Data Communication Fundamentals Quiz

Data Communications

• Data communication is the exchange of data between two devices through a medium, like a wire cable.
• Four fundamental characteristics that data communication depends on include:
  • Delivery: Data must be delivered to the correct destination.
  • Accuracy: Data must be delivered accurately.
  • Timeliness: Time is a factor in the delivery of data.
  • Jitter: Variation in packet arrival time can affect the quality of data, especially video.

Data Communication Systems Components

• Message: Information in any form (text, numbers, images, audio, video).
• Sender: Device initiating the data message (computer, workstation, camera).
• Receiver: Device receiving the data message (computer, television).
• Transmission medium: Physical path for data transmission (wire cable, coaxial cable, fiber optic cable).
• Protocol: Set of rules governing data communication between devices. Without protocols, two devices may be connected but not communicate.

Data Representation

• Text: Represented by bit patterns (sequences of 0s and 1s). Different coding systems exist, like Unicode (using 32 bits per symbol) and ASCII (American Standard Code for Information Interchange, with 127 characters).
• Numbers: Represented by bit patterns.
• Images: Composed of pixels (small dots). Pixel values represent the color (e.g., black = 00, white = 11).
• Audio: Recording or broadcasting of sound or music.
• Video: Recording or broadcasting of pictures or movies.

Data Flow

• Simplex: Unidirectional communication (one-way street). Only one device can transmit, the other only receives. (e.g., keywords and traditional monitors).
• Half-Duplex: Both devices can transmit and receive, but not simultaneously. (e.g., walkie-talkies, crossing road by a car).
• Full-Duplex: Both devices can transmit and receive simultaneously. (e.g., telephone network).

Network

• A network is an interconnection of devices for communication. (computers, desktops, laptops, cell phones).
• Criteria for networks include performance (measured by transit time and response time), reliability (measured by frequency of failure and recovery time), and security (protecting data from unauthorized access).

Physical Structures

• Types of connections: A network links two or more devices.
• Point-to-Point: Dedicated link between two devices; the entire link capacity is reserved for transmission. Examples include changing channels on a device from remote to TVs/satellite link.
• Multipoint: More than one device shares the same link.

LAN Topologies (Physical)

• LAN Topology: Geometric arrangement of LAN components.
• Mesh Topology: Every device has a dedicated point-to-point link to every other device. Dedicated point to point links carry traffic only between the two devices. The physical links for n nodes require n(n-1) links, or , n(n-1)/2 if both directions duplex mode is used.
• Advantages: Dedicated link guarantees data load; fault isolation/identification is easy; privacy/security possible.
• Disadvantages: The sheer bulk of wiring can exceed available space, increasing the number of I/O ports.
• Star Topology: A common point connects all devices; each device can access the media independently. Star topology is the dominant topology in modern LANs, rendering bus and ring topologies outdated.
• Advantages: Easier to manage, higher performance than bus topology, failure of one node or link does not affect the rest of the network.
• Disadvantages: If the central device fails, the entire network is down; costs increase with a switch or router as the central device.
• Bus Topology: All devices are connected to a single cable. Both ends of the cable must be terminated.
• Advantages: Easy to implement and extend (especially with temporary networks); typically less expensive.
• Disadvantages: Difficult to administer/troubleshoot; limited cable length and number of stations; a break in the cable disables the whole network; maintenance can be high in the long run; performance degrades with added computers.
• Ring Topology: Devices are connected in a closed loop. Data is transmitted unidirectionally around the ring.
• Advantages: Highly organized and efficient; eliminating the need for a network server; additional components do not affect network performance; each computer has equal access to resources. Advantages: Highly organized and efficient; eliminating the need for a network server; additional components do not affect network performance; each computer has equal access to resources.
• Disadvantages: If one workstation or port fails, the whole network suffers; the network depends entirely on the connecting cable.

Network Types

• LAN: Local Area Network. Covers a limited geographic area (less than 1km). Data flow capacity of 10 Mbps to 1 Gbps. Typical of a building or campus.
• MAN: Metropolitan Area Network. Covers a larger geographic area (1-10 km), linking local area networks, like a city.
• WAN: Wide Area Network. Network spans a large geographic area, including states, countries, or even the entire world.

Protocols and Standards

• Protocols: Set of rules and conventions for communication between entities in computer networks (computers, devices). An entity is capable of sending/receiving information.
• Key elements of a protocol: Syntax (structure/format of data); Semantics (meaning of bits); Timing (when data should be sent and how fast).
• Standards: Guidelines for manufacturers, vendors, and other service providers to ensure interconnectivity.
• Organizations that establish standards: ISO (International Organization for Standardization); ITU-T (International Telecommunication Union - Telecommunication Standards Sector); ANSI (American National Standards Institute); IEEE (Institute of Electrical and Electronics Engineers).

Network Models

• Protocol layering: An approach to structuring communication networks where layers operate in a hierarchical manner. Each layer builds upon the layer below it.
• Layered tasks: Each layer uses the services of the layers beneath to perform its assigned functions. This hierarchy makes design complexity more manageable.

OSI Model

• A standard reference model for communication between two end-users.
• Deals with connecting open systems (systems that can communicate with each other).
• Seven layers for communication: Application, Presentation, Session, Transport, Network, Data Link, and Physical.

TCP/IP Protocol Suite

• A practical layering model for the internet that emerged before the OSI model.
• Composed of five layers: Application, Transport, Network, Data Link, and Physical,
• Missing two layers compared to OSI.

Data Transfer (Connection Oriented/Connection Less)

• Connection-Oriented: Modeled after the telephone system; involves initial connection establishment, data transfer, and final disconnection. It is reliable and secure.
• Connectionless: Modeled after the postal system; each message has the complete destination information in the header and is routed independently of other messages. This type of method is faster but less secure.

Encapsulation/Decapsulation

• Encapsulation: Adding headers/trailers to data at each layer.
• Decapsulation: Removing headers/trailers at each layer in the receiving host. Routers take packets, remove headers/trailers from the top layer and add new headers/trailers.