Network Technologies and the Internet Fundamentals of the Internet

Introduction to Network Technologies

• Conceptual Overview: The study focus is on "Connecting people, places and things," covering the technologies underpinning networks, including the internet, wireless communication, the Internet of Things (IoT), and online communication tools.

• Communication as a Human Aspect: Communication is fundamental to being human. Our cognitive processes are specifically tuned for understanding others.     * Face-to-face communication is supported by evolution.     * Technology-mediated communication over distances is made possible by human ingenuity.

• The Internet as a Infrastructure: The internet serves as the backbone for global communication. The term "internet" is derived from the fact that it is a collection of many joined-together networks.

• Key Players in Communication:     * Broadband suppliers.     * Internet Service Providers (ISPs).     * Mobile phone operators.     * Wi-Fi access points.     * Local Area Networks (LAN) at workplaces.

• Network Representations: Various networks, such as home networks, campus networks, and branch office networks, can be interconnected via the internet.

• Equipment and Connectivity Parameters:     * Wi-Fi: Used for connecting laptops and iPads to a home hub.     * Ethernet: Used for physical connections, such as a printer plugged into a hub.     * Gateway Router: A router that acts as a bridge or gateway between two different networks (e.g., between a home network and an ISP).     * Local Area Network (LAN): A collection of networking equipment joined together in a localized area.     * Wide Area Network (WAN): Created when network segments (like a university and a regional office) are connected via privately leased links rather than the public internet.

• Client–Server Model:     * Definition: A relationship between a user's computer (client) and various network devices (servers) that provide services.     * Functional Definition: This relationship allows network devices to be defined by their function (what they do) rather than their physical appearance.

Network Layered Architecture

• Definition: The conceptual structuring of communication processes into layers is known as layered architecture.

• Features of Layered Architecture:     * Service Hierarchy: Each layer provides a service to the layer directly above it.     * Abstraction: A higher layer utilizes the services of the lower layer without needing to understand the internal operations of that lower layer.     * Peer Communication: The peers (endpoints) at each end of a communication link in any given layer must be able to understand each other; this requirement applies across all layers.

Data Transmission Principles

• Definition of Data: In networking and computing, "data" refers to the information being transmitted over a pathway to allow services (like email) to operate end-to-end.

• Digital Transmission: Modern systems transmit data as a sequence of $1s$ and $0s$. These bits are represented by physical quantities.

• Methods of Representation:     * Optical Fiber: Uses laser light.     * Ethernet/Wires: Uses electricity along a pair of wires.     * Wireless: Uses radio waves and microwave radiation through the air.

• On–Off Keying: In optical fiber, bits are sent by switching light on for a $1$ and off for a $0$. This is compared to signaling with a torch (flashlight).

• Regeneration: The process of detecting an incoming signal (similar to seeing a distant beacon) and sending out a new, fresh signal for the next stage of the journey. This is literally "re-generating" the signal.

• Attenuation: A form of loss that reduces the strength of a signal as it travels away from its source.     * Attenuation gradually distorts the data signal.     * Eventually, the signal can become unreadable by the receiver.

Electromagnetic Radiation Principles

• Wave Nature: Radio waves, microwaves, and light are all forms of electromagnetic waves.

• Properties of sine waves:     * Decay: As a wave moves away from its source, its energy is dissipated, causing the magnitude of the peaks and troughs to decrease. This is referred to as the wave "decaying."     * Wavelength ($\lambda$): The physical distance between successive peaks of the wave.     * Period ($T$): The duration of time it takes to complete one full cycle of the wave.     * Frequency ($f$): The number of cycles completed in a single second.

• Frequency Units and Scaling:     * Hertz ($Hz$): $1$ cycle per second.     * Kilohertz ($kHz$): $1000$ cycles per second.     * Megahertz ($MHz$): $1,000,000$ cycles per second.     * Gigahertz ($GHz$): $1,000,000,000$ cycles per second.     * Inverse Relationship: A shorter period results in more cycles per second, meaning a higher frequency.

• The Electromagnetic Spectrum: This is the full range of electromagnetic radiation organized by frequency range.     * Groups include radio waves, microwaves, and infrared.     * Microwaves are situated between radio waves and infrared radiation.

• Logarithmic Scales: The frequency axis in spectrum diagrams is often logarithmic. Each equal-length step corresponds to multiplying by a base (e.g., $10^2, 10^3, 10^4$) rather than adding equal amounts as in a linear scale.

• Bandwidth: This term has dual meanings:     1. The range of frequencies in the spectrum.     2. Data transmission rates (communication capacity), measured in bits per second ($bps$).

Comparative Media and Strategic Application

• Wireless vs. Wired:     * Cell phones require microwave frequencies as wires/fiber are impractical.     * Infrared: Used for line-of-sight wireless communication, such as TV remote controls.

• Signal Power: Measured in watts ($W$). Signal strength decreases the further it travels.

• Exponential Decay in Attenuation: Attenuation in metallic wires and optical fibers follows a "negative exponential" pattern. While exponential growth increases by the same factor, decay decreases by the same factor over fixed distances.

• Attenuation Example Table (assuming power drops by a factor of $10$ every $500\,m$ starting at $0.2\,W$):     * Distance $0\,m$: $0.2\,W$     * Distance $500\,m$: $0.02\,W$ ($2 \times 10^{-2}\,W$)     * Distance $1000\,m$: $0.002\,W$ ($2 \times 10^{-3}\,W$)     * Distance $1500\,m$: $0.0002\,W$ ($2 \times 10^{-4}\,W$)

• Media Comparison: Different media can be compared by measuring the distance over which signal power decreases by a fixed factor, such as a factor of $10$.

The Architecture of the Internet

• Success Factors:     1. Packet Technology: A flexible mechanism for carrying diverse services over one network.     2. Internet Protocol (IP) Addresses: A universal addressing scheme.     3. Protocols: Standards that allow new services to be integrated into existing architecture.

• Network Components:     * End Devices: Telephones, computers.     * Nodes: Points where multiple links join together. This is where end devices connect and where switches/routers are placed.     * Links: Physical cables or wireless connections.

Routing and Switching Principles

• Mechanisms:     * Routing: Finding the correct path to a destination.     * Switching: Joining links together to send data; this process is called Forwarding.

• Switching Methodologies:     * Circuit Switching: Used by telephone networks. Data follows a single end-to-end path through intermediate nodes. Once established, the path cannot carry data from other sources until the call is terminated.     * Packet Switching: Used by computer networks. Data is not sent over a continuous path. Information (email, video, voice) is broken into small pieces called segments.

• Data Packets:     * Segments are carried as a payload within a packet.     * The Header contains destination and source addresses, plus data type info.

• Address Types and Hardware:     * IP Addresses: $32$-bit addresses (IPv4) written in dotted decimal (e.g., $192.100.50.20$). Handled by Routers, common on the internet.     * Ethernet Addresses: $48$-bit addresses written in hexadecimal. Handled by Switches, common in LANs.

Internet History and Governance

• ARPANET: The internet originated from a $1969$ research project by the US government’s Advanced Research Project Agency (ARPA). Initially, only $4$ locations were linked. By $1980$, $15$ universities were connected.

• Standardization: The internet is not owned by a single organization. It functions because all interconnected networks conform to common standards to move data.

• Gateways: These ensure data from an individual network is compatible with the external internet.

• Backbones: These are the links that join different segments of networks (e.g., joining LANs to create a WAN).

Internet Protocols (TCP/IP)

• Segmentation and IP Delivery: Messages are broken into segments. Each segment gets its own destination IP header to form an IP packet.

• Encapsulation: At each gateway, another header (and sometimes a trailer) is added to make the packet suitable for the passing network. This extra data is removed when the packet exits that specific network.

• TCP/IP Family:     * IP (Internet Protocol): Responsible for getting packets across the internet (routing).     * TCP (Transmission Control Protocol): Concerned with the reliability and session management at sending/receiving devices.

• IPv4 Structure:     * Consists of $4$ bytes ($32$ bits).     * Each byte ranges from $0$ to $255$ ($2^8 = 256$ combinations).     * Example binary conversion for address $212.44.110.172$:         * Binary: $11010100.00101100.01101110.10101100$     * Total addresses: $2^{32} = 4,294,967,296$.

• IPv6 Structure:     * Introduced to handle increased demand.     * $16$ bytes ($128$ bits).     * Total addresses: $2^{128} = 3.4 \times 10^{38}$.

TCP Connectivity and Session Management

• Virtual Circuit: A connection that enables end devices to appear to communicate directly despite the complex physical routing between them.

• Three-Way Handshake: The process to establish a connection:     1. Computer requests connection to a server.     2. Server sends back an acceptance message.     3. Computer acknowledges the acceptance.

• Reliability through Acknowledgments: The receiver sends an acknowledgment ($ACK$) for each received packet. If the server does not receive an $ACK$, it resends the packet. This handles the problem of missing packets.

• Closing Connections: Once data transfer (e.g., loading a web page) is finished, both computers agree to close the virtual circuit.

The Four-Layer Protocol Stack

• Application Layer: Deals with specific application needs (e.g., HTTP for web browsing).

• Transport Layer: Manages end-to-end communication sessions (TCP). Uses Port Numbers to identify specific communication sessions or transactions.

• Internet Layer: Handles addressing and routing packets across different networks (IP).

• Network Access Layer: Manages the transmission of data over the physical medium (e.g., Ethernet).

• Encapsulation Workflow Example:     1. Application Layer: User data (e.g., a Wikipedia request) gets an HTTP header.     2. Transport Layer: The HTTP packet is encapsulated with a TCP header, containing a Port Number.     3. Internet Layer: An IP header containing the destination IP address is added.     4. Network Access Layer: An Ethernet header containing the gateway router’s address is added.

Questions & Discussion

• Q: What information in the header of an IP packet is used to direct the packet to its destination?     * A: Each packet header contains the destination IP address. The router uses this address to choose between different links to reach the destination.

• Q: Why is the IP address so important when trying to find a destination computer?     * A: Every computer on the internet can be uniquely identified by its IP address. Routers use these unique addresses to forward packets correctly.

• Q: Given that an IPv4 address is a sequence of four one-byte numbers, how many different IP addresses can there be?     * A: There are $32$ bits ($4 \times 8$). The total combinations is $2^{32}$, which is $4,294,967,296$.

• Q: How many different IP addresses does a 16-byte IPv6 address allow?     * A: $16\,bytes \times 8\,bits = 128\,bits$. Total is $2^{128}$, which is approximately $3.4 \times 10^{38}$.

• Q: Identify if the following applies to TCP or IP:     1. Sets up connections to send data: TCP     2. Operates in the internet layer: IP     3. Addresses packets and routes them: IP     4. Operates in the transport layer: TCP     5. Deals with missing packets: TCP

• Q: Match the sentence to the appropriate layer of the protocol stack:     1. Used to route packets across the internet: Internet layer     2. Used to route packets within the local network: Network layer (Network Access)     3. Delivers all the packets associated with a session: Transport layer     4. Looks after the application: Application layer

Witch broplem!why not answer the questions 😔