Chapter 1 Outline: Introduction to Computer Networks

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Chapter 1 Outline
:
Introduction to Computer Networks

Name:
Luis Arroyo

Class:

NET 101

Date:

10
-
15
-
12

Instructor:

David Rivera


Directions:
In 1

to 5 complete sentences, please give a brief explanation for each of the topics below.

An overview of
Computer Concepts:

Computer
and Information Literate is ...
The ability to understand and articulate your

Knowledge
, skills an
d values regarding the computer
and the information it helps to produce.

Basic Functions of a
Computer


A computer’s functions and
features can be broken down into the three basic tasks all computers
perform: input, processing, and output. Information is input to a compute
r from a

device such as a
keyboard or from a storage device such as a hard drive; the central processing unit (CPU
) processes the
information, and then output is

usually created. The following
example illustrates the process
:


Storage Components:

Storage devices include Hard Drives, USB Flash Drives, CD
-
ROM Drives, DVD
-
ROM Drives, Disk Drives,
and Tape Drives

Personal

Computer Hardware:

Hardware include
Input Devi
ces
-

used to enter data into a computer
The System

Unit
-

contains the
electronic
circuits that
cause the processing of data to occur

Output Devices
-

used to display
information

Sec
ondary Storage Devices


stores
instructions a
nd data when they are not being
used by
the system unit

this include motherboard Hard drive RAM BIOS/CMOS

Computer Boot Procedure:

The following six steps are necessary to take a computer from

a powered
-
off state to running
a current
OS, such as Windows or Linux:

1. Power

is applied to the motherboard.

2. The CPU starts.

3. The CPU carries out the BIOS startu
p routines, including the POST.
4. Boot devices, as specified in the BIOS configuration, are searched fo
r an OS.

5. The OS is loaded into RAM.


6. OS services are started



How t
he Operating System and Hardware Work Together:

A computer’s OS provides a number of critical services, inc
luding a user interface, memory
management, a file system, multitasking, and the interface
to hardware devices. Without an
OS, each
application would

have to provide these services, and if a us
er wanted to run multiple
applications at
once (multitasking), the applications woul
d have to run cooperatively. In

short, without an OS,
computing would still be in the proverbial Stone Age

The Fundamentals of N
etwork Communication:

A computer network consists of two or more computers connect
ed by some kind of transmission
medium, such as a cable or air waves. After they’re
connected, correctly configured
computers can
communicate with one another. The pr
imary mo
tivation for networking
was the need for people to
share resources, such a
s printers and hard drives, and information such as word
processing files and to
communi
cate by using applications such
as e
-
mail. These motivations remain, especially for businesses
,
but another motivating factor
for networking for both businesses and homes is to get “
online”

to
access the Internet.
The Internet, with its wealth of information, disinfor
mation, fun, and games, has
had
a tremendous impact on how and why networks are us
ed today.

Network Components:

Network interface card

A NIC is an add
-
on card that’s pl
ugged into a motherboard
expansion slot and
provides a connection between the computer and the network.

Network medium

A cable that plugs into t
he NIC and makes the connection
between a computer and
the rest of the network.

Interconnecting devices
allow two o
r more computers to communicate
on the network without having
to be connected directly to one another.

Steps of Network Communication:

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 to 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 medium.

Layers of the Network Com
munication Process:

Each step of a 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. Figure 1
-
6 depicts this proces
s, and Simulation 1 on the book’s CD shows an animation of this
process.



Sending machine








Receiving machine

user application








user application

network software








network software

network protocol







network protocol

network interface








network interface

Network

medium

Figure 1
-
6 Layers of the network communication process

How Two Computers Communicate on a LAN: Some Details:

Network Terms Explained:

Every profession has its own language with its own uniq
ue terms and acronyms. Learning
this language
is half the battle of becoming proficient in a profe
ssion, and it’s no different in
computer and
networking technology.

LANs, Internetworks, WANs, and MANs:

A small network, limited to a single collection of m
a
chines and
connected by one or
more interconnecting devices in a small geographic area,

is called a local area
network
(LAN). LANs also form the building blocks for cons
tructing larger networks called
“internetworks
.”

As a network’s scope expands to encomp
ass LANs in geographically dispersed
locations, internetworks become classified as wide area networks (WANs). A WAN spans distance
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.

Occasionally, you might encounter a network type called a metropolitan area network(MAN).
Essentially, MANs use WAN technologies to interconnect LANs in a specific geographic region, s
uch as a
county or city.

Packets and Frames:

When computers transfer information across a network, they do so in short bursts of about 1500 bytes
of data. Each burst, or chunk, of data has the same basic structure; specifically, each chunk of data
contains

the MAC addresses and IP addresses of both the sending (source) and receiving (destination)
computers.

Clients and Servers:

There are different types of clients and servers


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. Windows XP, Windows Vista,
Windows 7, and Mac OS X all fit
this description, as do certain distributions of Linux. A client OS is also
frequently referred to as a “desktop OS.”

Client computer

This computer’s prim
ary role in the network is to run user applications and access
network resources. Most computers in a network fit this description.
Client software

It’s the software that requests network resources from s
erver software running on
another computer. For example, a Web browser, an e
-
mail client (such as Microsoft Outlook), and
Client for Microsoft Networks fit into this category.

Server operating system

This term is used when the OS installed on a computer is

designed mainly to
share network resources and provide other network services, some of which are discussed later in
“Network Servers.” A server OS is tuned to be able to share files efficiently and perform network
operations in response to client requests
, even though the OS might also be able to run user
applications and client software. Windows Server 2008, Mac OS X Server, UNIX, and many Linux
distributions fit this description.

Server computer

This term is used when a computer’s primary role in the network is to give client
computers access to network resources and services. The computers that most often fit this
description are usually
found in the IT computer room or locked away in a closet.
Server software

It’s the software that responds to requests for network resources from client
software running on another computer. A Web server, such as Internet Informa
tion Services (IIS), an e
-
mail server, such as Microsoft Exchange, and File and Printer Sharing for Microsoft Networks fit into
this category.

Network Models:

A network model defines how and where resources are

shared and how access to these
resources is
r
egulated. Networks models fall into two major types: peer
-
to
-
peer and server

based
(also called
client/server). This discussion of network

models addresses the role that
computers play on the
network and how these roles interact
. Server
-
based networks are
the
most common in business
settings, but understanding both ty
pes is essential, especially as
they compare with one another.

Peer
-
to
-
peer/ Workgroup Model:


As you have learned, computers on a peer
-
to
-
peer network can take both a client and a server role.

Because all computers on this type of network are peers, these networks impose no centralized control
or security over shared resources. Any user can share resources on his or her computer with any other
user’s computer, and each user can determine what l
evel of access other users have to his or her
shared resources. Physically, a peer
-
to
-
peer network looks just like a server
-
based network; mainly,
location and control over resources differentiate the two.

Server/ Domain
-
Based Model:

Server
-
based networks
provide centralized control over network resources, mainly by providing an
environment in which users log on to the network with a single set of credentials maintained by one or
more servers running a server OS. Server OSs are designed to handle many simul
taneous user logons
and requests for shared resources efficiently. In most cases, servers are dedicated to running network
services and shouldn’t be used to run user applications. You want to reserve servers’ CPU power,
memory, and netw
ork performance for
user access
to network services.

Network Servers:

A server is at the heart of any network that’s too large for a

peer
-
to
-
peer configuration. In
fact, most
large networks with more than a few dozen workst
ations probably rely on several
network servers. 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 configure
d to satisfy
a single role or several roles at
once. Following are the mo
st commo
n server roles found on
networks, described in more det
ail in the
subsequent sections:

● Doma
in controller/dire
ctory servers

● File and print servers


● Application servers

● C
ommunications server

● E
-
mail/fax servers


● Web servers

Because you see different servers depicted in network drawings
, Figure 1
-
27 shows some common
representations of various types of servers.

Domain Controller/ Directory Servers:

Directory services make it possible for users to locate, store,

and secure information about a
network
and its resources. Windows servers per
mit combinin
g computers, users, groups, and
resources into
domains. Any user belonging to a specific doma
in can access all resources and
information he or she
has permission to use simply by loggin
g on to the domain. In Windows,
the server handling this lo
gon
service and managing the collection of c
omputers,
users, and so on in a domain is a domain controller.
As me
ntioned, the software needed to
make a Windows server a domain controller is Active Directory,
and the Linux directory service

add
-
on that’s com
patible with Active Directory is LDAP. LDAP is
included in most

Linux distributions and can be used for centralized log
on and resource management
on a
Linux network or to integrate Linux computers into a Windows network.

File and Print Servers:

File and pr
int servers are the mainstay of the server world because
they provide secure centralized
file
storage and sharing and access to networked prin
ters. With these servers, users
can run applications
locally but keep data files on the server. Any Win
dows or Lin
ux computer
can act as a file and print
server. However, using the Ser
ver version of Windows provides
advanced sharing features, such as
fault tolerance, l
oad balancing, and disk quotas.

Application Servers:

Application servers supply the server side of cl
ient/server applications, and often the data that goes
along with them, to network clients. A database server, for instance, maintains a database of
information and provides network clients with a method to send a query to retrieve data. Application
server
s differ from basic file and print servers by providing processing services as well as handling
requests for file or print services. In file and print services, the client does its own file handling and
print processing. Generally, clients must run special
ized client
-
side applications to communicate with
an application server. For these applications, typically the client side formulates requests and sends
them to the application server, which handles the entire request’s background processing and then
deliv
ers the results back to the client side. The client side then formats and displays these results to the
user. Application servers can also be specialized Web servers. For example, when you connect to a
shopping site such as Amazon.com, the processing requi
red to find items, process 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:

Commun
ication servers 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, more
commonly, through their existing Internet connection. Windows Serv
er includes a powerful
communication server, called Routing and Remote Access Services (RRAS), for handling dial
-
up
network connections and virtual private network (VPN) connections. A VPN provides a secure
connection to a private network through the Inter
net. Similar add
-
on products are available for
Linux/UNIX.

E
-
Mail/ Fax Servers:

Mail servers handle sending and receiving e
-
mail messages for network users. Microsoft Exchange
Server is sophisticated mail server software that runs on Windows servers, and
Lotus Notes is a
mainstay in many organizations. 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 new messages. 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.


Web Servers:

The World Wide Web is the most well
-
known aspect of the I
nternet, made up of millions of documents
that can be interlinked by using hyperlinks. Being able to view and retrieve documents with the click of
a mouse makes the Internet’s resources widely available. Windows Server includes a complete Web
server called

Internet Information Services (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.

Additional Networ
k Services:

In addition to the common server roles discussed, most networks require additional support services to
function efficiently. The most common are Domain Name System (DNS) and Dynamic Host
Configuration Protocol (DHCP). As discussed, DNS provides

name resolution services that allow users to
access both local and Internet servers by name rather than address. DHCP handles automatic
addressing for network clients, relieving network administrators from having to assign computer
addresses manually.

Ser
ver Hardware Requirements:

A server’s primary function is to handle client requests for network resources and other network
services. Handling service requests across a network adds to a machine’s processing load. The higher
this load, the more important i
t is to purchase computers with additional power to handle demands for
network resources. To get an idea of what’s
involved;

review Table 1
-
4, which compares the system
hardware requirements for Windows 7, Windows Vista, and Windows Server 2008.

Item



Wi
ndows 7


windows vista


windows server 2008

Item



Windows 7 Windows



Vista Windows



Server 2008

RAM




1 GB




1 GB





512 MB

Disk type




SATA




SATA




SCSI or SATA

Disk space



40 GB, with 16 GB available


40 GB, with 16 GB available



32
GB

CPU speed


1 GHz




1 GHz




1.4 GHz

Graphics




128 MB graphics memory;



DirectX 9 support

128 MB graphics memory;

DirectX 9 support

Super VGA


Specialized Networks:

LANs, internetworks, and WANs are the focus of this book, but you might come
across other network
types that are intended to connect peripheral devices rather than desktop and server computers. The
two specialized networks discussed in the next sections serve very different purposes; storage area
networks are used to connect storag
e devices via very high
-
speed links, and wireless personal area
networks are used to connect one person’s personal devices.

Storage Area Networks:

A storage area network (SAN) uses high
-
speed networking
technologies to provide servers
with fast
access to l
arge amounts of disk storage. The stor
age managed by a SAN appears to
the server OS as
though it’s physically attached to the server. Ho
wever, the storage is connected
to a high
-
speed
network technology and can be shared by mu
ltiple servers. The most commo
n
network technologies
used in SANs are Fibre Channel and iSCSI. These technol
ogies are
designed to connect large arrays of
hard drive storage that can be
accessed and shared by servers.
Client computers access the shared
data by contacting th
e servers via

the usual method,
and the servers retrieve the requested data from
the SAN devices
and pass it along to the client
computer
.

Wireless Personal Area Networks:

With all the wireless devices people carry and their need to be connected at all times, it’s no
wonder
that a networking technology designed to connect these devices was developed. A wireless personal
area network (WPAN) is a short
-
range networking technology designed to connect personal devices to
exchange information. These devices include cell pho
nes, personal digital assistants (PDAs), global
positioning system (GPS) devices, MP3 players, and even watches.