Development of Session Management Mechanism
for Cellular Phone with WWW Connection
Satoru Uehara†,‡ , Osamu Mizuno‡ and Tohru Kikuno‡†NTT Data Corporation, Japan‡
Department of Informatics and Mathematical Science,
Graduate School of Engineering Science, Osaka University, Japan{s-uehara, o-mizuno, kikuno}@ics.es.osaka-u.ac.jp
Abstract
The needs for accessibility of cellular phones to Web
based client-server systems are increasing. For this access, eﬃcient management of the context data must be implemented on the cellular phone. However, physical restrictions of the cellular phone make it diﬃcult to manage context data by applying the conventional methods. Additionally, the conventional methods do not show suﬃcient performance to tolerate heavy accesses from cellular phones.
We therefore design a new session management mechanism that enables cellular phone to use Web client-server
system eﬃciently. To do so, we decide to utilize key concepts
in the CDS mechanism, which was previously developed by
us in order to implement session management on the Web.
By utilizing the CDS mechanism, we develop a new session
management mechanism that connects cellular phone andWeb systems. Then, we can actually implement the session
management with high safety and reliability. The result of abenchmark evaluation shows that proposed mechanism has
higher performance than the conventional mechanism.

1 Introduction
Recently, the Web is becoming the main base systemon which client-server systems are developed. Many Web
servers have been provided, and functions and performance
have evolved.
On the other hand, mobile devices such as the cellular
phones that can access the Internet have been developed (theWeb cellular phone), and these mobile devices are becoming
widespread explosively [3]. These mobile devices have Webaccess capability, and Web browser software is on them. TheWeb browsers on mobile devices can show hyper text including graphical images, and can send the user’s input to aWeb server. Because of widespread use of mobile devices

with Web access, Web sites that these devices can use havealso been increasing.
The development of the Web-based client-server systems
has several problems that have not occurred in conventional
client-server systems. One problem concerns data shared
between user-sessions. The HTTP protocol is ‘sessionless’, so the connection between a client and a server is disconnected for each communication. When a Web browser
accesses a Web server and then successively accesses theserver again, the information of the previous access is not
maintained. The data shared among user-sessions must
therefore be maintained by another method. Hereafter, wecall such shared data “context data” and we call the management of several user sessions by keeping the context data
“session management”.
Several widely used methods for session management
have been proposed [2] and developed. However, for Web
browsers on workstations and mobile devices, these methods are not suﬃcient from the viewpoints of security, reliability, and performance.
In order to realize the session management for the Web
cellular phones, we will propose a new mobile context datastoring (Mobile CDS) mechanism. We design the Mobile
CDS mechanism to realize session management with highreliability, high security, and high performance, and it is freeof the physical restrictions of the Web cellular phones.

2Requirements for Web Cellular Phones

We analyze the requirements of session management for
Web cellular phones’ Web browsers. Web cellular phones
are becoming widespread explosively, and an eﬀective session management mechanism is necessary.
The requirements of session management for mobile devices are summarized as follows:
1) Independence from specifications

The specifications of the Web cellular phones are different and depend on the service provider. Web sites
should support such protocol specifications, contentlanguages, and so on [3]. Session management forWeb cellular phones should be applicable to the various specifications.

Client Computer(a)
CDS Server

Set Data

ID: xxx
NAME: yyCDSComponentWeb Browser

2) Unrestricted size of context data
Web sites that can be used by the Web cellular phones
are increasing. If the system has the same functions
as conventional Web systems, the amount of context
data will increase. So it is desirable that there is notrestriction on the size of the context data.

ID: xxx
Name: yy

SessionTransition(b)

Client Computer
CDS Server3) Invisibility
Since the context data may include data that should bekept secret from users, the context data must not be visible to users. Thus the session management mechanism
for Web cellular phones must have invisibility.
4) High reliability
If a trouble occurs at the Web server and context datais lost, the Web program must abort. However, if thecontext data is saved, it is possible to recover the Web
program. So the session management mechanism for
Web cellular phones must have high reliability.
5) High performance
When Web sites are built for consumers, high accessperformance is needed to meet the widespread use ofmobile devices, especially Web cellular phones. So
the session management mechanism for Web cellular
phones must have high performance.

3 Mobile CDS Mechanism
In this section, we propose the new context data storingmechanism for the Web cellular phones (hereafter, the Mobile CDS).

3.1 CDS mechanism
We have already proposed the context storing mechanism
for the workstations (hereafter, the CDS mechanism) [4, 5].
The CDS mechanism realizes document-view architectureon the Web system. And it has advantages of high reliability
and high security.
In order to execute the CDS mechanism, the invocationcommand of the CDS component must be described in a
HTML document. Then the CDS component is loaded into
the Web browser’s process. At the same time, the CDS
server is also invoked in a diﬀerent process (from the Webbrowser’s process) and it starts managing the context data.

ID: xxx
NAME: yy

Get Data
CDSComponent

ID: xxx
Name: yy

Web Browser

Figure 1. Basic behavior of CDS

The following shows an example to maintain a user’s ID
and a user’s name during successive sessions: First, assume
that user inputs ID and name. Then, the CDS component
and the CDS server are invoked at the same time. The CDS
component calls the method to create the keys, such as “ID”
and “NAME”, and to set the value for each key (for example, ID=xxx and Name=yyy as shown in Figure 1(a)). Next,
assume that the current session transits to the next session(as shown in Figure 1(b)). Just after the transition, the context data such as “ID” and “Name” are not maintained on theWeb browser. Then, the CDS component calls the methodof the CDS server to get these context data.

3.2 Structure of Mobile CDS
The Mobile CDS is a software component that uses theCDS and runs on the Web server computer. The Mobile
CDS is used by Web programs that also run on the Webserver computer.
Figure 2 shows the state of the Web server computerwhen the Web server and the Mobile CDS are running inmain memory. The Mobile CDS maintains plural context
data and receives method calls from Web programs. Methods calls are performed using inter-objects communication.
The Mobile CDS is implemented as an executable form(EXE) that runs independently from the Web server process.
Even if the Web server process fails, the context data is notlost. This makes it possible to recover the previous session.

are not maintained in the Web server. The Web program therefore calls an Mobile CDS method to get thecontext data for the session ID “0001”.

ServerServerComputer
Computer
Mobile CDSWeb ServerInter-objectCommunication
Call for methods

WebProgram

SESSION1
KEY1 VALUE1
KEY2 VALUE2
KEY3 VALUE3
SESSION2
KEY1 VALUE1
KEY2 VALUE2
KEY3 VALUE3Results..
.

Figure 2. Structure of Mobile CDS

3.3 Basic behavior of Mobile CDS
Figure 3 shows the basic behavior of the Mobile CDS. In
the figure, a Web cellular phones are using a Web program,and the unique session ID “0001” has been assigned to thesession in advance.

4) Finally, the context data is shown to the user.

3.4 Implementation of Mobile CDS
We implemented the Mobile CDS using Microsoft Visual C++. The Mobile CDS can be used in server-side programs. The following 8 major functions are manipulated
in the server-side programs: 1) PrepareContextDataSetmethod, 2) Remove method, 3) RemoveAll method, 4)
SetData method, 5) GetData method, 6) GetCountmethod, 7) GetName method, 8) SetTimeout method. Context data may be newly created or removed by applyingmethods 1), 2) and 3). The content of the context data canbe set or obtained by the methods 4), 5), 6), and 7). Finally,
the valid term of the context data is set by the method 8).

4Application to the Real System

ServerServerComputer
ComputerWeb
CellularPhone

Web Server

Set Data(a)
SESSION ID
0001

WebPG

Mobile CDS
0001
NAME

UeharaAGE

30Session
Transition

ServerServerComputer
ComputerWeb Server(b)Get Data

Web
PG

Mobile CDS
0001
NAME

UeharaAGE

30

SESSION ID
0001

Figure 3. Basic behavior of Mobile CDS
In the example shown in Figure 3 a user’s name and age
are maintained during successive sessions. Session management is performed as follows:
1) First, the user inputs their name and age in the form,and submits the form.
2) The Web program invokes a method of the Mobile
CDS, and allocates space for context data with the session ID “0001”. The Mobile CDS creates the keys,“NAME” and “AGE”, and stores their values.
3) The user moves to the next page. Just after the transition, the context data such as “NAME” and “AGE”

4.1 Performance comparison
We implemented the Mobile CDS and have applied it toa real system. The target system is based on the Web, andreceives a reservation for use of public facilities from theWeb cellular phones.
We evaluate the performance of Mobile CDS mechanism.
We performed benchmark tests using the Microsoft Web Capacity Analysis Tool (WCAT) that is software for a benchmark test of Web system. This software can simulate theWeb accesses of any number of Web clients by running multiple threads. The response from the Web server is recorded
in real time, so the average response time etc. may be found.
We compared the average response times of the Mobile
CDS method with the database method. (Note that we do notcompare with cookie methods since most of cellular phones
do not have any cookie mechanisms.) First, we implemented
session management using the Mobile CDS and then using adatabase. We used Microsoft SQL Server 7.0 as a database.
Next, we measured the performance of each Web server
quantitatively, while maintaining multiple accesses to theWeb servers. The Web programs accessed 20 context data
items per context data set access, because we considered thisreal use. The accesses consisted of references to the context
data and updates to the data, in the ratio of 8:2. We varied
the number of access at same time, selecting 25, 50, 75, or
100.
Table 1 and Table 2 show the results of the benchmark
tests. Table 1 indicates the average response time (in seconds) for each case, and Table 2 indicates the total numberof connections that were processed in an hour. From these4) High reliability
Table 1. Result of benchmark tests(average response time in seconds)

Mobile CDS
Database

We performed reliability tests. We stopped the Web
server serving during the operation of a Web systemthat was using the Mobile CDS mechanism. However, the Mobile CDS mechanism was unaﬀected by
the problems of the Web server, and continued to maintain the context data. We were able to recover thestate before the Web server was stopped, after the Web
server resumed serving.

Access at same time(times)
2550
75
100
0.64
1.40
2.14
2.68
18.25 36.68 54.85 73.57

Table 2. Result of benchmark tests(total number of connections in an hour)

According to the discussion above, we can say that theMobile CDS satisfies the requirements of session management for the application of mobile device’s Web browsers.

5Mobile CDS
Database

Access at same time(times)
2550
75
100
468,912 427,056 419,988 446,556
16,104
15,744
15,52815,072

results, the system with session management using the Mobile CDS showed dramatically higher performance than thedatabase system. Thus, we consider the Mobile CDS mechanism’s high performance verified.

4.2 Evaluation of other requirements
In this subsection, we evaluate the advantages of the Mobile CDS system and compare them with the other requirements explained in Section 2.
1) Independence from specifications
The Mobile CDS only requires Web cellular phones tosupport URL encoding method. URL encoding is supported by almost all mobile devices so the Mobile CDS
mechanism can be applied to mobile devices of variousspecifications.
2) Unrestricted size of context dataThe Mobile CDS maintains the context data in the main
memory of the server computer. Thus the size of context data doesn’t depend on the physical restrictions ofWeb cellular phones. We can say there is no restriction
on the size of data in the Mobile CDS.
3) Invisibility
The context data is stored in the Mobile CDS whichruns in the main memory of the server computer. We
performed tests and checked that it is quite diﬃcult toaccess the context data. So it can be said that the Mobile CDS mechanism has the advantage of invisibility.

Conclusion

In this paper, we designed a new mechanism for Web cellular phones to maintain the context data in Web systems
and implemented it. The proposed system showed high performance and reliability without restriction of Web cellularphones. We also applied the proposed mechanism to the actual system, and verified the advantage of proposed mechanism by benchmark tests. Future research includes the implementation of the Mobile CDS mechanism on the platform
independent from Microsoft’s one.

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