CS8601 4 MC NOTES.pdf

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MOBILE COMPUTING
Unit IV
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UNIT IV
MOBILE TRANSPORT LAYER AND
APPLICATION LAYER
Mobile TCP – WAP- Architecture – WDP – STLS – WTP- WSP- WAE- WTA
Architecture - WML
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Overview of TCP/IP
TCP/IP protocol suite is a collection of a large number of protocols.
The four layer of protocols are
• Application layer
• Transport layer
• Internet layer
• Network layer
• TCP/IP allows any of the standard protocols to be used for network
interface
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Architecture of TCP/IP
TCP/IP protocol consists of four layers. 1. Application layer, 2.Transport layer, 3.Internet layer and
4. Network access layer
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1. Application layer:
 Establish communication with other applications which may be running on separate hosts.
 Example http,ftp and telnet.
2. Transport layer:
 The purpose of Transport layer is to permit devices on the source and destination hosts to carry on a
conversation. Provides reliable end-to-end data transfer services.
 Also referred as host-to-host protocol.
 The main protocols included at Transport layer are
I. TCP (Transmission Control Protocol) and
II. UDP (User Datagram Protocol).
3. Internet layer
 Internet layer pack data into data packets known as IP datagrams,
 which contain source and destination address (logical address or IP address) information that is used to
forward the datagrams between hosts and across networks.
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4. Network access layer
 The Network Access Layer of the TCP/IP model is associated with the Physical Layer (Layer 1) and the Data Link
layer (Layer 2) of the OSI model.
 The Network Access Layer's function is to move bits (0s and 1s) over the network medium such as coaxial cable,
optical fiber, or twisted pair copper wire.
 The OSI Physical layer is responsible for converting the frame into a stream of bits suitable for the transmission
medium and synchronizes signals for the actual transmission.
 On the destination device, the Physical layer reassembles these signals into a data frame.
 The OSI Data Link layer is again subdivided into the following two sub layers according to their function:
 Media Access Control (MAC) Sublayer :— MAC sublayer provides an interface with the network adapter.
 Logical Link Control (LLC) Sublayer :— LLC sublayer is responsible for error-checking functions for frames
delivered also responsible for managing links between communicating devices.
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Comparison of TCP/IP and OSI network
models
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Comparison of TCP/IP and OSI network
models
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Adaptation of TCP Window
 TCP deploys a flow control technique to control congestion in a network.
 Traffic congestion occurs when the rate at which data is injected by a host into the
network exceeds the rate at which data can be delivered to the network.
I. Router buffer overflow.
II. Receiver buffer overflow
 A flow control technique by TCP helps adapt the rate at sending host end and to
prevent overrun at the slow receiver.
 The flow control mechanism by TCP called the sliding window protocol.
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Improvements of TCP Performance
Traditional networks
 Transport protocols typically designed for
 Fixed end-systems
 Fixed, wired networks
 TCP congestion control
 Packet loss in fixed networks typically due to (temporary) overload situations
 Routers discard packets as soon as the buffers are full
 TCP recognizes congestion only indirectly via missing acknowledgements
 Retransmissions unwise, they would only contribute to the congestion and make it even
worse
 Slow-start algorithm as reaction
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Classification of Schemes
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TCP Slow Start
 Sender calculates a congestion window for a receiver
 Start with a congestion window size equal to one segment
 Exponential increase of the congestion window up to the congestion threshold, then
linear increase
 Missing acknowledgement causes the reduction of the congestion threshold to one
half of the current congestion window
 Congestion window starts again with one segment
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Congestion avoidance
 It starts where slow start stops.
 Once congestion window reaches the congestion threshold level, then after that if an
acknowledgement is received the window size is increased linearly ic the window size
doubling is avoided.
 The TCP increases its rate linearly by adding one additional picket to its window at
each transmission time. If congestion is detected at any point the TCP is reduces its
transmission rate to half the previous value. Makes to right transmission rate.
 The is scheme is less aggressive than slow start phase.
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Fast Retransmit/ Fast Recovery
 TCP sends an acknowledgement only after receiving a packet.
 If a sender receives several acknowledgements for the same packet, this is due to a
gap in received packets at the receiver.
 However, the receiver got all packets up to the gap and is actually receiving packets
 Therefore, packet loss is not due to congestion, continue with current congestion
window (do not use slow-start)
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TCP in mobile networks
TCP assumes congestion if packets are dropped
 typically wrong in wireless networks, here we often have packet loss due to transmission
errors
 furthermore, mobility itself can cause packet loss, if e.g. a mobile node roams from one
access point (e.g. foreign agent in Mobile IP) to another while there are still packets in
transit to the wrong access point and forwarding is not possible
The performance of an unchanged TCP degrades severely
 however, TCP cannot be changed fundamentally due to the large base of installation in the
fixed network, TCP for mobility has to remain compatible
 the basic TCP mechanisms keep the whole Internet together
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Indirect TCP (I -TCP)
 Indirect TCP or I-TCP segments the connection
 no changes to the TCP protocol for hosts connected to the wired Internet, millions of computers use
(variants of) this protocol
 optimized TCP protocol for mobile hosts
 splitting of the TCP connection at, e.g., the foreign agent into 2 TCP connections, no real end-to-end
connection any longer
 hosts in the fixed part of the net do not notice the characteristics of the wireless part
mobile host
access point
(foreign agent) wired Internet
“wireless” TCP standard TCP
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I-TCP socket and state migration
mobile host
access point2
Internet
access point1
socket migration
and state transfer
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Indirect TCP II
 Advantages
 no changes in the fixed network necessary, no changes for the hosts (TCP protocol) necessary,
all current optimizations to TCP still work
 transmission errors on the wireless link do not propagate into the fixed network
 simple to control, mobile TCP is used only for one hop between, e.g., a foreign agent and mobile
host
 therefore, a very fast retransmission of packets is possible, the short delay on the mobile hop is
known
 Disadvantages
 loss of end-to-end semantics, an acknowledgement to a sender does not any longer mean that a
receiver really got a packet, foreign agents might crash
 higher latency possible due to buffering of data within the foreign agent and forwarding to a new
foreign agent
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Snooping TCP (S-TCP)
 Transparent extension of TCP within the foreign agent
 buffering of packets sent to the mobile host
 lost packets on the wireless link (both directions!) will be retransmitted immediately by the mobile host or
foreign agent, respectively (so called “local” retransmission)
 the foreign agent therefore “snoops” the packet flow and recognizes acknowledgements in both directions, it
also filters ACKs
 changes of TCP only within the foreign agent (+min. MH change)
„wired“ Internet
buffering of data
end-to-end TCP connection
local retransmission correspondent
host
foreign
agent
mobile
host
snooping of ACKs
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Snooping TCP II
 Data transfer to the mobile host
 FA buffers data until it receives ACK of the MH, FA detects packet loss via duplicated ACKs or time-out
 fast retransmission possible, transparent for the fixed network
 Data transfer from the mobile host
 FA detects packet loss on the wireless link via sequence numbers, FA answers directly with a NACK to
the MH
 MH can now retransmit data with only a very short delay
 Advantages:
 Maintain end-to-end semantics
 No change to correspondent node
 No major state transfer during handover
 Problems
 Snooping TCP does not isolate the wireless link well
 May need change to MH to handle NACKs
 Snooping might be useless depending on encryption schemes
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Mobile TCP(M-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
 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
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Mobile TCP(M-TCP)
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Fast retransmit/fast recovery
 Change of foreign agent often results in packet loss
 TCP reacts with slow-start although there is no congestion
 Forced fast retransmit
 as soon as the mobile host has registered with a new foreign agent, the MH sends duplicated
acknowledgements on purpose
 this forces the fast retransmit mode at the communication partners
 additionally, the TCP on the MH is forced to continue sending with the actual window size and not to
go into slow-start after registration
 Advantage
 simple changes result in significant higher performance
 Disadvantage
 further mix of IP and TCP (to know when there is a new registration), no transparent approach
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Freeze-TCP
Mobile hosts can be disconnected for a longer time
 no packet exchange possible, e.g., in a tunnel, disconnection due to overloaded cells or mux.
with higher priority traffic
 TCP disconnects after time-out completely
TCP freezing
 MAC layer is often able to detect interruption in advance
 MAC can inform TCP layer of upcoming loss of connection
 TCP stops sending, but does not assume a congested link
 MAC layer signals again if reconnected
Advantage
 scheme is independent of data and TCP mechanisms (Ack,SN) => works even with IPsec
Disadvantage
 TCP on mobile host has to be changed, mechanism depends on MAC layer
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Selective retransmission
 TCP acknowledgements are often cumulative
 ACK n acknowledges correct and in-sequence receipt of packets up to n
 if single packets are missing quite often a whole packet sequence beginning at the gap has to be
retransmitted (go-back-n), thus wasting bandwidth
 Selective retransmission as one solution
 RFC2018 allows for acknowledgements of single packets, not only acknowledgements of in-
sequence packet streams without gaps
 sender can now retransmit only the missing packets
 Advantage: much higher efficiency
 Disadvantage
 more complex software in a receiver, more buffer needed at the receiver
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Transaction oriented TCP
TCP phases
 connection setup, data transmission, connection release
 using 3-way-handshake needs 3 packets for setup and release, respectively
 thus, even short messages need a minimum of 7 packets!
Transaction oriented TCP
 RFC1644, T-TCP, describes a TCP version to avoid this overhead
 connection setup, data transfer and connection release can be combined
 thus, only 2 or 3 packets are needed
Advantage
 efficiency
Disadvantage
 requires changed TCP
 mobility no longer transparent
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WAP
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Layers of WAP Protocol
Application Layer
Wireless Application Environment (WAE). This layer is of most
interest to content developers because it contains among other
things, device specifications, and the content development
programming languages, WML, and WML Script.
Session Layer
Wireless Session Protocol (WSP). Unlike HTTP, WSP has been
designed by the WAP Forum to provide fast connection
suspension and reconnection.
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Transaction Layer
Wireless Transaction Protocol (WTP). The WTP runs on top of a datagram service, such as User
Datagram Protocol (UDP) and is part of the standard suite of TCP/IP protocols used to provide a
simplified protocol suitable for low bandwidth wireless stations.
Security Layer
Wireless Transport Layer Security (WTLS). WTLS incorporates security features that are based upon
the established Transport Layer Security (TLS) protocol standard. It includes data integrity checks,
privacy, service denial, and authentication services.
Transport Layer
Wireless Datagram Protocol (WDP). The WDP allows WAP to be bearer-independent by adapting the
transport layer of the underlying bearer. The WDP presents a consistent data format to the higher
layers of the WAP protocol stack, thereby offering the advantage of bearer independence to
application developers.
Each of these layers provides a well-defined interface to the layer above it. This means that the
internal workings of any layer are transparent or invisible to the layers above it. The layered
architecture allows other applications and services to utilise the features provided by the WAP-stack
as well. This makes it possible to use the WAP-stack for services and applications that currently are
not specified by WAP.
The WAP protocol architecture is shown below alongside a typical Internet Protocol stack.
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Wireless Application Protocol (WAP)
Empowers mobile users with wireless devices to easily access and interact with information
and services.
A “standard” created by wireless and Internet companies to enable Internet access from a
cellular phone
wapforum.org:
 co-founded by Ericsson, Motorola, Nokia, Phone.com
 450 members in 2000, comprise of Handset manufacturers, Wireless service providers, ISPs,
Software companies in the wireless industry
 Goals
 deliver Internet services to mobile devices
 enable applications to scale across a variety of transport options and device types
 independence from wireless network standards
 GSM, CDMA IS-95, TDMA IS-136, 3G systems (UMTS, W-CDMA)
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WAP: Main Features
Browser
 “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 world
Server
 “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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Internet Model
HTML
HTTP
TLS/SSL
TCP/IP
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Web Server
Content
CGI
Scripts
etc.
WML
Decks
with
WML-Script
WAP Gateway
WML Encoder
WMLScript
Compiler
Protocol Adapters
Client
WML
WML-Script
WTAI
Etc.
HTTP
WSP/WTP
WAP Architecture
Source: WAP Forum
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WAPApplication Server
Content
Application
Logic
WML
Decks
with
WML-Script
WML Encoder
WMLScript
Compiler
Protocol Adapters
Client
WML
WML-Script
WTAI
Etc.
WSP/WTP
WAP Application Server
Source: WAP Forum
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WAP Architecture
Another look
Key Components
• Origin/Web Server
• WAP Gateway/Proxy
• WAP Protocol Stack
• Micro Browser
• WML/WML Script
• Transcoders
• WTA
Source: WAP Forum
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WAP: Network Elements
wireless network
fixed network
WAP
proxy
WTA
server
filter/
WAP
proxy
web
server
filter
PSTN
Internet
Binary WML: binary file format for clients
Binary WML
Binary WML
Binary WML
HTML
HTML
HTML WML
WML
HTML
Source: Schiller
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WAP Specifies
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
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WAP Stack
MicroBrowser (WML, WMLScript, WTA,
WTAI)
Runs on top of WDP
Provided lightweight X-oriented service
• Unreliable 1-way request
• Reliable 1-way/2-way req./response
Lightweight SSL
Uses WIM/PKI-Cards
Datagram service on different bearers
Convergence between bearer services
Different Wireless Tech.
Source: WAP Forum
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WAP Stack
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.
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
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Wireless Application Environment
(WAE)
Goals
 device and network independent application environment
 for low-bandwidth, wireless devices
 considerations of slow links, limited memory, low computing power,
small display, simple user interface (compared to desktops)
 integrated Internet/WWW programming model
 high interoperability
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WAE Components
Architecture
 Application model, Microbrowser, Gateway, Server
User Agents
 WML/WTA/Others
 content formats: vCard, vCalendar, Wireless Bitmap, WML, ...
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)
Proxy (Method/Push)
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Origin Servers
WAE: Logical Model
web
server
other content
server
Gateway Client
other
WAE
user agents
WML
user agent
WTA
user agent
Push proxy
encoded
request
request
encoded
response
with
content
response
with
content
push
content
encoded
push
content
Method proxy
encoders
&
decoders
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WAP Microbrowser
Optimized for wireless devices
Minimal RAM, ROM, Display, CPU and keys
Provides consistent service UI across devices
Provides Internet compatibility
Enables wide array of available content and
applications
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WML: Wireless Markup Language
Tag-based browsing language:
 Screen management (text, images)
 Data input (text, selection lists, etc.)
 Hyperlinks & navigation support
Takes into account limited display, navigation
capabilities of devices
XML-based language
 describes only intent of interaction in an abstract
manner
 presentation depends upon device capabilities
Cards and Decks
 document consists of many cards
 User interactions are split into cards
 Explicit navigation between cards
 cards are grouped to decks
 deck is similar to HTML page, unit of content
transmission
Events, variables and state mgmt
Content (XML)
XSL Processor
HTTP Browser
HTML StyleSheet
WML Browsers
WML Stylesheet
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WML
The basic unit is a card. Cards are grouped together into Decks Document ~ Deck (unit of transfer)
All decks must contain
 Document prologue
 XML & document type declaration
 <WML> element
 Must contain one or more cards
<?xml version="1.0"?>
<!DOCTYPE WML PUBLIC "-//WAPFORUM//DTD WML 1.0//EN"
"http://www.wapforum.org/DTD/wml.xml">
<WML>
...
</WML>
WML File Structure
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WML Example
Input
Elements
Deck
Card
Navigation
Variables
<WML>
<CARD>
<DO TYPE=“ACCEPT”>
<GO URL=“#eCard”/>
</DO
Welcome!
</CARD>
<CARD NAME=“eCard”>
<GO URL=“/submit?N=$(N)&S=$(S)”/>
</DO>
Enter name: <INPUT KEY=“N”/>
Choose speed:
<SELECT KEY=“S”>
<OPTION VALUE=“0”>Fast</OPTION>
<OPTION VALUE=“1”>Slow</OPTION>
<SELECT>
</CARD>
</WML>
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Wireless Telephony Application
(WTA)
Collection of telephony specific extensions
 designed primarily for network operators
Example
 calling a number (WML)
wtai://wp/mc;07216086415
 calling a number (WMLScript)
WTAPublic.makeCall("07216086415");
Implementation
 Extension of basic WAE application model
 Extensions added to standard WML/WMLScript browser
 Exposes additional API (WTAI)
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WTA Features
Extension of basic WAE application model
 network model for interaction
 client requests to server
 event signaling: server can push content to the client
 event handling
 table indicating how to react on certain events from the network
 client may now be able to handle unknown events
 telephony functions
 some application on the client may access telephony functions
WTAI includes:
 Call control
 Network text messaging
 Phone book interface
 Event processing
Security model: segregation
 Separate WTA browser
 Separate WTA port
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Placing an outgoing call with WTAI:
Input Element
WTAI Call
<WML>
<CARD>
<GO URL=“wtai:cc/mc;$(N)”/>
</DO>
Enter phone number:
<INPUT TYPE=“TEXT” KEY=“N”/>
</CARD>
</WML>
WTA Example (WML)
Source: WAP Forum
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Placing an outgoing call with WTAI:
WTAI Call
function checkNumber(N) {
if (Lang.isInt(N))
WTAI.makeCall(N);
else
Dialog.alert(“Bad phone number”);
}
WTA Example (WMLScript)
Source: WAP Forum
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WTA Logical Architecture
other WTA
servers
Client
WAE
services
WTA
user agent
WAP Gateway
encoders
&
decoders
other telephone networks
WTA Origin Server
WTA & WML
server
WML
Scripts
WML
decks
WTA
services
mobile
network
firewall
third party
origin servers
network operator
trusted domain
Source: Schiller
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WTA Framework Components
Source: Heijden
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WTA User Agent
WTA User Agent
 WML User agent with extended functionality
 can access mobile device’s telephony functions through WTAI
 can store WTA service content persistently in a repository
 handles events originating in the mobile network
WTA User Agent Context
 Abstraction of execution space
 Holds current parameters, navigation history, state of user agent
 Similar to activation record in a process address space
Uses connection-mode and connectionless services offered by WSP
Specific, secure WDP ports on the WAP gateway
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WTA Events and Repository
WTA Events
 Network notifies device of event (such as incoming call)
 WTA events map to device’s native events
 WTA services are aware of and able to act on these events
 example: incoming call indication, call cleared, call connected
WTA Repository
 local store for content related to WTA services (minimize network traffic)
 Channels: define the service
 content format defining a WTA service stored in repository
 XML document specifying eventid, title, abstract, and resources that implement a service
 Resources: execution scripts for a service
 could be WML decks, WML Scripts, WBMP images..
 downloaded from WTA server and stored in repository before service is referenced
 Server can also initiate download of a channel
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WTA Channels and Resources
Source: Heijden
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WAP: Protocol Stack
Source: Schiller
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.
Transaction Layer (WTP)
additional services
and applications
WCMP
A-SAP
S-SAP
TR-SAP
SEC-SAP
T-SAP
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WDP: Wireless Datagram Protocol
Goals
 create a worldwide interoperable transport system by adapting 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 different technologies
 addressing uses port numbers
 WDP over IP is UDP/IP
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WDP: Service Primitives
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 Data
EC: Error Code
Source: Schiller
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WAP Over GSM Circuit-Switched
RAS - Remote Access Server
IWF - InterWorking Function
WSP
WAE
Subnetwork
IP
WSP
WAE Apps on
Other Servers
WAP Proxy/Server
CSD-RF
PPP
IP
Mobile
IWF
PSTN
Circuit
CSD-RF
ISP/RAS
Subnetwork
PSTN
Circuit
PPP
IP
WTP
UDP
WTP
UDP
Service, Protocol, and Bearer
Example
Source: WAP Forum
www.edubuzz360.com

WAP Over GSM Short Message Service
SMS
WDP
WTP
WSP
WAE
SMS
Subnetwork
WDP
WDP Tunnel Protocol
Subnetwork
WDP Tunnel
Protocol
WTP
WSP
WAE Apps on
other servers
SMSC
WAP Proxy/Server
Mobile
under development
Service, Protocol, and Bearer
Example
Source: WAP Forum
www.edubuzz360.com

WTLS:Wireless Transport Layer
Security
Goals
 Provide mechanisms for secure transfer of content, for applications needing privacy, identification,
message integrity and non-repudiation
 Provide support for protection against denial-of-service attacks
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
www.edubuzz360.com

Record Protocol
Handshake
Protocol
Alert Protocol Application
Protocol
Change Cipher Spec
Protocol
Transaction Protocol (WTP)
Datagram Protocol (WDP/UDP)
Bearer networks
WTLS
Record protocol
WTLS Internal Architecture
Source: WAP Forum
www.edubuzz360.com

WTLS: Secure session, Full
handshake
SEC-Create.req
(SA, SP, DA, DP, KES, CS, CM)
SEC-Create.ind
(SA, SP, DA, DP, KES, CS, CM)
originator
SEC-SAP
peer
SEC-SAP
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.ind
SEC-Commit.cnf
Source: Schiller
KES: Key Exchange Suite
CS: Cipher Suite
CM: Compression Mode
SNM: Sequence Number Mode
KR: Key Refresh Cycle
SID: Session Identifier
CC: Client Certificate
www.edubuzz360.com

WTLS: Transferring Datagrams
SEC-Unitdata.req
(SA, SP, DA, DP, UD) SEC-Unitdata.ind
(SA, SP, DA, DP, UD)
sender
SEC-SAP
receiver
SEC-SAP
Source: Schiller
www.edubuzz360.com

WTP: Wireless Transaction
Protocol
Goals
 different transaction services that enable applications to select reliability, efficiency levels
 low memory requirements, suited to simple devices (< 10kbyte )
 efficiency for wireless transmission
WTP
 supports peer-to-peer, client/server and multicast applications
 efficient for wireless transmission
 support for different communication scenarios
 class 0: unreliable message transfer
 unconfirmed Invoke message with no Result message
 a datagram that can be sent within the context of an existing Session
 class 1: reliable message transfer without result message
 confirmed Invoke message with no Result message
 used for data push, where no response from the destination is expected
 class 2: reliable message transfer with exactly one reliable result message
 confirmed Invoke message with one confirmed Result message
 a single request produces a single reply
www.edubuzz360.com

WTP Services and Protocols
WTP (Transaction)
 provides reliable data transfer based on request/reply paradigm
 no explicit connection setup or tear down
 optimized setup (data carried in first packet of protocol exchange)
 seeks to reduce 3-way handshake on initial request
 supports
 header compression
 segmentation /re-assembly
 retransmission of lost packets
 selective-retransmission
 port number addressing (UDP ports numbers)
 flow control
 message oriented (not stream)
 supports an Abort function for outstanding requests
 supports concatenation of PDUs
 supports User acknowledgement or Stack acknowledgement option
 acks may be forced from the WTP user (upper layer)
 default is stack ack
www.edubuzz360.com

WTP Class 0 Transaction
TR-Invoke.req
(SA, SP, DA, DP, A, UD, C=0, H) TR-Invoke.ind
(SA, SP, DA, DP, A, UD, C=0, H‘)
initiator
TR-SAP
responder
TR-SAP
Source: Schiller
A: Acknowledgement Type
(WTP/User)
C: Class (0,1,2)
H: Handle (socket alias)
www.edubuzz360.com

WTP Class 1 Transaction, no user
ack & user ack
TR-Invoke.req
initiator
TR-SAP
responder
TR-SAP
TR-Invoke.res
(H‘)
TR-Invoke.cnf
(H)
TR-Invoke.req
initiator
TR-SAP
responder
TR-SAP
TR-Invoke.cnf
(H)
Source: Schiller
www.edubuzz360.com

WTP Class 2 Transaction, no user
ack, no hold on
TR-Invoke.req
initiator
TR-SAP
responder
TR-SAP
TR-Result.req
(UD*, H‘)
TR-Result.ind
(UD*, H)
TR-Invoke.cnf
(H)
TR-Result.res
(H)
TR-Result.cnf
(H‘)
Source: Schiller
www.edubuzz360.com

WTP Class 2 Transaction, user ack
TR-Invoke.req
initiator
TR-SAP
responder
TR-SAP
TR-Result.ind
(UD*, H)
TR-Invoke.res
(H‘)
TR-Invoke.cnf
(H) TR-Result.req
(UD*, H‘)
TR-Result.res
(H)
TR-Result.cnf
(H‘)
Source: Schiller
www.edubuzz360.com

WTP Class 2 Transaction, hold on,
no user ack
TR-Invoke.req
initiator
TR-SAP
responder
TR-SAP
TR-Result.req
(UD*, H‘)
TR-Result.ind
(UD*, H)
TR-Invoke.cnf
(H)
TR-Result.res
(H)
TR-Result.cnf
(H‘)
Source: Schiller
www.edubuzz360.com

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
WSP Services
 provides shared state between client and server, optimizes content transfer
 session management (establish, release, suspend, resume)
 efficient capability negotiation
 content encoding
 push
WSP/B (Browsing)
 HTTP/1.1 functionality - but binary encoded
 exchange of session headers
 push and pull data transfer
 asynchronous requests
www.edubuzz360.com

WSP Overview
Header Encoding
 compact binary encoding of headers, content type identifiers and other well-known textual or
structured values
 reduces the data actually sent over the network
Capabilities (are defined for):
 message size, client and server
 protocol options: Confirmed Push Facility, Push Facility, Session Suspend Facility,
Acknowledgement headers
 maximum outstanding requests
 extended methods
 header code pages
Suspend and Resume
 server knows when client can accept a push
 multi-bearer devices
 dynamic addressing
 allows the release of underlying bearer resources
www.edubuzz360.com

WSP Sessions
Session Context and Push
 push can take advantage of session headers
 server knows when client can accept a push
Connection-mode
 long-lived communication, benefits of the session state, reliability
Connectionless-mode
 stateless applications, no session creation overhead, no reliability overhead
www.edubuzz360.com

WSP/B session establishment
S-Connect.req
(SA, CA, CH, RC) S-Connect.ind
(SA, CA, CH, RC)
client
S-SAP
server
S-SAP
S-Connect.res
(SH, NC)
S-Connect.cnf
(SH, NC)
WTP Class 2
transaction
Source: Schiller
CH: Client Header
RC: Requested Capabilities
SH: Server Header
NC: Negotiated Capabilities
www.edubuzz360.com

WSP/B session suspend/resume
S-Suspend.req S-Suspend.ind
(R)
client
S-SAP
server
S-SAP
S-Resume.res
WTP Class 2
transaction
S-Suspend.ind
(R)
~ ~
S-Resume.req
(SA, CA) S-Resume.ind
(SA, CA)
S-Resume.cnf
WTP Class 0
transaction
Source: Schiller
R: Reason for disconnection
www.edubuzz360.com

WSP/B session termination
S-Disconnect.ind
(R)
client
S-SAP
server
S-SAP
S-Disconnect.ind
(R) WTP Class 0
transaction
S-Disconnect.req
(R)
Source: Schiller
www.edubuzz360.com

WSP/B method invoke
S-MethodInvoke.req
(CTID, M, RU) S-MethodInvoke.ind
(STID, M, RU)
client
S-SAP
server
S-SAP
S-MethodInvoke.res
(STID)
S-MethodInvoke.cnf
(CTID)
WTP Class 2
transaction
S-MethodResult.req
(STID, S, RH, RB)
S-MethodResult.ind
(CTID, S, RH, RB)
S-MethodResult.res
(CTID) S-MethodResult.cnf
(STID) CTID: Client Transaction ID
M: Method Invoked
RU: Request URI
STID: Server Transaction ID
S: Response Status
RH: Response Header
RB: Response Body Source: Schiller
www.edubuzz360.com

WSP/B over WTP - method
invocation
S-MethodInvoke.req
S-MethodInvoke.ind
client
S-SAP
server
S-SAP
S-MethodInvoke.res
S-MethodInvoke.cnf
S-MethodResult.req
S-MethodResult.ind
S-MethodResult.res
S-MethodResult.cnf
TR-Invoke.req
initiator
TR-SAP
TR-Result.ind
TR-Invoke.cnf
TR-Result.res
TR-Invoke.ind
responder
TR-SAP
TR-Invoke.res
TR-Result.req
TR-Result.cnf
Source: Schiller
www.edubuzz360.com

WSP/B over WTP - asynchronous,
unordered requests
S-MethodInvoke_1.req
S-MethodInvoke_1.ind
client
S-SAP
server
S-SAP
S-MethodResult_1.ind
S-MethodResult_1.req
Source: Schiller
www.edubuzz360.com

WSP/B - confirmed/non-confirmed
push S-Push.req
(PH, PB)
client
S-SAP
server
S-SAP
WTP Class 1
transaction
S-Push.ind
(PH, PB)
S-ConfirmedPush.res
(CPID)
S-ConfirmedPush.ind
(CPID, PH, PB)
WTP Class 0
transaction
S-ConfirmedPush.req
(SPID, PH, PB)
client
S-SAP
server
S-SAP
S-ConfirmedPush.cnf
(SPID)
Source: Schiller
PH: Push Header
PB: Push Body
SPID: Server Push ID
CPID: Client Push ID
www.edubuzz360.com

WSP/B over WDP
S-Unit-MethodInvoke.req
(SA, CA, TID, M, RU)
client
S-SAP
server
S-SAP
S-Unit-MethodResult.ind
(CA, SA, TID, S, RH, RB)
S-Unit-Push.ind
(CA, SA, PID, PH, PB)
S-Unit-MethodInvoke.ind
(SA, CA, TID, M, RU)
S-Unit-MethodResult.req
(CA, SA, TID, S, RH, RB)
S-Unit-Push.req
(CA, SA, PID, PH, PB)
WDP Unitdata
service
Source: Schiller
www.edubuzz360.com

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