Data communications and computer networks

Data communication

The exchange of data between two or more networked or connected devices.
 

Basic Elements of a Communication System

Communication is the process of transferring a message from one point to another. The three basic elements of any communication system are:
  • A sender(source) that creates and sends a message.
  • A medium that carries the message.
  • A receiver(sink) that receives the message.
Electronic systems that transfer data from one point to another are called data communication systems.

Data Transmission Modes

Defines the direction of the flow of information between two communication devices.
There are three modes:
  1. Simplex
    It can transmit data in one direction only.It is suitable for connecting send-only(keyboard) or receive-only(printer) devices.Simplex circuits are seldom used.
  2. Half-duplex
    It can transmit data in both directions, but in only one direction at a time. Hence, it can alternately send and receive data. 
  3. Full-duplex
    It needs to switch direction each time the direction of data transfer reverses. 

Data Transmission Speed

The speed with which data is getting transmitted in computer.It is commonly measured in bits per second.Based on data transmission speeds,three basic categories of communication channels(paths) are:
  1. Narrowband
    It has a speed in the range of 45 to 300 baud.
  2. Voice band
    It has a speed up to 9600 baud.
  3. Broadband
    It has a speed of 1 million baud or more.
 

Data Transmission Media

It is a communication channel that carries the information from the sender to the receiver.
Some popular data transmission media are:
  1. Twisted-Pair Wire
  2. Coaxial Cable
  3. Microwave System
  4. Communications Satellite
  5. Optical Fibers

DIGITAL AND ANALOG DATA TRANSMISSION

Digital data transmission

The transfer of data from one digital device to another. 

Analog data transmission

Transmission method of conveying information using a continuous signal which varies in amplitude,phase or some other property in proportion to that information.
 

Modulation Techniques

Modulation is the process of converting data into electrical signals optimized for transmission.Modulation techniques are divided into four types:Analog,Digital,Pulse and Spread spectrum method.
Types of Modulations
  1. Amplitude Modulation(AM)
  2. Frequency Modulation(FM)
  3. Phase Modulation(PM)
 

Modems(Modulator-Demodulator)

A modem or broadband modem is a hardware device thats connects a computer or router to a broadband network.Ex:a cable modem and DSL modem.It is used because computers understand only digital data 0 and 1.
 

DATA TRANSMISSION SERVICES

DTS supports several data replication modes,including data migration,data integration,data synchronization and change tracking.
Services:
  1. Dial-up line(switched line)
  2. Leased line(private line or dedicated line)
  3. Integrated Services Digital Network(ISDN)
  4. Value Added Network(VAN)
 

MULTIPLEXING TECHNIQUES

Multiplexing is a technique by which different analog and digital streams of transmission can be simultaneously processed over a shared link.The two basic methods of multiplexing channels are Frequency Division Multiplexing(FDM) and Time Division Multiplexing(TDM).

FDM

In FDM multiple signals are combined for transmission on a single communications line or channel with each signal assigned to a different frequency within the main channel. FDM works on an "additive" principle by laying down material in layers.

TDM

It is a method of putting multiple data streams in a single signal by separating the signal into many segments each having a very short duration. TDM is based on the principle that for some drugs there is a close relationship between the plasma level of the drug and its clinical effect. 
 

ASYNCHRONOUS AND SYNCHRONOUS TRANSMISSION

Two modes of data transmission on a communication channel are asynchronous and synchronous.
  1. Asynchronous transmission
    Transmission of data in which each character is a self-contained unit with its own start and stop bits and an uneven interval between them.
    Ex: Emails and forum comments.
  2. Synchronous Transmission
    Synchronous is used to describe a continuous and consistent timed transfer of data blocks.It is efficient,reliable and is used for transferring a large amount of data. It provides real-time communication between connected devices.Ex:chat rooms,video conferencing and telephonic conversations.

SWITCHING TECHNIQUES

Switching is the techique by which nodes control or switch data to transmit it between specific points on a network.It is used to connect the systems for making one-to-one communication.
Types:
  • Circuit Switching
    It is a type of network configuration in which a physical path is obtained and dedicated to a single connection between two endpoints in the network for the duration of a dedication connection.It involves three phases-circuit establishment,data transfer and circuit disconnection.Ex:analog telephone network.
  • Message Switching
    A message is a logical unit of information of any length.It is a network switching technique in which data is routed in its entirety from the source node to the destination node,one hope at a time.
  • Packet Switching
    It is the transfer of small pieces of data across various networks.Types-connectionless(datagrame switching) and connection-oriented(virtual circuit switching).Ex:frame relay and IP.
 

ROUTING TECHNIQUES

It is a process that is performed by layer 3(or network layer) devices in order to deliver the packet by choosing an optimal path from one network to another.It is used for identifying or announcing network paths.
Types:
  • Static Routing
  • Default Routing
  • Dynamic Routing
 

NETWORK TOPOLOGIES

A network topology is the physical and logical arrangement of nodes and connections in a network.
Types:
  • Star Network
  • Ring Network
  • Hybrid Network
  • Multi-access Bus Network
  • Completely Connected Network
 

NETWORK TYPES

  1. PAN(personal-area network)
    The smallest computer network.Devices connected through bluetooth.
  2. LAN(local-area network)
    A series of computers linked together to form a network in a circumscribed location.Ex:home WiFi network.
  3. CAN(campus-area network)
    A CAN is a network that covers an educational or corporate campus.
  4. MAN(metropolitan-area network)
    A MAN is a network that spans a large area such as a town or city.
  5. WAN(wide-area network/long haul network)
    A computer network that connects smaller networks.Ex:internet.
 

COMMUNICATION PROTOCOLS

It allow different network devices to communicate with each other.
Roles:
  1. Data sequencing
  2. Data routing 
  3. Data formatting
  4. Flow control
  5. Error control
  6. Data security
  7. Protocol suite,protocol family or protocal stack are terms used to refer to a collection of protocols of a network system.
 

Network Interface Card(NIC)

NIC is the hardware device most essential to establishing communication between computers.Types:Etherent and Wireless Network NIC.
 

OSI Model

Open Systems Interconnection is a conceptual framework used to describe the functions of a networking system.
The 7 layers of the OSL model:
  1. Physical layer
  2. Data-Link layer
  3. Network layer
  4. Transport layer
  5. Session layer
  6. Presentation layer
  7. Application layer

INTERNETWORKING TOOLS

Interconnecting two or more networks to form a single network is called internetworking and the resulting network is called an internetwork.
Types:
  1. Bridge
  2. Router
  3. Gateway
 

WIRELESS NETWORKS

A wireless network is a computer network that uses wireless data connections between network nodes.
Types:
  • Fixed wireless system
  • Mobile wireless system
Issues:
  • lower bandwidth
  • higher error rate 
  • limited power
  • dynamically changing network
Applications:
  • mobile e-commerce application
  • web surfing using wireless devices
  • mobile video-on-demand application
 

WIRELESS TECHNOLOGIES

2G and 3G technologies

  • Wireless LAN(WLAN)
  • WiMAX(Worldwide Interoperability for Microwave Access)
  • Wireless Local Loops(WLLs)

Radio-router technology

  • Multihop Wireless Networks
  • Wireless Application Protocol(WAP)
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