IN NETWORKING BUSINESS
A thesis written at
WAGNER COLLEGE
in partial fulfillment of the requirements for the degree of
BACHELOR OF SCIENCE IN COMPUTER SCIENCE
by
DONNA ALISON CHAN
May 2002
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Table of Contents Introduction..........................................................................................................................4 Types of Networks ................................................................................................................4 Local Area Networks........................................................................................................4 Wide Area Networks.........................................................................................................4 Other Versions of Ethernet ...................................................................................................5 10Base-T ............................................................................................................................ Network Components ...........................................................................................................4 Hardware Devices of the Network.........................................................................................5 Network Topologies ..............................................................................................................6 Bus Topology ...................................................................................................................6 Star Topology...................................................................................................................6 Ring Topology..................................................................................................................7 Mesh Topology.................................................................................................................8 The OSI Model and Network Protocol..................................................................................8 Physical Layer...................................................................................................................9 Data Link Layer................................................................................................................9 Network Layer..................................................................................................................9 Transport Layer................................................................................................................9 Session Layer....................................................................................................................9 Presentation Layer............................................................................................................9 Application Layer............................................................................................................10 Protocols .............................................................................................................................10 TCP/IP ..........................................................................................................................10 IPX/SPX........................................................................................................................11 Hands-On Training: Internship in Information Services..................................................11-15
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List of Figures
Figure
Page
Figure 1: The Bus Topology Network ....................................................................................6 Figure 2: The Star Topology Network ....................................................................................7 Figure 3: The Ring Topology Network...................................................................................8 Figure 4: The Mesh Topology Network..................................................................................8 Figure 5: The OSI Model.....................................................................................................10 Figure 6: An Ethernet Cable.................................................................................................13 Figure 7: A Cross-Over Cable ..............................................................................................13
4 Every business depends on quick and easy access to information. Whether the business is relatively small and restricted within one city, or large and scattered across the country, their common system of information relies on a network. My summer spent as an intern at Petry Media Corporation, the parent company of Fox and Blair Television, enabled me to learn about networking in the Information Services Department, with professional ITs. Networking could consist of hardware sectors and software sectors. Networking, as related to hardware, simply put, is a group of computers that are able to share resources with each other (ie. Files, output devices, etc). Types of Networks There are two basic types of networks, typically known as LANs and WANs. LANs, or Local Area Networks, are the connections of one computer to another in a single location. A school, for example, such as Wagner College, runs on a LAN system. All the computers connected to each other on a single floor, are typically connected via LAN. Historically, the Xerox Corporation (which also credited for inventing the mouse) is credited for developing the Ethernet1. The Ethernet is a type of LAN and can safely be called the most common standard LAN connection. Ethernet allows transfer of data at a speed of 10 Mbps and thus is also known as 10Base-T. Companies that are continental or international, use WANs, or Wide Area Networks. In this situation, the computers connected by WAN use telephone lines or satellite links to communicate with each other. Not only are large companies connected by WAN, but the World Wide Web may be considered to be a Wide Area Network as well. Other Versions of Ethernet
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The Ether part of Ethernet denotes that the system is not meant to be restricted for use on only one medium type, copper cables, fibre cables and even radio waves can be used. (Rhys Haden, 1998)
5 When the transfer of data supports 100 Mbps, it is called 100Base-T, which is also known as Fast Ethernet. This 100Base-T is ten times faster than the old Ethernet standard of 10Base-T, hence its nickname Fast Ethernet. Since the Ethernet has multiple medium types (see footnote 1), there are other known Ethernets. As described in Webopedia, an Internet technology encyclopedia, there exists three other definitions. Not limited to the three, they are 100Base-TX, 100Base-T4, and 100Base-FX. The 100Base-TX describes an Ethernet in which two pairs of high-quality wires are twisted in pair, such as a Category 5 cable, a type of wire used in the Ethernet. The 100Base-T4 defines four pairs of normalquality wires in twisted pair, perhaps a Category 3, which is standard for Ethernet. The 100Base-FX is used in describing the Ethernet by fiber optic cables. As aforementioned, these are not the only cabling schemes known today. There are quite a few more, some different ones used in 100 Mbps transfer. Network Components The components of a network consist of the client, peer, and server. The client is the user of the computer on the network. On the school level, for example, any student who uses a computer in the Computer Center is considered a Client. A peer network is that in which users share all files on the local system. An example of a peer network might be the computers at the library, in which users do not need to log into a personal account. In this case, if people saved their work to the hard drive, other users in the future will be able to access the material saved. For this reason, peer networks are considered to be non-secure. Finally, a server simply is the computer or system that provides the network resources. Servers provide clients with services such as, but not limited to, saving files and printing. An example of this process is the student accounts at Wagner College. When a student wants to save his or her work onto the P: drive, for example, the server is called upon to process the
6 request. The P: drive in this case is not a physical storage space on the computer that the student is using, but rather, space that has been earmarked by the server, on the server. Since networks provide users with capabilities of sharing files and resources, security issues are always an issue. Network Administrators, who are people that are well trained for the system that the network is using, are able to control file access and share levels. Users are also assigned user names and a password. Login scripts could also be written, that control what applications or files a user is able to view and manipulate. Hardware Devices of the Network A hub or switch is a device that sends out electrical signals to all computers connected to it. It acts as a central station, so if the hub suddenly loses the signal, all the computers connected to it, will be offline as well. The hub has many ports built into it, which accept networking cables of a specified computer into its unit. Suppose there are 10 computers that are capable of being networked. These computers have what is known as a NIC or Network Interface Card. These NICs have one port, which the networking cable plugs into. The other opened end of the cable then fits into a socket such as a telephone socket. The hub accepts electrically, the socket of the computers, and essentially makes the connections in this manner. In this system, as aforementioned, when the hub fails, the connected computers are also disconnected from the network. However, if one computer fails, it does not affect the others in the network. The other computers remain on the network and continue to function. Besides the understanding of how each hardware component functions with each other, one must also ascertain knowledge of various network topologies. Network topology defines the way in which network connections are made. There are four main topologies: the bus, the star, the ring, and the mesh.
7 The Bus Topology The bus topology describes a group of computers that are connected by one long cable, meaning that computers can share information with only one other computer at any given time. If information is being sent via the bus, all computers on the same network will be sent the information, however, only one computer will accept it.
Figure 1: The Bus Topology Network
The Star Topology The star topology describes a set of computers that are connected to a central station, for example, a hub. Many cables are used to network computers on a star topology because the cables run from each individual computer to the location of the hub. To expand the versatility of the star topology, companies or organizations may run a cable from one hub to another hub, thus creating what is known as a hybrid star. The hybrid star is useful if a company is located on several floors of a building, or in a large school where there may be several computer labs. The main disadvantage with the start topology however, is that if the central hub fails, the entire network will fail. All transmissions rely on central station, whether it is a hub or a server.
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Figure 2: The Star Topology Network
The Ring Topology In a ring topology, information is sent in one direction by one computer to the next. Computers therefore are connected on a closed loop forming a ring, hence its name. Because connections run from one computer to the next until the loop is closed, any failures among the ringed network will affect the entire network. Troubleshooting the ring network is also a difficult task. The problem is that in the ring topology, the computers are connected in a series. For the same reason that a series of Christmas lights will fail because of one bulb failure, computer in network a ring topology will fail if a connection from one computer fails.
Figure 3: The Ring Topology Network
9 The Mesh Topology The mesh topology is probably one of the most difficult to understand, as it is a network that relies on excessive connections between computers. Every computer that is connected to at least two devices uses the mesh topology. In a mesh topology, every device is installed independently; meaning that every device has its own connection to another device. In this sense, it is easy to troubleshoot problems on the network.
Figure 4: The Mesh Topology Network
The OSI Model and Network Protocol OSI stands for Open Systems Interconnect, a model that is used to describe protocols. Put simply, protocol refers to rules of communication; network protocol refers to rules in which commands or messages are transmitted between computers on a network. The OSI model is divided into seven layers that describe how specific protocol implement and interact with each of the seven layers. This is an important model because a solid understanding of the OSI model can assist in troubleshooting when problems arise in communication between systems. The layers start with the first layer and work their way up. The first layer is the physical layer, which controls the interface of the network hardware. A NIC is an example of a component described in Layer 1. Layer 2 is known as the Data Link, which are protocols that govern the organization of data and transmission of logic. For example, the Data Link can be used to determine
10 which computer sent a message to the network it is the logical organization of transmission of data. Layer 3 is referred to as the Network Layer, which describes how addresses are assigned and how packets (units of data transmission) are forwarded from one computer to another. Email is an example of a component in Layer 3. Layer 4 is the Transport Layer, which concerns the way in which items are transported to its destination; if a message is too large, it is broken down into small packets. Since this is still a lower level layer, it concerns hardware more than software. For example, a user on a dial up modem is sending and receiving messages to and from the ISP. That data could be broken up into small packets, and by the time it reaches the ISP, it is reassembled. This is the type of transaction described by the Transport Layer. The fifth Layer is the Session Layer. Session protocols govern how communication sessions are handled. It defines how two computers establish, maintain, and end a session. This Session protocol is perhaps where software gets introduced. Connections that drop out lose transmission of data because they are disconnected from the network. Some software are able to identify that transmission is lost, and may auto-connect or at least keep trying to connect until a connection is reached. This is the type of behavior that Layer 5 encompasses. The sixth Layer is Presentation, which deals with how data is presented. The display of characters, whether it is encrypted data, or the format of the data are all examples of Presentation. How one computer is able to translate the data received from another computer is all dealt with in the Presentation Layer. The topmost layer, Layer 7, is the Application Layer. The Application Layer describes the way in which the network interacts with applications. America Onlines
11 Instant Messenger Program is an example of network software. Other examples are Internet Explorer or email programs.
Figure 5: The OSI Model
Protocols TCP/IP, or Transmission Control Protocol/Internet Protocol, are the guidelines that are assigned to Internet usage. The host computer is one that is used to connect to the Internet. To be recognized as a host computer, every computer that accesses the Internet must have an IP address. This IP address is a unique number that is a number divided into four sections denoted by a period between each section. Each section can have up to three digits and no more. To view each computers unique IP address, one should go to the Start > Run > and type winipcfg. This command will display a series of data related to the computers IP address. An example of an IP address is 192.168.12.1 (the typical span of numbers in each section ranges from the digit 1 through 254). In some cases, there may be an IP address conflict. Sometimes, an administrator or user may manually assign an IP address, thus if two computers have the same address, there may be network chaos trying to determine the error. On systems that rely on Novells NetWare, as most firms or academic institutions use, the protocol used is IPX/SPX, or Internetwork Packet Exchange/Sequenced Packet
12 Exchange. IPX/SPX provides file, print, message, and application services. The TCP/IP address and the IPX address are different and completely independent of each other. The IPX address is a definite unique number. In fact, no two computers should have the same IPX address for the very reason that IPX uses the MAC address. The MAC address is simply the address that is embedded into every network device when it is manufactured. For this reason, once it is embedded, it cannot be changed, so IPX address hardly suffer the same conflict that IP addresses may experience. Hands-On Training: Internship In Information Services I was an intern at the Information Services Department at Petry Media Corporation in New York City. Petry Media Corporation is the parent company of Blair Television and Fox Television, companies that deal with selling airtime. There are fifty-one chains around the United States, and at least fifteen of each branch. Petry New York is the main office, and acts like the hub of the entire network. The mail server and network operations flow through Petry New York before getting dispersed to the offices around the United States. Whenever there were network problems, including emailing problems, Petry New York is the target of the complaints. These three companies not only have a staff of mathematicians to calculate and analyze statistics of certain television show ratings to allot the most advantageous spot for commercials, but also employ a large number of ITs, especially in New York. Since Petry Media Corporation is one of the leading Spot companies, the Information Services Department is heavily relied on. When I started my internship, one of the big projects that had already been earmarked for the Information Services interns, was the swap over of computers. Blair Television was scheduled to move their office to another NYC location, and the interns had to disconnect over two hundred computers and output devices. It was hard
13 labor, as we then set up all the computers at the new location some days later. During the swap over, we were able to learn about networking fundamentals, and get a hands-on experience with routers, hubs, and cables. We had to set up the routers and hubs in a remote location and make sure that all the connections were live before the day ended. Besides configuring the actual PCs, we had to set up the network and troubleshoot it, until it was found ...