Data Communication Systems vs. Computer Networks

Data Communication System Overview

• Data communication systems transmit data over communication lines (e.g., telephone lines, cables).
• Computer networks connect multiple computers and resources using communication equipment.
• Key components for successful communication include: sending device, communication device (e.g., modem), communication channel, communication device (e.g., modem for receiving), and receiving device.

Types of Networks

• LAN (Local Area Network): connects devices within a limited geographical area (e.g., university).
• MAN (Metropolitan Area Network): covers an entire city.
• WAN (Wide Area Network): connects devices over vast distances (e.g., between countries).
• PAN (Personal Area Network): links devices close to a user (within a few meters).

Data Flow Modes

• Simplex: unidirectional communication (e.g., keyboard to monitor).
• Half-duplex: both devices can transmit and receive, but not simultaneously (e.g., walkie-talkies).
• Full-duplex: both devices can transmit and receive simultaneously (e.g., telephone networks).

Network Topologies

• Star Topology: all devices connect to a central hub or switch (server).

  • Advantages: robust, easy to install, less expensive
  • Disadvantages: dependent on the central hub/switch, potential for data exchange issues

• Ring Topology: devices arranged in a ring, with each device connected to two others.

  • Advantages: simple, dedicated connections
  • Disadvantages: single point of failure

• Bus Topology: devices connected to a single cable (backbone).

  • Advantages: simple, easy to install, less expensive
  • Disadvantages: single point of failure, entire system stops with a problem

• Mesh Topology: every device has a direct connection to every other device.

  • Advantages: flexible, robust (less dependent on nodes being used)
  • Disadvantages: costly, complex, very large scale of cabling required

OSI Model

• An open system that allows different systems to communicate.
• Seven separate layers: Application, Presentation, Session, Transport, Network, Data Link, Physical. Each layer handles different aspects of the communication process.
• Application layer: handles network applications (e.g., web browsers, email).
• Physical layer: physical characteristics of interfaces and medium (guided or unguided).

OSI Model Layer Functions

• Physical Layer: transmission medium, physical characteristics of interfaces, data representation.
• Data Link Layer: framing, physical addressing, error control, flow control, access control.
• Network Layer: logical addressing, routing.
• Transport Layer: process-to-process delivery, segmentation and reassembly, connection control, flow control, error control.
• Session Layer: establishes, maintains, and synchronizes communication between systems.
• Presentation Layer: handles data format conversion, encryption/decryption, compression.
• Application Layer: provides network services for applications.

TCP/IP Model

• Layered Internet protocol stack, supporting network applications.
• Application layer protocols (e.g., HTTP, SMTP, IMAP, DNS).
• Transport layer protocols (e.g., TCP, UDP).
• Network layer protocols (e.g., IP, routing protocols).

Addressing Schemes

• Physical (MAC) address: a unique identifier for each network interface.
• Logical (IP) address: a unique identifier for each host on a network.
• Port address: used to label processes on a computer for distinguishing which process a data packet should be sent to.

Communication Media

• Guided media: signals propagate in solid media (e.g., copper wire, fiber optic cable, coax).
• Unguided media: signals propagate freely in the atmosphere or outer space (e.g., radio waves, microwaves, infrared).

Communication Devices

• Modem: converts digital to analog signals.
• Hub: broadcasts data to all connected devices.
• Bridge: connects two similar LANs, forwards data based on MAC addresses.
• Switch: forwards data only to the intended recipient (based on MAC address).
• Router: forwards data packets based on IP addresses (connects different networks).
• Wireless Access Point: connects devices wirelessly to a network.

Link Layer

• Responsibilities: moving datagrams from one node to another connected node on a link.
• Frame encapsulates the datagram.
• Two types of link channels: broadcast and point-to-point.

Error Detection and Correction

• Parity checks: simple method to detect odd numbers of bit errors.
• Cyclic Redundancy Check (CRC): more sophisticated method to detect errors (and in some cases correct errors).

Multiple Access Links and Protocols

• Channel partitioning (e.g., TDM, FDM, CDMA): divides the channel into smaller time slots or frequency bands.
• Random access (e.g., ALOHA, CSMA/CD): nodes transmit when the channel is free.
• Taking turns (e.g., polling, token passing): nodes take turns transmitting in a defined sequence.

Switched Local Area Networks (LANs)

• Switches: forward data frames based on MAC addresses.
• Link-Layer Addressing: using MAC addresses to guide forwarding.
• ARP (Address Resolution Protocol): translates IP addresses to MAC addresses.
• VLAN (Virtual LAN): create different logical networks over a single physical network, segmenting traffic efficiently to support organizational needs.

This quiz explores the fundamental differences and relationships between data communication systems and computer networks. Each question addresses key concepts, functionalities, and technologies essential for understanding how these systems operate in tandem. Test your knowledge on this significant aspect of computer science.