6 Chapter 1: Building a Simple Network
These are the four major categories of physical components in a computer network:
■
Personal computers (PCs): The PCs serve as endpoints in the network, sending and
receiving data.
■
Interconnections: The interconnections consist of components that provide a means
for data to travel from one point to another point in the network. This category includes
components such as the following:
— Network interface cards (NICs) that translate the data produced by the
computer into a format that can be transmitted over the local network
— Network media, such as cables or wireless media, that provide the means
by which the signals are transmitted from one networked device to
another
— Connectors that provide the connection points for the media
■
Switches: Switches are devices that provide network attachment to the end systems
and intelligent switching of the data within the local network.
■
Routers: Routers interconnect networks and choose the best paths between networks.
Interpreting a Network Diagram
When designing and describing a computer network, you use a drawing or diagram to
describe the physical components and how they are interconnected.
The network diagram uses common symbols to capture information related to the network
for planning, reference, and troubleshooting purposes. The amount of information and the
details of that information differ from organization to organization. The network topology
is commonly represented by a series of lines and icons. Figure 1-3 shows a typical network
diagram.
In this diagram:
■
A cloud represents the Internet or WAN connection.

promoting more efficient collaboration on work projects.
■
Physical resources: The resources that can be shared include both input devices, such
as cameras, and output devices, such as printers.
SSH
SwitchX
RouterX
Main Router
ISP
Remote
Class
Fa0/1
Con 0
Con 0
Fa0/12
Fa0/0
Fa0/1
Fa0/11
S0/0/0
192.168.1.0/24
172.31.241.254
VPN
TFTP
Fa0/2
8 Chapter 1: Building a Simple Network
■
Network storage: Today the network makes storage available to users in several ways.
Direct attached storage (DAS) directly connects physical storage to a PC or a shared
server. Network attached storage (NAS) makes storage available through a special
network appliance. Finally, storage area networks (SAN) provide a network of storage

PC
PC
Exploring the Functions of Networking 9
Network User Applications
The key to utilizing multiple resources on a data network is having applications that are
aware of these communication mechanisms. Although many applications are available for
users in a network environment, some applications are common to nearly all users.
The most common network user applications include the following:
■
E-mail: E-mail is a valuable application for most network users. Users can
communicate information (messages and files) electronically in a timely manner, to
not only other users in the same network but also other users outside the network
(suppliers, information resources, and customers, for example). Examples of e-mail
programs include Microsoft Outlook and Eudora by Qualcomm.
■
Web browser: A web browser enables access to the Internet through a common
interface. The Internet provides a wealth of information and has become vital to the
productivity of both home and business users. Communicating with suppliers and
customers, handling orders and fulfillment, and locating information are now routinely
done electronically over the Internet, which saves time and increases overall
productivity. The most commonly used browsers are Microsoft Internet Explorer,
Netscape Navigator, Mozilla, and Firefox.
■
Instant messaging: Instant messaging started in the personal user-to-user space;
however, it soon provided considerable benefit in the corporate world. Now many
instant messaging applications, such as those provided by AOL and Yahoo!, provide
data encryption and logging, features essential for corporate use.
■
Collaboration: Working together as individuals or groups is greatly facilitated when
the collaborators are on a network. Individuals creating separate parts of an annual

Interactive applications, such as Enterprise Resource Planning (ERP) software, perform
tasks, such as inventory inquiries and database updates, that require more human
interaction. The user requests some type of information from the server and then waits for
a reply. With these types of applications, bandwidth becomes more important because users
are intolerant of slow responses. However, application response is not solely dependant on
the bandwidth of the network; the server and storage devices also play a part. However, in
cases where the network becomes a problem, other features such as quality of service (QoS)
System-to-System
Batch Applications
User Interactive
Applications
User Real-Time
Applications
Exploring the Functions of Networking 11
can alleviate some bandwidth limitations by giving the traffic from interactive applications
preference over batch applications.
Another type of application that can be affected heavily by the network is a real-time
application. Like interactive applications, real-time applications such as Voice over IP
(VoIP) and video applications involve human interaction. Because of the amount of
information that is transmitted, bandwidth is critical. In addition, because these
applications are time-critical, latency (delay through the network) is critical. Even
variations in the amount of latency (jitter) can affect the application. Not only is proper
bandwidth mandatory, but QoS is also mandatory. VoIP and video applications must be
given the highest priority.
In today’s environment, the end user is bombarded with ads indicating how much money
can be saved by converting to VoIP and how installation is as easy as dropping a VoIP router
into the network. Although this is often true in the home network, it can result in disaster in
a small office network. Applications that used to work start to run so slowly that they are
unusable, for example, when someone is on the phone, and voice quality is poor. This type
of implementation does not provide enough bandwidth to the Internet, nor does it provide

Percentage availability
([525600 – 15] / [525600]) * 100 = 99.9971
■
Scalability: Scalability indicates how well the network can accommodate more users
and data transmission requirements. If a network is designed and optimized for just the
current requirements, it can be very expensive and difficult to meet new needs when
the network grows.
■
Reliability: Reliability indicates the dependability of the components (routers,
switches, PCs, and so on) that make up the network. Reliability is often measured as a
probability of failure, or mean time between failures (MTBF).
■
Topology: Networks have two types of topologies: the physical topology, which is the
arrangement of the cable, network devices, and end systems (PCs and servers), and the
logical topology, which is the path that the data signals take through the physical
topology.
These characteristics and attributes provide a means to compare different networking
solutions. Increasingly, features such as security, availability, scalability, and reliability
have become the focus of many network designs because of the importance of the network
to the business process.
Physical Versus Logical Topologies
Building a reliable and scalable network depends on the physical and logical topology.
Topology defines the interconnection method used between devices including the layout of
the cabling and the primary and backup paths used in data transmissions. As previously
mentioned, each type of network has both a physical and a logical topology.
Physical Topologies
The physical topology of a network refers to the physical layout of the devices and cabling.
You must match the appropriate physical topology to the type of cabling that will be
installed. Therefore, understanding the type of cabling used is important to understanding
Exploring the Functions of Networking 13

example of a physical star topology with a logical bus topology.
Bus Topology Ring Topology Star Topology