A network is defined as two or more computers linked together for the purpose of communicating and sharing information and other resources. Most networks are constructed around a cable connection that links the computers. This connection permits the computers to talk (and listen) through a wire.
After this lesson, you will be able to:
Estimated lesson time: 40 minutes
- Define basic networking concepts and describe how a network functions.
- Configure and change network interface cards.
- Define Internet terms and functions.
In order for a network to function, three basic requirements must be met: it must provide connections, communications, and services.
Connections include the hardware (physical components) required to hook up a computer to the network. Two terms are important to network connections:
Communications establish the rules concerning how computers talk and understand each other. Because computers often run different software, in order to communicate with each other they must speak a "shared language." Without shared communications, computers cannot exchange information, and remain isolated.
A service defines those things a computer shares with the rest of the network. For example, a computer can share a printer or specific directories or files. Unless computers on the network are capable of sharing resources, they remain isolated, even though physically connected.
Next we look at how the basic elements of connections, communications, and services work together to make networks function properly:
A LAN (local area network) is a network that covers a limited distance (usually a single site or facility) and allows sharing of information and resources. A LAN can be as simple as two connected computers, or as complicated as a large site. This type of network is very popular because it allows individual computers to provide processing power and utilize their own memory, while programs and data can be stored on any computer in the network. Some of the older LANs also include configurations that rely totally on the power of a mini or mainframe computer (a server) to do all the work. In this case, the workstations are no more than "dumb" terminals (a keyboard and a monitor). With the increased power of today's personal computer, these types of networks are rare.
The primary benefit of a LAN is its ability to share. The following table lists some of the benefits of sharing the most common resources on a LAN.
|Data||The sharing of data files that reside in a common location makes multiple-user access easier. Also, it's much easier to maintain data integrity when there is a single, central database. Large customer databases and accounting data are ideal for a LAN system.|
|Peripherals||Sharing printers, for example, allows more than one user to send jobs to a single printer. This is useful when there is only one high-quality printer in an office and the entire office needs to use it. It also allows one user to access multiple printers, providing cost savings in hardware and redundant resources in case one device fails. Other low usage peripherals, such as scanners and plotters, will be better utilized.|
|Software||Sharing a single copy of an application can be cost-effective (many software manufacturers provide site licenses—licenses for multiple users on a server). It also allows easier maintenance and upgrading.|
|Storage||Larger, faster disk systems can be used cost-effectively for easy backups.|
In addition to the ability to share resources, LANs offer many other benefits that include:
A wide area network (WAN) spans relatively large geographical areas. Connections for these sites require the use of ordinary telephone lines, T1 lines, ISDN (Integrated Services Digital Network) lines, radio waves, or satellite links. WANs can be accessed through dial-up connections, using a modem, or leased line direct connection. The leased-line method is more expensive but can be cost-effective for transmission of large volumes of data.
There are essentially two types of networks. They differ in how information is stored, how security is handled, and how the computers on the network interact.
In a peer-to-peer network, each computer acts as either a server (sharing its data or services with other computers), or a client (using data or services on another computer) depending on the user's needs. Each user, or workstation, establishes its own security and determines which resources are available to other users. Typically these networks are limited in size (15 to 20 workstations). Microsoft Windows for Workgroups, Windows 95 and Windows 98, Windows NT Workstation, Windows 2000, Novell's NetWare, UNIX, and Linux are some software packages available for peer-to-peer networking.
A server network requires a central server (dedicated computer) to manage access to all shared files and peripherals. This is a secure environment suitable for most organizations. In this case, the server is a computer that runs the network operating system, manages security, and administers access to resources. The client is a computer that connects to the network and uses the available resources. The two most common server operating systems are Microsoft's NT4 Server and Novell's IntranetWare. Prior to the release of Windows NT, most dedicated servers worked only as hosts. Windows NT allows the server to also operate as an individual workstation. More than one server can provide services on the network, but only one can be responsible for the security and overall operation of the network.
LAN design is called topology. Topology describes the appearance or layout of a network and how data flows through the network. There are three basic types of topologies: star, bus, and ring. In the real world, you are likely to encounter some hybrid combinations of these topologies, but for the A+ exam, we focus only on these three.
The illustrations that follow should not be used as exact wiring diagrams, rather as sample network designs.
In a star network (see Figure 18.1), all devices are connected to a central point called a hub. These hubs collect and distribute the flow of data within the network. Signals from the sending computer go to the hub and are then transmitted to all computers on the network. Large networks can feature several hubs. A star network is easy to troubleshoot because all information goes through the hub, making it easier to isolate problems.
Figure 18.1 Star topology
In a bus network (see Figure 18.2), all devices are connected to a single linear cable called a trunk (also known as a backbone or segment). Both ends of the cable must be terminated (like a SCSI bus) to stop the signal from bouncing. Because a bus network does not have a central point, it is more difficult to troubleshoot than a star network. A break or problem at any point along the bus can cause the entire network to go down.
A bus network is often referred to as an Ethernet network.
Figure 18.2 Bus topology
In a ring network (see Figure 18.3), all workstations and servers are connected in a closed loop. There are no terminating ends; therefore, if one computer fails, the entire network will go down. Each computer in the network acts like a repeater and boosts the signal before sending it to the next station. This type of network transmits data by passing a "token" around the network. If the token is free of data, a computer waiting to send data grabs it, attaches the data and the electronic address to the token, and sends it on its way. When the token reaches its destination computer, the data is removed and the token sent on.
This type of network is commonly called a token ring network.
Figure 18.3 Ring topology
The network operating system (NOS) consists of a family of programs that run in networked computers. Some programs provide the ability to share files, printers, and other devices across the network. As previously mentioned, computers that share their resources are called servers; computers that use the resources on other computers are called clients. It is common to run client and server software on the same computer. This enables one user to access the resources on another computer while coworkers make use of resources on your computer.
Networking software can be a special program added on to the computer, such as Artisoft's LANtastic or Novell's NetWare, or it can be an integral part of an operating system such as Microsoft's Windows 95 or Windows 98, Windows NT, or Windows 2000.
Network interface cards (NICs) link a computer to the network cable system. They provide the physical connection between the computer's expansion bus and the network cabling. The low-powered digital signals that transmit data inside a computer are not powerful enough to travel long distances. A network interface card boosts these signals so they can cross a network cable. The interface card also must change the form of data from a wide parallel stream—coming in 8, 16, or 32 bits at a time—to a narrow stream, moving 1 bit at a time in and out of the network port (parallel to serial conversion—see Chapter 2, Lesson 2: The Computer Bus).
The network interface card takes data from the computer, packages the data for transmission, and acts as a gatekeeper to control access to the shared network cable. Because the NIC functions as an interface between the computer and the network cabling, it must serve two masters. Inside the computer, it moves data to and from RAM. Outside the computer, it controls the flow of data in and out of the network cable system. Because the computer is typically much faster than the network, the interface card must buffer the data between the computer and cable. This means it must temporarily store the data coming from the computer until it can place it on the network.
Installation of the network interface card (see Figure 18.4) is the same as for any other expansion card. It requires setup of the system resources: IRQ, address, and software. Most cards today allow connection for either thin Ethernet or UTP (unshielded twisted-pair) cabling. Thin Ethernet uses a round BNC connector, and UTP uses a RJ-45 connector (similar to a telephone jack).
Figure 18.4 Network interface card
Installing a NIC is just like installing any other expansion card. If you are installing a Windows 95-compliant Plug and Play card in a Windows 95 or Windows 98 machine, you'll simply need to physically install the card and boot up the computer. The card will be detected and, more than likely, install itself. You might only need to answer a few questions along the way. It requires a little more work to install a NIC in an operating system that is not Plug and Play-compliant. Installing network cards includes the following steps:
If you are replacing (upgrading) an existing NIC, follow the same steps as just described, with one addition. Before removing the card, document all its settings. Figure 18.5 shows an example of a NIC information card. You can use these cards to create a file documenting the specifics of the cards in your network.
Figure 18.5 Information card
An improperly configured network interface card could prohibit network access. Check your settings carefully.
All networks need cables. The three main types are twisted-pair cable (TP), coaxial cable, and fiber-optic cable (FDDI—Fiber Distributed Data Interface).
Twisted-pair cable, shown in Figure 18.6, consists of two insulated strands of copper wire twisted around each other to form a pair. One or more twisted pairs are used in a twisted-pair cable. The purpose of twisting the wires is to eliminate electrical interference from other wires and outside sources such as motors. By twisting the wires, any electrical noise from the adjacent pair will be canceled. The more twists per linear foot, the greater the effect.
Twisted-pair wiring comes in two types: shielded (STP) and unshielded (UTP). STP has a foil or wire braid wrapped around the individual wires of the pairs; UTP does not. The STP cable uses a woven-copper braided jacket, which is a higher-quality, more protective jacket than UTP.
Figure 18.6 Twisted pair cable
Of the two types, UTP is the most common. UTP cables can be further divided into five categories:
Twisted-pair cable has several advantages over other types of cable (coaxial and fiber-optic)—it is readily available, easy to install, and inexpensive. Among its disadvantages are its sensitivity to EMI (electromagnetic interference) and susceptibility to eavesdropping; it does not support communication at distances of greater than 100 feet; and it requires the addition of a hub (a multiple network connection point) if it is to be used with more than two computers.
Coaxial cable (see Figure 18.7) is made of two conductors that share the same axis; the center is a copper wire that is insulated by a plastic coating and then wrapped with an outer conductor (usually a wire braid). This outer conductor around the insulation serves as electrical shielding for the signal being carried by the inner conductor. Outside the outer conductor is a tough insulating plastic tube that provides physical and electrical protection. At one time, coaxial cable was the most widely used network cabling. However, with improvements and the lower cost of twisted-pair cables, it has lost its popularity.
Figure 18.7 Coaxial cable
Coaxial cable is found in two types: thin (ThinNet) and thick (ThickNet). Of the two, ThinNet is the easiest to use. It is about one-quarter of an inch in diameter, making it flexible and easy to work with (it is similar to the material commonly used for cable TV). ThinNet can carry a signal about 605 feet (185 meters) before the signal strength begins to suffer. ThickNet, on the other hand, is about three-eighths of an inch in diameter. This makes it a better conductor—it can carry a signal about 1,640 feet (500 meters) before signal strength begins to suffer. The disadvantage of ThickNet over ThinNet is that it is more difficult to work with. The ThickNet version is also known as standard Ethernet cable.
When compared to twisted-pair, coaxial cable is the better choice even though it costs more. It is a standard technology that resists rough treatment and EMI. Although more resistant, it is still susceptible to EMI and eavesdropping.
Use coaxial cable if you need:
A Mixed-Cable System
Many networks use both twisted-pair and coaxial cable. Twisted-pair cable is used on a per-floor basis to run wires to individual workstations. Coaxial cable is used to wire multiple floors together. Coaxial cable should also be considered for a small network because you can purchase prefabricated cables (with end connectors installed) in various lengths.
Fiber-optic cable (see Figure 18.8) is made of light-conducting glass or plastic fibers. It can carry data signals in the form of modulated pulses of light. The plastic-core cables are easier to install, but do not carry signals as far as glass-core cables. Multiple fiber cores can be bundled in the center of the protective tubing.
Figure 18.8 Fiber-optic cable
When both material and installation costs are taken into account, fiber-optic cable can prove to be no more expensive than twisted-pair or coaxial cable. Fiber has some advantages over copper wire; it is immune to EMI and detection outside the cable and provides a reliable and secure transmission media. It also supports very high bandwidths (the amount of information the cable can carry), so it can handle thousands of times more data than twisted-pair or coaxial cable.
Cable lengths can run from .25 to 2.0 kilometers depending on the fiber-optic cable and network. If you need to network multiple buildings, this should be the cable of choice. Fiber-optic cable systems require the use of fiber-compatible NICs.
In order to ensure trouble-free operation, network cabling must match the system requirements. Cable specifications are based on three factors: speed, bandwidth, and length. Cables are designated with names like 10Base5. Speed is the first number in the identification¾representing the maximum transmission speed (bandwidth) in Mbps. This will be 1, 5, 10, or 100. Band is the second part of the identification. It is either base or broad depending upon whether the cable is baseband or broadband. The last part of the identification refers to the cable length or cable type. If the unit is a number, it is the maximum length of the cable segments in hundreds of meters (1 meter is approximately 3.3 feet). In some cases, it can refer to 50-meter increments (1Base5 is five 50-meter increments—250 meters). In other cases, it represents cable type: T (twisted-pair) or F (fiber-optic). The following table shows the common types of cables and their specifications.
|10BaseT||Common||UTP twisted-pair||.5 to 100 meters||10 Mbps|
|10Base2||Ethernet ThinNet||Coaxial||185 meters||10 Mbps|
|10Base5||Thick Ethernet||Coaxial||500 meters||10 Mbps|
|100BaseT||Becoming common||Twisted-pair||.5 to 100 meters||100 Mbps|
The preceding table covers the basic cable requirements for the A+ networking objective; however, there are many other forms of network connections. For example, you'll find microwave links; forms of radio; and, for small offices and homes, power-line networks (whose NICs have connectors that plug into wall sockets, allowing regular wiring to carry the signal), and telephone-line networks that use standard phone jacks to plug into existing lines. These have relatively short ranges (generally limited to one office or one floor of a building).
A LAN is similar to a telephone system with one party line—not everyone can talk at the same time. The difference is that, with a LAN, the speed is so fast that it fosters the perception that many transactions are taking place at the same time. But just like a one-lane road, the heavier the traffic, the slower it moves.
Ethernet uses a system known as carrier sense multiple access with collision detection (CSMA/CD). It also uses the bus topology discussed earlier in this lesson. The term "carrier sense" means that the network card listens to the cable for a quiet period during which it can send messages. "Multiple access" refers to the fact that more than one computer can be connected to the same cable. And "collision detection" is the ability to detect whether messages have collided in transit (in which case neither message will arrive at its destination and both will be retransmitted).
Fast Ethernet was developed to meet the increasing demands on networks. Fast Ethernet works on the same principals as the original Ethernet, but operates at 10 times the speed. Ethernet transmits at 10 Mbps, and Fast Ethernet transmits at 100 Mbps.
As described earlier, a token ring network uses a "token" as the basis for deciding who can communicate on the network. Token rings transmit at 4 or 16 Mbps.
A network protocol is a set of rules that govern the way computers communicate over a network. In order for computers using different software to communicate, they must follow the same set of networking rules and agreements, called protocols. A protocol is like a language; unless both computers are speaking and listening in the same language, no communication will take place.
Networking protocols are grouped according to their functions, such as sending and receiving messages from the NIC, or talking to the computer hardware and making it possible for applications to function in a network. Early computer networks had manufacturer-unique inflexible hardware and strict protocols. Today's protocols are designed to be open, which means they are not vendor-, hardware-, or software-specific. Protocols are generically referred to as protocol families or protocol suites because they tend to come in groups (usually originating from specific vendors).
The following is a list of standard network protocols:
Depending on the operating systems and the function of the network you work on, you will probably use more than one network protocol. It's important to get and install LAN drivers that can switch between one protocol and another as needed. The aforementioned protocol information provides you with a rudimentary understanding of basic network techniques and terminology. However, networks are a very complicated subject, and additional training resources should be obtained before installing a network on your own.
The previous section on network cables mentioned some limits to the length of cables. The requirements of today's LANs will often exceed the capability of these cables. The following table lists several devices that can be used to extend a LAN network beyond its normal limits.
|Repeaters||The main purpose of a repeater is to extend the length of a network beyond its normal cable lengths. A repeater works like an amplifier to increase or boost the signal to allow transmissions over longer distances. Repeaters are used to connect network segments (groups of computers on the same network). They can also be used to connect segments composed of different media (for instance, a ThinNet segment to a fiber-optic segment).|
|Bridges||Bridges work like repeaters, but offer additional advantages. They can isolate network traffic or problems. Should any problems occur within one segment, the bridge will isolate that segment and not affect other segments on the network, thereby reducing the load on the network as a whole. Bridges can also link segments that are unalike (such as Ethernet and token ring).|
|Routers||Routers provide interconnectivity between like and unlike devices on the LAN and WAN. Routers work like bridges, but can connect networks using different protocols. They are able to select the best route from one network to another network based on traffic load. Routers determine the flow of data based on such factors as least-cost, minimum delay, minimum distance, and least congestion. Routers are generally used to create a WAN and connect dissimilar networks.|
|Gateways||Gateways provide all the connectivity of, and even greater functionality than, routers and bridges. A gateway usually resides on a dedicated computer that acts as a translator between two completely dissimilar systems or applications. Because gateways are both translators and routers, they tend to be slower than bridges or routers. Gateways also provide access to special services such as e-mail or fax functions.|
Maintaining and troubleshooting networks differ according to the operating system. Therefore, you will need to refer to the operating systems' manuals for detailed troubleshooting procedures. A thorough understanding of network troubleshooting is not a requirement of the A+ Certification program. (The section that follows describes some advanced certification programs that focus on networks.) As an A+ technician, you should be familiar with some generic troubleshooting concepts as presented in the following table.
|Reduced bandwidth||Called a bottleneck, this occurs when the network doesn't handle as much data as usual. A bottleneck is some constraint that limits the rate at which a task can be completed. If a task uses the processor, network, and disk resources, and spends more of its time transferring data to and from the disk, you could have a memory bottleneck. A memory bottleneck might require additional RAM.|
|Loss of data||If data transfers are incomplete or inaccurate, check to ensure that all network cabling and connectors are intact.|
|Slow loading of programs and files||Fragmentation (see Chapter 8, Lesson 2: Hard Disk Drives) occurs when the operating system saves, deletes, and moves information. You must defragment the drive. If slow loading persists even after defragmenting, check for memory bottlenecks.|
|Unauthorized software||You must manage software distribution to ensure that users are not loading unlicensed software and computer viruses on the network. One way is to load only software from a centralized location or server and then remotely copy it to local hard disk drives.|
|Traffic overloads||A hardware or software failure can bring a LAN to a halt, or the failure can result in more data traffic than the network is designed to handle. You might receive an error message or you might not see any signs other than poor network performance. You must have a system in place that can monitor and manage network traffic. To resolve this problem, you will need to reduce the traffic on the LAN or expand its capabilities.|
|Common mode failures||Some LAN-component failures affect other components. This is known as a common mode failure. For example, the on-board logic of a NIC might jumble the data format. The NIC will hand the result to the network operating system, which might not detect the error. If the network operating system puts that data into a file, the file will become corrupt.|
|Network-security violations||Entire books address the subject of network security alone. Every operating system is different, and every customer requires a different level of security. First determine the customer's needs, and then find and read the appropriate documentation.|
This chapter is designed to give you a foundation in networks and a general understanding of network design and applications. Technician certification is a growing trend in the computer industry. The A+ examination touches on network terminology and design; however, some of the most popular networking certification programs are available through Microsoft and other NOS manufacturers. These companies offer many levels of certification; you should consult check manufacturer Web sites and community colleges for detailed course contents. Let's take a look at some of the available programs.
Microsoft Certified Product Specialist (MCPS) certification is designed for advanced end users, computer service technicians, and network administrators who seek the fastest-growing certification in the computer industry. The MCPS certification is useful for those who want to demonstrate expertise with a particular Microsoft product, such as Windows NT Server or Windows NT Workstation. This is also the first step toward becoming an MCSE.
The Microsoft Certified Systems Engineer (MCSE) certification is the most sought-after certification in the computer industry. Qualified MCSEs plan, implement, maintain, and support information systems in a wide range of computing environments using the Microsoft Windows NT Server and the Microsoft BackOffice integrated family of server products. To become an MCSE, you must pass four core modules and two elective exams. For a detailed outline of the MCSE certification track, please visit www.microsoft.com.
The Certified Novell Administrator (CNA) certification is frequently the first credential earned by NetWare career professionals. CNA training provides you with the critical day-to-day maintenance and management skills you need to survive in the world of Novell NetWare and IntranetWare. The CNA certification is the first step to becoming a Certified Novel Engineer (CNE).
The Certified Novell Engineer (CNE) certification is currently one of the most popular credentials in the field of networking. It can give a tremendous boost to the career of any serious networking professional. Novell's certification curriculum is 50 percent industry-generic—as a Certified Novell Professional, you are qualified to support Novell-specific products as well as non-Novell products. Novell certifications are recognized worldwide as the standard of excellence for supporting Novell's Internet, Network, and GroupWare products. One of the leading vendor-certification programs in the IT industry, CNE training gives you the skills to provide high-end, solutions-based technical support.
The Internet, also known as "the Net," is the most WAN in the world—a network of networks working together. This relatively new communication technology has begun to affect our lives as significantly as television and the telephone. When most people talk about using the Internet, they talk about which Web sites they have visited or who they've met online.
Most LANs make use of passwords and other forms of security, but the Internet is one of the most open networks in the world. Some common Internet uses include communication; locating lost friends and family; researching information for school or work; and locating businesses, products, or services (such as travel). The Internet can be your most valuable resource for virtually anything and everything.
A thorough knowledge of the Internet and how it works is not a requirement of A+ Certification. However, as an A+ technician, you might find that it becomes the single most valuable information tool at your disposal.
The Internet is really a collection of services. Let's take a look at the most important services and the major concepts behind them.
When people say they were "surfing" the net, they were probably visiting the collection of hyperlinked Web sites known as the World Wide Web. These Web sites are located around the world, and their numbers continue to grow by the thousands every day. Each Web site within the World Wide Web has a unique address called a Universal Resource Locator (URL).
The World Wide Web (usually abbreviated as "the Web") is not the Internet—it is only part of the Internet. Although it is currently the largest, most popular, and fastest growing part of the Internet, it represents only a fraction of Internet services available that include FTP, Gopher, and Telnet.
Electronic mail, usually known as e-mail (sometimes spelled E-mail or email), is the most commonly used function of the Internet, allowing users to send and receive messages (and files) electronically to and from millions of people all over the world. Electronic mailing lists allow users to join group discussions with people who share their interests. Like regular mail (also called snail mail), e-mail is also sent to an address (a virtual one).
The File Transfer Protocol (FTP) is a special application used for uploading and downloading files to and from the Internet.
The Transmission Control Protocol/Internet Protocol (TCP/IP) is the language (network protocol) used by computers to talk to each other over the Net. TCP/IP has also become a common protocol for LANs. Regardless of which operating system or software is being used, your commands travel through the Internet in TCP/IP format. The services of the Internet and the World Wide Web could not be provided without TCP/IP.
Each machine on a network is given a unique 32-bit address. These addresses are normally expressed in decimal values of 4 bytes, separated with periods; for example, 127.0.0.1. Without a unique address, there would be conflicts and chaos. This is the same concept as the hardware addresses discussed in Chapter 10, Lesson 2: Configuring Expansion Cards, except that it is a software address. It designates the location of its assigned device (usually a NIC) on the network.
Internet service providers furnish the connection between dial-up (modem) users and the Internet. While some are big names with millions of users, there are many more that serve local areas with both dial-up and hosting plans.
As mentioned, the Uniform Resource Locator is the Web's address system. To access a Web site, the user must enter the designated URL on the network. Each URL begins with the character sequence "http://". The letters "HTTP" are an acronym for the Hypertext Transfer Protocol, which identifies the Web site as an address. The rest of the URL is the name of the site. For example Microsoft's URL is http://www.microsoft.com. (Because it is universal, it is seldom necessary to first type the characters "http://" when typing a URL in a search engine; most engines take it for granted.)
An Internet domain is a site with a common general interest or purpose, often run by a single firm or institution. The domain suffix gives a general idea of the site's purpose: .com, for businesses, or .edu, for educational institutions. The following table lists common Internet domains.
|.net||Networks (the backbone of the Internet)|
|.gov||US Government nonmilitary institutions|
|.mil||US Government armed services|
|.xx||Two-letter country code.|
A domain-name server is a computer that matches IP addresses with domain names. The domain name makes it possible for you to use the easy-to-remember domain name BigCompany.com without having to memorize the string of numbers in the IP address.
These days, many computer professionals spend a lot of their time getting clients online.
The first thing you need to do to get a client connected is to make sure they have a service provider (we're assuming your client has a computer and a modem). Most people connect to the Internet using independent ISPs that provide local community-based service to Internet users, but popular national ISPs such as The Microsoft Network (MSN) are useful if you travel because many of them have 800 numbers for dial-up access, or many local numbers throughout the country. Local ISPs are great for customers who are looking for a cost-effective company that offers local (including technical) support.
You also need to consider which browser(s) to use. Most ISPs (especially the local ones) provide only the connection or gateway to the Internet. Others provide their own browser software package. Most ISPs allow you to use your choice of browsers. Some local and national ISPs provide a startup CD that includes their recommended browser, as well as FTP tools and other Internet utilities. From time to time, Web surfers will encounter pages that work only with a specific browser. In this case it might be necessary to install both browsers.
The following points summarize the main elements of this lesson: