Data Communications 2 Module 2

Module 2 Advances in global communication technology

Contents

1. Client-server architecture
2. ISDN and Broad-band ISDN
• ISDN network access
• ISDN in the network backbone
• B-ISDN technologies
3. Switched intemetworks

Module 2, Topic 4 Client-server architecture

Aims

At the end of this topic you should gain

• a deeper knowledge of some technical features of the Internet, especially issues significant for the operation of services on the Internet;
• a knowledge of the emerging integrated global telecommunications network. Specifically knowledge about the Internet, how it is likely to affect the provision of computer systems in organisations;
• a knowledge of some technological alternatives which provide the infra-structure for the global telecommunications network (the Internet);
• a mastery of the skills required to enable effective use of the Internet as an organisation or personal provider of information; as a user of interpersonal communications systems; and as an Internet based researcher.

Syllabus

• Client-server architecture
• Fundamentals
• Types of Servers
• Global Client/Server applications over the Internet
• Creating a simple Web based 3-tier client server application

1. Fundamentals

In the preface to their book (our course text book) The essential client/server survival guide, Orfali et. al. make the case that the client/server revolution in computing has itself been overtaken by another revolution that is the Internet WEB based client/server revolution. As you read the Preface and chapters 1-3, you will come to understand why client/server computing has been taken on by industry as a way of providing computing services.

2. Types of Servers

The section in chapter 2 called "What is Client/Server" has a brief summary of the key concepts. The subsequent sections on File Servers, Database Servers and Transaction Servers are a good introduction to chapters 3, 10 and 16 respectively. You should read these chapters.

3. Global Client/Server applications over the Internet

Orfali describes the second client/server revolution in chapter 28 (see the section called "3-Tier Client/Server Web-style"). See the Figure 28.1 in particular. Read chapters 28, 29 and 30 again.

4. Creating a simple Web based 3-tier client server application

During the last topic (Topic 3, Question 7) you were asked to prepare a simple web page, if that was in a file TESTPAGE.HTM in the directory C:\TESTING; Then that page can be viewed using your browser at URL file:///C|/TESTING/TESTPAGE.HTM

It is a more difficult task to have you the student prepare a client/server based DBMS transaction or inquiry using only a stand-alone PC. Based on the material in chapters 28, 29 and 30 you will be able to prepare an HTML page containing a transaction form such as this testform. The test form in on a UNIX Apache web server. Note the form header in the source of this form.

<FORM METHOD="POST" ACTION="http://www.ct.monash.edu.au/cgi-bin/testform.pl">

The ACTION is a perl script that invokes a UNIX shell script that lists the data values returned to the Apache server when the submit button on the testform is clicked. This "Tier 2" CGI app (see Orfali figure 28.1) is rather minimal, but it does provide a nice debugging and development environment for HTML form writers and CGI programmers. It displays all the variable names and the variable values available to a programmer writing a "real" cgi application to process the form.

If you don't have access to a web server, you can use this particular action (see the FORM line above) even if your HTML form file is on your PC. When you view such a HTML file, and when the submit button is clicked, the form data is sent to the WEB server at http://www.ct.monash.edu.au and the form data is processed by the CGI program (written in Perl) called cgi-bin/testform.pl.

If you have access to the Internet, you can try all the following exercise: Question 8 below. If you don't have Internet access, you can still prepare the form, but your won't be able to submit the data in the form to the server.

Required reading

Orfali, Robert, Harkey, Dan and Edwards, Jeri (1996) The essential client/server survival guide (2nd. ed.), John Wiley & Sons Inc. pp. 675: The Preface and chapters 1, 2, 3, 10, 16, 19, 28, 29 and 30.

Exercises

Module 2, Topic 5 ISDN and Broad-band ISDN

Aims

At the end of this topic you should gain

• a deeper knowledge of some technical features of the Internet, especially the use of ISDN for individual and organisation access the Internet;
• a knowledge of some network management issues relevant to ISDN;
• a knowledge of the technological alternatives which provide the infra-structure for the global telecommunications network (the Internet);
• an ability to locate and assimilate information about the strategic business applications being created using ISDN.

Syllabus

• ISDN and Broad-band ISDN
• ISDN network access
• ISDN in the network backbone
• B-ISDN technologies

1. ISDN Introduction

Integrated Services Digital Network (ISDN) is a term describing the current generation of technologies used by telecommunications carriers (telephone companies) to provide their communications services. There are three types of ISDN services, Basic rate services (a replacement for plain old telephone services POTS providing up to two telephone or data calls on one pair of wires), Primary rate services (a replacement for leased lines providing 1.2 or 2 megabit/s leased lines carrying 23 or 30 telephone or data calls, data aggregation is possible), Asynchronous Transfer Mode (also known as B-ISDN or Broad-band ISDN a new service providing data rates to 150 megabit/s).

In this topic, we will study these three technologies, the topic is organised around the application of the technology. First we will study the use of ISDN for end user Internet access. This is usually done with Basic rate services. Then we will study the use of Primary services in the Internet backbone. Finally we will study ATM or B-ISDN.

2. ISDN Basic rate services

In this section, you will learn about how ISDN is used to allow access to the Internet for an individual or for a small office.

In many localities (but not all) telephone subscribers have the option of choosing a digital telephone service.

Ask the carriers that operate in your area if you can have ISDN at your home? What is the installation fee? What is the annual rental? What are the call charges?

If you install a basic rate service (Telstra calls this a Microlink), you will need a digital telephone. This digitises your voice and sends the data stream down the pair of wires installed in your home. One voice call uses 64,000 bit/s. This is known as a B channel. One BRI (basic rate interface) supports two B channels. Your house will have at least 2 telephone numbers and you can have a variety of equipment attached to the BRI S bus installed in your home. Equipment such as a PC adaptor card or an ISDN "modem".

Look at the specification of an ISDN Modem.

• Motorola Information Systems Group Home Page
• BitSurfer ISDN Modem recommendation - BitSURFR(R) Pro Recognised By PC Magazine As "Best Product" Of '96
• BitSURFR Pro ISDN Terminal Adaptor overview
• BitSURFR Pro Spec Sheet
• BitSURFR Pro Applications

Note that it has an ISDN interface, an RS-232 interface for say a PC, and two analogue telephone ports. This modem has the voice digitisers built in so you can use cheap telephones. Calls arriving over an ISDN line carry information such as call type. Hence the call can cause the telephone to ring (if it is tagged voice) or can connect to the RS-232 port (if it is tagged data). Note that a call from a standard modem is a voice call, the data is carried as audio tones. Calls made from one of the analogue telephones will be carried digitally, and will be tagged as voice calls. Calls made from the RS-232 interface (using the standard AT modem command set) will be tagged data. Some devices provide the ability to aggregate data on two B channels. In this case you would be able to make 128,000 bit/s data connections between two such devices.

Ask your Internet Service Provider if they provide ISDN access. What are the charges? What standards do they use? What equipment does your ISP suggest you use? Can you do channel aggregation?

Read about ISDN access in your text book page 49&50 and in your reader, article number 8 Pettersson, Gunnar (1995) ISDN : from custom to commodity service, in IEEE spectrum, Volume 32, Number 6, June 1995, pp. 26-31.

I find the following web reference to be one of the best sources of information on basic rate ISDN.

Look through Dan Kegel's ISDN Page

In the next section, we will look at the use of high capacity ISDN lines for interconnecting local area networks. Basic rate services too can be used in the network backbone but because the data rate is so low, they are usually used in the home to office or small office environment. There are many router products designed to link sub-networks via basic rate ISDN. Here is an ISDN BRI router product family and the details of a small router made by ASCEND a major Internet hardware provider. Cisco systems, the largest Internet hardware provider also has ISDN BRI routers products and the details are here.. Motorola has ISDN BRI routers as well as ISDN modems. There is an excellent description of the use of BRI routers in the small office environment here too.

3. ISDN Primary rate services

An organisation connecting two office buildings together, may lease ISDN primary rate services from a telecommunications carrier. This allows up to 30 simultaneous B channel connections. The 1-2 megabit/s transfer rates possible over these services make then suitable for linking separate LANs. In this section we will look at the use of ISDN in the network backbone.

There are two standards for these services. One is the USA standard of 24 channels of 64,000 bit/s each. The other is the European and Australian standard of 30 channels. Remember that as you read the following excellent overview of the use of primary rate ISDN. Digital Dial-Up Bandwidth on Demand and Inverse Multiplexing

Those network connections needing even higher data rates will in the near future be connected with Broard-band ISDN.

4. Broad-band ISDN

Read the two tutorials listed below. As you do, focus your attention on the difference between and relationship of ATM and B-ISDN.

• PC Webopaedia - Definition and Links for Broad-band ISDN (B-ISDN)
• Broad-band ISDN Tutorial
• Another Tutorial on ATM and B-ISDN

The following state of the art articles describe experiments and demonstrations of the maturity of ATM and B-ISDN standards. They demonstrate that the key players in international communications can inter-work with these technologies.

• ITU Special Experimentation with B-ISDN
• Pricing ISDN and B-ISDN to take account of the socially vital role of the Internet
• Overview of ISDN and B-ISDN, what is it, how is it used in Europe, how ATM is used in Europe

The ATM and B-ISDN market is maturing. Here is some product information.

• Cisco ATM products

Required reading

Orfali, Robert, Harkey, Dan and Edwards, Jeri (1996) The essential client/server survival guide (2nd. ed.), John Wiley & Sons Inc. pp. 675. Read about Internet access on pages 49 and 50.

Pettersson, Gunnar (1995) ISDN : from custom to commodity service, in IEEE spectrum, Volume 32, Number 6, June 1995, pp. 26-31; reader item 8.

Exercises

Module 2, Topic 6 Switched internetworks

Aims

At the end of this topic you should have gained

• a knowledge of some technical features of the Internet, especially issues significant for the operation of services on the Internet such as switched internetworks;
• a deeper knowledge of another of the technological alternatives which provide the infra-structure for the global telecommunications network (the Internet);

Syllabus

• Switched internetworks
1. Introduction: the factors causing change
2. Switched Internetwork Architectures
3. ATM, a switched technology
4. Frame Relay, another switched technology
5. Implementing Switched Internetworks

1. Introduction: the factors causing change

In this topic we will study one set of new technologies being used in the Internet. We will study switched internetworks. The main aim of network switching is traffic control, especially in situations of high broadcast traffic and in internetworks, networks linking parts of an organisations internal networks.

Here is a table (Source: Cisco Systems) showing network software/type and broadcast traffic. Those with high levels of broadcast should gain most from a move to a switched network architecture.

The relative values high and low in the table provide a general range for these protocols. A particular situation and implementation will determine the magnitude of broadcast traffic. For instance, the level of broadcast traffic generated in an AppleTalk EIGRP environment depends on the setting of the EIGRP hello-timer interval. Another issue relates to the size of the internetwork. In a small-scale internetwork, the amount of broadcast traffic generated by EIGRP nodes might be higher than with a comparable RTMP-based internetwork. However, for large-scale internetworks EIGRP nodes generate substantially less broadcast traffic than RTMP-based nodes.

Bay Networks is an Internet technology provider. They have an excellent tutorial/text on-line on the Internet. We shall use this reference Making the Move to Switched Internetworks to study some of the options for using switching in internetworks.

The Internet and the business applications and services on the Internet are changing. This has led to a requirement for changing the internetwork architecture.

Begin by considering some of the factors causing change in internetworking technology, chapter one of our reference for this topic, Internetwork Architectures Today details business, applications and network changes. Read that chapter then go on.

2. Switched Internetwork Architectures

ATM, Frame Relay and hybrids of these two are the alternatives. As you read chapter five of our reference on Switched Internetwork Architectures, consider this:- in these architectures, routing is used between the Internet and the organisation which uses switching in it's backbone. So in the tutorial by Bay Networks, switched internetworks are seen as technologies for intranets. The Internet itself will in the near term be interfaced with routers.

Read more about the role of routing in switched internetworks here.

• Overview: The Role of Routing in a Switched LAN

3. ATM, a switched technology

Scan through this very long on-line paper by Cisco Systems, it describes in detail, the functioning of ATM switches.

• ATM Internetworking

4. Frame Relay, another switched technology

Scan through this very long on-line paper by Cisco Systems, it describes in detail, the functioning of packet and frame relay switches.

• Designing Packet Service Internetworks

5. Implementing Switched Internetworks

In the last chapter of their tutorial, Bay Networks describe some of the devices for switching available from their product range. Cisco Systems too have switching products. Browse through the following information on specific products for use in switched internetworks.

• CiscoWorks for Switched Internetworks
• Bay Networks Book Making the Move to Switched Internetworks chapter 6 Migration Strategy
• CiscoFusion: An Architecture for Switched Internetworks
• 3Com Corporation Introduces Next Steps in the Evolution of Switched Internetworks
• System 5000 ATM Backbone Solution
• Cisco Introduces New Catalyst 5000 Switch Solutions For Wiring Closets

Required reading

See the online references above.

Exercises

A yellow balls indicates you, the student, must do the indicated task.