CCNA Guide to Cisco Networking Fundamentals, Fourth Edition 1-1
Chapter 1
Introducing Networks
At a Glance
Instructor’s Manual Table of Contents
• Overview
• Objectives
• Teaching Tips
• Quick Quizzes
• Class Discussion Topics
• Additional Projects
• Additional Resources
• Key Terms
CCNA Guide to Cisco Networking Fundamentals, Fourth Edition 1-2
Lecture Notes
Overview
This chapter introduces the fundamentals of computer networking. You will learn about the
reasons for networking, some networking terminology, and a bit about the different types of
networks. Specifically, you will learn about networking standards and types of networking
equipment. Throughout this book, you will periodically revisit these concepts, learning
about them in more detail.
Chapter Objectives
• Identify and describe the functions of each of the seven layers of the OSI reference
model
• Identify the reasons why the networking industry uses a layered model
• Define and explain the conversion steps of data encapsulation
• Define and describe the function of a MAC address
• Describe connection-oriented network service and connectionless network service, and
identify the key differences between them
Teaching Tips
Introduction to Networking
1. Explain that a computer network, or simply a network, refers to the connection of two
or more computers by some type of medium.
Teaching
Tip
Learn more about computer networks at:
http://en.wikipedia.org/wiki/Computer_network.
2. Mention that you can connect a computer to a network using the following:
a. Public telephone system
b. Wire cables
Origin of Networking
1. Mention that industry experts find it difficult to date the precise origin of networking,
2. Explain that in the early days of computing, mainframe computers were sometimes
connected to each other by cables. Today, systems that are part of a network do not
Why Do We Use Networks?
1. This question can be answered in one word: convenience. People expect interoperability
from electronic devices.
2. Explain that computer networks allow:
a. For the transfer of files, data, and even shared applications without copying
3. Mention that networked computers can share data and peripherals.
Networking Terminology
1. Define media as the wire cabling that forms the connections in most networks. Some
networks use wireless transmission media, such as infrared or radio signals.
3. Describe the following types of servers:
a. Print server
4. Explain that when every computer on a network acts as both a client and a server, the
5. Define the following types of networks:
a. Local area network (LAN)
b. Wide area network (WAN)
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Teaching
Tip
The devices on a SAN are physically separate from the servers. This makes the
network more scalable and flexible, because any server can exchange data with
any storage device, and additional storage devices can be added more quickly
and simply.
6. Mention that a network operating system (NOS) allows communication, security, and
distribution of data, files, and applications over a network.
8. Explain that the term networking hardware describes all the physical components of a
9. Define a virtual private networks (VPN) as a network that uses a public
10. Define the extranet as the part of the company’s network that allows access to
Understanding the OSI Model
1. Explain that the Open Systems Interconnection (OSI) model was presented in 1984 by
2. Explain that the OSI model allows vendors to implement networks that permit
communication among the wide variety of network implementations.
3. Mention that the OSI model is not an absolute standard for computer networks; it is
used as a reference model.
Teaching
Tip
Refer your students to http://www.webopedia.com/quick_ref/OSI_Layers.asp for
additional explanation about the seven layers of the OSI model.
Reasons for Layering
1. Describe the following advantages of a layered networking model:
a. Simplifies the networking model
2. Use Figure 1-1 to illustrate the OSI reference model.
3. Define a protocol as a defined method for communicating between systems. Computers
Peer OSI Communication
1. Explain that in a peer communication, each layer will only talk to its peer on the
2. Mention that each layer provides services to the layer above it and receives services
Quick Quiz 1
1. The term computer network, or simply ____, refers to the connection of two or more
computers by some type of medium.
2. The term ____ refers to the wire cabling, such as coaxial or the more commonly used
twisted-pair that form the connections in most networks.
3. When every computer on a network acts as both a client and a server, the network is
a(n) ____ network.
4. A(n) ____ is a defined method for communicating between systems.
Layer Functions
1. Mention that the OSI model was developed as an industry standard for companies to use
when developing network hardware and software to ensure complete compatibility.
2. Explain that each layer in the OSI model performs a specific function in the
4. Describe the following responsibilities of the Physical layer (Layer 1):
a. Defines the physical characteristics of the network hardware, including cable
5. Describe the following responsibilities of the Data Link layer (Layer 2):
a. NIC software functions, including the identification of the source and
6. Use Figures 1-4 and 1-5 to describe the following sublayers of the Data Link layer:
7. Describe the following responsibilities of the Network layer (Layer 3):
8. Mention that protocols at the Network layer allow computers to route packets to remote
networks using a logical address.
9. Describe the following responsibilities of the Transport layer (Layer 4):
a. End-to-end, error-free transmission and delivery between the ultimate sender
11. Describe the following services of the Session layer (Layer 5):
a. Control for data exchange (full or half duplex)
12. Explain that the Session layer allows the transfer of a large set of data across the
network. Examples of Session layer protocols include NetBIOS, SQL, RPC, and X-
CCNA Guide to Cisco Networking Fundamentals, Fourth Edition 1-7
Teaching
Tip
Read more about NetBIOS at: http://en.wikipedia.org/wiki/NetBIOS.
13. Describe the following responsibilities of the Presentation layer (Layer 6):
a. Data translation
14. Explain that the Presentation layer also provides encryption services when data
encryption is used in network communications.
15. Describe the following responsibilities of the Application layer (Layer 7):
16. Explain that the Application layer is concerned with user interaction with the computer
17. Explain that data is sent from one computer to another in a data packet. Each layer in
the protocol stack may add a protocol data unit (PDU) to the data as it is passed down
the layers. The addition of a header and/or trailer is called encapsulation. Use Figure 1-6
and Table 1-1 to illustrate your explanation.
Quick Quiz 2
1. The ____layer of the OSI model defines the mechanical, electrical, and procedural
events that occur during the physical transmission of electronic signals on the wire.
2. ____ are devices that boost a signal.
3. The protocols at the Network layer allow computers to route packets to remote
networks using a(n) ____ address.
4. ____ protocols, such as TCP, require an acknowledgment (ACK) of the receipt of data
packets.
CCNA Guide to Cisco Networking Fundamentals, Fourth Edition 1-8
Class Discussion Topics
1. What are the origins of networking?
2. What are the advantages and disadvantages of both connection-oriented and
connectionless protocols?
Additional Projects
1. Ask your students to read the following article at
2. Ask your students to read more about the International Organization for Standardization
Additional Resources
1. Networking Basics – Key Concepts in Computer Networking
3. How OSI works
4. How Encapsulation Works Within the TCP/IP Model
5. NetBIOS over TCP/IP Name Resolution and WINS
Key Terms
➢ ASCII (American Standard Code for Information Interchange) A standardized
method for formatting binary information and text for communications and printer
➢ client A computer that operates on a network and requests and uses the services of other
computers on the network, but does not necessarily provide any services to other
computers.
➢ client/server A type of networking in which a few dedicated computers, called servers,
share files, printers, disk drives, and other resources with a group of client computers.
sending and receiving information across the network media. It encodes and frames data
for transmission and provides error detection and control. This layer has two parts: LLC
and MAC.
➢ datagram A message or packet that is sent across a network and does not require
acknowledgment by the destination station.
➢ EBCDIC (Extended Binary Coded Decimal Interchange Code) A standardized
formatting method for both binary and text files for communications and printer control.
IBM developed EBCDIC. The acronym EBCDIC is pronounced “eb-see-dick.”
➢ extranet An area of a company’s network allowing access by nonemployees such as
business partners, vendors, and suppliers.
➢ infrared Invisible light at the upper end of the electromagnetic spectrum. It is used in
most hand-held remote control devices for televisions, stereos, and videocassette
players. It is also used in some types of computer networking, especially for data
transfers between laptop and desktop systems.
➢ Institute of Electrical and Electronics Engineers (IEEE) A technical professional
model.
➢ Logical Link Control (LLC) layer A sublayer of the Data Link layer that forms the
connection between the other software in the protocol stack and the networking
hardware (such as the NIC and the cables).
➢ media The cable, glass, or telephone lines that host the signal from one computer to
electronic signals on a network.
➢ Network layer The third layer of the OSI conceptual networking model, which allows
communications to be routed on a network. It provides a logical address for computers
on a network.
➢ network operating system (NOS) Operating software that has networking components
servers.
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➢ peer communication The method of communication among the levels of the OSI
model, in which each protocol in the OSI protocol stack encodes its own protocol data
unit into the network hierarchy, so that it can communicate with the equivalent layer on
protocol stack. It can be header or trailer information that is attached to the data packet
prior to transmission.
➢ Remote Procedure Call (RPC) A method used to establish communications between
computer systems at the Session layer.
➢ repeater A device that repeats or boosts a network signal along network wire. It
reassembles data frames. It also provides for connection-oriented and connectionless
communications.
➢ virtual private network (VPN) A private communications link over public
communications infrastructure, such as the Internet.
➢ WAV A Windows Audio file, an audio file format used with Microsoft Windows