Chapter 2 - Connecting Network Components

On This Page

	The Case Study
	Lesson 1: Network Cablingthe Physical Media
	Lesson 2: Wireless Network Communications
	Lesson 3: Network Adapter Cards
	Chapter 2 Review

The Case Study

In the case study for this unit you will evaluate the recommendations for a cabling scheme for your company's new office building.

The Troubleshooter

You will get a chance to troubleshoot a problem that arises when new client computers are added to an existing network.

The LAN Planner

The LAN Planner contains questions you need to ask when selecting cabling and network adapter cards for your network.

Top of page

Lesson 1: Network Cablingthe Physical Media

What This Lesson Does

This lesson presents the essential LAN cabling concepts.

You will learn about the major cable types including their construction, features, and operation. This information will help you determine what type of cabling is best for any networking situation.

Objectives

By the end of this lesson, you will be able to:

Estimated lesson time 50 minutes

Primary Cable Types

The vast majority of networks today are connected by some sort of wire or cabling, which act as the network transmission medium carrying signals between computers. There is a variety of cable that can meet the varying needs and sizes of networks, from small to large.

Cabling can be confusing. Belden, a leading cable manufacturer, publishes a catalog that lists more than 2,200 types of cabling. Fortunately, only three major groups of cabling connect the majority of networks:

The next part of this lesson will describe the features and components of these three major cable types. Understanding their differences will help you determine when to use each type of cabling.

Coaxial

At one time, coaxial cable was the most widely used network cabling. There were a couple of reasons for coaxial's wide usage. Coaxial was relatively inexpensive, and it was light, flexible, and easy to work with. It was so popular that it became a safe, easily supported installation.

In its simplest form, coaxial consists of a core made of solid copper surrounded by insulation, a braided metal shielding, and an outer cover. One layer of foil insulation and one layer of braided metal shielding is referred to as dual shielded. However, quad shielding is available for environments that are subject to higher interference. Quad shielding consists of two layers of foil insulation and two layers of braided metal shielding.

Figure 2.1: Coaxial cable showing various layers
See full-sized image.

Shielding refers to the woven or stranded metal mesh (or other material) that surrounds some types of cabling. Shielding protects transmitted data by absorbing stray electronic signals, called noise, so that they do not get onto the cable and distort the data.

The core of a coaxial cable carries the electronic signals which make up the data. This core wire can be either solid or stranded. If the core is solid, it is usually copper.

The core is surrounded by a dielectric insulating layer which separates it from the wire mesh. The braided wire mesh acts as a ground and protects the core from electrical noise and crosstalk. Crosstalk is signal overflow from an adjacent wire.

The conducting core and the wire mesh must always be separated from each other. If they touch, the cable will experience a short, and noise or stray signals on the mesh will flow onto the copper wire. This will destroy the data.

The entire cable is surrounded by a non-conducting outer shield, usually made of rubber, Teflon, or plastic.

Coaxial cable is more resistant to interference and attenuation than twisted-pair cabling. Attenuation is the loss of signal strength which begins to occur as the signal travels further along a copper cable.

Figure 2.2: Attenuation causes signals to deteriorate
See full-sized image.

The stranded, protective sleeve can absorb stray electronic signals so they do not affect data being sent over the inner copper cable. For this reason, coaxial is a good choice for longer distances and for reliably supporting higher data rates with less sophisticated equipment.

Types of Coaxial Cable

There are two types of coaxial cable:

What type you select depends on the needs of your particular network.

Thinnet

Thinnet is a flexible coaxial cable about .25 inch thick. Because this type of coaxial is flexible and easy to work with, it can be used in almost any type of network installation. Networks that use thinnet have the cable connected directly to a computer's network adapter card.

Figure 2.3: Close-up view of thinnet cable showing where it connects to a computer
See full-sized image.

Thinnet coaxial cable can carry a signal up to approximately 185 meters (about 607 feet) before the signal starts to suffer from attenuation.

Cable manufacturers have agreed upon certain designations for different types of cable. Thinnet is included in a group referred to as the RG-58 family and has a 50-ohm impedance. Impedance is the resistance, measured in ohms, to alternating current flowing in a wire. The main difference in the RG-58 family is the center core of copper. It can either be a stranded wire or solid copper core.

Figure 2.4: RG-58 coaxial showing stranded wire and the solid copper cores
See full-sized image.

Thicknet

Thicknet is a relatively rigid coaxial cable about 0.5 inch in diameter. It is sometimes referred to as Standard Ethernet because it was the first type of cable used with the popular network architecture Ethernet. The copper core is thicker than a thinnet core.

Figure 2.5: Thicknet cable has a thicker core than thinnet
See full-sized image.

The thicker the copper core, the farther the cable can carry signals. This means that thicknet can carry signals farther than thinnet. Thicknet can carry a signal for 500 meters (about 1,640 feet). Therefore, because of thicknet's ability to support data transfer over longer distances, it is sometimes used as a backbone to connect several smaller thinnet-based networks.

A device called a transceiver connects the thinnet coaxial to the larger thicknet coaxial cable.

Figure 2.6: Thicknet cable transceiver with detail of a vampire tap piercing the core
See full-sized image.

A transceiver designed for thicknet Ethernet includes a connector known as a vampire tap or a piercing tap to make the actual physical connection to thicknet core. This connector is pierced through the insulating layer and makes direct contact with the conducting core. Connection from the transceiver to the network adapter card is made using a transceiver cable (drop cable) to connect to the attachment unit interface (AUI) port connector on the card. An AUI port connector for thicknet is also known as a Digital Intel Xerox (DIX) connector after the three companies that developed it and its related standards, or as a DB-15 connector.

Thinnet vs. Thicknet

As a general rule, the thicker the cable, the more difficult it is to work with. Thin cable is flexible, easy to install, and relatively inexpensive. Thick cable does not bend easily and is, therefore, harder to install. This is a consideration when an installation calls for pulling cable through tight spaces such as conduits and troughs. Thick cable is more expensive than thin cable, but will carry a signal farther.

Coaxial Connection Hardware

Both thinnet and thicknet use connection components, known as a BNC (British Naval Connector), to make the connections between the cable and the computers. There are several important components in the BNC family, including the following:

•	The BNC cable connector The BNC cable connector is either soldered or crimped to the end of a cable. Figure 2.7: BNC cable connector
•	The BNC T connector This connector joins the network interface card in the computer to the network cable. Figure 2.8: BNC T connector
•	The BNC barrel connector This connector is used to join two lengths of thinnet cable to make one longer length. Figure 2.9: BNC barrel connector
•	The BNC terminator A BNC terminator closes each end of the bus cable to absorb stray signals. Without BNC terminators, a bus network will not function. Figure 2.10: BNC terminator

Coaxial Cable Grades and Fire Codes

The type of cable grade that you should use depends on where the cables will be in your office. Coaxial cables come in two grades:

Polyvinyl chloride (PVC) is a type of plastic used to construct the insulation and the cable jacket for most types of coaxial cable. PVC coaxial cable is flexible and can be easily routed in the exposed areas of an office. However, when it burns, it gives off poisonous gases.

A plenum is the short space in many buildings between the false ceiling and the floor above; it is used to circulate warm and cold air through the building. Fire codes are very specific on the type of wiring that can be routed through this area, because any smoke or gas in the plenum will eventually become part of the air breathed by everyone in the building.

Figure 2.11: Plenum grade cabling is required by fire code in the plenum
See full-sized image.

Plenum cabling refers to coaxial that contains special materials in its insulation and cable jacket. These materials are certified to be fire resistant and produce a minimum amount of smoke. This reduces poisonous chemical fumes. Plenum cable can be used in the plenum area and in vertical runs (for example, in a wall) without conduit. However, plenum cabling is more expensive and less flexible than PVC cable.

Note: Please consult your local fire and electrical codes for specific regulations about running networking cable in your office.

Coaxial Considerations

Consider these coaxial capabilities when making a decision on the type of cabling to use.

Use coaxial cable if you need:

Q & A

This is a two-part exercise. In the first part, supply the missing word(s) to complete the sentence. In the second part, identify the types of cable shown.

Answers

Identify the following components.

Answers

Twisted-Pair Cable

In its simplest form, twisted-pair cable consists of two insulated strands of copper wire twisted around each other. There are two types of twisted-pair cable: unshielded twisted-pair (UTP) and shielded twisted-pair (STP).

Figure 2.12: Unshielded twisted-pair and shielded twisted-pair cables
See full-sized image.

A number of twisted-pair wires are often grouped together and enclosed in a protective sheath to form a cable. The actual number of pairs in a cable varies. The twisting cancels out electrical noise from adjacent pairs and from other sources such as motors, relays, and transformers.

Unshielded Twisted-Pair (UTP)

UTP using the 10BaseT specification is the most popular type of twisted-pair cable and is fast becoming the most popular LAN cabling. The maximum cable length segment is 100 meters or about 328 feet.

UTP consists of two insulated copper wires. Depending on the particular purpose, there are UTP specifications which govern how many twists are permitted per foot of cable. In the North American continent, UTP cable is the most commonly used cable for existing telephone systems and is already installed in many office buildings.

Figure 2.13: UTP cable
See full-sized image.

UTP is specified in the Electronic Industries Association and the Telecommunications Industries Association (EIA/TIA) 568 Commercial Building Wiring Standard. EIA/TIA 568 used UTP in creating standards that apply to a variety of building and wiring situations and ensure consistency of products for customers. These standards include five categories of UTP:

Most telephone systems use a type of UTP. In fact, one reason why UTP is so popular is because many buildings are prewired for twisted-pair telephone systems. As part of this prewiring, extra UTP is often installed to meet future cabling needs. If preinstalled twisted-pair cable is of sufficient grade to support data transmission, it can be used in a computer network. Caution is required, however, because common telephone wire may not have the twisting and other electrical characteristics required for clean, secure, computer data transmission.

One potential problem with all types of cabling is crosstalk. You may remember that crosstalk is defined as signals from one line getting mixed with signals from another line. UTP is particularly susceptible to crosstalk. Shielding is used to reduce crosstalk.

Figure 2.14: Crosstalk occurs when signals from one line mix into another line
See full-sized image.

Shielded Twisted-Pair (STP)

STP uses a woven copper braid jacket which is a higher-quality, more protective jacket than UTP has. STP also uses a foil wrap between and around the wire pairs, and internal twisting of the pairs. This gives STP excellent shielding to protect the transmitted data from outside interference.

What this means is that STP is less susceptible to electrical interference and supports higher transmission rates over longer distances than UTP.

Figure 2.15: STP cable
See full-sized image.

Twisted-Pair Cabling Components

•

Connection hardware Twisted-pair uses RJ-45 telephone connectors to connect to a computer. This is similar to the RJ-11 telephone connector. Although they look alike at first glance, there are crucial differences between them. The RJ-45 is slightly larger, and will not fit into the RJ-11 telephone jack. The RJ-45 houses eight cable connections, while the RJ-11 only houses four. Figure 2.16: RJ-45 connector and jack See full-sized image.

Several components are available to help organize large UTP installations and make them easier to work with. These include:

•	Distribution racks and rack shelves Distribution racks and rack shelves can create more room for cables where there isn't much floor space. They are a good way to centralized and organize a network that has a lot of connections.
•	Expandable patch panels These come in various versions that support up to 96 ports and transmission speeds of 100 Mbps.
•	Jack couplers These single or double RJ-45 jacks snap into patch panels and wall plates and support data rates to 100 Mbps.
•	Wall plates These support two or more couplers. Figure 2.17: Various twisted-pair cabling components See full-sized image.

Twisted-Pair Considerations

Use twisted-pair cable if:

Do not use twisted-pair cable if:

Q & A

Fill in the blanks in the following sentences.

Answers

Fiber-Optic Cable

In fiber-optic cable, optical fibers carry digital data signals in the form of modulated pulses of light. This is a relatively safe way to send data because no electrical impulses are carried over the fiber-optic cable. This means that fiber-optic cable cannot be tapped and the data stolen, which is possible with any copper-based cable carrying data in the form of electronic signals.

Fiber-optic cable is good for very high-speed, high-capacity data transmission because of the lack of attenuation and the purity of the signal.

Fiber-Optic Composition

Optical fibers consists of an extremely thin cylinder of glass, called the core, surrounded by a concentric layer of glass, known as the cladding. The fibers are sometimes made of plastic. Plastic is easier to install, but cannot carry the light pulses as far as glass.

Each glass strand passes signals in only one direction, so a cable consists of two strands in separate jackets. One strand transmits and one receives. A reinforcing layer of plastic surrounds each glass strand while kevlar fibers provide strength. See Figure 2.18 for an example of kevlar fibers. The kevlar fibers in the fiber-optic connector are placed between the two cables, which are encased in plastic.

Figure 2.18: Fiber-optic cable
See full-sized image.

Fiber-optic cable transmissions are not subject to electrical interference and are extremely fast (currently transmitting about 100 Mbps with demonstrated rates of up to > 1Gbps). They can carry a signalthe light pulsefor many miles.

Fiber-Optic Considerations

Use fiber-optic cable if you:

Do not use fiber-optic cable if you:

Q & A

Fill in the blanks in the following sentences.

Answers

Signal Transmission

Two techniques can be used to transmit the encoded signals over cablebaseband and broadband transmission.

Baseband Transmission

Baseband systems use digital signaling over a single frequency. Signals flow in the form of discrete pulses of electricity or light. With baseband transmission, the entire communication channel capacity is used to transmit a single data signal. The digital signal uses the complete bandwidth of the cable, which constitutes a single channel. A cable's total bandwidth is the difference between the highest and lowest frequencies that are carried over that cable.

Each device on a baseband network transmits bidirectionally, and some can transmit and receive at the same time.

Figure 2.19: Baseband transmission showing bidirectional digital wave
See full-sized image.

As the signal travels along the network cable, it gradually decreases in strength and can become distorted. If the cable length is too long, the result is a signal that is weak or distorted. The received signal may be unrecognizable or misinterpreted.

As a safeguard, baseband systems sometimes use repeaters to receive an incoming signal and retransmit it at its original strength and definition to increase the practical length of a cable.

Broadband Transmission

Broadband systems use analog signaling and a range of frequencies. With analog transmission, the signals are continuous and nondiscrete. Signals flow across the physical medium in the form of electromagnetic or optical waves. With broadband transmission, signal flow is unidirectional.

Figure 2.20: Broadband transmission showing unidirectional analog wave
See full-sized image.

If sufficient total bandwidth is available, multiple analog transmission systems such as cable television and network transmissions can be supported simultaneously on the same cable.

Each transmission system is allocated a part of the total bandwidth. All devices associated with a given transmission system, such as all computers using a LAN cable, must then be tuned so that they use only the frequencies that are within the allocated range.

While baseband systems use repeaters, broadband systems use amplifiers to regenerate analog signals at their original strength.

Because broadband transmission signal flow is unidirectional, there must be two paths for data flow in order for a signal to reach all devices. There are two common ways to do this:

Q & A

Fill in the blanks in the following sentences.

Answers

The IBM Cabling System

IBM developed its own cabling system, complete with its own numbers, standards, specifications, and designations. Many of these parameters, however, are similar to non-IBM specifications.

The IBM cabling system was introduced in 1984 in order to define these components:

The IBM cabling component that is unique is the IBM connector. The IBM connector is different from standard BNC or other connectors because it is neither male nor female but hermaphroditic in that two of them can be connected to each other. These IBM connectors required special face plates and distribution panels to accommodate their unique shape.

The IBM cabling system classifies cable as types. For example, Category 3 cable (voice grade UTP) is referred to by the IBM system as Type 3.

The cable definitions specify which cable would be appropriate for a given application or environment. The wire indicated in the system conforms to American Wire Gauge (AWG) standards.

AWGthe Standard Cable Measurement

In cable measurements you will often see the word gauge followed by the initials AWG. AWG is a measurement system for wire that specifies its thickness. As the thickness of the wire increases, the AWG number decreases. Telephone wire is often used as a reference point. It has a thickness of 22 AWG. A wire of 14 AWG would be thicker than telephone wire, and 26 AWG would be thinner than telephone wire.

IBM Cabling System

Selecting Cabling

To determine which cabling is the best for a particular site you need to answer the following questions:

The more the cable protects against internal and external electrical noise, the farther and faster the cable will carry a clear signal. However, the better the speed, clarity, and security, the higher the cabling cost.

Cabling Considerations

As with most network components, there are trade-offs with the type of cable you purchase. If you work for a large organization and choose the least expensive cable, the accountants may initially be pleased, but you may soon notice that the LAN is inadequate in both transmission speed and data security.

Cabling depends on the needs of a particular site. The cabling you purchase to set up a LAN for a small business has different requirements than those of a larger organization, such as a major banking institution.

Some of the considerations which affect cabling price and performance include:

Cable Comparison Summary

* Usable cable length can vary with specific network installations. As technology improves, usable cable length also increases.

** Transmission rates for specific cable types are beginning to blur. Again, technological advances are producing copper wire that can carry a signal faster than has ever been considered possible.

Summary

Choosing the appropriate network cable depends on several factors including installation logistics, shielding, security requirements, transmission speed (in Mbps), and attenuation. There are three primary types of cable: coaxial, twisted-pair, and fiber-optic.

There are two types of coaxial cable, thinnet and thicknet. Both have a copper core surrounded by wire mesh that absorbs noise and crosstalk. Coaxial cable is a good choice for data transmission of long distances.

Twisted-pair cable is available both unshielded and shielded. Unshielded twisted-pair (UTP) is available in five categories of which Category 5 is the most popular for network installations. Shielded twisted-pair (STP) supports higher transmission rates over longer distances than UTP.

Fiber-optic cable is faster and more secure than copper wire cable, but it is relatively expensive and requires some expertise to install.

Broadband and baseband are two transmission techniques. Broadband uses analog signaling to transmit multiple simultaneous transmissions on the same cable. Baseband sends single channel, digital signals.

IBM has its own cabling system complete with its own types. IBM Type 3 cabling, for example, is a voice grade, shielded twisted-pair cable otherwise known as STP.

Your Next Step

Cables are the most commonly used way to transmit data between computers. However, the wireless environment is an emerging collection of topologies that may someday do away with the need for physical connections. You will learn about the basics of wireless communication technology in the next lesson.

Top of page

Lesson 2: Wireless Network Communications

What This Lesson Does

This lesson presents an overview of wireless network technology. In this lesson you will learn the differentiation between the various wireless environments and learn about the major wireless transmission and receiving components.

Objectives

By the end of this lesson, you will be able to:

Estimated lesson time 25 minutes

The Wireless Environment

The wireless environment is emerging as a viable networking option. As the technology matures, vendors will be offering more products at attractive prices which, in turn, will mean increased sales and demand. As demand increases, the wireless environment will grow and improve.

The phrase wireless environment is misleading because it implies a network completely free of cabling. In most cases, this is not true. Most wireless networks actually consist of wireless components communicating with a network that uses cables in a mixed component network called a hybrid.

Wireless Capabilities

The idea of wireless networks is attracting attention because wireless components can:

Uses for Wireless

Difficulty implementing cable is a factor which will continue to push wireless environments toward greater acceptance. Wireless can be especially useful for networking:

Types of Wireless Networks

Wireless networks can be divided into three categories based on their technology:

The primary difference between these categories is the transmission facilities. Wireless LANs and extended LANs use transmitters and receivers owned by the company in which the network operates. Mobile computing uses public carriers such as AT&T, MCI, Sprint and the local telephone companies and their public services, to transmit and receive signals.

Local Area Networks

A typical wireless network looks and acts almost like a cabled network except for the media. A wireless network adapter card with a transceiver is installed into each computer, and users communicate with the network just as if they were at cabled computers.

Access Points

The transceiver, sometimes called an access point, broadcasts and receives signals to and from the surrounding computers and passes data back and forth between the wireless computers and the cabled network.

These wireless LANs use small wall-mounted transceivers to connect to the wired network. The transceivers establish radio contact with portable networked devices. This is not a true wireless LAN because it uses a wall-mounted transceiver to connect to a standard cabled LAN.

Figure 2.21: Wireless portable computer connecting to a cabled network access point
See full-sized image.

Transmission Techniques

Wireless LANs use four techniques for transmitting data:

Infrared

All infrared wireless networks operate by using an infrared light beam to carry the data between devices. These systems need to generate very strong signals because weak transmission signals are susceptible to light from sources such as windows.

This method can transmit signals at high rates because of infrared light's high bandwidth. An infrared network can normally broadcast at 10 Mbps.

There are four types of infrared networks:

•	Line-of-sight networks As the name implies, this version of infrared transmits only if the transmitter and receiver have a clear line of sight between them.
•	Scatter infrared networks This technology broadcasts transmissions so they bounce off walls and ceilings and eventually hit the receiver. This has an effective area limited to about 100 feet and has a slow signal because of all of the signal bouncing.
•	Reflective networks In this version of infrared networks, optical transceivers situated near the computers transmit toward a common location which redirects the transmissions to the appropriate computer.
•	Broadband optical telepoint This version of infrared wireless LAN provides broadband services. This wireless network is capable of handling high quality multimedia requirements that can match those provided by a cabled network. Figure 2.22: Wireless portable computer using an infrared light beam to print See full-sized image.

While the speed of infrared and its conveniences are generating interest, infrared has difficulty transmitting distances greater than 100 feet. It is also subject to interference from the strong ambient light found in most business environments.

Laser

Laser technology is similar to infrared technology in that it requires a direct line of sight, and any person or thing that breaks the laser beam will block the transmission.

Narrow-Band (Single-Frequency) Radio

This approach is similar to broadcasting from a radio station. The user tunes both the transmitter and the receiver to a certain frequency. This does not require line of sight focusing because the broadcast range is 5000 meters square. However, because the signal is high frequency, it cannot go through steel or load-bearing walls.

Customers subscribe to this method from a service provider such as Motorola. The service provider handles all of the Federal Communications Commission (FCC) licensing requirements. This method is relatively slow; transmission is in the 4.8 Mbps range.

Spread-Spectrum Radio

Spread-spectrum radio broadcasts signals over a range of frequencies. This helps it avoid narrow-band communication problems.

The available frequencies are divided into channels or hops. The spread-spectrum adapters tune in to a specific hop for a predetermined length of time and then switch to a different hop. A hopping sequence determines the timing. The computers in the network are all synchronized to the hop timing. This type of signaling provides some "built-in" security in that the frequency hopping algorithm of the network would have to be "known" in order to tap into the data stream.

To further enhance secuity and to keep unauthorized users from listening in to the broadcast, the sender and the receiver can encrypt (code) the transmission.

The typical speed of 250 Kbps (kilobits per second) makes this method much slower than the others. However, some implementations of spread-spectrum radio can offer transmission speeds of 4 Mbps over distances of two miles outdoors and > 800 feet indoors.

This is one area where the technology actually provides for a truly wireless network. For example, two or more computers equipped with Xircom CreditCard Netwave Adapters and an operating system such as Microsoft Windows 95 or Microsoft Windows NT can act as a peer-to-peer network with no connecting cables. However, if you have an existing Windows NT Server-based network, you can tie the above wireless network into it by adding a Netwave Access Point to one of the computers on the Windows NT Server-based network.

Point-to-Point Transmission

This method of data communication does not fall neatly into the present definitions of networking. It uses a point-to-point technology that transfers data from one computer to another as opposed to communicating among several computers and peripherals. However, additional components such as single and host transceivers are available. These can be implemented in either stand-alone computers or computers already on a network to form a wireless data transfer network.

This technology involves wireless serial data transfer that:

This type of system will transfer data between computers, and between computers and other devices such as printers or bar code readers.

Extended Local Area Networks

Other types of wireless components are able to do jobs in the extended LAN environment similar to their cabled counterparts. A wireless LAN bridge, for example, can connect networks up to three miles apart.

Multipoint Wireless Connectivity

A component called a wireless bridge offers an easy way to link buildings without using cable. As a foot bridge provides a path between two points for people, a wireless bridge provides a data path between two buildings. The AIRLAN/Bridge Plus, for example, uses spread-spectrum radio technology to create a wireless backbone to tie locations together over distances beyond the reach of LANs. Depending on conditions, this can be up to three miles.

The cost of such a component may be justified because it eliminates the expense of leased lines.

Figure 2.23: Wireless bridge connecting two LANs
See full-sized image.

The Long-Range Wireless Bridge

If the wireless bridge will not reach far enough, an organization might consider a long-range wireless bridge. These also use spread-spectrum radio technology to provide both Ethernet and Token Ring bridging for up to 25 miles.

As with the original wireless bridge, the cost of the long range bridge may be justified because it eliminates the need for T1 line or microwave connections. T1 is the standard digital line service and provides transmission rates of 1.544 Mbps. It can carry both voice and data.

Q & A

Fill in the blanks in the following sentences.

Answers

Mobile Computing

Wireless, mobile networks involve telephone carriers and public services to transmit and receive signals using:

Traveling employees can use this technology with portable computers or PDAs (Personal Digital Assistants) to exchange e-mail, files, or other information.

While this form of communication offers conveniences, it is slow. Transmission rates range from 8 Kbps to 19.2 Kbps. The rates get even slower when error correction is included.

Mobile computing incorporates wireless adapters that use cellular telephone technology to connect portable computers with the cabled network. Portable computers use small antennas to communicate with radio towers in the surrounding area. Satellites in near-earth orbit pick up low-powered signals from portable and mobile networked devices.

Packet-Radio Communication

This system breaks a transmission into packets, similar to other network packets, that include:

The packets are uplinked to a satellite which broadcasts them. Only devices with the correct address can receive the broadcast packets.

Cellular Networks

Cellular Digital Packet Data (CDPD) uses the same technology and some of the same systems as cellular telephones. It offers computer data transmissions over existing analog voice networks between voice calls when the system is not busy. This is very fast technology that only suffers subsecond delays, which makes it reliable enough for real-time transmission.

As in other wireless networks, there must be a way to tie in to the existing cabled network. Nortel out of Mississauga, Ontario, Canada is one company that makes an Ethernet interface unit (EIU) that can provide this connection.

Satellite Stations

Microwave systems are good for interconnecting buildings in small, short-distance systems such as those on a campus or in an industrial park.

Microwave is currently the most widely used long distance transmission method in the United States. It is excellent for communicating between two line of sight points such as:

A microwave system consists of:

Q & A

Fill in the blanks in the following sentences.

Answers

Summary

Wireless networking is emerging as a transmission method for local area networks, extended local area networks, and mobile computing. A typical wireless network acts like a cabled network. A wireless network adapter card with a transceiver is installed into each computer, and users communicate with the network just as if they were at cabled computers.

Wireless networks use infrared, laser, narrow-band radio, and spread-spectrum radio transmission techniques. An additional type of technology is point-to-point. It transfers data from one computer to another as opposed to communicating among several computers and peripherals.

LANs can be extended using a component called a wireless bridge. It provides a way to link buildings separated by 25 miles or less without using cable.

Mobile computing involves telephone carriers and public services to transmit and receive signals using packet-radio communication, cellular networks, and satellite stations.

Your Next Step

Now that you have been introduced to the technology and the components that connect computers to each other, you are ready to learn about the component that acts as the point-of-data entry and exit between the computer and the networkthe network adapter card. Knowing the key features of network adapter cards will help you select the appropriate one for your site.

Top of page

Lesson 3: Network Adapter Cards

What This Lesson Does

This lesson introduces the basic features and functions of network adapter cards and how they can affect network performance. It describes the different cable media connector types as well as the configuration options for a network adapter card.

This lesson provides you with all of the information you need to select the right network adapter cards for your network.

Objectives

By the end of this lesson, you will be able to:

Estimated lesson time 85 minutes

The Role of the Network Adapter Card

Network adapter cards act as the physical interface or connection between the computer and the network cable. The cards are installed in an expansion slot in each computer and server on the network.

After the card has been installed, the network cable is attached to the card's port to make the actual physical connection between the computer and the rest of the network.

Figure 2.24: Sample network adapter card
See full-sized image.

The role of the network adapter card is to:

The network adapter card also receives incoming data from the cable and translates it into bytes the computer's CPU can understand.

Stated at a more technical level, the network adapter card contains the hardware and firmware (software routines stored in read-only memory) programming that implements the Logical Link Control and Media Access Control functions (in the Data Link layer function of the OSI model).

Preparing the Data

Before data can be sent over the network, the network adapter card must change it from a form the computer can understand to another form which can travel over a network cable.

Data moves through a computer along paths called busses. These are actually several data paths placed side by side. Because several paths are side by side (parallel), data can move along them in groups instead of a single (serial) data stream.

Older busses, such as those used in the original IBM personal computer, were known as 8-bit busses because they could move data 8 bits at a time. The IBM PC/AT used a 16-bit bus, which means it could move data 16 bits at a time. Many computers use 32-bit buses. When data travels on a computer's bus, it is said to be traveling in parallel because the 16 or 32 bits are moving along side by side. Think of a 16-bit bus as being a 16-lane highway with 16 cars moving side by side (moving in parallel), each carrying one bit of data.

On the network cable, data must travel in a single bit stream. When data travels on a network cable it is said to be traveling as a serial transmission because one bit follows another. In other words, the cable is a one-lane highway. The data on these highways always travel in one direction. The computer is either sending or receiving data.

The network adapter card takes data traveling in parallel as a group and restructures it so that it will flow through the 1-bit wide serial path of the network cable. This is accomplished through the translation of the computer's digital signals into electrical and optical signals that can travel on the network's cables. The component responsible for this is the transceiver (transmitter/receiver).

Figure 2.25: Parallel data stream converted to a serial data stream
See full-sized image.

Network Address

In addition to transforming data, the network adapter card also has to indicate its location, or address, to the rest of the network to distinguish it from all of the other cards on the network.

Network addresses are determined by the IEEE (Institute of Electrical and Electronics Engineers, Inc.) committee. The committee assigns blocks of addresses to each network adapter card manufacturer. The manufacturers hardwire these addresses into chips on the card by a process known as burning the address into the card. With this process each card, and therefore each computer, has a unique address on a network.

The network adapter card also participates in several other functions in taking data from the computer and getting it ready for the network cable.

Data can often move faster than the network adapter card can handle it, so the data is sent to the card's buffer (RAM) where it is held temporarily during both the transmission and reception of data.

Sending and Controlling Data

Before the sending network adapter card actually sends data over the network, it carries on an electronic dialog with the receiving card so that both cards agree on the following:

If a newer, faster, more sophisticated card needs to communicate with an older, slower model, both cards need to find a common transmission speed each can accommodate. Some newer network adapter cards incorporate circuitry that allows the card to adjust to the rate of the slower card.

Each card signals to the other indicating its parameters and accepting or adjusting to the other card's parameters. When all of the communication details have been determined, the two cards begin sending and receiving data.

Q & A

For the following sentences, circle True if the statement is true or False if the statement is false.

Answers

Configuration Options and Settings

Network adapter cards often have configurable options that must be set for the network adapter card to function properly. Examples include:

Note: Sometimes it is possible to specify network adapter card settings in software, but these settings commonly must match jumper or dual inline package (DIP) switch settings configured on the network adapter card. See the network card product documentation for DIP switch settings. (*Note: Many newer network adapter cards use the Plug-and-Play (PnP) technology, which makes manually setting the network adapter card options obsolete).

Figure 2.26: Older network adapter card with DIP switches

Interrupt (IRQ)

Interrupt request lines are hardware lines over which devices such as input/output ports, the keyboard, disk drives, and network adapter cards can send interrupts or requests for service to the computer's microprocessor.

Interrupt request lines are built into the computer's internal hardware and are assigned different levels of priority so that the microprocessor can determine the relative importance of incoming service requests.

When the network adapter card sends a request to the computer, it uses an interruptan electronic signal sent to the computer's CPU. Each device in the computer must use a different interrupt request line or interrupt (IRQ). The interrupt line is specified when the device is configured. See the examples in the following table.

In most cases, IRQ3 or IRQ5 can be used for the network adapter card. IRQ5 is the recommended setting if it is available, and it is the default for most systems. Use a system diagnostic tool such as Microsoft Diagnostic (MSD) to determine which IRQs are already being used.

If neither IRQ3 nor IRQ5 is available, you can refer to the following table for alternative values to use. The IRQs listed as available usually can be used for a network adapter card. If the computer does not have the hardware device listed for a specific IRQ, that IRQ should be available.

Base I/O Port

The base input/output (I/O) port specifies a channel through which information flows between the computer's hardware (such as the network adapter card) and its CPU. The port appears to the CPU as an address.

Each hardware device in a system must have a different base I/O port number. The port numbers (in hexadecimal format) in the following table are usually available to assign to a network adapter card unless they are already in use. Those with a device listed next to them are addresses commonly used for the devices. Check the computer documentation to determine which addresses are already in use.

Base I/O Port Settings

Base Memory Address

The base memory address identifies a location in a computer's memory (RAM). This location is used by the network adapter card as a buffer area to store the incoming and outgoing data frames. This setting is sometimes called the RAM start address.

Often, the base memory address for a network adapter card is D8000. (For some network adapter cards, the final "0" is dropped from the base memory addressfor example, D8000 would become D800.) It is necessary to select a base memory address that is not already being used by another device.

Note: Some network adapter cards do not have a setting for the base memory address because they do not use any system RAM addresses.

Some network adapter cards contain a setting that allows you to specify the amount of memory to be set aside for storing data frames. For example, for some cards you can specify either 16K or 32K of memory. Specifying more memory provides better network performance but leaves less memory available for other uses.

Selecting the Transceiver

The network adapter card may have other settings that need to be defined during configuration. For example, some cards come with an external and an on-board transceiver. In this case, you would have to determine which transceiver you want to use and then make the appropriate choice on your card.

The choice on the card is usually done with jumpers. Jumpers are small connectors that tie two pins together to determine which circuits the card will use.

Figure 2.27: Network adapter card showing external and on-board transceivers
See full-sized image.

Q & A

Fill in the blanks in the following sentences.

Answers

Network Adapter Card Compatibility

To ensure compatibility between the computer and the network, the network adapter card must:

A card that would work in an Apple computer communicating in a bus network, for example, would not work in an IBM computer in a ring environment. The ring requires cards that are physically different from those used in a bus, and Apple uses a different type of network communication method.

Data Bus Architecture

In the personal computer environment, there are four types of computer bus architectures: ISA, EISA, Micro Channel, and PCI. Each type of bus is physically different from the others. It is essential that the network adapter card and the bus match.

•	ISA (Industry Standard Architecture) ISA is the architecture used in the IBM PC, XT and AT computers and all of their clones. It allows various adapters to be added to the system by means of inserting plug-in cards in expansion slots. ISA was expanded from an 8-bit path to a 16-bit path in 1984 when IBM introduced the IBM PC/AT. ISA refers to the expansion slot itself (an 8-bit slot or a 16-bit slot). The 8-bit slots are shorter than the 16-bit slots which actually consist of two slots, one behind the other. An 8-bit card could fit into a 16-bit slot, but a 16-bit card could not fit into an 8-bit slot. ISA was the standard personal computer architecture until Compaq and several other companies developed the EISA bus.
•	EISA (Extended Industry Standard Architecture) This is the bus standard introduced in 1988 by a consortium of nine computer-industry companies: AST Research, Inc., Compaq, Epson, Hewlett-Packard, NEC, Olivetti, Tandy, Wyse Technology, and Zenith. EISA offers a 32-bit data path and maintains compatibility with ISA while providing for additional features introduced by IBM in its Micro Channel Architecture bus.
•	Micro Channel Architecture IBM introduced this standard in 1988 as part of its PS/2 roll out. Micro Channel Architecture is electrically and physically incompatible with the ISA bus. Unlike the ISA bus, the Micro Channel functions as either a 16-bit or a 32-bit bus and can be driven independently by multiple bus master processors.
•	PCI (peripheral component interconnect) This is a 32-bit local-bus used in most Pentium computers and in the Apple Power Macintosh. The current PCI bus architecture meets most of the requirements for providing Plug and Play functionality. Plug and Play is both a design philosophy and a set of personal computer architecture specifications. The goal of Plug and Play is to enable changes to a personal computer configuration with no intervention by the user. The installation of any device should be a simple, fail-safe operation. Microsoft Windows 95 is a Plug and Play-compliant operating system. Figure 2.28: ISA, EISA, Micro Channel, and PCI network adapter cards See full-sized image.

Network Cabling and Connectors

The network adapter card performs three important functions in coordinating activities between the computer and the cabling:

To select the appropriate card for your network, you need to determine the type of cabling and cabling connectors it will have.

Each type of cable has different physical characteristics which the network adapter card must accommodate. Therefore, each card is built to accept a particular type of cable such as coaxial, twisted-pair, or fiber-optic.

Some network adapter cards have more than one interface connector. For example, it is not uncommon for a network adapter card to have both a thinnet and thicknet connector, or a twisted-pair and a thicknet connector.

If a card has more than one interface connector, make a selection either by setting jumpers or DIP switches on the card itself, or by using a software-selectable option. Consult the network adapter card documentation for information on how to properly configure the card. Three examples of typical connectors found on network adapter cards follow.

A thinnet network connection uses a coaxial BNC connector as shown in Figure 2.29.

Figure 2.29: Thinnet network connection for a coaxial BNC connector

A thicknet network connection uses a 15-pin attachment unit interface (AUI) cable to connect the 15-pin (DB-15) connector on the back of the network adapter card to an external transceiver. As you may recall from Lesson 1, "Network Cablingthe Physical Media," the external transceiver uses a vampire tap to connect into the thicknet cable.

Figure 2.30: Thicknet network connection for a 15-pin AUI
See full-sized image.

Caution: Be careful not to confuse a joystick port with an AUI network adapter port. They both look alike. You will need to be familiar with the specific hardware configuration in order to know whether the connector is for a network adapter card or a joystick.

An unshielded twisted-pair connection uses an RJ-45 connector, as shown in Figure 2.31. The RJ-45 connector is similar to an RJ-11 telephone connector but is larger in size because it has eight conductors; an RJ-11 only has 4 conductors.

Figure 2.31: RJ-45 connector

Some proprietary twisted-pair networking topologies use the RJ-11 connector. These topologies are sometimes referred to as pre-10BaseT. The RJ-11 connector is the same connector that is used on a telephone wire.

Q & A

Fill in the blanks for questions 1 through 4, and then identify the connectors illustrated for letters A through C.

Answers

Identify the Ethernet media connector types:

1.	Connector:_______________ See full-sized image.
2.	Connector:________________
3.	Connector:________________

Answers

Network Performance

Because of the effect it has on data transmission, the network adapter card has a great affect on the performance of the entire network. If the card is slow, data will not pass to and from the network quickly. On a bus network, where no one can use the network until the cable is clear, a slow card can increase wait times for all users.

After identifying the physical requirements of the cardthe type of connector it needs and the type of network in which it will be usedit will be necessary to consider several other factors which affect the capabilities of the card.

Although all network adapter cards conform to certain minimum standards and specifications, some cards feature enhancements which greatly improve server, client, and network performance.

You can speed up the movement of data through the card with the following:

Servers

Because they handle such high volumes of network traffic, servers should be equipped with the highest-performance cards possible.

Workstations

Workstations can use less expensive cards if their main network activities are limited to applications that do not generate great volumes of network traffic, such as word processing. Other applications, such as databases or engineering applic