cs2402-mobile and pervasive computing

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MOBILE AND PERVASIVE COMPUTING

UNIT I 1. Cellular Wireless Networks: Importance of Wireless

Freedom of movement

No loss of connectivity

Increase in productivity

Cellular Network Organization

Use multiple low-power transmitters (100 W or less)

Areas divided into cells

Each served by its own antenna

Served by base station consisting of transmitter, receiver, and

control unit

Band of frequencies allocated

Cells set up such that antennas of all neighbors are equidistant

(hexagonal pattern)

Frequency Reuse

Adjacent cells assigned different frequencies to avoid interference or

crosstalk

Objective is to reuse frequency in nearby cells

10 to 50 frequencies assigned to each cell

Transmission power controlled to limit power at that frequency

escaping to adjacent cells

The issue is to determine how many cells must intervene between

two cells using the same frequency

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Cellular System

Overview

Cellular Systems Terms

Base Station (BS) includes an antenna, a controller, and a number of

receivers

Mobile telecommunications switching office (MTSO) connects calls

between mobile units

Two types of channels available between mobile unit and BS

Control channels used to exchange information having to do with

setting up and maintaining calls

Traffic channels carry voice or data connection between users

2. GSM formerly: Groupe Spciale Mobile (founded 1982)

now: Global System for Mobile Communication Pan-European standard (ETSI, European Telecommunications

Standardisation Institute)


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simultaneous introduction of essential services in three phases (1991, 1994, 1996) by the European telecommunication

administrations (Germany: D1 and D2) seamless roaming within Europe possible

today many providers all over the world use GSM (more than 200 countries in Asia, Africa, Europe, Australia, America)

more than 1.2 billion subscribers in more than 630 networks

more than 75% of all digital mobile phones use GSM (74% total) over 200 million SMS per month in Germany, > 550 billion/year

worldwide (> 10% of the revenues for many operators) [be aware: these are only rough numbers]

Performance characteristics of GSM

1. Communication

-mobile, wireless communication; support for voice and data services

2. Total mobility -international access, chip-card enables use of access points of

different providers 3. Worldwide connectivity

-one number, the network handles localization

4. High capacity -better frequency efficiency, smaller cells, more customers per cell

5. High transmission quality -high audio quality and reliability for wireless, uninterrupted phone calls at higher speeds (e.g., from cars, trains)

6. Security functions -access control, authentication via chip-card and PIN

Disadvantages of GSM

There is no perfect system!!

no end-to-end encryption of user data

no full ISDN bandwidth of 64 kbit/s to the user, no transparent B-channel

reduced concentration while driving

electromagnetic radiation

abuse of private data possible

roaming profiles accessible

high complexity of the system

several incompatibilities within the GSM standards GSM: Mobile Services

GSM offers

several types of connections


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voice connections, data connections, short message service multi-service options (combination of basic services)

Three service domains Bearer Services

Telematic Services Supplementary Services

Bearer Services

Telecommunication services to transfer data between access points Specification of services up to the terminal interface (OSI layers 1-3)

Different data rates for voice and data (original standard) data service (circuit switched)

synchronous: 2.4, 4.8 or 9.6 kbit/s

asynchronous: 300 - 1200 bit/s data service (packet switched)

synchronous: 2.4, 4.8 or 9.6 kbit/s asynchronous: 300 - 9600 bit/s

Today: data rates of approx. 50 kbit/s possible will be covered later! 3. Architecture of the GSM system GSM is a PLMN (Public Land Mobile Network)

components

MS (mobile station) BS (base station) MSC (mobile switching center)

LR (location register) subsystems

RSS (radio subsystem): covers all radio aspects

NSS (network and switching subsystem): call forwarding, handover, switching

OSS (operation subsystem): management of the network

GSM: elements and interfaces

GSM-PLMN transit network (PSTN, ISDN)

source/ destination

network TE TE

bearer services

R, S

(U, S, R)

U

m

MT

MS


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4. GSM protocol layers for signaling

NSS

M

S

M

S

B

TS

B

SC

G

MS

C

IW

F

O

MC

B

TS

B

SC

M

SC

M

SC

Abis

U

m

EIR

HLR

VLR

VLR

A

BSS

PDN

ISDN, PSTN

RSS

radio cell

radio cell

M

S

A

UC

OSS

signaling

O


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5. CONNECTION ESTABLISHMENT

Mobile Terminated Call

1: calling a GSM subscriber 2: forwarding call to GMSC

3: signal call setup to HLR 4, 5: request MSRN from VLR 6: forward responsible MSC to GMSC

7: forward call to current MSC 8, 9: get current status of MS

10, 11: paging of MS 12, 13: MS answers 14, 15: security checks

16, 17: set up connection

CM

MM

RR

MM

LAPDm

radio

LAPDm

radio

LAPD

PCM

RR

BTSM

CM

LAPD

PCM

RR BTS

M

16/64 kbit/s

Um Abis A

SS7

PCM

SS7

PCM

64 kbit/s / 2.048 Mbit/s

MS

BTS

BSC

MSC

BSSAP

BSSAP


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Mobile Originated Call

7.FREQUENCY ALLOCATION

calling station

PSTN GMSC

HLR VLR

BSS BSS BSS

MSC

MS

1 2

3

4

5

6

7

8 9

10

11 12

13 16

10 10

11 11 11

14 15

17

PSTN GMSC

VLR

BSS

MSC

MS 1

2

6 5

3 4

9

10

7 8


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VLF = Very Low Frequency UHF = Ultra High Fequency LF = Low Frequency SHF = Super High Frequency MF = Medium Frequency EHF = Extra High Frequency HF = High Frequency UV = Ultraviolet Light VHF = Very High Frequency Frequencies kHz Range (Low and Very Low frequencies) Used for short distances using twisted copper wires

Several KHz to MHZ (Medium and High Frequencies) For transmission of hundreds of radio stations in the AM and

FM mode Use co-axial cables Transmission power is several kW.

Several MHz to Terra Hz Range (VHF and UHF) Typically 100 MHz to 800 MHz and extending to terraHz) Conventional Analog TV (174-230 MHz and 470-790

MHz) DAB Range (220 1472 MHz)

Frequency Ranges

1 m

300 MHz

1 Mm 300

Hz

10 km 30 kHz

100 m 3 MHz

10 mm 30 GHz

100 m

3 THz

1 m

300 THz

visible

light VLF LF MF HF VHF UHF SHF EHF infrare

d UV

optical transmission coax cable twisted

pair


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DTV (470 872 MHz) Digital GSM (890-960MHz)

3G Mobile Systems (1900-2200 MHz) Super High(SH) and Extremely Super High(ESH)

Hundreds of GHz Fixed Satellite Services Close to infra-red.

For Several TerraHz : Optical Transmission

Why do we need very high transmission frequencies?

The information content in video, satellite data etc is enormous.

If we need to accommodate many signals simultaneously, we need a high bit rate which in turn demands high frequency.

Europe USA Japan

Cellular Phones

GSM 450-457, 479-486/460-467,489-496, 890-915/935-960, 1710-1785/1805-1880 UMTS (FDD) 1920-1980, 2110-2190 UMTS (TDD) 1900-1920, 2020-2025

AMPS, TDMA, CDMA 824-849, 869-894 TDMA, CDMA, GSM 1850-1910, 1930-1990

PDC 810-826, 940-956, 1429-1465, 1477-1513

Cordless Phones

CT1+ 885-887, 930-932 CT2 864-868 DECT 1880-1900

PACS 1850-1910, 1930-1990 PACS-UB 1910-1930

PHS 1895-1918 JCT 254-380

Wireless LANs

IEEE 802.11 2400-2483 HIPERLAN 2 5150-5350, 5470-5725

902-928 IEEE 802.11 2400-2483 5150-5350, 5725-5825

IEEE 802.11 2471-2497 5150-5250

Others RF-Control 27, 128, 418, 433, 868

RF-Control 315, 915

RF-Control 426, 868


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8.ROUNTING

Routing :-

Routing is the means of discovering paths in computer networks along which

information (split up into packets) can be sent. Circuit-based networks, such as the

voice telephone network, also perform routing, to find paths for telephone calls through the network fabric.

Routing is usually directed by routing tables, which maintain a record of the best

routes to various network locations in order to keep up with the packet arrival rate.

Small networks may involve hand configuration. Large networks involve complex topologies and may change constantly, making the constructing of routing tables

very problematic. Automatic routing protocols attempt to solve this problem with

dynamically updated routing tables. These are updated intermittently by the routing software, based on information carried by the routing protocol, and allow the network

to be nearly autonomous in avoiding network failures and blockages.

Routing directs forwarding, the passing of logically addressed packets from their

local sub network toward their ultimate destination. In large networks, packets may pass through many intermediary destinations before reaching their destination.

The hardware used in routing includes hubs, switches and routers.

Difference between Wired and Wireless Rrouting:-

The concept of link abstraction ie. considering the two connected nodes as a link is not valid in the case of wireless as opposed to the wired systems. This is for the

following reasons

- This can be zero or close to zero in case of wired

networks but in case of wireless this value is much greater than zero.

- The neighbouring links disturb the

transfer of packets in a link. A link can be understood as a connection of the

two nodes that are talking to each other.

-interference (within a path):- Each link of a wireless network is a half duplex link which means that there will be a two way transmission at the intermediary

node. Hence, there will be interference within the link itself.

- The medium of transmission in wireless networks is

broadcast. This causes the packet to be transmitted over the entire network.

In wired networks however it is not transmitted over the entire network.

NOTE : 2P MAC reduces the differences between wireless and wired networks-

It has directional, point to point links, hence the thing comes close to wired.


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By using SynOp and appropriate transmit power the interference can be

avoided.

Routing Metrics:- The routing metrics for wired networks are

i. Hop-Count- It is related to the total number of hops between two nodes. ii. Queuing delay- This corresponds to the load of the link ie. the traffic going on

in the line.

For wireless networks the metrics are

i. Hop-Count ii. RTT(Round Trip Time)

iii. Packet Pair

iv. ETx(Expected Transmission Count)

Hop-Count:

Advantages o Easy to evaluate

o Simple

o Little Overhead

Shortcomings It does not consider

o Transmit rate

o Load o Interference

o Packet Loss Rate

RTT:

Since this value is congestion dependent this value needs to be calculated again and again. Probe and Probe Ack are sent between the two neighbours every 500 ms

to calculate the Round Trip Time.

9. Security in GSM Security services

access control/authentication user SIM (Subscriber Identity Module): secret PIN

(personal identification number) SIM network: challenge response method

confidentiality voice and signaling encrypted on the wireless link

(after successful authentication)


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anonymity temporary identity TMSI

(Temporary Mobile Subscriber Identity) newly assigned at each new location update (LUP) encrypted transmission

3 algorithms specified in GSM A3 for authentication (secret, open interface) A5 for encryption (standardized) A8 for key generation (secret, open interface)

10.General Packet Radio Service (GPRS)

New service that uses packet-mode to transfer data over GSM radio

networks. Supplements todays Short Message Service (SMS) and Circuit Switched

Data Service (CSDS). Packets are in IP formats (but can carry other packet data protocol such

as X.25).

Since it is built on top of the current GSM network and can run several times faster, it is considered a migration path to 3G (up to 2 Mbps)

TDMA (Time Division Multiple Access) popular in North and South America will also support GPRS

Can use up to 8 time slots per TDMA frame

Theoretical maximum speed is 171.2 Kbps Commercial performance will probably be somewhere between 56K to

115Kbps Initial speeds are from 20K to 40Kbps (GSM CSD runs at 9.6Kbp) By reserving timeslots for a connection, quality of service can be provided

effective utilization of bandwidth instant connection (no dial-up modem connection is necessary) - always

connected charging based on amount of data transferred, not connection time Internet aware - services available to the Internet (such as FTP, web

browsing, email, chat, telnet) will be available over the the mobile network via GPRS

allows SMS transfer over GPRS radio channels addresses to send and receive GPRS packets is likely to be IP addresses

rather than phone numbers

Launched in the UK in summer 2000 Expected to be publicly available in HK in Fall 2001

Quality of service


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GPRS architecture and interfaces

GPRS protocol architecture

Reliability

class

Lost SDU

probability

Duplicate

SDU

probability

Out of

sequence

SDU probability

Corrupt SDU

probability

1 10-9

10-9

10-9

10-9

2 10-4

10-5

10-5

10-6

3 10-2

10-5

10-5

10-2

Delay SDU size 128 byte SDU size 1024 byte

class mean 95 percentile mean 95 percentile

1 < 0.5 s < 1.5 s < 2 s < 7 s

2 < 5 s < 25 s < 15 s < 75 s

3 < 50 s < 250 s < 75 s < 375 s

4 unspecified

MS

BSS GGSN

SGSN

MSC

U

m

EIR

HLR/ GR

VLR

PDN

G

b G

n G

i

SGS

N

G

n


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UNIT II

1. Wireless LANs

Characteristics of wireless LANs

Advantages

very flexible within the reception area

Ad-hoc networks without previous planning possible

(almost) no wiring difficulties (e.g. historic buildings, firewalls)

more robust against disasters like, e.g., earthquakes, fire - or users

pulling

a plug...

Disadvantages

typically very low bandwidth compared to wired networks (1-10 Mbit/s)

apps.

IP/X.25

LLC

GTP

MAC

radio

MAC

radio

FR RLC

BSSGP

IP/X.25

FR

Um Gb Gn

L1/L2 L1/L2

MS BSS SGSN GGSN

UDP/TCP

Gi

SNDCP

RLC BSSGP IP IP

LLC UDP/TCP

SNDCP

GTP


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many proprietary solutions, especially for higher bit-rates, standards

take their time (e.g. IEEE 802.11)

products have to follow many national restrictions if working wireless, it

takes a vary long time to establish global solutions like, e.g., IMT-2000

Design goals for wireless LANs

global, seamless operation

low power for battery use

no special permissions or licenses needed to use the LAN

robust transmission technology

simplified spontaneous cooperation at meetings

easy to use for everyone, simple management

protection of investment in wired networks

security (no one should be able to read my data), privacy (no one should

be able to collect user profiles), safety (low radiation)

transparency concerning applications and higher layer protocols, but also

location awareness if necessary

Personal area network (PAN)

A personal area network (PAN) is a computer network used for

communication among computer devices (including telephones and

personal digital assistants) close to one person. The devices may or may

not belong to the person in question. The reach of a PAN is typically a few

meters. PANs can be used for communication among the personal

devices themselves (intrapersonal communication), or for connecting

to a higher level network and the Internet (an uplink).

2. IEEE 802.11 STANDARD


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SYSTEM ARCHITECTURE

Station (STA)

- terminal with access mechanisms to the wireless medium and radio contact

to the access point

Basic Service Set (BSS)

- group of stations using the same radio frequency

Access Point

- station integrated into the wireless LAN and the distribution system

Portal

- bridge to other (wired) networks

Distribution System

- interconnection network to form one logical network (EES: Extended

Service Set) based

on several BSS


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802.11 - Architecture of an ad-hoc network

Direct communication within a limited range

Station (STA):

terminal with access mechanisms to the wireless medium

Basic Service Set (BSS):

group of stations using the same radio frequency

Distribution

System

Portal

802.x LAN

Acce

ss

Point BSS2

802.11 LAN

BSS1

Acce

ss

Point

STA1

STA2 STA3

ESS


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IEEE standard 802.11

802.11

LAN

BSS2

802.11 LAN

BSS1 STA1

STA4

STA5

STA2

STA3


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802.11 - Layers and functions

MAC

- access mechanisms, fragmentation, encryption

MAC Management

- synchronization, roaming, MIB, power management

PLCP Physical Layer Convergence Protocol

- clear channel assessment signal (carrier sense)

PMD Physical Medium Dependent

- modulation, coding

PHY Management

- channel selection, MIB

Station Management

- coordination of all management functions

mobile terminal

access point

server

fixed terminal

application

TCP

802.11 PHY

802.11 MAC

IP

802.3 MAC

802.3 PHY

application

TCP

802.3 PHY

802.3 MAC

IP

802.11 MAC

802.11 PHY

LLC

infrastructure network

LLC LLC


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802.11 - Physical layer

3 versions: 2 radio (typ. 2.4 GHz), 1 IR

data rates 1 or 2 Mbit/s

FHSS (Frequency Hopping Spread Spectrum)

spreading, despreading, signal strength, typ. 1 Mbit/s

min. 2.5 frequency hops/s (USA), two-level GFSK modulation

DSSS (Direct Sequence Spread Spectrum)

DBPSK modulation for 1 Mbit/s (Differential Binary Phase Shift Keying),

DQPSK for 2 Mbit/s (Differential Quadrature PSK)

preamble and header of a frame is always transmitted with 1 Mbit/s, rest

of transmission 1 or 2 Mbit/s

chipping sequence: +1, -1, +1, +1, -1, +1, +1, +1, -1, -1, -1 (Barker code)

max. radiated power 1 W (USA), 100 mW (EU), min. 1mW

Infrared

850-950 nm, diffuse light, typ. 10 m range

carrier detection, energy detection, synchonization

FHSS PHY packet format

Synchronization

PMD

PLCP

MAC

LLC

MAC Management

PHY Management

P

HY

DL

C

Sta

tion

Ma

na

ge

me

nt


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synch with 010101... pattern

SFD (Start Frame Delimiter)

0000110010111101 start pattern

PLW (PLCP_PDU Length Word)

length of payload incl. 32 bit CRC of payload, PLW < 4096

PSF (PLCP Signaling Field)

data of payload (1 or 2 Mbit/s)

HEC (Header Error Check)

CRC with x16+x12+x5+1

DSSS PHY packet format

Synchronization

synch., gain setting, energy detection, frequency offset compensation

SFD (Start Frame Delimiter)

1111001110100000

Signal

data rate of the payload (0A: 1 Mbit/s DBPSK; 14: 2 Mbit/s DQPSK)

Service Length

future use, 00: 802.11 compliant length of the payload

HEC (Header Error Check)

protection of signal, service and length, x16+x12+x5+1

synchronization SFD PLW PSF HEC payload

PLCP

preamble

PLCP

header

8

0

1

6

1

2

4 1

6

variabl

e

bit

s

synchronization SFD signal

service

HEC payload

PLCP preamble PLCP header

128 16 8 8 16 variable bits

length

16


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802.11 - MAC layer I - DFWMAC

Traffic services

Asynchronous Data Service (mandatory)

exchange of data packets based on best-effort

support of broadcast and multicast

Time-Bounded Service (optional)

implemented using PCF (Point Coordination Function)

Access methods

DFWMAC-DCF CSMA/CA (mandatory)

collision avoidance via randomized back-off mechanism

minimum distance between consecutive packets

ACK packet for acknowledgements (not for broadcasts)

DFWMAC-DCF w/ RTS/CTS (optional)

Distributed Foundation Wireless MAC

avoids hidden terminal problem

DFWMAC- PCF (optional)

access point polls terminals according to a list

802.11 - MAC layer II

Priorities

defined through different inter frame spaces

no guaranteed, hard priorities

SIFS (Short Inter Frame Spacing)

highest priority, for ACK, CTS, polling response

PIFS (PCF IFS)

medium priority, for time-bounded service using PCF

DIFS (DCF, Distributed Coordination Function IFS)

lowest priority, for asynchronous data service


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802.11 - CSMA/CA access method I

station ready to send starts sensing the medium (Carrier Sense based on

CCA, Clear Channel Assessment)

if the medium is free for the duration of an Inter-Frame Space (IFS), the

station can start sending (IFS depends on service type)

if the medium is busy, the station has to wait for a free IFS, then the

station must additionally wait a random back-off time (collision

avoidance, multiple of slot-time)

if another station occupies the medium during the back-off time of the

station, the back-off timer stops (fairness)

802.11 - CSMA/CA access method II

Sending unicast packets

station has to wait for DIFS before sending data

receivers acknowledge at once (after waiting for SIFS) if the packet was

received correctly (CRC)

automatic retransmission of data packets in case of transmission errors

HiperLAN

t

medium busy SIFS

PIFS

DIFS DIFS

next frame contention

direct access if medium is free DIFS


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Bluetooth

Idea

Universal radio interface for ad-hoc wireless connectivity

Interconnecting computer and peripherals, handheld devices, PDAs, cell

phones replacement of IrDA

Embedded in other devices, goal: 5/device (2005: 40/USB bluetooth)

Short range (10 m), low power consumption, license-free 2.45 GHz ISM

Voice and data transmission, approx. 1 Mbit/s gross data rate

Characteristics

2.4 GHz ISM band, 79 (23) RF channels, 1 MHz carrier spacing

Channel 0: 2402 MHz channel 78: 2480 MHz

G-FSK modulation, 1-100 mW transmit power

FHSS and TDD

Frequency hopping with 1600 hops/s

Hopping sequence in a pseudo random fashion, determined by a master

Time division duplex for send/receive separation

Voice link SCO (Synchronous Connection Oriented)

FEC (forward error correction), no retransmission, 64 kbit/s duplex, point-

to-point, circuit switched

Data link ACL (Asynchronous ConnectionLess)


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Asynchronous, fast acknowledge, point-to-multipoint, up to 433.9 kbit/s

symmetric or 723.2/57.6 kbit/s asymmetric, packet switched

Topology and Overlapping piconets (stars) forming a scatternet


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UNIT III

1.Mobile IP

Motivation for Mobile IP

Routing

based on IP destination address, network prefix (e.g. 129.13.42)

determines physical subnet

change of physical subnet implies change of IP address to have a

topological correct address (standard IP) or needs special entries in

the routing tables

Specific routes to end-systems?

change of all routing table entries to forward packets to the right

destination

does not scale with the number of mobile hosts and frequent

changes in the location, security problems

Changing the IP-address?

adjust the host IP address depending on the current location

almost impossible to find a mobile system, DNS updates take to

long time

TCP connections break, security problems

Requirements:

Transparency

mobile end-systems keep their IP address

continuation of communication after interruption of link possible

point of connection to the fixed network can be changed

Compatibility

support of the same layer 2 protocols as IP

no changes to current end-systems and routers required


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mobile end-systems can communicate with fixed systems

Security

authentication of all registration messages

Efficiency and scalability

only little additional messages to the mobile system required

(connection typically via a low bandwidth radio link)

world-wide support of a large number of mobile systems in the

whole Internet

Terminology

Mobile Node (MN)

system (node) that can change the point of connection

to the network without changing its IP address

Home Agent (HA)

system in the home network of the MN, typically a router

registers the location of the MN, tunnels IP datagrams to the COA

Foreign Agent (FA)

system in the current foreign network of the MN, typically a router

forwards the tunneled datagrams to the MN, typically also the

default router for the MN

Care-of Address (COA)

address of the current tunnel end-point for the MN (at FA or MN)

actual location of the MN from an IP point of view

can be chosen, e.g., via DHCP

Correspondent Node (CN)

communication partner

Problems with mobile IP


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Security

authentication with FA problematic, for the FA typically belongs to

another organization

no protocol for key management and key distribution has been

standardized in the Internet

patent and export restrictions

Firewalls

typically mobile IP cannot be used together with firewalls, special

set-ups are needed (such as reverse tunneling)

QoS

many new reservations in case of RSVP

tunneling makes it hard to give a flow of packets a special

treatment needed for the QoS

Security, firewalls, QoS etc. are topics of current research and

discussions!

Security in Mobile IP

Security requirements (Security Architecture for the Internet

Protocol, RFC 1825)

Integrity

any changes to data between sender and receiver can be detected

by the receiver

Authentication

sender address is really the address of the sender and all data


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received is really data sent by this sender

Confidentiality

only sender and receiver can read the data

Non-Repudiation

sender cannot deny sending of data

Traffic Analysis

creation of traffic and user profiles should not be possible

Replay Protection

receivers can detect replay of messages

2. DHCP: Dynamic Host Configuration Protocol

Application

simplification of installation and maintenance of networked

computers

supplies systems with all necessary information, such as IP

address, DNS server address, domain name, subnet mask, default

router etc.

enables automatic integration of systems into an Intranet or the

Internet, can be used to acquire a COA for Mobile IP

Client/Server-Model

the client sends via a MAC broadcast a request to the DHCP server

(might be via a DHCP relay)

DHCP characteristics

Server

several servers can be configured for DHCP, coordination not yet

standardized (i.e., manual configuration)

Renewal of configurations

IP addresses have to be requested periodically, simplified protocol


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Options

available for routers, subnet mask, NTP (network time protocol)

timeserver, SLP (service location protocol) directory,

DNS (domain name system)

Big security problems!

no authentication of DHCP information specified

3.Ad hoc networks

Sometimes there is no infrastructure

remote areas, ad-hoc meetings, disaster areas

cost can also be an argument against an infrastructure

Sometimes not every station can hear every other station

Data needs to be forwarded in a multihop manner

Standard Mobile IP needs an infrastructure

Home Agent/Foreign Agent in the fixed network

DNS, routing etc. are not designed for mobility

Sometimes there is no infrastructure!

remote areas, ad-hoc meetings, disaster areas

cost can also be an argument against an infrastructure!

Main topic: routing

no default router available

every node should be able to forward

Traditional routing algorithms

Distance Vector

periodic exchange of messages with all physical neighbors that

contain information about who can be reached at what distance


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selection of the shortest path if several paths available

Link State

periodic notification of all routers about the current state of all

physical links

router get a complete picture of the network

Example

ARPA packet radio network (1973), DV-Routing

every 7.5s exchange of routing tables including link quality

updating of tables also by reception of packets

routing problems solved with limited flooding

An ad-hoc network as a graph

A node is a mobile station

All nodes are equal (are they?)

Iff node v can hear node u, the graph has an arc (u,v)

These arcs can have weights that represent the signal strength

Close-by nodes have MAC issues such as hidden/exposed terminal problems

Optional: links are symmetric

Optional: the graph is Euclidian, i.e., there is a link between two

nodes iff the distance d of the nodes is less than D

4.Proactive and Reactive Routing Protocols

Distance Vector (IP example RIP):

Periodic exchange of messages with all physical neighbors that contain


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information about who can be reached at what distance

Selection of the shortest path if several paths available

Link State (IP example OSPF):

Periodic notification of all routers about the current state of all physical links

Routers get a complete picture of the network

Example:

ARPA packet radio network (1973), DV-Routing

Every 7.5 s exchange of routing tables including link quality

Updating of tables also by reception of packets

Routing problems solved with limited flooding

.. Dynamic of the topology:

Frequent changes of connections, connection quality, participants

.. Limited performance of mobile systems:

Periodic updates of routing tables need energy without contributing to the

transmission of user data, sleep modes difficult to implement

Limited bandwidth of the system is reduced even more due to the exchange of

routing information

Links can be asymmetric, i.e., they can have a direction-dependent transmission

quality

.. Key problem:

Protocols have been designed for fixed networks with infrequent changes and

typically assume symmetric links!

Early work:


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On-demand version: AODV (Ad-hoc On-demand Distance Vector)

Expansion of distance vector routing

Sequence numbers for all routing update packets:

Assures in-order execution of all updates

Avoids loops and inconsistencies

Decrease of update frequency:

Store time between first and best announcement of a path

Inhibit update, if it seems to be unstable (based on the stored time values)

5.Multicast Routing

Concept: Single Source, Multiple Destinations, Duplication only at branch points.

Present Day Support:

Communication satellites.

e-mail lists, internet news distribution.

Tomorrow's multimedia applications require:

efficient use of bandwidth.

near simultaneous delivery.

Applications: Multicast & Multi-point

One to Many

Video Distribution

Wide scale Information dissemination.

Many to Many

Video Conferencing

Computer Supported Common Work.

Distributed interactive simulation.

Large scale distributed (super)computing.


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Distributed Games

Advantages.

SRSPTs are easy to compute. Use the classic unicast routing tables.

Efficient distributed implementations are possible

Entire global topology not required.

There can be no loops in the path returned.

Disadvantages

Does not minimize total cost of distribution

Does not scale well.

One piece of state information per source and per group is kept in each router.

May fail badly if the underlying unicast routing is asymmetric.

UNIT IV

1.Mobile TCP

Special handling of lengthy and/or frequent disconnections

M-TCP splits as I-TCP does

unmodified TCP fixed network to supervisory host (SH)

optimized TCP SH to MH

Supervisory host

no caching, no retransmission

monitors all packets, if disconnection detected

set sender window size to 0


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sender automatically goes into persistent mode

old or new SH reopen the window

Advantages

maintains semantics, supports disconnection, no buffer forwarding

Disadvantages

loss on wireless link propagated into fixed network

adapted TCP on wireless link

2. WAP - Wireless Application Protocol

Goals

deliver Internet content and enhanced services to mobile devices

and users (mobile phones, PDAs)

independence from wireless network standards

open for everyone to participate, protocol specifications will be

proposed to standardization bodies

applications should scale well beyond current transport media and

device types and should also be applicable to future developments

Platforms

e.g., GSM (900, 1800, 1900), CDMA IS-95, TDMA IS-136, 3rd

generation systems (IMT-2000, UMTS, W-CDMA)

Forum

WAP Forum, co-founded by Ericsson, Motorola, Nokia, Unwired

Planet


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WAP - scope of standardization

Browser

micro browser, similar to existing, well-known browsers in the

Internet

Script language

similar to Java script, adapted to the mobile environment

WTA/WTAI

Wireless Telephony Application (Interface): access to all telephone

functions

Content formats

e.g., business cards (vCard), calendar events (vCalender)

Protocol layers

transport layer, security layer, session layer etc.

Working Groups

WAP Architecture Working Group, WAP Wireless Protocol Working

Group, WAP Wireless Security Working Group, WAP Wireless

Application Working Group

World Wide Web and mobility

Protocol (HTTP, Hypertext Transfer Protocol) and language

(HTML, Hypertext Markup Language) of the Web have not been

designed for mobile applications and mobile devices, thus

creating many problems!

Typical transfer sizes

HTTP request: 100-350 byte

responses avg.

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The Web is no file system

Web pages are not simple files to download

static and dynamic content, interaction with servers via forms,

content transformation, push technologies etc.

many hyperlinks, automatic loading and reloading, redirecting

a single click might have big consequences!

WWW example

Request to port 80

GET / HTTP/1.0

Response from server

HTTP/1.1 200 OK

Date: Fri, 06 Nov 1998 14:52:12 GMT

Server: Apache/1.3b5

Connection: close

Content-Type: text/html

Institut fr Telematik


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4. WDP - Wireless Datagram Protocol

Protocol of the transport layer within the WAP architecture

uses directly transports mechanisms of different network

technologies

offers a common interface for higher layer protocols

allows for transparent communication using different transport

technologies

Goals of WDP

create a worldwide interoperable transport system with the help of

WDP adapted to the different underlying technologies

transmission services such as SMS in GSM might change, new

services can replace the old ones

5. WTLS - Wireless Transport Layer Security

Goals

data integrity

prevention of changes in data

privacy

prevention of tapping

authentication

creation of authenticated relations between a mobile device and a

server

protection against denial-of-service attacks

protection against repetition of data and unverified data

WTLS

is based on the TLS (Transport Layer Security) protocol (former

SSL, Secure Sockets Layer)

optimized for low-bandwidth communication channels


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6. WTP - Wireless Transaction Protocol

Goals

different transaction services, offloads applications

application can select reliability, efficiency

support of different communication scenarios

class 0: unreliable message transfer

class 1: reliable message transfer without result message

class 2: reliable message transfer with exactly one reliable result message

supports peer-to-peer, client/server and multicast applications

low memory requirements, suited to simple devices (< 10kbyte )

efficient for wireless transmission

segmentation/reassembly

selective retransmission

header compression

optimized connection setup (setup with data transfer)

7. WSP - Wireless Session Protocol

Goals

HTTP 1.1 functionality

Request/reply, content type negotiation, ...

support of client/server, transactions, push technology

key management, authentication, Internet security services

session management (interruption, resume,...)

Services

session management (establish, release, suspend, resume)

capability negotiation

content encoding

WSP/B (Browsing)


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HTTP/1.1 functionality - but binary encoded

exchange of session headers

push and pull data transfer

asynchronous requests

8. WAE - Wireless Application Environment

Goals

network independent application environment for low-bandwidth,

wireless devices

integrated Internet/WWW programming model with high interoperability

Requirements

device and network independent, international support

manufacturers can determine look-and-feel, user interface

considerations of slow links, limited memory, low computing power, small

display, simple user interface (compared to desktop computers)

Components

architecture: application model, browser, gateway, server

WML: XML-Syntax, based on card stacks, variables, ...

WMLScript: procedural, loops, conditions, ... (similar to JavaScript)

WTA: telephone services, such as call control, text messages, phone

book, ... (accessible from WML/WMLScript)

content formats: vCard, vCalendar, Wireless Bitmap, WML, ...

9. Wireless Telephony Application (WTA)

Collection of telephony specific extensions

Extension of basic WAE application model

content push

server can push content to the client


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client may now be able to handle unknown events

handling of network events

table indicating how to react on certain events from the network

access to telephony functions

any application on the client may access telephony functions

Example

calling a number (WML)

wtai://wp/mc;07216086415

calling a number (WMLScript)

WTAPublic.makeCall("07216086415");

11. Wireless Markup Language (WML)

WML follows deck and card metaphor

WML document consists of many cards, cards are grouped to

decks

a deck is similar to an HTML page, unit of content transmission

WML describes only intent of interaction in an abstract manner

presentation depends on device capabilities

Features

text and images

user interaction

navigation

context management

WML example


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This is a simple first card!

On the next you can choose ...

... your favorite pizza:

Margherita

Funghi

Vulcano

12. WMLScript

Complement to WML

Provides general scripting capabilities

Features

validity check of user input

check input before sent to server

access to device facilities

hardware and software (phone call, address book etc.)

local user interaction

interaction without round-trip delay

extensions to the device software

configure device, download new functionality after deployment

WMLScript example

function pizza_test(pizza_type) {

var taste = "unknown";


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if (pizza_type = "Margherita") {

taste = "well... ";

}

else {

if (pizza_type = "Vulcano") {

taste = "quite hot";

};

};

return taste;

};

Unit V


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1.Pervasive Computing

Pervasive computing is the third wave of computing

technologies to emerge since computers first

appeared:

First Wave - Mainframe computing era: one computer

shared by many people, via workstations.

Second Wave - Personal computing era: one

computer used by one person, requiring a conscious

interaction. Users largely bound to desktop.

Third Wave Pervasive (initially called ubiquitous)

computing era: one person, many computers.

Millions of computers embedded in the environment,

allowing technology to recede into the background

Pervasive Environment

The most important characteristics of pervasive environments are:

Heterogeneity: Computing will be carried out on a wide spectrum of

client devices, each with different configurations and functionalities.

Prevalence of "Small" Devices: Many devices will be small, not only

in size but also in computing power, memory size, etc.

Limited Network Capabilities: Most of the devices would have some

form of connection. However, even with the new networking standards

such as GPRS, Bluetooth, 802.11x, etc., the bandwidth is still relatively

limited compared to wired network technologies. Besides, the

connections are usually unstable.

High Mobility: Users can carry devices from one place to another

without stopping the services.

User-Oriented: Services would be related to the user rather than a

specific device, or specific location.


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Highly Dynamic Environment: An environment in which users and

devices keep moving in and out of a volatile network.

Evolution

Distributed Computing

intersection of personal computers and local area networks.

Mobile Computing

The appearance of full- function laptop computers and wireless LANs in the

early 1990s led researchers to confront the problems that arise in building a distributed

system with mobile clients. The field of mobile computing was thus born.

Pervasive Architecture

Architecture is an abstraction of the system. Architecture defines the system elements and how they interact.

Architecture suppresses the local information about the elements.

Defines the properties of the components Provided services, required services, performance characteristics, fault handling, resource usage


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Device Technology

Hardware

Battery

Displays

Memory

Processors

Interfaces

Keyboards

HARDWARE - Battery

Expected lifetime for NiCad, NiMH, and Li ion batteries

Chemistry Standby time (h) Talk time (m)

NiCad 12-27 85-160

NiMH 16-37 110-210

Li ion 21-50 170-225

Hardware-Displays

LCDs are already replacing the bulky cathode ray tubes.

larger and more readable

dramatic weight, size, and power consumption benefits of LCD technology outweigh

their relatively high cost.

Today's PDAs usually feature dual-scan (DSTN) displays that control individual display

elements via passive matrix addressing.

This technology consumes consid-erably less power than the thin-film transistor (TFT)

active matrix technology.

This latter technology is more expensive, but is capable of sig-nificantly superior

display performance and thus is generally used in portable computers.


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Hardware-Memory

Memory is becoming cheaper, while the demand from applications is growing.

Development is driven in part by smart phones, digital cameras, MP3 players and

PDAs.

For these mobile devices, the currently available technologies and their associated costs

have reached a point where it is now feasible to integrate several megabytes of memory

into a mobile device with an acceptable form factor.

On PCs, permanent data can be stored on hard disk drives.

For mobile devices, this is often not an option because neither the space nor the power

supply is available.

Recently, extremely small removable disk drives like the IBM Microdrive became

available.

Their capacity ranges between 340 MB and 1 GB, and is sufficient to store, for

example, several hundred pictures when used in a digital camera

Hardware-Processors

During the last couple of years, the clock rate of microprocessors and the processing

power available from them has increased steadily.

Rapid improvements in the CMOS manufacturing process have created ever-smaller

structures and delivered higher and higher numbers of transistors per chip.

At the same time, the processor core voltage was low-ered from the industry standard

3.3 V in 1995 to 1.35 V in 2000.

This means lower heat emissions, which in turn paves the way for new improvements

like larger on-die caches.

This, together with advances in packaging technologies, delivers the modern Central

Processing Units (CPUs) found in mobile computers and PDAs today.

Hardware-Human-machine interfaces

Like their PC predecessors, many mobile devices also use keyboards and displays to

interface with their users.


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However, these are usually much smaller and specialized for the application and the

form factor of particu-lar devices.

Phones, for example, tend to have only number keys, plus a few extra keys for the built-

in menus.

This is because the size of the device is important and because users enter less text than

on a PC.

Other devices try to limit the number of mechanical keys to an absolute mini-mum,

using them only to trigger the most important applications and for menu navigation.

An example is the PDA.

Finally, there are devices that have no means of display or keyboard whatsoever.

These so-called head-less devices are most often used as controllers and interface only

to other devices.

Hardware-Human-machine interfaces

When reaching a haptic mark, the user feels a resistance generated by the motor against

the turning direction.

This force increases until a spe-cific position is reached.

When the knob passes that position, the force gets smaller again.

This can be used to create the impression of a knob that can be put into a programmable

number of positions.

It allows a single knob to be used for navigating through a menu structure where each

menu choice is represented by one position.

Biometrics

Definition

Biometrics is the science of verifying and establishing the identity of an

individual

through physiological features or behavioral traits.

Examples


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o Physical Biometrics

Fingerprint

Hand Geometry

Iris patterns

o Behavioral Biometrics

Handwriting

Signature

Speech

Gait

o Chemical/Biological Biometrics

Perspiration

Skin composition(spectroscopy)

Advantages of biometrics

Uniqueness

No need to remember passwords or carry tokens

Biometrics cannot be lost, stolen or forgotten

More secure than a long password

Solves repudiation problem

Not susceptible to traditional dictionary attacks

Software-Operating systems

The core functionality of every pervasive computing device is determined by its

operating system.

The major differences of operating systems for pervasive devices from the user's point

of view are the human-machine interface, and the speed with which a task can be

performed.

For pervasive devices, there will likely be no equivalent to the Windows/Intel

monopoly in the near future because pervasive devices do have a wide range of usages

(from mobile phones to set-top boxes) with very con-strained hardware.


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There are two trends visible for pervasive computing operating systems.

For personal use, the two major PDA operating systems, Palm OS and Windows CE,

are becoming more similar, and can integrate phone functionality in a new device that

combines a PDA with a cell phone.

For home use, the development is directed towards high-performance multimedia

operating systems, such as embedded Linux or BeOS.

Security

Issues in biometrics

o Biometrics is secure but not secret

o Permanently associated with user

o Used across multiple applications

o Can be covertly captured

Types of circumvention

o Denial of service attacks(1)

o Fake biometrics attack(2)

o Replay and Spoof attacks(3,5)

o Trojan horse attacks(4,6,7)

o Back end attacks(8)

o Collusion

o Coercion

Fingerprints

Minutiae: Local anomalies in the ridge flow

Pattern of minutiae are unique to each

Individual

Pervasive web Application Architecture


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This is an architecture for pervasive computing applications that support multiple

devices, such as PCs, WAP phones, PDA and voice-only phones enabled to access Web

servers through voice gate-ways.

The architecture addresses the special problems associated with pervasive computing,

including diversity of devices, markup language and authentication methods.

shows how pervasive computing applications based on this architecture can be secured.

Users have many different devices that look and behave in very different ways.

Examples of several kinds of pervasive computing devices includes WAP phones,

PDAs, and voice-recognition devices.

These devices proving different user interfaces, use different markup languages, use

differrent communication protocols, and have different ways of authenticating themselves

to servers.

Ideally, Web applications that support pervasive computing should adapt to whatever

device their users are using.

Applications must provide content in a form that is appropriate for the user's particular

device - WML for WAP phones, Voice XML for voice interaction via a voice browser,

HTML for PCs, and so on.

Scalability and availability

Given the ever-growing number of pervasive computing devices, scalability of

pervasive computing applications is a very important issue.

Large telecommunication companies expect millions of users to subscribe for some

applications, for example.

Availability is of particular importance in the pervasive computing environment.

Unlike PC users, most users of pervasive computing devices and applications will

neither understand nor accept comments like 'server currently down for maintenance' - if

a service is not available when they need it, they will assume that it does not work, and

will stop using the application or switch to another service provider.


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Both issues can be resolved by system topologies that employ parallelism and

redundancy to guarantee scalability and availability.

Pervasive application architecture

The model-view-controller (MVC) pattern is a good choice when implementing Web

applications.

standard mapping of the pattern to servlets, JSPs, and EJBs, where controller is

implemented as a servlet, the model implemented as a secure EJBs, and the views as

JSPs.

Pervasive computing applications, however, add an additional level of complexity.

As devices are very different from each other, we can assume that one controller will fit

all device classes. In the MVC pattern the controller encapsulates the dialog flow of an

application.

This flow will be different for different classes of devices, such as WAP phone, voice-

only phones, PCs, or PDAs.

Thus, we need different controller for different classes of devices.

To support multiple controllers, we replace the servlet's role to that of a simple

dispatcher that invokes the appropriate controller depending on the type of device being

used


cs2402-mobile and pervasive computing

Documents

communication mobile

gsm standards gsm

mobile units

smaller cells

nearby cells

frequency http

world use gsm

groupe spciale mobile