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:
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.
It can transmit data in both directions, but in only one direction at a time. Hence, it can alternately send and receive data.
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:
It has a speed in the range of 45 to 300 baud.
- Voice band
It has a speed up to 9600 baud.
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:
- Twisted-Pair Wire
- Coaxial Cable
- Microwave System
- Communications Satellite
- 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 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
- Amplitude Modulation(AM)
- Frequency Modulation(FM)
- Phase Modulation(PM)
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.
- Dial-up line(switched line)
- Leased line(private line or dedicated line)
- Integrated Services Digital Network(ISDN)
- Value Added Network(VAN)
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).
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.
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.
- 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.
- 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 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.
- 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.
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.
- Static Routing
- Default Routing
- Dynamic Routing
A network topology is the physical and logical arrangement of nodes and connections in a network.
- Star Network
- Ring Network
- Hybrid Network
- Multi-access Bus Network
- Completely Connected Network
- PAN(personal-area network)
The smallest computer network.Devices connected through bluetooth.
- LAN(local-area network)
A series of computers linked together to form a network in a circumscribed location.Ex:home WiFi network.
- CAN(campus-area network)
A CAN is a network that covers an educational or corporate campus.
- MAN(metropolitan-area network)
A MAN is a network that spans a large area such as a town or city.
- WAN(wide-area network/long haul network)
A computer network that connects smaller networks.Ex:internet.
It allow different network devices to communicate with each other.
- Data sequencing
- Data routing
- Data formatting
- Flow control
- Error control
- Data security
- 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.
Open Systems Interconnection is a conceptual framework used to describe the functions of a networking system.
The 7 layers of the OSL model:
- Physical layer
- Data-Link layer
- Network layer
- Transport layer
- Session layer
- Presentation layer
- Application layer
Interconnecting two or more networks to form a single network is called internetworking and the resulting network is called an internetwork.
A wireless network is a computer network that uses wireless data connections between network nodes.
- Fixed wireless system
- Mobile wireless system
- lower bandwidth
- higher error rate
- limited power
- dynamically changing network
- mobile e-commerce application
- web surfing using wireless devices
- mobile video-on-demand application
2G and 3G technologies
- Wireless LAN(WLAN)
- WiMAX(Worldwide Interoperability for Microwave Access)
- Wireless Local Loops(WLLs)
- Multihop Wireless Networks
- Wireless Application Protocol(WAP)