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
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