NIELIT ACC key terms

The range of frequencies a channel can carry, or the maximum data rate a link supports, usually measured in hertz or bits per second. Higher bandwidth lets more data move per unit time.

The process of varying a carrier wave's amplitude, frequency, or phase to encode information so it can travel over a medium. Demodulation reverses it at the receiver.

Combining several independent signals onto one shared channel so they can be sent together. Common forms divide the channel by frequency, time, or wavelength, improving link utilisation.

The actual rate at which useful data is delivered across a link, always lower than raw bandwidth because of protocol overhead, errors, and congestion. It measures real performance, not theoretical capacity.

The time delay between sending a request and receiving the response, made up of propagation, transmission, queuing, and processing delays. It matters most for interactive and real-time applications.

Variation in packet arrival delay across a network. High jitter disrupts voice and video because packets arrive unevenly, so buffers are used to smooth playback.

A seven-layer conceptual framework describing how network functions are organised, from physical signalling up to application services. It guides design, troubleshooting, and protocol comparison rather than prescribing implementations.

The practical protocol stack the Internet runs on, organised into link, internet, transport, and application layers. It defines addressing, routing, and reliable or unreliable delivery services.

Wrapping data with protocol headers (and sometimes trailers) as it moves down the layers, so each layer adds the control information its peer needs. Decapsulation strips these headers at the receiver.

A numeric label assigned to a network interface so packets can be routed to it. IPv4 uses 32-bit addresses; IPv6 uses 128-bit addresses to overcome address exhaustion.

Dividing a network address range into smaller logical subnetworks by borrowing bits for the prefix. It improves address efficiency, limits broadcast traffic, and supports structured routing.

The process of selecting a path for packets across interconnected networks and forwarding them hop by hop. Routers build tables from static configuration or dynamic protocols such as OSPF and BGP.

Forwarding frames within a local network based on hardware addresses, typically using a MAC address table. It contrasts with routing, which moves packets between different networks.

The data unit at the data-link layer, containing a header with source and destination hardware addresses, the payload, and a trailer with error-checking information.

The Domain Name System translates human-readable names into IP addresses through a distributed hierarchy of servers, so users need not remember numeric addresses.

The request-response application protocol browsers use to fetch web resources. It is stateless, and HTTPS secures it with TLS encryption and server authentication.

Transport Layer Security provides encrypted, authenticated channels between client and server using certificates and negotiated cipher suites. It underpins HTTPS and many other secure protocols.

A security device or program that permits or blocks traffic according to rules based on addresses, ports, or inspected content. It enforces a boundary between trusted and untrusted networks.

A Virtual Private Network creates an encrypted tunnel over a public network so remote users or sites communicate as if on a private link, protecting confidentiality and hiding internal addressing.

A monitoring system that inspects network or host activity for signs of attack and raises alerts. A prevention variant can also block detected traffic automatically.

Any software written to harm, disrupt, or gain unauthorised access to systems, including viruses, worms, trojans, and ransomware. Protection relies on patching, filtering, and endpoint tools.

A social-engineering attack that impersonates a trusted party through email, messages, or fake sites to trick users into revealing credentials or installing malicious software.

A cryptographic value computed over a message with a private key and verified with the matching public key, proving origin and detecting tampering. It provides authentication and integrity, not confidentiality.

A one-way algorithm that maps input of any length to a fixed-length digest. Good cryptographic hashes are collision-resistant and are used for integrity checks, passwords, and signatures.

Transforming readable data into ciphertext using a key so that only authorised parties can recover it. Symmetric schemes share one key; asymmetric schemes use a public and private key pair.

A material whose conductivity lies between conductors and insulators and can be controlled by doping or applied voltage. Silicon dominates because it supports reliable, cheap integrated fabrication.

The boundary formed when p-type and n-type semiconductor regions meet, creating a depletion zone that conducts easily in one direction. It is the basis of diodes and of bipolar transistors.

A three-terminal semiconductor device that amplifies signals or acts as an electronic switch. Bipolar junction and field-effect types are the building blocks of nearly all modern electronics.

A basic circuit that performs a Boolean operation such as AND, OR, NOT, NAND, or NOR on one or more binary inputs to produce an output. Gates combine to form adders, registers, and processors.

A bistable digital circuit that stores one bit of state and changes it on a clock edge or control input. Registers and counters are built from groups of flip-flops.

A combinational circuit that selects one of several inputs and routes it to a single output under the control of select lines. It is a standard building block in data routing and logic design.

A programmable integrated circuit that fetches, decodes, and executes instructions, containing an arithmetic unit, control unit, and registers. It forms the central processing unit of a computer.

The collection of machine instructions a processor can execute, defining its operations, addressing modes, and registers. It determines what software must be compiled for.

The layered arrangement of registers, cache, main memory, and secondary storage, balancing speed, size, and cost. Frequently used data is kept in faster, smaller levels close to the processor.

System software that manages hardware resources, schedules processes, allocates memory, and provides file and device services to applications through a controlled interface.

A software-defined computer that runs its own operating system on shared physical hardware through a hypervisor. It improves hardware utilisation and isolates workloads.

On-demand delivery of computing resources over a network with self-service provisioning and pay-per-use billing. Service models include infrastructure, platform, and software as a service.

An organised collection of related data managed so it can be queried, updated, and protected consistently. Relational systems store data in tables linked by keys and queried with SQL.

Structuring relational tables to reduce redundancy and avoid update anomalies by organising attributes according to dependencies. It usually proceeds through numbered normal forms.

A thin glass or plastic strand that guides light by total internal reflection, carrying data at very high rates with low loss and immunity to electrical interference.