A Network Simulation Experiment of WAN Based on OPNET

A Network Simulation Experiment of WAN Based on OPNET

Yao Lin,

Zhang Bo ,

Liu Puyu

Modern Education Technology Center, Liaoning Medical University, Jinzhou, Liaoning,

China,[email protected]

*2

College of Engineering, Bohai University, Jinzhou, Liaoning, China , [email protected]

Department of Computer Science,

Eastern Michigan University, US,

[email protected]

Abstract

With the development of the computer technology, simulation plays an important role in analyzing and designing complex systems, such as network. In this paper, we use the OPNET into computer network experimental and design WAN simulation experiment. Through the process of simulation modeling study of WAN, we can intuitively understand WAN performance, and it also showed that the OPNET in the computer network experimental teaching has a good application prospect.

Keywords

1. Introduction

Along with the development of the social informatization, computer network technology used more widely[1]. With the continues expanding of network application field, network technical personnel who not only master network foundation but also have practical ability are needed in social industries. The computer network course is available in many universities, through higher education university can cultivate professional talents of network to meet the requirements of social development. The computer network is a very practical and theoretical course, but in actual teaching, theoretical teaching is greater proportion; In addition, the experimental teaching environment need high input and platform build difficulty, so it is difficult to be beneficial supplement of theoretical teaching[2-3] .Reform network teaching is one of the most urgently problem should be solved in order to improve the weak experiment teaching. Therefore, OPNET can be used in computer network experiment teaching, through the software simulation to improve the students' practical ability. Students not only understand course better, but also master a research tool, at the same time by using this the problem of high input about the experimental platform can be solved. WAN covers a broad area; the related experiments cannot be doing in laboratories, so use OPNET network simulation software to design the experiment of WAN[4].

2. The summary and technical features of OPNET

OPNET company was founded by two doctors of Massachusetts in 1986,and found that the network simulation are very valuable, so in 1987 established commercial OPNET. The OPNET published the first commercial network simulation software since 1987, after that the OPNET developed quickly and steadily. As a high-tech network planning, simulation and analysis tools, OPNET has been widely recognized and adoption in communication, national defense and computer network domain. Tens of thousands of organization use OPNET software to optimize the performance of the networks ， maximize communication network and application of usability [5]. Its product line include Modeler, IT Guru, SP Guru, OPNET Development Kit and WDM Guru, etc.

OPNET has the outstanding characteristic of below, which can meet the need of large and complex network simulation[6-7]:

(1)Provide three layer modeling mechanism. The Bottom is Process model, use the state machine to describe the protocol; followed is Node model, consist of the corresponding protocol model, which reflect the characteristics of equipment; the top is network model. Three layer models corresponding to the actual network, the equipment and the protocol hierarchy, comprehensively reflect the network related characteristics.

(2)Provide a relatively complete library of the basic model, including: router, switch, server, client, ATM equipment, DSL equipment, ISDN equipment and so on.

(3)Using the discrete event to drive simulation mechanism, its efficiency is greatly improved than using the time to drive.

(4) The hybrid modeling mechanism combine the analysis method based on package with the mathematical modeling method based on statistic, by using this OPNET can get more detailed result of simulation and improve the simulated efficiency.

(5) OPNET has rich statistics collection and analysis capabilities. It can directly collect performance statistical parameters of each commonly used network levels, and it is convenient to prepare and output simulation report.

(6) Provide the interface of network management system and flow monitoring system, it can set up the simulation model conveniently with the existing topology and the flow of data, at the same time it can verify the simulation results.

OPNET has some shortcomings such as limited model library and inefficient when the simulation network scale and flow is very big, etc. But the network simulation can construct virtual environment in computer to reflect the reality of the network environment, through the mathematical method to simulate the reality of the network behavior. OPNET effectively improve the reliability and accuracy of network planning and design, it obviously reduce the network investment risk and unnecessary investment waste.

3. WAN Overview

3.1. WAN Definition and Classification

The wide area network (WAN) also called remote network, a kind of network used to interconnect LAN or MAN in different regions, it provide computer communication among different regions, cities and countries[8]. It’s distribution range up to hundreds of kilometers or even farther, it can cover an area, a country even around the world.

WAN can be divided into public transport network, dedicated transmission network and wireless transmission network.

(1)Public Transport Network

Generally the telecom sector of government establish, manage and control the public transport network, transmit and exchange devices within network can be provided (or rented) to any department or unit to use. Public transport network can be divided into two categories[9]:

①Circuit-switched networks, including the Public Switched Telephone Network (PSTN) and the Integrated Services Digital Network (ISDN).

②Packet-switched networks, including x.25 packet switching network, frame relay and switched multi-megabit data service (SMDS).

(2) Dedicated Transmission Network

An organization or group build, use, control and maintenance of a private communications network. Dedicated transmission network is digital data network (DDN).

(3) Wireless Transmission Network

The main is mobile wireless networks[10]. The typical wireless transmission network use GSM and GPRS technologies.

3.2. The Main Features of WAN

(1)Mainly provides the service for communication, and support the user to use the computer for long-distance exchange of information;

(2)Covering a wide range of communication distance, more factors need to be considered, such as the cost of the media, the cable redundancy, the utilization of media bandwidth and error handling, etc.;

(3) The telecom sector or company is responsible for building, management and maintenance, and provide paid services, traffic statistics and billing to all users of the whole society.

4.1. Experiment Purpose and overview

This experiment Constructs a LAN which is designed for a company, through a T1 line to research the company’s actual performance. Also plans to add redundant links to the design of the network between LAN and ISP. This company’s LAN includes 20 users of PCs, three shared printers and a local file and mail server. These users run different online applications including E-mail, web browser, video fluid and FTP, at the same time still run local service program, such as E-mail, printer and database access in the intranet. The purpose of the design is to research the response time of the two mission-critical, FTP download and Web Page download, and to analyze the link between LAN and ISP. Through the initial assessment, the LAN is divided into two smaller parts, and adds a T1 link between the LAN and ISP increased the available capacity up to twice, two T1 links can equal to use after load balancing.

Figure 1. Network Structure Design of the Company

4.2.

Experimental Design and Procedures

Step 1: Start the IT Guru, open Lab1.

The company shares the local E-mail and File server.

As an experiment, add an server from the Object Palette, and configure the sharing application about E-mail and file. Illustrate how many objects configured to change network model.

Step 2: Open Object Palette to add a local server.

Step 3: Configure the local server to support E-mail and file sharing. Configure a new server to support E-mail and file sharing applications.

Step 4: Configure and run the simulation. Through the above steps, the local E-mail and file sharing servers have been configured successfully; next assess the performance of network in a busy hour within a single day.

Step 5: Observe the results. Observe variety of statistics such as response time of Web Application (HTTP page), FTP download response time and WAN link utilization.

Experimental results and conclusions: Download the link utilization averaged 92%.

Web Application (HTTP page) response time close to 1.3 seconds. FTP downloads response time close to 2.5 seconds.

Such high download link utilization can’t give available bandwidth to potential user.

Figure 2. Download link utilizationcurves of simulation

Design another experiment, add a new T1 link to expand capacity up to twice, load balancing to ensure that two links traffic distribute balance, analyze the advantages of adding new link.

Step 6: Switch to next scheme.

Figure 4. Add another T1 link and load-balancing

The company's network is divided into two small parts each connected to a switch. The LAN connected to the Internet through two T1 lines. The EIGRP used to load balance between them.

Step 7: Configure and run the simulation. Re-run the previous simulation, compare two links and observe whether the load balance. Set the simulation duration and run the simulation as mentioned steps

Step 8: Compare the results. Compare the response time of link utilization, the Web Application and FTP download. Expect the new link to ISP can reduce the application response time and these two links should be calculated the link utilization separately.

Figure 5. The contrast of tow simulation results

Experimental results and conclusions:

As expected, the utilization of the lower link decreased from 92% to 55%, the new link utilization close to 40.8%. Therefore, the load balancing worked.

The response time of FTP download reduce from 1.25 seconds to 0.45 seconds. This is very important improvement in two aspects of link utilization and response time. The advantage of add a new T1line appear when one of router or link breakdown.

5. Conclusions

We design simulation and analysis results by using the OPNET to simulate experiment of WAN, and get a real and profound understanding of theoretical knowledge of the WAN. At present network experiment equipment is expensive, so expanding the network laboratories cost larger. Using OPNET, just through establish the OPNET simulation in computer without additional network hardware, to realize all aspects of simulations about network. By design of the simulation test, teachers can study computer network in-depth and optimize the teaching. So it’s practicability and effectiveness is obvious.

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