© 2007 Cisco Systems, Inc. 
 8.0
Introduction 

This chapter will provide an overview of network principles, standards, and purposes. The following types of networks will be discussed in this chapter:

list of 3 items
• Local Area Network (LAN) 
• Wide Area Network (WAN) 
• Wireless LAN (WLAN) 
list end

The different types of network topologies, protocols, and logical models as well as the hardware needed to create a network will also be discussed in this
chapter. Configuration, troubleshooting, and preventive maintenance will be covered. You will also learn about network software, communication methods,
and hardware relationships.

After completing this chapter, you will meet these objectives:

list of 12 items
• Explain the principles of networking. 
• Describe types of networks. 
• Describe basic networking concepts and technologies. 
• Describe the physical components of a network. 
• Describe LAN topologies and architectures. 
• Identify standards organizations. 
• Identify Ethernet standards. 
• Explain OSI and TCP/IP data models. 
• Describe how to configure a NIC and a modem. 
• Identify names, purposes, and characteristics of other technologies used to establish connectivity. 
• Identify and apply common preventive maintenance techniques used for networks. 
• Troubleshoot a network. 

 8.1
Explain the principles of networking 

Networks are systems that are formed by links. Websites that allow individuals to link to each other’s pages are called social networking sites. A set of
related ideas can be called a conceptual network. The connections you have with all your friends can be called your personal network.

People use the following networks every day:

list of 5 items
• Mail delivery system 
• Telephone system 
• Public transportation system 
• Corporate computer network 
• The Internet 
list end

Computers can be linked by networks to share data and resources. A network can be as simple as two computers connected by a single cable or as complex as
hundreds of computers connected to devices that control the flow of information. Converged data networks can include general purpose computers, such as
PCs and servers, as well as devices with more specific functions, including printers, phones, televisions, and game consoles.

All data, voice, video, and converged networks share information and use various methods to direct how this information flows. The information on the network
goes from one place to another, sometimes via different paths, to arrive at the appropriate destination.

The public transportation system is similar to a data network. The cars, trucks, and other vehicles are like the messages that travel within the network.
Each driver defines a starting point (source) and an ending point (destination). Within this system, there are rules such as stop signs and traffic lights
that control the flow from the source to the destination. 

After completing this section, you will meet these objectives:

list of 2 items
• Define computer networks. 
• Explain the benefits of networking. 

  8.1  
Explain the principles of networking      
8.1.1  
Define computer networks   
table end

A computer data network is a collection of hosts connected by networking devices. A host is any device that sends and receives information on the network.
Peripherals are devices that are connected to hosts. Some devices can serve either as hosts or peripherals. For example, a printer connected to your laptop
which is on a network is acting as a peripheral. If the printer is connected directly to a networking device, such as a hub, switch, or router, it is acting
as a host. 

Computer networks are used globally in businesses, homes, schools, and government agencies. Many of the networks are connected to each other through the
Internet.

Many different types of devices can connect to a network:

list of 7 items
• Desktop computers 
• Laptop computers 
• Printers 
• Scanners 
• PDAs 
• Smartphones 
• File/print servers 
list end

A network can share many different types of resources:

list of 3 items
• Services, such as printing or scanning 
• Storage space on removable devices, such as hard drives or optical drives 
• Applications, such as databases 
list end

You can use networks to access information stored on other computers, print documents using shared printers, and synchronize the calendar between your computer
and your Smartphone. 

Network devices link together using a variety of connections: 

list of 3 items
• Copper cabling – Uses electrical signals to transmit data between devices 
• Fiber-optic cabling – Uses glass or plastic wire, also called fiber, to carry information as light pulses 
• Wireless connection – Uses radio signals, infrared technology (laser), or satellite transmissions 

  8.1  
Explain the principles of networking      
8.1.2  
Explain the benefits of networking   
table end

The benefits of networking computers and other devices include lower costs and increased productivity. With networks, resources can be shared, which results
in less duplication and corruption of data. 

Fewer Peripherals Needed
Figure 1 shows that many devices can be connected on a network. Each computer on the network does not need to have its own printer, scanner, or backup
device. Multiple printers can be set up in a central location and shared among the network users. All network users send print jobs to a central print
server that manages the print requests. The print server can distribute print jobs over multiple printers, or queue jobs that require a specific printer.

Increased Communication Capabilities 
Networks provide several different collaboration tools that can be used to communicate between network users. Online collaboration tools include e-mail,
forums and chats, voice and video, and instant messaging. With these tools, users can communicate with friends, family, and colleagues.

Avoid File Duplication and Corruption 
A server manages network resources. Servers store data and share it with users on a network. Confidential or sensitive data can be protected and shared
with the users who have permission to access that data. Document tracking software can be used to prevent users from overwriting files, or changing files
that others are accessing at the same time.

Lower Cost Licensing
Application licensing can be expensive for individual computers. Many software vendors offer site licenses for networks, which can dramatically reduce
the cost of software. The site license allows a group of people or an entire organization to use the application for a single fee.

Centralized Administration
Centralized administration reduces the number of people needed to manage the devices and data on the network, reducing time and cost to the company. Individual
network users do not need to manage their own data and devices. One administrator can control the data, devices, and permissions of users on the network.
Backing up data is easier because the data is stored in a central location. 

Conserve Resources
Data processing can be distributed across many computers to prevent one computer from becoming overloaded with processing tasks.    

Activity 

Advantages and Disadvantages of Networking
Complete the network matching activity in Figure 2

 
 8.2
Describe types of networks 

Data networks continue to evolve in complexity, use, and design. To communicate about networks, different types of networks are given different descriptive
names. A computer network is identified by the following specific characteristics:

list of 6 items
• The area it serves 
• How the data is stored 
• How the resources are managed 
• How the network is organized 
• The type of networking devices used 
• The type of media used to connect the devices
list end

After completing this section, you will meet these objectives:

list of 5 items
• Describe a LAN. 
• Describe a WAN. 
• Describe a WLAN. 
• Explain peer-to-peer networks. 
• Explain client/server networks. 

  8.2  
Describe types of networks      
8.2.1  
Describe a LAN   
table end

Local Area Network (LAN) refers to a group of interconnected devices that is under the same administrative control. In the past, LANs were considered to
be small networks that existed in a single physical location. Àlthough LANs can be as small as a single local network installed in a home or small office,
over time, the definition of LANs has evolved to include interconnected local networks consisting of many hundreds of devices, installed in multiple buildings
and locations. 

The important thing to remember is that all of the local networks within a LAN are under one administrative control group that governs the security and
access control policies that are in force on the network. In this context, the word “Local” in Local Area Network refers to local consistent control rather
than being physically close to each other. Devices in a LAN may be physically close, but it is not a requirement.

  8.2  
Describe types of networks      
8.2.2  
Describe a WAN   
table end

Wide Area Networks (WANs) are networks that connect LANs in geographically separated locations. The most common example of a WAN is the Internet. The Internet
is a large WAN that is composed of millions of interconnected LANs. Telecommunications service providers (TSP) are used to interconnect these LANs at different
locations. 

  8.2  
Describe types of networks      
8.2.3  
Describe a WLAN   
table end

In a traditional LAN, devices are connected together using copper cabling. In some environments, installing copper cabling may not be practical, desirable,
or even possible. In these situations, wireless devices are used to transmit and receive data using radio waves. These networks are called wireless LANs,
or WLANs. As with LANs, on a WLAN you can share resources, such as files and printers, and access the Internet.

In a WLAN, wireless devices connect to access points within a specified area. Access points are typically connected to the network using copper cabling.
Instead of providing copper cabling to every network host, only the wireless access point is connected to the network with copper cabling. WLAN coverage
can be small and limited to the area of a room or can have greater range.   

Activity 
Network Types
Complete the network type matching activity in Figure 2

 
  8.2  
Describe types of networks      
8.2.4  
Explain peer-to-peer networks   
table end

In a peer-to-peer network, devices are connected directly to each other without any additional networking devices between them. In this type of network,
each device has equivalent capabilities and responsibilities. Individual users are responsible for their own resources and can decide which data and devices
to share. Because individual users are responsible for the resources on their own computers, there is no central point of control or administration in
the network. 

Peer-to-peer networks work best in environments with ten or fewer computers. Because individual users are in control of their own computers, there is no
need to hire a dedicated network administrator.

Peer-to-peer networks have several disadvantages:

list of 4 items
• There is no centralized network administration which makes it difficult to determine who controls resources on the network. 
• There is no centralized security. Each computer must use separate security measures for data protection. 
• The network becomes more complex and difficult to manage as the number of computers on the network increases. 
• There may be no centralized data storage. Separate data backups must be maintained. This responsibility falls on the individual users. 
list end

Peer-to-peer networks still exist inside larger networks today. Even on a large client network, users can still share resources directly with other users
without using a network server. In your home, if you have more than one computer, you can set up a peer-to-peer network. You can share files with other
computers, send messages between computers, and print documents to a shared printer.

  8.2  
Describe types of networks      
8.2.5  
Explain client/server networks   
table end

In a client/server network, the client requests information or services from the server. The server provides the requested information or service to the
client. Servers on a client/server network commonly perform some of the processing work for client machines; for example, sorting through a database before
delivering only the records requested by the client.

One example of a client/server network is a corporate environment in which employees use a company e-mail server to send, receive, and store e-mail. The
e-mail client on an employee computer issues a request to the e-mail server for any unread e-mail. The server responds by sending the requested e-mail
to the client.

In a client/server model, the servers are maintained by network administrators. Data backups and security measures are implemented by the network administrator.
The network administrator also controls user access to the network resources. All of the data on the network is stored on a centralized file server. Shared
printers on the network are managed by a centralized print server. Network users with the proper permissions can access both the data and shared printers.
Each user must provide an authorized username and password to gain access to network resources that they are permitted to use. 

For data protection, an administrator performs a routine backup of all the files on the servers. If a computer crashes, or data is lost, the administrator
can easily recover the data from a recent backup.
 
 8.3
Describe basic networking concepts and technologies 

As a computer technician, you will be required to configure and troubleshoot computers on a network. To effectively configure a computer on the network,
you should understand IP addressing, protocols, and other network concepts. 

After completing this section, you will meet these objectives:

list of 5 items
• Explain bandwidth and data transmission. 
• Describe IP addressing. 
• Define DHCP. 
• Describe Internet protocols and applications. 
• Define ICMP. 


  8.3  
Describe basic networking concepts and technologies      
8.3.1  
Explain bandwidth and data transmission   
table end

Bandwidth is the amount of data that can be transmitted within a fixed time period. When data is sent over a computer network, it is broken up into small
chunks called packets. Each packet contains headers. A header is information added to each packet that contains the source and destination of the packet.
A header also contains information that describes how to put all of the packets back together again at the destination. The size of the bandwidth determines
the amount of information that can be transmitted.

Bandwidth is measured in bits per second and is usually denoted by any of the following units of measure:

list of 3 items
• bps – bits per second 
• Kbps – kilobits per second 
• Mbps – megabits per second 
list end

NOTE: One byte is equal to 8 bits, and is abbreviated with a capital B. One MBps is approximately 8 Mbps. 

Figure 1 shows how bandwidth on a network can be compared to a highway. In the highway example, the cars and trucks represent the data. The number of lanes
on the highway represents the amount of cars that could travel on the highway at the same time. An eight-lane highway can handle four times the number
of cars that a two-lane highway can hold. 

The data that is transmitted over the network can flow using one of three modes: simplex, half-duplex, or full-duplex.

Simplex
Simplex, also called unidirectional, is a single, one-way transmission. An example of simplex transmission is the signal that is sent from a TV station
to your home TV.

Half-Duplex
When data flows in one direction at a time, it is known as half-duplex. With half-duplex, the channel of communications allows alternating transmission
in two directions, but not in both directions simultaneously. Two-way radios, such as police or emergency communications mobile radios, work with half-duplex
transmissions. When you press the button on the microphone to transmit, you cannot hear the person on the other end. If people at both ends try to talk
at the same time, neither transmission gets through.

Full-Duplex
When data flows in both directions at the same time, it is known as full-duplex. Although the data flows in both directions, the bandwidth is measured
in only one direction. A network cable with 100 Mbps in full-duplex mode has a bandwidth of 100 Mbps.

A telephone conversation is an example of full-duplex communication. Both people can talk and be heard at the same time.

Full-duplex networking technology increases network performance because data can be sent and received at the same time. Broadband technology allows multiple
signals to travel on the same wire simultaneously. Broadband technologies, such as digital subscriber line (DSL) and cable, operate in full-duplex mode.
With a DSL connection, for example, users can download data to the computer and talk on the telephone at the same time. 

  8.3  
Describe basic networking concepts and technologies      
8.3.2  
Describe IP addressing   
table end

An IP address is a number that is used to identify a device on the network. Each device on a network must have a unique IP address to communicate with other
network devices. As noted earlier, a host is a device which sends or receives information on the network. Network devices are devices that move data across
the network including hubs, switches, and routers. On a LAN, each host and network device must have an IP address within the same network to be able to
communicate with each other.

A person's name and fingerprints usually do not change. They provide a label or address for the physical aspect of the person – the body. A person's mailing
address, on the other hand, relates to where the person lives or picks up mail. This address can change. On a host, the Media Access Control (MAC) address
(explained below) is assigned to the host NIC and is known as the physical address. The physical address remains the same regardless of where the host
is placed on the network in the same way that fingerprints remain with the person regardless of where the person goes.

The IP address is similar to the mailing address of a person. It is known as a logical address because it is logically assigned based on the host location.
The IP address, or network address, is based on the local network and is assigned to each host by a network administrator. This process is similar to the
local government assigning a street address based on the logical description of the city or village and neighborhood.

An IP address consists of a series of 32 binary bits (ones and zeros). It is very difficult for humans to read a binary IP address. For this reason, the
32 bits are grouped into four 8-bit bytes called octets. An IP address, even in this grouped format, is hard for humans to read, write and remember; therefore,
each octet is presented as its decimal value, separated by a decimal point or period. This format is referred to as dotted-decimal notation. When a host
is configured with an IP address, it is entered as a dotted decimal number, such as 192.168.1.5. Imagine if you had to enter the 32-bit binary equivalent
of this: 11000000101010000000000100000101. If just one bit were mistyped, the address would be different and the host may not be able to communicate on
the network. 

The logical 32-bit IP address is hierarchical and is composed of two parts. The first part identifies the network and the second part identifies a host
on that network. Both parts are required in an IP address. As an example, if a host has IP address 192.168.18.57, the first three octets, 192.168.18, identify
the network portion of the address, and the last octet, 57 identifies the host. This is known as hierarchical addressing, because the network portion indicates
the network on which each unique host address is located. Routers only need to know how to reach each network and not the location of each individual host.

IP addresses are divided into the following five classes:

list of 5 items
• Class A – Large networks, implemented by large companies and some countries 
• Class B – Medium-sized networks, implemented by universities 
• Class C – Small networks, implemented by ISP for customer subscriptions 
• Class D – Special use for multicasting 
• Class E – Used for experimental testing 
list end

Subnet Mask
The subnet mask is used to indicate the network portion of an IP address. Like the IP address, the subnet mask is a dotted decimal number. Usually all
hosts within a LAN use the same subnet mask. Figure 1 shows default subnet masks for usable IP addresses that are mapped to the first three classes of
IP addresses:

list of 3 items
• 255.0.0.0 – Class A, which indicates that the first octet of the IP address is the network portion 
• 255.255.0.0 – Class B, which indicates that the first two octets of the IP address is the network portion 
• 255.255.255.0 – Class C, which indicates that the first three octets of the IP address is the network portion 
list end

If an organization owns one Class B network but needs to provide IP addresses for four LANs, the organization would have to subdivide the Class B address
into four smaller parts. Subnetting is a logical division of a network. It provides the means to divide a network, and the subnet mask specifies how it
is subdivided. An experienced network administrator typically performs subnetting. After the subnetting scheme has been created, the proper IP addresses
and subnet masks can be configured on the hosts in the four LANs. These skills are taught in the Cisco Networking Academy courses related to CCNA level
networking skills.

Manual Configuration
In a network with a small number of hosts, it is easy to manually configure each device with the proper IP address. A network administrator who understands
IP addressing should assign the addresses and should know how to choose a valid address for a particular network. The IP address that is entered is unique
for each host within the same network or subnet. 

To manually enter an IP address on a host, go to the TCP/IP settings in the Properties window for the Network Interface Card (NIC). The NIC is the hardware
that enables a computer to connect to a network. It has an address called the Media Access Control (MAC) address. Whereas the IP address is a logical address
that is defined by the network administrator, a MAC address is "burned-in" or permanently programmed into the NIC when it is manufactured. The IP address
of a NIC can be changed, but the MAC address never changes. 

The main difference between an IP address and a MAC address is that the MAC address is used to deliver frames on the LAN, while an IP address is used to
transport frames outside the LAN. A frame is a data packet, along with address information added to the beginning and end of the packet before transmission
over the network. Once a frame is delivered to the destination LAN, the MAC address is used to deliver the frame to the end host on that LAN.

If more than a few computers comprise the LAN, manually configuring IP addresses for every host on the network can be time-consuming and prone to errors.
In this case, the use of a Dynamic Host Configuration Protocol (DHCP) server would automatically assign IP addresses and greatly simplify the addressing
process.  

Worksheet 

IP Address Class
Identify the IP address class for an IP address
Class D addresses are used for multicast groups. There is no need to allocate octet or bits to separate network and host addresses. Class E addresses are
reserved for research use only.

  8.3  
Describe basic networking concepts and technologies      
8.3.3  
Define DHCP   
table end

Dynamic Host Configuration Protocol (DHCP) is a software utility used to dynamically assign IP addresses to network devices. This dynamic process eliminates
the need for manually assigning IP addresses. A DHCP server can be set up and the hosts can be configured to automatically obtain an IP address. When a
computer is set to obtain an IP address automatically, all of the other IP addressing configuration boxes are dimmed, as shown in Figure 1. The server
maintains a list of IP addresses to assign, and manages the process so that every device on the network receives a unique IP address. Each address is held
for a predetermined amount of time. When the time expires, the DHCP server can use this address for any computer that joins the network.

This is the IP address information that a DHCP server can assign to hosts: 

list of 4 items
• IP address 
• Subnet mask 
• Default gateway 
• Optional values, such as a Domain Name System (DNS) server address 
list end

The DHCP server receives a request from a host. The server then selects IP address information from a set of predefined addresses that are stored in a database.
Once the IP address information is selected, the DHCP server offers these values to the requesting host on the network. If the host accepts the offer,
the DHCP server leases the IP address for a specific period of time. 

Using a DHCP server simplifies the administration of a network because the software keeps track of IP addresses. Automatically configuring TCP/IP also reduces
the possibility of assigning duplicate or invalid IP addresses. Before a computer on the network can take advantage of the DHCP server services, the computer
must be able to identify the server on the local network. A computer can be configured to accept an IP address from a DHCP server by clicking the "Obtain
an IP address automatically" option in the NIC configuration window, as shown in Figure 2.

If your computer cannot communicate with the DHCP server to obtain an IP address, the Windows operating system will automatically assign a private IP address.
If your computer is assigned an IP address in the range of 169.254.0.0 to 169.254.255.255, your computer will only be able to communicate with other computers
in the same range. An example of when these private addresses would be useful is in a classroom lab where you want to prevent access outside of your network.
This operating system feature is called Automatic Private IP Addressing (APIPA). APIPA will continually request an IP address from a DHCP server for your
computer.

  8.3  
Describe basic networking concepts and technologies      
8.3.4  
Describe Internet protocols and applications   
table end

A protocol is a set of rules. Internet protocols are sets of rules governing communication within and between computers on a network. Protocol specifications
define the format of the messages that are exchanged. A letter sent through the postal system also uses protocols. Part of the protocol specifies the position
on the envelope that the delivery address needs to be written. If the delivery address is written in the wrong place, the letter cannot be delivered.

Timing is crucial to network operation. Protocols require messages to arrive within certain time intervals so that computers will not wait indefinitely
for messages that may have been lost. Therefore, systems maintain one or more timers during transmission of data. Protocols also initiate alternative actions
if the network does not meet the timing rules. Many protocols consist of a suite of other protocols that are stacked in layers. These layers depend on
the operation of the other layers in the suite to function properly.

These are the main functions of protocols:

list of 5 items
• Identifying errors 
• Compressing the data 
• Deciding how data is to be sent 
• Addressing data 
• Deciding how to announce sent and received data 
list end

Although there are many other protocols, Figure 1 summarizes some of the more common protocols used on networks and the Internet.

To understand how networks and the Internet work, you must be familiar with the commonly used protocols. These protocols are used to browse the web, send
and receive e-mail, and transfer data files. You will encounter other protocols as your experience in IT grows, but they are not used as often as the common
protocols described here.

In Figure 2, click the protocol names to learn more about each one.

The more you understand about each of these protocols, the more you will understand how networks and the Internet work.  

Activity 

Network Protocols Activity
Complete the matching activity in Figure 3

  8.3  
Describe basic networking concepts and technologies      
8.3.5  
Define ICMP   
table end

Internet Control Message Protocol (ICMP) is used by devices on a network to send control and error messages to computers and servers. There are several
different uses for ICMP, such as announcing network errors, announcing network congestion, and troubleshooting. 

Packet internet groper (ping) is commonly used to test connections between computers. Ping is a simple but highly useful command line utility used to determine
whether a specific IP address is accessible. You can ping the IP address to test IP connectivity. Ping works by sending an ICMP echo request to a destination
computer or other network device. The receiving device then sends back an ICMP echo reply message to confirm connectivity.

Ping is a troubleshooting tool used to determine basic connectivity. The command line switches that can be used with the ping command are shown in Figure
1. Four ICMP echo requests (pings) are sent to the destination computer. If it is reachable, the destination computer responds with four ICMP echo replies.
The percentage of successful replies can help you to determine the reliability and accessibility of the destination computer.

You can also use ping to find the IP address of a host when the name is known. If you ping the name of a website, for example, www.cisco.com, as shown in
Figure 2, the IP address of the server displays.

Other ICMP messages are used to report undelivered packets, data on an IP network that includes source and destination IP addresses, and whether a device
is too busy to handle the packet. Data, in the form of a packet, arrives at a router, which is a networking device that forwards data packets across networks
toward their destinations. If the router does not know where to send the packet, the router deletes it. The router then sends an ICMP message back to the
sending computer informing it that the data was deleted. When a router becomes very busy, it may send a different ICMP message to the sending computer
indicating that it should slow down because there is congestion on the network.

 8.4
Describe the physical components of a network 

There are many devices that can be used in a network to provide connectivity. The device you use will depend on how many devices you are connecting, the
type of connections that they use, and the speed at which the devices operate. These are the most common devices on a network:

list of 5 items
• Computers 
• Hubs 
• Switches 
• Routers 
• Wireless access points 
list end

The physical components of a network are needed to move data between these devices. The characteristics of the media determine where and how the components
are used. These are the most common media used on networks:

list of 3 items
• Twisted-pair 
• Fiber-optic cabling 
• Radio waves 
list end

After completing this section, you will meet these objectives:

list of 2 items
• Identify names, purposes, and characteristics of network devices. 
• Identify names, purposes, and characteristics of common network cables. 

these are some Physical Network Components 
INTERNET
Cable Modem or DSL Modem
Wireless Access Point
(WAP45A)
Network Cable
10/100 LAN Card 
(LNE100TX)
EtherFast Cable/DSL Firewall Router (BEFSX41)
Network Cable
EtherFast 10/100
Card Bus PC Card (PCMPC200)
Wireless PC Card (WPC54A)
Network Cable
USB Cable
(Optional)
EtherFast 10/100 Compact USB Network Adaptor (USB 100m)


  8.4  
Describe physical components of a network      
8.4.1  
Identify names, purposes, and characteristics of network devices   
table end

To make data transmission more extensible and efficient than a simple peer-to-peer network, network designers use specialized network devices, such as hubs,
switches, routers, and wireless access points, to send data between devices.

Hubs
Hubs, shown in Figure 1, are devices that extend the range of a network by receiving data on one port, and then regenerating the data and sending it out
to all other ports. This process means that all traffic from a device connected to the hub is sent to all the other devices connected to the hub every
time the hub transmits data. This causes a great amount of network traffic. Hubs are also called concentrators, because they serve as a central connection
point for a LAN. 

Bridges and Switches 
Files are broken up into small pieces of data, called packets, before they are transmitted over a network. This process allows for error checking and easier
retransmission if the packet is lost or corrupted. Address information is added to the beginning and to the end of packets before they are transmitted.
The packet, along with the address information, is called a frame.

LANs are often divided into sections called segments, similar to the way a company is divided into departments. The boundaries of segments can be defined
using a bridge. A bridge is a device used to filter network traffic between LAN segments. Bridges keep a record of all the devices on each segment to which
the bridge is connected. When the bridge receives a frame, the destination address is examined by the bridge to determine if the frame is to be sent to
a different segment, or dropped. The bridge also helps to improve the flow of data by keeping frames confined to only the segment to which the frame belongs.

Switches, shown in Figure 2, are sometimes called multiport bridges. A typical bridge may have just two ports, linking two segments of the same network.
A switch has several ports, depending on how many network segments are to be linked. A switch is a more sophisticated device than a bridge. A switch maintains
a table of the MAC addresses for computers that are connected to each port. When a frame arrives at a port, the switch compares the address information
in the frame to its MAC address table. The switch then determines which port to use to forward the frame.

Routers 
Whereas a switch connects segments of a network, routers, shown in Figure 3, are devices that connect entire networks to each other. Switches use MAC addresses
to forward a frame within a single network. Routers use IP addresses to forward frames to other networks. A router can be a computer with special network
software installed, or a router can be a device built by network equipment manufacturers. Routers contain tables of IP addresses along with optimal destination
routes to other networks. 

Wireless Access Points
Wireless access points, shown in Figure 4, provide network access to wireless devices such as laptops and PDAs. The wireless access point uses radio waves
to communicate with radios in computers, PDAs, and other wireless access points. An access point has limited range of coverage. Large networks require
several access points to provide adequate wireless coverage.

Multipurpose Devices
There are network devices that perform more than one function. It is more convenient to purchase and configure one device that serves all of your needs
than to purchase a separate device for each function. This is especially true for the home user. In your home, you would purchase a multipurpose device
instead of a switch, a router, and a wireless access point. The Linksys 300N, shown in Figure 5, is an example of a multipurpose device. 

  8.4  
Describe physical components of a network      
8.4.2  
Identify names, purposes, and characteristics of common network cables   
table end

Until recently, cables were the only medium used to connect devices on networks. A wide variety of networking cables are available. Coaxial and twisted-pair
cables use copper to transmit data. Fiber-optic cables use glass or plastic to transmit data. These cables differ in bandwidth, size, and cost. You need
to know what type of cable to use in different situations so that you are able to install the correct cables for the job. You will also need to be able
to troubleshoot and repair problems that you encounter. 

Twisted-Pair 
Twisted-pair is a type of copper cabling that is used for telephone communications and most Ethernet networks. A pair of wires forms a circuit that can
transmit data. The pair is twisted to provide protection against crosstalk, which is the noise generated by adjacent pairs of wires in the cable. Pairs
of copper wires are encased in color-coded plastic insulation and twisted together. An outer jacket protects the bundles of twisted pairs.

When electricity flows through a copper wire, a magnetic field is created around the wire. A circuit has two wires, and in a circuit, the two wires have
oppositely-charged magnetic fields. When the two wires of the circuit are next to each other, the magnetic fields cancel each other out. This is called
the cancellation effect. Without the cancellation effect, your network communications become slow due to the interference caused by the magnetic fields.

There are two basic types of twisted-pair cables: 

list of 2 items
• Unshielded twisted-pair (UTP) – Cable that has two or four pairs of wires. This type of cable relies solely on the cancellation effect produced by the
twisted-wire pairs that limits signal degradation caused by electromagnetic interface (EMI) and radio frequency interference (RFI). UTP is the most commonly
used cabling in networks. UTP cables have a range of 328 feet (100 m). 
• Shielded twisted-pair (STP) – Each pair of wires is wrapped in metallic foil to better shield the wires from noise. Four pairs of wires are then wrapped
in an overall metallic braid or foil. STP reduces electrical noise from within the cable. It also reduces EMI and RFI from outside the cable. 
list end

Although STP prevents interference better than UTP, STP is more expensive because of extra shielding, and more difficult to install because of the thickness.
In addition, the metallic shielding must be grounded at both ends. If improperly grounded, the shield acts like an antenna picking up unwanted signals.
STP is primarily used outside North America. 

Category Rating 
UTP comes in several categories that are based on two factors:

list of 2 items
• The number of wires in the cable 
• The number of twists in those wires 
list end

Category 3 is the wiring used for telephone systems and for Ethernet LAN at 10 Mbps. Category 3 has four pairs of wires.

Category 5 and Category 5e have four pairs of wires with a transmission rate of 100 Mbps. Category 5 and 5e are the most common network cables used. Category
5e has more twists per foot than Category 5 wiring. These extra twists further prevent interference from outside sources and the other wires within the
cable.

Some Category 6 cables use a plastic divider to separate the pairs of wires, which prevents interference. The pairs also have more twists than Category
5e cable. A twisted pair cable is shown in Figure 1.

Coaxial Cable 
Coaxial cable is a copper-cored cable surrounded by a heavy shielding. Coaxial cable is used to connect computers in a network. There are several types
of coaxial cable:

list of 4 items
• Thicknet or 10BASE5 – Coax cable that was used in networks and operated at 10 megabits per second with a maximum length of 500 meters 
• Thinnet 10BASE2 – Coax cable that was used in networks and operated at 10 megabits per second with a maximum length of 185 meters 
• RG-59 – Most commonly used for cable television in the U.S. 
• RG-6 – Higher quality cable than RG-59, with more bandwidth and less susceptibility to interference 
list end

A coaxial cable is shown in Figure 2.

Fiber-Optic Cable 
An optical fiber is a glass or plastic conductor that transmits information using light. Fiber-optic cable, shown in Figure 3, has one or more optical
fibers enclosed in a sheath or jacket. Because it is made of glass, fiber-optic cable is not affected by electromagnetic interference or radio frequency
interference. All signals are converted to light pulses to enter the cable, and converted back into electrical signals when they leave it. This means that
fiber-optic cable can deliver signals that are clearer, can go farther, and have greater bandwidth than cable made of copper or other metals.

Fiber-optic cable can reach distances of several miles or kilometers before the signal needs to be regenerated. Fiber-optic cable is usually more expensive
to use than copper cable and the connectors are more costly and harder to assemble. Common connectors for fiber-optic networks are SC, ST, and LC. These
three types of fiber-optic connectors are half-duplex, which allows data to flow in only one direction. Therefore, two cables are needed.

These are the two types of glass fiber-optic cable:

list of 2 items
• Multimode – Cable that has a thicker core than single-mode cable. It is easier to make, can use simpler light sources (LEDs), and works well over distances
of a few kilometers or less. 
• Single-mode – Cable that has a very thin core. It is harder to make, uses lasers as a light source, and can transmit signals dozens of kilometers with
ease. 
list end

A fiber-optic cable, shown in Figure 3, is one or more optical fibers enclosed together in a sheath or jacket.

 8.5
Describe LAN topologies and architectures 

Most of the computers that you work on will be part of a network. Topologies and architectures are building blocks for designing a computer network. While
you may not build a computer network, you need to understand how they are designed in order to work on computers that are part of a network.

There are two types of LAN topologies: physical and logical. A physical topology, shown in Figure 1, is the physical layout of the components on the network.
A logical topology, shown in Figure 2, determines how the hosts communicate across a medium, such as a cable or the airwaves. Topologies are commonly represented
as network diagrams.

A LAN architecture is built around a topology. LAN architecture comprises all the components that make up the structure of a communications system. These
components include the hardware, software, protocols, and sequence of operations.

After completing this section, you will meet these objectives:

list of 2 items
• Describe LAN topologies. 
• Describe LAN architectures. 


  8.5  
Describe LAN topologies and architectures      
8.5.1  
Describe LAN topologies   
table end

A physical topology defines the way in which computers, printers, and other devices are connected to a network. A logical topology describes how the hosts
accesses the medium and communicates on the network. The type of topology determines the capabilities of the network, such as ease of setup, speed, and
cable lengths.

Physical Topologies
Figure 1 shows the common LAN physical topologies:

list of 5 items
• Bus 
• Ring 
• Star 
• Hierarchical or Extended Star 
• Mesh 
list end

Bus Topology
In the bus topology, each computer connects to a common cable. The cable connects one computer to the next, like a bus line going through a city. The cable
has a small cap installed at the end, called a terminator. The terminator prevents signals from bouncing back and causing network errors.

Ring Topology
In a ring topology, hosts are connected in a physical ring or circle. Because the ring topology has no beginning or end, the cable does not need to be
terminated. A specially-formatted frame, called a token, travels around the ring, stopping at each host. If a host wants to transmit data, the host adds
the data and the destination address to the frame. The frame then continues around the ring until the frame stops at the host with the destination address.
The destination host takes the data out of the frame.

Star Topology
The star topology has a central connection point, which is normally a device such as a hub, switch, or router. Each host on a network has a cable segment
that attaches the host directly to the central connection point. The advantage of a star topology is that it is easy to troubleshoot. Each host is connected
to the central device with its own wire. If there is a problem with that cable, only that host is affected. The rest of the network remains operational.


Hierarchical or Extended Star Topology
A hierarchical or extended star topology is a star network with an additional networking device connected to the main networking device. Typically, a network
cable connects to one hub, and then several other hubs connect to the first hub. Larger networks, such as those of corporations or universities, use the
hierarchical star topology.

Mesh Topology
The mesh topology connects all devices to each other. When every device is connected to every other device, a failure of any cable will not affect the
network. The mesh topology is used in WANs that interconnect LANs.

Logical Topologies
The two most common types of logical topologies are broadcast and token passing. 

In a broadcast topology, each host addresses either data to a particular host or to all hosts connected on a network. There is no order that the hosts must
follow to use the network – it is first come, first served for transmitting data on the network.

Token passing controls network access by passing an electronic token sequentially to each host. When a host receives the token, it can send data on the
network. If the host has no data to send, it passes the token to the next host and the process repeats itself.

these are some LAN Physical Topologies 
Bus Topology
Hierarchical or Extended Star Topology
Ring Topology
LAN Physical Topologies 
Star Topology
Mesh Topology

  8.5  
Describe LAN topologies and architectures      
8.5.2  
Describe LAN architectures   
table end

LAN architecture describes both the physical and logical topologies used in a network. Figure 1 shows the three most common LAN architectures. 

Ethernet
The Ethernet architecture is based on the IEEE 802.3 standard. The IEEE 802.3 standard specifies that a network use the Carrier Sense Multiple Access with
Collision Detection (CSMA/CD) access control method. In CSMA/CD, hosts access the network using the first come, first served broadcast topology method
to transmit data.

Ethernet uses a logical bus or broadcast topology and either a bus or star physical topology. As networks expand, most Ethernet networks are implemented
using an extended star or hierarchical star topology, as shown in Figure 1. Standard transfer rates are 10 Mbps and 100 Mbps, but new standards outline
Gigabit Ethernet, which is capable of attaining speeds up to 1000 Mbps (1 Gbps).

Token Ring
IBM originally developed Token Ring as a reliable network architecture based on the token-passing access control method. Token Ring is often integrated
with IBM mainframe systems. Token Ring is used with computers and mainframes. 

Token Ring is an example of an architecture in which the physical topology is different from its logical topology. The Token Ring topology is referred to
as a star-wired ring because the outer appearance of the network design is a star. The computers connect to a central hub, called a multistation access
unit (MSAU). Inside the device, however, the wiring forms a circular data path, creating a logical ring. The logical ring is created by the token traveling
out of an MSAU port to a computer. If the computer does not have any data to send, the token is sent back to the MSAU port and then out the next port to
the next computer. This process continues for all computers and therefore resembles a physical ring.

FDDI
FDDI is a type of Token Ring network. The implementation and topology of FDDI differs from the IBM Token Ring LAN architecture. FDDI is often used to connect
several buildings in an office complex or on a university campus.

FDDI runs on fiber-optic cable. FDDI combines high-speed performance with the advantages of the token-passing ring topology. FDDI runs at 100 Mbps on a
dual-ring topology. The outer ring is called the primary ring and the inner ring is called the secondary ring. 

Normally, traffic flows only on the primary ring. If the primary ring fails, the data automatically flows onto the secondary ring in the opposite direction.


An FDDI dual ring supports a maximum of 500 computers per ring. The total distance of each length of the cable ring is 62 miles (100 km). A repeater, which
is a device that regenerates signals, is required every 1.2 miles (2 km). In recent years, many token ring networks have been replaced by faster Ethernet
networks.

this needs work 
these are LAN Architectures
Architecture
Physical Topology
Logical Topology
Ethernet
Bus
 Star
 Extended Star
Bus
Token Ring
Star
Ring
Fiber-Distributed 
Data Interface (FDDI)
Double Ring
Ring


 8.6
Identify standards organizations 

Several worldwide standards organizations are responsible for setting networking standards. Standards are used by manufacturers as a basis for developing
technology, especially communications and networking technologies. Standardizing technology ensures that the devices you use will be compatible with other
devices using the same technology. The standards groups create, examine, and update standards. These standards are applied to the development of technology
to meet the demands for higher bandwidth, efficient communication, and reliable service.

Click each of the standards in Figure 1 to learn more information.

this is content from the figure needs work 

Standards Organizations
Standards Organizations 
CCITT
Comité Consultatif International Téléphonique et Télégraphique
                        – This committee defines international communications standards. The CCITT defined the standard for sending fax documents and the
standards that define data transmission over telephone lines such as V.90 that allows transmissions up to 56000 bps. After 1992, this organization became
the ITU Telecommunication Standardization Sector (ITU-T).
IEEE
ISO
IAB
IEC
ANSI
TIA/EIA


 8.7
Identify Ethernet standards 

Ethernet protocols describe the rules that control how communication occurs on an Ethernet network. To ensure that all Ethernet devices are compatible with
each other, the IEEE developed standards for manufacturers and programmers to follow when developing Ethernet devices.

After completing this section, you will meet these objectives:

list of 2 items
• Explain cabled Ethernet standards. 
• Explain wireless Ethernet standards. 

this is problematic 
Interoperability Between Standards
Interoperability Between Standards
Switch
Router
Wan
Protocol:

802.3 (Ethernet)
Protocol:

802.11 (Wi-Fi)
Wireless Acess Point

  8.7  
Identify Ethernet standards      
8.7.1  
Explain cabled Ethernet standards   
table end

IEEE 802.3
The Ethernet architecture is based on the IEEE 802.3 standard. The IEEE 802.3 standard specifies that a network implement the CSMA/CD access control method.


In CSMA/CD, all end stations "listen" to the network wire for clearance to send data. This process is similar to waiting to hear a dial tone on a phone
before dialing a number. When the end station detects that no other host is transmitting, the end station will attempt to send data. If no other station
sends any data at the same time, this transmission will arrive at the destination computer with no problems. If another end station observed the same clear
signal and transmitted at the same time, a collision will occur on the network media. 

The first station that detects the collision, or the doubling of voltage, sends out a jam signal that tells all stations to stop transmitting and to run
a backoff algorithm. A backoff algorithm calculates random times in which the end station will start to try network transmission again. This random time
is typically in one or two milliseconds (ms), or thousandths of a second. This sequence occurs every time there is a collision on the network and can reduce
Ethernet transmission by up to 40%.

Ethernet Technologies
The IEEE 802.3 standard defines several physical implementations that support Ethernet. Some of the common implementations are described here.

Ethernet
10BASE-T is an Ethernet technology that uses a star topology. 10BASE-T is a popular Ethernet architecture whose features are indicated in its name: 

list of 3 items
• The ten (10) represents a speed of 10 Mbps. 
• BASE represents baseband transmission. In baseband transmission, the entire bandwidth of a cable is used for one type of signal. 
• The T represents twisted-pair copper cabling. 
list end

Advantages of 10BASE-T: 

list of 3 items
• Installation of cable is inexpensive compared to fiber-optic installation. 
• Cables are thin, flexible, and easier to install than coaxial cabling. 
• Equipment and cables are easy to upgrade. 
list end

Disadvantages of 10BASE-T: 

list of 2 items
• The maximum length for a 10BASE-T segment is only 328 feet (100 m). 
• Cables are susceptible to electromagnetic interference (EMI). 
list end

Fast Ethernet
The high bandwidth demands of many modern applications, such as live video conferencing and streaming audio, have created a need for higher data-transfer
speeds. Many networks require more bandwidth than 10 Mbps Ethernet.

100BASE-TX is much faster than 10BASE-T and has a theoretical bandwidth of 100 Mbps.

Advantages of 100BASE-TX: 

list of 2 items
• At 100 Mbps, transfer rates of 100BASE-TX are ten times that of 10BASE-T. 
• 100BASE-X uses twisted-pair cabling, which is inexpensive and easy to install. 
list end

Disadvantages of 100BASE-TX: 

list of 2 items
• The maximum length for a 100BASE-TX segment is only 328 feet (100 m). 
• Cables are susceptible to electromagnetic interference (EMI). 
list end

1000BASE -T is commonly known as Gigabit Ethernet. Gigabit Ethernet is a LAN architecture. 

Advantages of 1000BASE-T: 

list of 2 items
• The 1000BASE-T architecture supports data transfer rates of 1 Gbps. At 1 Gbps, it is ten times faster than Fast Ethernet, and 100 times faster than Ethernet.
This increased speed makes it possible to implement bandwidth-intensive applications, such as live video. 
• The 1000BASE-T architecture has interoperability with 10BASE-T and 100BASE-TX. 
list end

Disadvantages of 1000BASE-T:

list of 4 items
• The maximum length for a 1000BASE-T segment is only 328 feet (100 m). 
• It is susceptible to interference. 
• Gigabit NICs and switches are expensive. 
• Additional equipment is required. 
list end

10BASE-FL, 100BASE-FX, 1000BASE-SX and LX are fiber-optic Ethernet Technologies.

this needs work 
Cabled Ethernet Standards
10BASE-T
Media
100BASE-TX
EIA/TIA

Category 3, 4, 5 UTP, two

pair
1000BASE-T
EIA/TIA 

Category 5, 5e UTP, two pair
EIA/TIA

Category 5, 5e

UTP, four pair
Maximum

Segment

Length
100 m (328 feet)
100 m (328 feet)
100 m (328 feet)
Topology
Star
Connector
Star
ISO 8877

(RJ-45)
Star
ISO 8877

(RJ-45)
ISO 8877

(RJ-45)


  8.7  
Identify Ethernet standards      
8.7.2  
Explain wireless Ethernet standards   
table end

IEEE 802.11 is the standard that specifies connectivity for wireless networks. IEEE 802.11, or Wi-Fi, refers to the collective group of standards – 802.11a,
802.11b, 802.11g, and 802.11n. These protocols specify the frequencies, speeds, and other capabilities of the different Wi-Fi standards.

802.11a
Devices conforming to the 802.11a standard allow WLANs to achieve data rates as high as 54 Mbps. IEEE 802.11a devices operate in the 5 GHz radio frequency
range and within a maximum range of 150 feet (45.7 m). 

802.11b
802.11b operates in the 2.4 GHz frequency range with a maximum theoretical data rate of 11 Mbps. These devices operate within a maximum range of 300 feet
(91 m).

802.11g
IEEE 802.11g provides the same theoretical maximum speed as 802.11a, which is 54 Mbps, but operates in the same 2.4 GHz spectrum as 802.11b. Unlike 802.11a,
802.11g is backward-compatible with 802.11b. 802.11g also has a maximum range of 300 feet (91 m).

802.11n
802.11n is a newer wireless standard that has a theoretical bandwidth of 540 Mbps and operates in either the 2.4 GHz or 5 GHz frequency range with a maximum
range of 984 feet (250 m).

this needs work 

Wireless Ethernet Standards
Standard
Bandwidth
Frequency 
IEEE 802.11a
Range
Up to 54 Mbps
Interoperability
5 GHz band
150 ft 

(45.7 m)
Not interoperable 

with 802.11b, 

802.11g, 802.11n
IEEE 802.11b
Up to 11 Mbps
2.4 GHz band
300 ft 

(91 m)
IEEE 802.11g
Interoperable 

with 802.11g
Up to 54 Mbps
2.4 GHz band
300 ft 

(91 m)
IEEE 802.11n 

(Pre - standard)
Interoperable 

with 802.11b
Up to 540 Mbps
2.4 GHz band
984 ft 

(250 m)
Interoperable with

802.11b, 802.11g

 8.8
Explain OSI and TCP/IP data models 

An architectural model is a common frame of reference for explaining Internet communications and developing communication protocols. It separates the functions
of protocols into manageable layers. Each layer performs a specific function in the process of communicating over a network. 

The TCP/IP model was created by researchers in the U.S. Department of Defense (DoD). The TCP/IP model is a tool used to help explain the TCP/IP suite of
protocols, which is the dominant standard for transporting data across networks. This model has four layers, as shown in Figure 1.

In the early 1980s, the International Standards Organization (ISO) developed the Open Systems Interconnect (OSI) model, which was defined in ISO standard
7498-1, to standardize the way devices communicate on a network. This model has seven layers, as shown in Figure 1. This model was a major step forward
toward ensuring that there would be interoperability between network devices. 

After completing this section, you will meet these objectives:

list of 3 items
• Define the TCP/IP model. 
• Define the OSI model. 
• Compare OSI and TCP/IP. 


this needs work 
TCP/IP Model vs. OSI Model
TCP/IP Model
OSI Model
Application
Application
Presentation
Session
Transport
Transport
Internet
Network
Network Access
Security Chapter Introduction
Data Link
Physical


  8.8  
Explain OSI and TCP/IP data models      
8.8.1  
Define the TCP/IP model   
table end

The TCP/IP reference model provides a common frame of reference for the development of the protocols used on the Internet. It consists of layers that perform
functions necessary to prepare data for transmission over a network. The chart in Figure 1 shows the four layers of the TCP/IP model.

A message begins at the op layer, the Application layer and moves down the TCP/IP layers to the bottom layer, the Network Access layer. Header information
is added to the message as it moves down through each layer and is then transmitted. After reaching the destination, the message travels back up through
each layer of the TCP/IP model. The header information that was added to the message is stripped away as the message moves up through the layers toward
its destination.

Application Protocols 
Application layer protocols provide network services to user applications such as web browsers and e-mail programs. Explore some of the more common Internet
protocols in Figure 2, the Application layer, to learn more about the protocols that operate in this layer.

Transport Protocols 
Transport layer protocols provide end-to-end management of the data. One of the functions of these protocols is to divide the data into manageable segments
for easier transport across the network. Explore each of the protocols in Figure 3, the Transport layer, to learn more about the protocols that operate
in this layer.

Internet Protocols 
Internet layer protocols operate in the third layer from the top in the TCP/IP model. These protocols are used to provide connectivity between hosts in
the network. Explore each of the protocols in Figure 4, the Internet layer, to learn more about the protocols that operate in this layer.

Network Access Protocols
Network Access layer protocols describe the standards that hosts use to access the physical media. The IEEE 802.3 Ethernet standards and technologies,
such as CSMA/CD and 10BASE-T are defined in this layer.

needs work 
TCP/IP Internet Layer Protocols 
2
2
3
3
4
4
IP
Internet Protocol (IP) provides source and destination addressing, much like the address and return address on a postal envelope. In conjunction with routing
protocols, IP provides packet forwarding information from one network to another.
ICMP
RIP
ARP


  8.8  
Explain OSI and TCP/IP data models      
8.8.2  
Define the OSI model   
table end

The OSI model is an industry standard framework that is used to divide network communications into seven distinct layers. Although other models exist, most
network vendors today build their products using this framework.

A system that implements protocol behavior consisting of a series of these layers is known as a protocol stack. Protocol stacks can be implemented either
in hardware or software, or a combination of both. Typically, only the lower layers are implemented in hardware, and the higher layers are implemented
in software.

Each layer is responsible for part of the processing to prepare data for transmission on the network. The chart in Figure 1 shows what each layer of the
OSI model does.

In the OSI model, when data is transferred, it is said to virtually travel down the OSI model layers of the sending computer, and up the OSI model layers
of the receiving computer.

When a user wants to send data, such as an e-mail, the encapsulation process starts at the Application layer. The Application layer is responsible for providing
network access to applications. Information flows through the top three layers and is considered to be data when it gets down to the Transport layer.

At the Transport layer, the data is broken down into more manageable segments, or Transport layer protocol data units (PDUs), for orderly transport across
the network. A PDU describes data as it moves from one layer of the OSI model to another. The Transport layer PDU also contains information such as port
numbers, sequence numbers, and acknowledgement numbers, which is used for reliable data transport.

At the Network layer, each segment from the Transport layer becomes a packet. The packet contains logical addressing and other layer-3 control information.

At the Data Link layer, each packet from the Network layer becomes a frame. The frame contains physical address and error correction information.

At the Physical layer, the frame becomes bits. These bits are transmitted one at a time across the network medium.

At the receiving computer, the de-encapsulation process reverses the process of encapsulation. The bits arrive at the Physical layer of the OSI model of
the receiving computer. The process of virtually traveling up the OSI model of the receiving computer will bring the data to the Application layer, where
an e-mail program will display the e-mail.

NOTE: Mnemonics can help you remember the seven layers of the OSI. Some examples include: "All People Seem To Need Data Processing" and "Please Do Not Throw
Sausage Pizza Away".

OSI Model
OSI Model 
Layer
Description
Application
Responsible for network services to applications
7
Presentation
Transforms data formats to provide a standard interface for the Application layer
6
Session
Establishes, manages and terminates the connections between the local and remote application
5
Transport
4
Provides reliable transport and flow control across a network
Network
3
Responsible for logical addressing and the domain of routing
Data Link
2
Provides physical addressing and media access procedures
Physical
1
Defines all the electrical and physical specifications for devices

  8.8  
Explain OSI and TCP/IP data models      
8.8.3  
Compare OSI and TCP/IP   
table end

The OSI model and the TCP/IP model are both reference models used to describe the data communication process. The TCP/IP model is used specifically for
the TCP/IP suite of protocols and the OSI model is used for development of standard communication for equipment and applications from different vendors.

The TCP/IP model performs the same process as the OSI model, but uses four layers instead of seven. The chart in Figure 1 shows how the layers of the two
models compare.  

Activity 
OSI Model
Complete the OSI model matching activity in Figure 2

this is content from that graphic 
OSI Model and TCP/IP Model Compared
2
2
OSI Reference Model
Application
TCP/IP Model
Presentation
Session
Application
Transport
Network
Transport
Data Link
Internet
Physical
Network

Interface


 8.9
Describe how to configure a NIC and a modem 

A network interface card (NIC) is required to connect to the Internet. The NIC may come preinstalled or you may have to purchase one on your own. In rare
cases, you may need to update the driver. You can use the driver disc that comes with the motherboard or adapter card, or you can supply a driver that
you downloaded from the manufacturer.

After the NIC and the driver have been installed, you can connect the computer to the network. 

In addition to installing a NIC, you may also need to install a modem to connect to the Internet.

After completing this section, you will meet these objectives: 

list of 3 items
• Install or update a NIC driver. 
• Attach the computer to an existing network. 
• Describe the installation of a modem. 


  8.9  
Describe configuring a NIC and a modem       
8.9.1  
Install or update a NIC driver    
table end

Sometimes, a manufacturer will publish new driver software for a NIC. A new driver may enhance the functionality of the NIC, or it may be needed for operating
system compatibility.

When installing a new driver, be sure to disable virus protection software so that none of the files is incorrectly installed. Some virus scanners detect
a driver update as a possible virus attack. Also, only one driver should be installed at a time; otherwise, some updating processes may conflict updating
processes may conflict.

A best practice is to close all applications that are running so that they are not using any files associated with the driver update. Before updating a
driver, you should visit the manufacturer's website. In many cases, you can download a self-extracting executable driver file that will automatically install
or update the driver. Alternatively, you can click the Update Driver button in the toolbar of the Device Manager.

The "+" next to the Network adapters category allows you to expand the category and show the network adapters installed in your system. To view and change
the properties of the adapter, or update the driver, double-click the adapter. In the adapter properties window select the Driver tab.

After the update has been completed, it is a good idea to reboot the computer even if you do not receive a message telling you to reboot. Rebooting the
computer will ensure that the installation has gone as planned and that the new driver is working properly. When installing multiple drivers, reboot the
computer between each update to make sure that there are no conflicts. This step takes extra time but will ensure a clean installation of the driver.

Uninstall a NIC Driver
If a new NIC driver does not perform as expected after it has been installed, the driver can be uninstalled, or rolled back, to the previous driver. Double-click
the adapter in the Device Manager. In the Adapter Properties window, select the Driver tab and click Roll Back Driver. If there was no driver installed
before the update, this option will not be available. In that case, you will need to find a driver for the device and install it manually if the operating
system could not find a suitable driver for the NIC.  

Worksheet 
Internet Search for NIC Drivers
Research NIC drivers

  8.9  
Describe configuring a NIC and a modem       
8.9.2  
Attach computer to existing network   
table end

Now that the NIC drivers are installed, you are ready to connect to the network. Plug a network cable, also called an Ethernet patch or straight-through
cable, into the network port on the computer. Plug the other end into the network device or wall jack.

After connecting the network cable, look at the LEDs, or link lights, next to the Ethernet port on the NIC to see if there is any activity. Figure 1 shows
network activity on a NIC. If there is no activity, this may indicate a faulty cable, a faulty hub port, or even a faulty NIC. You may have to replace
one or more of these devices to correct the problem.

After you have confirmed that the computer is connected to the network and the link lights on the NIC indicate a working connection, the computer will need
an IP address. Most networks are set up so that the computer will receive an IP address automatically from a local DHCP server. If the computer does not
have an IP address, you will need to enter a unique IP address in the TCP/IP properties of the NIC.

Every NIC must be configured with the following information:

list of 3 items
• Protocols – The same protocol must be implemented between any two computers that communicate on the same network. 
• IP address – This address is configurable and must be unique to each device. The IP address can be manually configured or automatically assigned by DHCP.

• MAC address – Each device has a unique MAC address. The MAC address is assigned by the manufacturer and cannot be changed. 
list end

After the computer is connected to the network, you should test connectivity with the ping command. Use the ipconfig command, shown in Figure 2, to find
out what your IP address is. Ping your own IP address to make sure that your NIC is working properly. After you have determined that your NIC is working,
ping your default gateway or another computer on your network, as shown in Figure 3. A default gateway allows a host to communicate outside of your network.
If you have an Internet connection, ping a popular website, such as www.cisco.com. If you can ping an Internet site or another computer on your network
successfully, everything is working properly with your connection. If you cannot ping one of these, you will need to begin troubleshooting the connection. 


Lab 
DHCP Configuration for Ethernet NIC
Configure NIC to use DHCP from 300N

  8.9  
Describe configuring a NIC and a modem       
8.9.3  
Describe the installation of a modem   
table end

A modem is an electronic device that transfers data between one computer and another using analog signals over a telephone line. Examples of modems are
shown in Figure 1. The modem converts digital data to analog signals for transmission. The modem at the receiving end reconverts the analog signals back
to digital data to be interpreted by the computer. The process of converting analog signals to digital and back again is called modulation/demodulation.
Modem-based transmission is very accurate, despite the fact that telephone lines can be noisy due to clicks, static, and other problems.

An internal modem plugs into an expansion slot on the motherboard. To configure a modem, jumpers may have to be set to select the IRQ and I/O addresses.
No configuration is needed for a plug-and-play modem, which can only be installed on a motherboard that supports plug-and-play. A modem using a serial
port that is not yet in use must be configured. Additionally, the software drivers that come with the modem must be installed for the modem to work properly.
Drivers for modems are installed the same way drivers are installed for NICs.

External modems connect to a computer through the serial and USB ports.

When computers use the public telephone system to communicate, it is called dial-up networking (DUN). Modems communicate with each other using audio tone
signals. This means that modems are able to duplicate the dialing characteristics of a telephone. DUN creates a Point-to-Point Protocol (PPP) connection
between two computers over a phone line. 

After the line connection has been established, a "handshaking sequence" takes place between the two modems and the computers. The handshaking sequence
is a series of short communications that occur between the two systems. This is done to establish the readiness of the two modems and computers to engage
in data exchange. Dial-up modems send data over the serial telephone line in the form of an analog signal. Because the analog signals change gradually
and continuously, they can be drawn as waves. In this system, the digital signals are represented by 1s and 0s. The digital signals must be converted to
a waveform to travel across telephone lines. They are converted back to the digital form, 1s and 0s, by the receiving modem so that the receiving computer
can process the data. 

AT Commands 
All modems require software to control the communication session. Most modem software uses the Hayes-compatible command set. The Hayes command set is based
on a group of instructions that always begins with a set of attention characters (AT), followed by the command characters. These are known as AT commands.
The AT command set is shown in Figure 2.

The AT commands are modem control commands. The AT command set is used to issue dial, hang up, reset, and other instructions to the modem. Most user manuals
that come with a modem contain a complete listing of the AT command set. 

The standard Hayes-compatible code to dial is ATDxxxxxxx. There are usually no spaces in an AT string. If a space is inserted, most modems will ignore it.
The "x" signifies the number dialed. There will be seven digits for a local call and 11 digits for a long-distance call. A W indicates that the modem will
wait for an outside line, if necessary, to establish a tone before proceeding. Sometimes, a T is added to signify tone dialing or a P is added to signify
pulse dialing. 

 8.10
Identify names, purposes, and characteristics of other technologies used to establish connectivity 

There are many ways to connect to the Internet. Phone, cable, satellite, and private telecommunications companies offer Internet connections for businesses
and home use.

In the 1990s, the Internet was typically used for data transfer. Transmission speeds were slow compared to the high-speed connections that are available
today. Most Internet connections were analog modems that used the "plain old telephone system" (POTS) to send and receive data. In recent years, many businesses
and home users have switched to high-speed Internet connections. The additional bandwidth allows for transmission of voice and video as well as data. 

You should understand how users connect to the Internet and the advantages and disadvantages of different connection types. 

After completing this section, you will meet these objectives:

list of 4 items
• Describe telephone technologies. 
• Define power line communication. 
• Define broadband. 
• Define VOIP. 


  8.10  
Identify names, purposes, and characteristics of other technologies for establishing connectivity      
8.10.1  
Describe telephone technologies   
table end

There are several WAN solutions available for connecting between sites or to the Internet. WAN connection services provide different speeds and levels of
service. Before committing to any type of Internet connection, research all available services to determine the best solution to match the needs of your
customer.

Analog Telephone
This technology uses standard voice telephone lines. This type of service uses a modem to place a telephone call to another modem at a remote site, such
as an Internet Service provider. There are two major disadvantages of using the phone line with an analog modem. The first is that the telephone line cannot
be used for voice calls while the modem is in use. The second is the limited bandwidth provided by analog phone service. The maximum bandwidth using an
analog modem is 56 Kbps, but in reality, it is usually much lower than that. An analog modem is not a good solution for the demands of busy networks.

Integrated Services Digital Network (ISDN)
The next advancement in WAN service is ISDN. ISDN is a standard for sending voice, video, and data over normal telephone wires. ISDN technology uses the
telephone wires as an analog telephone service. However, ISDN uses digital technology to carry the data. Because it uses digital technology, ISDN provides
higher-quality voice and higher-speed data transfer than traditional analog telephone service.

There are three services offered by ISDN digital connections: Basic Rate Interface (BRI), Primary Rate Interface (PRI), and Broadband ISDN (BISDN). ISDN
uses two different types of communications channels. The "B" channel is used to carry the information – data, voice, or video – and the "D" channel is
usually used for controlling and signaling, but can be used for data.

Click the names of the types of ISDN in Figure 1 to learn more.

Digital Subscriber Line (DSL)
DSL is an "always-on" technology. “Always on” means that there is no need to dial up each time to connect to the Internet. DSL uses the existing copper
telephone lines to provide high-speed digital data communication between end users and telephone companies. Unlike ISDN, where the digital data communications
replaces the analog voice communications, DSL shares the telephone wire with analog signals.

The telephone company limits the bandwidth of the analog voice on the lines. This limit allows the DSL to place digital data on the phone wire in the unused
portion of the bandwidth. This sharing of the phone wire allows voice calls to be placed while DSL is connecting to the Internet.

There are two major considerations when selecting DSL. DSL has distance limitations. The phone lines used with DSL were designed to carry analog information.
Therefore, the length that the digital signal can be sent is limited and cannot pass through any form of multiplexer used with analog phone lines. The
other consideration is that the voice information and the data carried by DSL must be separated at the customer site. A device called a splitter separates
the connection to the phones and the connection to the local network devices.

Asymmetric Digital Subscriber Line (ADSL)
ADSL is currently the most commonly used DSL technology. ADSL has different bandwidth capabilities in each direction. ADSL has a fast downstream speed
– typically 1.5 Mbps. Downstream is the process of transferring data from the server to the end user. This is beneficial to users who are downloading large
amounts of data. The high speed upload rate of ADSL is slower. ADSL does not perform well when hosting a web server or FTP server, both of which involve
upload-intensive Internet activities. 

Click the types of DSL in Figure 2 to learn more.

ISDN Types
2
2
ISDN Types
ISDN Basic Rate Interface offers a dedicated 128 Kbps connection using two 64 Kbps B channels.

ISDN BRI also uses one 16 Kbps

D channel for call setup, control,

and teardown.
BRI
PRI
BISDN

  8.10  
Identify names, purposes, and characteristics of other technologies for establishing connectivity      
8.10.2  
Define power line communication    
table end

Power line communication (PLC) is a communication method that uses power distribution wires (local electric grid) to send and receive data.

PLC is known by other names:

list of 3 items
• Power Line Networking (PLN) 
• Mains Communication 
• Power Line Telecoms (PLT) 
list end

With PLC, an electric company can superimpose an analog signal over the standard 50 or 60 Hz AC that travels in power lines. The analog signal can carry
voice and data signals.

PLC may be available in areas where other high-speed connections are not. PLC is faster than an analog modem, and may cost much less than other high-speed
connection types. As this technology matures, it will become more common to find and may increase in speed.

You can use PLC to network computers within your home instead of installing network cabling or wireless technology. PLC connections can be used anywhere
there is an electrical outlet. You can control lighting and appliances using PLC without installing control wiring.

  8.10  
Identify names, purposes, and characteristics of other technologies for establishing connectivity      
8.10.3  
Define broadband   
table end

Broadband is a technique used to transmit and receive multiple signals using multiple frequencies over one cable. For example, the cable used to bring cable
television to your home can carry computer network transmissions at the same time. Because the two transmission types use different frequencies, they do
not interfere with each other.

Broadband is a signaling method that uses a wide range of frequencies that can further be divided into channels. In networking, the term broadband describes
communication methods that transmit two or more signals at the same time. Sending two or more signals simultaneously increases the rate of transmission.
Some common broadband network connections include cable, DSL, ISDN, and satellite.

Cable
A cable modem connects your computer to the cable company using the same coaxial cable that connects to your cable television. A cable modem is shown in
Figure 1. You can plug your computer directly into the cable modem, or you can connect a router, switch, hub, or multipurpose network device so that multiple
computers can share the connection to the Internet.

DSL
With DSL, the voice and data signals are carried on different frequencies on the copper telephone wires. A filter is used to prevent DSL signals from interfering
with phone signals. A DSL filter is shown in Figure 2. Plug the filter into a phone jack and plug the phone into the filter. 

The DSL modem does not require a filter. The DSL modem is not affected by the frequencies of the telephone. Like a cable modem, a DSL modem can connect
directly to your computer, or it can be connected to a networking device to share the Internet connection with multiple computers.

ISDN
ISDN is another example of broadband. ISDN uses multiple channels and can carry different types of services; therefore, it is considered a type of broadband.
ISDN can carry voice, video, and data.

Satellite
Broadband satellite is an alternative for customers who cannot get cable or DSL connections. A satellite connection does not require a phone line or cable,
but uses a satellite dish for two-way communication. Download speeds are typically up to 500 Kbps; uploads are closer to 56 Kbps. It takes time for the
signal from the satellite dish to relay to your Internet Service Provider (ISP) through the satellite orbitting the Earth.

People who live in rural areas often use satellite broadband because they need a faster connection than dial-up and no other broadband connection is available.
  

Worksheet 

Broadband
Identify the different types of broadband

  8.10  
Identify names, purposes, and characteristics of other technologies for establishing connectivity      
8.10.4  
Define VoIP   
table end

Voice over IP (VoIP) is a method to carry telephone calls over the data networks and Internet. VoIP converts the analog signals of our voices into digital
information that is transported in IP packets. VoIP can also use an existing IP network to provide access to the public switched telephone network (PSTN).

When using VoIP, you are dependent on an Internet connection. This can be a disadvantage if the Internet connection experiences an interruption in service.
When a service interruption occurs, the user cannot make phone calls.


VoIP Phones
Linksys IP Phone
Cisco IP Phone 

 8.11
Identify and apply common preventive maintenance techniques used for networks 

There are common preventive maintenance techniques that should continually be performed for a network to operate properly. In an organization, if there
is one malfunctioning computer, generally only one user is affected. But if the network is malfunctioning, many or all users will be unable to work.

One of the biggest problems with network devices, especially in the server room, is heat. Network devices, such as computers, hubs, and switches, do not
perform well when over heated. Often, excess heat is generated by accumulated dust and dirty air filters. When dust gathers in and on network devices,
it impedes the proper flow of cool air and sometimes even clogs fans. It is important to keep network rooms clean and change air filters often. It is also
a good idea to have replacement filters available for prompt maintenance.

Preventive maintenance involves checking the various components of a network for wear. Check the condition of network cables because they are often moved,
unplugged, and kicked. Many network problems can be traced to a faulty cable. You should replace any cables that have exposed wires, are badly twisted,
or are bent.

Label your cables. This practice will save troubleshooting time later. Refer to wiring diagrams and always follow your company's cable labeling guidelines.

 8.12
Troubleshoot a network 

Network issues can be simple or complex. To assess how complicated the problem is, you should determine how many computers on the network are experiencing
the problem.

If there is a problem with one computer on the network, start the troubleshooting process at that computer. If there is a problem with all computers on
the network, start the troubleshooting process in the network room where all computers are connected. As a technician, you should develop a logical and
consistent method for diagnosing network problems by eliminating one problem at a time.

Follow the steps outlined in this section to accurately identify, repair, and document the problem. The troubleshooting process is shown in Figure 1.

After completing this section, you will meet these objectives:

list of 2 items
• Review the troubleshooting process. 
• Identify common network problems and solutions. 

Troubleshooting Process  
1 Gather Data from the Customer 
2 Verify the Obvious Issues
3 Try Quick Solutions First
4 Gather Data from the Computer 
5 Evaluate the Problem and Implement the Solution
6 Close with the Customer

  8.12  
Troubleshoot the network      
8.12.1  
Review the troubleshooting process   
table end

Network problems can result from a combination of hardware, software, and connectivity issues. Computer technicians must be able to analyze the problem
and determine the cause of the error in order to repair the network issue. This process is called troubleshooting. 

The first step in the troubleshooting process is to gather data from the customer. Figures 1 and 2 list open-ended and closed-ended questions to ask the
customer.

Once you have talked to the customer, you should verify the obvious issues. Figure 3 lists some issues for networks.

After the obvious issues have been verified, try some quick solutions. Figure 4 lists some quick solutions for networks.

If quick solutions did not correct the problem, it is time to gather data from the computer. Figure 5 shows different ways to gather information about the
problem from the network.

At this point, you will have enough information to evaluate the problem, research, and implement possible solutions. Figure 6 shows resources for possible
solutions.

After you have solved the network problem, you will close with the customer. Figure 7 is a list of the tasks required to complete this step.

Open-Ended Questions
What problems are you experiencing with your computer or network?
What software has been installed on your computer recently?
What were you doing when the problem was identified?
What error messages have you received on your computer?
What type of network connection is the computer using?


  8.12  
Troubleshoot the network      
8.12.2  
Identify common network problems and solutions   
table end

Network problems can be attributed to hardware, software, connectivity issues, or some combination of the three. You will resolve some types of network
problems more often than others. Figure 1 is a chart of common network problems and solutions.  

Worksheet 

Network Problem
Help desk activity to diagnose a network problem

 8.13
Summary 

This chapter introduced you to the fundamentals of networking, the benefits of having a network, and the ways to connect computers to a network. The different
aspects of troubleshooting a network were discussed with examples of how to analyze and implement simple solutions. The following concepts from this chapter
are important to remember:

list of 16 items
• A computer network is composed of two or more computers that share data and resources. 
• A Local Area Network (LAN) refers to a group of interconnected computers that are under the same administrative control. 
• A Wide Area Network (WAN) is a network that connects LANs in geographically separated locations. 
• In a peer-to-peer network, devices are connected directly to each other. A peer-to-peer network is easy to install, and no additional equipment or dedicated
administrator is required. Users control their own resources, and a network works best with a small number of computers. A client/server network uses a
dedicated system that functions as the server. The server responds to requests made by users or clients connected to the network. 
• A LAN uses a direct connection from one computer to another. It is suitable for a small area, such as in a home, building, or school. A WAN uses point-to-point
or point-to-multipoint, serial communications lines to communicate over greater distances. A WLAN uses wireless technology to connect devices together.

• The network topology defines the way in which computers, printers, and other devices are connected. Physical topology describes the layout of the wire
and devices, as well as the paths used by data transmissions. Logical topology is the path that signals travel from one point to another. Topologies include
bus, star, ring, and mesh. 
• Networking devices are used to connect computers and peripheral devices so that they can communicate. These include hubs, bridges, switches, routers,
and multipurpose devices. The type of device implemented depends on the type of network. 
• Networking media can be defined as the means by which signals, or data, are sent from one computer to another. Signals can be transmitted either by cable
or wireless means. The media types discussed were coaxial, twisted-pair, fiber-optic cabling, and radio frequencies. 
• Ethernet architecture is now the most popular type of LAN architecture. Architecture refers to the overall structure of a computer or communications system.
It determines the capabilities and limitations of the system. The Ethernet architecture is based on the IEEE 802.3 standard. The IEEE 802.3 standard specifies
that a network implement the CSMA/CD access control method. 
• The OSI reference model is an industry standard framework that is used to divide the functions of networking into seven distinct layers. These layers
include Application, Presentation, Session, Transport, Network, Data Link, and Physical. It is important to understand the purpose of each layer. 
• The TCP/IP suite of protocols has become the dominant standard for the Internet. TCP/IP represents a set of public standards that specify how packets
of information are exchanged between computers over one or more networks. 
• A NIC is a device that plugs into a motherboard and provides ports for the network cable connections. It is the computer interface with the LAN. 
• A modem is an electronic device that is used for computer communications through telephone lines. It allows data transfer between one computer and another.
The modem converts byte-oriented data to serial bit streams. All modems require software to control the communication session. The set of commands that
most modem software uses is known as the Hayes-compatible command set. 
• The three transmission methods to sending signals over data channels are simplex, half-duplex, and full-duplex. Full-duplex networking technology increases
performance because data can be sent and received at the same time. DSL, two-way cable modem, and other broadband technologies operate in full-duplex mode.

• Network devices and media, such as computer components, must be maintained. It is important to clean equipment regularly and use a proactive approach
to prevent problems. Repair or replace broken equipment to prevent downtime. 
• When troubleshooting network problems, listen to what your customer tells you so that you can formulate open-ended and closed-ended questions that will
help you determine where to begin fixing the problem. Verify obvious issues and try quick solutions before escalating the troubleshooting process. 
list end