Computer Networks Foundation - Study Notes

Computer Networks Foundation
Study Notes
+W Series - Technology Skills For Women1
http://SlideShare.net/OxfordCambridge
1 Men are allowed to read too, if they wish, as the language style and the document format are universal.

Study Notes http://SlideShare.net/OxfordCambridge
2 | P a g e C o m p u t e r N e t w o r k s F o u n d a t i o n
Table of Contents
About “+W Series - Technology Skills For Women”..............................................................................................................................................5
References.................................................................................................................................................................................................................................6
Course Objectives..................................................................................................................................................................................................................7
I. NETWORKING BASICS:...........................................................................................................................................................8
A. NETWORKING OVERVIEW..............................................................................................................................................................................9
1. Core network components...........................................................................................................................................................................................9
Quiz............................................................................................................................................................................................................................................ 11
2. Network architectures................................................................................................................................................................................................ 11
Quiz............................................................................................................................................................................................................................................ 13
Quiz............................................................................................................................................................................................................................................ 13
Summary................................................................................................................................................................................................................................. 13
B. TYPES OF NETWORKS..................................................................................................................................................................................14
1. Local area networks (LANs)..................................................................................................................................................................................... 14
Quiz............................................................................................................................................................................................................................................ 15
2. Wide area networks (WANs)................................................................................................................................................................................... 15
Quiz............................................................................................................................................................................................................................................ 16
Quiz............................................................................................................................................................................................................................................ 17
3. Metropolitan area networks (MANs)................................................................................................................................................................... 17
Quiz............................................................................................................................................................................................................................................ 17
4. Intranets and extranets .............................................................................................................................................................................................. 18
Quiz............................................................................................................................................................................................................................................ 18
Quiz............................................................................................................................................................................................................................................ 19
Summary................................................................................................................................................................................................................................. 19
C. THE OSI MODEL ..........................................................................................................................................................................................20
1. The OSI reference model............................................................................................................................................................................................ 20
Quiz............................................................................................................................................................................................................................................ 22
2. Layers of the OSI model.............................................................................................................................................................................................. 23
Quiz............................................................................................................................................................................................................................................ 26
3. Encapsulation and de-encapsulation................................................................................................................................................................... 26
Quiz............................................................................................................................................................................................................................................ 30
4. The TCP/IP stack........................................................................................................................................................................................................... 34
Quiz............................................................................................................................................................................................................................................ 37
Quiz............................................................................................................................................................................................................................................ 38
Summary................................................................................................................................................................................................................................. 39
D. UNDERSTANDING BASIC NETWORKING CONCEPTS.................................................................................................................................40
Exercise overview.............................................................................................................................................................................................................. 40
Task 1: Identifying networks........................................................................................................................................................................................ 40
Step 1 of 3............................................................................................................................................................................................................................... 41
Result........................................................................................................................................................................................................................................ 41
Step 2 of 3............................................................................................................................................................................................................................... 41
Result........................................................................................................................................................................................................................................ 41
Step 3 of 3............................................................................................................................................................................................................................... 42
Result........................................................................................................................................................................................................................................ 42
Task 2: Identifying characteristics of data encapsulation .............................................................................................................................. 42
Step 1 of 3............................................................................................................................................................................................................................... 43
Result........................................................................................................................................................................................................................................ 43
Step 2 of 3............................................................................................................................................................................................................................... 44
Result........................................................................................................................................................................................................................................ 44
Step 3 of 3............................................................................................................................................................................................................................... 44
Result........................................................................................................................................................................................................................................ 45
II. NETWORKING DEVICES AND TOPOLOGIES:.................................................................................................................46
E. COMPONENTS OF A NETWORK PC............................................................................................................................................................47
1. PC components............................................................................................................................................................................................................... 47
Quiz............................................................................................................................................................................................................................................ 53
2. Network interface cards............................................................................................................................................................................................. 54
Quiz............................................................................................................................................................................................................................................ 57
Quiz............................................................................................................................................................................................................................................ 57
Summary................................................................................................................................................................................................................................. 58

F. NETWORK DEVICES.....................................................................................................................................................................................59
1. OSI layer 1 devices........................................................................................................................................................................................................ 60
Quiz............................................................................................................................................................................................................................................ 61
Quiz............................................................................................................................................................................................................................................ 65
Quiz............................................................................................................................................................................................................................................ 70
4. Multiple layer devices.................................................................................................................................................................................................. 70
Quiz............................................................................................................................................................................................................................................ 73
Quiz............................................................................................................................................................................................................................................ 73
Summary................................................................................................................................................................................................................................. 73
G. NETWORK TOPOLOGIES..............................................................................................................................................................................74
1. Distinguishing physical and logical topologies............................................................................................................................................... 74
Quiz............................................................................................................................................................................................................................................ 76
2. Identifying topology types ........................................................................................................................................................................................ 77
Quiz............................................................................................................................................................................................................................................ 81
Quiz............................................................................................................................................................................................................................................ 81
Summary................................................................................................................................................................................................................................. 81
H. IDENTIFYING NETWORK DEVICES AND TOPOLOGIES..............................................................................................................................82
Exercise overview.............................................................................................................................................................................................................. 82
Task 1: Identifying network device functions...................................................................................................................................................... 82
Step 1 of 3............................................................................................................................................................................................................................... 83
Result........................................................................................................................................................................................................................................ 83
Step 2 of 3............................................................................................................................................................................................................................... 84
Result........................................................................................................................................................................................................................................ 84
Step 3 of 3............................................................................................................................................................................................................................... 84
Result........................................................................................................................................................................................................................................ 84
Task 2: Selecting network topologies....................................................................................................................................................................... 85
Step 1 of 3............................................................................................................................................................................................................................... 85
Result........................................................................................................................................................................................................................................ 86
Step 2 of 3............................................................................................................................................................................................................................... 86
Result........................................................................................................................................................................................................................................ 86
Step 3 of 3............................................................................................................................................................................................................................... 87
Result........................................................................................................................................................................................................................................ 87
III. PHYSICAL MEDIA: .............................................................................................................................................................89
I. NETWORK CABLING AND WIRELESS MEDIA.............................................................................................................................................90
1. Unshielded and shielded twisted pair cable..................................................................................................................................................... 90
Quiz............................................................................................................................................................................................................................................ 93
2. Coaxial cable..................................................................................................................................................................................................................... 94
Quiz............................................................................................................................................................................................................................................ 97
3. Fiber optic cable............................................................................................................................................................................................................. 97
Cable types...........................................................................................................................................................................................................................101
Quiz..........................................................................................................................................................................................................................................102
4. Wireless communications.......................................................................................................................................................................................102
Complete list of cable types.........................................................................................................................................................................................106
Quiz..........................................................................................................................................................................................................................................106
Summary...............................................................................................................................................................................................................................107
J. NETWORK CABLE CONNECTORS..............................................................................................................................................................108
1. Twisted pair and coaxial cable connectors.....................................................................................................................................................108
Quiz..........................................................................................................................................................................................................................................113
2. Fiber optic cable connectors..................................................................................................................................................................................114
Quiz..........................................................................................................................................................................................................................................116
3. The IEEE 1394 standard ..........................................................................................................................................................................................117
Quiz..........................................................................................................................................................................................................................................118
Summary...............................................................................................................................................................................................................................119
K. NETWORK INSTALLATION TOOLS............................................................................................................................................................120
1. Patch panels and wiring tools................................................................................................................................................................................120
Quiz..........................................................................................................................................................................................................................................123
2. Media testing tools......................................................................................................................................................................................................123
Quiz..........................................................................................................................................................................................................................................128
Summary...............................................................................................................................................................................................................................128
L. CONNECTING THE NETWORK (EXERCISE).............................................................................................................................................130
Exercise overview............................................................................................................................................................................................................130
Task 1: Choosing a network media type ...............................................................................................................................................................130

Step 1 of 1.............................................................................................................................................................................................................................131
Result......................................................................................................................................................................................................................................131
Task 2: Recognizing media specifications............................................................................................................................................................132
Step 1 of 3.............................................................................................................................................................................................................................132
Result......................................................................................................................................................................................................................................133
Step 2 of 3.............................................................................................................................................................................................................................133
Result......................................................................................................................................................................................................................................133
Step 3 of 3.............................................................................................................................................................................................................................134
Result......................................................................................................................................................................................................................................134
Task 3: Recognizing cable connector types.........................................................................................................................................................135
Step 1 of 4.............................................................................................................................................................................................................................135
Result......................................................................................................................................................................................................................................135
Step 2 of 4.............................................................................................................................................................................................................................136
Result......................................................................................................................................................................................................................................136
Step 3 of 4.............................................................................................................................................................................................................................137
Result......................................................................................................................................................................................................................................137
Step 4 of 4.............................................................................................................................................................................................................................137
Result......................................................................................................................................................................................................................................138
IV. ANNEXES: ..........................................................................................................................................................................139
The OSI model Illustrated.............................................................................................................................................................................................140
M. GLOSSARY ...................................................................................................................................................................................................143
N. ANSWERS TO QUIZZES..............................................................................................................................................................................166

About “+W Series - Technology Skills For Women”
Study Notes in the field of technology will be put together under this category for the following reasons:
 to encourage ladies, who wish to do so, to stand up and look over the fence into technology related
topics;
 with no apprehension or fear;
 and perhaps consider embracing a career move into a technological path;
 or simply as to broaden their general knowledge; after all ICT is in most aspects of everyday life;
 no matter the decision, their skills, professional strengths, and contribution can only be something
positive for technical and technological fields.
Enjoy!

References
Network + Study Guide, David Groth, Sybex Inc
OSI model (Open Systems Interconnection model), http://en.wikipedia.org/wiki/OSI_model , on 18 April 2014 at
11:00
Computo integrado, http://avecomputointe.blogspot.fr/2012_02_01_archive.html , February 2012

Computer Networks Foundation
I. Networking basics:
A. Networking overview
B. Types of networks
C. The OSI model
D. Understanding basic networking concepts
II. Networking devices and topologies:
E. Components of a network PC
F. Network devices
G. Network topologies
H. Identifying network devices and topologies
III. Physical media:
I. Network cabling and wireless media
J. Network cable connectors
K. Network installation tools
L. Connecting the network
Course Objectives
Topic Name When you have completed this topic, you should be able to
Networking overview identify the primary components of a network and distinguish between the two main network
architectures.
Types of networks distinguish between the main types of networks
The OSI model distinguish between the OSI reference model and the TCP/IP stack.
Understanding basic networking
concepts
distinguish between common network categorizations and identify the characteristics of data
encapsulation.
Components of a network PC identify the major components of a network PC and list the resources required to install a NIC.
Network devices identify the functions, features, and operation of network devices used at different layers of the
OSI model.
Network topologies distinguish between different network topologies
Identifying network devices and
topologies
match network devices to their functions and distinguish between different network topologies.
Network cabling and wireless media differentiate between types of network media.
Network cable connectors recognize the types of cable connectors used in modern networks.
Network installation tools determine the most appropriate network tool to use in a given scenario.
Connecting the network determine the appropriate network media and connectors to use in a given scenario.

I. Networking basics:
C. The OSI model
After completing this section, you should be familiar with:
 identifying the primary components of a network and distinguish between the two main network
architectures
 distinguishing between the main types of networks


After completing section, you should be able to identify the primary components of a network and
distinguish between the two main network architectures.
1. Core network components
2. Network architectures |
1. Core network components
A network consists of two or more computers connected together which share resources such as data,
printers, and an Internet connection.
The term "networking" refers to the sharing of resources on a network.
Networks can consist of a small group of computers localized to a building or they can extend over large
geographic areas, as follows.
 local area network (LAN)
 wide area network (WAN)

local area network (LAN)
A LAN is a network that is confined to a small geographic area – for example, within a building. Each
individual computer can access data and devices anywhere on the LAN.
wide area network (WAN)
A WAN is a computer network that spans a relatively wide area. A WAN consists of a system of
interconnected LANs. The Internet is an example of a global WAN.
A network consists of the following three primary components.
 Server
 Workstation
 Host
Server
A server is a powerful computer that provides resources to other computers on the network. Servers are
often dedicated, meaning that they perform no other tasks besides their server tasks.
Workstation

A workstation is any computer on a network that can request resources and is used to do work. A
workstation may have multiple CPUs, making it faster and more capable than a personal computer.
Workstations and clients are different. A client is any device on a network that can request resources.
Host
A host is any network device that has a Transmission Control Protocol/Internet Protocol (TCP/IP)
address. Workstations and servers that have TCP/IP addresses can be considered hosts. Each host has a
unique IP address.
Quizi
Match each network component with its description.
Options:
1. Host
2. Server
3. Workstation
Targets:
A. A powerful computer that provides resources to other computers on the network
B. Any computer on a network that can request resources and is used to do work
C. Any network device that has a TCP/IP address
2. Network architectures
The purpose of a network is to share resources. The following are two common network types.
 Peer-to-peer
 Client/server
Peer-to-peer
In a peer-to-peer network, the computers have no centralized authority. All of the computers have server
and client capabilities and equal responsibilities on the network. Access rights to resources in a peer-to-
peer network are handled by the machine holding the resource.
Peer-to-peer networks are generally used in situations where security needs are minimal.

Client/server
With the client/server model, the entire network is managed from a central point and some computers
are dedicated to serving the others. Each computer is either a client or a server and each client relies on a
server for resources. The Internet is based on the client/server model.
Client/server networks hold several advantages over peer-to-peer networks. A client/server network is
more organized than a peer-to-peer network, because all files and resources are stored on servers and
are easier to locate.
Client/server networks are more secure than peer-to-peer networks, because passwords and
usernames are stored on a dedicated server. Unlike peer-to-peer networks, client/server networks can
be scaled almost infinitely in size.

Quizii
What are the characteristics of the client/server network model?
Options:
1. Centralized management
2. Clients have server functionality
3. Good security
4. Scalability
Quiziii
What are the advantages of using a client/server network over a peer-to-peer network?
Options:
1. Access rights handled by clients
2. Easier to manage
3. More efficient
4. More secure
Summary
A network is made up of two or more computers linked together. Networking is the term used to refer to
the sharing of resources on the network. Networks can vary in size from local area networks (LANs),
which are contained in a building, to wide area networks (WANs), such as the Internet. The three
primary components of a network are a server, a workstation, and a host.
Two of the most common network types are client/server and peer-to-peer. Peer-to-peer networks have
no centralized authority while client/server networks are managed from a centralized point.
Client/server networks have several advantages over peer-to-peer networks such as ease of
management and better security.

After completing this section, you should be able to distinguish between the main types of networks.
1. Local area networks (LANs)
2. Wide area networks (WANs)
3. Metropolitan area networks (MANs)
4. Intranets and extranets
1. Local area networks (LANs)
Local area networks (LANs) are one of the most widely used types of networks.
LANs are high-speed, low-error, data networks that are confined to a small area, usually within a
building. LANs connect workstations, servers, and peripheral devices, such as printers, together.
Ethernet LANs are the most common type of LANs. This term is often used to refer to all types of LANs.
Different types of Ethernet LAN are
 Ethernet
 Fast Ethernet
 Gigabit Ethernet
Network standards are defined by the Institute of Electrical and Electronics Engineers (IEEE).

In the middle of the 1980s, an IEEE workgroup defined a standard for Ethernet called Ethernet 802.3.
Today, this standard is commonly referred to as Ethernet.
Quiziv
Identify the correct statement about a LAN.
Options:
1. Limited to a specific area
2. Covers a large geographic area
3. Can only be a client/server network
4. Not scalable
2. Wide area networks (WANs)
A wide area network, or WAN, is a network that covers a large geographic area. WANs can operate
beyond the geographic scope of a LAN.
The Internet is the best known example of a WAN. The Internet is public but WANs can also be private,
linking the worldwide locations of a corporation together, for example.
WANs differ from LANs in a number of ways:
 they cover greater distances than LANs
 WAN speeds are slower
 LANs primarily use private network transports while WANs can use public or private network
transports

Internet service providers, or ISPs, are used to facilitate the large geographic reach of a WAN. If a
corporation wanted to link up its American headquarters with its European office, it would use an ISP to
establish the network over this great distance.
WANs require several core devices to function.
 Routers
 WAN switches
 Modems
Routers
Routers are used to direct traffic on a network to its correct destination. A router is connected to at least
two networks, and it is located where the networks connect.
WAN switches
WAN switches are used to logically connect routers on the WAN using virtual circuits.
Modems
Modems provide remote access to networks by converting digital signals to analog ones so that the data
can be transmitted over analog communication facilities such as telephone lines.
Quizv
In what ways do WANs differ from LANs?

Options:
1. Cover large geographic areas
2. Only connect cities together
3. WAN connections are more expensive than LAN connections
4. WANs primarily use private network transports
Quizvi
Match each WAN device to its function.
Options:
1. Modem
2. Router
3. WAN switch
Targets:
A. Directs traffic on a network to the correct destination
B. Connects routers on a WAN
C. Provides remote access to a network
3. Metropolitan area networks (MANs)
A metropolitan area network, or MAN, is a network that covers a metropolitan area such as a city or
suburban area. MANs are larger than LANs but smaller than WANs.
A MAN is usually created when two or more LANs are connected together, offering high-speed
connections.
Quizvii
Which statement correctly describes a MAN?

Options:
1. Connects workstations, peripherals, terminals, and other devices in a single building
2. Interconnected by routers and other devices and functions as a single global network
3. Serves users across a wide geographic area
4. Spans a metropolitan area such as a city or suburban area
4. Intranets and extranets
An intranet is a private network that exists within a business. It can consist of many interlinked LANs.
Only people within the company or organization can access the intranet.
The main purpose of an intranet is to share company information and resources between employees. An
intranet looks like a private version of the Internet.
When part of a company's intranet becomes available to customers, suppliers, or anyone outside the
company, the network is known as an extranet.
Extranets use Internet Protocol (IP) and a public communication system to share part of an
organization's information and resources with its customers, suppliers, or other businesses. A firewall is
used to ensure security on the network.
Quizviii
Identify the features of extranets.
Options:
1. Available to users outside the business
2. Available only within a business

3. Requires security
Quizix
Match each network type to its description.
Options:
1. LAN
2. MAN
3. WAN
Targets:
A. Covers a city or suburban area
B. Confined to a small area
C. Covers a large geographic area
Summary
A local area network (LAN) is used to connect workstations, servers, and peripheral devices, such as
printers, together. It is confined to a small area, usually within a building.
A wide area network (WAN) covers a large geographic area. WANs can be public or private. WANs have
slower connection speeds than LANs. WANs use routers, WAN switches, and modems. The Internet is an
example of a global WAN.
A metropolitan area network (MAN) extends across a city or a large suburban area. A MAN develops
when two or more LANs are connected together.
An intranet is a private network contained inside a company. It can contain many LANs linked together.
It allows employees to share information and access company resources. An extranet is part of a
company's intranet that can be accessed by anyone outside the company.

C. The OSI model
After completing this topic, you should be able to distinguish between the OSI reference model and the
TCP/IP stack.
1. The OSI reference model
2. Layers of the OSI model
3. Encapsulation and de-encapsulation
4. The TCP/IP stack
1. The OSI reference model
The Open System Interconnection (OSI) model was developed in 1984 by the International Organization
for Standardization (ISO) to resolve the problem of incompatible networks. There had been a big
increase in the number and sizes of networks in the middle of the 1980s. Companies began to
experience difficulties due to all the expansions they had made as a result of the early development of
LANs, MANs, and WANs.
Many companies could not communicate with each other because they were using different network
specifications and implementations. They realized that the proprietary technologies, which were
privately developed, owned, and controlled by individual or a group of companies, were a hindrance to
developing networking systems.
A standard or a technology can be described as follows.
 proprietary
 open

proprietary
A proprietary standard means that one company (or a small group of companies) controls the technology
rights and usage.
Proprietary is the opposite to open when referring to standards or technologies in the computer industry.
open
An open standard means that the technology usage is available for free implementation to the public.
The ISO researched different network schemes and proposed a seven-layer model.

The OSI model is a reference model for describing how information should be exchanged between points
on a network. For example, it describes how data from a word processing application on one computer
is sent to another computer when the sender and receiver are connected using different network media.
The OSI model has a number of advantages:
 enables compatibility between different types of networks
 provides like standards for vendors
 facilitates an understanding of how data travels within a network
enables compatability between different types of networks
The OSI model enables greater compatibility and interoperability between the different network
technologies produced by companies around the world.
provides like standards for vendors
The OSI model provides vendors with a set of standards that enables them to implement compatible
networks.
facilitates an understanding of how data travels within a network
Many network vendors relate their products to the OSI model, especially when they want to educate
customers on the use of their products. It is considered as a standard for teaching people about sending
and receiving data on a network.
Quizx
Identify the true statements about the OSI model.

Options:
1. Facilitates compatibility between different networks
2. Specifies how information travels through networks
3. Speeds up network communication
4. Defines the network functions that occur at each layer
2. Layers of the OSI model
The process of data transfer between computers is represented by the seven layers of the OSI model -
each of which addresses an essential networking task.
The OSI model is divided into seven numbered layers. The layers are:
 application
 presentation
 session
 transport
 network
 data-link
 physical

application
The application layer provides file, print, message, and application database services. It provides network
services to applications that require access to the network. It controls how these services are advertised
and made available. It does not provide services to any other layer. This layer also deals with user
authentication and privacy.
presentation
The presentation layer manages data representation. It transforms data into a mutually agreed format
that each application can understand. It formats and structures data, ensuring it is readable between
hosts. An example of this would be the implementation of character sets such as the American Standard
Code for Information Interchange (ASCII) and Extended Binary-Coded Decimal Interchange Code
(EBCDIC). It also organizes the syntax of data transfer for the application layer. Data compression and
encryption take place at this layer.
session
The session layer provides communication between hosts. It does this by connection establishment, data
transfer, and connection release. This includes the authentication, creation, management, and termination
of sessions between different applications. It provides its services to the presentation layer.
transport
The transport layer aids point-to-point communications. It provides reliability in the transportation of
data between hosts and ensures complete data transfer. The transport layer uses error detection and
recovery information flow control to establish, maintain, and terminate all virtual circuits.
network
The network layer ensures data delivery by providing connectivity and path selection between two host
systems. It selects the most appropriate path for sending data, and routes data packets. In the network
layer, logical addressing and resolving names to host physical addresses is carried out. This layer works
with the commonly used IP addresses assigned to hosts. The network layer provides logical LAN-to-LAN
communications by supporting the routing of data between different networks.
data-link
The data-link layer arranges bits from the physical layer into logical chunks of data, known as frames. A
frame is a contiguous series of data with a common function. Framing enables the network to organize
bits into a logical data format and send them to the correct computer. This layer also controls how data is
formatted and how transmission on the network is controlled.
physical
The physical layer is responsible for providing the most basic element of data transport – binary
transmission. This layer outlines the functional, procedural, electrical, and mechanical specifications for
controlling physical links. The specifications relate to the activation, maintenance, and deactivation of
physical links. It also controls the transmitting of data onto physical media.
Each layer in the OSI model contains a set of functions or protocols performed by programs to enable
data packets to travel from A to B on a network. The protocols that operate at each layer offer a solution
to a networking challenge.
The OSI model is conceptualized in a way that may seem upside down. Data is received from the

network and sent up from the physical layer at the bottom to the application layer - which, in turn, sends
data it generates back down through the layers. When it reaches the physical layer again, it is sent out on
the network.
The advantages of layering network functions are:
 accelerates evolution
 ensures interoperable technology
 facilitates modular engineering
 reduces complexity
 standardizes interfaces
 simplifies teaching and learning
accelerates evolution
Layering accelerates evolution by supporting updates and improvements to individual components. It can
do this without affecting other components or having to rewrite the entire protocol.
ensures interoperable technology
Layering ensures interoperable technology and quicker development by preventing changes in one layer
from affecting the other layers.
facilitates modular engineering
Layering facilitates modular engineering by allowing different types of network hardware and software to
communicate with each other.

reduces complexity
Layering reduces complexity by breaking network communication into smaller, simpler components.
standardizes interfaces
Layering standardizes network component interfaces, which provides vendors with a set of standards
that ensures greater compatibility between the various network technologies.
simplifies teaching and learning
Layering simplifies teaching and learning by breaking up the task of networking into a number of distinct
layers.
Quizxi
Match these OSI layers to a description of their functions.
Options:
1. Application
2. Data-link
3. Network
4. Presentation
5. Session
6. Transport
Targets:
A. Ensures data delivery
B. Ensures reliable data transfer between hosts
C. Formats and structures data
D. Synchronizes and maintains communication between hosts
E. Provides access to the network media
F. Provides network services to applications
3. Encapsulation and de-encapsulation
When one computer wants to send data to another computer, the data must first be packaged through a
process called encapsulation. Encapsulation wraps the data with the required protocol information
before transmitting the data to the network.

Encapsulation can be compared to placing a letter in an envelope, then writing the name and address on
it so that it can be delivered to the right destination.

As data moves through the layers of the OSI model, each layer adds a header (and a trailer, if applicable).
The process starts at the application layer and moves down to the physical layer. These headers and
trailers contain information for devices and receiving hosts to ensure that the data is delivered reliably.
They also ensure that the receiver can understand and use that data accordingly.
These are the eight steps in the encapsulation process:
 step 1
 step 2
 step 3
 step 4
 step 5
 step 6
 step 7
 step 8

step 1
The user data is sent from an application to the seventh layer of the OSI model - the application layer.
step 2
The application layer adds the header (L7) to the user data. The L7 header and the original user data
become the data that is now passed down to the presentation layer.
step 3
The presentation layer adds the presentation layer header (L6) to the data. This now becomes the data
that is passed down to the session layer.
step 4
The session layer adds the session layer header (L5) to the data. This now becomes the data that is passed
down to the transport layer.
step 5
The transport layer adds the transport layer header (L4) to the data. This now becomes the data that is
passed down to the network layer.
step 6
The network layer adds the network layer header (L3) to the data. This now becomes the data that is
passed down to the data-link layer.
step 7

The data-link layer adds the data-link layer header (L2) to the data. This now becomes the data that is
passed down to the physical layer.
step 8
The last layer of the OSI model - the physical layer - then transmits the bits onto the network media.
Quizxii
Rank the layers of the OSI model in the order in which encapsulation occurs, after the data first passes
through the application layer.
Option Description
A Data-link
B Network
C Physical
D Presentation
E Session
F Transport
De-encapsulation occurs when information is received - first it is checked for errors and, if none is
found, it is then stripped of its header. The physical layer passes the frame to the data-link layer for
manipulation - this process can be divided into four tasks within the data-link layer.

De-encapsulation is similar to checking the address on a letter to see if it's for you or not, then removing
the letter from the envelope if it's addressed to you.
The data-link layer performs the following tasks in the de-encapsulation process:

 task 1
 task 2
 task 3
 task 4
task 1
It checks the data-link trailer to see if the data contains any errors.
task 2
If the data contains any errors, it may be discarded - the data-link layer may ask that the data be
retransmitted.
task 3
If the data has no errors, the data-link layer reads and interprets the control information in the data-link
header.
task 4
The data-link layer strips the data of its header and trailer, and then passes the remaining data up to the
network layer based on the control information in the data-link header.
It is necessary to have peer-to-peer communication for the encapsulation process so that packets can
travel from the source to the destination. During the encapsulation process, the protocols at each layer
exchange information, called protocol data units (PDUs), between the peer layers.

At the transport layer, this information is exchanged in units known as segments. At the network layer,
the information is exchanged as packets. At the data-link layer, the information is exchanged as frames.
Finally, at the physical layer, the information is exchanged as bits.
When discussing data at different layers, this makes it easier for people to understand which layer is
being referred to, instead of simply calling all data units packets.
Data packets always originate at a source and then travel to a destination point on a network. Each layer
is dependent on the service provided by the OSI layer below it. The lower layer carries out the

encapsulation process to take the PDU from the upper layer into its data field. It then adds the necessary
headers to the layer to perform its function.
Remember that data packets can only travel on a network if each layer of the OSI model at the source
communicates with its peer layer at the destination. This form of communication is known as peer-to-
peer communication.
4. The TCP/IP stack
As well as the universally recognized OSI reference model, there is another open standard traditionally
applied to the Internet – the Transmission Control Protocol/Internet Protocol (TCP/IP) stack.
Both the TCP/IP stack and the OSI model use layering. TCP/IP comprises the following four layers:
 application
 transport
 Internet
 network access
Although some of the layers in the TCP/IP stack are the same as those in the OSI reference model, they
do not function in the same manner.

The following are the functions of the four layers of the TCP/IP stack.
 application
 transport
 internet
 network access

application
The main function of the application layer is to manage high-level protocols. This includes aspects
relating to dialog control, encoding, and representation. The TCP/IP stack groups all application aspects
into one layer and ensures that application-related data is properly packaged for the layer below.
transport
The main function of the transport layer is to handle such quality-of-service issues as reliability, flow
control, and any error correction. The TCP protocol, which is part of the TCP/IP suite of protocols,
provides reliable network communication.
internet
The main function of the Internet layer is to provide packet delivery and hierarchical addressing services.
It sends source packets from any network on the internetwork and ensures they arrive at the correct
destination, no matter what path they have taken to get there.
network access
The network access layer is also known as the host-to-network layer. It looks after all the issues handled
by the OSI physical and data-link layers. This layer includes the LAN and WAN protocols.
The TCP/IP stack and the OSI model share some similarities.
The main similarities between the two models are:
 application layers
 packet-switched technology
 transport and network layers
application layers
Although both models have application layers, the functions of these layers in each model are slightly
different.

packet-switched technology
Both models operate on the premise that packet-switched, rather than circuit-switched technology, is in
use.
transport and network layers
The functions of the transport and network layers are comparable in each model.
Quizxiii
Identify the similarities between the OSI reference model and the TCP/IP stack.

Options:
1. Both models have an application layer
2. The Internet layer is common to both models
3. They both deal with packet-switched technology
4. They have similar transport and network layer functions
There are also a number of differences between the TCP/IP stack and the OSI reference model:
 the OSI data-link and physical layers are combined into the network access layer in the TCP/IP
 TCP/IP also combines the OSI presentation and session layers into its application layer
 the TCP/IP stack is the standard around which the Internet developed, while the OSI model is
generally only used as a guide
Quizxiv
In the TCP/IP stack, which layer deals with reliability, flow control, and error correction?
Options:
1. Application
2. Internet
3. Network Access
4. Transport

Summary
The Open System Interconnection (OSI) reference model was developed by the International
Organization for Standardization (ISO) to correct the problem of incompatible network communications.
It is a reference model that describes how information is exchanged between points on a network.
The OSI model is divided into seven layers - these are the application, presentation, session, transport,
network, data-link, and physical layers. Some of the advantages of layering network functions include
accelerating evolution, reducing complexity, and standardizing network component interfaces.
Encapsulation refers to the process of packaging information before it is transmitted. Encapsulation
occurs in descending order from the application layer through to the physical layer. Headers and trailers
are placed around the data as it passes through each layer.
Data packets always travel from source to destination on a network. They can only travel on a network if
each layer of the OSI model at the source communicates with its peer layer at the destination. This form
of communication is known as peer-to-peer communication.
Another open standard traditionally applied to the Internet is the Transmission Control
Protocol/Internet Protocol (TCP/IP) stack. Like the OSI model, it uses layering and is comprised of the
application, transport, Internet, and network access layers. The TCP/IP and OSI models are similar in a
number of ways. Both models have application, network, and transport layers, and they both deal with
packet-switched technology.

After completing this section, you should be able to distinguish between common network
categorizations and identify the characteristics of data encapsulation.
Exercise overview
Task 1: Identifying networks
Task 2: Identifying characteristics of data encapsulation
Exercise overview
In this exercise, you're required to distinguish between common network categorizations and identify
characteristics of data encapsulation.
This involves the following tasks:
 identifying networks
 identifying characteristics of data encapsulation
Task 1: Identifying networks
There are different categorizations of networks used to identify their size, structure, and purpose.

Step 1 of 3
This network type covers a large geographic area and can be used to link together the worldwide locations
of a corporation.
Identify which network fits this description.
Options:
1. LAN
2. MAN
3. WAN
Result
A WAN is a network that covers a large geographic area and can be used to link together the worldwide
locations of a corporation.
Option 1 is incorrect. The structure of a LAN is usually identified by a simple network structure, comprising an
easily manageable number of devices.
Option 2 is incorrect. A MAN could incorporate multiple office locations for a large company.
Option 3 is correct. A WAN can span continents. The Internet is the best known example of a large-scale WAN.
Step 2 of 3
This network type covers a large city or suburban area and consists of several LANs connected together.
Options:
1. LAN
2. MAN
3. WAN
Result
A MAN covers a large city or suburban area and consists of several LANs connected together.
Option 1 is incorrect. A LAN is usually the easiest type of network to access regarding the number of devices it
contains.
Option 2 is correct. A MAN will connect businesses and homes together in a city or suburban area.
Option 3 is incorrect. A WAN extends across larger geographic areas than those covered by MANs.

Step 3 of 3
This network is a high-speed, low error data network that is confined to a small area, usually within a
building.
Options:
1. LAN
2. MAN
3. WAN
Result
A LAN is a high-speed, low error data network that is confined to a small area, usually within a building.
Option 1 is correct. A LAN is typically set up within a company to connect several computers, a server, and
peripheral devices so that resources can be shared.
Option 2 is incorrect. A MAN is an extension of a LAN. MANs connect many buildings together in a city or large
suburban area.
Option 3 is incorrect. A WAN operates on a national or international scale, connecting locations over great
distances.
You are now familiar with different types of networks.
Task 2: Identifying characteristics of data encapsulation
Data encapsulation occurs when data is systematically and consistently packaged before it is sent over
the network.

Step 1 of 3
Match each OSI layer to its corresponding header in the encapsulation process.
Options:
1. Session
2. Presentation
3. Application
Targets:
A. L7
B. L6 L7
C. L5 L6 L7
Result
In the encapsulation process, the application layer contains the L7 header, the presentation layer contains
the L6 L7 headers, and the session layer contains the L5 L6 L7 headers.
The session layer contains the L5 L6 L7 headers. At the session layer the L5 header is added to the data and this
becomes the data that is passed down to the transport layer.
The presentation layer contains the L6 L7 headers. The L7 header is added to the data at the application layer,
and at the presentation layer the L6 header is also added.
The application layer contains the L7 header, it adds this header to the user data and passes the data and
header down to the next layer.

Step 2 of 3
Match the packet headers with the correct OSI layers.
Options:
1. L4 L5 L6 L7
2. L3 L4 L5 L6 L7
3. L2 L3 L4 L5 L6 L7
Targets:
A. Data-link
B. Network
C. Transport
Result
A data packet contains the L4 L5 L6 L7 header at the transport layer, the L3 L4 L5 L6 L7 header at the
network layer, and the L2 L3 L4 L5 L6 L7 header at the data-link layer.
The transport layer receives the data from the session layer and adds the L4 header.
The network layer adds the L3 header. This now becomes the data that is passed down to the data-link layer.
The data-link layer adds the L2 header. This is the last header added to the data before it is passed to the
physical layer and the bits transmitted onto the network media.
Step 3 of 3
Match the encapsulation terms with the correct OSI layer.
Options:
1. Bits
2. Frames
3. Packets
4. Segments
Targets:
A. Data-link
B. Network
C. Physical
D. Transport

Result
Bits are associated with the physical layer, frames with the data-link layer, packets with the network layer,
and segments with the transport layer.
The physical layer receives the bits and sends them to the data-link layer for de-encapsulation.
The data-link layer checks the data for any errors and if none are found, it encapsulates the data as a frame and
passes it up to the network layer.
The network layer exchanges the information as packets and defines the logical addressing of hosts in the
network.
The transport layer ensures that segments are delivered without errors to the receiving device.
You are now familiar with the characteristics of data encapsulation.

II. Networking devices and topologies:
F. Network devices
H. Identifying network devices and topologies
After completing this section, you should be familiar with:
 potential future developments in wireless services.
 identifying the characteristics and benefits of the principal and enabling technologies of 4G.

After completing this section, you should be able to identify the major components of a network PC and
list the resources required to install a NIC.
1. PC components
2. Network interface cards
1. PC components
The components used by a computer to enable network connectivity include the:
 central processing unit (CPU)
 bus
 drives
 memory components
 ports
 cards
These are all located in the system unit, in the case of a desktop PC.

Some networking devices such as routers, hubs, and bridges have similar components to computers.
A computer is composed of a number of key components.
 Drives
 CPU
 Expansion slots
 Bus
 Backplane components
 Motherboard

Drives
The drives on a computer include the
 CD-ROM
 DVD-ROM
 floppy disk
 hard disk
The CD-ROM drive reads information from a CD-ROM disk. Modern CD-ROM drives can both read from,
and write to, CD disks.
A DVD-ROM drive reads information from DVD disks. DVD-ROM drives are also available that can both
read from, and write to, DVD disks.

You can use the floppy disk drive to read and write to floppy disks. The hard disk drive is the computer's
internal device for reading and writing data also.
CPU
The CPU (central processing unit) processes, manipulates, and interprets computer data sent to it from
software or the user, and performs the requested operations of the hardware devices connected within
the computer. The microprocessor is a silicon chip within a CPU.
Expansion slots
Expansion slots in a computer are used for adding cards that provide additional functionality to the
computer. Some examples are Firewire cards, modem cards, and sound cards, but there are many other
types of cards available also.
Bus
A bus is an electrical connection used to pass data and control information between different components
within a computer. It also connects all the internal components of the computer to the CPU. The memory
bus and Peripheral Component Interconnect (PCI) bus are typical examples of the types of buses found in
a computer.

Backplane components
You can plug external devices, such as your mouse, keyboard, and power cable, into the backplane.
A number of components form the backplane.
A number of components form the backplane as follows:

- Interfaces allow external hardware to be connected to the computer's backplane.
You insert a network card into the backplane of your computer if you want to connect it to a computer
network.
- You use the parallel port to connect devices that require the simultaneous transfer of more than one bit,
such as a printer.
- You can add a sound card to the backplane to enable sound functions on your computer.
- The Universal Serial Bus (USB) port is used for fast serial connection transmissions of one bit at a time.
- You plug a video card into a computer to enable video capabilities.
Motherboard
The large printed circuit board (PCB), to which everything connects within your computer, is called the
motherboard. This provides a single connection for, and between, all the components and devices within
the computer.
Random access memory (RAM) and read-only memory (ROM) are located on the motherboard.

Random access memory (RAM) and read-only memory (ROM) are located on the motherboard as follows.
Random access memory (RAM) is the primary memory of your computer. Data stored here can be read
from, and written to, at very fast speeds. The data stored is only temporary; it is either cleared by being
replaced or lost when the power is turned off.
Losing the power in your computer while it is turned on can result in the loss of data stored in RAM -
unless you have saved it.
Read-only memory (ROM) is non-volatile, which means it stays there even if you lose power. In general,
you can read from this type of memory, but you cannot write to it. To write to it, you need special types of
ROM memory that provide specific functions to the computer.
Quizxv
Match the PC components to their descriptions.
Options:
1. Backplane
2. Bus
3. CPU
4. Expansion slot
5. CD-ROM drive
Targets:
A. It allows additional cards to be plugged into the motherboard
B. It allows external devices to be connected
C. It connects all the internal computer components to the CPU
D. It is where most of the calculations take place
E. It can read and write to compact discs

2. Network interface cards
A network interface card (NIC) allows a computer to communicate with other computers over a
network. The NIC provides a port for the computer to physically connect to a network using a cable. A
NIC is also known as a LAN adapter. It uses a serial connection to communicate with the network, but
communicates with the computer over a parallel connection.
You need drivers to operate a NIC in your computer. You also need memory space for its functions
within the operating system - for example, Windows.
A NIC uses its MAC address to identify its host computer to the network it is connected to. This MAC
address is a unique address assigned to this NIC only.
A MAC address is 48 bits long, and is derived partly from a unique NIC vendor-assigned number, and
partly from numbers the vendor assigns to its devices.
As well as drivers and memory, you need
 an input/output (I/O) address
 an interrupt request line (IRQ) signal

an input/output (I/O) address
The NIC needs the input/output (I/O) address to read or write data to the computer. The address
identifies a part of memory that is assigned for use by the NIC.
an interrupt request line (IRQ) signal
An interrupt request line (IRQ) signal identifies which device in the computer is requesting the CPU to
perform a function. For example, when data arrives into a NIC, its IRQ indicates to the CPU that it has data
that needs to be processed for the NIC.
Your choice of NIC depends on your
 cable
 expansion slots
 network

cable
Different NICs use different port connector types. This depends on the type of network implemented and
the cable being used - for example, Ethernet RJ-45 connectors on twisted pair cable.
expansion slots
Peripheral Component Interconnect (PCI) expansion slots are standard, but older computers may have
Industry Standard Architecture (ISA) slots.
network
If you are connecting to a Token Ring LAN, you should use a Token Ring NIC, for example.
To install a NIC, you need to understand the configuration and operation of:
 erasable programmable read-only memory (EPROM)
 jumpers and switch settings
 plug-and-play software
If there is a problem with the NIC, you should be familiar with the network card diagnostics – such as
loopback tests and the diagnostics procedure supplied by the NIC vendor. You should also be able to fix
hardware resource conflicts with IRQs and direct memory access (DMA). DMA enables RAM to
communicate with a device directly without using the CPU.

Some NICs have specialized functions in networks and require specific technical expertise.
Quizxvi
What should you know before installing a NIC?
Options:
1. How the network card is configured
2. How to configure specialized functions in different types of network cards
3. How to fix hardware resource conflicts
4. How to use the network card diagnostics
Quizxvii
What factors should you consider before installing a NIC?
Options:
1. Cable type
2. Network type
3. Type of CPU
4. Type of expansion slot

Summary
To enable network connectivity, a computer uses components such as the central processing unit (CPU),
bus, drives, cards, ports, and memory. A computer is composed of drives, the CPU, expansion slots, a bus,
a motherboard, and a backplane.
A network interface card (NIC) is a device that enables a computer to communicate with a network.
Selecting a NIC depends on the type of network, cable, and expansion slot on your computer. If installing
a NIC, you should be able to configure it, perform its diagnostics, and resolve hardware conflicts.

F. Network devices
After completing this section, you should be able to identify the functions, features, and operation of
network devices used at different layers of the OSI model.
1. OSI layer 1 devices
4. Multiple layer devices
The Open System Interconnection (OSI) model is used as a reference model to relate network
components to their functions.
Components used in layers 1 to 3 include devices such as:

 routers, switches and firewalls
 hubs and bridges
 repeaters
 network interface cards
 AAA services
There are a number of commonly used layer 1 (physical layer) devices. These include:
 repeaters
 hubs
repeaters
In layer 1 of the OSI model, repeaters regenerate and retransmit the electrical network signals, so that
they can travel greater distances without deteriorating. They are used to increase the area a network can
cover by extending the reach of the network cables used. Repeaters are considered layer 1 devices
because they operate at bit level. A multiport repeater is called a hub.
hubs
Like repeaters, some hub types can regenerate and retransmit network signals, but while a repeater has
only two ports, a hub can have several – up to 20 – ports. A hub receives on one port and retransmits the
signal to all other ports.

There are hubs that can amplify and propagate signals, and are used as network concentration points.
Hubs do not perform filtering, nor do they perform path determination. They are commonly used in
Ethernet 10BaseT or 100BaseT networks.
Hubs increase the reliability of a network because the failure of one cable connection to the central hub
will not result in network failure, as only that port is affected.
Quizxviii
Identify the functions of a hub.
Options:
1. Forwards network signals at bit level
2. Receives data on several ports and transmits on one port
3. Creates a central connection point for network cables
4. Performs path determination and switching
Layer 2 (data-link layer) devices facilitate the transmission of data. There are a number of devices that
operate at this layer.
 Network Interface cards (NICs)
 Bridges
 Switches

Network Interface cards (NICs)
Network Interface Cards (NICs) are defined as layer 2 devices because each one has a unique Media
Access Control (MAC) address identifying the host on the network. NICs are used to control data
communications.
Bridges
Bridges are layer 2 devices that create local area network (LAN) segments. A bridge provides extra
bandwidth needed for data exchange by:
 filtering local LAN traffic,
 maintaining connectivity between network segments directly connected to it.
Bridges are preferable over hubs because they can efficiently manage data transmission between
connected segments based on the MAC addresses, and filter out unnecessary traffic from reaching a
segment.

By transmitting data only to the required network segment based on the MAC addresses used, bridges are
able to forward data quickly and efficiently without clogging up network segments.
One of the functions of a bridge is to ensure that data is delivered only to the required segments of the
network. This means that there is more bandwidth available on the individual segments as they are not
receiving data from every segment.
Bridges gather and manage MAC addresses in tables. On a bridge, each port creates a separate collision
domain, so a collision on one segment does not affect other segments. This means several devices can
communicate simultaneously in a LAN without affecting each other.
Bridges use their MAC address tables to gauge whether the destination of a packet is on the same segment
or a different segment to that of the sender. It then sends the data to the destination segment only. This
has the effect of reducing network traffic, as data is not needlessly sent throughout the LAN.
Description of how a bridge operates on a network follows.
Two small network segments containing approximately four computers each are connected by a bridge.
The bridge only allows data from one segment to cross the bridge to the other segment if it is using a
destination address from there.

Switches
Switches are hardware devices used at layer 2, which create multiple bridge connections. Switches are
often used instead of hubs, and can reduce the disruption caused by data traffic on a network. Switches
connect LAN segments into single networks, and use MAC addresses to decide where to forward traffic.
They are faster than bridges, because the switching decisions are performed using specialized hardware
instead of software.
A switch port connected to a host behaves like a separate bridge and provides the host with the full
bandwidth of the cable. This is often called micro segmentation.
Description of how switches forward traffic follows.
A switch uses the MAC address of a data packet sender to identify it.
It locates the packet's destination based on the destination's MAC address.

Quizxix
What are the advantages of using a bridge?
Options:
1. It allows more than one device to transmit simultaneously
2. It can rapidly forward data
3. It does not process all received data
4. It keeps track of which MAC addresses are on each side of the bridge
In network communications, two types of addressing are used:
 layer 2
 layer 3
layer 2
The layer 2 addressing scheme uses the MAC address (physical address) to identify network hosts.

layer 3
The layer 3 addressing scheme uses a logical address, such as an IP address, to identify network hosts.
The purpose of a router is to use layer 3 (network layer) addresses to transmit data packets between
networks. It uses IP addresses instead of MAC addresses to decide on the optimum path to be used for
data delivery.

Routers have become important to the maintenance of the Internet because of their ability to transmit
packets based on layer 3 information.
They can also be used to connect different layer 2 technologies - for example, Token Ring and Ethernet -
which enables virtually any kind of computer to communicate with any other computer anywhere on the
globe.

Routers can also examine layer 4 information when sending data between devices or networks.
Multilayer switches are similar to layer 2 switches except that they use layer 3 network addresses (IP)
as well as using layer 2 MAC addresses.

Using software processes to carry out layer 3 routing can frequently cause bottlenecks, but layer 3
routing functions can now be carried out in the switch hardware. High-speed hardware-based
multilayer switches can now deliver layer 3 functions with the same speed as layer 2 functions.
Using hardware to enable layer 3 routing functions provides an improved quality of service. Hardware-
based layer 3 routing functions use the location of the sender and receiver in each transmission to
prioritize the packets being delivered.

This allows hardware-based functions to prevent traffic from unnecessarily entering networks for which
it is not intended.
Quizxx
How does a router establish the destination network for data?
Options:
1. It examines the destination IP address
2. It examines the destination MAC address only
3. It examines the destination MAC and IP addresses
4. Multiple layer devices
A gateway is a complex network device that connects disparate network environments - for example, a
LAN environment to a mainframe environment. A gateway uses a combination of hardware and
software, and can carry out translations at various layers of the OSI model.

E-mail programs typically use gateways to communicate with Internet mail servers. They use gateways
to translate LAN-based mail messages into Simple Mail Transfer Protocol (SMTP) format.
There are other network devices that work at and above the lower three layers. These include:
 firewalls
 AAA servers

firewalls
Firewalls are positioned on the edge of private networks, and protect them from any unwanted traffic or
attacks attempting to access the internal network. A firewall examines all traffic and packets to ensure
that they are legitimate, dropping any that fail to conform to its rules of entry.
When there is more than one internal network, a firewall can control access to them from the outside, and
traffic between the internal networks also.
AAA servers
An authentication, authorization, and accounting (AAA) server processes requests from users to gain
access to network resources. The AAA server:
 only allows authenticated users onto the network
 gives users access only to the resources they are authorized to use
 keeps an account of user behavior

Quizxxi
Which sentence best describes the function of a gateway?
Options:
1. A device used by e-mail programs to determine routing paths for IP traffic
2. A combined hardware/software device that connects dissimilar network environments
3. A translation device that operates solely at layer 1 of the OSI model
Quizxxii
Match each network device with a description of its function.
Options:
1. Bridge
2. Repeater
3. Router
Targets:
A. Creates separate collision domains on each port
B. Employs layer 3 addresses to transmit data packets between networks
C. Regenerates and retransmits network signals at layer 1 of the OSI model
Summary
Hubs, switches, and routers are all networking devices used to connect networks. Networking devices
operate chiefly at the lower three layers of the Open System Interconnection (OSI) model. Layer 1
devices, such as repeaters and hubs, are used to propagate network signals at bit level.
Network Interface Cards (NICs), bridges, and switches are OSI layer 2 devices used to transmit data.
Every NIC has a unique Media Access Control (MAC) address that is used to identify its host to switches
and bridges. These devices forward traffic based on the host's MAC address.
Routers use layer 3 addresses to transmit packets between networks. Multilayer switches use layer 3
network addresses (IP) as well as layer 2 MAC addresses to manage packet traffic. Hardware-based
layer 3 routing functions provide faster operation than software versions.
Gateways are used to connect disparate network environments. Firewalls and AAA (authentication,
authorization, and accounting) servers protect networks from unauthorized attacks and unauthorized
access.

After completing this section, you should be able to distinguish between the features of different
network topologies.
1. Distinguishing physical and logical topologies
2. Identifying topology types
1. Distinguishing physical and logical topologies
Networks can have different topologies. A network topology describes how the network is laid out, and
how data is transmitted on it.
A network has two topologies:
 logical topology
 physical topology
logical topology
The logical topology describes the structure and the path connection types between the different parts of
the network. It defines how data flows in the network.

physical topology
The physical topology describes the physical arrangement of the devices and cables on a network. It
shows the actual paths taken by data when traveling around the network.
A network can have the same logical and physical topologies, but this is not always the case. A network
with a logical bus topology, for example, can also have a physical bus topology structure.

The physical layout of a network does not necessarily determine how data flows in it. For example, a
Token Ring network can have a physical star topology, but use a logical ring topology to communicate
data.
A Token Ring network can use a logical ring topology with either a physical ring or physical star
topology. Ethernet can use either of these two physical topologies with a logical bus topology.
Quizxxiii
Identify the correct statements about network topologies.
Options:
1. A logical topology defines precisely the arrangement of devices on the network
2. A physical topology describes the paths that signals use to travel from one point on the network to
another
3. Networks can have a physical and a logical topology
4. The physical topology defines the way in which network devices are connected together

2. Identifying topology types
Different network topologies are used as template structures to define how best to implement networks.
The topology outlines the way in which the computers, printers, and other network devices are linked
together.
 Bus
 Star
 Ring
 Mesh
Bus
A bus topology functions like a single path with all devices connecting to it. In this topology, all the
computers are connected by a single cable, and all data communications pass through this cable in a
linear fashion.
At the end of the main cable, a terminator device is used to absorb the signal when it arrives at the end of
the cable. Without the terminator, the signal can bounce back and cause problems on the network. This
type of problem is called signal reflection.
A bus topology is also known as a linear bus.

Computer Networks Foundation - Study Notes

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Computer Networks Foundation - Study Notes