client server network paper
TRANSCRIPT
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[ Computer Communication]
CSC3352
Client/Server System:NetworkingInfrastructure
[Final Project]
[By: Amine Lasfar]
[27/04/2011]
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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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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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