Challenges in Mobile Adhoc Networking rkc at nitttrchd.ac.in

Challenges in Mobile Adhoc Networking Email: rkc at nitttrchd.ac.in
Dr. C. Rama Krishna Dept. of CSE NITTTR, Chandigarh rkc at nitttrchd.ac.in

Which Technology ? Cellular Technologies Wireless LAN Technology
2G Systems 2.5G Systems 3G Systems 4G Systems NextG Systems Wireless LAN Technology 2.4/5 GHz Wireless LAN Ad-hoc / Infrastructure Mode Short range Technologies Home RF Bluetooth ZigBee Long Range Technologies Internet

Outline History and Introduction Brief Introduction to Physical Layer
Medium Access Control (MAC) Layer Routing and Transport Layer Issues Quality-of-Service Issues Security Issues Additional Resources

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 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) – Data can be relayed by intermediate nodes – Routing infrastructure created dynamically traffic from A D is relayed by nodes B and C D A C B radio range of node A

Why an Ad hoc Network? Does not depend on pre-existing infrastructure
Ease of deployment Speed of deployment Anytime-Anywhere-Any device network paradigm

Mobile 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 Emergency operations
soldiers, tanks, planes Emergency operations search-and-rescue Personal area networking cell phone, laptop, etc. Civilian environments meeting rooms, sports stadiums, hospitals Education virtual classrooms, conferences Sensor networks homes, environmental applications

Ad hoc Network Architecture
physical Data link network transport application wireless link Source Destination Intermediate node

Some Challenges Limited wireless transmission range
Broadcast nature of wireless medium hidden terminal and exposed terminal problems – MAC problem Mobility-induced route changes – routing problem Packet losses due to: transmission errors and node mobility – transport problem Battery constraints – energy efficiency problem Ease of snooping - security problem

Physical Layer

IEEE 802.11 WLAN standards Standard Specification 1 802.11
Sl.No Standard Specification 1 802.11 Physical Layer & MAC Layer 2 802.11a Physical Layer 3 802.11b 4 5 6 QoS enhancement in MAC 7 8 802.11g 9 10 802.11i Security enhancement in MAC 802.11e 802.11n 600 Mbps with MIMO 802.11ac Very High Throughput 802.11ad Very High Throughput 802.11p WAVE

IEEE 802.11 standard 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 based infrastructure WLAN
PC Wire line Access Point (AP) Laptop Basic Service Set (BSS) Basic service area (BSA)

Independent Basic Service Set (IBSS)
IEEE based infrastructure-less Adhoc Network Independent Basic Service Set (IBSS) Laptop

IEEE 802.11 Physical Layer Specification
Standard Parameter 802.11 802.11a 802.11b Bandwidth 83.5MHz 300MHz Frequency band GHz GHz and – GHz Channels 3 12 Data Rate ( in Mbps) 1, 2 6, 9, 12, 18, 24, 36, 48 and 54 1, 2, 5.5, and 11 Transmission Scheme FHSS, DSSS with QPSK OFDM (with PSK and QAM ) DSSS(with QPSK & CCK modulation)

Physical Layer for high speed MANET
Present physical Layer IEEE , 11a, b and g 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 Physical layer design for high data rate transmission up to 54 Mbps [ a & g]

Medium Access Control (MAC)

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

Classification of Wireless MAC Protocols
Distributed Centralized Random Access Random Access Guaranteed Access Hybrid Access 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

Frames are transmitted as they are generated (No discipline!).
Pure ALOHA MAC Protocol Frames are transmitted as they are generated (No discipline!).

Modeling of Pure ALOHA MAC Protocol
The transmission x is successful: if and only if: There are no transmission attempts that begins (=arrives) during the time interval (t-1, t+1] Therefore: Prob. [ a transmission attempt is successful ] = Prob. [ 0 arrivals in the period (t-1,t+1] ] = Prob. [ 0 arrivals in 2 time units ] = e−2G

Throughput of Pure ALOHA MAC Protocol
Throughput = Offered Load (G) × Prob. [ a transmission attempt is successful ] = G × e−2G

The throughput for pure ALOHA is S = G × e −2G The maximum throughput
Smax = , when G = 0.5

Frames are transmitted only at slot boundaries (some discipline!).
Slotted ALOHA MAC Protocol Frames are transmitted only at slot boundaries (some discipline!).

The throughput for slotted ALOHA is S = G × e−G
The maximum throughput Smax = 0.368, when G = 1

Throughput for pure and slotted ALOHA

Carrier Sense Multiple Access (CSMA) MAC Protocol
Max. throughput : pure ALOHA % and slotted ALOHA % Listen to the channel before transmitting a packet (better disciplined!) CSMA improves throughput compared to ALOHA protocols

Variants of CSMA Nonpersistent CSMA CSMA Persistent CSMA
Unslotted Nonpersistent CSMA Nonpersistent CSMA Slotted Nonpersistent CSMA CSMA Unslotted persistent CSMA Persistent CSMA Slotted persistent CSMA 1-persistent CSMA p-persistent CSMA

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?

Carrier Sense Multiple Access (CSMA)
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

Hidden Terminal Problem
C B A Note: colored circles represent the Tx range of each node ! 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

Exposed Terminal Problem
C A ? 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

Multiple Access Collision Avoidance (MACA)
Uses Request-To-Send (RTS) and Clear-To-Send (CTS) handshake to reduce 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 Drawback: Cannot avoid RTS/CTS control packet collisions

RTS-CTS Handshake in Action
radio range of B radio range of A A B C E D RTS D CTS C A B E DATA 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

MACA for Wireless LANs (MACAW)
B C E D RTS D CTS C A B E DATA ACK 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

IEEE 802.11 MAC Protocol 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

Distributed Coordination Function (DCF)
Two schemes: Basic access scheme (CSMA/CA) CSMA/CA with RTS (Request-to-Send)/CTS (Clear-to-Send) handshake (optional)

CSMA/CA with RTS/CTS RTS A B C D E F RTS = Request-to-Send

CSMA/CA with RTS/CTS (contd.)
B C D E F NAV = 20 RTS = Request-to-Send NAV (Net Allocation Vector) = indicates remaining duration to keep silent

B C D E F CTS = Clear-to-Send

B C D E F NAV = 15 CTS = Clear-to-Send NAV (Net Allocation Vector) = indicates remaining duration to keep silent

DATA packet follows CTS. Successful data reception acknowledged using ACK. DATA A B C D E F

ACK A B C D E F ACK = Acknowledgement packet

Reserved area for transmission between node C and D ACK A B C D E F

Limitations of 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
B D CTS RTS CTS C 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 Protocols
Divides bandwidth into multiple channels 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
B PAB D Bandwidth PAB PCD PEF PCD A time C (a) Single Channel PEF E PAB Channel 1 F Bandwidth PCD Channel 2 PEF Channel 3 Node A, C and E are in radio range time (b) Multiple Channels (3 channels)

Use of Directional Antennas
Wireless nodes traditionally use omni-directional antennas e.g., IEEE MAC Disadvantage: Increases exposed node problem Example: IEEE MAC G RTS F RTS CTS RTS A C D E B CTS CTS X Node B, E, G & H (colored red) are exposed nodes, hence cannot communicate H Reserved Area

Example: Directional Antennas
F E G D C B X A H Node B only is exposed for communication between C & D Communication between E & X is possible Use of directional antennas reduces exposed terminals

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 Cost of beam forming antennas is a concern

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 Reduces interference and increases spatial reuse
Energy Saving Radio range When node C transmits to D at a higher power level, B cannot receive A’s transmission due to interference from C (Fig. 1) C D A B Fig.1 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) C D A B Radio range Fig. 2

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 Shortest route despite mobility

Classification of Unicast Routing Protocols
Proactive Reactive Hybrid STAR DSDV WRP OLSR CSGR FSR DSR ABR TORA SSR LAR AODV ZRP LANMAR PR 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 Routing DSR: 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

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 type of traffic and mobility patterns

Transmission Control Protocol (TCP)

Transmission Control Protocol (TCP)
Reliable ordered delivery Implements congestion control Reliability achieved by means of retransmissions End-to-end semantics Acknowledgements (ACKs) sent to TCP sender confirm delivery of data received by TCP receiver

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 (cwnd) reducing congestion window in response to transmission errors is unnecessary Route failures due to mobility leads to packet losses

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

Quality-of-Service (QOS)
Guarantee by the network to satisfy a set of pre-determined service performance constraints for the user: - end-to-end delay - available bandwidth - probability of packet loss - delay and jitter (variation in delay) 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

Issues and Difficulties
QoS support in MANETs: Issues and Difficulties 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 Issues in Mobile Ad Hoc Networking

Open Problems Physical layer modeling to support broadband services
Efficient MAC protocols to support mobility, QoS and security Efficient routing protocols with scalability, QoS and security QoS issues at other layers Security issues at other layers Interoperation with Internet

References [1] C.E. Perkins, Ad Hoc Networking, Addison-Wesley, 2002
[2] J. Broch et al., “A Performance Comparison of Multi-hop Wireless Ad hoc Network Routing Protocols,” Proceedings of the 4th International Conference on Mobile Computing and Networking (ACM MOBICOM’98), pp , October 1998. [3] 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 , 1999. [4] C.E. Perkins, E.M. Royer, and Samir Das, “Ad hoc On-Demand Distance Vector Routing,” (work in progress), February 2003. [5] L. Bajaj et al., “GloMoSim: A Scalable Network Simulation Environment,” CSD Technical Report, #990027, UCLA, 1997.

References (contd.) [6] IEEE Standards Department, Wireless LAN Medium Access Control (MAC) and PHYsical layer (PHY) specifications, IEEE standard , 1997. [7] B.P. Crow et al., “IEEE Wireless Local Area Networks,” IEEE Communications Magazine, Vol. 35, Issue 9, pp , September 1997. [8] C-K. Toh, Ad Hoc Mobile Wireless Networks: Protocols and Systems, Prentice-Hall, 2002. [9] Yiyan Wu and WilliumY. Zou, “Orthogonal Frequency Division Multiplexing,” IEEE Trans.Consumer electronics, vol.41, no.3, pp , Aug [10] Ramjee Prasad and Shinsuke Hara, “DS-CDMA,MC-CDMA and MT-CDMA for Mobile Multimedia Communications” in Proc. IEEE VTC’96, pp , April 1996.

References (contd.) [11] Hyumb Yang, Kiseon Kim, ”Multimedia Ad hoc wireless LANs with Distributed Channel Allocation based on OFDM-CDMA,” in Proc. ICT’03,p.p ,Feb [12] M.Conti et.al, “ Cross layering in mobile ad hoc network design,” Computer, IEEE computer society, pp , February 2004. [13] F.H.P.Fitzek,Diego Angelini, G Mazzini, M.Z.U. Di Ferrara, “Design and Performance of an Enhanced IEEE MAC Protocol for Multi-hop Coverage Extension,” IEEE Wireless communication, PP , Dec.2004. [14] Zhou Wenam, Li zheen, Song Junde, and Wang Daoyi, “Applying OFDM in the Next Generation Mobile Communications,” in Proc. IEEE Canadian Conf. Electrical & Computer Engineering 2002, pp

References (contd.) [15] R.V.Nee and Ramjee Prasad, OFDM for Wireless Multimedia Communications, Artech House, Boston,London,2000. [16] 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 [17] G.Gaertner, V.Cahill, “Understanding Link Quality in Mobile Ad hoc Networks,” IEEE Internet computing, pp , Jan.-Feb [18] X.Shugong,T.Saadawi,“Does the IEEE MAC protocol work well in multi-hop wireless ad hoc networks?” IEEE Comm. magazine, pp ,June 2001.

References (contd.) [19] T. Goff, N. B. Abu-Ghazaleh, D. S. Phatak, and R. Kahvecioglu, “ Preemptive routing in ad hoc networks,” Proc. of ACM MOBICOM’2001, [20] M.Tubaishat, S.Madria, ”Sensor networks: an overview,” IEEE potentials, pp.20-23,April-May-2003. [21] Prasant Mohapatra, J.Li, Chao Gui,” QoS in Mobile Ad hoc Networks,” IEEE Wireless Communication, pp.44-52,June-2003. [22] N,Choi,Y.Seok,Y.Choi, “Multi-channel MAC for Mobile Ad hoc Networks,” Proc.VTC’03, pp , Oct [23] I.Bradaric and A.P.Petropulu, “Analysis of physical layer performance of IEEE a in an Ad hoc Network Environment,” in Proc. MILICOM’03, vol.2, pp , Oct. 2003

References (contd.) [24] C. Rama Krishna, S. Chakrabarti, and D. Datta, “A Modified Backoff Algorithm for IEEE DCF-based MAC Protocol in a Mobile Ad hoc Network,” Proc. of the International Conference IEEE TENCON 2004, Chiang Mai, Thailand, November 2004. [25] Nah-Oak, et. al, “Enhancement of IEEE Distributed Coordination Function with Exponential Increase and Exponential Decrease Backoff Algorithm,” Proc. of the 57th IEEE Semiannual Vehicular Technology Conference 2003-Spring, vol. 4, pp , April 2003. [26] V. Bhargavan et al., “MACAW: A New Media Access Protocol for Wireless LANs,” Proc. of ACM SIGCOMM, pp , 1994. [27] P. Karn, “MACA – A New Channel Access Method for Packet Radio,” in ARRL/CRRL Amateur Radio 9th Computer Networking Conference, pp , 1990

References (contd.) [28] A.Chandra, V.Gummalla, J.O.Limb, “Wireless Medium Access Control Protocols,” IEEE Communications Survey, pp.2-15, Second Quarter 2000. [29] T. Camp, Jeff Boleng, and V. Davis, “A Survey of Mobility Models for Ad Hoc Network Research,” Wireless Communication & Mobile Computing (WCMC): Special issue on Mobile Ad Hoc Networking: Research, Trends and Applications, vol. 2, no. 5, pp , 2002. [30] L.Bajaj, M.Takai, R.Ahuja, K.Tang, R.Bagrodia, and M.Gerla, “GlomoSim: A Scalable Network Simulation Environment,” CSD Technical report, #990027,UCLA,1997. [31] P. Karn, “MACA – A New Channel Access Method for Packet Radio,” in ARRL/CRRL Amateur Radio 9th Computer Networking Conference, pp , 1990

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