Transcript Week-2

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
Integrity of replicated
point of failure on the network 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.)
Server
Connect
Accept
Request
Time
Reply
Disconnect
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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
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requests.
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 telecommunications company can be used to interconnect LANs and MANs
– Referred to as wide area networks (WANs).
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Providing Global Services (Contd.)
LAN
Router
Client
Wide Area Netw ork
Client
LAN
MAN
Router
Router
LAN
Router
Client
Server
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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
Transmission
Control Protocol
Reliable Delivery
Transmission
Control Protocol
Internet
Protocol
Addressing and Relay
Internet
Protocol
Network
Interface
Communications
Subsystem
Physical Communication
Network
Interface
Communications
Subsystem
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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.
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– Replies from the server follow the reverse path.
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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