Understanding the Internet

What is the Internet?

• The Internet is a global network of interconnected computers.
• These computers communicate using standardized protocols.
• It enables data exchange and resource sharing among billions of devices.

Hosts, End Systems

• Hosts, or end systems, are devices like computers, smartphones, and servers.
• They connect to the Internet, running apps and exchanging data.

Protocol

• It is a set of rules for data communication between network devices.
• It defines message formats, transmission methods, and error handling.

Network Edge and Network Core

• The network edge includes end systems and access networks connecting them to the Internet.
• The network core consists of high-speed routers and data links facilitating data transfer.

Access Networks: Wired and Wireless

• Access networks connect end systems to the Internet.
• Wired access includes DSL and cable, while wireless access includes Wi-Fi and cellular networks.

Network Core: Circuit Switching and Packet Switching

• The network core uses two main methods: circuit switching and packet switching.

Circuit Switching

• Establishes a dedicated communication path between hosts for the session duration.

Packet Switching

• Packet switching divides data into packets sent independently across the network.
• It allows for efficient resource utilization.

Circuit Switching: FDMA, TDMA

• It employs Frequency Division Multiple Access (FDMA).
• FDMA allocates separate frequency bands, and Time Division Multiple Access (TDMA) assigning time slots to users.

Packet Switching: Store-and-Forward Concept

• The concept involves routers storing incoming packets temporarily before forwarding them to the next node.
• This ensures integrity during transmission.

Packet Switching: Statistical Multiplexing

• Statistical multiplexing dynamically allocates network resources based on demand.
• This optimizes bandwidth by sharing it among multiple data streams.

Packet Switching vs. Circuit Switching: Number of Users Supported; Probability Calculations

• Packet switching supports more users than circuit switching due to dynamic resource allocation.
• Probability calculations help assess metrics like packet loss and delay.

The Internet: A Network of Networks (Internetwork)

• The Internet is an internetwork, connecting various smaller networks into a vast, global system.
• It allows seamless data exchange across infrastructures.

Delay, Loss, Throughput in Packet-Switched Networks

• "Delay" refers to the time taken for data to traverse the network.
• "Loss" refers to packets that fail to reach their destination.
• "Throughput" refers to the rate of successful data delivery over a network link.

Types of Delay: Processing, Queueing, Transmission, Propagation

• Processing Delay happens when examining and processing packet headers.
• Queueing Delay occurs while packets spend time waiting in queues.
• Transmission Delay occurs when pushing packet bits onto the link.
• Propagation Delay refers to the time for signals to travel through the medium.

Average Queueing Delay vs. Traffic Intensity

• Average queueing delay increases with higher traffic intensity.
• The ratio of arrival rate to service rate leads to congestion and longer delays.

Throughput in Computer Networks

• Throughput measures the rate at which data is successfully transmitted over a network.
• It is influenced by bandwidth, network congestion, and protocol efficiency.

Protocol Layers

• Network communication is structured into layers.
• Each layer provides services, simplifying design and troubleshooting with modular functionality.

Layering as an Architectural Principle, Services Provided by Each Layer, Encapsulation/Decapsulation

• Layering organizes network functions into hierarchical layers.
• Each layer offers services to the layer above and utilizes services from the layer below.
• Data encapsulation adds headers as data descends layers.
• Decapsulation removes headers as data ascends.

Layers in OSI, TCP/IP Models

• OSI model has seven layers: Physical, Data Link, Network, Transport, Session, Presentation, Application.
• The TCP/IP model comprises four layers: Link, Internet, Transport, Application.

Principles of Network Applications

• Network applications enable communication over networks, following client-server or P2P architectures.
• Utilizes protocols like HTTP, SMTP, or FTP.

Possible Architectures of Applications: Client-Server vs. P2P Architectures

• Client-server architecture has centralized servers serving multiple clients.
• Peer-to-peer (P2P) architecture allows direct communication between peers.

Client vs. Server

• Clients request services or resources.
• Servers provide services, handling multiple client requests simultaneously.

Communicating Processes

• Processes communicate by exchanging messages over the network.

Addressing a Process: IP Address and Port Number

• Processes are identified using IP addresses.
• Port numbers ensure accurate data delivery.

Network Application Requirements: Data Integrity, Throughput, Timing

• Data Integrity requires accurate and unaltered data delivery.
• Throughput requires sufficient data transfer rates.
• Timing requires constraints.

Transport Services: Reliable vs. Unreliable Data Transfer

• Reliable data transfer ensures error-free delivery (e.g., TCP).
• Unreliable data transfer does not guarantee error-free delivery (e.g., UDP).

TCP vs. UDP Services

• TCP (Transmission Control Protocol) provides reliable transfer, ensuring data is delivered without errors.
• UDP (User Datagram Protocol) offers unreliable service.
• UDP is faster but does not guarantee delivery.

Web and HTTP: Base HTML File and Referenced Objects

• An HTML file can include objects such as images, videos, and scripts.
• Referenced objects use tags which the browser loads when rendering.

HTTP Request and Response Concepts

• HTTP (Hypertext Transfer Protocol) is a stateless protocol for transferring data.
• When a client makes a request the server responds with requested data.

Persistent and Non-Persistent HTTP

• Persistent HTTP maintains the connection between client and server open for multiple requests and response.
• Non-persistent HTTP opens a new connection for each request and response.

HTTP Using TCP as the Transport Later

• HTTP typically uses TCP (Transmission Control Protocol) for communication.
• TCP ensures data packets are reliably delivered in the correct order.

HTTP Request/Response Messages

• HTTP messages consist of request and response messages.
• A typical GET request asks the server to send a resource.
• The server returns the resource in the response message.

HTTP Cookies

• Cookies are small pieces of data stored on the client's machine.
• Cookies are used for session management, personalization, and tracking user behavior.

Web Caching and Performance Improvement

• Caching stores frequently accessed resources closer to the client.
• This improves performance and reduces latency.

Conditional GET

• Conditional GET requests allows the client to ask the server for a resource change.
• This achieved using If-Modified-Since headers, avoiding unnecessary data transfers.

Head-of-Line Blocking

• HOL blocking occurs when a packet at the front of a queue delays all subsequent packets.

Email Components and Protocols: SMTP, POP3, and IMAP

• SMTP (Simple Mail Transfer Protocol) is the protocol used for sending emails between servers.
• POP3 (Post Office Protocol version 3) used by email clients to retrieve emails from a server.
• IMAP (Internet Message Access Protocol) allows email clients to access and manage emails on a mail server.

DNS (Domain Name System)

• DNS is a distributed system that translates human-readable domain names into IP addresses.
• DNS has root servers, top-level domains, and authoritative name servers.

Iterative vs. Recursive Queries

• Interative Queries: the DNS resolver queries other DNS servers directly and either resolves the query.
• Recursive Queries: The DNS resolver takes responsibility querying other DNS servers client until it finds the answer.

DNS Resource Records and Messages

• DNS uses resource records (RRs) for domain names.
• They are included in DNS messages to answer queries.

P2P Applications

• P2P File Distribution vs. Client-Server
• P2P file distribution allows peers to share files directly without a server.systems rely on a central server.
• P2P systems can scale better require efficient management and protocols.

BitTorrent

• BitTorrent is a P2P protocol for sharing large files.
• Divides into smaller pieces to distribute peers upload and download.

Video Streaming and Content Distribution Networks (CDN)

• CDNs are the networks serve content close to the user reducing latency, and improves video streaming.

DASH(Dynamic Adaptive Streaming over HTTP)

• DASH is a protocol streaming video HTTP adapting the video based the network for playback when bandwidth fluctuates.

TCP andUDP Socket Programming

• TCP socket creates a server/client communication reliable channel to a specific IP and port.
• UDP socket communication is connectionless and unreliable protocols like real-time streaming or gaming.

Transport-Layer Services

• The transport layer provides end-to-end for application reliable data control, and multiplexing.
• The transport layer is between the application and network layer.

Logical End-to End connection Between Hosts

• End-to-end connection between the Hosts: Its Host to host on the network layer.
• End to end connection between processors: Enables communication IP addresses & Port numbers.
• The transport Layer delivers between even Network Player only to host communication.

Multiplexing and Demultiplexing in UDP vs.TCP

• Refers to combining multiple streams from different streams for transmission.
• Refers to reverse process Transport players direct receive Data by destination.
• Used in port Number for the transport players handles multiplexing and demultiplexing.
• The TCP is connection oriented.
• Source in designation IP addresses for number identifiers for data to transport on correct costs.
• The transport layer uses port Number to see just which is running on a host.
• Every IP address source to designated to make communication point.

Advantages and Disadvantages of UDP

• It is a connection list not guarantee order of package.
• Faster like it will be making real-time communication.
• Disadvantages: Unreliable the packet is lost, and no flow control.
• The UDP has full fields; source , designation port, data check some of air checking and for air-checking UDP is for iPV4, and required for iPV6.

TCP: Transmission Control Protocol services

• Reliable: TCP guarantees the delivery of data .
• UDP: Do not provide reliability .

Flow control

• Flow control to control too much fast data overwhelms.

Communication Orientated in TCP

• TCP it is connection Orientated to make sure connection is established.

TCP header structure

• Tcp headers larger structure for reliable communication.

Congestion Control in TCP

• TCP has congestion to make network more reliable.

TCP Connection management

• TCPs connection management ensures reliable communication .

Comparison of TCP and UDP

• TCP (Reliable , connection-oriented) guarantees to deliver data.
• UDB is faster to minimize but does not delivery and suitable in real time communication,