CHAPTER 1
Introduction to Computer Networks
Objectives:
 Explain the fundamentals of network communication
 Define common networking terms
 Compare different network models
 Identify the functions of various network server types
 Describe specialized networks
The Fundamentals of Network Communication
 A computer network consists of two or more computer connected by some kind of transmission medium, such
as a cable or air waves.
 The primary motivation for networking was the need for people to share resources, such as printers and hard
drives, and information such as work-processing and to communicate by using applications such as e-mail.
 Another motivating factor for networking for both business and homes is to get “online”- to access the Internet.
Network Components
 Imagine a computer without networking components – no networking hardware, no networking software.
 Computer main purpose was to run applications such as work-processing and spreadsheets programs, not Web
browsers and e-mail. –Stand–alone Computer.
1 - Network Interface Card
 A NIC is an add-on card that’s plugged into a motherboard expansion slot and provides a connection between
the computer and the network.
2 – Network Medium
 A cable that plugs into the NIC and makes the connection between a computer and the rest of the network.
 Network media can also be air waves, as in wireless networks
3 – Interconnecting Device
 Most networks include one or several computer and devices connected to each other.
 Interconnecting devices allows two or more computers to communicate on the network without having to be
connected directly to one another.
 The include switches, hubs, routers, and wireless access point.
4 – Network Clients and Servers
 Network client software request information that’s stored on another network computer or devices.
- Web Browsers and E-Mail Programs
 Network server software allows a computer to share its resources by fielding resource request generated by
network clients.
 For example: Client for Microsoft Networks, allows a word processor to open a file that’s shared on another
Windows computer or print to a printer attached to another.
 In this setup, the server software called File and Printer Sharing for Microsoft Networks receives the request the
client generates and provides access to the shared file or printer.
5 – Protocols
 The rules and formats a computer must use when sending information across the network.
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 Network Protocols do all the behind-the-scenes tasks required to make networking work.
 Most of the complexity in networking is handled by these protocols.
 Examples of network protocols include TCP/IP and IPX/SPX.
6 – NIC Driver
 Every NIC card installed in a computer must have an associated device driver installed in the OS.
 The device driver software manages the details of communicating with the NIC hardware to send and receive
data to and from network media.
 NIC driver receive data from protocols and then forward this data to the physical NIC, which transmits data onto
the medium.
 When the data arrives at the NIC from the medium, the NIC hands it off to the NIC drivers, which then hands it
off to the network protocols.
Steps of Network Communication (Origin)
1. An application tries to access a network resource by attempting to send a message to it.
2. Network client software detects the attempt to access the network. Client software formats the message
generated by the application and passes the message on to the network protocol.
3. The protocol packages the message in a format suitable for the network and sends it the NIC driver.
4. The NIC driver sends the data in the request to the NIC card, which converts it into the necessary signals to be
transmitted across the network.
Steps of Network Communication (Destination)
1. The NIC card on the server receives signals from the network medium and converts them into message data,
which is read by the NIC driver.
2. The NIC driver passes the message to the network protocol.
3. The network protocol determines which server software the message is targeting and passes the message to this
destination software.
4. The server software receives the message and responds by sending the requested data to the client computer,
using the four steps outlined previously.
Layers of the Network Communication Process
 Each step of the client accessing network resources is often referred to as a “layer” in the network
communication process.
 Each layer has a specific function to accomplish, and all the layers work together.
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How Two Computers Communicate on a LAN
 In a network using a protocol such as TCP/IP, computers have two addresses, a logical address and a physical
address.
 With TCP/IP (logical – IP Address), (physical – Media Access Control [MAC] Address)
Ex:
The two addresses much like the addresses used to send mail through the postal system.
When a message is sent on a network:
 The IP address is used to get the message to the correct network,
 The MAC address is used to get the message to the correct computer on this network.
What if the sender and receiver are on the same network?
 The IP address in the message is used primarily as a means to ascertain the destination computer’s MAC
address.
Following are the steps of this communication process
1. A user at Computer A types ping 10.1.1.2 at a command prompt.
2. The network software creates a ping message.
3. The network protocol packages the message by adding IP addresses of the sending and destination computers
and acquires the destination computer’s MAC address.
4. The network interface software adds MAC addresses of the sending and destination computers and sends the
message to the network medium as bits.
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5. Computer B receives the message, verifies that the addresses are correct, and then sends a reply to Computer A,
using Steps 2 through 4
Similarly, computers use an address book of sorts, called a name server, to get the IP address of a computer, given its
name.
A name server translates domain names into IP address. This makes it possible for a user to access a website by typing
in the domain name instead of the website’s actual IP address.
Following are the steps of this communication process
1. A user at Computer A types ping Computer B at a command prompt.
2. A name lookup is performed to retrieve Computer B’s IP address.
3. The network software creates a ping message.
4. The network protocol packages the message by adding IP addresses of the sending and destination computer
and acquires the destination computer’s MAC address.
5. The network interface software adds MAC addresses of the sending and destination computers and sends the
message to the network medium as bits.
6. Computer B receives the message, verifies that the addresses are correct, and then sends a reply to Computer A,
using Steps 3 through 5
Network Terms
LANs, Internetworks, WANs, and MANs
LAN (Local Area Network)
 A small network, limited to a single collection of machines and connected by one or more interconnecting devices
in a small geographic area.
LANs are represented in other ways, as in this figure. Note the different symbols for a hub and a switch.
Internetwork
 Is a networked collection of LANs tied together by devices such as routers.
 When LANs are connected to form a building blocks to construct a larger network.
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Internetworks are usually created for these reasons:
 Two or more groups of users and their computers should be logically separated on the network yet still allow
the groups to communicate.
 The number of computers in a single LAN has grown to the point that network communication is no longer
efficient.
 The distance between two groups of computers exceeds the capabilities of most LAN devices, such as hubs and
switches.
WAN (Wide Area Network)
 As a network’s scope expands to encompass LANs in geographically dispersed locations, internetworks become
classified as wide area networks
 WAN spans distances measured in miles and links two or more separate LANs.
 WANs use the services of third-party communication providers, such as phone companies, to carry network
traffic from one location to another.
 Internetworks that are geographically dispersed and use third party communication providers to provide
connectivity between locations
The internet is both an internetwork and , because it spans the globe, a very large WAN.
MAN (Metropolitan Area Network)
 MANs use WAN technologies to interconnect LANs in a specific geographic region, such as country or city.
 An internetwork confined to a geographic region, such as a city or country; Uses third-party communication
providers to provide connectivity between locations.
LANs, Internetworks, WANs, MANs
 LANs and Internetworks – for local access.
 MANs – for regional or citywide access.
 WANs – for access to remote sites elsewhere in the country or around the world.
Example:
A nationwide bank. The main branch in a large city has a building with multiple floors and hundreds of computers. Each
floor constitutes a LAN, and these LANs are connected to form a internetwork. The internetwork at main branch is then
connected to other branches throughout the city to form a MAN. In addition, the main branch is connected to other
branch is connected to other branches in other cities and states to form a WAN.
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Packets and Frames
 When computers transfer information across a network, they do so in short bursts of about 1500 bytes of data.
 Each data burst, or chunk, of data has the same basic structures; specifically, each chunk of data contains the
MAC address and IP address of both the sending and receiving computers.
During pause; Data is transferred in this way for a number of reasons:
 The pause between bursts might be necessary to allow other computers to transfer data during pauses.
 Ta pause allows the receiving computer to process received data, such as writing it to disk.
 The pause allows the receiving computer to receive data from other computers at the same time.
 The pause gives the sending computer an opportunity to receive data form other computers and other
processing tasks.
 If an error occurs the sending transmission of a large file, only the chunks of data involved in the error have to
be sent again, not the entire file.
Packets
 The chunks of data sent across the network are usually called packets and frames.
 Often used generally to mean a chunk of data sent over the network.
 It’s a chunk of data with a source and destination IP address added to it.
 In relation to the layers of the network communication process, packets are generated by and processed by the
network protocol.
 A chunk of data with source and destination IP addresses (as well as other IP information) added to it. Packets
are generated and processed by network protocols
Original Data
Data broken into packets
Frames
 Frame is a packet with the source and destination MAC addresses added and an error-checking code added to
the back end.
 Frames are generated by and processed by the network interface.
 The packet is “framed” by MAC addresses on one end and an error-checking code on the other.
 The final state of data before it gets placed on the network medium as bits.
 The network interface is the layer of the network communication process that works with frames.
Packets are now frames and ready for delivery
Encapsulation
 The process of adding header and trailer information to chunks of data.
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The process of adding IP address and then MAC addresses to chunks of data.
Data is encapsulated several times as it works its way down from the sending application until it makes it to the
network interface as a frame.
When the destination computer receives the frame, the process is reversed.
Decapsulation / Capsulation
 The process of removing the header and trailer on the receiving node/device.
 The process continues until the packet arrives at the receiving application or service as the original data.
Header and Trailer
 Header – the information added at the front of data
 Trailer – the information added at the end of data.
Clients and Servers
Client
 A client, in networking terms, can be a workstation running a client OS, such as Windows 7.
 It can also refer to the network software on a computer that requests network resources from server.
 It can refer also to physical computer as a client computer.
Term used to describe an OS designed mainly to access network resources, a computer’s primary role in a network
(running user applications and accessing network resources), and software that requests network resources from server.
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Client operating system – the OS installed on a computer is designed mainly to access network resources, even
though it might be capable of sharing its own resources.
Client computer – this computer’s primary role in the network is to run user applications and access network
computer.
Client software – the software that requests network resources form server software running on another
computer. Ex. Web browser.
Server
 A computer becomes a server when software is installed on it that provides a network service to client
computers.
 Anybody can install certain software on an inexpensive laptop computer and make it act as a server.
 A huge tower computer with six hard drives and 16 Gb of RAM can be used as a workstation for a single user.
 What makes a computer a server is the software installed on it.
 Term used to describe an OS designed mainly to share network resources, a computer with the primary role of
giving client computers access to network resources, and the software responds to requests for network
resources from client computers.

Server Operating System – when the OS installed on a computer is designed mainly to share network resources
and provide other network services.
Ex. Windows Server 2008, Mac OS X Server….

Server Computer – when a computer’s primary role in the network is to give client computers access to network
resources and services.

Server Software – the software that responds to requests for network resources from client software running on
another computer.
Ex. Internet Information Service(IIS), E-Mail Server….
Network Model

A model defining how and where resources are shared and how access to these resources is regulated.
Two major types:
Peer-to-peer
Server based (also called Client/Server)
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Note: Peer-to-peer networks running Windows operating systems are referred to as “workgroup networks” and Serverbased networks running Windows Server are referred to as “domain-based networks”.
Peer-to-Peer/Workgroup Model
A network model in which all computers can function as clients or servers as needed, and there’s no centralized control
over network resources.
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In a peer-to-peer network, every user must act as the administrator of his or her computer’s resources.
On a Windows-based peer-to-peer network, computers are members of a workgroup, but workgroup is simply
an identifier and doesn’t constitute a network security boundary.
 Most peer-to-peer networks consist of collection of desktop PCs linked by a common network medium and
network connectivity device such as switch.
Server/Domain-Based Model
A network model in which servers taken on specialized roles to provide client computers with network services and to
provide centralized control over network resources.
 Server OSs are designed to handle many simultaneous user logons and requests for shared resources efficiently.
 When using Windows Server Oss in server-based network with centralized logon, you’re running a Windows
domain.
 The Linux OS supports a centralized logon service called Network Information Service (NIS)
Domain
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It is a collection of users and computers whose accounts are managed by Windows servers called domain
controllers.
Users and computers in domain are subject to network access and security policies defined by the network
administrator and enforced by domain controllers.
The software managing centralized access and security is referred as a directory service.
Domain controller
A computer running Windows Server with Active Directory installed; maintains a database of user and computer
accounts as well as network access policies in a Windows domain.
Directory service
 The software that manages centralized access and security in a server based network.
Network Information Service(NIS)
 A Linux directory service that supports centralized logon.
Tip:
Windows desktop OSs limit the number of simultaneous network connections to 10 (20 for Windows 7), making use of
peer-to-peer/workgroup networking with only the desktop version of Windows Oss impractical when there are more than
10 computers on the network.
Network Servers
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Servers is at the heart of any network that’s too large for a peer-to-peer configuration.
A network server can fulfill many roles on your network.
Most roles entail the server providing one or more network services.
A single server can be configured to satisfy a single role or serer roles at once.
Most Common Server Roles
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Domain controller/directory servers
File and print servers
Application servers
Communication servers
E-mail/fax servers
Web servers
Domain Controller/Directory Servers
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Domain Controller is a computer running Windows Server with Active Directory installed; maintains a database
of user and computer accounts as well as network access policies in Windows domain.
Directory Service is the software that manages centralized access and security in the server based network
The software needed to make a windows server a domain controller is Active Directory.
The Linux directory service add-on that’s compatible with Active Directory is LDAP.
File and Print Servers
 Computers that provide secure centralized file storage, sharing and access to networked printers.
 With these servers, users can run applications locally by keep data files on the server.
 Using the Server version of Windows provides advanced sharing features, such as fault tolerance, load
balancing, and disk quotas.
Application Servers

Computers that supply the server side of client/server applications, and often the data that goes along with
them, to network clients.
For Ex:
 When you connect to a shopping site such as Amazon.com, the processing required items, processes the
shopping cart, and handle payment is handled by the application servers at Amazon.com. Your Web browser is
simply a client to the application with the main job of displaying information onscreen.
Communication Servers
 Computers that provide a mechanism for users to access a network’s resources remotely.
 They enable users who are traveling or working at home to dial in to the network via a modem or, through their
existing Internet connection.
Windows – Routing and Remote Access Services (RRAS)
It handles dial-up network connections and virtual private network (VPN) connection.
VPN- provides a secure connection to a private network through the Internet.
E-mail/Fax Servers
 Mail servers handle sending and receiving e-mail messages for network users.
 Mail servers generally handle at least two widely used e-mail protocols: Post Office Protocol version 3 (POP3)
and Simple Mail Transfer Protocol (SMTP).
 POP3 is used by client e-mail programs to contact the mail server to download a new messages.
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SMTP is used by client e-mail programs to send e-mail messages and by the mail server to transfer messages
from one server to another.
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Fax servers manage fax traffic for a network.
They receive incoming faxes via telephone, distribute them to recipients over the network, and collect outgoing
faxes across the network before sending them via telephone
 Some fax servers integrated with the e-mail system so that users can receive and sometimes send faxes with
their e-mail client.
Web Servers
 A computer running software that allows users to access HTML and other document types with a Web browser.
 Windows Server includes a complete Web server called Internet Information Service (IIS) as well as File Transfer
Protocol (FTP) services.
 The excellent Apache Web Server is available as part of most Linux distributions. In fact. Apache remains the
most widely used Web server in the world.
Specialized Networks
Storage Area Network (SAN)
 A specialized network that uses high-speed networking technologies to give servers fast access to large amounts
of disk storage.
 The storage managed by a SAN appears to the server OS as though it’s physically attached to the server.
However, the storage is connected to a high-speed network technology and can be shared by multiple servers.
 The most common network technologies used in SANs are Fibre Channel and iSCI.
Wireless Personal Area Networks
 A short-range networking technology designed to connect personal device to exchange information.
 A personal area network – a network for interconnecting devices centered around an individual person’s
workspace – in which the connections are wireless.
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Chapter Summary

All computers perform three basic tasks; input, processing, and output. Some components of today’s computers
are designed to perform only one of these three functions, others are designed to perform two ore all three
functions.
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Storage is a major part of computer’s configuration. Storage types include short-term storage (RAM) and longterm storage (disk drives and flash drives)

PC hardware consists of four major components’ motherboard, hard drive, RAM, and BIOS/CMOS. The
motherboard is the nerve of the computer and contains the CPU, expansion slots, and RAM slots.

The operating system (OS) and device drivers control access to hardware and provide a user interface, memory
management, and multitasking.

The components needed to make a stand-alone computer a networked computer include a NIC, network
medium, and usually a device to interconnect with other computers. In addition, network software consisting of
client and server software, protocols, and the NIC driver are needed to enable the computer to communicate on
the network.

The layers of the network communication process can be summarized as user application, network software,
network protocol, and network interface

The terms used to describe networks of different scope are LAN, internetwork, WAN, and MAN. A LAN is a
single collection of devices operating in a small geographic area. An internetwork is a collection of a LAN tied to
together by routers, and a WAN and MAN are geographically dispersed internetworks.

Packets and frames are the units of data handled by different network components. Packets, which are
processed by the network protocol, are units of data with source destination IP address added. Frames, which
are processed by the network interface, have MAC addresses and an error code added to the packet.

A client is the computer or network software that requests network data, and a server is the computer or
network software that makes network data available to requesting clients.

A peer-to-peer network model has no centralized authority over resources; a server-based network usually uses
a directory service for centralized resource management.

Network servers can perform a number of specialized roles, including directory service, file and print server,
application server, communication server, e-mail/fax server, and Web server.

Specialized networks can include storage area networks (SANs) and wireless personal area networks (WPANs)
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Key Terms:
Application Servers - Computers that supply the server side of client/server applications, and often the data that goes
along with them, to network clients.
Bus - A collection of wires that carry data from one place to another on a computer’s motherboard.
Client - Term used to describe an OS designed mainly to access network resources, a computer’s primary role in a
network
(running user applications and accessing network resources), and software that request network
resources from servers.
Communication Servers - Computers that provide a mechanism for users to access a network’s resources remotely.
Core - An instance of a processor inside a single CPU chip. See also multicore CPU.
Credentials - A username and password or another form of identify used to access a computer.
Device Driver - Software that provides the interface between the OS and computer hardware.
Directory Service - The software that manages centralized access and security in a server- based network.
Domain - A collection of users and computers in a server-based network whose accounts are managed by Windows servers
called domain controllers. See also domain controller.
Domain Controller - A computer running Windows Server with Active Directory installed; maintains a database of users
and computer accounts as well as network access policies in a Windows domain. See also directory service.
Encapsulation - The process of adding header and trailer information to chunks of data.
File and print servers - Computers that provide secure centralized file storage, sharing, and access to networked
printers.
Frame - A packet with source and destination.MAC address added and an error-checking code added to the back end.
Frames are generated by and processed by the network interface. See also packet.
Header - Information added to the front end of a chunk of data so that the data can be correctly interpreted and
processed by network protocols.
Internetwork - A networked collection of LANs tied together by devices such as routers. See also local area network (LAN).
Local Area Network (LAN) - A small network, limited to a single collection of machines and linked by interconnecting devices
in a small geographic area.
Mail Servers - Computers that handle sending and receiving e-mail messages for network users.
Metropolitan area network (MAN) - An internetwork confined to a geographic region, such as a city or country; uses thirdparty communications providers to provide connectivity between locations. See also internetwork.
Multicore - CPU A CPU containing two or more processing cores. See also core.
Multitasking - An operating system’s capability to run more than one application or process at the same time.
Name server - A computer that stores names and address of computers on a network, allowing other computers to user
computer names rather than addresses to communicate with one another.
Network - Two or more computers connected by a transmission medium that enables them to communicate.
Network Client Software - The application or OS service that can request information stored on another computer.
Network Information Service (NIS) - A Linux directory service that supports centralized logon.
Network Model - A model defining how and where resources are shared and how access to these resources in
regulated.
Network protocols - The software defining the rules and formats a computer must use when sending information
across
the network.
Network Server Software - The software that allows a computer to share its resources by fielding request generated by
network clients.
Packet - A chunk of data with source and destination IP addresses (as well as other IP information) added to it. Packets
are generated by and processed by network protocols.
Peer- to- peer - network A network model in which all computers can function as clients or servers as needed, and there’s
no centralized control over network resources.
Server - Term used to described an OS designed mainly to share network resources, a computer with the primary role of
giving client computers access to network resources, and the software that responds to requests for network
resources from client computers.
Server-based network - A network model in which servers taken on specialized roles to provide client computers with
network services and to provide centralized control over network resources.
Stand-alone Computer - A computer that doesn’t have the necessary hardware or software to communicate on a
network.
Storage area network (SAN) - A specialized network that uses high-speed networking technologies to give servers fast
access to large amounts of disk storage.
Trailer - Information added to the back end of a chunk of data so that the data can be correctly interpreted and
processed by network protocols.
Web server - A computer running software that allows users to access HTML and other document types with a Web
browser.
Wide Area Networks (WANs) - Internetworks that are geographically dispersed and used third-party communication
providers to provide connectivity between locations. See also internetwork.
Wireless personal area network (WPAN) - A short-range networking technology designed to connect personal devices
to exchange information.
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