Related to the Use of Multiple Channels

13

C B A

Interface1

Interface2

Interface1

Interface2

Interface1

Interface2 Interface3

Ch1

Ch11

Ch6

Ch6

Ch11 Ch1 Ch6

Ch6



Multi-Channel MAC Approaches

• Dedicated control channel – One channel for control messages and others for data traffic – Needs usually 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 interface

• Common hopping sequence

– All nodes follow the same channel hopping sequence – Works with one interface

• Multiple rendezvous

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

14



Dedicated Control Channel

15

A B

RTS CTS DATA

Ch0 (control) Ch1 Ch2 Ch3

RTS1 CTS1 Data (A B)

RTS2 CTS2

Data (C D)

A B

D

2 C

1 3

2 4

A B

D

1 C A B

D

3 C

C D

Ch0

Ch1

Ch0

A B

D

4 C Ch2

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

- C exchanges RTS/CTS with D to determine the channel to be used 4. After that, C sends data to D as well.

16



Split Phase

17

Control phase

Wai

t for

dat

a ph

ase

Data phase

Ch0 Ch1 Ch2 Ch3

RTS1 CTS1 RTS2 CTS2

Data (C D)

RTS CTS DATA

1 2

3

A B

D

1 C

Ch0

A B

D 2 C

C D

Ch0

A B

A B

D 3 C

A B and C D

Ch0

Ch2

Data (A B)



Split Phase

• Control phase 1. A wants to send data to B (AB)

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

2. After a while, C wants to send data to D as well (CD) − C 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 wait

for the start of the following data phase

• Data phase

3. A begins sending data to B and C begins sending data to D Notice that the channel (Ch0) is used to send data as well. Moreover, no control

messages are allowed to be exchanged during a data phase

18



Common Hopping Sequence

A B C D

No

com

mun

icat

ion

3 6

RTS CTS DATA

x y

Ch0 Ch1 Ch2 Ch3

RTS1 CTS1 Data (A B)

RTS2 CTS2 Data (C D) Data (A D) RTS3 CTS3 Idle

Idle

Idle

Idle

1

4

7 2

3 5

6

8

Idle

A B

D C

Ch0

1

A B

D C

Ch0

2

No

com

mun

icat

ion

A B

D C

Ch2

4

A B

D C

Ch2

5

Ch0

Ch0

19



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 B 2. A sends data to B 3. There is no communication 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 D

5. C sends data to D 6. There is no communication between nodes (y)

20



Multiple Rendezvous

A B 1

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

A B 2

3

Ch3 Ch0

Ch2 Ch3

A B Ch0 Ch2

4 A B Ch1 Ch1

A B Ch1 Ch1

5

A B

A B Ch1 Ch2

Ch0 Ch0

A B Ch2 Ch3

10

11

12

13

Ch0 Ch1 Ch2 Ch3

RTS/CTS Data exchange Hopping sequence Actual hopping sequence of A Actual hopping sequence of B

Default hopping sequence of A Default 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

21



Multiple Rendezvous

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

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

– 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 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 hopping sequence

22



Use of Multiple Channels - Discussion

Dedicated control channel and split phase (referred to as single rendezvous 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 as multiple 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

23



Routing in (Single Channel) MANETs

24



Routing Challenges

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

• Dynamics 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

25



Routing Protocols for MANETs

• Protocols for wired networks (e.g., RIP, OSPF) cannot be applied – Slow convergence – High overhead

• MANET routing protocols must converge fast with low bandwidth consumption for control traffic

• Different metrics for “shortest path” possible – Minimum number of hops – Minimum delay – Minimum packet loss probability – Minimum congestion (load balancing) – Minimum interference – Maximum signal stability, stable route – Maximum battery lifetime of mobile device – Maximum lifetime of entire network

• E.g. until network is partitioned due to nodes running out of power



Classification of Routing Protocols in MANETs

Topology based: • Proactive or table-driven (Examples: DSDV, GSR, WRP, OLSR)

– Routes are calculated before needed – Keep routing information to all nodes up-to-date

• Reactive or on-demand (Examples: AODV, DSR, LMR, ABR) – Routes are only calculated when needed – Do not keep routing information to all nodes up-to-date

• Hybrid (Examples: ZRP, SHARP, Safari) – Reactive and Proactive at the same time

27

Ad hoc routing approaches

Topology based

Proactive Reactive Hybrid

Position based (Geographical)

Greedy forwarding

Face routing Hybrid



Proactive Routing Protocols

• Nodes constantly construct and maintain routes to all other nodes – Distance Vector Routing

• Each node computes for each destination – Next hop on the route – Length of the route

• These information are sent to all neighbors periodically • Examples

– Wired networks: Routing Information Protocol (RIP) – Ad hoc networks: Destination-Sequenced Distance Vector Protocol (DSDV)

– Link State Routing • Each node sends periodically

– Its own link state – The link state received by the neighbors

• Thus, each node knows entire network topology • Examples

– Wired networks: Open Shortest Path First (OSPF) – Ad hoc networks: Optimized Link State Routing (OLSR)



Reactive Routing Protocols

• Basic principle – Node knows only routes that it is currently using – No periodic route maintenance

• Tasks of a reactive routing protocol – Route discovery

• Triggered if route to destination is unknown – Route maintenance

• Only for routes that are currently in use • Comparison to proactive protocols

– Advantages • No unnecessary construction & maintenance of routes • No periodic messages lower resource consumption

– Disadvantages • Delay at the beginning of communication due to route discovery • Control overhead depends on number of connections and mobility

29



Route discovery – Sender S floods route request (RREQ) for destination T

• RREQ contains source and destination address – Nodes that forward RREQ save pairs of source address and nodes

from which the RREQ was received • Construction of reverse path to sender S • Only works for bidirectional links!

– When RREQ reaches destination T a route reply (RREP) is generated • RREP contains destination and source address

– RREP is forwarded towards S on reverse path • Construction of forward path to destination T

– Forward and reverse path are used for forwarding data packets • If route from S to T is established, we have automatically a route from

T to S

Ad-hoc On-Demand Distance Vector Routing (AODV)



AODV: Flooding of RREQs I

Nodes in mutual transmission range (bidirectional links)

Nodes that have already received RREQ

B A

E

F

H C

G

D Sender

Destination

S

T

Route discovery from S to T:



AODV: Flooding of RREQs II

• RREQ is transmitted by broadcast – Received by all nodes in transmission range

32

B A

E

F

H C

G

D

Broadcast

S

T

RREQ



AODV: Flooding of RREQs III

• Every node that receives RREQ forwards it by broadcast – Of course S does not forward its own RREQ

33

B A

E

F

H C

G

D

S

T

RREQ

RREQ



AODV: Flooding of RREQs IV

• Nodes remember “from where” the RREQ was received – If multiple RREQ are received the one with the lowest hop count is

selected – Reverse path is constructed

34

B A

E

F

H C

G

D

Constructed reverse path

S

T

RREQ

RREQ



AODV: Flooding of RREQs V

• Duplicate RREQ are detected by sequence numbers and discarded – Requires state maintenance

35

B A

E

F

H C

G

D


S

T

RREQ



AODV: Flooding of RREQs VI

• Destination T has received the RREQ – Complete reverse path from T to S has been constructed

36

B A

E

F

H C

G

D

S

T

RREQ




AODV: Flooding of RREQs VII

B A

E

F

H C

G

D

S

T

RREP RREP

RREP

RREP

RREQ


• Node T replies with RREP to S using reverse path – Each hop on reverse path can be directly addressed (no broadcast)



AODV: Flooding of RREQs VII

B A

E

F

H C

G

D

S

T

Constructed forward path


• Forward path from S to T is constructed – Can be used for data transport between S and T (bidirectional)

• Unused reverse path entries will be discarded after timeout



• Each node maintains a destination sequence number – Determines the “freshness” of routing information – Sequence number is always increased before sending

• … a RREQ to avoid conflicts with old reverse path entries • … a RREP

• RREQ contains last known sequence number of destination

• RREP also contains sequence number

AODV: Sequence Numbers



• Reverse/Forward path entries are discarded after timeout – Soft state approach

• Entries are “refreshed” if data is transmitted on a route – Reset of timers – Optional hello messages to check if next hop is still available

• Link failure detection – No ACK on MAC-Layer – No hello messages

• Handling of link failures: Sending a route error (RERR) packet – Forwarded to sender – Sender initiates new route discovery with RREQ – RREQ contains new sequence number

• Loops are prevented by sequence numbers – A sends to D, link failure between C and D

AODV: Route Maintenance

A B C D

E



Example from ICS Research Routing in Ad Hoc Networks



Example from Mehdi Harounabadi’s Work

• Proposal: Self Organized Routing in Cognitive Radio Ad hoc Networks (CRAHNs) Using Opportunistic Geographical Routing

• Problems in conventional routing schemes: – Dead-end nodes

• Longer packet delays – QoS

• Lack of QoS support • No service differentiation

– Route maintenance • Costs of rerouting • Adapting to network changes

42

Destination

Source



Introduction to Geographical Routing

• Based on location information – GPS information

• Forwarding sector – Candidate neighbors

• Hop-by-hop decision making

– No need for topology information – Based on the destination location

• Assumption: destination location exists in source

• Local information

– Periodic or on-demand Beacons

Destination

Forwarding Sector

Source

43



Proposed Contributions

• 1st contribution: – Potential dead-end avoidance

• Avoid existing dead-end nodes • Consider potential dead-end nodes

• 2nd contribution: – Route maintenance

• Fast • Low cost mechanism

• 3rd contribution: – QoS-based relay selection

• Data flow requirements • Conditions at candidate nodes (error rate, mobility, energy, etc.)

44



• Prioritization of candidates in source – Utility function

• QoS requirement • Beacon information

– (D, L) • Resource Map

– (PU)

• Decision in candidates – Environmental condition

• (E, M)

Destination

A

B

Source

C

E

F

PU

ACK

D: Distance L: Load PU: PU appearance E: Error rate M: mobility PU: Primary user

Opportunistic Geographical Routing

45



Learning

ACK

ACK

A B C Source

Destination A

B

Source

C

E

F

PU

Wait (t1)

Wait (t2)

t2 < t1

Priority list for 1st packet {A, B, C}

Learning Algorithm

Priority list for 2nd packet {B, A, C}

46



Potential Application

• Packet routing in disaster scenarios • Nodes:

– Used on the ground by • Rescue teams • Command center • Victims

– In the air • UAV swarm

PU

Delay sensitive traffic Delay tolerant traffic

Command Center Rescue Teams

Victims

UAV

47



Conclusion



Current Research in Ad Hoc Networks

• Research activities in many areas – Auto-configuration

• E.g. distributed assignment of IP addresses – Service Awareness

• Usually networks are constructed to access services – Multicast-Routing

• Many group applications are based on multicast communication – Integration with wired Internet

• How to apply mobility supporting protocols (e.g., MobileIP) and routing in a hybrid context?

– Power Control • Controlling topology and reducing interference by changing transmission

power – Security

• Recall that this is difficult in a decentralized setting – Scalability, ...



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

50



References

51

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

Publication, 2004 Medium 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.txt Interworking 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 Ilmenau Helmholtzplatz 5 Zuse Building, room 1032/1070 D-98693 Ilmenau

fon: +49 (0)3677 69 2819/4123 fax: +49 (0)3677 69 1226 e-mail: mitsch, [email protected]

www.tu-ilmenau.de/ics


Prof. Dr.-Ing. habil. Andreas Mitschele-Thiel MSc. Mehdi Harounabadi

Contact

http://www.tu-ilmenau.de/ics

ad hoc networks - technische universität ilmenau · ad hoc networks advanced mobile ... – fixed...

Documents