=Paper=
{{Paper
|id=Vol-242/paper-6
|storemode=property
|title=Mobile Host: A feasibility analysis of mobile Web Service provisioning
|pdfUrl=https://ceur-ws.org/Vol-242/paper6.pdf
|volume=Vol-242
|authors=Satish Srirama,Matthias Jarke,Wolfgang Prinz
|dblpUrl=https://dblp.org/rec/conf/caise/SriramaJP06
}}
==Mobile Host: A feasibility analysis of mobile Web Service provisioning==
https://ceur-ws.org/Vol-242/paper6.pdf
942 Ubiquitous Mobile Information and Collaboration Systems
Mobile Host: A feasibility analysis of mobile
Web Service provisioning
Satish Srirama1 , Matthias Jarke1,2 , and Wolfgang Prinz1,2
1
RWTH Aachen, Informatik V
Ahornstr.55, 52056 Aachen, Germany
2
Fraunhofer FIT
Schloss Birlinghoven, 53754 Sankt Augustin, Germany
{srirama, jarke}@i5.informatik.rwth-aachen.de
wolfgang.prinz@fit.fraunhofer.de
Abstract. This paper, discusses the feasibility of mobile Web Service
provisioning from Smart Phones, confluencing two major recent trends
in distributed information systems engineering: the evolution from static
content via personalized adaptive information provisioning to Web Ser-
vices, and the emergence of mobile terminals with sufficient speed to
serve as parts of information systems. The research of mobile Web Ser-
vices has been mainly concentrated on Web Service client systems. Mo-
bile Web Service provisioning was ignored, since a realization seemed
beyond the resource capabilities of present mobile terminals. Comple-
menting this work, here we discuss one such prototype of a mobile Web
Service provider, developed and evaluated in cooperation with a major
mobile phone vendor. We also present a detailed performance analysis of
this Mobile Host, proving its feasibility.
1 Introduction
Web Services are software components that can be accessed over the Internet
using established web mechanisms, XML-based open standards and transport
protocols such as SOAP [1] and HTTP [2]. Public interfaces of Web Services
are described using Web Service Description Language (WSDL) [3]. Examples
of Web Services range from simple requests, such as stock quotes or user authen-
tication, to more complex tasks, such as comparing and purchasing items over
the Internet.
With the introduction of Third and Interim Generation mobile communica-
tion technologies in the cellular domain like UMTS, GPRS/EDGE [4], the speed
of wireless data transmission has increased significantly. Also processing power
and device capabilities of mobile phones have increased drastically, thereby en-
abling better applications and usage of mobile devices in different application
domains.
Combining these developments it is a logical next step to turn mobile de-
vices into wireless Web Service requestors (clients) and even providers (Mobile
Hosts). This enables communication via open XML Web Service interfaces and
UMICS'06 943
standardized protocols also on the radio link, where today still proprietary and
application- and terminal-specific interfaces are required. Mobile Web Services
lead to manifold opportunities to mobile operators, wireless equipment vendors,
third-party application developers, and end users. It is easy to imagine that in
the future mobile applications based on Web Services will generate a large per-
centage of all Web Service requests, and the first such solutions are currently
appearing on the market. [5–7]
Performance of mobile Web Service clients was extensively studied, proving
their feasibility also with commercial applications [8]; even though some ques-
tions were raised having such a verbose SOAP communication over the slow
wireless networks [9]. Our study mainly focuses at extending this study also to
mobile Web Service providers, proving their feasibility. In this paper, we explore
this idea of Mobile Hosts and their performance, based on our experiences from
a cooperation project with a major mobile & telecom service provider in which
the prototype of such a Mobile Host was developed and tested on a smart mobile
phone. The paper is organized as follows:
Section 2, introduces the concept and applications of mobile Web Service
provisioning. Section 3 briefly describes the theoretical performance model for
mobile Web Service invocation. Section 4 discusses the means of accessing the
Mobile Host in mobile operator network from Internet and section 5 describes
the detailed performance analysis conducted and its evaluation results. Finally
section 6 discusses conclusions and further research directions.
2 Mobile Web Service Provisioning
The basic architecture for Web Services is built upon its three components:
Service Requestor (Client), Service Provider and Service Registry. The service
provider publishes its Web Services with the service registry. The service re-
questor later searches (”Find”) the UDDI registry [10] for the services, and the
UDDI compatible service registry refers the respective WSDL for the service.
The service requestor accesses the described Web Service, using SOAP. Similar
to this, the basic architecture of the mobile terminal as Web Service provider
can be established with the Web Service provider (”Mobile Host”) being imple-
mented on the smart phone.
The Mobile Host has been developed as a Web Service handler built on top of
a normal Web server. The Web Service requests sent by HTTP tunneling are di-
verted and handled by the Web Service handler. The Mobile Host was developed
in PersonalJava [11] on a SonyEricsson P800 Smart Phone. The footprint of our
fully functional prototype is only 130 KB. Open source kSOAP [12] was used for
creating and handling the SOAP messages. Most recently kSOAP is redesigned
to kSOAP 2 [13] and the Mobile Host was upgraded to this new version, without
much effort. But most of the performance analysis results discussed in this paper
are with respect to kSOAP. [6]
Even though the Web Service provider is implemented on the Smart Phone,
the standard WSDL can be used to describe the services, and the standard
944 Ubiquitous Mobile Information and Collaboration Systems
UDDI registry can be used for publishing and un-publishing the services. This
of course presents the challenge to design the mobile terminal with the same
general architecture as on any standard desktop system, even under the low-
resource considerations of the Smart Phone. An alternative for the mobile Web
Service discovery is being studied, where we are trying to realize Mobile Host in
a Peer to Peer (P2P) network, there by leveraging the advertising and searching
of WSDL to the P2P network. A detailed explanation of this procedure is beyond
the scope of this paper.
Mobile Host opens up a new set of applications that has not been explored
very much up to now, since a realization seemed beyond the resource capabili-
ties of present mobile terminals. It can be used in domains like location based
services, mobile community support and pervasive gaming etc. From a commer-
cial viewpoint, it also renders possibility for small mobile operators to set up
their own mobile Web Service business without resorting to stationary office
structures. [14]
Of course, this additional flexibility generates a large number of interesting
research questions which need further exploration, the immediate topics of inter-
est being checking the feasibility of Mobile Host in handling reasonable services.
The following sections will explain the considered performance analysis model
and the results.
3 Performance Model
The developed Mobile Host was extensively tested for performance issues like the
memory load, server-processing load etc. For this evaluation, a simple request-
response scenario was started, in which a standalone Axis [15] client (The client
can be any standard Web Service client) program was developed, which accesses
the Mobile Host as a Web Service requester. The client calls for different services
deployed on the Mobile Host and the performance of the Mobile Host is observed
while it is processing the Web Service request. The considered services and the
access methods are discussed in the latter sections. Figure 1 shows different
operations performed and time components that constitute one complete Web
Service invocation cycle.
The client initiates the call for the Web Service and the Mobile Host pro-
cesses the request, populates the response, and sends response back to the client.
The total time taken for this mobile Web Service invocation (Tmwsp ) constitutes,
the time taken by client for constructing valid SOAP message (Tcc ), the time
taken to transmit the SOAP request to Mobile Host (Treqt ), the time taken for
de-serializing the XML based SOAP message to SOAPEnvelope object (Tsd ),
the time taken by the Mobile Host to execute the respective business logic and
to populate the response (Tprocess ), the time taken for serializing the SOAPEn-
velope object back to XML data streams (Tss ), the time taken to transmit the
SOAP response back to the client (Trest ) and lastly the time taken by the client
to process the response (Tcp ). The invocation process is shown in figure 1 and the
total time taken for the mobile Web Service invocation is given in the following
UMICS'06 945
Fig. 1. Mobile Web Service invocation: operations and time stamps
equation.
Tmwsp = Tcc + Treqt + Tsd + Tprocess + Tss + Trest + Tcp (1)
The request and response messages are transferred to the Mobile Host in
the form of TCP packets. So some delay could be caused by packet loss, TCP
congestion control etc. The delay is shown in the figure as the slanting lines
for request and response transmissions. Ttcp represents this delay caused by the
transmission protocol.
Ttcp = δreqt + δrest (2)
where δreqt , δrest are the respective propagation delays caused while trans-
mitting the SOAP request and response messages. In the proposed performance
model the transmission times (Treqt , Trest ) also include these tcp delays and an
estimation of the tcp delays is not specifically observed.
4 Mobile Terminal Access
Once a Web Service is developed and deployed with the Mobile Host, the mobile
terminal, that is registered and connected within the mobile operator network,
requires some means of identification and addressing, that allows the Web Service
to be accessible also from Internet.
946 Ubiquitous Mobile Information and Collaboration Systems
Generally, computers and devices in a TCP/IP network are identified using
an IP address. The IP address, that is required for the data transfer to and
from Smart Phones (as for any other IP communication client as Web servers,
Intranet workstations, etc.), is assigned during the communication configuration
phase. Typically, the IP address assigned to mobile devices using GPRS is only
temporarily available, and is known only within the mobile operators network,
which makes it difficult to use the IP address in the client applications.
The study has identified different means of resolving the IP address in HSCSD
(High-Speed Circuit Switched Data) dial-up connection, GPRS (General Packet
Radio Service) environments and thereby making the data transmission with a
mobile terminal, possible. Here we discuss two of these identified methods.
4.1 HSCSD
Figure 2 illustrates the architecture used to connect the Mobile Host to the
prototyping network using a HSCSD dial-up connection. In this architecture
a HSCSD connection is established between the mobile terminal and the pro-
totyping network, which is connected to the Internet. The connection uses a
Public Land Mobile Network (PLMN) and the Public Switch Telephone Net-
work (PSTN / ISDN) for making the data call to the server. The connection is
setup by using PPP (Point-to-Point Protocol) over a circuit-switched data call
to a modem that is connected to one of the servers in the network. On top of
this PPP link a TCP/IP end-to-end connection between the mobile terminal
and the dial-in server is established. Hence, as long as the data call persists,
the mobile terminal can be addressed using the IP address assigned to it by the
dial-in server. Thus the Web Service deployed on the mobile terminal can be
accessed from any client within the network environment.
Fig. 2. Architecture for an end-to-end TCP/IP connection between the mobile terminal
and the prototyping network using HSCSD connection
Using an appropriate NAT configuration, the mobile Web Service can be
accessed by any service requestor from the Internet. Using the NAT, the network
provides a DNS name for the Mobile Host. The only requirement towards the
UMICS'06 947
PPP daemon is that the mobile terminal should always receive the same IP
address when it connects to the dial-in server.
The main drawback with the HSCSD solution is the circuit switched connec-
tion, which would have to persist as long as the Mobile Host should be available
for the access of its Web Services. The billing of circuit switched data connections
is based on the time the connection persists, not on the amount of data trans-
mitted across the network. This makes this scenario unfeasible for commercial
purposes. Volume based charging is a major advantage enabled by GPRS.
4.2 GPRS
Once the GPRS connection is established the mobile can be identified by the
temporary IP provided by the mobile operator network. It is also feasible to
have a public IP for the mobile terminal, a feature provided by very few opera-
tors today. The operational setup for accessing the mobile terminal in a GPRS
network is given in figure 3. The mobile TCP/IP connection between the Web
Service client and the Mobile Host is deployed on top of a GPRS link into the
mobile operator network. From there the traffic is routed through the Internet
to/from the Web Service client.
Fig. 3. The operational setup of Mobile Host in a live GPRS environment
The problem of addressing each mobile node with IP is not a big issue and
it could be solved with Mobile IP version 6(Mobile IPv6). [16]
5 Performance Evaluation
To prove the feasibility of the Mobile Host, different services were developed
and deployed with the Mobile Host on P800 Smart Phone. The following sub-
sections first describe these services and then explain the test setup, experiments
conducted and obtained results.
948 Ubiquitous Mobile Information and Collaboration Systems
5.1 Test Case Services
Mobile Photo Album Service Todays high-end mobile terminals become
more and more advanced, and are generally being equipped with an integrated
digital camera. The photographs taken with these mobile phones can later be
uploaded or transferred to PCs through cables or by using wireless methods like
Infrared or Bluetooth. Using currently available technologies, if a user wants to
publish the photographs he had taken with the mobile terminal to the public or
friends, he has to upload the photos to a Web server, from which they can be
accessed. The user can also send the images through MMS or some other means
of messaging to the clients. Here the mobile owner bears the payment for the
communication between his Smart Phone and the Web server or the receivers
device. With a mobile Web Service provider, implemented and deployed on the
Smart Phone, interested people can access the Mobile Host using a standard
Web Service client or a Web client, and can browse through the pictures they
are interested in. Here the responsibility for payment shifts to the actual clients,
browsing the pictures provided by the Mobile Host. The service is comparable to
any other online image album service, but implemented on the mobile terminal.
Also for the performance evaluation, the service was quite useful. The re-
sponse of the service is comparitively large (approximately 40KB) and this gives
a large scope for observing the effects of different parameters like transmission
delays, the encoding performed on the response messages, the actual service de-
lay, and etc. on the performance of Mobile Host. For the test cases, 15 different
images were selected with memory sizes ranging from 3KB to 100KB.
Location (GPS) Data Provisioning Service This dedicated Web Service
provides the exact location information of the mobile terminal, such as GPS
(Global Positioning System) data [17]. The service uses a Socket GPS receiver
for getting the GPS co-ordinates. The external device is connected to the Smart
Phone via Bluetooth. The service returns just a small string (approximately 2
KB) containing the GPS data as the response, which gives the scope for observ-
ing the behavior of the Mobile Host under concurrent requests from multiple
clients, there by observing the robustness of the Mobile Host.
Many application were developed and demonstrated using these two services,
for example in a distress call, the mobile terminal could provide a geographi-
cal description of its location along with location details. Another interesting
application scenario involves the co-ordination between journalists and their re-
spective organizations. The scenario is illustrated in figure 4. Journalists can be
at different locations across the globe, covering different events like the sport
events, conferences, etc. An editor can always keep track of the location of ”his”
journalists and the content they have gathered. He can browse through the pic-
tures taken by the journalist at any instance. Standard client applications can
be developed for the editor, which synchronize the information stored by editor
and data at the Mobile Host. The key difference to the more traditional solu-
tions where journalists upload their contents to a server held by the Editor is
UMICS'06 949
that parallel access to the Mobile Host by both the journalist and the editor is
possible; even other journalists in the team can look at the mobile information
thus better synchronizing their activities, e.g. in the coverage of some major
distributed event. Thus, the journalists can concentrate more on their job of
collecting, as they dont have to upload the data, every time they get something
interesting. The data can later be synchronized with a server for archives, when
the journalists are free and off the event site.
Fig. 4. The Mobile Host in collaborative journalism scenario
Applications using location data provisioning service are generally useful in
the people-to-people-to-geographical-places(P3 Systems) in the social networks
domain [18]. These location-aware community sytems throw many privacy con-
cerns like possibility of ”stalking” or simple violations of users’ desire for privacy.
Our current research in this domain also includes these security concerns and
they can be eliminated with user intervened authorization, where the mobile
user, providing the service can validate the authenticity of the location data re-
quester. Also the process can be automated with a rule based intermediary com-
ponent called ”Mobile Web Services Mediation Framework”, which maintains
the individual user profiles and personalization settings. A detailed discussion
of these security issues is beyond the scope of this paper. Apart from this, some
research results show that people are less concerned about their location being
tracked, as long as they find the service useful [19].
Apart from the Mobile photo album service and Location data provisioning
service, some more basic services like echo, ls services and etc. were also used in
the performance analysis.
950 Ubiquitous Mobile Information and Collaboration Systems
5.2 Test setup and results
For the evaluation, a standalone Axis Web Service client was used to access
the services deployed on the Mobile Host. Both the HSCSD and GPRS mobile
terminal access methods discussed in section 4 were used for identifying the Mo-
bile Host. First the mobile picture service was used for calculating the SOAP
processing delay of the server. The results showed a significant difference (ap-
proximately 20%) between the time taken for Web Service access and the normal
HTTP access. Figure 5 shows these times for the HSCSD connection.
Fig. 5. Difference between round-trip durations for the Web Service and HTTP re-
quests
The SOAP overhead and the Base64 encoding performed on the images before
serialization of the response, has caused the size of the response to increase by
more than 50%. The actual SOAP overhead caused to the size of the response is
observed to be only 578 bytes. This was observed using the Echo service with a
single character request. The increase in the size has increased the transmission
delay and there by increasing the delay in response.
In order to identify the actual times taken for different activities on the Mo-
bile Host like Tsd , Tss , Trest etc., the location based service was requested by the
client and the time stamps were taken at the Mobile Host while it was processing
the request. These time stamps were later processed to get the operational time
delays. Figure 6 shows the time delays of different activities, for the Location
data provisioning service using the GPRS connection.
The observation of these results suggest that the total WS processing time
as a combination of de-serialization, SOAP processing and serialization, at the
UMICS'06 951
Fig. 6. Time stamps for the GPS data provisioning service
Mobile Host, is only a small fraction of the total request-response time (<10%)
and rest all being mostly transmission delay. The test also conducted with the
mobile picture service revealed that WS processing time is still negligible and
the total response time linearly increased with the size of the image.
In terms of performance of the Mobile Host, the key question was whether a
reasonable number of clients could be supported with an overhead that would not
prevent the main mobile user from using his or her Smart Phone in the normal
fashion (either to supply the services or just for usual local phone functions).
Concurrent requests were generated for the services deployed on the Mobile Host,
simulating multiple clients. The results of this regression analysis for checking
the scalability of the Mobile Host are very encouraging and the Mobile Host was
successful in handling 8 concurrent accesses for reasonable service like location
data provisioning service. But it was observed that the concurrent access can
affect the Mobile Hosts ability to access internal and external resources. The
comparison of the time stamps for the GPS data provisioning in unique and
concurrent access revealed that the only drastic difference was at the Tprocess .
The study of the memory footprints revealed that memory usage was not a
problem with Mobile Host, as most of the time, the amount of free memory was at
least 20% of the total memory allocated for the JVM (max value approximately
330 KB) and the ”Out of Memory error” was never encountered during the
execution of the tests.
Apart from these results, the comparison of results for HSCSD and GPRS
connections suggested that the increase in transmission rates can increase the
processing capability of the Mobile Host. Approximately 200 data traces were
observed as the experiments were repeated several times in order to have statis-
tically valid results.
952 Ubiquitous Mobile Information and Collaboration Systems
6 Conclusion and future work
In this paper, we analyzed the feasibility of mobile Web Service provider for
the Smart Phones. First we introduced the concept and the developed Mo-
bile Host. Once the Mobile Host prototype was developed, it was extensively
tested considering performance aspects in different real-time working environ-
ments/conditions. The evaluation clearly showed that service delivery as well as
service administration can be done with reasonable ergonomic quality by normal
mobile phone users. As the most important result, it turns out that the total
WS processing time at the Mobile Host is only a small fraction of the total
request-response time (<10%) and rest all being transmission delay.
Next steps on the technical side include a broader and more detailed, component-
oriented performance analyses and means of improving the performance, an ap-
proach for discovering the services deployed on the Mobile Host; especially in a
peer-to-peer network, and perhaps most importantly a detailed study of the
QoS implications of this approach. Equally important is the study of specific ap-
plication domains and usability analysis; our research mainly focuses on mobile
community support and pervasive gaming.
Acknowledgment
The work is supported by German Research Foundation (DFG) as part of
the Graduate School ”Software for Mobile Communication Systems” at RWTH
Aachen University. The authors would also like to thank M. Gerdes and R.
Levenshteyn of Ericsson Research for their help and support.
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