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Characteristics of Communication Systems
Characteristics of Communication Systems
A communication system allows its users to send and receive data and information. The framework for communication systems is in the diagram below: (This example if or Skype/MSN as a communication system)
Functions performed within communication systems to send a message:
Functions performed within communication systems to send a message:
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Message creation
The organisation of packets at the interface between source and transmitter
Signal generation by the transmitter
Transmission via a medium
Synchronising the exchange
Addressing and routing
Error detection and correction
Security and management
Protocols in communication:
Protocols in communication:
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A protocol is a set of rules that governs a communication process
‘Handshaking’ is the process of establishing a communication link and agreeing on which protocol to use
Protocols can include sophisticated techniques for detecting and recovering from transmission errors and for encoding and decoding data.
Common Protocols:
Common Protocols:
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TCP/IP: Transmission Control Protocol/Internet Protocol – rules that split data into packets for transfer across the internet
HTTP: Hyper Text Transfer Protocol – allow the displaying of files containing hypertext links across a network
FTP: File Transfer Protocol – the protocol defining the transfer of files over a network or the internet
SMTP: Simple Mail Transfer Protocol – sending of e-mail messages
POP: Post Office Protocol – retrieves e-mail messages
SSL: Secure Sockets Layer – used for encryption of data for secure data transmission
The Client-Server Architecture
The Client-Server Architecture
Notes on Client-Server architecture
There are two different types of computers present on the network, namely servers and clients.
The server provides particular processing resources and services to each client machine.
The client machines also perform their own local processing.
Client–server processing is a form of distributed processing where different computers are used to perform the specific information processes necessary to achieve the system's purpose.
Client-server processing occurs sequentially – when a particular operation is being performed either the client is processing or the server is processing – but not at the same time. (read more...)
On larger LANs it is common for all network tasks to be performed by one or more servers using client-server architecture.
These servers commonly run a network operating system (NOS) such as :
LINUX
NOVELL NETWARE
WINDOWS SERVER
When a client machine has its own applications installed that are executed by the CPU it is called a “fat client”.
A “thin client” relies on the server to perform all the real processing. These terminals only perform basic processing tasks, such as receiving data, displaying it on the screen and also transmitting input back to the mainframe.
Types of servers:
File Servers
Print Servers
Database Servers
Mail Servers
Web Servers
Proxy Server
Thin & Fat Clients
Thin & Fat Clients
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Thin clients:
A thin client is designed to be especially small so that the bulk of the data processing occurs on the server; a thin client is a network computer without a hard disk drive.
Thin clients can be found in medical offices, airline ticketing, schools, etc.
Easy to install, lower total costs than fat clients
Examples include: web browsers, e-mail clients
Fat clients:
Performs the bulk of the processing in client/server applications
Can handle higher bandwidths, operating systems and software that do not run on thin clients can run on fat/thick clients as it has its own resources.
Examples include: a laptop or computer
The diagram below shows the difference between fat clients (on the left), where each user has a standalone device. This is most common today as computers are very cheap. In previous years, when computers were very expensive, it was far more economical to have one mainframe server and a bunch of thin clients connect to it. The Thin Clients have enough processing power to connect ot the main processor and then all processign is controlled by the server.
This was an economic benefit to universities and large companies at the time because a monitor / keyboard, which is all a Thin Client is, was far cheaper than a full computer setup per person.
Servers
Servers
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Types of servers:
File Servers: Google drive is a file server as it stores files for you
Print Servers: Handles print jobs
Database Servers: Emails, tax return. Contains data on a server
Mail Servers: Email
Web Servers: House and serve web pages to clients. In this case a client is a web browser that displays pages sent from the web server. The client device can be any internet enabled device, such as a mobile phone, tablet, computer or laptop.
Proxy Server: Go between the user and the internet.
Advantages and Disadvantages of Client-Server Architecture
Advantages and Disadvantages of Client-Server Architecture
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Advantages:
Centralised resources; given that the server is the centre of the network, it can manage resources that are common to all users
It is possible to remove or add clients without affecting the operation of the network and without the need for major modification
Disadvantages:
Client-server networks can become congested and overload the server with requests
Increased costs due to the technical complexity of the server
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