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Client Server Architecture over the Internet

Week - 2

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Reference• Chapter 4: Internet Architecture from Electronic

Commerce-From Vision to Reality by Elias M. Awad.

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A computer network is collection of

computers interconnected for the purpose

of communication and sharing resources.

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Peer to Peer Networks• A network of computers where each computer

is consider equivalent to others.

• No centralised repository of information and services.

• Information and applications need to be replicated in each computer on the network.

• Administration of application becomes difficult when the size of the network increase.

• Integrity of replicated information is questionable.

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Relative Advantages and Disadvantages

Key Advantages Key Disadvantages

User control over resources Individual security policies

Easy installation and configuration

Difficult administration

Cost effective for small businesses

Backup of replicated information results in higher cost

Fault tolerant as no single point of failure on the network

Integrity of replicated resources is questionable

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Client Server Architecture• Server

– A special purpose computer or specialised hardware and software designed for specific functions.

• Client– A computer connected to one or more servers on a

network or the Internet.

• Client Server Networks– A cluster of client computers connected to one or

more servers on a network.– Servers provide centralised repository of

information and services.

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Typical Services over a Network• Application services

– Server based programs

• Instant messaging services– Winpop, IRC chat, Netmeeting, MSN & Yahoo

Meeangers

• E-mail services• Database services• Information services

– File services

• Communication services– Fax, data relay, Internet access

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Typical Client Server Interaction• Servers wait for clients to send a request for

accessing a resource.

• Clients requiring access to a resource connect to the server and submit a request for the resource.

• Servers accept clients’ requests and respond with the access to the requested resource.

• Clients disconnect from the servers.

• This protocol is known as the request-reply protocol and forms the basis of client server architecture.

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Typical Client Server Interaction(Contd.)

Client Server

Connect

Request

Reply

Accept

Disconnect

Network

Time

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Relative Advantages and Disadvantages

Key Advantages Key Disadvantages

Centralised administration Specialised installation and configuration

Scalable Requires installation of specialised servers

Integrity of shared resources guaranteed

Single points of failures

Can be extended over the Internet

Require high speed access to accommodate large number of requests.

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Providing Global Services• Clients and servers installed over local area

networks (LANs)– A LAN is a cluster of computers within a confined

space, e.g., an office building, a department etc.

• LANs within a particular geographical area can be interconnected via metropolitan area networks (MANs).– E.g., city-wide networks

• A backbone network owned by a tele-communications company can be used to inter-connect LANs and MANs– Referred to as wide area networks (WANs).

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Providing Global Services (Contd.)

LAN

MAN

Wide Area Network

Server

Client

RouterRouter

Router

LAN

Client

Router

Client

LAN

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Addressing Machines• Each computer connected to the network has to

be identified uniquely on that network.– Computers connected to networks that form part of

the Internet must have globally unique identification.

• Computers are identified in two ways,– Using machine understandable numeric addresses.– Using human understandable names.

• Humans address computers using their names.

• Before communications takes place, computer names are to be translated into their numeric addresses.

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IP Addresses – Numeric Address for the Internet

• Two types of IP addresses– IPv4 addresses: 32 bit numeric integers– IPv6 addresses: 128 bit numeric integers

• IPv4 addresses represented as 4 dotted decimal integer ranging from 0 to 255.– E.g., 192.168.0.234

• Each IP address is divided into network address and the host address.– E.g., 192.168.0.0 is the network address and 234 is

a host residing on that network.

• Network addresses are used to locate the networks where the destination hosts reside.

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Internet Zones and Domains• Internet host names are decoded from right to

left.

• E.g., www.stanford.edu– edu is the zone name and is used to categorise the

host.– stanford is the name of the host.– Traditionally 3 letter zone names have been

specified for US, e.g., edu, com, mil, net, org.– For other countries two letter zones have been

specified to identify geographical locations• E.g., ae, uk, pk, fr, etc.,

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Information Transfer

Client Server

CommunicationsSubsystem

CommunicationsSubsystem

TransmissionControl Protocol

TransmissionControl Protocol

Reliable Delivery

Internet Protocol

InternetProtocol

Addressing and Relay

NetworkInterface

NetworkInterfacePhysical Communication

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Information Transfer (Contd.)

• Application components (i.e., clients and servers) communicate virtually.

• Physically – Clients pass requests to their communication

subsystems.– Communications subsystems communicate client

requests to the communications subsystems of the server.

– Communications subsystem of the server passes the request to the server subsystem.

– Replies from the server follow the reverse path.

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Information Transfer (Contd.)

• Communication subsystem of the Internet Protocol suite– Transmission Control Protocol (TCP)

• Provides reliable message delivery.

– Internet Protocol (IP)• Provides addressing of hosts and best effort relay of

packets to the destination.

– Network Interface• Provides physical communication over the Internet.

• Messages of arbitrary lengths are segmented into packets, size and structure of which are pre-specified for efficient communication.

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Designing a Network• Essential Considerations

– Location, physical layout and installation– Capacity requirements– Scalability requirements– Cost– Security

• Architectural Design– Hardware requirements– Software requirements– Disaster recovery and fault tolerance– Corporate culture and organisational factors

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Designing a Network• Essential Considerations

– Location, physical layout and installation– Capacity requirements– Scalability requirements– Cost– Security

• Architectural Design– Hardware requirements– Software requirements– Disaster recovery and fault tolerance– Corporate culture and organisational factors

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