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Mobile InternetWireless Network Architectures and Applications
Sridhar Iyer K R School of Information Technology
IIT Bombay
[email protected]://www.it.iitb.ac.in/~sri
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Outline
Introduction and OverviewWireless LANs: IEEE 802.11Mobile IP routing
TCP over wirelessGSM air interfaceGPRS network architecture
Wireless application protocolMobile agentsMobile ad hoc networks
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ReferencesJ. Schiller, Mobile Communications, Addison Wesley, 2000802.11 Wireless LAN, IEEE standards, www.ieee.orgMobile IP, RFC 2002, RFC 334, www.ietf.orgTCP over wireless, RFC 3150, RFC 3155, RFC 3449A. Mehrotra, GSM System Engineering, Artech House, 1997
Bettstetter, Vogel and Eberspacher, GPRS: Architecture, Protocolsand Air Interface, IEEE Communications Survey 1999, 3(3).M.v.d. Heijden, M. Taylor. Understanding WAP, Artech House, 2000Mobile Ad hoc networks, RFC 2501
Others websites: www.palowireless.com www.gsmworld.com; www.wapforum.org www.etsi.org; www.3gtoday.com
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Wireless networks
Access computing/communication services, on the move
Cellular Networks traditional base station infrastructure systems
Wireless LANs infrastructure as well as ad-hoc networks possible very flexible within the reception area low bandwidth compared to wired networks (1-10 Mbit/s)
Ad hoc Networks useful when infrastructure not available, impractical, or expensive military applications, rescue, home networking
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Some mobile devices
Clamshell handhelds Tablets
Netenabled mobilehones
Palm-sized
Laptop computers
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Limitations of the mobile environment
Limitations of the Wireless Network limited communication bandwidth frequent disconnections heterogeneity of fragmented networks
Limitations Imposed by Mobility route breakages lack of mobility awareness by system/applications
Limitations of the Mobile Device short battery lifetime limited capacities
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Wireless v/s Wired networksRegulations of frequencies Limited availability, coordination is required useful frequencies are almost all occupied
Bandwidth and delays Low transmission rates
few Kbits/s to some Mbit/s. Higher delays several hundred milliseconds
Higher loss rates susceptible to interference, e.g., engines, lightning
Always shared medium Lower security, simpler active attacking radio interface accessible for everyone Fake base stations can attract calls from mobile phones secure access mechanisms important
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Cellular systems: Basic idea
Single hop wireless connectivity Space divided into cells A base station is responsible to communicate with
hosts in its cell
Mobile hosts can change cells while communicating Hand-off occurs when a mobile host starts
communicating via a new base station
Factors for determining cell size No. of users to be supported Multiplexing and transmission technologies
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Cellular conceptLimited number of frequencies => limited channelsHigh power antenna => limited number of usersSmaller cells => frequency reuse possible => more users
Base stations (BS): implement space division multiplex Cluster : group of nearby BSs that together use all available
channels
Mobile stations communicate only via the base station FDMA, TDMA, CDMA may be used within a cell
As demand increases (more channels are needed) Number of base stations is increased Transmitter power is decreased correspondingly to avoid
interference
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Cellular system architecture
Each cell is served by a base station (BS)Each BSS is connected to a mobile switching center (MSC) throughfixed linksEach MSC is connected to other MSCs and PSTN
MSC MSC
HLR
VLR
HLR
VLR
To other MSCs
PSTNPSTN
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Outgoing call setup
Outgoing call setup : User keys in the number and presses send Mobile transmits access request on uplink signaling
channel If network can process the call, BS sends a channel
allocation message Network proceeds to setup the connectionNetwork activity : MSC determines current location of target mobile
using HLR, VLR and by communicating with other MSCs
Source MSC initiates a call setup message to MSCcovering target area
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Incoming call setup
Incoming call setup : Target MSC (covering current location of mobile)initiates a paging message
BSs forward the paging message on downlink
channel in coverage area If mobile is on (monitoring the signaling channel), it
responds to BS BS sends a channel allocation message and
informs MSCNetwork activity : Network completes the two halves of the connection
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Hand-OffsBS initiated :
Handoff occurs if signal level of mobile falls below threshold Increases load on BS
Monitor signal level of each mobile Determine target BS for handoff
Mobile assisted : Each BS periodically transmits beacon Mobile, on hearing stronger beacon from a new BS, initiates
the handoff
Intersystem : Mobile moves across areas controlled by different MSCs Handled similar to mobile assisted case with additional
HLR/VLR effort
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Effect of mobility on protocol stack
Application new applications and adaptations
Transport congestion and flow control
Network addressing and routing
Link
media access and handoff Physical transmission errors and interference
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Mobile applications - 1
Vehicles transmission of news, road condition etc ad-hoc network with near vehicles to prevent
accidents
Emergencies early transmission of patient data to the hospital ad-hoc network in case of earthquakes, cyclones military ...
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Mobile applications - 2
Travelling salesmen direct access to central customer files consistent databases for all agents
Web access outdoor Internet access intelligent travel guide with up-to-date
location dependent information
Location aware services find services in the local environment
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Mobile applications - 3
Information services push: e.g., stock quotes pull: e.g., weather update
Disconnected operations mobile agents, e.g., shopping
Entertainment ad-hoc networks for multi user games
Messaging
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Mobile applications in the Industry
Wireless access: (phone.com) openwaveAlerting services: myalert.com
Location services: (airflash) webraska.comIntranet applications: (imedeon) viryanet.comBanking services: macalla.com
Mobile agents: tryllian.com.
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Bandwidth and applications
Speed, kbps2G
CDMA 2.5GGPRS, CDMA 2000
EDGEUMTS
Transaction ProcessingMessaging/Text Apps
Voice/SMSLocation Services
Still Image Transfers
Internet/VPN AccessDatabase AccessDocument Transfer
Low Quality VideoHigh Quality Video
9.6 14.4 28 64 144 384 2000
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Evolution of cellular networks
First-generation : Analog cellular systems (450-900 MHz) Frequency shift keying; FDMA for spectrum sharing NMT (Europe), AMPS (US)
Second-generation : Digital cellular systems (900, 1800 MHz) TDMA/CDMA for spectrum sharing; Circuit switching GSM (Europe), IS-136 (US), PDC (Japan)
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GSM to GPRS
Radio resources are allocated for only one or afew packets at a time, so GPRS enables many users to share radio resources, and allow
efficient transport of packets
connectivity to external packet data networks volume-based charging
High data rates (up to 171 kbps in ideal case)GPRS carries SMS in data channels rather thansignaling channels as in GSM
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UMTS: Universal Mobile Telecomm. Standard
Global seamless operation in multi-cell environment(SAT, macro, micro, pico)Global roaming: multi-mode, multi-band, low-costterminal, portable services & QoS
High data rates at different mobile speeds: 144kbps atvehicular speed (80km/h), 384 kbps at pedestrianspeed, and 2Mbps indoor (office/home)
Multimedia interface to the internetBased on core GSM, conforms to IMT-2000W-CDMA as the air-interface
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Evolution to 3G Technologies
IS-95BCDMA
2G 3G
cdma2000
GSM FDD
TDD
W-CDMA
GPRS
IS-136TDMA UWC-136
EDGE & 136HS outdoor
136 HSindoor
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384 Kbps
56 Kbps
54 Mbps
72 Mbps
5-11 Mbps
1-2 Mbps 802.11
Wireless Technology Landscape
Bluetooth
802.11b
802.11{a,b}Turbo .11a
Indoor
10 30m
IS-95, GSM, CDMA
WCDMA, CDMA2000
Outdoor
50 200m
Mid rangeoutdoor
200m 4Km
Long rangeoutdoor
5Km 20Km
Long distancecom.
20m 50Km
wave p-to-p links
.11 p-to-p link
2G
3G
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3G Network Architecture
Mobile AccessRouter
Mobile AccessRouter
WirelessAccess Network
IPBase Stations
IPBase Stations
GatewayGatewayTelephoneNetwork
Core Network
User Profiles &Authentication
(HLR)
3G AirInterface
Wired Access
802.11
IP Intranet
IP Intranet
ProgrammableSoftswitch
ProgrammableSoftswitch
Application
Server
ApplicationServer
802.11
Access
Point
Access
Point
AccessPoint
AccessPoint
Internet
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Wireless LANs
Infrared (IrDA) or radio links (Wavelan)Advantages very flexible within the reception area Ad-hoc networks possible (almost) no wiring difficultiesDisadvantages low bandwidth compared to wired networks
many proprietary solutions
Infrastructure v/s ad-hoc networks (802.11)
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Infrastructure vs. Adhoc Networksinfrastructurenetwork
ad-hoc network
APAP
AP
wired network
AP: Access Point
Source: Schiller
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Difference Between Wired andWireless
If both A and C sense the channel to be idle at the sametime, they send at the same time.Collision can be detected at sender in Ethernet.Half-duplex radios in wireless cannot detect collision atsender.
A B CA
B
C
Ethernet LAN Wireless LAN
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A and C cannot hear each other. A sends to B, C cannot receive A. C wants to send to B, C senses a free medium
(CS fails) Collision occurs at B.
A cannot receive the collision (CD fails). A is hidden for C.
Hidden Terminal Problem
BA C
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IEEE 802.11
Acknowledgements for reliabilitySignaling packets for collision avoidance RTS (request to send)
CTS (clear to send) Signaling ( RTS/CTS ) packets contain sender address receiver address duration (packet size + ACK)
Power-save mode
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Spectrum War: Status todayEnterprise 802.11Network
Public 802.11Wireless Carrier
Source: Pravin Bhagwat
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Spectrum War: EvolutionEnterprise 802.11Network
Public 802.11Wireless Carrier
Market consolidationEntry of WirelessCarriersEntry of new playersFootprint growth
Source: Pravin Bhagwat
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Spectrum War: Steady StateEnterprise 802.11Network
Public 802.11Wireless Carrier
Virtual Carrier
Emergence of virtualcarriersRoaming agreements
Source: Pravin Bhagwat
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Routing and Mobility
Finding a path from a source to a destinationIssues Frequent route changes Route changes may be related to host movement Low bandwidth links
Goal of routing protocols
decrease routing-related overhead find short routes find stable routes (despite mobility)
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Mobile IP: Basic Idea
Router 1
Router 3
Router 2
S MN
Homeagent
Source: Vaidya
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Mobile IP: Basic Idea
Router 1
Router 3
Router 2
S MN
Home agent
Foreign agent
move
Packets are tunneledusing IP in IP
Source: Vaidya
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TCP over wireless
TCP provides reliable ordered delivery (uses retransmissions , if
necessary) cumulative ACKs (an ACK acknowledges all
contiguously received data) duplicate ACKs (whenever an out-of-order segment is
received) end-to-end semantics (receiver sends ACK after data
has reached) implements congestion avoidance and control using
congestion window
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TCP over wireless
Factors affecting TCP over wireless: Wireless transmission errors
may cause fast retransmit, which results in reduction incongestion window size
reducing congestion window in response to errors isunnecessary
Multi-hop routes on shared wireless medium Longer connections are at a disadvantage compared to
shorter ones, because they have to contend for wirelessaccess at each hop
Route failures due to mobility
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Indirect TCP (I-TCP)
I-TCP splits the TCP connection no changes to the TCP protocol for wired hosts TCP connection is split at the foreign agent hosts in wired network do not notice
characteristics of wireless part no real end-to-end connection any longer
mobile hostaccess point(foreign agent) wired Internet
wireless TCP standard TCP
Source: Schiller
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Mobile TCP (M-TCP)
Handling of lengthy or frequent disconnectionsM-TCP splits as I-TCP does unmodified TCP for fixed network to foreign agent
optimized TCP for FA to MHForeign Agent monitors all packets, if disconnection detected
set sender window size to 0 sender automatically goes into persistent mode
no caching, no retransmission
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Application Adaptations for Mobility
Design Issues System transparent v/s System aware Application transparent v/s Application aware
Models conventional, unaware client/server model client/proxy/server model
caching/pre-fetching model mobile agent model
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World Wide Web and Mobility
HTTP characteristics designed for large bandwidth, low delay stateless, client/server, request/response
communication
connection oriented, one connection per request TCP 3-way handshake, DNS lookup overheads
HTML characteristics designed for computers with high performance,
color high-resolution display, mouse, hard disk typically, web pages optimized for design, not for
communication; ignore end-system characteristics
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The Client/Proxy/Server Model
Proxy functions as a client to the fixed networkserver Proxy functions as a mobility-aware server tomobile client
Proxy may be placed in the mobile host (Coda),or the fixed network, or both (WebExpress)
Enables thin client design for resource-poor mobile devices
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Web Proxy in WebExpress
The WebExpress Intercept Model
Source: Helal
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Wireless Application Protocol
Browser Micro browser, similar to existing web browsersScript language Similar to Javascript, adapted to mobile devices
Gateway Transition from wireless to wired worldServer Wap/Origin server, similar to existing web servers
Protocol layers Transport layer, security layer, session layer etc.Telephony application interface Access to telephony functions
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WAP: Network Elements
wireless networkfixed network
WAPproxy
WTA
server
filter/WAPproxyweb
server
filter
PSTN
Internet
Binary WML: binary file format for clients
Binary WML
Binary WML
Binary WML
HTML
HTML
HTML WML
WMLHTML
Source: Schiller
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WAP: Reference Model
Bearers (GSM, CDPD, ...)
Security Layer (WTLS)
Session Layer (WSP)
Application Layer (WAE)
Transport Layer (WDP)TCP/IP,
UDP/IP,media
SSL/TLS
HTML, Java
HTTP
Internet WAP
WAE comprises WML (Wireless Markup Language), WML Script, WTAI etc.
Source: Schiller
Transaction Layer (WTP)
additional servicesand applications
WCMP
A-SAP
S-SAP
TR-SAP
SEC-SAP
T-SAP
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WAP Stack OverviewWDP functionality similar to UDP in IP networks
WTLS functionality similar to SSL/TLS (optimized for wireless)
WTP Class 0: analogous to UDP Class 1: analogous to TCP (without connection setup overheads) Class 2: analogous to RPC (optimized for wireless) features of user acknowledgement, hold on
WSP WSP/B: analogous to http 1.1 (add features of suspend/resume) method: analogous to RPC/RMI features of asynchronous invocations, push (confirmed/unconfirmed)
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The Mobile Agent Model
Mobile agent receives client request andMobile agent moves into fixed network
Mobile agent acts as a client to the server Mobile agent performs transformations and filtering
Mobile agent returns back to mobile platform, whenthe client is connected
M bil Ag t E l
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Mobile Agents: Example
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Outline
Introduction and Overview Wireless LANs: IEEE 802.11Mobile IP routing
TCP over wirelessGSM air interfaceGPRS network architectureWireless application protocolMobile agentsMobile ad hoc networks
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How Wireless LANs are different
Destination address does not equal destinationlocationThe media impact the design wireless LANs intended to cover reasonable
geographic distances must be built from basiccoverage blocks
Impact of handling mobile (and portable)stations Propagation effects Mobility management power management
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802.11: Motivation
Can we apply media access methods from fixed networksExample CSMA/CD Carrier S ense Multiple Access with Collision Detection send as soon as the medium is free, listen into the medium if a
collision occurs (original method in IEEE 802.3)
Medium access problems in wireless networks signal strength decreases proportional to the square of the
distance sender would apply CS and CD, but the collisions happen at the
receiver sender may not hear the collision, i.e., CD does not work CS might not work, e.g. if a terminal is hidden
Hidden and exposed terminals
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Solution for Hidden/Exposed Terminals
A first sends a Request-to-Send (RTS) to BOn receiving RTS , B responds Clear-to-Send (CTS)Hidden node C overhears CTS and keeps quiet Transfer duration is included in both RTS and CTS
Exposed node overhears a RTS but not the CTS Ds transmission cannot interfere at B
A B CRTS
CTS CTS
DATA
DRTS
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IEEE 802.11
Wireless LAN standard defined in the unlicensedspectrum (2.4 GHz and 5 GHz U-NII bands)
Standards covers the MAC sublayer and PHY layersThree different physical layers in the 2.4 GHz band FHSS, DSSS and IR
OFDM based PHY layer in the 5 GHz band
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Components of IEEE 802.11architecture
The basic service set (BSS) is the basic buildingblock of an IEEE 802.11 LANThe ovals can be thought of as the coverage areawithin which member stations can directlycommunicateThe Independent BSS (IBSS) is the simplest LAN. Itmay consist of as few as two stations
ad-hoc networkBSS2
BSS1
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802.11 - ad-hoc network (DCF)
Direct communicationwithin a limited range Station (STA):
terminal with accessmechanisms to thewireless medium
Basic Service Set (BSS):group of stations using the
same radio frequency
802.11 LAN
BSS 2
802.11 LAN
BSS 1STA 1
STA 4
STA 5
STA 2
STA 3
Source: Schiller
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Distribution System
Portal
802.x LAN
AccessPoint
802.11 LAN
BSS 2
802.11 LAN
BSS 1Access
Point
802.11 - infrastructure network (PCF)Station (STA) terminal with access mechanisms
to the wireless medium and radiocontact to the access pointBasic Service Set (BSS) group of stations using the same
radio frequencyAccess Point
station integrated into the wirelessLAN and the distribution systemPortal bridge to other (wired) networksDistribution System interconnection network to form
one logical network (EES:Extended Service Set) basedon several BSS
STA 1
STA 2 STA 3
ESS
Source: Schiller
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Distribution System (DS) concepts
The Distribution system interconnects multiple BSSs802.11 standard logically separates the wirelessmedium from the distribution system it does notpreclude, nor demand, that the multiple media besame or differentAn Access Point (AP) is a STA that provides accessto the DS by providing DS services in addition toacting as a STA.Data moves between BSS and the DS via an APThe DS and BSSs allow 802.11 to create a wirelessnetwork of arbitrary size and complexity called theExtended Service Set network (ESS)
802 11 in the TCP/IP stack
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802.11- in the TCP/IP stack
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 - Layers and functions
PLCP Physical Layer ConvergenceProtocol
clear channel assessmentsignal (carrier sense)
PMD Physical Medium Dependent modulation, codingPHY Management channel selection, MIBStation Management
coordination of allmanagement functions
PMD
PLCP
MAC
LLC
MAC Management
PHY Management
MAC access mechanisms,
fragmentation, encryptionMAC Management synchronization, roaming,
MIB, power management
PHY
DLC
Station
Ma
7.8.1
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802.11 - Physical layer
3 versions: 2 radio (typically 2.4 GHz), 1 IR data rates 1, 2, or 11 Mbit/s
FHSS (Frequency Hopping Spread Spectrum) spreading, despreading, signal strength, typically 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 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. 1mWInfrared 850-950 nm, diffuse light, typ. 10 m range carrier detection, energy detection, synchonization
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Spread-spectrum communications
Source: Intersil
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DSSS Barker Code modulation
Source: Intersil
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DSSS properties
Source: Intersil
802 11 MAC layer
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802.11 - MAC layer
Traffic services Asynchronous Data Service (mandatory) DCF Time-Bounded Service (optional) - PCF
Access methods DCF CSMA/CA (mandatory) collision avoidance via randomized back-off mechanism ACK packet for acknowledgements (not for broadcasts)
DCF w/ RTS/CTS (optional)
avoids hidden terminal problem PCF (optional)
access point polls terminals according to a list
802 11 C i S i
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802.11 - Carrier Sensing
In IEEE 802.11, carrier sensing is performed at the air interface ( physical carrier sensing ), and at the MAC layer ( virtual carrier sensing )Physical carrier sensing detects presence of other users by analyzing all detected
packets Detects activity in the channel via relative signal strength
from other sourcesVirtual carrier sensing is done by sending MPDU durationinformation in the header of RTS/CTS and data framesChannel is busy if either mechanisms indicate it to be Duration field indicates the amount of time (in microseconds)
required to complete frame transmission Stations in the BSS use the information in the duration field to
adjust their network allocation vector (NAV)
802 11 - Reliability
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802.11 Reliability
Use of acknowledgements
When B receives DATA from A, B sends an ACK If A fails to receive an ACK, A retransmits the DATA Both C and D remain quiet until ACK (to prevent collision of
ACK) Expected duration of transmission+ACK is included in
RTS/CTS packets
A B CRTS
CTS CTS
DATA
DRTS
ACK
802 11 P i i i
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802.11 - Priorities
defined through different inter frame spaces mandatory idle timeintervals between the transmission of framesSIFS (Short Inter Frame Spacing) highest priority, for ACK, CTS, polling response SIFSTime and SlotTime are fixed per PHY layer (10 s and 20 s respectively in DSSS)PIFS (PCF IFS) medium priority, for time-bounded service using PCF PIFSTime = SIFSTime + SlotTimeDIFS (DCF IFS) lowest priority, for asynchronous data service DCF-IFS ( DIFS ): DIFSTime = SIFSTime + 2xSlotTime
802 11 CSMA/CA
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t
medium busy
DIFSDIFS
next frame
contention window(randomized back-off mechanism)
802.11 - CSMA/CA
station ready to send starts sensing the medium (Carrier Sensebased 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)
slot timedirect access if medium is free DIFS
802 11 CSMA/CA example
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802.11 CSMA/CA example
t
busy
bo e
station 1
station 2
station 3
station 4
station 5
packet arrival at MAC
DIFSbo e
bo e
bo e
busy
elapsed backoff time
bo r residual backoff time
busy medium not idle (frame, ack etc.)
bo r
bo r DIFS
bo e
bo e
bo e bo r DIFS
busy
busy
DIFSbo e busy
bo e
bo e
bo r
bo r
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802.11 - Collision AvoidanceCollision avoidance: Once channel becomes idle, thenode waits for a randomly chosen duration beforeattempting to transmitDCF When transmitting a packet, choose a backoff interval in the
range [0, cw ]; cw is contention window Count down the backoff interval when medium is idle Count-down is suspended if medium becomes busy When backoff interval reaches 0, transmit RTS
Time spent counting down backoff intervals is part of MAC overhead
DCF E l
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DCF Example
data
waitB1 = 5
B2 = 15
B1 = 25
B2 = 20
data
wait
B1 and B2 are backoff intervalsat nodes 1 and 2cw = 31
B2 = 10
802 11 - Congestion Control
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802.11 Congestion Control
Contention window (cw ) in DCF: Congestioncontrol achieved by dynamically choosing cwlarge cw leads to larger backoff intervalssmall cw leads to larger number of collisions
Binary Exponential Backoff in DCF: When a node fails to receive CTS in response to
its RTS , it increases the contention window cw is doubled (up to a bound CWmax ) Upon successful completion data transfer, restore
cw to CW min
802 11 CSMA/CA II
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802.11 - CSMA/CA II
station has to wait for DIFS before sending data
receivers acknowledge at once (after waiting for SIFS) if the packetwas received correctly (CRC)automatic retransmission of data packets in case of transmissionerrors
t
SIFS
DIFS
data
ACK
waiting time
other stations
receiver
sender data
DIFS
contention
802 11 RTS/CTS
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802.11 RTS/CTSstation can send RTS with reservation parameter after waiting for DIFS(reservation determines amount of time the data packet needs the medium)acknowledgement via CTS after SIFS by receiver (if ready to receive)sender can now send data at once, acknowledgement via ACKother stations store medium reservations distributed via RTS and CTS
t
SIFS
DIFS
data
ACK
defer access
other stations
receiver
sender data
DIFS
contention
RTS
CTSSIFS SIFS
NAV (RTS)NAV (CTS)
Fragmentation
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Fragmentation
t
SIFS
DIFS
data
ACK1
other stations
receiver
sender frag 1
DIFS
contention
RTS
CTSSIFS SIFS
NAV (RTS)NAV (CTS)
NAV (frag 1)NAV (ACK 1)
SIFSACK2
frag 2
SIFS
802 11 Point Coordination Function
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802.11 - Point Coordination Function
802 11 PCF I
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802.11 - PCF I
PIFS
stationsNAV
wirelessstations
pointcoordinator
D1
U1SIFS
NAV
SIFSD2
U2SIFS
SIFS
SuperFramet0
medium busy
t1
802 11 PCF II
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802.11 - PCF II
tstationsNAV
wirelessstations
pointcoordinator
D3
NAV
PIFSD4
U4SIFS
SIFSCF end
contentionperiod
contention free period
t2 t3 t4
CFP structure and Timing
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CFP structure and Timing
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PCF- Data transmission
Polling Mechanisms
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Polling Mechanisms
With DCF, there is no mechanism to guaranteeminimum delay for time-bound servicesPCF wastes bandwidth (control overhead) whennetwork load is light, but delays are bounded
With Round Robin (RR) polling, 11% of time wasused for pollingThis values drops to 4 % when optimized polling isused
Implicit signaling mechanism for STAs to indicatewhen they have data to send improves performance
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Coexistence of PCF and DCF
PC controls frame transfers during a Contention FreePeriod (CFP). CF-Poll control frame is used by the PC to invite a station to
send data
CF-End is used to signal the end of the CFPThe CFP alternates with a CP, when DCF controlsframe transfers The CP must be large enough to send at least one
maximum-sized MPDU including RTS/CTS/ACK
CFPs are generated at the CFP repetition rate andeach CFP begins with a beacon frame
802 11 Frame format
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802.11 - Frame formatTypes
control frames, management frames, data framesSequence numbers important against duplicated frames due to lost ACKs
Addresses receiver, transmitter (physical), BSS identifier, sender (logical)
Miscellaneous sending time, checksum, frame control, data
Frame
Control
Duration
ID
Address
1
Address
2
Address
3
Sequence
Control
Address
4Data CRC
2 2 6 6 6 62 40-2312bytes
version, type, fragmentation, security, ...
Frame Control Field
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Frame Control Field
Types of Frames
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Types of Frames
Control Frames RTS/CTS/ACK CF-Poll/CF-End
Management Frames Beacons Probe Request/Response Association Request/Response Dissociation/Reassociation
Authentication/Deauthentication ATIM
Data Frames
MAC address format
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MAC address formatscenario to DS from
DSaddress 1 address 2 address 3 address 4
ad-hoc network 0 0 DA SA BSSID -infrastructurenetwork, from AP
0 1 DA BSSID SA -
infrastructurenetwork, to AP
1 0 BSSID SA DA -
infrastructure
network, within DS
1 1 RA TA DA SA
DS: Distribution SystemAP: Access PointDA: Destination AddressSA: Source AddressBSSID: Basic Service Set Identifier RA: Receiver AddressTA: Transmitter Address
802.11 - MAC management
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802.11 MAC management
Synchronization try to find a LAN, try to stay within a LAN timer etc.
Power management sleep-mode without missing a message
periodic sleep, frame buffering, traffic measurementsAssociation/Reassociation integration into a LAN roaming, i.e. change networks by changing access points
scanning, i.e. active search for a networkMIB - Management Information Base managing, read, write
802 11 - Synchronization
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802.11 Synchronization
All STAs within a BSS are synchronized to a commonclock PCF mode: AP is the timing master
periodically transmits Beacon frames containing Timing
Synchronization function (TSF) Receiving stations accepts the timestamp value in TSF
DCF mode: TSF implements a distributed algorithm Each station adopts the timing received from any beacon that has
TSF value later than its own TSF timer
This mechanism keeps the synchronization of the TSFtimers in a BSS to within 4 s plus the maximumpropagation delay of the PHY layer
Synchronization using a Beacon
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(infrastructure)
beacon interval
tmedium
accesspoint
busy
B
busy busy busy
B B B
value of the timestamp B beacon frame
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802 11 - Power management
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802.11 Power managementIdea: switch the transceiver off if not needed States of a station: sleep and awake
Timing Synchronization Function (TSF) stations wake up at the same time
Infrastructure Traffic Indication Map (TIM)
list of unicast receivers transmitted by AP Delivery Traffic Indication Map (DTIM)
list of broadcast/multicast receivers transmitted by AP
Ad-hoc Ad-hoc Traffic Indication Map (ATIM)
announcement of receivers by stations buffering frames more complicated - no central AP collision of ATIMs possible (scalability?)
802 11 - Energy conservation
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802.11 Energy conservation
Power Saving in IEEE 802.11 (InfrastructureMode) An Access Point periodically transmits a beacon
indicating which nodes have packets waiting for them Each power saving (PS) node wakes up periodically
to receive the beacon If a node has a packet waiting, then it sends a PS-
Poll After waiting for a backoff interval in [ 0,CW min ]
Access Point sends the data in response to PS-poll
Power saving with wake-up patterns
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(infrastructure)
TIM interval
t
medium
accesspoint
busy
D
busy busy busy
T T D
T TIM D DTIM
DTIM interval
BB
B broadcast/multicast
station
awake
p PS poll
p
d
d
d data transmissionto/from the station
Power saving with wake-up patterns
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(ad-hoc)
awake
A transmit ATIM D transmit datat
station 1B1 B1
B beacon frame
station 2B2 B2
random delay
A
a
D
d
ATIM
window beacon interval
aacknowledge ATIM
dacknowledge data
802.11 - Roaming
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802.11 RoamingNo or bad connection in PCF mode? Then perform:
Scanning scan the environment, i.e., listen into the medium for beacon signals or send probes into the medium and wait for an answer
Reassociation Request station sends a request to one or several AP(s)
Reassociation Response success: AP has answered, station can now participate failure: continue scanning
AP accepts Reassociation Request signal the new station to the distribution system the distribution system updates its data base (i.e., location information)
typically, the distribution system now informs the old AP so it can releaseresources
Hardware
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Hardware
Original WaveLAN card (NCR) 914 MHz Radio Frequency Transmit power 281.8 mW Transmission Range ~250 m (outdoors) at 2Mbps SNRT 10 dB (capture)
WaveLAN II (Lucent) 2.4 GHz radio frequency range Transmit Power 30mW Transmission range 376 m (outdoors) at 2 Mbps (60m
indoors) Receive Threshold = 81dBm Carrier Sense Threshold = -111dBm
802.11 current status
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802.11 current status
MAC
MIB
DSSS FH IRPHY
WEP
LLC
MACMgmt
802.11b
5,11 Mbps
802.11g20+ Mbps
802.11a6,9,12,18,24
36,48,54 Mbps
OFDM
802.11isecurity
802.11f Inter Access Point Protocol
802.11eQoS enhancements
IEEE 802 11 S
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IEEE 802.11 Summary
Infrastructure (PCF) and adhoc (DCF) modes
Signaling packets for collision avoidance Medium is reserved for the duration of the transmission Beacons in PCF RTS-CTS in DCF
Acknowledgements for reliabilityBinary exponential backoff for congestion controlPower save mode for energy conservation
Outline
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Introduction and Overview Wireless LANs: IEEE 802.11Mobile IP routingTCP over wirelessGSM air interfaceGPRS network architectureWireless application protocolMobile agentsMobile ad hoc networks
Traditional Routing
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g
A routing protocol sets up a routing table inrouters
Routing protocol is typically based onDistance-Vector or Link-State algorithms
Routing and Mobility
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Routing and Mobility
Finding a path from a source to a destinationIssues Frequent route changes
amount of data transferred between route changes may
be much smaller than traditional networks Route changes may be related to host movement Low bandwidth links
Goal of routing protocols decrease routing-related overhead find short routes find stable routes (despite mobility)
Mobile IP (RFC 3220) : Motivation
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( )Traditional routing
based on IP address; network prefix determines the subnet change of physical subnet implies change of IP address (conform to new subnet), or special routing table entries to forward packets to new subnet
Changing of IP address DNS updates take to long time TCP connections break security problems
Changing entries in routing tables does not scale with the number of mobile hosts and frequent
changes in the location security problems
Solution requirements retain same IP address, use same layer 2 protocols
authentication of registration messages,
Mobile IP: Basic Idea
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Router 1
Router 3
Router 2
S MN
Homeagent
Mobile IP: Basic Idea
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Router 1
Router 3
Router 2
S MN
Home agent
Foreign agent
move
Packets are tunneledusing IP in IP
Mobile IP: Terminology
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gyMobile Node (MN)
node that moves across networks without changing its IP addressHome Agent (HA)
host in the home network of the MN, typically a router registers the location of the MN, tunnels IP packets to the COA
Foreign Agent (FA) host in the current foreign network of the MN, typically a router forwards tunneled packets to the MN, typically the default router
for 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
Correspondent Node (CN) host with which MN is corresponding (TCP connection)
Data transfer to the mobile system
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Internet
sender
FA
HA
MN
home network
foreignnetwork
receiver
1
2
3
1. Sender sends to the IP address of MN,HA intercepts packet (proxy ARP)
2. HA tunnels packet to COA, here FA,by encapsulation
3. FA forwards the packet to the MN
Source: Schiller
CN
Data transfer from the mobile system
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Internet
receiver
FA
HA
MN
home network
foreignnetwork
sender
1
1. Sender sends to the IP addressof the receiver as usual,FA works as default router
Source: Schiller
CN
Mobile IP: Basic Operation
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Agent Advertisement
HA/FA periodically send advertisement messages into their physical subnets MN listens to these messages and detects, if it is in home/foreign
network MN reads a COA from the FA advertisement messages
MN Registration MN signals COA to the HA via the FA HA acknowledges via FA to MN limited lifetime, need to be secured by authentication
HA Proxy
HA advertises the IP address of the MN (as for fixed systems) packets to the MN are sent to the HA independent of changes in COA/FA
Packet Tunneling HA to MN via FA
Agent advertisement
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g
preference level 1router address 1
#addressestype
addr. size lifetimechecksum
COA 1COA 2
type sequence number length
0 7 8 15 16 312423code
preference level 2router address 2
. . .
registration lifetime
. . .
R B H F M G V reserved
Registration
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t
MN HAr e g i s t r a t i o n
r e q u e s t
r e g i s t r a t i o
n
r e p l y
t
MN FA HAr e g i s t r a t i o n
r e q u e s t
r e g i s t r a t i o n r e q u e s t
r e g i s t r a t i o
n
r e p l y
r e g i s t r a t i o
n
r e p l y
Registration request
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home agenthome address
type lifetime0 7 8 15 16 312423
rsv
identification
COA
extensions . . .
SBDMGV
IP-in-IP encapsulation
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IP-in-IP-encapsulation (mandatory in RFC 2003) tunnel between HA and COA
Care-of address COAIP address of HA
TTLIP identificationIP-in-IP IP checksumflags fragment offset
lengthTOSver. IHL
IP address of MNIP address of CN
TTLIP identification
lay. 4 prot. IP checksumflags fragment offset
lengthTOSver. IHL
TCP/UDP/ ... payload
Mobile IP: Other Issues
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Reverse Tunneling firewalls permit only topological correct addresses a packet from the MN encapsulated by the FA is now
topological correct
Optimizations Triangular Routing
HA informs sender the current location of MN
Change of FA new FA informs old FA to avoid packet loss, old FA now
forwards remaining packets to new FA
Mobile IP Summary
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Mobile node moves to new location
Agent Advertisement by foreign agentRegistration of mobile node with home agentProxying by home agent for mobile node
Encapsulation of packetsTunneling by home agent to mobile node viaforeign agent
Reverse tunnelingOptimizations for triangular routing
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Transmission Control Protocol (TCP)
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Reliable ordered delivery Acknowledgements and Retransmissions
End-to-end semantics Acknowledgements sent to TCP sender confirm
delivery of data received by TCP receiver Ack for data sent only after data has reached
receiver Cumulative Ack
Implements congestion avoidance and control
Window Based Flow Control
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Sliding window protocolWindow size minimum of receivers advertised window - determined by
available buffer space at the receiver
congestion window - determined by the sender,based on feedback from the network
2 3 4 5 6 7 8 9 10 11 131 12
Senders window
Acks received Not transmitted
Basic TCP Behaviour
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02
4
6
8
10
12
14
0 1 2 3 4 5 6 7 8
Time (round tri
C o n g e s t i o n W i n d o w
s i z e
( s e g m e n t s )
Slow start
Congestionavoidance
Slow startthreshold
Example assumes that acks are not delayed
TCP: Detecting Packet Loss
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g
Retransmission timeout Initiate Slow Start
Duplicate acknowledgements Initiate Fast Retransmit
Assumes that ALL packet losses are due tocongestion
TCP after Timeout
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0
5
10
15
20
25
0 3 6 9 1 2 1 5 2 0 2 2 2 5
Time (round trips)
C o n g e s
t i o n
w i n d o w
( s e g m
ssthresh = 8 ssthresh = 10
cwnd = 20
After timeout
TCP after Fast Retransmit
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0
2
4
6
8
10
0 2 4 6 8 1 0 12 14
Tim e (round tri
W i n d o w
s i z e ( s e g m e n t s )
After fast retransmit and fast recovery window sizeis
reduced in half
Receivers advertized window
After fast recovery
Impact of Transmission Errors
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Wireless channel may have bursty random errors
Burst errors may cause timeoutRandom errors may cause fast retransmitTCP cannot distinguish between packet lossesdue to congestion and transmission errors
Unnecessarily reduces congestion windowThroughput suffers
Split Connection Approach
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End-to-end TCP connection is broken into oneconnection on the wired part of route and oneover wireless part of the route
Connection between wireless host MH and fixedhost FH goes through base station BSFH-MH = FH-BS + BS-MH
FH MHBS
Base Station Mobile HostFixed Host
I-TCP: Split Connection Approach
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physical
link
network
transport
application
physical
link
network
transport
application
physical
link
network
transport
applicationrxmt
Per-TCP connection state
TCP connection TCP connection
Snoop Protocol
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Buffers data packets at the base station BS to allow link layer retransmission
When dupacks received by BS from MH retransmit on wireless link, if packet present in buffer
drop dupack
Prevents fast retransmit at TCP sender FH
FH MHBS
Snoop Protocol
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FH MHBSwireless
physical
link
network
transport
application
physical
link
network
transport
application
physical
link
network
transport
application
rxmt
Per TCP-connection state
TCP connection
Impact of Handoffs
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Split connection approach hard state at base station must be moved to new base station
Snoop protocol soft state need not be moved while the new base station builds new state, packet losses may
not be recovered locally
Frequent handoffs a problem for schemes that rely onsignificant amount of hard/soft state at base stations hard state should not be lost soft state needs to be recreated to benefit performance
M-TCP
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Similar to the split connection approach, M-TCP
splits one TCP connection into two logical parts the two parts have independent flow control as in I-
TCP
The BS does not send an ack to MH, unless BShas received an ack from MH maintains end-to-end semantics
BS withholds ack for the last byte ackd by MH
FH MHBS
Ack 1000Ack 999
M-TCP
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When a new ack is received with receiversadvertised window = 0, the sender enterspersist modeSender does not send any data in persist mode
except when persist timer goes off
When a positive window advertisement isreceived, sender exits persist mode
On exiting persist mode, RTO and cwnd aresame as before the persist mode
FreezeTCP
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M-TCP needs help from base station Base station withholds ack for one byte The base station uses this ack to send a zero window
advertisement when a mobile host moves to another cell
FreezeTCP requires the receiver to send zerowindow advertisement (ZWA)
FH MHBS
MobileTCP receiver
TCP over wireless summary
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Assuming that packet loss implies congestion is
invalid in wireless mobile environmentsInvoking congestion control in response topacket loss is in appropriate
Several proposals to adapt TCP to wirelessenvironmentsModifications at Fixed Host Base Station Mobile Host
Outline
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Introduction and OverviewWireless LANs: IEEE 802.11Mobile IP routingTCP over wirelessGSM air interfaceGPRS network architectureWireless application protocol
Mobile agentsMobile ad hoc networks
GSM: System Architecture
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Base Transceiver Station (BTS)
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One per cell
Consists of high speed transmitter and receiver Function of BTS
Provides two channel
Signalling and Data ChannelMessage schedulingRandom access detection
Performs error protection coding for the radiochannel
Rate adaptation
Identified by BTS Identity Code (BSIC)
Base Station Controller (BSC)
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Controls multiple BTS
Consists of essential control and protocolintelligence entitiesFunctions of BSC
Performs radio resource management Assigns and releases frequencies and time slots for all the
MSs in its area Reallocation of frequencies among cells Hand over protocol is executed here
Time and frequency synchronization signals to BTSs Time Delay Measurement and notification of an MS
to BTS Power Management of BTS and MS
Mobile Switching Center (MSC)
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Switching node of a PLMNAllocation of radio resource (RR)
Handover
Mobility of subscribers Location registration of subscriber
There can be several MSC in a PLMN
Gateway MSC (GMSC)
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Connects mobile network to a fixed network Entry point to a PLMN
Usually one per PLMNRequest routing information from the HLR androutes the connection to the local MSC
Air Interface: Physical Channel
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Uplink/Downlink of 25MHz 890 -915 MHz for Up link 935 - 960 MHz for Down link
Combination of frequency division and timedivision multiplexing
FDMA 124 channels of 200 kHz 200 kHz guard band
TDMA
BurstModulation used
Gaussian Minimum Shift Keying (GMSK)
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Bursts
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Building unit of physical channel
Types of bursts Normal Synchronization Frequency Correction
Dummy Access
Normal Burst
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Normal Burst 2*(3 head bit + 57 data bits + 1 signaling bit) + 26
training sequence bit + 8.25 guard bit
Used for all except RACH, FSCH & SCH
Air Interface: Logical Channel
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Traffic Channel (TCH)
Signaling Channel Broadcast Channel (BCH) Common Control Channel (CCH) Dedicated/Associated Control Channel
(DCCH/ACCH)
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Traffic Channel
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Transfer either encoded speech or user dataBidirectional
Full Rate TCH Rate 22.4kbps Bm interface
Half Rate TCH Rate 11.2 kbps Lm interface
Full Rate Speech Coding
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Speech Coding for 20ms segments 260 bits at the output Effective data rate 13kbps
Unequal error protection 182 bits are protected
50 + 132 bits = 182 bits 78 bits unprotected
Channel Encoding Codes 260 bits into (8 x 57 bit blocks) 456 bits
Interleaving 2 blocks of different set interleaved on a normal
burst (save damages by error bursts)
Speech 20 ms 20 ms
Speech Coder Speech Coder
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3 4 87651 2
1 26 8.253 57 1 57 3
260 260
456 bit 456 bit
Channel Encoding Channel Encoding
Interleaving
NORMAL BURST
Out of first 20 msOut of second 20ms
Traffic Channel Structure for Full Rate Coding
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T
23 4 18765432187651 2
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 26
T T T T T T T T TT T T S T T T T I
Slots
Bursts for Users allocated in Slot
T = TrafficS = Signal( contains information about the signal strength inneighboring cells)
23 4 18765432187651 2Slots
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T
Traffic Channel Structure for Half Rate CodingT
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 26
T T T T T T S T T
Burst for one users
T
=
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 26
T T T T T T T T S
Bursts for another users allocated in alternate Slots
BCCH
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Broadcast Control Channel (BCCH) BTS to MS Radio channel configuration
Current cell + Neighbouring cells Synchronizing information
Frequencies + frame numbering
Registration Identifiers LA + Cell Identification (CI) + Base Station Identity Code
(BSIC)
FCCH & SCH
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Frequency Correction Channel Repeated broadcast of FB
Synchronization Channel Repeated broadcast of SB Message format of SCH
PLMN color3 bits
BS color3 bits
T1 Superframeindex 11 bits
T2 multiframeindex 11 bits
T3 block frameindex 3bits
BSIC 6 bits "FN 19bits
RACH & SDCCH
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Random Access Channel (RACH) MS to BTS Slotted Aloha
Request for dedicated SDCCH
Standalone Dedicated Control Channel(SDCCH)
MS BTS Standalone; Independent of TCH
AGCH & PCH
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Access Grant Channel (AGCH) BTS to MS Assign an SDCCH/TCH to MS
Paging Channel (PCH) BTS to MS
Page MS
SACCH & FACCHSl A i d C l Ch l (SACCH)
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Slow Associated Control Channel (SACCH)
MS
BTS Always associated with either TCH or SDCCH Information
Optimal radio operation; Commands for synchronization Transmitter power control; Channel measurement
Should always be active; as proof of existence of physical radio connection
Fast Associated Control Channel (FACCH) MS BTS
Handover Pre-emptive multiplexing on a TCH, Stealing Flag (SF)
Example: Incoming Call SetupMS BSS/MSC ------ Paging request (PCH)MS BSS/MSC Ch l (RACH)
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MS BSS/MSC ------ Channel request (RACH)MS BSS/MSC ------ Immediate Assignment (AGCH)MS BSS/MSC ------ Paging Response (SDCCH)MS BSS/MSC ------ Authentication Request (SDCCH)MS BSS/MSC ------ Authentication Response (SDCCH)MS BSS/MSC ------ Cipher Mode Command (SDCCH)MS BSS/MSC ------ Cipher Mode Compl. (SDCCH)MS BSS/MSC ------ Setup (SDCCH)MS BSS/MSC ------ Call Confirmation (SDCCH)MS BSS/MSC ------ Assignment Command (SDCCH)MS BSS/MSC ------ Assignment Compl. (FACCH)
MS BSS/MSC ------ Alert (FACCH)MS BSS/MSC ------ Connect (FACCH)MS BSS/MSC ------ Connect Acknowledge (FACCH)MS BSS/MSC ------ Data (TCH)
Power On Scan Channels,monitor RF levels
Select the channel withhighest RF level amongthe control channels
Scan the channel for the
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YES
NO
NO
NO
YES
YES
Scan the channel for theFCCH
IsFCCH detected?
Scan channel for SCH
IsSCH detected?
Read data from BCCHand determine is it BCCH?
Isthe current BCCHchannel included?
Camp on BCCH andstart decoding
Select the channel withnext highest Rf level fromthe control list.
From the channel dataupdate the control channellist
Adaptive Frame Synchronization
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Timing AdvanceAdvance in Tx time corresponding topropagation delay
6 bit number used; hence 63 steps63 bit period = 233 micro seconds (round trip
time) 35 Kms
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GSM: Channel Mapping SummaryL i l h l
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Logical channels
Traffic Channels; Control ChannelsPhysical Channel
Time Slot Number; TDMA frame; RF Channel Sequence
Mapping in frequency 124 channels, 200KHz spacing
Mapping in time TDMA Frame, Multi Frame, Super Frame, Channel
Two kinds of multiframe: 26-frame multiframe; usage -Speech and Data 51-frame multiframe; usage -Signalling
1 Hyper frame = 2048 Super frames =2715648 TDMA frames ( 3h 28 min 53 sec 760 ms)
1 Super frame = 1326 TDMA frames (6.12s)
0 1 2 3 2045 2046 2047
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p ( )= 51(26 frames) Multi frame
1(26 frames) Multi frame = 26 TDMA frames (120 ms) 1(51 frames) M ulti fram e = 51 TD M A frame s (3060/1 3 ms)
1 time slot = 156.25 bit du ratio n (15 /26 or 0.5 77 m s)(1 bit durati o n = 48/13 or 3.69 s)
1 T DM A fra me
= 8 t ime slo t s (12 0/2 6 o r 4 .615 ms )
0 1 2 3 4 5 76
0 1 2
30 1 2
3 50
23 24 25
49 50T0 T1 I 1 2T2 3T12
(SACCH)T23 0
1 Super frame = 1326 TDMA frames (6.12s)= 26(51 frames) Multi frame
Outline
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Introduction and OverviewWireless LANs: IEEE 802.11Mobile IP routingTCP over wireless
GSM air interfaceGPRS network architectureWireless application protocol
Mobile agentsMobile ad hoc networks
GSM architecture
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GSM multiple access
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GSM call routing1. MSISDN
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2. MSISDN
VLRHLR
AUCEIR
GMSC/IWF
MSC
BSC
BSC
BTS
BTS
BTS
ISDN
3. MSRN
4. MSRN
5. MSRN
6. TMSI
7. TMSI
7. TMSI
7. TMSI
8. TMSI
LA2
LA1
MS
MS
Options for data transfer
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Two enhancements to GSM for data HSCSD - High Speed Circuit Switched Data GPRS - General Packet Radio Service
Both have capacity to use new coding schemes
and to make multislot allocationGPRS, being a packet switched service, isknown to be more efficient and flexible for datatransfer purposesIt delivers circuit and packet-switched services inone mobile radio network
GPRS features
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Radio resources are allocated for only one or afew packets at a time, so GPRS enables many users to share radio resources, and allow
efficient transport of packets
fast setup/access times connectivity to external packet data n/w volume-based charging
GPRS also carries SMS in data channels rather than signaling channels as in GSM
GPRS Architecture
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GPRS Architecture
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Requires addition of a new class of nodes calledGSNs (GPRS Support Nodes) SGSN: Serving GPRS Support Node, GGSN: Gateway GPRS Support Node
BSC requires a PCU (Packet Control Unit) andvarious other elements of the GSM n/w requiresoftware upgradesAll GSNs are connected via an IP-basedbackbone. Protocol data units (PDUs) areencapsulated and tunneled between GSNs
GGSN
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Serves as the interface to external IP networkswhich see the GGSN as an IP router serving allIP addresses of the MSsGGSN stores current SGSN address and profile
of the user in its location register It tunnels protocol data packets to and from theSGSN currently serving the MSIt also performs authentication and charging
GGSN can also include firewall and packet-filtering mechanisms
SGSN
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Analog of the MSC in GSMRoutes incoming and outgoing packetsaddressed to and from any GPRS subscriber located within the geographical area served bythe SGSNLocation Register of the SGSN storesinformation (e.g. current cell and VLR) and user profiles (e.g. IMSI, addresses) of all GPRSusers registered with this SGSN
BSC and others
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BSC must get a Packet Control Unit to set up, supervise and disconnect packet-switched
calls also support cell change, radio resource
configuration and channel assignmentMSC/VLR, HLR and SMS Center must beenhanced for interworking with GPRS
MS must be equipped with the GPRS protocolstack
HLR - Home Location Register
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Shared database, with GSMIs enhanced with GPRS subscriber data androuting informationFor all users registered with the network, HLR
keeps user profile, current SGSN and PacketData Protocol (PDP) address(es) informationSGSN exchanges information with HLR e.g.,informs HLR of the current location of the MS
When MS registers with a new SGSN, the HLRsends the user profile to the new SGSN
MSC/VLR-Visitor Location Register
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VLR is responsible for a group of location areas.It stores data of only those users in its area of responsibilityMSC/VLR can be enhanced with functions andregister entries that allow efficient coordinationbetween GPRS and GSM services combined location updates combined attachment procedures
GPRS Transmission Plane
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Air Interface U m
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Is one of the central aspects of GPRS Concerned with communication between MS and
BSS at the physical, MAC and RLC layers Physical channel dedicated to packet data traffic is
called a packet data channel (PDCH)Capacity on Demand: Allocation/Deallocation of PDCH to GPRS traffic is
dynamic
BSC controls resources in both directions No conflicts on downlink Conflicts in uplink are resolved using slotted ALOHA
Data transfer between MS and SGSN
SNDCP f IP/X 25 k i LLC f
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SNDCP transforms IP/X.25 packets into LLC frames,
after optional header/data compression, segmentationand encryptionMaximum LLC frame size is 1600 bytesAn LLC frame is segmented into RLC data blocks whichare coded into radio blocksEach radio block comprises four normal bursts (114 bits)in consecutive TDMA framesRLC is responsible for transmission of data across air-interface, including error correctionMAC layer performs medium allocation to requests,including multi-slot allocationPHY layer is identical to GSM
Data transfer between GSNs
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Although the GPRS network consists of severaldifferent nodes, it represents only one IP hopGTP enables tunneling of PDUs betweenGSNs, by adding routing information
Below GTP, TCP/IP and IP are used as theGPRS backbone protocols
MS - state model
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In Idle State MS is notreachableWith GPRS Attach MSmoves into ready state
With Detach, it returns toIdle state: all PDPcontexts are deletedStandby state is reachedwhen MS does not senddata for a long periodand ready timer expires
GPRS PDP context
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MS gets a packet temporary mobile subscriber identity(p-TMSI) during AttachMS requests for one or more addresses used in thepacket data network, e.g. IP addressGGSN creates a PDP context for each session PDP type (IPV4), PDP address (IP) of MS, requested quality of service (QoS) and address of GGSN
PDP context is stored in MS, SGSN and GGSNMapping between the two addresses, enables GGSN totransfer packets between MS and the PDN
GPRS - Routing
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GPRS - Routing
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MS from PLMN-2 is visiting PLMN-1.IP address prefix of MS is the same as GGSN-2Incoming packets to MS are routed to GGSN-2GGSN-2 queries HLR and finds that MS iscurrently in PLMN-1It encapsulates the IP packets and tunnels themthrough the GPRS backbone to the appropriate
SGSN of PLMN-1SGSN decapsulates and delivers to the MS
GPRS Summary
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Enables many users to share radio resourcesby dynamic, on-demand, multi-slot allocationProvides connectivity to external packet datanetworks
Modification to the GSM air-interfaceAddition of new GPRS Support NodesAssignment of PDP context to MS
Enables volume-based charging as well asduration based charging
Outline
Introduction and Overview
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Introduction and Overview
Wireless LANs: IEEE 802.11Mobile IP routingTCP over wireless
GSM air interfaceGPRS network architectureWireless application protocol
Mobile agentsMobile ad hoc networks
Variability of the mobile environment
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Connectivity connected semi-connected
(asymmetric) disconnected
Mobile Device Capability form factor GUI
multimedia real-time multimedia
Mobility stationary nomadic (pedestrian speed) mobile (vehicular speed) roaming (mobile across networks)
Wireless Application Protocol (WAP)
HTTP/HTML have not been designed for
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HTTP/HTML have not been designed for
mobile devices and applications
WAP empowers mobile users with wireless
devices to easily access and interact withinformation and services.
A standard created by wireless and Internetcompanies to enable Internet access from acellular phone
Why is HTTP/HTML not enough?
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Big pipe - small pipe syndromeWireless network
NNN Interactive
NNNInteractive
InternetEnter name:
010011010011110110010011011011011101010010011010
Content encoding
HTTP/HTML WAP
Source: WAP Forum
WHY WAP?
Wireless networks and phones
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Wireless networks and phones
have specific needs and requirements not addressed by existing Internet technologies
WAP Enables any data transport
TCP/IP, UDP/IP, GUTS (IS-135/6), SMS, or USSD.
Optimizes the content and air-link protocols Utilizes plain Web HTTP 1.1 servers
utilizes standard Internet markup language technology (XML) all WML content is accessed via HTTP 1.1 requests
WML UI components map well onto existing mobile phone UI no re-education of the end-users leveraging market penetration of mobile devices
WAP: main featuresBrowser
Micro browser similar to existing web browsers
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Micro browser, similar to existing web browsers
Markup language Similar to HTML, adapted to mobile devices
Script language Similar to Javascript, adapted to mobile devices
Gateway Transition from wireless to wired worldServer Wap/Origin server, similar to existing web servers
Protocol layers Transport layer, security layer, session layer etc.
Telephony application interface Access to telephony functions
Internet model
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HTML
HTTP TLS/SSL TCP/IP
WAP architecture
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Web Server
Content
CGIScripts
etc.
WMLDecks
withWML-ScriptWAP Gateway
WML Encoder
WMLScriptCompiler
Protocol Adapters
Client
WML
WML-Script
WTAI
Etc.
HTTPWSP/WTP
Source: WAP Forum
WAP application server
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WAP Application Server
Content
ApplicationLogic
WMLDecks
withWML-ScriptWML Encoder
WMLScriptCompiler
Protocol Adapters
Client
WML
WML-Script
WTAI
Etc.
WSP/WTP
Source: WAP Forum
WAP specifies
Wireless Application Environment
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Wireless Application Environment WML Microbrowser WMLScript Virtual Machine WMLScript Standard Library Wireless Telephony Application Interface (WTAI) WAP content types
Wireless Protocol Stack Wireless Session Protocol (WSP) Wireless Transport Layer Security (WTLS)
Wireless Transaction Protocol (WTP) Wireless Datagram Protocol (WDP) Wireless network interface definitions
WAP stack
WAE (Wireless Application Environment) :
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WAE (Wireless Application Environment) : Architecture: application model, browser, gateway,
server WML: XML-Syntax, based on card stacks,
variables, ... WTA: telephone services, such as call control,
phone book etc.
WSP (Wireless Session Protocol) :
Provides HTTP 1.1 functionality Supports session management, security, etc.
WAP stack (contd.)
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WTP (Wireless Transaction Protocol) : Provides reliable message transfer mechanisms Based on ideas from TCP/RPC
WTLS (Wireless Transport Layer Security) :
Provides data integrity, privacy, authentication functions Based on ideas from TLS/SSL
WDP (Wireless Datagram Protocol) : Provides transport layer functions Based on ideas from UDP
Content encoding, optimized for low-bandwidth channels,simple devices
WDP: Wireless Datagram Protocol
Goals
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create a worldwide interoperable transport system byadapting WDP to the different underlying technologies
transmission services, such as SMS in GSM might change,new services can replace the old ones
WDP
Transport layer protocol within the WAP architecture uses the Service Primitive T-UnitData.req .ind
uses transport mechanisms of different bearer technologies offers a common interface for higher layer protocols
allows for transparent communication despite differenttechnologies addressing uses port numbers WDP over IP is UDP/IP
WDP: service primitives
T SAP T SAP
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T-SAP T-SAP
T-DUnitdata.req(DA, DP, SA, SP, UD) T-DUnitdata.ind
(SA, SP, UD)T-DUnitdata.req(DA, DP, SA, SP, UD)
T-DError.ind(EC) SAP: Service Access Point
DA: Destination Address
DP: Destination Port
SA: Source Address
SP: Source Port
UD: User DataEC: Error Code
Source: Schiller
WAP Over GSM Circuit Switched
Service, Protocol, Bearer: Example
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WAP Over GSM Circuit-Switched
RAS - Remote Access Server IWF - InterWorking Function
WSP
WAE
Subnetwork
IP
WSP
WAE Apps onOther Servers
WAPProxy/Server
CSD-RF
PPP
IP
Mobile
IWF
PSTNCircuit
CSD-RF
ISP/RAS
SubnetworkPSTNCircuit
PPP
IP
WTP
UDP
WTP
UDP
Source: WAP Forum
WAP Over GSM Short Message Service
Service, Protocol, Bearer: Example
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SMS
WDP
WTP
WSP
WAE
SMS
Subnetwork
WDP
WDP Tunnel
ProtocolSubnetwork
WDP Tunnel
Protocol
WTP
WSP
WAE Apps onother servers
SMSC
WAPProxy/Server Mobile
Source: WAP Forum
WTLS:Wireless Transport Layer SecurityGoals Provide mechanisms for secure transfer of content, for
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applications needing privacy, identification, message integrityand non-repudiation
WTLS is based on the TLS/SSL (Transport Layer Security) protocol optimized for low-bandwidth communication channels
provides privacy (encryption) data integrity (MACs) authentication (public-key and symmetric)
Employs special adapted mechanisms for wireless usage Long lived secure sessions Optimised handshake procedures Provides simple data reliability for operation over datagram
bearers
WTLS: secure session, full handshake
SEC Create req
originator SEC-SAP
peer SEC-SAP
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SEC-Create.req
(SA, SP, DA, DP, KES, CS, CM) SEC-Create.ind(SA, SP, DA, DP, KES, CS, CM)
SEC-Create.cnf (SNM, KR, SID, KES, CS, CM)
SEC-Create.res(SNM, KR, SID, KES, CS, CM)
SEC-Exchange.req
SEC-Exchange.ind
SEC-Exchange.res(CC)SEC-Commit.req SEC-Exchange.cnf
(CC)
SEC-Commit.indSEC-Commit.cnf
Source: Schiller
KES: Key Exchange SuiteCS: Cipher Suite
CM: Compression Mode
SNM: Sequence Number Mode
KR: Key Refresh Cycle
SID: Session Identifier
CC: Client Certificate
WTP: Wireless Transaction Protocol
Goalsd ff h bl l
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different transaction services that enable applications toselect reliability, efficiency levels
low memory requirements, suited to simple devices (B to end.
D is outside the range of A, therefore waiting is notnecessary.
A and C are exposed terminals
A BC
D
Routing ProtocolsProactive protocols Traditional distributed shortest-path protocols
Maintain routes between every host pair at all times
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Maintain routes between every host pair at all times Based on periodic updates; High routing overhead Example: DSDV (destination sequenced distance vector)
Reactive protocols Determine route if and when needed Source initiates route discovery Example: DSR (dynamic source routing)
Hybrid protocols Adaptive; Combination of proactive and reactive Example : ZRP (zone routing protocol)
Dynamic Source Routing (DSR)
Route Discovery Phase: Initiated by source node S that wants to send packet to
destination node D
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destination node D Route Request (RREQ) floods through the network Each node appends own identifier when forwarding RREQ
Route Reply Phase:
D on receiving the first RREQ, sends a Route Reply (RREP) RREP is sent on a route obtained by reversing the routeappended to received RREQ
RREP includes the route from S to D on which RREQ wasreceived by node D
Data Forwarding Phase: S sends data to D by source routing through intermediate nodes
Route Discovery in DSR
Z
Y
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B
A
S EF
H
J
D
C
G
IK
Z
Represents a node that has received RREQ for D from S
M
N
L
Route Discovery in DSR