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Section 4.1• Identify important network connectivity devices• Define hubs, switches, routers, and gateways• Describe modem functionality
Section 4.2• Differentiate between types of network cabling• Select cabling based on network needs
Section 4.3• Explain how a NIC functions• Understand NIC configurations
Section 4.4• Describe types of wireless network technologies• Explain risks of wireless networking
pp. 104-1094.1
Main Ideas
Nodes, hubs, switches, and routers are all connective devices that allow the transmission of communications traffic over networks. The traffic moves between nodes on the network. Modems are devices that allow remote nodes to access a network.
Key Terms
repeater
segment
bridge
switch
router
brouter
gateway
modulation
demodulation
Guide to Reading
Network Connectivity Devices
pp. 104-1094.1
Hubs
The hub is a central hardware component for many LANs. Hubs operate at the Physical Layer in the OSI model. Hubs contain multiple ports, and can connect to other hubs to expand the network.
Network Connectivity Devices
pp. 104-1094.1
RepeatersRepeaters operate at the Physical Layer of the OSI model. Essentially, repeaters allow smaller LANs to grow into larger LANs by moving transmissions from one network segmentsegment to another.
repeater A device that can be used to connect two cables and that boosts the signal before sending it along. (p. 105)
segment A section of the network that includes the cable and nodes that are connected to a device, such as a repeater, hub, or bridge. (p. 105)
Repeaters
Network Connectivity Devices
pp. 104-1094.1
BridgesBridges can be used to connect dissimilar network segments that use different methods of transferring data.
In today’s networks, it is uncommon to find bridges because switchesswitches provide “multibridge” capability.
bridge A device used to connect two network segments together. (p. 105)
switch A multiport bridge that allows several segments of a network to communicate with one another. (p. 106)
Bridges and Switches
Network Connectivity Devices
pp. 104-1094.1
Bridges and Switches
An important function of bridges and switches is to minimize collision of data packets by creating collision domains. Bridges and switches prevent the passing of collisions from one network segment to another.
Network Connectivity Devices
pp. 104-1094.1
Bridges are clever devices, but they are not as smart as routersrouters. Brides forward data from one network segment to another, routers:
• forward packets from one network to another
• determine the best route to use to deliver the data
router A network device used to connect networks of different types and that forwards packets from one network to another, even those separated by great distances. A router determines the best route to use to deliver the data. (p. 107)
Routers
Network Connectivity Devices
pp. 104-1094.1
BroutersBrouters are hybrids that combine the capabilities of bridges and routers. Like bridges, they work at the Data Link Layer to transfer and filter network traffic. Like routers, they also work at the Network Layer to route packets from one network to another.
brouter A network hybrid device that combines the capabilities of bridges and routers. (p. 108)
Routers
Network Connectivity Devices
pp. 104-1094.1
Gateways enable dissimilar networks to communicate. Gateways operate at higher levels in the OSI model such as the Application, Presentation, and Session layers. In some cases, they operate at all seven layers.
gateway A dedicated network computer whose job is to convert data packets from one network protocol to another. Enables dissimilar networks to communicate. (p. 109)
Gateways
Network Connectivity Devices
pp. 104-1094.1
A modem is a computer-to-computer communication device that converts digital signals from the computer to analog signals for the telephone lines. The word “modem” comes from the two operations it handles:
• modulationmodulation
• demodulationdemodulation
modulation The process on changing the digital signal to an analog signal on the sending computer. (p. 109)
demodulation The process of converting the analog signal back to a digital signal on the receiving computer. (p. 109)
Modems
Network Connectivity Devices
pp. 111-1164.2
Main Ideas
Cable is used to connect network devices. There are many types of networking cable in use today. Different types of cable have particular strengths and weaknesses, most notably in the speed at which they can transfer information.
Key Terms
shieldingnoisecrosstalkattenuationBNC connectortwisted-pair cableunshielded twisted-pair (UTP)shielded twisted-pair (STP)fiber optic cable
Guide to Reading
Network Media
pp. 111-1164.2
Cables
The vast majority of networks are connected by some sort of cabling. The cables are the network transmission media that carry signals between computers.
Three major groups of cabling connect the majority of networks:
• coaxial
• twisted-pair
• fiber optic
Network Media
pp. 111-1164.2
Coaxial cable consists of a core of copper wire surrounded by insulation, a braided metal shieldingshielding, and an outer cover.
shielding A layer of covering that grounds a cable and protects it from electric noise and crosstalk. (p. 111)
Cables
Network Media
pp. 111-1164.2
The shielding layer grounds the cable and protects it from electrical noisenoise and crosstalkcrosstalk so the data are not distorted.
Coaxial cable is more resistant to interference and attenuationattenuation than twisted-pair cabling.
The farther the signal travels, the more the signal fades. Coaxial cable is more resistant to interference and attenuation than twisted-pair cabling.
noise Stray electronic signals that interfere with data transmissions along a cable and slow the transmission speed. (p. 111)
crosstalk Signal overflow from an adjacent wire that distorts the data signal. (p. 111)
attenuation The process of data losing signal strength as the data are transmitted along a cable. (p. 112)
Cables
Network Media
pp. 111-1164.2
Connection Hardware
10Base2 and 10Base5 cabling use special connection components, known as BNC BNC connectorsconnectors.
BNC connector A hardware component used to make the connections between the cable and the computers. (p. 112)
Cables
Network Media
pp. 111-1164.2
Cables
Network Media
There are several components in the BNC family, such as:
• The BNC cable connector
• The BNC T connector
• The BNC barrel connector
• The BNC terminator
pp. 111-1164.2
The twisting of the twisted-pairtwisted-pair cablecable wire cancels out crosstalk from adjacent pairs of cable. The higher the number of twists per foot of cable, the more effectively it cancels out crosstalk.
The total number of pairs in a cable varies, depending on the purpose of the cable.
twisted-pair cable A type of cable that consists of two insulated strands of copper wire twisted around each other. (p. 113)
Cables
Network Media
pp. 111-1164.2
Two types of twisted-pair cable are:
• unshielded twisted-pair unshielded twisted-pair (UTP)(UTP)• shielded twisted-pair shielded twisted-pair (STP)(STP)
Of the two types, UTP cable is most prevalent. Its popularity can be attributed to the fact that most buildings are prewired for telephone service.
unshielded twisted-pair (UTP) A type of twisted-pair cabling that does not have an extra shielding layer to help eliminate noise interference. However, it is highly affordable. (p. 113)
shielded twisted-pair (STP) A type of twisted-pair cabling that uses a woven copper-braid jacket to protect the transmitted data from outside interference. (p. 113)
Cables
Network Media
pp. 111-1164.2
Cables
Twisted-pair cabling uses RJ-45 connectors, which are similar to RJ-11 telephone connectors, to connect to a computer.
Network Media
pp. 111-1164.2
In a fiber optic cablefiber optic cable, pulses of light travel down extremely thin tubes of glass or plastic to transmit data.
The signal—a light pulse—can be transmitted over many miles very quickly.
fiber optic cable A type of cable made up of extremely thin tubes of glass or plastic that allow pulses of light to travel through it to transmit data. (p. 115)
Cables
Network Media
pp. 111-1164.2
Selecting Cabling
The cabling you select depends on the needs of a particular site. To determine which type of cable is best, consider the following guidelines.
Network Media
pp. 111-1164.2
You Try It
• Activity 4A – Making Your Own Network Cable (p. 114)
Network Media
pp. 117-1234.3
Main Ideas
The NIC is the direct link between the computer and the cable. Choose NICs carefully by identifying the computer’s bus architecture and the connector type used on the network. Specialized NICs allow connections through different media.
Key Terms
programmable read-only memory (PROM)
boot-on-LAN
Guide to Reading
Network Interface Cards
pp. 117-1234.3
The Role of the NIC
The NIC has four primary roles:
1. The NIC prepares data from the computer for the network cable.
2. It sends the data to another computer. 3. It controls the flow of data between the computer and the
cabling system. 4. It receives incoming data from the cable and translates the
data into bytes that can be understood by the computer’s central processing unit (CPU).
Network Interface Cards
pp. 117-1234.3
The Role of the NIC
Before data are sent over the network, a conversation between the sending and receiving NICs takes place. The following items must be determined before any transmission can begin:
• maximum size of the data groups to be sent
• amount of data to be sent before confirmation of receipt is given
• time intervals between sending data chunks
• amount of time to wait before confirmation is sent
• how much data each NIC can hold before it overflows
• data transmission speed
Network Interface Cards
pp. 117-1234.3
Installation of a NIC
NICs act as the physical interface between the computer and the network cable.
Network Interface Cards
pp. 117-1234.3
Selecting the Right NIC
To ensure compatibility between the computer and the network, the NIC must:
• fit with the computer’s internal structure (data bus architecture).
• contain the correct type of cable connector for the cabling.
Network Interface Cards
pp. 117-1234.3
Selecting the Right NIC
The NIC performs three important functions to coordinate activities between the computer and the cabling:
1. Makes the physical connection to the cable
2. Generates the electrical signals that travel over the cable
3. Controls access to the cable by following specific rules
Network Interface Cards
pp. 117-1234.3
You may encounter some situations that require the use of specialized network cards. Some examples include:
• wireless NICs
• fiber optic NICs
• programmable read-only programmable read-only memorymemory (PROM)
• boot-on-LANboot-on-LAN
programmable read-only memory (PROM) A chip that contains the hardwired code to start the computer and connect the user to the network. With remote-boot PROMs, diskless workstations can join the network when they start. (p. 122)
boot-on-LAN The process that enables the PC to boot from a server rather than the local hard drive. (p. 122)
Specialized NICs
Network Interface Cards
pp. 117-1234.3
You Try It
• Activity 4B – Installing a Network Interface Card (p. 119)
Network Interface Cards
pp. 125-1284.4
Main Ideas
Infrared signals use light beams to transmit from computer to device. Narrowband radio signals use radio frequencies to transmit data. Spread-spectrum radio broadcasts data over a range of frequencies. Microwave technology includes ground to satellite transmission.
Key Terms
infrarednarrowband radiospread-spectrum radiohopmicrowavewired encryption privacy (WEP)
Guide to Reading
Wireless Networking
pp. 125-1284.4
There are four types of infraredinfrared networks:
• line-of-sight
• scatter infrared
• reflective
• broadband optical telepoint
infrared A type of light beam used in wireless networks to transmit the data between devices. (p. 125)
Infrared Light
Wireless Networking
pp. 125-1284.4
Narrowband radioNarrowband radio is similar to broadcasting from a radio station. The broadcast range is 3,000 meters (9,842 feet), and does not require line-of-sight focusing. However, because the signal is high frequency, it is subject to attenuation from steel and load-bearing walls.
narrowband radio A high-frequency transmission similar to broadcasting from a radio station. The user tunes both the transmitter and the receiver to a certain frequency. (p. 126)
Narrowband Radio
Wireless Networking
pp. 125-1284.4
Spread-spectrum radioSpread-spectrum radio broadcasts signals over a range of frequencies. This helps it avoid narrowband communication problems. The available frequencies are divided into channels, known as hopshops.
spread-spectrum radio A transmission technology that broadcasts signals over a range of frequencies, thus providing security for the transmission. (p. 126)
hop One portion of a transmission’s journey between two points. (p. 126)
Spread-Spectrum
Wireless Networking
pp. 125-1284.4
MicrowaveMicrowave systems can be used for the following:
• satellite-to-ground links
• between two buildings
• across large, flat, and open areas, such as bodies of water or deserts
microwave Part of the electromagnetic spectrum, and a form of radiation that can be used for short- and long-distance communications systems. (p. 127)
Microwave Technology
Wireless Networking
pp. 125-1284.4
Microwave Technology
A microwave system can be used to transmit data from building to building.
Wireless Networking
pp. 125-1284.4
Wireless technology is somewhat more prone to security risks. Due to the fact that the signal is broadcast in a certain radius, anyone within that radius can potentially intercept that signal.
Most wireless NICs and access points have a built-in security feature, called wired encryption wired encryption privacy (WEP)privacy (WEP).
wired encryption privacy (WEP) A security feature that, when activated, encrypts the data prior to transmission by the NIC. At the receiving end, the data are decrypted. Most wireless NICs and access points have this security feature built in. (p. 128)
Security Risks
Wireless Networking
Resources
For more resources on this chapter, go to the Introduction to Networks and Networking Web site at http://networking.glencoe.com.
Chapter 4
