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Clients and Servers
Client and Server Roles
• All computers connected to a network that participate directly in network communication are
classified as hosts.
• In modern networks, computer hosts can act as a client, a server, or both.
• The software installed on the computer determines which role the computer plays.
Type Description
Email
The email server runs email server software.
Clients use mail client software, such as Microsoft Outlook, to access email on the
server.
Web
The web server runs web server software.
Clients use browser software, such as Windows Internet Explorer, to access web pages
on the server.
File
The file server stores corporate and user files in a central location.
The client devices access these files with client software such as the Windows File
Explorer.
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Clients and Servers
Client and Server Roles (Cont.)
• Servers are hosts that have software installed which enable them to provide information, like
email or web pages, to other hosts on the network.
• Each service requires separate server software.
• For example, a host requires web server software in order to provide web services to the
network.
• Every destination that you visit online is provided to you by a server located somewhere
on a network that is connected to the global internet.
• Clients are computer hosts that have software installed enabling the hosts to request and
display the information obtained from the server.
• An example of client software is a web browser, such as Internet Explorer, Safari, Mozilla
Firefox, or Chrome.
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Clients and Servers
Peer-to-Peer Networks
• Client and server software usually run on separate computers, but it is also possible for one
computer to run both client and server software at the same time.
• This type of network is called a peer-to-peer (P2P) network.
• Small businesses and homes may operate a P2P network to share resources.
• The simplest P2P network consists of two directly connected computers using either a wired or
wireless connection.
• Both computers are then able to use this simple network to exchange data and services
with each other, acting as either a client or a server, as necessary.
• Multiple PCs can also be connected to create a larger P2P network, but this requires a network
device, such as a switch, to interconnect the computers.
• In larger businesses, because of the potential for high amounts of network traffic, it is often
necessary to have dedicated servers to support the number of service requests.
4

Clients and Servers
Peer-to-Peer Networks (Cont.)
Advantages of P2P networking:
• Easy to set up
• Less complex
• Lower cost because network devices and dedicated servers may not be required
• Can be used for simple tasks such as transferring files and sharing printers
Disadvantages of P2P networking:
• No centralized administration
• Not as secure
• Not scalable
• All devices may act as both clients and servers which can slow their performance
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Clients and Servers
Peer-to-Peer Applications
• A P2P application allows a device to act as both a
client and a server.
• Every client is a server and every server is a client.
• Both clients can simultaneously send and receive
messages.
• P2P applications require that each end device
provide a user interface and run a background
service.
• Some P2P applications use a hybrid system where
resource sharing is decentralized, but the indexes
that point to resource locations are stored in a
centralized directory.
• In a hybrid system, each peer accesses an index
server to get the location of a resource stored on
another peer.
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Clients and Servers
Multiple Roles in the Network
• A computer with server software can provide services
simultaneously to one or many clients.
• A single server can be a file server, a web server, and an
email server.
• A client computer can also connect to multiple servers
using client software such web browser, client email
application, and more.
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2.2 Network Components
8

Network Components
End Devices
• The network devices that people are most familiar with are called end devices, or hosts.
• Computers (workstations, laptops, file servers, web servers)
• Network printers
• Telephones and teleconferencing equipment
• Security cameras
• Mobile devices (such as smart phones, tablets, PDAs, and wireless debit/credit card readers
and barcode scanners)
• An end device (or host) is either the source or destination of a message transmitted over the
network.
• To uniquely identify hosts, addresses are used.
• When a host initiates communication, it uses the address of the destination host to specify where the
message should be sent.
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2.3 ISP Connectivity Options
10

ISP Connectivity Options
ISP Services
• An Internet Service Provider (ISP) provides
the link between a network and the internet.
• Many ISPs also offer additional services to
their contract subscribers as shown in the
figure.
11

ISP Services (Cont.)
• Each ISP connects to other ISPs to form a network of links that interconnect users all over
the world.
• ISPs are connected in a hierarchical manner that ensures that internet traffic generally takes the
shortest path from the source to the destination.
• ISPs provides high-speed data links to connect the various service provider networks in major
metropolitan areas around the world.
• The primary medium that connects the internet backbone is fiber-optic cable installed underground
to connect cities within continents and under the sea to connect continents, countries, and cities.
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ISP Connections
• The interconnection of ISPs that forms the backbone of the internet is a complex web of fiber-optic
cables with expensive networking switches and routers that direct the flow of information between
source and destination hosts.
• The simplest ISP connection option consists of a modem that provides a direct connection between
a computer and the ISP.
• However, this is not a secure option as a computer is not protected on the internet.
• A router (or wireless router) is required to securely connect a computer to an ISP.
• The router includes a switch to connect wired hosts and a wireless AP to connect wireless
hosts.
• The router also provides client IP addressing information and security for inside hosts.
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ISP Connections (Cont.)
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Cable and DSL Connections
Most home network users connect to the internet using either Cable or DSL.
Cable
• Typically offered by cable television service
providers option, the internet data signal is
carried on the same coaxial cable that delivers
cable television.
• It provides a high bandwidth, always on,
connection to the internet.
• A special cable modem separates the internet
data signal from the other signals carried on
the cable and provides an Ethernet connection
to a host computer or LAN.
15

Cable and DSL Connections (Cont.)
DSL
• Digital Subscriber Line (DSL) provides a high bandwidth, always on, connection to the internet.
• It requires a special high-speed modem that separates the DSL signal from the telephone signal
and provides an Ethernet connection to a host computer or LAN.
• DSL runs over a telephone line, with the line split into three channels.
• One channel is used for voice telephone calls. This channel allows an individual to receive
phone calls without disconnecting from the internet.
• A second channel is a faster download channel, used to receive information from the
internet.
• The third channel is used for sending or uploading information. This channel is usually
slightly slower than the download channel.
• The quality and speed of the DSL connection depends mainly on the quality of the phone line
and the distance from the central office of your phone company. The farther you are from the
central office, the slower the connection.
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Additional Connectivity Options
• Other ISP connection options for home users include the following:
• Cellular – Connects using the same cell service as smartphones to provide roaming
internet connectivity. However, additional service charges may apply.
• Satellite – Provides acceptable bandwidth internet connectivity to remote areas.
However, equipment and installation costs can be high with a moderate monthly fee
thereafter.
• Dial-up Telephone – An inexpensive option that uses any land phone line and a
modem. This provides the lowest bandwidth option and should only be considered
when higher speed connection options are not available.
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