XML Based Service Provisioning in Converged Voice and Data Networks E-Book

Sertac Cetiner

• Herausgeber: GRIN Verlag
• Sprache: Englisch

Veröffentlichungsjahr: 2008

Beschreibung

Diploma Thesis from the year 2001 in the subject Electrotechnology, grade: 1,7, University of Ulm, language: English, abstract: In today’s world, there are mainly two types of communication networks: circuitswitched networks and packet-switched networks. The current telephone networks are mostly based on the circuit-switched networks, whereas the Internet is mainly based on the packetswitched networks, which are also called IP networks. However, there is a strong tendency to combine both of these networks, which points to the direction that the IP networks are going to replace services provided by current telephone networks. This would eventually mean that IP networks might replace the telephone networks, in the future. Following are some reasons why IP networks seem to replace the circuit-switched networks: · First of all, the IP networks provide cheaper communication. Considering that the Internet access is nearly free, the cost advantage of IP networks gets clearer [25]. · Secondly, IP networks provide the ability of integrating the data and voice applications, and even some other applications, like video-conferencing, integrated voice mail, e-mail, and the like [26]. · Another important reason is that IP networks allow open implementation of end systems. With a reasonable programming knowledge everybody could implement an end system for IP networks. In the classical telephony end users cannot implement any end system, but have to use whatever provided by the service providers. [27]

Leseprobe

Table of Content

1 Introduction

2 Fundamentals.

2.1 Extensible Markup Language (XML)

2.1.1 XML Overview

2.1.2 XML Specifications

2.1.2.1 Document Type Definition (DTD)

2.1.2.2 Well-Formed XML Documents

2.1.2.3 Valid XML documents.

2.1.3 How XML works.

2.1.4 SGML

2.1.5 HTML.

2.1.6 XML vs. HTML

2.2 Session Initiation Protocol (SIP)

2.2.1 SIP Characteristics

2.2.2 SIP Basics.

2.2.3 SIP Addresses.

2.2.4 SIP Messages.

2.2.5 SIP Operation

2.3 Intelligent Networks (IN)

2.3.1 IN Architecture.

2.3.2 Benefits of Intelligent Networks

2.3.3 IN Services

3 Call Processing Language (CPL)

3.1 Language Specifications

3.1.1 Top Level Actions

3.1.2 Switches.

3.1.3 Location Modifiers

3.1.4 Signaling Actions

3.1.5 Non-signaling actions.

3.1.6 Subactions

3.2 Examples.

3.2.1 Example 1: Simple call forwarding.

3.2.2 Example 2: A more complicated example

3.3 Extensibility

4 Architecture

4.1 SIP User

4.2 SIP Server

4.3 Location Database.

4.4 CPL Engine.

4.4.1 Design.

4.4.2 Flow diagram.

4.4.3 Tag Classes.

4.5 CPL Repository.

4.5.1 Flat File vs. Database

4.5.1.1 Flat File.

4.5.1.2 Database

4.5.2 Active vs. Passive Repository

4.6 CPL User Editor.

4.7 The relations of the components.

5 Tools used in the project

5.1 XML Parser.

5.1.1 Document Object Model (DOM)

5.1.2 Simple API for XML (SAX)

5.1.3 DOM vs. SAX

5.2 Common Object Request Broker Architecture (CORBA)

5.2.1 History of Distributed Systems

5.2.2 Alternatives of CORBA

5.2.2.1 Socket Programming

5.2.2.3 OSF Distributed Computing Environment (DCE)

5.2.2.4 Microsoft Distributed Component Object Model (DCOM)

5.2.2.5 Java Remote Method Invocation (RMI)

5.2.3 Advantages of CORBA

5.2.4 The TAO CORBA.

5.2.5 The Naming Service.

5.2.6 The Event Service

5.3 Lightweight Directory Access Protocol (LDAP)

6 Implementation.

6.1 SIP Server

6.2 CPL Engine.

6.2.1 General overview

6.2.2 CORBA Interface

6.2.3 Classes

6.3 CPL Repository.

6.4 CPL User Editor.

6.5 Evaluation Results

6.6 Performance Measurements.

6.7 Suggestions for further studies

7 Conclusions

Appendix A: CPL Tags.

Appendix B: CPL DTD.

Appendix C: The IDL definition of the CORBA interface

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Preface

This master thesis has been written at the University of Ulm, Germany. The thesis consisted of a project work at Siemens AG in Munich, Germany. Three groups were involved in this project. Each group had different locations, and different tasks to work on. The first group was responsible for the design and the development of the SIP Server. The complete SIP server was developed and integrated into the CPL environment by that group. The second group was responsible for the design and the development of the CPL User Editor, whereas the third group was responsible for the design and the development of the CPL Engine and the coordination of the project.

Two persons formed the third group: The author and Giovanni Benini (Siemens AG, Munich), the supervisor of the thesis. Mr. Benini coordinated the project, while the author was responsible for the design and the development of the CPL Engine. I would like to express my respect to the University of Ulm, especially to the Communications Technology Program for providing me the opportunity to do my MSc. at the Univeristy of Ulm.

I would like to thank Giovanni Benini for his invaluable support during all the project work. His friendly personality helped a lot completing the project successfully. Thanks to Prof. Bossert for his interest and guidance. And, thanks to Hermann Granzer, Achim Fahrner, Zonya Dengi and Nashwa Abdel-Baki for reading and commenting on the thesis. Finally, thanks a lot to my family for their unconditional support.

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List of Abbreviations

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1 Introduction

In today’s world, there are mainly two types of communication networks: circuitswitched networks and packet-switched networks. The current telephone networks are mostly based on the circuit-switched networks, whereas the Internet is mainly based on the packetswitched networks, which are also called IP networks. However, there is a strong tendency to combine both of these networks, which points to the direction that the IP networks are going to replace services provided by current telephone networks. This would eventually mean that IP networks might replace the telephone networks, in the future. Following are some reasons why IP networks seem to replace the circuit-switched networks:

Beside these attractive advantages, IP networks face an important problem compared to the circuit-switched networks [25]. The circuit-switched networks provide a guaranteed level of voice quality, while IP networks cannot guarantee certain level of voice quality, since the data transfer is based on random access in the IP networks. However, with ongoing research in this field, the voice quality requirements are going to be met in coming years. Internet Telephony is defined as the provision of telephone-like services over the Internet. Some consider it as the next stage of the telephone network and the first incarnation of the long-held goal of an “integrated services” network [20]. The integrated services here means, for example, the integration of data delivery, voice delivery, video conferencing, and other possible services provided by the Internet and the telephone networks. Although the Internet Telephony offers very low call costs, the current pricing schemes of the classical telephony are getting lower every day, and there may not be any significant difference in the future [25]. Because of that, the additional services offered by the Internet Telephony achieve a bigger importance to be able to beat the classical telephony. The more advanced features Internet Telephony offers, the more customers switch from the traditional telephone networks to the Internet Telephony. The purpose of this thesis was to design, implement, and evaluate the creation of additional services using Extensible Markup Language (XML [3]) as the data definition format. The Call Processing Language (CPL [6]), developed by the Internet Engineering Task Force (IETF), is the XML based service creation language for the Internet Telephony. As a result, the CPL is going to be the main focus of this thesis to create the additional (intelligent) services for the Internet Telephony.

Without using any additional services, simple Internet Telephony provides the ability to connect two or more call requests through the IP networks. However, the CPL offers

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additional services, such asforward on busy, redirection, decisions based on the origin of call, generating log of calls, e-mail notification, rejection, call waiting, multiple line signaling, and so on.These services are expected to make the Internet Telephony more attractive and functional for the end users.

The Call Processing Language (CPL) is evaluated in this thesis for creating the additional services, as mentioned above. Session Initiation Protocol (SIP) [4], which is again developed by the Internet Engineering Task Force (IETF), is used as the signaling protocol for the Internet Telephony. However, basically, these services could also be applied to the H.323 [21] protocol, which is developed by the International Telecommunications Union. Organization of the thesis is as following: Chapter 2 gives the fundamentals underlying the project work. Chapter 3 explains the details of the Call Processing Language (CPL). Chapter 4 presents the architecture of the project, and details each component in the architecture. Chapter 5 gives some information about the tools used to implement the project. Chapter 6 goes into the details of the implementation. Results are discussed in Chapter 0, while chapter 7 discusses the conclusions of the project. Some suggestions for further studies can be found in chapter 0, as well.

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2 Fundamentals

The project is based on two main standards: Extensible Markup Language (XML) and Session Initiation Protocol (SIP). Another standard, the Intelligent Networks (IN), is the current implementation of the intelligent services for traditional telephone networks, e.g. the 0800 free phone call services.

Considering the goals of this project, it is important to understand what these standards define, and how they work in the telephone networks. In the following sub-chapters these three standards are going to be explained briefly.

The services and the architecture implemented in this project are very similar to the services and architecture of the IN. However, Internet Telephony allows new services to be provided comparing to the traditional telephone networks allow.

2.1 Extensible Markup Language (XML)

The Extensible Markup Language (XML) has been developed by World Wide Web Consortium (W3C) [34]. The main purpose of the XML is to provide a standard markup language for the Internet world (World Wide Web). It was released as a recommendation of the W3C in February 1998. Since then, many supporting standards have been released by W3C and some other bodies. For example, the Namespaces recommendation was released in January 1999, and the XML Schema recommendation was released just a few days ago (2 May 2001). So, XML is getting more stable every day.

In the following subchapters first an XML overview will be given, and then the XML specifications will be discussed in detail. After that a brief discussion of how XML works is given in 2.1.3. SGML as the super set of the XML, and HTML as the subset of XML are explained in the coming subchapters. At the end, a comparison of HTML and XML takes place to clarify their differences.

2.1.1 XML Overview

The Extensible Markup Language is a subset of Standard Generalized Markup Language (SGML, see chapter 2.1.4). XML is the universal format for structured documents and data on the Web [3]. The design goals of the XML are:

a. XML shall be straightforwardly usable over the Internet. b. XML shall support a wide variety of applications. c. XML shall be compatible with SGML.

d. It shall be easy to write programs, which process XML documents. e. The number of optional features in XML is to be kept to the absolute minimum, ideally zero.

f. XML documents should be human-legible and reasonably clear. The XML design should be prepared quickly. g. The design of XML shall be formal and concise. h. XML documents shall be easy to create. i. Terseness in XML markup is of minimal importance.

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As can be seen, the first and the most important goal is that XML should be usable over the Internet. Combining this with its simple use and wide range of available applications XML is a candidate to be the standard document language in the Internet. Human readability makes maintenance of XML documents easy. An XML expert may fix errors in an XML document simply by reading it. XML also provides compatibility among the programs using a document, since it is in the text format. For example an EMACS text editor cannot work with an MS Word document, however any text editor can work with an XML document.

Another important aspect of XML comes from its name: extensibility. Any XML document can be in the future extended or converted to another document. For example, a CPL (see chapter 3) document can be converted to another type of document some time in the future, if it is necessary, or there can be some additions to the current CPL. Additions could be some new tags, or new properties, or new text fields.