Mobile Networks Prof. Jean-Pierre Hubaux EPFL The Playground of - - PDF document

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Mobile Networks

• Prof. Jean-Pierre Hubaux

EPFL

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The Playground of Communication Networks

PSTN IP network Cellular network Gateway

BS Switch Router WLAN Station MSC: Mobile services Switching Center BS: Base Station WLAN: Wireless LAN PSTN: Public Switched Telephone NW MSC MSC Control server Control server Information server Information server Control server

Wireless communication and mobility

g Aspects of mobility:

iuser mobility: users communicate “anytime, anywhere, with anyone” idevice portability: devices can be connected anytime, anywhere to the

network

g Wireless vs. mobile Examples

• stationary computer (desktop)
• laptop connected to an Ethernet network
• desktops in historic buildings
• Personal Digital Assistant (PDA)

g The demand for mobile communication creates the need for

integration of wireless networks or mobility mechanisms into existing fixed networks:

itelephone network cellular telephony (e.g., GSM) ilocal area networks Wireless LANs (e.g.,IEEE 802.11) iInternet Mobile IP

Wireless systems: development over the last 20 years

cellular phones satellite networks cordless phones wireless LAN, wireless PAN

1992: GSM 1994: DCS 1800 2002 - ?: UMTS/IMT-2000 CDMA-2000 (USA) 1987: CT1+ 1982: Inmarsat-A 1992: Inmarsat-B Inmarsat-M 1998: Iridium 1989: CT 2 1991: DECT 199x: proprietary 1995/96/97: IEEE 802.11, HIPERLAN 2001 - ?: IEEE 802.15 Bluetooth 1988: Inmarsat-C analog digital 1991: D-AMPS 1991: CDMA (USA: IS-95) 1981: NMT 450 1986: NMT 900 1980: CT0 1984: CT1 1983: AMPS 1993: PDC

NMT: Nordic Mobile Telephone DECT: Digital Enhanced Cordless Telecom. AMPS: Advanced Mobile Phone System (USA) DCS: Digital Cellular System CT: Cordless Telephone PDC: Pacific Digital Cellular UMTS: Universal Mobile Telecom. System PAN: Personal Area Network

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Mobile devices

performance performance

Pager

• receive only
• tiny displays
• simple text

messages Mobile phones

• voice, data
• simple text displays

PDA

• simple graphical displays
• character recognition
• simplified WWW

Laptop

• functionally eq. to desktop
• standard applications

Wireless sensors

• Limited proc. power
• Small battery

RFID tag

• A few thousands
• f logical gates
• Responds only

to the RFID reader requests (no battery)

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Upcoming wireless networks

g Personal communications g Vehicular networks g Sensor networks g RFID

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Upcoming wireless networks: personal communications

g Proliferation of small operators g Operators in shared spectrum g Mesh networks g Hybrid ad hoc networks g Mesh networks

Internet HS TAP3 TAP1 TAP2 TAP5 TAP4 TAP6 TAP7

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Preventing greedy behavior at the MAC layer in WiFi hotspots

Well-behaved node Cheater

The access point is trusted The access point is trusted For more information: http://domino.epfl.ch

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Wireless Operators in a Shared Spectrum

max

i

i iu P j ju j

P g N P g ⎡ ⎤ ⋅ ⎢ ⎥ ⎢ ⎥ + ⋅ ⎢ ⎥ ⎣ ⎦

∑

g

game G = (Players, Strategy, Utility function)

g

• perators → players

g

radio range → strategy

g

utility: useful coverage of their pilot signal:

coverage interference

i i i i

U γ = − ⋅

2

1

iu iu

g d =

where the channel gain:

g

freely roaming users

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power control of the pilot signal

g

users attach to the base station with the best pilot signal: Static game – Pareto-optimal Nash equilibria

Small : Large :

A B MAX A B MIN

r r R r r R γ γ = = = =

Repeated game – A Nash equilibrium based on RMIN is enforceable using punishments

: maximum power range (regulator) : minimum power range (for coverage)

MAX MIN

R R

http://winet-coop.epfl.ch/

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Vehicular communications: why?

g Combat the awful side-effects of road traffic

iIn the EU, around 40’000 people die yearly on the roads;

more than 1.5 millions are injured

iTraffic jams generate a tremendous waste of time and of

fuel

g Most of these problems can be solved by providing

appropriate information to the driver or to the vehicle

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Example of attack : Generate “intelligent collisions”

SLOW DOWN The way is clear Similar attack: stop a highway For more information: http://ivc.epfl.ch

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European Project SeVeCom

• SeVeCom: Secure Vehicular Communications
• Started January 2006; Duration: 3 years; Total budget: 3 MEuros
• Research topics: key management, secure communication,

privacy, tamper-proof device

• http://www.sevecom.org
• A small, well-balanced consortium, with a precise goal
• Partners:

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Sensor network for environmental monitoring

http://www.commonsense.ch

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Reference model

Application Transport Network Data Link Physical Data Link Physical Application Transport Network Data Link Physical Data Link Physical Network Network Radio link

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Layer model

i security i service location i Signal processing i new applications, multimedia i adaptive applications i congestion and flow control i quality of service i addressing, routing,

mobility management

i hand-over i authentication i media access i multiplexing i media access control i encryption i modulation i interference i attenuation i frequency allocation

g Application layer g Transport layer g Network layer g Data link layer g Physical layer

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Overlay Networks - the global view

wide area metropolitan area campus-based in-house vertical hand-over horizontal hand-over Integration of heterogeneous fixed and mobile networks with varying transmission characteristics

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The classical solution for mobile networks

g 2nd generation (GSM, IS-41,…) deployed, 3rd generation (UMTS,…)

recently deployed

g Huge, expensive fixed infrastructure g Operational responsibility: network operators (telcos, ISPs)

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The new paradigm: mobile ad hoc networks

g Terminal and node merge g Everything is potentially mobile g Initial applications: communication in the battlefield (Packet

Radio Networks, in the 70’s)

g The network is self-organized when it is run by the users

themselves

g Similar trend at the application layer (Napster Gnutella)

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Upper bound for the throughput of ad hoc networks

If we have:

• identical randomly located nodes
• each capable of transmitting

bits/s Then the throughput ( ) obtainable by each node for a destination is ( ) log n W n randomly chosen W n n n λ λ ⎛ ⎞ = Θ⎜ ⎟ ⎜ ⎟ ⎝ ⎠

Ref: P. Gupta, P. Kumar, The Capacity of Wireless Networks IEEE Transactions on Information Theory, March 2000

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Intuition behind the upper bound

N nodes (users) O(N) users O(N) users Cut set ~

N

O(N) transmissions from left to right

• ver

O( ) transmission links mean O( ) capacity per attempted transmission

N

1 N

Ways to improve scalability:

• Directional antennas
• Locality of the traffic
• Hybrid system

Ways to improve scalability:

• Directional antennas
• Locality of the traffic
• Hybrid system

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Terminal + Node = Terminode www.terminodes.org

g All network functions (packet forwarding, flow control, error control,…) and terminal functions (coding/decoding, A/D and D/A, storage, ciphering,…) are embedded in the terminode g A communication must be relayed by intermediate terminodes g The network is self-organized: it is operated by its users g All terminodes are wireless and battery-operated g All terminodes are potentially mobile g There exist gateways to other networks (e.g., Internet and cellular networks) Destination Source

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References

g J. Schiller: Mobile Communications, Addison-Wesley,

Second Edition, 2004

g B. Walke: Mobile Radio Networks, Wiley, Second

Edition, 2002

g T. Rappaport: Wireless Communications, Prentice

Hall, Second Edition, 2001

g M. Schwartz: Mobile Wireless Communications,

Cambridge University Press, 2004