adhoc networking and challenges

National Workshop on C. Rama Krishna NITTTR, ChandigarhMobile Communication Technology & Networking (MCTN-09)on March 14, 2009 at KIST, Bhubaneswar

C. Rama Krishna

Assistant Professor

Dept. of CSENITTTR, Chandigarh

Email: rkc_97 at yahoo.com


Outline

• History and Introduction

• Brief overview to Physical Layer

• Issues in Medium Access Control (MAC)

• Issues in Routing and Transport Layers

• Quality-of-Service Issues

• Security Issues

• Additional Resources


Cellular Technologies 2G Systems 2.5G Systems 3G Systems 4G Systems Next G Systems

Other Short-range Technologies Home RF Bluetooth ZigBee

Wireless LAN Technology

• 2.4 GHz Wireless LAN

• 5 GHz Wireless LAN

• Ad-hoc Mode

• Infrastructure Mode

Long Range Technologies

Internet

Which Technology ?


History and Introduction


History

• Packet Radio NETwork (PRNET) by DARPA - late 1960s• Military Communications• Disaster Management

• Survivable Packet Radio Networks (SURAN) – 1980s

• MANET group formed under Internet Engineering Task Force (IETF) – 1990s

• IEEE released 802.11 PHY and MAC standard – 1995 (later updated versions evolved)


What is an Ad hoc Network ?

• Network of wireless nodes (may be static/mobile)– No infrastructure (e.g. base stations, fixed links, routers,

centralized servers, etc.)– Data can be relayed by intermediate nodes– Routing infrastructure created dynamically

AB C

D

radio range of node A

traffic from A D is relayed by nodes B and C


• Does not depend on pre-existing infrastructure

• Ease to deploy

• Speed of deployment

• Anytime-Anywhere-Any device-Anyone (A4) network paradigm

Why an Ad hoc Network?


Ad hoc Network Example

• Communication between nodes may be in single/multi-hop

• Each of the nodes acts as a host as well as a router


Typical Applications

• Military environments• soldiers, tanks, planes

• Emergency operations• search-and-rescue

• Personal area networking• cell phone, laptop, etc.

• Civilian environments• meeting rooms, sports stadiums, hospitals, etc.

• Education• virtual classrooms, conferences, etc.

• Sensor networks• homes, environmental applications, etc.

• And many more …


Some Challenges

• Limited wireless transmission range

• Broadcast nature of the wireless medium• hidden terminal and exposed terminal

problems – MAC problem

• Packet losses due to: transmission errors and mobility

• Mobility-induced route changes – routing problem

• Battery constraints

• Ease of snooping - security problem


Physical Layer


IEEE 802.11 WLAN standards

Sl.No

Standard Specification

1 802.11 Physical Layer & MAC Layer2 802.11a Physical Layer

3 802.11b Physical Layer4 802.11c Support of 802.11 frames5 802.11d New support for 802.11

frames6 802.11e QoS enhancement in MAC7 802.11f Inter Access Point Protocol

8 802.11g Physical Layer9 802.11h Channel selection and

power control10 802.11i Security enhancement in MAC


• Supports networking in two modes:

• Infrastructure based WLAN using access points (APs)

• Infrastructure-less ad hoc networks – widely used in simulation studies and testbeds of MANET

IEEE 802.11 standard


Access Point (AP)

Basic Service Set (BSS)

Wire line

PC

Laptop

IEEE 802.11 based infrastructure WLAN


Independent Basic Service Set (IBSS)

Laptop

IEEE 802.11 based infrastructure-less Adhoc Network


IEEE 802.11 PHY Layer Specification

StandardParameter

802.11 802.11a 802.11b

Bandwidth 83.5MHz 300MHz 83.5MHz

Frequency band

2.4-2.4835 GHz

5.15-5.35 GHz and 5.725 – 5.825 GHz

2.4-2.4835 GHz

Channels 3 12 3

Data Rate( in Mbps)

1, 2 6, 9, 12, 18, 24, 36, 48 and 54

1, 2, 5.5, and 11

Transmission Scheme

FHSS, DSSSwith QPSK

OFDM (with PSK and QAM )

DSSS(with QPSK & CCK modulation)


• Present PHY Layer• IEEE 802.11, 11a, 802.11b and 802.11g

• Supports 1/ 2 /11/ 22/ 54 Mbps data rate in static indoor environment

• DSSS is not suitable for data rate more than 10Mbps

• OFDM based PHY layer design for high data rate transmission up to 54 Mbps [ 802.11a & g]

Physical Layer for high speed MANET


Medium Access Control (MAC) & Issues


Need for a MAC Protocol

• Wireless channel is a shared medium and bandwidth is a scarce resource

• Need access control mechanism to avoid collision(s)

• To maximize probability of successful transmissions by resolving contention among users

• To avoid problems due to hidden and exposed nodes

• To maintain fairness amongst all users

• MAC protocol design has been an active area of research in recent years


Classification of Wireless MAC Protocols

Wireless MAC protocols

Distributed Centralized

RandomAccess

HybridAccess

GuaranteedAccess

RandomAccess

• Guaranteed Access and Hybrid Access protocols require infrastructure such as Base Station or Access Point – Not suitable for MANETs • Random Access protocols can be operated in either architecture – suitable for MANETS


Distributed Random Access Protocols


Pure ALOHA MAC Protocol

• In pure ALOHA, frames are transmitted at completely arbitrary times.


The throughput for pure ALOHA is S = G × e −2G

The maximum throughputSmax = 0.184 , when G = 0.5


Slotted ALOHA MAC Protocol

• In slotted ALOHA, frames are transmitted only at slot boundaries.


The throughput for slotted ALOHA is S = G × e−G

The maximum throughput Smax = 0.368, when G = 1


Throughput versus offered load for pure and slotted ALOHA


Carrier Sense Multiple Access (CSMA) Protocol

• Max. throughput achievable by pure ALOHA is 0.184 and slotted ALOHA is 0.368

• CSMA gives improved throughput compared to ALOHA protocols

• Listens to the channel before transmitting a packet (reduces collisions)


Variants of CSMA

CSMA

Nonpersistent CSMA

Persistent CSMA

Unslotted Nonpersistent CSMA

Unslotted persistent CSMA

Slotted Nonpersistent CSMA

Slotted persistent CSMA

1-persistent CSMA

p-persistent CSMA


Behavior of three persistence methods


CSMA/CD

• Adds collision detection capability to CSMA; greatly reduces time wasted due to collisions

• Standardized as IEEE 802.3, most widespread LAN

• Developed by Robert Metcalfe during early 1970s..... led to founding of “3COM” company. [later Metcalfe sold his company for $400M)• The name 3COM comes from the company's focus on "COMputers,

COMmunication and COMmpatibility"


Why can’t we use CSMA or CSMA/CD in a Wireless LAN or Adhoc Network?


• If the channel is idle, transmit

• If the channel is busy, wait for a random time

• Waiting time is calculated using Binary Exponential Backoff (BEB) algorithm

• Limitations of carrier Sensing

- hidden terminals

- exposed terminals

Carrier Sense Multiple Access (CSMA)


Hidden Terminal Problem

!

• Node A can hear both B and C; but B and C cannot hear each other

• When B transmits to A, C cannot detect this transmission using the carrier

sense mechanism• If C also transmits to A, collision will occur at node A• Increases data packet collisions and hence reduces throughput• Possible solution: RTS (request-to-Send)/ CTS (Clear-to-Send)

handshake

CB A Note: colored circles represent the Tx rangeof each node


Exposed Terminal Problem

DB CA ?

• When A transmits to B, C detects this transmission using carrier sense

mechanism

• C refrains from transmitting to D, hence C is exposed to A’s transmission

• Reduces bandwidth utilization and hence reduces throughput

• Possible solution: Directional Antennas, separate channels for control

and data


• Uses Request-To-Send (RTS) and Clear-To-Send (CTS) handshake to mitigate the effects of hidden terminals

• Data transfer duration is included in RTS and CTS, which helps other nodes to be silent for this duration

• If a RTS/CTS packet collides, nodes wait for a random time which is calculated using BEB algorithm

Multiple Access Collision Avoidance (MACA)

Drawback:

• Cannot avoid RTS/CTS control packet collisions


A BC

D

EDATA

A BC EDRTS

CTS

RTS-CTS Handshake in Action

• A is the source which is in the range of B, D and C• B is the destination which is in the range of A, D and E

radio range of Aradio range of B


A BC

D

EDATA

RTS

CTS

• A is the source which is in the range of B, D and C• B is the destination which is in the range of A, D and E• B sends ACK after receiving one data packet • Improves link reliability using ACK

MACA for Wireless LANs (MACAW)

ACK

A BC ED


• Has provision for two modes- Point Coordination Function (PCF)- Distributed Coordination Function

(DCF)

• Point Coordination Function- Provides contention-free access- Requires Access Point (AP) for

coordination- Not suitable for a MANET

IEEE 802.11 MAC Protocol


Two schemes:

• Basic access scheme (CSMA/CA)

• CSMA/CA with RTS (Request-to-Send)/CTS (Clear-to-Send) handshake (optional)

Distributed Coordination Function (DCF)


Node X

Node A

Node B

Node C

DIFS (DCF Inter-Frame Space)

Time

Data packet

Data packet

Data packet

Basic Access Scheme (CSMA/CA)

-- Data packet

-- Backoff slot


CSMA/CA with RTS/CTS

C FA B EDRTS

RTS = Request-to-Send


CSMA/CA with RTS/CTS (contd.)

C FA B EDRTS

RTS = Request-to-Send

NAV = 20

NAV (Net Allocation Vector) = indicates remaining duration to keep silent



C FA B EDCTS

CTS = Clear-to-Send



C FA B EDCTS

CTS = Clear-to-Send

NAV = 15

NAV (Net Allocation Vector) = indicates remaining duration to keep silent



C FA B EDDATA

• DATA packet follows CTS. Successful data reception

acknowledged using ACK.



C FA B EDACK

ACK = Acknowledgement packet



C FA B EDACK

Reserved area for transmission betweennode C and D


Limitations of IEEE 802.11 DCF MAC

• Performance of Basic Access Method (CSMA/CA) degrades due to

hidden and exposed node problems

• CSMA/CA with RTS/CTS – consumes additional bandwidth for

control packets transmission• may introduce significant delay in data packet

transmission if RTS/CTS control packets experience frequent collisions and retransmissions (possible in case of high node concentration)


Example: RTS/CTS packet collisions

A BRTS

CTSC

CTSRTS

RTSD

E

• Node C (which is hidden from node A) misses the CTS packet from node B due to a collision with an RTS packet from D


Multi-Channel MAC

• Divides bandwidth into multiple channels using frequency division or by using orthogonal CDMA codes

• Selects any one of the idle channels

Advantages:• Improves throughput performance in the network by distributing traffic over time as well as over bandwidth

Disadvantages:• Increases hardware complexity


Example: Single-channel/Multiple-Channel MAC Protocol

PEF

D

C

PAB

Ban

dwid

th

(a) Single Channeltime

PAB PCD PEF

PAB

PCD

PEF

Channel 1

Channel 2

Channel 3

time

Ban

dwid

th

(b) Multiple Channels (3 channels)

PCDA

B

E

F

• Node A, C and E are in radio range


Use of Directional Antennas

• Wireless nodes traditionally use omni-directional antennas

e.g., IEEE 802.11.MAC• Disadvantage: Increases exposed node problem

RTS

CTS

A B C D

G

E

H

RTS

RTS

CTS

CTS

F

X

Reserved Area

Example: IEEE 802.11 MAC

Node B, E, G & H are exposed nodes, hence cannot communicate


Example: Directional Antennas

• Node B only is exposed for communication between C & D• Communication between E & X is possible• Use of directional antennas reduces exposed terminals

C

D

E

XBA

G

H

F


Directional Antennas: Advantages & Disadvantages

• Reduces interference to neighboring nodes- helps in frequency reuse- increases packet success probability (or reduces number of collisions)

• Higher gain due to their directivity- allows transmitters to operate at a smaller transmission power and still

maintain adequate signal-to-interference-plus-noise ratio (SINR)- reduces average power consumption in the nodes

• Requires a mechanism to determine direction for transmission and reception


Energy Conservation

• Many wireless nodes are powered by batteries, hence needs MAC protocols which conserve energy

• Two approaches to reduce energy consumption

- power save: Turn off wireless interface when not required

- power control: Reduce transmit power

• Need for power-aware MAC protocols


Power Control

A B C D

Radio

rang

e

Fig.1

• When node C transmits to D at a higher power level, B cannot receive A’s transmission due to interference from C (Fig. 1)

A B C D

Fig. 2

• If node C reduces Tx power, it still communicates with D (Fig. 2)

- Reduces energy consumption at node C

- Allows B to receive A’s transmission (spatial reuse)

• Reduces interference and increases spatial reuse• Energy Saving

Radio

rang

e


Routing Protocols


Importance of Routing in MANET• Host mobility

• link failure due to mobility of nodes

• Rate of link failure may be high when nodes move fast

• Some desirable features of routing protocols

• Minimum route discovery and maintenance time• Minimum routing overhead• Stable and optimum route despite mobility• Shortest route, etc.


Classification of Unicast Routing Protocols

STAR: Source Tree Adoptive Routing DSDV: Destination Sequence Distance Vector WRP: Wireless Routing Protocol OLSR: Optimized Link State Routing, CSGR: Cluster Switch Gateway Routing (CSGR) FSR : Fisheye State RoutingDSR: Dynamic Source Routing, ABR: Associativity Based Routing TORA: Temporally Ordered Routing, SSR : Signal Stability-based Routing AODV: Ad hoc On-Demand Distance Vector Routing LAR: Location Aided Routing, LANMAR: Landmark Ad hoc Routing Protocol ZRP: Zone Routing Protocol, PR: Preemptive Routing

STAR

Proactive Reactive Hybrid

DSDV WRP CSGR DSR AODV ZRPABR LANMARTORA LARSSROLSR FSR PR

Unicast Routing Protocols


Proactive Routing Protocols


Characteristics of Proactive Routing Protocols

• Distributed, shortest-path protocols

• Maintain routes between every host pair at all times

• Based on Periodic updates of routing table

• High routing overhead and consumes more bandwidth

• Example: Destination Sequence Distance Vector (DSDV)


Reactive Routing Protocols


Characteristics of Reactive Routing Protocols

• Reactive protocols

• Determine route if and when needed

• Less control packet overhead

• Source initiates route discovery process

• More route discovery delay

• Example: Ad hoc On-Demand Distance Vector Routing (AODV)


Proactive and Reactive Protocol Trade-Off

• Latency of route discovery• Proactive protocols may have lower latency

since routes are maintained at all times• Reactive protocols may have higher latency

because a route from X to Y will be found only when X attempts to send a packet to Y

• Overhead of route discovery and maintenance• Reactive protocols may have lower overhead

since routes are determined only if needed• Proactive protocols may result in higher

overhead due to continuous route updating• Which approach achieves a better trade-off

depends on the traffic and mobility patterns


Transmission Control Protocol

(TCP)


Transmission Control Protocol (TCP)

• Reliable ordered delivery

• Implements congestion avoidance and control

• Reliability achieved by means of retransmissions if necessary

• End-to-end semantics• Acknowledgements (ACKs) sent to TCP

sender confirm delivery of data received by TCP receiver

• ACK for data sent only after data has reached the destination


TCP in MANET

Several factors affect TCP performance in a MANET:

• Wireless transmission errors– may cause fast retransmit, which results in

• retransmission of a lost packet• reduction in congestion window size

– reducing congestion window in response to errors is unnecessary

• Route failures due to mobility


Impact of Transmission Errors on TCP

• TCP cannot distinguish between packet losses due to congestion and mobility induced transmission errors

• Unnecessarily reduces congestion window size

• Throughput suffers


QoS Issues


• Guarantee by the network to satisfy a set of pre-determined service performance constraints for the user:

- end-to-end delay - throughput

- probability of packet loss- delay jitter (variance)

• Enough network resources must be available during service invocation to honor the guarantee

• Power consumption and service coverage area- other QoS attributes specific to MANET

• QoS support in MANETs encompasses issues at physical layer, MAC layer, network, transport and application layers

Quality-of-Service (QOS)


QoS support in MANETs: Issues

• Unpredictable link properties

• Node mobility

• Limited battery life

• Hidden and exposed node problem

• Route maintenance

• Security


Security Issues


Security Issues in Mobile Ad Hoc Networks

• Wireless medium is easy to snoop

• Due to ad hoc connectivity and mobility, it is hard to guarantee access to any particular node

• Easier for trouble-makers to insert themselves into a mobile ad hoc network (as compared to a wired network)


Open Issuesin

Mobile Ad Hoc Networking


Open Problems

• Better PHY layer required to support high speed services

• Efficient MAC protocols to support mobility, QoS, energy conservation, etc.

• Efficient routing protocols with scalability, QoS and security, etc.

• Security issues at other layers• Interoperation with Internet• Many more …


References

• C.E. Perkins, Ad Hoc Networking, Addison-Wesley, 2002

• E. Royer and C.K. Toh, “A Review of Current Routing Protocols for Ad hoc Mobile Wireless Networks,” IEEE Personal Communications Magazine, Vol. 6, Issue 2, pp. 46-55, 1999.

• C.E. Perkins, E.M. Royer, and Samir Das, “Ad hoc On-Demand Distance Vector Routing,” http://www.ietf.org/internet-drafts/draft-ietf-manet-aodv-13.txt, (work in progress), February 2003.

• L. Bajaj et al., “GloMoSim: A Scalable Network Simulation Environment,” CSD Technical Report, #990027, UCLA, 1997.

• IEEE Standards Department, Wireless LAN Medium Access Control (MAC) and PHYsical layer (PHY) specifications, IEEE standard 802.11-1997, 1997.


References (contd.)

• B.P. Crow et al., “IEEE 802.11 Wireless Local Area Networks,” IEEE Communications Magazine, Vol. 35, Issue 9, pp. 116-126, September 1997.

• C-K. Toh, Ad Hoc Mobile Wireless Networks: Protocols and Systems, Prentice-Hall, 2002.

• Yiyan Wu and WilliumY. Zou, “Orthogonal Frequency Division Multiplexing,” IEEE Trans.Consumer electronics, vol.41, no.3, pp. 392-399, Aug. 1995.

• R.V. Nee and Ramjee Prasad, OFDM for Wireless Multimedia Communications, Artech House, Boston,London,2000.

• A.Chandra, V.Gummalla, J.O.Limb, “Wireless Medium Access Control Protocols,” IEEE Communications Survey, pp.2-15, Second Quarter 2000.


References (contd.)

• Y. B. Ko, V. Shankarkumar, and N. H. Vaidya, “Medium Access Control Protocols using Directional Antennas in Ad hoc Networks,” In Proceedings of IEEE INFOCOM’2000, Mar. 2000.

• G.Gaertner, V.Cahill, “Understanding Link Quality in 802.11 Mobile Ad hoc Networks,” IEEE Internet computing, pp. 55-60, Jan.-Feb. 2004.

• X.Shugong,T.Saadawi,“Does the IEEE MAC protocol work well in multi-hop wireless ad hoc networks?” IEEE Comm. magazine, pp. 130-137,June 2001.

• M.Tubaishat, S.Madria, ”Sensor networks: an overview,” IEEE potentials, pp.20-23,April-May-2003.


References (contd.)

• Prasant Mohapatra, J.Li, Chao Gui,” QoS in Mobile Ad hoc Networks,” IEEE Wireless Communication, pp.44-52,June-2003.

• N,Choi,Y.Seok,Y.Choi, “Multi-channel MAC for Mobile Ad hoc Networks,” Proc.VTC’03, pp.1379-1383, Oct. 2003.

• C. Rama Krishna, S. Chakrabarti, and D. Datta, “A Modified Backoff Algorithm for IEEE 802.11 DCF-based MAC Protocol in a Mobile Ad hoc Network,” Proc. of the International Conference IEEE TENCON 2004, Chiang Mai, Thailand, 21-24 November 2004.

• V. Bhargavan et al., “MACAW: A New Media Access Protocol for Wireless LANs,” Proc. of ACM SIGCOMM, pp. 212-225, 1994.

• P. Karn, “MACA – A New Channel Access Method for Packet Radio,” in ARRL/CRRL Amateur Radio 9th Computer Networking Conference, pp. 134-140, 1990

adhoc networking and challenges

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