EGR 199:
Fundamentals of Engineering
 Internet Internals
Draft 09/09/99 Prabhaker Mateti
 

 

 
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Table of Contents

Procedures

Concluding Activities

Executive Summary

This chapter is about the infrastructure of the Internet: LANs and WANs, and how the network of network functions.  The lab experiments illustrate the setup of a LAN using PCs running Linux.

Educational Objectives

After performing this experiment, students should be able to:

Suggested Preparation

Please refer to the Appendix A if you would like to find out what an acronym used in this document. Prior to performing the experiments of this Lab,  visit the sites listed in Appendix B: Further Reading Links and explore.

Background Information

Web v Internet

The Internet is comprised of thousands of regional networks scattered throughout the globe. On any given day,  a hundred million users in over 50 countries are connected to it. The Web refers to a body of information - an abstract space of knowledge, while the Internet refers to the physical side of the global network, a giant mass of cables and computers.

Nobody owns the Internet. Nobody owns the World-Wide Web. Having access to the Internet usually means that one has access to a TCP/IP based server, typically called an Internet Service Provider (ISP). The WWW uses the Internet to transmit hypermedia documents between computer users internationally.

Your request for a Web page, while on a home computer, travels through a labyrinth that is generally referred to as the Internet infrastructure.

Networks

A LAN (Local Area Network) is a network of computers within a relatively small geographic area, such as an office building  A WAN (wide area network) is a geographically dispersed telecommunications network. A wide area network may be privately owned or rented, but the term usually connotes the inclusion of public (shared user) networks. An intermediate form of network in terms of geography is a metropolitan area network (MAN).

Network Topology refers to how the computers are connected.  In the Star Topology, all the computers are connected to a common point.  It is fault-tolerant, and is easy to add new clients and easy  for management and monitoring of network performance.  The Bus Topology is a straight line with a tap for each computer.  It is simple, easy to add new computers by inserting a T-connector, but problems are hard to isolate and the slows down during periods of heavy use.

Addresses

The Internet has an addressing scheme that every computer on the network understands. An IP (Internet Protocol) address is a 4-byte number  that uniquely identifies a specific computer connected to the Internet; we write it as four numbers, separated by periods.  Groups of these numbers are assigned by a world-wide authority.  For example, all computers at WSU have IP addresses of the form 130.108.*.* and 130.108.1.20 is the address of a specific server at WSU. When you connect to an ISP,  your computer has an IP address (the same one all the time or a different address each time you connect).  Isolated LANs, such as at home, should have IP addresses in the group of 192.168.*.*.

Internet domain names are the next level of Internet addressing, just as the street name is followed by the city and state. Domain names create a single identity for a set of locally connected computers used by a company or an institution. So while there may be 38 servers at a given company, each with its own IP address, they all share a common domain name, such as wright.edu.

The domain name identifies all the computers in a group. But if you want to get to a specific page stored on any of those computers, you'll need an even more precise address. That's why every Web page on the Internet, and even the pictures you see displayed on Web pages, has its own unique address, known as a Uniform Resource Locator (URL), which tells your browser exactly where to go on the server to find a page.

Clients and Servers

Local Area Networks

Without a Server
In a peer-to-peer network, a group of PCs are hooked together, with each PC, having equal status in the network. All the PCs can share files, send each other messages, and share a printer or two. Windows 9x/NT comes with all required software to setup a peer-to-peer LAN.

A LAN with a Server
You can setup one of the computers as a server.  The other PCs are then known as client computers.  The server stores the applications, files, and e-mail messages. This server delivers applications such as database, word processors, as well as data and e-mail.  It also acts as the center for sharing printers, doing backup, etc.

LAN Hardware

Network Interface Cards

There are many ways of setting up a LAN.  The ruling king of such technologies is Ethernet for the hardware layer, and TCP/IP for software layer.

Network interface cards (NICs) are hardware boards that you insert into empty slots in the PC.  Today (1999), a good PCI-based card for 10 or 100 megabits/sec (Mb/s) sells for about $15.  A typical card will have two connectors at the back:  a telephone-jack like RJ45, and an RCA-like BNC connector. Through this physical connection,  the data  bits go  from the computer to the cable and back again when receiving. Each NIC is identified by a unique 6-byte number called its Ethernet address that is stored, at manufacture time, in a ROM on the card.

 

RJ45 FEMALE CONNECTORThe RJ45 Twisted Pair Cable, whose connector is shown at left, is made from insulated strands of wire twisted together inside a sheath that may or may not be shielded. Unshielded Twisted Pair (UTP) is the most commonly used cable for small LANs. It is often referred to as 10BaseT because the most popular size of this cable can carry 10 Mb/s. It comes in different categories that carry between 4 Mb/s and 100 Mb/s of data to about 300 feet before the signal strength suffers.

If you connecting only two computers, you do not any hubs.  You use one RJ45 cross over cable that has two of their signal wires transposed between the connectors as described below.

Pin Name End1 Pin End2 Pin Pin Name
TX+ 1 3 RX+
TX- 2 6 RX-
RX+ 3 1 TX+
RX- 6 2 TX-
(You may also connect 4-4, 5-5, 7-7, 8-8.)  This cable can be used to cascade hubs, or for connecting two Ethernet stations back-to-back without a hub. It works with both 10Base-T and 100Base-TX.

To connect more than two computers, you need  network hubs.  All the PCs connect to the hub.  An inexpensive starter network kit for home  sells for $50 (in 1999) and includes two NICs and a hub that has 5 RJ45 ports.

The Thin Coaxial Cable looks similar to a TV cable but its impedance rating and other characteristics are different. It has a core of solid or braided copper wire surrounded by insulation, braided metal shielding, and an outer cover. These cables can carry a signal about 600 feet before the signal starts to suffer from loss of strength. The thin coaxial cable  does not need hubs.  Imagine it as a long unbroken line of cable terminated with 50-ohm resistors at either end, and with a T-connector for each computer.

Routers, Gateways, Hubs

Typically, a packet may travel through a number of network points with routers before arriving at its destination

A router is a connector between LANs that use identical protocols; packets are received, examined and then sent on. It is a hardware device or, software in a computer, that determines the next network point to which a packet should be forwarded toward its destination. The router is connected to at least two networks and decides which way to send each information packet based on its current understanding of the state of the networks it is connected to. A router creates or maintains a table of the available routes and their conditions and uses this information along with distance and cost algorithms to determine the best route for a given packet.

A gateway is a computer that lies at the intersection of two networks, and routes traffic correctly between them, while keeping traffic internal to the two networks separated. A hub is a place of convergence where data arrives from one or more directions, and the switch is what determines how and where data is forwarded.

Modems

Strictly speaking, a modem belongs in the wide area network hardware group.

Modem stands for MOdulator/DEModulator. A modem converts (modulates) digital signals generated by the computer into analog signals which can be transmitted over a telephone line and transforms (demodulates) incoming analog signals into their digital equivalents. The specific techniques used to encode the digital bits into analog signals are called modulation protocols. This encoding process puts the transmission into a mode that is compatible with the various transmission media used by the telephone company, such as copper wire, microwave, satellite, and fiber optics.  Most new modems can send and receive data at 57.6 kbps (kilo bits per second) and faxes at 14.4 kbps.  ISDN (Integrated Services Digital Network) modems use digital telephone lines to achieve a transmission speed of 128 kbps.

LAN Software

The network operating system controls the operations of the server, lets you decide who can have access to it, and regulates information flowing from the various clients on the network to each other; to the printers, modems, or CD-ROM drives that are shared by the client computers, and from the client computer to itself.

Protocols

In information technology, a protocol is the set of rules that a telecommunication connection uses when the two end points send signals back and forth. Protocols exist at several levels in a telecommunication connection. There are hardware telephone protocols. There are protocols between the end points in communicating programs within the same computer or at different locations. Both end points must recognize and observe the protocol.

Protocols are implemented as software in the network operating system.

TCP/IP

Transports are  the enabling network components that let clients talk to the server and that let one network talk with another network of a different brand. NetBEUI stands for Network Basic End User Interface. It supports small LANs and it is fast and simple.

On the Internet, there are the TCP/IP protocols, consisting of: TCP (Transmission Control Protocol), which uses a set of rules to exchange messages with other Internet points at the information packet level. IP (Internet Protocol), which uses a set of rules to send and receive messages at the Internet address level.  These were developed to be routable and can accomodate large networks.

HTTP

The Web is based on a set of rules for exchanging text, images, sound, video, and other multimedia files, which is collectively known as HTTP, or hypertext transfer protocol. Web pages can be exchanged over the Net because browsers (which read the pages) and Web servers (which store the pages) both understand HTTP.

SSL

SSL (Secure Sockets Layer) is a program layer created by Netscape for managing the security of message transmissions in a network. SSL uses the public-and-private key encryption system from RSA, which also includes the use of a digital certificate. SSL is an integral part of a browser.

Telnet

Telnet is the way you can access someone else's computer, assuming they have given you permission. (Such a computer is frequently called a host computer.) More technically, Telnet is a user command and an underlying TCP/IP protocol for accessing remote computers. The Web or HTTP protocol and the FTP protocol allow you to request specific files from remote computers, but not to actually be logged on as a user of that computer. With Telnet, you log on as a regular user with whatever privileges you may have been granted to the specific applications and data on that computer. A Telnet command request looks like this: telnet paladin.wright.edu The result of this request would be an invitation to log on with a userid and a prompt for a password. If accepted, you would be logged on like any user who used this computer every day. Telnet is most likely to be used by program developers and anyone who has a need to use specific applications or data located at a particular host computer.

FTP

FTP (File Transfer Protocol)  is an application protocol that uses the Internet's TCP/IP protocols. FTP is commonly used to transfer Web page files from their creator to the computer that acts as their server for everyone on the Internet. It's also commonly used to download programs and other files to your computer from other servers.  You need to log on to an FTP server.  Publicly available files are accessed by logging in as user anonymous and with your e-mail address as your password

SMTP Simple Mail Transfer Protocol

Sends your e-mail messages from your computer to an e-mail server.

Internet2

Internet2 is a U.S. governement project to create a powerful leading edge network for universities and the national research community. Internet2 is not a physical network that will replace the Internet. Rather, Internet2's goal is to develop new technologies that can be deployed in the Internet. Internet2 is working to enable applications, such as telemedicine, digital libraries and virtual laboratories that are not possible with the technology underlying today's Internet. Read more about it at http://www.internet2.edu/.

Procedures

Concluding Activities

 

Appendix A: Acronyms

FTP File Transfer Protocol
FDDI (Fiber Distributed Data Interface).
HTML Hyper Text Markup Language
HTTP Hypertext Transfer Protocol
IP Internet Protocol
LAN Local Area Network
NNTP Network News Transfer Protocol
PGP Pretty Good Privacy
POP Post Office Protocol
SMTP Simple Mail Transfer Protocol
URL Uniform Resource Locator
WAN Wide Area Network
WWW World Wide Web
X11 GUI server that originated in Unix, now on Windows also
A few acronyms and their expansions are collected in the table here. If you are curious about an acronym or term not listed, type it in the input box below, and then press

the button to look it up in the TechEncyclopedia.

Appendix B: Further Reading Links

"Unix for the Impatient'' by Paul W. Abrahams, Bruce Larson, Addison-Wesley; ISBN: 0201823764.
http://www.randomhouse.com/features/davebarry/ Dave Barry's Emoticons
http://www.annoyances.org/ Are you annoyed at Windows?
http://slashdot.org/ A Linux advocacy site
http://www.eff.org/ Electronic Frontier Foundation

Achievement Test

The achievement test is replaced with a journal, in which you record the answers to various questions posed as you proceed in the experiments. Pointers to all these questions are collected below; click on them to see the context for the questions. You are working in groups of two but these answers must be your own.
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Send comments to pmateti@cs.wright.edu