GAP

GAP: A Tool to Solve the Problem of the Web Contents Visualization in
Pocket PC Devices.
J. Carlos Olivares R., J. Gabriel González S., Azucena Montes R., Víctor J. Sosa S. e I. Rafael
Ponce M.
Centro Nacional de Investigación y Desarrollo Tecnológico(cenidet)
Cuernavaca, Morelos, México
{jcolivares04c, gabriel, amr, vjsosa, rafaxzero4c}@cenidet.edu.mx
Abstract
This tool intends to fill the existing ‘GAP’ in the
Web sites visualization in mobile devices, such as
Pocket PC. In order to guarantee that the users can
correctly visualize the Web resources, two things are
needed: a mechanism for controlling disconnections,
and allowing visualization of Web content despite of
the device connection state (hoarding), and a
mechanism that can adapt the Web content to the
specific mobile device features (transcoding). GAP is a
tool that integrates these two mechanisms and allows
improving of the user’s navigation experience in the
Mobile Web.
Keywords: Pocket PC, Visualization, Web Resources,
Hoarding, Transcoding.
1. Introduction
Mobile devices are each time closer in time,
according with [1]: "By 2009, more than a half of the
microprocessors made in the world will be intended for
mobile devices." "The software that will really make
mobile devices useful isn’t developed yet." These
statistics reflect that the use of mobile devices is
increasing due to their tiny size and that its power of
processing and versatility is growing day by day.
The problem of Web resources visualization in
mobile devices is the fact that the great majority of
Web sites in Internet have not been designed for this
type of devices. The mobile devices have limited
resources like small screens, little memory, low
processing speeds, etc; in comparison with traditional
computers equipment.
On other hand, the Web and the protocol that
manages it: HTTP are connection oriented (they are
based on TCP) what causes the transaction to fail if
the user, by any reason, becomes disconnected from
the network . In this case, it might not be possible to
visualize the Web resources in the mobile client.
Disconnections are frequent in this type of devices,
mainly because of their main advantage: mobility.
In this work a system which development is in
progress is described. It focuses in attacking the
problem of Web resources visualization on mobile
devices. The main characteristic of this work is that
great part of the system is executed in this kind of
devices, in comparison to the great majority of the
existing solutions that are executed in traditional
platforms.
2. Alternatives of solution
In order to solve this problem several alternatives
are presented: to design a new protocol, to modify and
existed protocol or to implement intermediary services
that solve the problem.
2.1 New protocols
In this scheme is possible to mention the WAP
protocol and the WML language, they work in an
analogous way as HTTP-HTML in the traditional Web.
The problem strives in that WAP only works with
mobile equipment and this would bring the same
fragmentation that today has the Web (special pages
for all class of devices). In addition, WAP was
originally designed for devices with limited resources
capacities (monochrome screens, lower bandwidth, etc)
which is actually solving day by bay through
bandwidth wireless connection (WCDMA, UTMS,
802.11g, WiMax, etc) and with more and more
powerful equipment.
The best solution would be to create a new protocol.
The problem is that this one must be totally compatible
with the existing ones, because if not, it would let
unusable thousands of existing resources (it would be
necessary to modify as much Web servers as Web
clients).
2.2 Modification of protocols
Within this alternative exits the case of having a
new request scheme of Web resources. This new

scheme receives the name of Push, whereas traditional
scheme receives the name of Pull [2].
The Pull scheme receives the name of “over
demand’. Under this scheme, the client (user) is who
visualizes a resource in an explicit way. In our case, if
a user wants to see the page of cenidet, must write in
the Web browser the next URL:
http://www.cenidet.edu.mx/.
The Push scheme also receives the name of
'subscription-notification'. In this scheme, the user
subscribes itself to a service and when some event of
interest happens a notification is sent for alerting the
user about the event.
Generally these two schemes do not live on isolated
way. Hybrid schemes (Pull&Push) have been applied
in diverse existing services, so is the case of the
reception of SMS/MMS messages, where the send of
messages is Pull and the reception is Push, since it
notifies to users about the existence of new messages.
Another service that has made famous devices like
the Blackberry to become successful is the Push-mail
[3]. This service comes to solve the problem of email
visualization in mobile environments. Under the
traditional scheme of the electronic mail, for consulting
the email, a user must be connected all the time to
receive it. This originates great costs if the network
connection generates costs per time. With this new
scheme, the user is not connected to the mail server.
When a new mail in the server is received, it notifies
the client of the existence of the new mail and sends it
to the mobile client.
For this type of schemes, protocols like HTTPU
(HTTP over UDP) or HTTPMU (HTTP over multicast
UDP) have been proposed, and basically works similar
to the HTTP but using datagrams, which are not in an
oriented connection way. With these protocols are
possible to offer a better quality in the mobile Web [4].
2.3 Intermediary services
This is the more extended solution to solve the
problem of Web resources visualization and many
other problems present on Web, like the case of
firewalls that solve some of the Web security problems
like the access control, or proxies’ caches that tries to
reduce the access latency to the information.
The scheme of intermediaries is widely used
because it doesn’t need to modify neither the clients
nor the servers; in fact, the client and server processes
do not notice the existence of these intermediary
services. These services are in charge of the hard work
and are transparent to the users.
The tool that is described in this article, works
under the scheme of intermediary services.
3. Proposal of solution
The hoarding process solves the problem of Web
resources visualization without concerning the state of
the connection of the mobile device. For this, it
becomes necessary that the user has already stored, in
local way, in his device the resources that he o she will
use.
As can be observed, the amount of resources to
occupy can be immense, whereas the capacity of
storage of the devices is limited. In order to give
solution against this new problem is necessary to have
an effective way to know the resources that a user
could use. With hoarding is possible to reduce this,
through algorithms of association rules applied on Web
logs, is determined the optimal set of resources that
will be replicated to the mobile clients [5].
A mechanism which tries to solve the adaptation
problem of Web resources to the displaying capacities
on mobile devices is transcoding. It consists of
transformation of resources, distilling and processing
of all those characteristics that are not available in the
device is needed. The used mechanism of transcoding
uses HTML to a subgroup of HTML transformer,
using XML.
The system is based on client-server architecture
with an intermediate tier on the server side as on the
client side. The system is shown in Figure 1.
Figure 1. General architecture proposed.
The general system has been denominated GASWT
(Gestor de Acaparamiento de Sitios Web
Transcodificados: Hoarding Manager of Transcoding
Web Sites). The intermediary in the client side is
denominated GAP (Gestor de Acaparamiento para
Pocket PC: Hoarding Manager for Pocket PC),
whereas the server side is denominated GAT (Gestor
de Acaparamiento y Transcodificación, Hoarding
Manager and Transcoding). The GAT is composed by
MA (Mecanismo Acaparador: Hoarding Mechanism)
and by MT (Mecanismo Transformador: Transcoding

Mechanism). The communication between the
processes is made through a HTTP request-response
scheme.
As much the MA as TM are taken from other
projects that together with this one, comprise the
Moviware project [6], whose main function is to offer
a set of services to mobile clients that have frequent
disconnections.
The general operation of the system is described in
the next lines. The user introduces an URL from the
Web browser (which has been previously configured to
redirect his exit towards the GAP). The GAP receives
the request and determines if it is in the local cache of
the device, if found, the hoarded resource is sends to
the Web browser.
When the resource is not hoarded, the system
validates the connection existence in order to obtain
the resource on line. If for some reason the resource
cannot be shown, (because it doesn’t exist or has
detected an error in the connection) the system notifies
the user by sending an error message.
On the other hand, if the Web resource is not
hoarded and a pattern of the site in the local device
doesn’t exist, the MA sends the Web resources if a
pattern for this site exists. If the pattern exists but the
hoarded resources in the MA aren’t present, it obtains
them by requesting them to MT and soon compresses
the resources in zip format to optimize the process.
Once the MA has sent the hoarded Web site, the
mobile device must decompress the Web site and
update its list of patterns. This process happens in
transparent way, in a way that the user never notices.
MT is responsible of collecting documents and if
they are HTML, it transforms them if the configuration
parameters indicate that. The transcoding is made on
line, because the process is slowed down if the
document is too large.
The actions that the user can make on the system
consist in visualizing Web sites on line, visualizing
Web sites on disconnection mode, visualizing error
messages, visualization of the requests states and
finally, set up the system.
The GAP is basically conformed of three main
modules which are: Observer, GAL (Gestor de
Acaparamiento Local: Local Hoarding Manager) and
GDL (Gestor de Desconexión Local: Manager of Local
Disconnection).
The Observer is responsible of processing each
request and to give back the result to the navigator.
The GAL is responsible of the manipulation and
control of the cache in the device. The users decide
which resources are susceptible of hoarding, as well as
limiting the storage space.
The GDL is responsible of determining the state of
the connection. The control of the disconnections has
been used drilling the network during three seconds.
Observing the quality of the results, a threshold of 30%
of accepted connections determines if the client is
connected (if the threshold is surpassed or equaled) or
is on disconnection mode (if it is below the threshold)
[7].
For the implementation of this tool, we used .NET
Compact Framework 1.0 with C # language, because it
is the best option to program in Pocket PC platform
[8].
The modifications of the MA and MT are being
made in Java so that it is language in which these
modules are programmed.
4. Results
The tool described in the present document has been
proven in diverse equipment like Pocket PC 2000
(Compaq iPAQ H3630), Pocket PC 2002 (HP Jornada
5500), Pocket PC 2003 (HP rx3115), emulators of
Windows CE, desktop PC (Compaq Presario with
Pentium 4 1.4 Ghz. processor, 512 Mb of RAM
memory).
The first test scenario consisted of acceding to the
Web resources in on line mode. We obtained
satisfactory results (see Figure 2).
In the number two test scenario, the GAP was
executed without being connected to the network.
Additionally we had a pattern of a hoarded Web site
(http://www.cenidet.edu.mx/) and resources. In this
case not existing images in the original site were used,
because it was possible to verify that the hoarded
resources are correctly displayed.
The number three test scenario (see Figure 3),
demonstrates that it is possible to transcoding the
resources in the device as well as showing them in a
local way if they are hoarded and without transcoding.
It is Also possible to execute the GAP in other
platforms like Smartphones (SmartGAP) and a desktop
PC (WinGAP). GAP, WinGAP and SmartGAP are the
same program but with different name, to differentiate
the platforms in which they’re running.
5 Conclusions
With the presented tool is being demonstrated that it
is possible to execute complex services in Pocket PC
devices, so is the case of an intermediary service that it
allows to visualize Web resources when it exists or not
a network connection.
At this time we have verified in an isolated way
most of the functions of the system (it lacks the
methods of decompression of the hoarded site), it

would be necessary the respective integration of
components and testing to the system in its totality.
Figure 2. Case of test 1: Visualization of Web
resources with network connection.
Figure 3. Visualization of Web sites in
disconnection mode with hoarded Web resources
and without transcoding.
Figure 4. Case of test 3: Visualization of Web sites
in connection mode, with hoarded and transcoding
resources.
The expected benefits at the conclusion of this
investigation work are: 1) Visualization of Web sites
without mattering if the devices are connected or not.
2) Reduction of latency in the access to the
information, if the resource is hoarded locally. 3)
Energy Saving by the fact to work in disconnection
mode. 4) Saving money if the user decides not to
connect to a network that receives the service and
generates expenses by the access time. 5) Facility of
administration of Web sites when not having different
versions to each device.
6. Acknowledgments
We want to give thanks to Rocío Vargas Arroyo for
her contribution in correct this paper.
7. References
[1] SG magazine, http://www.softwareguru.com.mx [visited
march 2006]
[2] Purushottam Kuikarni, et al., “Handling Client Mobility
and Intermittent Connectivity in Mobile Web Accesses”,
Department of Computer Science, University of
Massachussets.
[3] Blackberry’s push technology,
http://www.blackberry.com/products/software/integrations/p
ush_email.shtml [visited march 2006].
[4] UPnP Forum, http://www.upnp.org/, [visited march
2006]
[5] David Valenzuela, “Mecanismos para predicción de
acaparamiento de datos en sistemas clientes/servidor
móviles”, masther thesis, cenidet, august 2002.
[6] Gabriel González. “Plataforma middleware reflexiva para
aplicaciones de cómputo móvil en Internet (Movirware)”,
cenidet.
[7] J. Carlos Olivares, et al, “Control de desconexiones en la
visualización de páginas Web en dispositivos móviles
Windows CE”, for appear in XVI CIECE’06, april 5,6 and 7
2006, Cd. Obregón, Sonora, México.
[8] Gabriel González, Azucena Montes, J. Carlos Olivares,
“Comparativa y evaluación de las herramientas de
programación para desarrollar aplicaciones en plataforma
Pocket PC”. VI CICC’05, Colima, Colima, México,
september 2005.

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