eitf45 -L1- introduction.pdf

# Evolution of computer communications and the internet This topic outlines the historical development of telecommunications, tracing the path from early electrical communication methods to the establishment of the modern internet [3](#page=3) [7](#page=7) [8](#page=8) [9](#page=9). ### 1.1 Early telecommunications The foundation of modern computer communications can be traced back to the 19th century with the advent of the electrical telegraph, which saw its initial deployment at the beginning of the century and later spanned across the Atlantic. Following this, telephony was patented in 1876, and the demand for this technology increased rapidly [3](#page=3). ### 1.2 The concept of circuit switching Circuit switching is a communication method where all data exchanged between a sender and receiver travels along a single, predefined path. This established a dedicated connection for the duration of the communication session [4](#page=4). ### 1.3 The emergence of packet switching The 1960s marked a significant shift with the first publications suggesting packet switching as an alternative to circuit switching. This innovative approach proposed breaking data into smaller units called packets [5](#page=5). ### 1.4 The ARPANET project The Advanced Research Projects Agency Network, or ARPANET, was conceptualized to address the need for a unified communication system. Robert Taylor of ARPA articulated the vision for a network where a single terminal could connect to any system, using a common language for communication. He highlighted the inefficiency of having multiple terminals and login procedures for different systems. This idea directly led to the development of the ARPANET [6](#page=6). The ARPANET officially began in 1969. It was the first packet-switched network and initially connected four university sites: UCLA (University of California, Los Angeles), SRI (Stanford Research Institute), UCSB (University of California, Santa Barbara), and the University of Utah [7](#page=7). ### 1.5 Internet evolution and standardization The growth of the internet necessitated common languages, or protocols, for terminals and switches to communicate effectively. It also required a system for identification, leading to the development of addresses. To facilitate the scaling up of these interconnected networks, Robert E. Kahn and Vincent Cerf developed an "internetwork protocol" in 1973. This protocol was later standardized as TCP/IP (Transmission Control Protocol/Internet Protocol) in 1982 [8](#page=8). ### 1.6 The internet today Currently, the internet has evolved into a converged network supporting a wide range of services, including data communication, IPTV, Video on Demand, broadcast radio, and telephony, among others. From a user's perspective, the internet provides access to these diverse services while from an engineer's view, it represents a complex infrastructure enabling these connections [10](#page=10) [11](#page=11) [9](#page=9). --- # Network models and layered architecture Network models, particularly the Internet Protocol suite (TCP/IP model), are essential for organizing digital communications through a layered architecture. This approach is rooted in the "divide and conquer" principle, aiming to simplify the complex process of sending data across networks [13](#page=13) [14](#page=14). ### 2.1 Benefits of a layered architecture A layered architecture offers several significant advantages for managing the complexities of digital communications [14](#page=14): * **Specialization:** Each layer is responsible for a specific set of functions and services. This allows for specialized development and optimization within each layer, rather than trying to handle all aspects of communication in a monolithic design [14](#page=14). * **Simplification:** By breaking down the overall communication process into smaller, manageable layers, the design and implementation become significantly simpler. Developers can focus on one layer at a time without needing to understand the intricate details of all other layers [14](#page=14). * **Managing complexity:** Digital communication involves many distinct tasks, from handling physical signals to running user applications. A layered architecture effectively segments these tasks, making the entire system easier to understand, build, and maintain [14](#page=14) [15](#page=15). ### 2.2 Components of a layered architecture A typical layered architecture for digital communications can be conceptually understood by considering the journey of data: * **Digital communications:** This encompasses the entire process, starting from raw electrical signals and progressing through the representation of data as bits, and finally to the formation of packets for transmission [15](#page=15). * **Using the physical infrastructure (Network access):** This layer deals with the physical transmission of data over the network medium. It defines how data is encoded into signals and transmitted through devices like cables or wireless interfaces [15](#page=15). * **Finding your way (Addressing, routing):** This layer is responsible for ensuring data reaches its intended destination. It involves mechanisms for identifying devices (addressing) and determining the best paths for data to travel across the network (routing) [15](#page=15). * **Making use of it all (Applications):** This is the topmost layer, where user-facing applications interact with the network. Examples include web browsers, email clients, and file transfer programs [15](#page=15). The network model provides a framework for understanding these different functional layers and how they interact to enable communication [26](#page=26). > **Tip:** When studying network models, visualize data flowing down through the layers on the sending side and up through the layers on the receiving side. Each layer adds or removes its own header information as the data passes through. --- # Application layer paradigms and the World Wide Web This section explores fundamental application layer paradigms and delves into the architecture and components of the World Wide Web. ### 3.1 Application layer paradigms The application layer in computer networking provides services directly to user applications. Two prominent paradigms exist for structuring these services: client-server and peer-to-peer [16](#page=16). #### 3.1.1 Client-server paradigm In the client-server paradigm, dedicated servers provide resources or services to multiple clients. Clients initiate requests, and servers respond to them. This model is widely used for applications like web browsing, email, and file sharing [17](#page=17). Performance challenges in the client-server model include: * The need for standardized protocols like HTTP to manage communication [18](#page=18). * Heavy traffic loads that can overload servers [18](#page=18). * Delays caused by congested access networks [18](#page=18). * The risk of a single point of failure, where the server's unavailability disrupts service for all clients [18](#page=18). #### 3.1.2 Peer-to-peer paradigm In contrast, the peer-to-peer (P2P) paradigm allows each node in a network to act as both a client and a server. Participants can share resources and services directly with each other without relying on a central server. P2P networks can offer increased scalability and robustness, as the failure of one node does not necessarily impact the entire network [19](#page=19). ### 3.2 The World Wide Web (WWW) The World Wide Web (WWW) was initially proposed by Tim Berners-Lee in 1989 at CERN with the goal of enabling researchers at different locations to access each other's findings. The commercialization of the WWW began in 1993 [20](#page=20). #### 3.2.1 Components of the WWW The WWW is comprised of several key components [21](#page=21): * **Web documents (pages):** These are the content accessed via the web. * **Static documents:** Primarily created using HyperText Markup Language (HTML) [21](#page=21). * **Dynamic documents:** Generated by script languages such as PHP, ASP, JSP, and CGI [21](#page=21). * **Universal Resource Locator (URL):** A standardized method for identifying the location of web documents [21](#page=21). * **HyperText Transfer Protocol (HTTP):** The protocol used to access documents from a web server [21](#page=21). #### 3.2.2 Universal Resource Locator (URL) A web document is identified by four components: protocol, host, port, and path. The general format of a URL is [22](#page=22): `protocol://host:port/path` The standard HTTP port is 80, which can often be omitted. An example URL is `http://www.eit.lth.se/course/etsf15` [22](#page=22). #### 3.2.3 HyperText Transfer Protocol (HTTP) HTTP is a text-based protocol used for communication on the web. It facilitates two primary types of messages: requests and responses. HTTP establishes and utilizes a TCP connection for its operations [23](#page=23). > **Tip:** HTTP is a stateless protocol, meaning each request is independent and the server does not retain information about previous client requests. The diagram shows typical HTTP request and response interactions. Common HTTP methods include GET and PUT. The process of retrieving a document involves these HTTP exchanges [24](#page=24) [25](#page=25). --- ## Common mistakes to avoid - Review all topics thoroughly before exams - Pay attention to formulas and key definitions - Practice with examples provided in each section - Don't memorize without understanding the underlying concepts

| Term | Definition | |------|------------| | Electrical telegraph | An early 19th-century telecommunications technology used for transmitting messages over long distances using electrical signals, predating widespread telephony. | | Telephony | A telecommunications system that transmits voice or other sounds over distances, typically using electrical signals, patented in 1876. | | Circuit switching | A network communication method where a dedicated, predefined path is established between two endpoints for the duration of a communication session. | | Packet switching | A network communication method where data is broken down into smaller units called packets, each routed independently across the network and reassembled at the destination. | | ARPANET | The Advanced Research Projects Agency Network, established in 1969, which was the first operational packet-switched network and a precursor to the modern internet. | | Protocol | A set of rules or procedures governing the exchange or transmission of data between electronic devices, ensuring compatible communication. | | Internetwork protocol | A protocol designed to enable communication between different types of networks, forming an internetwork. TCP/IP is a prominent example. | | TCP/IP | Transmission Control Protocol/Internet Protocol, a suite of communication protocols used to interconnect network devices on the internet. | | Network model | A conceptual framework that standardizes the functions of a communication system by dividing it into distinct layers, such as the TCP/IP model or OSI model. | | Layered architecture | A design principle in networking where the overall system is divided into a series of layers, with each layer performing a specific function and interacting with the layers immediately above and below it. | | Physical infrastructure | The tangible components of a network, including cables, switches, routers, and other hardware, that support data transmission. | | Addressing | The process of assigning unique identifiers to devices or locations within a network to enable data to be directed to the correct destination. | | Routing | The process of selecting paths in a network along which to send network traffic, determining the best route for data packets. | | Applications | Software programs that utilize network services to perform specific user tasks, such as web browsing, email, or file transfer. | | Client-server paradigm | A distributed application structure that partitions tasks or workloads between providers of a resource or service, called servers, and service requesters, called clients. | | Peer-to-peer paradigm | A distributed application architecture that partitions tasks or workloads between peers, where each peer can act as both a client and a server. | | World Wide Web (WWW) | An information system on the internet that allows documents to be connected to other documents by hypertext links, enabling the user to search for information by moving from one document to another. | | HyperText Markup Language (HTML) | The standard markup language for documents designed to be displayed in a web browser, defining the structure and content of web pages. | | Dynamic web pages | Web pages that are generated in real-time based on user input or other variables, often using scripting languages. | | Universal Resource Locator (URL) | A web address that specifies the location of a resource on the internet, including the protocol, host, port, and path. | | HyperText Transfer Protocol (HTTP) | An application protocol for distributed, collaborative, hypermedia information systems, commonly used to transfer data over the World Wide Web. | | GET | An HTTP request method used to retrieve data from a specified resource. | | PUT | An HTTP request method used to upload a representation of the specified resource. |