Networking Essentials: LAN, WAN, and Data Transmission

Posted on Apr 5, 2025 in Computer Engineering

Networking Fundamentals

LAN vs. WAN

LAN (Local Area Network): Local networking, typically found in homes, businesses, or schools, and geographically limited. It is owned by an independent organization.

WAN (Wide Area Network): Covers a large geographical area and is typically used by service providers.

Network Infrastructure

Hardware: Routers, switches, NICs (Network Interface Cards)

Software: Network operating/management systems, operating systems, firewalls, network security applications

Services: T-1 Line, DSL, satellite, protocols, IP addressing

Key Applications (Client-Server): Email, web, IM (Instant Messaging), remote login, P2P file sharing, MMO (Massively Multiplayer Online games), video streaming, VOIP (Voice over IP)

Data Transmission Methods

Serial: Used for external connections. Only one wire carries data, and each bit is transmitted one at a time.

Parallel: Used in processors. Employs a parallel bus to transfer data. For example, the PCI bus uses 64 wires (8 bytes of data at once).

Communication Modes

Simplex: One-way communication only (sender -> receiver). Cannot send back.

Half-Duplex: Communication in both directions, but not simultaneously. The channel must be clear before transmitting.

Full-Duplex: Communication in both directions simultaneously, using two parallel channels (e.g., cell phone).

Data Rate, Throughput, and Bandwidth

Data Rate: The amount of data transmitted in a specific time period (often quoted by ISPs).

Throughput: The actual amount of data transmitted successfully.

Bandwidth: The bit rate of available capacity, expressed in multiples of bits per second.

Data rate is the rate at which bits are placed on the link, throughput means how many bytes/second of useful data can be transferred through the link.

Analog Bandwidth: The difference between the highest and lowest frequency points on a wave of transmission.

Digital Bandwidth: Essentially the same as data rate.

Packet Switching vs. Circuit Switching

Packet Switching

Pros:

  1. Network efficiency (circuit switching needs a dedicated allotment of time; other devices can’t use the network until the first two finish).
  2. Error detection.
  3. Cost-effective (scalability).

Cons:

  1. No dedicated path.
  2. Packets can get lost.
  3. Every hop incurs delay.

Circuit Switching

Pros:

  1. Guaranteed bandwidth (the route is exclusive until the session terminates).
  2. Low per-packet overhead (forwarding is based on time slot; no IP (and TCP/UDP) header is needed on each packet).

Cons:

  1. Keeps resources busy; no multiplexing can occur.
  2. Takes time to set up a dedicated circuit; delay is upfront before transmission.

Modulation

Modulation is the process of varying one or more properties of a periodic waveform (carrier signal) with a modulating signal that contains the information to be transmitted. A carrier signal is a waveform that is modulated with an input signal for the purpose of conveying information. It is usually of a much higher frequency than the input signal. The purpose is to either transmit information through space as an electromagnetic wave or allow several carriers at different frequencies to share a common physical medium by frequency division multiplexing.

Needed for: multiplexing, allowing several analog signals to be processed by one analog-to-digital (ADC) converter, and in telecom, several phone calls on one wire.

Multiplexing Techniques

Frequency Division Multiplexing

A technique by which the total bandwidth available in a medium is divided into a series of non-overlapping frequency sub-bands to carry each signal separately.

Time Division Multiplexing

Uses synchronized switches at each end of the transmission so each signal appears on the line only for a fraction of time in an alternating pattern.

Wave Division Multiplexing

Multiplexes a number of optical carrier signals onto a single optical fiber by using different wavelengths of laser light.