1. Mobile Applications Cellular Networks Wireless LANs Ad-hoc Networks
/Web/Location services
Intranet application access
Wireless application protocol
Wireless LANs
Client-Server adaptations
Disconnected operations
Ad-hoc Networks
Vehicular applications
Emergencies
Data broadcasting
Mobile agents

2. Variability of the Mobile Environment
Connectivity
connected
semi-connected
(asymmetric)
weakly connected
disconnected
Mobile Device Capability
form factor
Windows based GUI
multimedia
real-time multimedia
Mobility
stationary
nomadic (pedestrian speed)
mobile (vehicular speed)
roaming (mobile across networks)
Source: Helal

3. Mobile Applications - 1 Vehicles Emergencies Traveling salesmen
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 ...
Traveling salesmen
direct access to central customer files
consistent databases for all agents
mobile office

4. Mobile Applications - 2 Web access Information services
outdoor Internet access
intelligent travel guide with up-to-date location dependent information
Information services
push: stock quotes; pull: nearest cash ATM
find nearest printer (Jini services)
Disconnected operations
file-system caching for off-line work
mobile agents, e.g., shopping
Entertainment
ad-hoc networks for multi user games

5. World Wide Web and Mobility
HTTP/HTML have not been designed for mobile applications/devices
HTTP 1.0 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
big protocol headers, uncompressed content transfer
primitive caching (often disabled, dynamic objects)
security problems (using SSL/TLS with proxies)
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

6. System Support for Mobile WWW
Enhanced browsers
client-aware support for mobility
Proxies
Client proxy: pre-fetching, caching, off-line use
Network proxy: adaptive content transformation for connections
Client and network proxy
Enhanced servers
server-aware support for mobility
serve the content in multiple ways, depending on client capabilities
New protocols/languages
WAP/WML

7. Wireless Application Protocol
wapforum.org: co-founded by Ericsson, Motorola, Nokia, Phone.com
Goals
deliver Internet services to mobile devices
independence from wireless network standards
GSM, CDMA IS-95, TDMA IS-136, 3G systems (UMTS, W-CDMA)
Browser
“Micro browser”, similar to existing web browsers
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

8. WAP: Reference model and protocols
Internet
WAP
A-SAP
HTML, Java
Application Layer (WAE)
additional services and applications
S-SAP
HTTP
Session Layer (WSP)
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.
Source: Schiller

9. WAP: Stack Overview WDP (Wireless Datagram Protocol):
Provides transport layer functions
Based on ideas from UDP
WTLS (Wireless Transport Layer Security):
Provides data integrity, privacy, authentication functions
Based on ideas from TLS/SSL
WTP (Wireless Transaction Protocol):
Provides reliable message transfer mechanisms
Based on ideas from TCP
WSP (Wireless Session Protocol):
Provides HTTP 1.1 functionality
Supports session management, security, etc.
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.
Content encoding, optimized for low-bandwidth channels, simple devices

10. WAP: Network elements fixed network wireless network Internet WAP
proxy
WML
Binary WML
HTML
filter
WML
HTML
HTML
filter/
WAP
proxy
Binary WML
web
server
HTML
WTA
server
Binary WML
PSTN
Binary WML: binary file format for clients
Source: Schiller

11. WAE: Logical model Origin Servers Gateway Client WTA user agent web
response
with
content
encoded
response
with
content
encoders
&
decoders
WML
user agent
other content
server
push
content
encoded
push
content
other
WAE
user agents
request
encoded
request
Source: Schiller

12. Wireless Markup Language (WML)
Cards and Decks
Document consists of many cards, cards are grouped to decks
Deck is similar to 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
WMLScript
Provides general scripting capabilities
Validity check of user input, local user interaction
Access to device facilities (phone call, address book etc.)

13. WML: Example <WML> <CARD> <DO TYPE="ACCEPT">
<GO URL="#card_two"/>
</DO>
This is a simple first card!
On the next you can choose ...
</CARD>
<CARD NAME="card_two">
... your favorite pizza:
<SELECT KEY="PIZZA">
<OPTION VALUE=”M”>Margherita</OPTION>
<OPTION VALUE=”F”>Funghi</OPTION>
<OPTION VALUE=”V”>Vulcano</OPTION>
</SELECT>
</WML>
Source: Schiller

14. Application Adaptations for Mobility
System-transparent, application-transparent
the conventional, “unaware” client/server model
System-aware, application-transparent
the client/proxy/server model
the disconnected operation model
System-transparent, application-aware
dynamic client/server model
data broadcasting/caching
System-aware, application-aware
the mobile agent model

15. The Client/Proxy/Server Model
Proxy functions as a client to the fixed network server
Proxy functions as a mobility-aware server to mobile client
Proxy may be placed in the mobile host (Coda), or the fixed network, or both (WebExpress)
Enables thin client design:
Resource-poor mobile computers
Application resides on the server
Keyboard and mouse inputs sent from client to server
Display outputs sent from server to client

16. Web Proxy in WebExpress
The WebExpress Intercept Model
Source: Helal

17. Disconnected Operations: File Systems
Goals
Efficient/transparent access to shared files within a mobile environment
Support for disconnected operations while maintaining data consistency
Standard file systems (e.g., NFS) are very inefficient, almost unusable
Approaches
Replication of data (copying, cloning, caching)
Getting data in advance (hoarding, pre-fetching)
Main problem: consistency
Typical mechanisms: strong consistency (via atomic updates)
Invalidation of caches through a server
Cannot be used in mobile environments
Mobile computer may not be connected to network
One solution: weak consistency
Tolerate occasional inconsistencies
Apply conflict resolution strategies subsequently
Use version numbering, time-stamps (content independent)
Use dependency graphs (content dependent)

18. File Systems: Coda
Application transparent extensions of client and server
changes in the cache manager of a client
applications use cache replicates of files
extensive, transparent hoarding
Consistency
system keeps record of changes; compares files upon reconnection
if different users have changed the same file, manual reintegration of the file into the system is necessary
optimistic approach, coarse grained (file size)
mobile client
cache
application
server
Source: Schiller

19. File Systems - Coda Hoarding States of a client Consistency
user can pre-determine a file list with priorities
contents of the cache determined by the list and LRU strategy
explicit pre-fetching possible
periodic updating
Consistency
asynchronous, background comparison of files
system weighs speed of updating against minimization of network traffic
Cache misses
function of file size and bandwidth
modeling of user patience: how long can a user wait for data without an error message?
States of a client
hoarding
strong
connection
weak
connection
disconnection
write
disconnected
connection
disconnection
emulating
Source: Schiller

20. Mobile Data Management
Maximize query capacity of servers, minimize energy/query at client
asymmetric links (high b/w from server to client; low b/w from client to server)!
Pull data delivery: clients demand, servers respond
clients request (validate) data by sending uplink messages to server
Push data delivery: servers broadcast data, clients listen
servers push data (and validation reports) through a broadcast channel,to a community of clients
data are selected based on profiles and registration in each cell
client energy is saved by needing receive mode only
scales to any number of clients
Push and Pull data dissemination: Sharing the channel
Selective Broadcast: Servers broadcast "hot" information only
On-demand Broadcast: Servers choose the next item based on requests

21. Organization of Broadcast Data
Flat: cyclically broadcast the union of the requested data
Skewed (Random):
broadcast different items with different frequencies
goal is that the inter-arrival time between two instances of the same item matches the clients' needs
A B C
A A B C

22. Broadcast Disks B C A
Disk1
Disk2
A B A C
Periodic broadcast of one or more disks using a broadcast channel
Disks can of different sizes and can be broadcast at different speed
Frequency of broadcasting each item depends on its access probability
Disk speed can be changed based on client access pattern
Source: Helal

23. Indexing on Air Server dynamically adjusts broadcast hotspot
inx
Server dynamically adjusts broadcast hotspot
Clients read the index, enters into doze mode, and then perform selective tuning
Query Time: time taken from point a client issues a query until answer is received
Listening Time: time spent by client listening to the channel
Source: Helal

24. Client Caching in Broadcasting
Data are cached at clients to improve access time
Lessen dependency on the server's choice of broadcast priority
Traditionally, clients cache "hottest" data to improve hit ratio
Cache data based on PIX:
Probability of access (P)/Broadcast frequency (X).
Cache data replacement
cost-based is not practical
requires perfect knowledge of access probabilities
comparison of PIX values with all resident pages
Alternative: LIX, LRU with broadcast frequency
pages are placed on lists based on their frequency (X)
lists are ordered based on L, the running avg. of interaccess times
page with lowest LIX = L/X is replaced

25. Client Cache Invalidation
Why?
Value of data may have changed since caching by client
When?
Synchronous: send invalidation reports periodically
Asynchronous: send invalidation information for an item, as soon as its value changes
To whom?
Stateful server: to affected clients
Stateless server: broadcast to everyone
What to send?
invalidation: only which items were updated
propagation: the values of updated items are sent
aggregated information/ materialized views
Another issue
Commit of transactions involving read and write by clients
Synchronous invalidation adds some latency in query processing

26. The Mobile Agent Model Mobile agent receives client request and
Mobile 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, when the client is connected

27. Mobile Code Definition: Approaches: (Not a totally new concept)
Capability to dynamically change the bindings between code fragments and the location where they are executed
Approaches: (Not a totally new concept)
Remote batch job submission & use of PostScript to control printers
Distributed OS led to more structured approach
Process Migration
Object Migration (Mobile Objects)
Mobile Code Systems (Mobile Agents)

28. Process Migration Transfer of OS process from one m/c to other
Migration mechanisms handle bindings between
process and execution environment (e.g. open fds, env variables)
Provide for load balancing
Most of these facilities provide transparent process migration
Other like Locus provide for some control
like external signal or migrate( ) system call

29. Object Migration Makes possible to move objects among address spaces
finer grained mobility with respect to processes
e..g Emerald system : Different granularity levels - small to complex objects
does not provide complete transparency
COOL (oo extension of Chorus OS) allows total transparent migration
Process and Object migration address issues when
code and state are moved among hosts of loosely coupled, small scale distributed systems
insufficient when applied to large scale settings

30. Mobile Code Systems Code mobility is exploited on Internet Scale
Large scale, heterogeneous hosts, technologies
Strong v/s weak mobility
Mobility is location aware
Programming language
provides mechanisms and abstractions that enable shipping/ fetching of code to/from nodes
Underlying run-time
supports marshalling, code, check in , security etc
no knowledge of migration policies
Applications
Not just for load balancing
E-commerce, distributed information retrieval, workflow…

31. Mobile Code Systems: Design
Several Paradigms:
Client Server
Remote Evaluation
Code on Demand
Mobile Agent
Example:
Two friends Sita and Gita
interact to make a cake (results of service)
recipe is needed (know-how about service)
also ingredients (movable resources)
oven to bake (hard to move resource)
a person to mix ingredients as per recipe (computational component responsible for execution of code)
prepare the cake (execute the service)
where the cake is prepared (site of execution)

32. Client-Server: CS Sita would like to have chocolate cake:
she does not know the recipe
she does not have the required ingredients nor an oven
Sita knows that Gita (who likes baking cakes)
knows the recipe
has a well supplied kitchen
Sita calls Gita asking:
“Can you make me a chocolate cake please?”
Gita makes the cake and delivers it back to Sita

33. Remote Evaluation: REV
Sita would like to have chocolate cake:
she knows the recipe
she does not have the required ingredients nor an oven
Sita knows that Gita (who likes baking cakes)
has a well supplied kitchen
does not know the recipe
Sita calls Gita asking:
“Can you make me a chocolate cake please? Here is the recipe…”
Gita makes the cake and delivers it back to Sita

34. Code on Demand : COD Sita would like to have chocolate cake:
she has the required ingredients and an oven
she does not know the recipe
Sita knows that Gita
knows the recipe (and is willing to share it)
Sita calls Gita asking:
“Can you tell me the recipe for making chocolate cake please?”
Gita tells her the recipe and Sita makes the cake

35. Mobile Agent: MA Sita would like to have chocolate cake:
she has the recipe and the required ingredients
she does not have an oven
Sita knows that Gita
has an oven (and is willing to share it)
Sita could
prepare the batter
go to Gita’s place
bake the cake
Several other variations are also possible

36. Mobile Agents: Example

37. Mobile Applications in Industry
Wireless access: phone.com
Alerting services: myalert.com
Location services: airflash.com
Intranet applications: imedeon.com
Banking services: macalla.com
Mobile agents: tryllian.com ….
wapforum.org
palowireless.com