Computer Networks EssentialsCheatsheet, MCQs & Interview Points

Module 1 – Networking Fundamentals

Networking Fundamentals

• A computer network is a collection of connected computers, servers, devices, and communication links used to share data and resources.
• A network protocol is a set of rules that defines how devices communicate.
• Communication between devices requires agreement about:
• Data format.
• Addressing.
• Transmission speed.
• Error handling.
• Delivery method.
• An IP address identifies a device or network interface logically.
• An IP address performs two main functions:
• Identifying the host or interface.
• Identifying its location in the network.
• A MAC address is a physical or hardware address assigned to a network interface.
• A packet is a unit of data transmitted at the network layer.
• A frame is a unit of data transmitted at the data-link layer.
• A segment is generally the transport-layer data unit used by TCP.
• A datagram commonly refers to a UDP transport-layer unit or an IP packet.
• Bandwidth is the maximum data-transfer capacity of a link.
• Bandwidth is usually measured in bits per second, such as Mbps or Gbps.
• Latency is the time delay between sending data and receiving the corresponding response.
• Throughput is the actual amount of data successfully transferred per unit of time.
• Packet loss occurs when transmitted packets fail to reach their destination.
• Jitter is the variation in packet-arrival time.
• Jitter is especially harmful to voice calls, video calls, and live streaming.
• Network congestion occurs when traffic exceeds the capacity of network links or devices.
• Quality of Service (QoS) manages and prioritizes traffic according to application requirements.
• LAN stands for Local Area Network.
• A LAN covers a small geographical area such as a home, office, building, or campus.
• WAN stands for Wide Area Network.
• A WAN covers large geographical areas and connects multiple LANs.
• MAN stands for Metropolitan Area Network and generally covers a city or metropolitan region.
• PAN stands for Personal Area Network and connects devices around an individual.
• The Internet is a global interconnection of networks.
• An intranet is a private network used within an organization.
• An extranet provides selected private-network resources to authorized external users.
• A protocol stack is a group of layered protocols that work together.
• The Internet primarily uses the TCP/IP protocol suite.

Network Topologies

• Network topology describes the physical or logical arrangement of network devices and connections.
• In a bus topology, all devices share a common communication medium.
• Bus topology is simple and inexpensive for small networks.
• A major disadvantage of bus topology is that failure of the main cable can affect the entire network.
• In a star topology, all devices connect to a central hub or switch.
• Star topology makes it easy to add, remove, or troubleshoot individual devices.
• Failure of one end-device cable normally affects only that device in a star topology.
• Failure of the central switch or hub can affect the entire star network.
• In a ring topology, each device is connected to two neighboring devices.
• Data travels around the ring until it reaches the destination.
• Failure of one device or link may disrupt a traditional ring network.
• In a mesh topology, devices have multiple interconnections.
• A full mesh connects every device to every other device.
• A partial mesh connects only selected devices.
• Mesh topology provides high redundancy and fault tolerance.
• Its disadvantages include high cabling cost and configuration complexity.
• A tree topology combines hierarchical and star-like structures.
• A hybrid topology combines two or more different topologies.
• A point-to-point topology provides a direct connection between two devices.
• A wireless mesh topology allows nodes to forward data for other nodes.

OSI Model

The OSI model contains seven layers. Rember the order from top to bottom: Application, Presentation, Session, Transport, Network, Data Link, Physical

A common mnemonic is

All People Seem To Need Data Processing

• The OSI model is a conceptual seven-layer framework developed by ISO.
• The OSI model standardizes communication functions.
• The Physical layer is Layer 1.
• It transmits raw bits over a physical medium.
• It defines:
• Voltage levels.
• Connectors.
• Cables.
• Radio signals.
• Data rates.
• Modulation.
• The Data Link layer is Layer 2.
• It provides node-to-node delivery.
• Major Data Link responsibilities include:
• Framing.
• MAC addressing.
• Error detection.
• Media access control.
• Link-level flow control.
• The Data Link layer has two important sublayers:
• Logical Link Control, or LLC.
• Media Access Control, or MAC.
• The Network layer is Layer 3.
• It provides logical addressing and routing.
• Routers operate primarily at the Network layer.
• IP is a Network-layer protocol.
• The Transport layer is Layer 4.
• It provides end-to-end communication between processes.
• Major Transport-layer functions include:
• Segmentation.
• Reassembly.
• Reliability.
• Flow control.
• Error recovery.
• Multiplexing.
• Demultiplexing.
• TCP and UDP operate at the Transport layer.
• The Session layer is Layer 5.
• It establishes, manages, synchronizes, and terminates communication sessions.
• The Presentation layer is Layer 6.
• It handles:
• Data translation.
• Encryption and decryption.
• Compression and decompression.
• Character-set conversion.
• The Application layer is Layer 7.
• It provides network services directly to applications and users.
• Examples include HTTP, FTP, SMTP, DNS, and SNMP.
• Data is called a bit at the Physical layer.
• Data is called a frame at the Data Link layer.
• Data is called a packet at the Network layer.
• Data is called a segment for TCP at the Transport layer.