Transcript Support for Mobility - Witchita State University

Mobile Communications Chapter
10: Support for Mobility
File systems
 Data bases
 WWW and Mobility
 WAP (Wireless Application Protocol), i-mode & Co.

File systems - Motivation
Goal

efficient and transparent access to shared files within a mobile environment
while maintaining data consistency
Problems





limited resources of mobile computers (memory, CPU, ...)
low bandwidth, variable bandwidth, temporary disconnection
high heterogeneity of hardware and software components (no standard PC
architecture)
wireless network resources and mobile computer are not very reliable
standard file systems (e.g., NFS, network file system) are very inefficient,
almost unusable
Solutions

replication of data (copying, cloning, caching)
 data collection in advance (hoarding, pre-fetching)
File systems - consistency problems
THE big problem of distributed, loosely coupled systems

are all views on data the same?
 how and when should changes be propagated to what users?
Weak consistency

many algorithms offering strong consistency (e.g., via atomic updates)
cannot be used in mobile environments
 invalidation of data located in caches through a server is very problematic if
the mobile computer is currently not connected to the network
 occasional inconsistencies have to be tolerated, but conflict resolution
strategies must be applied afterwards to reach consistency again
Conflict detection

content independent: version numbering, time-stamps
 content dependent: dependency graphs
File systems for limited connectivity I
Symmetry

Client/Server or Peer-to-Peer relations
 support in the fixed network and/or mobile computers
 one file system or several file systems
 one namespace for files or several namespaces
Transparency

hide the mobility support, applications on mobile computers should not
notice the mobility
 user should not notice additional mechanisms needed
Consistency model

optimistic or pessimistic
Caching and Pre-fetching

single files, directories, subtrees, partitions, ...
 permanent or only at certain points in time
File systems for limited connectivity II
Data management

management of buffered data and copies of data
 request for updates, validity of data
 detection of changes in data
Conflict solving

application specific or general
 errors
Several experimental systems exist

Coda (Carnegie Mellon University), Little Work (University of Michigan),
Ficus (UCLA) etc.
Many systems use ideas from distributed file systems such as, e.g., AFS
(Andrew File System)
File systems - Coda I
Coda is the successor of AFS and offers two different types of replication:

Server replication and caching on clients.
Coda is transparent extension of client’s cache manager.

Applications use cached replicates of files.
 Coda offers extensive mechanisms for pre-fetching of files while still
connected, called “Hoarding“.
 While the client is disconnected, applications work on the replicates, called
emulating.
Consistency



system keeps a record of changes in files and compares files after
reconnection
if different users have changed the same file a manual reintegration of the
file into the system is necessary
optimistic approach, coarse grained working on whole files.
mobile client
application
cache
server
File systems - Coda II
Hoarding
States of a client

user can pre-determine a file list with
priorities
 contents of the cache determined by
the list and LRU strategy (Last
Recently Used)
 explicit pre-fetching possible
 periodic updating
Comparison of files

asynchronous, background
 system weighs speed of updating
against minimization of network
traffic
Cache misses

modeling of user patience: how long
can a user wait for data without an
error message?
 function of file size and bandwidth
hoarding
disconnection
strong
connection
weak
connection
write
disconnected
connection
disconnection
emulating
File systems - Little Work


Only changes in the cache manager of the client
More client states to maintain consistency:
Connected
Method
normal
Partially
Connected
delayed write
to the server
continuous
bandwidth
Network
continuous
requirements high
bandwidth
Application
office, WLAN packet radio
Fetch only
Disconnected
optimistic
replication of files
connection on
demand
abort at cache
miss
none
cellular systems
(e.g., GSM) with
costs per call
independent
File systems - further examples
Ficus

not a client/server approach
 optimistic use of replicates, detection of write conflicts, conflict resolution
on directories
 use of „gossip“ protocols: a mobile computer does not necessarily need
to have direct connection to a server, with the help of other mobile
computers updates can be propagated through the network
MIo-NFS (Mobile Integration of NFS)

NFS extension, pessimistic approach, only token holder can write
 Three different modes:
 Connected: The server handles all access to files.
 loosely connected: Clients use local replicates, exchange tokens, and
update files via the network.
 Disconnected: The client uses only local replicates. Writing is only
allowed if the client is token-holder.
File systems - further examples
Rover

Relocatable dynamic objects are objects that can be dynamically
loaded into a client computer from a server to reduce client-server
communication.
 Queued remote procedure calls allow for non-blocking RPCs when a
host is disconnected.
 Requests and responses are exchanged as soon as a connection is
available.
 Conflict resolution is done in the server and is application specific.
Mobiware

A mobile middleware environment using CORBA and Java.
Mazer/Tardo

file synchronization layer between application and local file system
 caching of complete subdirectories from the server
 “Redirector” responses to requests locally if necessary, via the network if
possible
 periodic consistency checks with bi-directional updating
Database systems in mobile environments
Request processing

power conserving, location dependent, cost efficient
 example: find the fastest way to a hospital
Replication management

similar to file systems
Location management

tracking of mobile users to provide replicated or location dependent
data in time at the right place (minimize access delays)
 example: with the help of the HLR (Home Location Register) in
GSM a mobile user can find a local towing service
Transaction processing
“mobile” transactions can not necessarily rely on the same models
as transactions over fixed networks (ACID: atomicity, consistency,
isolation, durability)
 therefore models for “weak” transaction

World Wide Web and mobility
Protocol (HTTP, Hypertext Transfer Protocol) and language (HTML,
Hypertext Markup Language) of the Web have not been
designed for mobile applications and mobile devices, thus
creating many problems!
Typical transfer sizes

HTTP request: 100-350 byte
 responses avg. <10 kbyte, header 160 byte, GIF 4.1kByte, JPEG
12.8 kbyte, HTML 5.6 kbyte
 but also many large files that cannot be ignored
The Web is no file system

Web pages are not simple files to download
 static and dynamic content, interaction with servers via forms,
content transformation, push technologies etc.
 many hyperlinks, automatic loading and reloading, redirecting
 a single click might have big consequences!
WWW example
Request to port 80:
or:
GET / HTTP/1.0
GET / HTTP/1.1
Host: www.inf.fu-berlin.de
Response from server
HTTP/1.1 200 OK
Date: Wed, 30 Oct 2002 19:44:26 GMT
Server: Apache/1.3.12 (Unix) mod_perl/1.24
Last-Modified: Wed, 30 Oct 2002 13:16:31 GMT
ETag: "2d8190-2322-3dbfdbaf"
Accept-Ranges: bytes
Content-Length: 8994
Connection: close
Content-Type: text/html
non persistent
<DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html>
<head>
<title>FU-Berlin: Institut f&uuml;r Informatik</TITLE>
<base href="http://www.inf.fu-berlin.de">
<link rel="stylesheet" type="text/css" href="http://www.inf.fuberlin.de/styles/homepage.css">
<!--script language="JavaScript" src="fuinf.js"-->
<!--/script-->
</head>
<body onResize="self.location.reload();">
...
HTTP 1.0 and mobility I
Characteristics

stateless, client/server, request/response
 needs a connection oriented protocol (TCP), one connection per
request (some enhancements in HTTP 1.1)
 primitive caching and security
Problems

designed for large bandwidth (compared to wireless access) and
low delay
 big and redundant protocol headers (readable for humans,
stateless, therefore big headers in ASCII)
 uncompressed content transfer
 using TCP

huge overhead per request (3-way-handshake) compared with the
content, e.g., of a GET request
 slow-start problematic

DNS lookup by client causes additional traffic
HTTP 1.0 and mobility II
Caching

quite often disabled by information providers to be able to create user
profiles, usage statistics etc.
 dynamic objects cannot be cached

numerous counters, time, date, personalization, ...

mobility quite often inhibits caches
 security problems


how to use SSL/TLS together with proxies?
today: many user customized pages, dynamically generated on request via
CGI, ASP, ...
POSTing (i.e., sending to a server)

can typically not be buffered, very problematic if currently disconnected
Many unsolved problems!
HTML and mobile devices
HTML
designed for computers with “high” performance, color highresolution display, mouse, hard disk
 typically, web pages optimized for design, not for communication

Mobile devices

often only small, low-resolution displays, very limited input
interfaces (small touch-pads, soft-keyboards)
Additional “features”


animated GIF, Java AWT, Frames, ActiveX Controls, Shockwave,
movie clips, audio, ...
many web pages assume true color, multimedia support, highresolution and many plug-ins
Web pages ignore the heterogeneity of end-systems!

e.g., without additional mechanisms, large high-resolution pictures
would be transferred to a mobile phone with a low-resolution
display causing high costs
Approaches toward WWW for mobile devices
Application gateways, enhanced servers

simple clients, pre-calculations in the fixed network
 compression, filtering, content extraction
 automatic adaptation to network characteristics
Examples





picture scaling, color reduction, transformation of the document
format (e.g., PS to TXT)
detail studies, clipping, zoom
headline extraction, automatic abstract generation
HDML (handheld device markup language): simple language
similar to HTML requiring a special browser
HDTP (handheld device transport protocol): transport protocol for
HDML, developed by Unwired Planet
Problems

proprietary approaches, require special enhancements for browsers
 heterogeneous devices make approaches more complicated
Some new issues that might help mobility?

Push technology


HTTP/1.1








real pushing, not a client pull needed, channels etc.
client/server use the same connection for several request/response
transactions
multiple requests at beginning of session, several responses in
same order
enhanced caching of responses (useful if equivalent responses!)
semantic transparency not always achievable: disconnected,
performance, availability -> most up-to-date version...
several more tags and options for controlling caching
(public/private, max-age, no-cache etc.)
relaxing of transparency on app. request or with warning to user
encoding/compression mechanism, integrity check, security of
proxies, authentication, authorization...
Cookies: well..., stateful sessions, not really integrated...
System support for WWW in a mobile world I
Enhanced browsers
mobile client
integrated
enhancement

Pre-fetching, caching, off-line use
 e.g. Internet Explorer, Netscape
browser
web
server
Additional, accompanying application

Pre-fetching, caching, off-line use
 e.g. original WebWhacker
 Problem – not transparent, two different
ways of accessing content:
mobile client
browser
additional
application

Directly to the web server
 Via the additional application
web
server
System support for WWW in a mobile world II
Client Proxy acts as server for the browser
and as client for the web server.

Pre-fetching, caching, off-line use
 e.g., Caubweb, TeleWeb, Weblicator,
WebWhacker, WebEx, WebMirror
mobile client
browser
client
proxy
web
server
Network Proxy supports a mobile client on
the network side.
mobile client

adaptive content transformation
for bad connections, pre-fetching,
caching
 e.g., TranSend, Digestor
browser
network
proxy
web
server
System support for WWW in a mobile world III
Client and network proxy
mobile client

combination of benefits plus
simplified protocols
 e.g., MobiScape, WebExpress
Special network subsystem

adaptive content transformation
for bad connections, pre-fetching,
caching
 e.g., Mowgli
Additional many proprietary server
extensions possible

“channels”, content negotiation, ...
browser
client
proxy
web
server
network
proxy
mobile client
browser
client
proxy
web
server
network
proxy
WAP - Wireless Application Protocol
WAP (Wireless Application Protocol)
 a specification for a set of communication protocols to standardize the way
that wireless devices, such as cellular telephones and radio transceivers,
can be used for Internet access, including e-mail, the World Wide Web,
newsgroups, and Internet Relay Chat (IRC).
Goals
 deliver Internet content and enhanced services to mobile devices and users
(mobile phones, PDAs)
 independence from wireless network standards
 open for everyone to participate, protocol specifications will be proposed to
standardization bodies
 applications should scale well beyond current transport media and device
types and should also be applicable to future developments
Platforms
 e.g., GSM (900, 1800, 1900), CDMA IS-95, TDMA IS-136, 3rd generation
systems (IMT-2000, UMTS, W-CDMA, cdma2000 1x EV-DO, …)
Forum
 was: WAP Forum, co-founded by Ericsson, Motorola, Nokia, Unwired
Planet, further information www.wapforum.org
 now: Open Mobile Alliance www.openmobilealliance.org
(Open Mobile Architecture + WAP Forum + SyncML + …)
WAP - scope of standardization
Browser

“micro browser”, similar to existing, well-known browsers in the
Internet
Script language

similar to Java script, adapted to the mobile environment
WTA/WTAI

Wireless Telephony Application (Interface): access to all telephone
functions
Content formats

e.g., business cards (vCard), calendar events (vCalender)
Protocol layers

transport layer, security layer, session layer etc.
WAP 1.x - reference model and protocols
Internet
HTML, Java
A-SAP
WAP
Application Layer (WAE)
S-SAP
additional services
and applications
Session Layer (WSP)
HTTP
TR-SAP
Transaction Layer (WTP)
SEC-SAP
SSL/TLS
Security Layer (WTLS)
T-SAP
TCP/IP,
UDP/IP,
media
Transport Layer (WDP)
WCMP
Bearers (GSM, CDPD, ...)
WAE comprises WML (Wireless Markup Language), WML Script, WTAI etc.
WAP
The Wireless Application Environment (WAE) - Application layer
 a general-purpose application environment based on a combination of
World Wide Web (WWW) and mobile telephony technologies. WAE
includes a micro-browser environment containing the following
functionalities:
 Wireless Markup Language (WML)
A lightweight markup language, similar to HTML, but optimized for use
in hand-held mobile terminals;
 WMLScript
A lightweight scripting language, similar to JavaScript
 Wireless Telephony Application (WTA)
Telephony services and programming interfaces.
Wireless Session Protocol (WSP) - Session layer
 gives the functionality of HTTP but in a more optimized way.
Wireless Transaction Protocol (WTP) – Session layer
 runs on top of a datagram service and provides as a light-weight
transaction-oriented protocol.
Wireless Transport Layer Security (WTLS) – Transport layer
 a security protocol analogous to the industry-standard Transport Layer
Security (TLS) protocol, formerly known as Secure Sockets Layer (SSL) in
WWW model.
Wireless Datagram Protocol (WDP) – Transport layer
 The Transport layer protocol in the WAP architecture is referred to as the
Wireless Datagram Protocol (WDP).
WAP - network elements
fixed network
Internet
HTML
wireless network
WML
HTML
filter
WAP
proxy
Binary WML
WML
HTML
web
server
HTML
filter/
WAP
proxy
WTA
server
Binary WML
Binary WML
PSTN
Binary WML: binary file format for clients
WDP - Wireless Datagram Protocol
Protocol of the transport layer within the WAP architecture

uses directly transports mechanisms of different network technologies
 offers a common interface for higher layer protocols
 allows for transparent communication using different transport technologies
(GSM [SMS, CSD, USSD, GPRS, ...], IS-136, TETRA, DECT, PHS, IS-95,
...)
Goals of WDP


create a worldwide interoperable transport system with the help of WDP
adapted to the different underlying technologies
transmission services such as SMS, GPRS in GSM might change, new
services can replace the old ones
Additionally, WCMP (wireless Control Message Protocol) is used for
control/error report (similar to ICMP in the TCP/IP protocol suite)
WDP - Service Primitives
T-SAP
T-DUnitdata.req
(DA, DP, SA, SP, UD)
T-DUnitdata.req
(DA, DP, SA, SP, UD)
T-DError.ind
(EC)
T-SAP
T-DUnitdata.ind
(SA, SP, UD)
Usage of WDP
Wireless Data Gateway
WTLS
WDP &
Adaptation
SMS
GSM-SMS
Tunnel
WTLS
WDP &
Adaptation
Tunnel
Subnetwork
Subnetwork
SMS
WAP
Proxy
GSM-CSD
WTLS
Internet Service Provider
Remote Access Service
UDP
IP
PPP
CSD-RF
Interworking
Function
CSD-RF
PSTN
Circuit
IP
PPP
PSTN
Circuit
Subnetwork
WTLS
UDP
IP
Subnetwork
WTLS - Wireless Transport Layer Security
Goals

data integrity


privacy


prevention of tapping
authentication


prevention of changes in data
creation of authenticated relations between a mobile device and a server
protection against denial-of-service attacks

protection against repetition of data and unverified data
WTLS

is based on the TLS (Transport Layer Security) protocol (former SSL,
Secure Sockets Layer)
 optimized for low-bandwidth communication channels
Secure session, full handshake
originator
SEC-SAP
SEC-Create.req
(SA, SP, DA, DP, KES, CS, CM)
peer
SEC-SAP
SEC-Create.ind
(SA, SP, DA, DP, KES, CS, CM)
SEC-Create.res
(SNM, KR, SID, KES‘, CS‘, CM‘)
SEC-Create.cnf
(SNM, KR, SID, KES‘, CS‘, CM‘)
SEC-Exchange.req
SEC-Exchange.ind
SEC-Exchange.res
(CC)
SEC-Commit.req
SEC-Commit.cnf
SEC-Exchange.cnf
(CC)
SEC-Commit.ind
SEC-Unitdata - transferring datagrams
sender
SEC-SAP
SEC-Unitdata.req
(SA, SP, DA, DP, UD)
receiver
SEC-SAP
SEC-Unitdata.ind
(SA, SP, DA, DP, UD)
WTP - Wireless Transaction Protocol
Goals

different transaction services, offloads applications


application can select reliability, efficiency
support of different communication scenarios

class 0: unreliable message transfer
 class 1: reliable message transfer without result message
 class 2: reliable message transfer with exactly one reliable result message

supports peer-to-peer, client/server and multicast applications
 low memory requirements, suited to simple devices (< 10kbyte )
 efficient for wireless transmission

segmentation/reassembly
 selective retransmission
 header compression
 optimized connection setup (setup with data transfer)
Details of WTP I
Support of different communication scenarios

Class 0: unreliable message transfer


Example: push service
Class 1: reliable request

An invoke message is not followed by a result message
 Example: reliable push service

Class 2: reliable request/response

An invoke message is followed by exactly one result message
 With and without ACK
 Example: typical web browsing
No explicit connection setup or release is available
Services for higher layers are called events
Details of WTP II
Used Mechanisms

Reliability

Unique transaction identifiers (TID)
 Acknowledgements
 Selective retransmission
 Duplicate removal





Optional: concatenation & separation of messages
Optional: segmentation & reassembly of messages
Asynchronous transactions
Transaction abort, error handling
Optimized connection setup (includes data transmission)
WTP Class 0 transaction
initiator
TR-SAP
TR-Invoke.req
(SA, SP, DA, DP, A, UD, C=0, H)
responder
TR-SAP
TR-Invoke.ind
(SA, SP, DA, DP, A, UD, C=0, H‘)
WTP Class 1 transaction, no user ack & user ack
initiator
TR-SAP
TR-Invoke.req
(SA, SP, DA, DP, A, UD, C=1, H)
responder
TR-SAP
TR-Invoke.ind
(SA, SP, DA, DP, A, UD, C=1, H‘)
TR-Invoke.cnf
(H)
initiator
TR-SAP
TR-Invoke.req
(SA, SP, DA, DP, A, UD, C=1, H)
TR-Invoke.cnf
(H)
responder
TR-SAP
TR-Invoke.ind
(SA, SP, DA, DP, A, UD, C=1, H‘)
TR-Invoke.res
(H‘)
WTP Class 2 transaction, no user ack, no hold on
initiator
TR-SAP
TR-Invoke.req
(SA, SP, DA, DP, A, UD, C=2, H)
TR-Invoke.cnf
(H)
responder
TR-SAP
TR-Invoke.ind
(SA, SP, DA, DP, A, UD, C=2, H‘)
TR-Result.req
(UD*, H‘)
TR-Result.ind
(UD*, H)
TR-Result.res
(H)
TR-Result.cnf
(H‘)
WTP Class 2 transaction, user ack
initiator
TR-SAP
TR-Invoke.req
(SA, SP, DA, DP, A, UD, C=2, H)
TR-Invoke.cnf
(H)
TR-Result.ind
(UD*, H)
TR-Result.res
(H)
responder
TR-SAP
TR-Invoke.ind
(SA, SP, DA, DP, A, UD, C=2, H‘)
TR-Invoke.res
(H‘)
TR-Result.req
(UD*, H‘)
TR-Result.cnf
(H‘)
WTP Class 2 transaction, hold on, no user ack
initiator
TR-SAP
TR-Invoke.req
(SA, SP, DA, DP, A, UD, C=2, H)
TR-Invoke.cnf
(H)
responder
TR-SAP
TR-Invoke.ind
(SA, SP, DA, DP, A, UD, C=2, H‘)
TR-Result.req
(UD*, H‘)
TR-Result.ind
(UD*, H)
TR-Result.res
(H)
TR-Result.cnf
(H‘)
WSP - Wireless Session Protocol
Goals

HTTP 1.1 functionality

Request/reply, content type negotiation, ...

support of client/server, transactions, push technology
 key management, authentication, Internet security services
 session management (interruption, resume,...)
Open topics




QoS support)
Group communication
Isochronous media objects
management
WSP protocols
WSP
Connection mode
(uses WTP)
Connectionless mode
(uses WDP or WTLS)
• Session Management (class 0, 2)
• Method Invocation
• Method Invocation (Kl. 2)
• Push
• Error Report
(in general unreliable)
• Push (class 0)
• Confirmed Push (class 1)
• Session suspend/resume (class 0, 2)
WSP/B session establishment
client
S-SAP
server
S-SAP
S-Connect.req
(SA, CA, CH, RC)
S-Connect.ind
(SA, CA, CH, RC)
S-Connect.res
(SH, NC)
S-Connect.cnf
(SH, NC)
WTP Class 2
transaction
WSP/B session suspend/resume
client
S-SAP
server
S-SAP
S-Suspend.req
S-Suspend.ind
(R)
S-Suspend.ind
(R)
S-Resume.req
(SA, CA)
WTP Class 0
transaction
~
~
S-Resume.ind
(SA, CA)
S-Resume.res
S-Resume.cnf
WTP Class 2
transaction
WSP/B session termination
client
S-SAP
server
S-SAP
S-Disconnect.req
(R)
S-Disconnect.ind
(R)
S-Disconnect.ind
(R)
WTP Class 0
transaction
WSP/B method invoke
client
S-SAP
server
S-SAP
S-MethodInvoke.req
(CTID, M, RU)
S-MethodInvoke.ind
(STID, M, RU)
S-MethodInvoke.res
(STID)
S-MethodInvoke.cnf
(CTID)
S-MethodResult.req
(STID, S, RH, RB)
S-MethodResult.ind
(CTID, S, RH, RB)
S-MethodResult.res
(CTID)
S-MethodResult.cnf
(STID)
WTP Class 2
transaction
WSP/B over WTP - method invocation
client
S-SAP
initiator
TR-SAP
responder
TR-SAP
server
S-SAP
S-MethodInvoke.req TR-Invoke.req
TR-Invoke.ind S-MethodInvoke.ind
TR-Invoke.res S-MethodInvoke.res
S-MethodInvoke.cnf TR-Invoke.cnf
TR-Result.req S-MethodResult.req
S-MethodResult.ind
TR-Result.ind
S-MethodResult.res
TR-Result.res
TR-Result.cnf S-MethodResult.cnf
WSP/B over WTP - asynchronous, unordered requests
client
S-SAP
server
S-SAP
S-MethodInvoke_1.req
S-MethodInvoke_2.req
S-MethodInvoke_2.ind
S-MethodInvoke_1.ind
S-MethodInvoke_3.req
S-MethodResult_1.ind
S-MethodResult_3.ind
S-MethodResult_1.req
S-MethodInvoke_3.ind
S-MethodResult_3.req
S-MethodResult_2.req
S-MethodInvoke_4.req
S-MethodInvoke_4.ind
S-MethodResult_4.ind
S-MethodResult_2.ind
S-MethodResult_4.req
WSP/B - confirmend/non-confirmed push
client
S-SAP
S-Push.ind
(PH, PB)
server
S-SAP
S-Push.req
(PH, PB)
WTP Class 0
transaction
client
S-SAP
S-ConfirmedPush.ind
(CPID, PH, PB)
server
S-SAP
S-ConfirmedPush.req
(SPID, PH, PB)
S-ConfirmedPush.res
(CPID)
S-ConfirmedPush.cnf
(SPID)
WTP Class 1
transaction
WSP/B over WDP
S-Unit-MethodInvoke.req
(SA, CA, TID, M, RU)
client
S-SAP
server
S-SAP
S-Unit-MethodInvoke.ind
(SA, CA, TID, M, RU)
S-Unit-MethodResult.req
(CA, SA, TID, S, RH, RB)
S-Unit-MethodResult.ind
(CA, SA, TID, S, RH, RB)
S-Unit-Push.req
(CA, SA, PID, PH, PB)
S-Unit-Push.ind
(CA, SA, PID, PH, PB)
WDP Unitdata
service
WAE - Wireless Application Environment
Goals

network independent application environment for low-bandwidth,
wireless devices
 integrated Internet/WWW programming model with high interoperability
Requirements

device and network independent, international support
 manufacturers can determine look-and-feel, user interface
 considerations of slow links, limited memory, low computing power, small
display, simple user interface (compared to desktop computers)
Components





architecture: application model, browser, gateway, server
WML: XML-Syntax, based on card stacks, variables, ...
WMLScript: procedural, loops, conditions, ... (similar to JavaScript)
WTA: telephone services, such as call control, text messages, phone
book, ... (accessible from WML/WMLScript)
content formats: vCard, vCalendar, Wireless Bitmap, WML, ...
WAE logical model
Origin Servers
web
server
other content
server
Gateway
response
with
content
push
content
request
encoders
&
decoders
Client
encoded
response
with
content
encoded
push
content
encoded
request
WTA
user agent
WML
user agent
other
WAE
user agents
Wireless Markup Language (WML)
WML (Wireless Markup Language) is a language that allows the text
portions of Web pages to be presented on cellular telephones and
personal digital assistants (PDAs) via wireless access.
WML follows deck and card metaphor

WML document consists of many cards, cards are grouped to decks
 a deck is similar to an HTML page, unit of content transmission
 WML describes only intent of interaction in an abstract manner
 presentation depends on device capabilities
Features

text and images
 user interaction
 navigation
 context management
WML – example I
<?xml version="1.0"?>
<!DOCTYPE wml PUBLIC "-//WAPFORUM//DTD WML 1.1//EN"
"http://www.wapforum.org/DTD/wml_1.1.xml">
<wml>
<card id="card_one" title="simple example">
<do type="accept">
<go href="#card_two"/>
</do>
<p>
This is a simple first card!
<br/>
On the next one you can choose ...
</p>
</card>
WML – example II
<card id="card_two" title="Pizza selection">
<do type="accept" label="cont">
<go href="#card_three"/>
</do>
<p>
... your favorite pizza!
<select value="Mar" name="PIZZA">
<option value="Mar">Margherita</option>
<option value="Fun">Funghi</option>
<option value="Vul">Vulcano</option>
</select>
</p>
</card>
<card id="card_three" title="Your Pizza!">
<p>
Your personal pizza parameter is <b>$(PIZZA)</b>!
</p>
</card>
</wml>
WMLScript
WMLScript is the scripting language used in WML pages .
Complement to WML
Provides general scripting capabilities
Features

validity check of user input


access to device facilities


hardware and software (phone call, address book etc.)
local user interaction


check input before sent to server
interaction without round-trip delay
extensions to the device software

configure device, download new functionality after deployment
WMLScript - example
function pizza_test(pizza_type) {
var taste = "unknown";
if (pizza_type = "Margherita") {
taste = "well... ";
}
else {
if (pizza_type = "Vulcano") {
taste = "quite hot";
};
};
return taste;
};
Wireless Telephony Application (WTA)
The Wireless Telephony API is an API and framework for accessing
telephony and network services.
Collection of telephony specific extensions
Extension of basic WAE application model

content push

server can push content to the client
 client may now be able to handle unknown events

handling of network events


table indicating how to react on certain events from the network
access to telephony functions

any application on the client may access telephony functions
Example

calling a number (WML)
wtai://wp/mc;07216086415

calling a number (WMLScript)
WTAPublic.makeCall("07216086415");
WTA logical architecture
other telephone networks
WTA server
client
WML
scripts
WTA & WML
server
mobile
network
WTA
user agent
WAP gateway
repository
WML
decks
WTA
services
network operator
trusted domain
third party
servers
encoders
&
decoders
other
servers
firewall
device
specific
functions
Voice box example
WTA-User-Agent
WTA-Gateway
WTA-Server
Mobile network
Indicate new voice message
Voice box server
Generate new deck
Service Indication
Display deck;
user selects
WSP Get
Binary WML
Display deck;
user selects
WSP Get
Binary WML
Push URL
HTTP Get
WML
Respond with content
HTTP Get
WML
Respond with card
for call
Play requested voice message
Wait for call
Call setup
Setup call
Setup call
Accept call
Accept call
Accept call
Voice connection
WTAI - example with WML only
<?xml version="1.0"?>
<!DOCTYPE wml PUBLIC "-//WAPFORUM//DTD WML 1.1//EN"
"http://www.wapforum.org/DTD/wml_1.1.xml">
<wml>
<card id="card_one" title="Tele voting">
<do type="accept">
<go href="#card_two"/>
</do>
<p> Please choose your candidate! </p>
</card>
<card id="card_two" title="Your selection">
<do type="accept">
<go href="wtai://wp/mc;$dialno"/>
</do>
<p> Your selection:
<select name="dialno">
<option value="01376685">Mickey</option>
<option value="01376686">Donald</option>
<option value="01376687">Pluto</option>
</select>
</p>
</card>
</wml>
WTAI - example with WML and WMLScript I
function voteCall(Nr) {
var j = WTACallControl.setup(Nr,1);
if (j>=0) {
WMLBrowser.setVar("Message", "Called");
WMLBrowser.setVar("No", Nr);
}
else {
WMLBrowser.setVar("Message", "Error!");
WMLBrowser.setVar("No", j);
}
WMLBrowser.go("showResult");
}
WTAI - example with WML and WMLScript II
<?xml version="1.0"?>
<!DOCTYPE wml PUBLIC "-//WAPFORUM//DTD WML 1.1//EN"
"http://www.wapforum.org/DTD/wml_1.1.xml">
<wml>
<card id="card_one" title="Tele voting">
<do type="accept"> <go href="#card_two"/> </do>
<p> Please choose your candidate! </p>
</card>
<card id="card_two" title="Your selection">
<do type="accept">
<go href="/myscripts#voteCall($dialno)"/> </do>
<p> Your selection:
<select name="dialno">
<option value="01376685">Mickey</option>
<option value="01376686">Donald</option>
<option value="01376687">Pluto</option>
</select> </p>
</card>
<card id="showResult" title="Result">
<p> Status: $Message $No </p>
</card>
</wml>
WAP push architecture with proxy gateway
Push Access Protocol

Content transmission between server and PPG (Push Proxy Gateway)
 First version uses HTTP
Push OTA (Over The Air) Protocol

Simple, optimized
 Mapped onto WSP
Client
User Agents
Push OTA
Protocol
Push Proxy
Gateway
Coding,
checking
Push
Access
Protocol
Push Initiator
Server
application
Push/Pull services in WAP I
Service Indication

Service announcement using a pushed short message
 Service usage via a pull
 Service identification via a URI
<?xml version="1.0"?>
<!DOCTYPE si PUBLIC "-//WAPFORUM//DTD SI 1.0//EN"
"http://www.wapforum.org/DTD/si.dtd">
<si>
<indication href="http://www.piiiizza4u.de/offer/salad.wml"
created="2002-10-30T17:45:32Z"
si-expires="2000-10-30T17:50:31Z">
Salad special: The 5 minute offer
</indication>
</si>
Push/Pull services in WAP II
Service Loading

short message pushed to a client containing a URI
 User agent decides whether to use the URI via a pull
 Transparent for users, always looks like a push
<?xml version="1.0"?>
<!DOCTYPE sl PUBLIC "-//WAPFORUM//DTD SL 1.0//EN"
"http://www.wapforum.org/DTD/sl.dtd">
<sl
href="http://www.piiiizza4u.de/offer/salad.wml">
</sl>
Examples for WAP protocol stacks (WAP 1.x)
WAP standardization
WAE user agent
outside WAP
WAE
WSP
transaction based
application
WTP
WTP
WTLS
datagram based
application
WTLS
WTLS
UDP
WDP
UDP
WDP
UDP
WDP
IP
non IP
IP
non IP
IP
non IP
(GPRS, ...) (SMS, ...)
(GPRS, ...) (SMS, ...)
(GPRS, ...) (SMS, ...)
1.
2.
3.
typical WAP
application with
complete protocol
stack
pure data application
with/without
additional security
i-mode – first of all a business model!
i-mode is a proprietary packet-based information service for mobile
phones by NTT DoCoMo.
Access to Internet services in Japan provided by NTT DoCoMo

Services


Big success – more than 30 million users




Email, short messages, web, picture exchange, horoscope, ...
Many use i-mode as PC replacement
For many this is the first Internet contact
Very simple to use, convenient
Technology


9.6 kbit/s (enhancements with 28.8 kbit/s), packet oriented (PDC-P)
Compact HTML (cHTML) plus proprietary tags, special transport layer (Stop/go, ARQ, push,
connection oriented)
mobile terminal
mobile network
cHTML + tags
HTTP(S)
TL
TL
PDC-P
PDC-P
TCP
IP
L2
L1
gateway
TCP
IP
L2
L1
TCP
IP
L2
L1
content provider
cHTML + tags
HTTP(S)
TCP
IP
L2
L1
Email example: i-mode push with SMS
application
WSP
WTP
Popular misconception:
WAP was a failure, i-mode is different
and a success – wrong from a
technology point of view, right from a
business point of view…
WDP
SMS
Operator sends an SMS containing a
push message if a new email has
arrived. If the user wants to read the
email, an HTTP get follows with the
email as response.
i-mode as a business model:
- content providers get >80%
of the revenue.
- independent of technology
(GSM/GPRS in Europe,
PDC-P in Japan – but also
UMTS!)
i-mode protocol stack based on WAP 2.0
user equipment
gateway
server
cHTML
cHTML
HTTP
HTTP
SSL
SSL
WTCP
WTCP
TCP
TCP
IP
IP
IP
IP
L2
L2
L2
L2
L1
L1
L1
L1
i-mode can use WAP 2.0/Internet protocols (example: i-mode in Germany over GSM/GPRS)
i-mode – technical requirements
Functions
Descriptions
Status
Requirement
WEB Access
Portal Site / Internet Access
M
i-mode HTML (cHTML+tags)
E-mail
Internet e-mail and inter-terminal email
M
HTTP 1.1
Security
End-End security
O
SSL (Version 2, 3), TLS 1
Java
Java application made available
O
Compatible i-mode JAVA
Ringing tone download
Ringing melody download
M
SMF based
Image download
Stand-by screen download
M
GIF (O: JPEG)
Voice call notification during imode session
Voice termination notified and responded during i-mode
communications
M
3GPP standard system
Content charge billing
Per content charge billed to user
M
Specifications depend on each
operator’s billing system
Third party payment collection
Content charge collection on behalf of Content Provider
M
Specifications depend on each
operator’s billing system
Reverse billing
Packet usage charges can be billed to third party
O
Specifications depend on each
operator’s billing system
Subscriber ID transmission
Hashed subscriber ID from the operator’s portal to the CP
transmission on each content access
M
The ID generation algorithm
should be determined by each
operator and has to be secret
Number of characters per email
Number of characters (byte) per e-mail
M
To be defined by operators (e.g.
500 byte, 1K byte, 10K byte)
Character code set supported
Character code set supported by browser and used to develop content
M
To be defined by operators
User Agent
Browser specifications to be notified
M
HTTP 1.1
i-mode button
Dedicated button
O
Hard or soft key
i-mode examples I
i-mode examples II
i-mode examples III
WAP 2.0 (July 2001)
WAP 2.0 supports:

XHTML with a mobile profile (XHTMLMP)
 TCP with „Wireless Profile“
 HTTP
WAP 2.0 framework consists of:

Bearer networks: GPRS
 Transport services: TCP, WDP or UDP
 Transfer services: HTTP, Multi-media messaging Service (MMS)
 Session services: push OTA (Over The Air)
New applications






Color graphics
Animation
Large file download
Location based services
Synchronization with PIMs
Pop-up/context sensitive menus
Goal: integration of WWW, Internet, WAP, i-mode
External
services EFI
Crypto
libraries
WAE/WTA User Agent
(WML, XHTMLMP)
Push
Provisioning
Authentication
Identification
Service
Lookup
PKI
Secure
transport
Secure
bearer
Push
OTA
Cookies
Synchronisation
Hypermedia transfer
(WTP+WSP, HTTP)
CSD
IPv6
MMS
Connections
(TCP with
wireless profile)
Datagrams
(WDP, UDP)
IPv4
Streaming
Transport
Navigation
Discovery
Capability Negotiation
USSD
SMS
GPRS
FLEX
MPAK
...
...
Protocol framework
Content
formats
Session
Multimedia Messaging
(Email)
Transfer
Security
services
Bearer
Service
discovery
Application
framework
WAP 2.0 architecture
WAP 2.0 example protocol stacks
WAP device
WAE
WSP
WTP
WTLS
WDP
bearer
WAP gateway
WSP
WTP
WTLS
WDP
bearer
Web server
WAE
HTTP
HTTP
TLS
TCP
IP
TLS
TCP
IP
WAP 1.x Server/Gateway/Client
WAP device
WAE
HTTP
TLS
TCP‘
IP
WAP proxy
TCP‘
IP
TCP
IP
Web server
WAE
HTTP
TLS
TCP
IP
WAP Proxy with TLS tunneling
WAP device
WAE
HTTP‘
TCP‘
IP
WAP proxy
HTTP‘
TCP‘
IP
HTTP
TCP
IP
Web server
WAE
HTTP
TCP
IP
WAP HTTP Proxy with profiled TCP and HTTP
WAP device
WAE
HTTP
TCP
IP
IP router
IP
IP
WAP direct access
Web server
WAE
HTTP
TCP
IP
Java 2 Platform Micro Edition
„Java-Boom expected“ (?)

Desktop: over 90% standard PC architecture, Intel x86 compatible,
typically MS Windows systems
 Do really many people care about platform independent applications?
BUT: Heterogeneous, “small“ devices

Internet appliances, cellular phones, embedded control, car radios, ...
 Technical necessities (temperature range, form factor, power consumption,
…) and economic reasons result in different hardware
J2ME

Provides a uniform platform
 Restricted functionality compared to standard java platform (JVM)
Applications of J2ME
Example cellular phones

NTT DoCoMo introduced ippli
 Applications on PDA, mobile phone, ...
 Game download, multimedia applications,
encryption, system updates
 Load additional functionality with a push on a
button (and pay for it)!
Embedded control

Household devices, vehicles, surveillance
systems, device control
 System update is an important factor
Characteristics and architecture
Java Virtual Machine

Virtual Hardware (Processor)
 KVM (K Virtual Machine)



Min. 128 kByte, typ. 256 kByte
Optimized for low performance devices
Might be a co-processor
Configurations

Subset of standard Java libraries depending technical
hardware parameters (memory, CPU)
 CLDC (Connected Limited Device Configuration)

Basic libraries, input/output, security – describes Java
support for mobile devices
Profiles
Applications
Profile
(MIDP)
Configurations
(CDC, CLDC)
Java Virtual Machine
(JVM, KVM)
Operating system
(EPOC, Palm, WinCE)

Interoperability of heterogeneous devices belonging to
the same category
 MIDP (Mobile Information Device Profile)

Defines interfaces for GUIs, HTTP, application support, …
Hardware
(SH4, ARM, 68k, ...)
Hardware independent development
Summary J2ME
Idea is more than WAP 1.x or i-mode

Full applications on mobile phones, not only a
browser
 Includes system updates, end-to-end encryption
Platform independent via virtualization

As long as certain common interfaces are used
 Not valid for hardware specific functions
Limited functionality compared to JVM

Thus, maybe an intermediate solution only – until
embedded systems, mobile phones are as
powerful as today’s desktop systems