Data communication requires five components: message, sender, receiver, transmission medium, and protocol. These components work together to ensure accurate data delivery.
In distributed processing, multiple computers are used to process data collectively. Each processor handles a subset of tasks and communicates over the network.
Standard organizations include ISO, ITU-T, IEEE, ANSI, and IETF. They define protocols and frameworks to ensure network interoperability.
Defines how devices are connected:
Network topology refers to the physical or logical layout of devices in a network. Types include:
Defines the direction of data flow:
Networks are categorized by geographic scope:
OSI Model: 7 layers (Physical, Data Link, Network, Transport, Session, Presentation, Application).
TCP/IP Model: 4 layers (Network Interface, Internet, Transport, Application).
OSI provides a generic framework, while TCP/IP is practical and widely used.
DTE-DCE Interface: Connects user devices (DTE) with network devices (DCE). Common interface standards include RS-232.
Modems: Convert digital signals to analog for transmission over telephone lines, and vice versa.
Cable Modems: Use coaxial cable lines for high-speed internet access, supporting both data and television signals.
Transmission media can be classified as:
Attenuation refers to the reduction in signal strength as it travels over a transmission medium. It is measured in decibels (dB).
Distortion occurs when the signal changes form or shape. It is typically caused by varying propagation speeds of signal components.
Noise refers to unwanted signals that interfere with the original message. Common types include thermal noise, crosstalk, and impulse noise.
Throughput is the actual rate at which data is successfully transmitted over a communication channel. It is usually less than the bandwidth.
Propagation speed is the rate at which a signal travels through the medium. Propagation time is the time it takes for a signal to travel from source to destination.
Wavelength is the distance between two consecutive peaks of a signal. It is inversely proportional to frequency (λ = v/f).
The Shannon Capacity defines the theoretical maximum data rate of a channel without error, based on bandwidth and signal-to-noise ratio (SNR).
Example:
C = B × log2(1 + S/N)
Where:
C = Capacity (bps), B = Bandwidth (Hz), S/N = Signal-to-noise ratio
A comparison of various transmission media:
Multiplexing is the technique of combining multiple signals into one medium. Types include:
Used to ensure data integrity during transmission.
ISDN is a circuit-switched telephone network system that provides digital transmission.
Network devices help manage, direct, and amplify data flow in networks. Key devices include:
The Network Layer is responsible for routing, addressing, and packet forwarding. It ensures data reaches the correct destination across networks.
Routing algorithms determine the best path through the network:
Used to handle network traffic efficiently:
QoS ensures consistent network performance by managing delay, bandwidth, and packet loss—important for real-time services like voice and video calls.
Internetworking is the connection of multiple distinct networks to function together using devices like routers and protocols like TCP/IP.
The Internet relies on the IP protocol at the network layer for communication. Supporting protocols include:
The transport layer provides reliable data transfer between devices. Key responsibilities include:
The transport layer establishes, maintains, and terminates virtual circuits between sender and receiver.
Example: TCP uses a three-way handshake to establish a connection between hosts.
Step 1: Client sends SYN
Step 2: Server replies with SYN-ACK
Step 3: Client responds with ACK — connection established
The session layer manages sessions or dialogues between computers. It provides mechanisms for opening, closing, and managing sessions between end-user applications.
This layer ensures that the data is in a readable format for the application layer. It performs:
The application layer is closest to the end-user and provides services like email, file transfer, and web browsing.
Example: When you browse a website, the browser (application layer) communicates using HTTP protocol to fetch web content.