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Contents

Contents ............................................................. 2

Introduction to Client/Server Systems .................. 1

History of client/server systems ............................................................................................................ ...1

Motivations, benefits, and negatives ........................................................................................................3

Examples of use of client/server systems .................................................................................................3

Client/Server System Architecture & Infrastructure

4

Types of client/server architectures [2] .......................................................................................... ..... .....4

2-Tier Architecture .......................................................................................................................... ....4

N-Tier Architecture ..............................................................................................................................5Client Hardware and Software ............................................................................................................. ....5

Server Hardware and Software ................................................................................................... ..... ..... ...6

Networking Infrastructure ................................... 6

Local Area Client/Server Networks .........................................................................................................6

Comparing Peer-to-Peer & Client/Server ...................................................................... ..... ..... ..... ..... ..... .6

Client & Server Network Functionality ................................................................................ ..... ..... ..... ....7

Wide Area Networking Concepts ................................................................................................ ..... ..... ..7

WAN Definition ......................................................................................................................... .........7

WAN Switching Technologies ...................................................................................... ..... ..... ..... ..... ..8

WAN Transmission .............................................................................................................................9

WAN Services .....................................................................................................................................9Remote Access and Wireless Technologies .................................................................................... ..... ..10

Remote Access Architecture ..............................................................................................................10

Remote Access Technology ...............................................................................................................10Wireless Networking Services ....................................................................................................... ....11

Conclusion ........................................................ 11

References ........................................................ 13


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Abstract

The Client/server system is a distributed system architecture that

partitions the distribution of tasks between applicants for the service, named

clients and the supplier or service providers, named servers. In many cases,

servers and clients communicate over a computer network on different

devices, but the server and the client can be located in the same system.

The distributed nature of client/server information systems implies a strong

dependence on a distributed networking infrastructure to physically link the

clients and servers and provide dependable mechanism for the delivery of

collaborative computing power. The aim of this project is to give an overview

of the issues surrounding the analysis and choice of those networking

technologies used to build network infrastructure for client/server

information systems.

Introduction to Client/Server Systems

History of client/server systems

Client/server systems evolved from computing environment consisting

of Mainframe and dumb terminals about more than a decade ago, when

dumb terminals were being replace by Personal Computers (PCs) with

processing power. It was realized that computing power of PCs was being

wasted, so organizations introduced processing demands splitting or sharing

between the server or the mainframe and the PC. Because great computing


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control and add more computing value, Client/server technology evolved out

of this movement[1].

Client server system was based on the principle that every single function

related to an application must reside on the computer that is most capable of

managing that function. The clients and servers are connected over a LAN or

WAN (such as Internet).

The first generation of client/server model came as 2-tier architecture

that consists of a client and an application server. A GUI (Graphical User

Interface) is presented by the client to the user and acts on users action to a

certain request the information located in a server running on a different

machine. An example of 2-tier architecture is shown in figure I.1.1.

The 3-tier architecture appeared in second generation of client/server

model to enhance the network performance by inserting a medium tier

between server and client. 3-tier system consists of three separate logical

layers, i.e. presentation layer, functionality layer, and data layer. The

3-tier architecture was developed in a way to overcome some of the

limitations that were faced in the 2-tier schemes. The idea was to separate

presentation, processing, and data into separate distinct entities [1]. Since

the middle tier can supply connections to several types of services, coupling

them to the client, and integrate each other, the architecture was extended

up to N-tiers [1].

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Motivations, benefits, and negatives

The main motivation behind using client / server architectures was the

realization to use computing power of client PCs replacing dumb terminals in

Mainframe environment. This computing power could be used in a way to

share, or split the processing demands between server and PC. Later on, it

was realized that new architecture provided greater control and more

computing value, which resulted in evolution of multi-tier architectures.

There are several advantages associated with client/server model, for

example, centralized resources, ability to make changes to the server with

disturbing the clients, scalability, i.e. add or remove clients without affecting

the network, enhanced security, and server level administration.

However, there are some disadvantages also, for example, the

congestion over a particular server when many clients access a particular

servers particular functionality, denial of access to server in case of break in

weak link, and enhanced cost due to complexity of the server.

Examples of use of client/server systems

Many popular applications on Internet are based on client/server

model, for example, web services, email, file transfer protocol (FTP) services,

etc. In each of these applications, the client has a user interface, GUI or

command-line, and the client application allows user to connect to server, for

instance, in FTP servers, the user has to enter IP address of the server into

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the user interface to access the server. The same is the case with email

server, such as Microsoft Exchange Server, in which client can connect to

Exchange Sever through web browser by typing web address of the server

and keying username and password, or use a client application such as

Microsoft Outlook with given settings.

Client/Server System Architecture & Infrastructure

Types of client/server architectures [2]

The client/server model is classified into different architectures based

on tiers in the model. The client/server architectures are classified into three

major categories, i.e. 2-tier architecture, 3-tier architecture, and N-tier

architecture.

2-Tier Architecture

The 2-tier architecture describes a client/server model in which client

send requests of certain services to the server, and the server directly

responds to the requests using its own resources, meaning the server

doesnt have to call a different application to provide the requested service.

The 2-tier architecture is shown in Figure II.1.1.

3-Tier Architecture

The 3-tier architecture describes a client/server model where there is a

middle tier between client and server. The system is logically divided into

presentation, application, and data layers. In this architecture, the client is

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installed with user interface, usually a web browser to make the request. The

middle tier, which is called middleware or application server, functions to

provide the requested resources by calling another server, i.e. data server.

The function of data server is to provide requested data to middleware,

which is ultimately provided to the requesting client. Figure II.1.2 shows the

3-tier architecture.

The 3-tier architecture supports a great degree of flexibility, enhanced

performance, and improved security by virtue of sharing functions between

the servers.

N-Tier Architecture

The N-tier architecture uses more than more than one intermediary

between clients and servers provide specialized resources. The 3-tier

architecture is also a N-tier architecture with N=3. The conceptual diagram

of N-tier architecture is shown in Figure II.1.3.

Client Hardware and Software

Client hardware is normally a PC installed with networking hardware for

connectivity and network application for requesting and presenting the

information from the server over the network. Client hardware can also be a

portable computer or a mobile device such as Smartphone. Client software is

usually an operating system with network support, and an application with

user interface that can get user input, make a request based on the user

input, and handle and present the response received from server to the user.

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Server Hardware and Software

Since the server hardware has to handle complex applications and

respond to many clients at a time, its hardware consists of typically high-

power, high speed processors, larger memory, and larger and faster hard

drives. The server hardware also typically has an element of redundancy as a

server provides centralized resources to many clients.

The sever software includes a Network Operating System (NOS) such as

UNIX, Windows Server, Linux etc. and the applications that typically support

multiple sessions, for example, Internet Information Server application for

Web services. Normally, the server applications may not need user interface,

except for management; however, sometimes a server can be a client too. In

that case, it may have client applications too.

Networking Infrastructure

Local Area Client/Server Networks

Local client/server systems are often available in homes and offices

without being noticed. An example of local client/server system is DHCP

server built into wireless access point (WAP) commonly used for sharing DSL

Internet connection. Another such system is a computer on network with a

shared printer. It acts as print server.

Comparing Peer-to-Peer & Client/Server

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Peer-to-peer approach in networking uses computers having equivalent

capability and control over applications running on them, while client/server

approach uses specialized computers to act as servers and clients, with

enhanced capabilities and control lying with server(s). According to Bradley

Mitchell In client/server systems, software applications are separated into

modular pieces, and each piece is installed on clients or servers specialized

for that subsystem. It also allows more users to access the database or

applications installed on the server(s). Compared to this, peer-to-peer

networks provide more flexibility in growing the system for better handling of

large number of clients. However, client/server networks provide a better

security to the stored data [3].

Client & Server Network Functionality

The client and server are two different software entities as opposed to

common perception that they must be on separate hardware. The client and

server can reside on same hardware and may not need a network to connect

with each other. It just describes the mechanism how the resources are

accessed. The client is the entity that requests some data or service from

server, which responds with the requested data or service. The simple

process of client/server interaction is depicted in Figure III.1.1 [4].

Wide Area Networking Concepts

WAN Definition

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A network that spans a wide geographical area is known as Wide Area

Network, or WAN in short. This large geographical area can be a region, a

country, or may comprise more than one country. WANs are used to connect

multiple Local Area Networks (LANs), Metropolitan Area Networks (MANs),

Campus Area Networks (CANs), etc. Internet is the most common example of

WAN. The WANs are also owned by large companies with remote branch

offices, universities with multiple campuses, and other organizations having

distributed geographic presence. They are built upon private leased lines, or

VPNs through Internet. Some WANs are typically built using totally private

infrastructure that uses microwave transmission.

WAN Switching Technologies

There are three common types of switching technologies that can be

employed in WAN, i.e. Circuit switching, Packet switching, and Cell relay [5].

Circuit switching involves establishing a dedicated circuit between end nodes

on connection request for transmission of data. Once the circuit is

established, it remains intact till there is tear-down request from any of the

nodes connected. The Dial-up connection and Integrated Services Digital

Network (ISDN) are most common examples of circuit switching for WAN.

Packet switching involves sharing of a single point-to-point link for data

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transmission between network devices that send the data in the form of

packets from source to destination across a carriers network [6]. X.25,

Frame Relay, and Switched Multimegabit Data Service (MSDS) are a few

examples of packet switched WAN technologies. The difference between Cell

Relay and packet switching is that Cell Relay uses fixed length cells instead

of variable length packets. Then, the data is converted into cells and

transported across the link in virtual circuits [5]. The most common example

of Cell Relay is Asynchronous Transmission Mode (ATM) switching.

WAN Transmission

WAN Transmission refers to the technologies for transporting data from

one point to another point. The transmission of data in WAN can be carried

out through various technologies (transmission channels), such as Wireless,

Co-axial cable, Twisted Pair Cables, Optic Fiber Cables, etc. The technologies

further differ in terms of frame format and methods of management, for

example, DWDM, SDH, or SONET over optical fiber, SDH over Microwave

wireless, etc.

WAN Services

WAN Services encompass the services provided by a telecom carrier

company for establishment of WAN. These services may include, but not

limited to, Leased Line, VPN, Frame Relay, ISDN, and ATM etc. Those services

may be provided over various access methods such as Digital Subscriber

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Line (DSL), Digital Cross Connect (DXX), Fiber-to-the-Home (FTTH), Metro

Ethernet, etc.

Remote Access and Wireless Technologies

Remote access pertains to ability to communicate with a PC or Server

from a distant location through any WAN transmission technology including

dialup connection [7]. Remote access allows a client to connect to a LAN

from a remote location, and work with the data resource like a local client.

Remote access can be employed by a home user to connect with his office

PC, or by remote branch offices to connect with resources in corporate

central office.

Remote Access Architecture

Remote Access architecture uses a Remote Access Server, also known as

communication server, a firewall, and a router to enable a WAN connection.

The remote client can be a simple PC with remote access application and

network connectivity. The remote client requests connection to the remote

access server, and if it meets certain criteria defined in remote access policy,

the connection is allowed. The figure III.1.2 shows a corporate remote access

scenario.

Remote Access Technology

Remote Access Server is a technology that enables remote users (clients)

to connect to the LAN connected to that Remote Access Server. Once

connected to remote access server, the clients can access the resources of

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the LAN like other LAN clients if they have relevant permissions; however,

they are authenticated before being granted access to the LAN resources.

Wireless Networking Services

The most common wireless networking technology for remote access is

Wi-Fi that uses radio frequencies to connect with a Wireless LAN, or WLAN. It

uses standard protocol IEEE 802.11, which is based on a Wireless Access

Point (WAP). In order to access the WLAN for remote users, or clients on

WLAN to access remote office resources, and Internet, the client needs to

connect with WAP first [8].

Conclusion

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Client/server network is one of the approaches of managing network

applications that offers various advantages over other alternatives such as

mainframe approach and peer to peer approach. These advantages include

optimal usage of computing power, enhanced efficiency, centralization of

resources, ability to make changes to specific servers and clients without

affecting other servers or clients on the network, enhanced security, and

control.

However, this approach has some disadvantages, such as resources become

unavailable in case of congestion or disconnection. As the computing

services are going to center around Internet, client/server architecture is

going to be the choice of future distributed computing endeavors with

client/server applications operating over the Internet. In order to harness

maximum advantage of Internet, client/server model is the best approach.

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References

1. The Evolution of Client/Server Computing

(http://cis.cuyamaca.net/draney/214/web_server/client.htm ) retrieveddated 26-04-2011

2. http://en.kioskea.net/contents/cs/cs3tier.php3 retrieved dated 27-04-

2011

3. Bradley Mitchell, Introduction to Client Server Networks,

(http ://compnetworking .about .com /od /basicnetworkingfaqs /a /client -

server .htm) retrieved dated 26-04-2011

4. http://www.december.com/web/text/csmodel.html, retrieved dated 27-

04-201

5. http://en.wikipedia.org/wiki/Wide_area_network , retrieved dated 27-04-

2011.6. Introduction to WAN Technologies, Internetworking Technology

Overview, Cisco Press, June 1999

7. http://searchmidmarketsecurity.techtarget.com/definition/remote-

access, retrieved dated 27-04-2011

8. http://www.ehow.com/about_5046061_remote-access-

technologies.html, retrieved dated 27-04-2011

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http://cis.cuyamaca.net/draney/214/web_server/client.htmhttp://en.kioskea.net/contents/cs/cs3tier.php3%20retrieved%20dated%2027-04-2011http://en.kioskea.net/contents/cs/cs3tier.php3%20retrieved%20dated%2027-04-2011http://en.kioskea.net/contents/cs/cs3tier.php3%20retrieved%20dated%2027-04-2011http://compnetworking.about.com/od/basicnetworkingfaqs/a/client-server.htmhttp://compnetworking.about.com/od/basicnetworkingfaqs/a/client-server.htmhttp://compnetworking.about.com/od/basicnetworkingfaqs/a/client-server.htmhttp://www.december.com/web/text/csmodel.htmlhttp://www.december.com/web/text/csmodel.htmlhttp://en.wikipedia.org/wiki/Wide_area_networkhttp://searchmidmarketsecurity.techtarget.com/definition/remote-accesshttp://searchmidmarketsecurity.techtarget.com/definition/remote-accesshttp://www.ehow.com/about_5046061_remote-access-technologies.htmlhttp://www.ehow.com/about_5046061_remote-access-technologies.htmlhttp://cis.cuyamaca.net/draney/214/web_server/client.htmhttp://en.kioskea.net/contents/cs/cs3tier.php3%20retrieved%20dated%2027-04-2011http://en.kioskea.net/contents/cs/cs3tier.php3%20retrieved%20dated%2027-04-2011http://compnetworking.about.com/od/basicnetworkingfaqs/a/client-server.htmhttp://compnetworking.about.com/od/basicnetworkingfaqs/a/client-server.htmhttp://compnetworking.about.com/od/basicnetworkingfaqs/a/client-server.htmhttp://compnetworking.about.com/od/basicnetworkingfaqs/a/client-server.htmhttp://compnetworking.about.com/od/basicnetworkingfaqs/a/client-server.htmhttp://compnetworking.about.com/od/basicnetworkingfaqs/a/client-server.htmhttp://compnetworking.about.com/od/basicnetworkingfaqs/a/client-server.htmhttp://compnetworking.about.com/od/basicnetworkingfaqs/a/client-server.htmhttp://compnetworking.about.com/od/basicnetworkingfaqs/a/client-server.htmhttp://compnetworking.about.com/od/basicnetworkingfaqs/a/client-server.htmhttp://compnetworking.about.com/od/basicnetworkingfaqs/a/client-server.htmhttp://compnetworking.about.com/od/basicnetworkingfaqs/a/client-server.htmhttp://compnetworking.about.com/od/basicnetworkingfaqs/a/client-server.htmhttp://compnetworking.about.com/od/basicnetworkingfaqs/a/client-server.htmhttp://compnetworking.about.com/od/basicnetworkingfaqs/a/client-server.htmhttp://compnetworking.about.com/od/basicnetworkingfaqs/a/client-server.htmhttp://compnetworking.about.com/od/basicnetworkingfaqs/a/client-server.htmhttp://compnetworking.about.com/od/basicnetworkingfaqs/a/client-server.htmhttp://compnetworking.about.com/od/basicnetworkingfaqs/a/client-server.htmhttp://compnetworking.about.com/od/basicnetworkingfaqs/a/client-server.htmhttp://www.december.com/web/text/csmodel.htmlhttp://en.wikipedia.org/wiki/Wide_area_networkhttp://searchmidmarketsecurity.techtarget.com/definition/remote-accesshttp://searchmidmarketsecurity.techtarget.com/definition/remote-accesshttp://www.ehow.com/about_5046061_remote-access-technologies.htmlhttp://www.ehow.com/about_5046061_remote-access-technologies.html


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Figure I.1.1

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Figure II.1.1

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Figure II.1.2

Figure II.1.3

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Figure III.1.1

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Figure III.1.2

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Documents

Client Server Network Paper