Computer Networks Lecture 02: Application Layer
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Questions and Answers

What method does HTTP/2 use to manage multiple responses over a single connection?

  • Sequential processing of requests
  • Cloning connections for each response
  • Interleaving frames (correct)
  • Using multiple TCP connections

    • How does the framing sublayer in HTTP/2 enhance performance?

  • By increasing frame size
  • Through binary encoding of frames (correct)
  • By using a text-based encoding
  • By reducing the number of connections

    • What role does the weight assigned to requests serve in HTTP/2?

  • Informs the server about timeouts
  • Determines the size of the request
  • Indicates the priority of responses (correct)
  • Specifies the connection type

    • What is the primary purpose of the Domain Name System (DNS)?

    <p>To translate hostnames to IP addresses</p> Signup and view all the answers

    What transport protocol does DNS primarily utilize?

    <p>UDP</p> Signup and view all the answers

    Which protocol would typically make use of DNS for transiting hostnames to addresses?

    <p>SMTP</p> Signup and view all the answers

    What defines an IP address in terms of its structure?

    <p>It has a rigid hierarchical structure consisting of four bytes.</p> Signup and view all the answers

    How can a server respond to a client's request without waiting for each individual request?

    <p>By sending pushed additional objects</p> Signup and view all the answers

    What best describes a primary feature of P2P architecture?

    <p>It facilitates direct communication between peers.</p> Signup and view all the answers

    What is the primary role of a socket in process communication?

    <p>To send and receive messages over a network.</p> Signup and view all the answers

    Which of the following services is NOT typically offered by transport-layer protocols like TCP and UDP?

    <p>Timing guarantees</p> Signup and view all the answers

    Which description is correct about the client-server model?

    <p>The roles of client and server can switch in a P2P environment.</p> Signup and view all the answers

    What is the primary purpose of the HyperText Transfer Protocol (HTTP)?

    <p>To facilitate hypertext data transfer on the web.</p> Signup and view all the answers

    Which of the following best outlines a challenge associated with P2P architecture?

    <p>Performance and security issues due to decentralization.</p> Signup and view all the answers

    What aspect of transport services do both TCP and UDP neglect to provide guarantees for?

    <p>Throughput and timing</p> Signup and view all the answers

    How are popular applications assigned unique identifiers in the context of transport-layer protocols?

    <p>By using well-known port numbers</p> Signup and view all the answers

    What is a key advantage of using CDNs like Akamai and Limelight over dedicated CDNs?

    <p>Potentially better coverage and redundancy</p> Signup and view all the answers

    What is the purpose of the If-Modified-Since: header line in an HTTP request?

    <p>To validate the freshness of a cached object</p> Signup and view all the answers

    How does HTTP/2 primarily aim to reduce perceived latency?

    <p>By enabling request and response multiplexing over a single TCP connection</p> Signup and view all the answers

    What is a significant issue with using a single TCP connection to send all objects in a web page?

    <p>Head of Line (HOL) blocking</p> Signup and view all the answers

    Which method do HTTP/1.1 browsers typically use to work around the HOL blocking issue?

    <p>Opening multiple parallel TCP connections</p> Signup and view all the answers

    What is the main strategy of HTTP/2 to solve HOL blocking?

    <p>Breaking messages into frames and interleaving them</p> Signup and view all the answers

    What does TCP congestion control primarily aim to achieve?

    <p>Ensure fair bandwidth sharing among connections</p> Signup and view all the answers

    How do dedicated CDNs like Google and Netflix primarily differ from shared CDNs?

    <p>They are specifically tailored to their services</p> Signup and view all the answers

    Study Notes

    Computer Networks Lecture 02: Application Layer

    • Lecture focused on the Application Layer in computer networks.
    • Presented by Dr. Sahar M. Ghanem.
    • Course is offered by the Computer and Systems Engineering Department, Faculty of Engineering, Alexandria University.

    Outline

    • Principles of Network Applications
    • The Web and HTTP
    • Electronic Mail in the Internet
    • DNS—The Internet's Directory Service
    • Peer-to-Peer File Distribution
    • Video Streaming and Content Distribution Networks
    • Socket Programming: Creating Network Applications

    Applications (1/2)

    • 1970s/1980s: text email, remote computer access, file transfers, newsgroups.
    • Mid-1990s: World Wide Web, web surfing, search, e-commerce.
    • New Millennium: voice over IP (VoIP) video conferencing (Skype, FaceTime, Google Hangouts), user generated video (YouTube), movies on demand (Netflix), multiplayer online games (Second Life, World of Warcraft), social networking (Facebook, Instagram, Twitter).
    • Smartphone and 4G/5G Internet access: location-based apps (Yelp, Tinder, Waze), mobile payment apps (WeChat, Apple Pay), messaging apps (WeChat, WhatsApp).

    Client-Server Architecture

    • Always-on host (server) serving requests from multiple hosts (clients).
    • Clients do not directly communicate.
    • Servers have fixed, well-known IP addresses.
    • Data centers often house servers, creating powerful virtual servers (hundreds of thousands of servers).

    P2P Architecture

    • Minimal reliance on dedicated servers in data centers.
    • Direct communication between intermittently connected hosts (peers).
    • Example: file-sharing application BitTorrent.
    • Strong features: self-scalability, cost-effectiveness.
    • Key challenges: security, performance, and reliability due to decentralized structure.

    Process Communication

    • Processes on different hosts (potentially different operating systems) communicate via messages.
    • Processes communicate across the computer network, exchanging messages.
    • A process can be both a client and a server (e.g., peer-to-peer file sharing).
    • Network communication happens through a software interface called a socket.

    Transport Layer Services

    • Applications are assigned specific port numbers.
    • Internet standard protocols have well-known port numbers (found at www.iana.org).
    • Transport layer protocols provide services like reliable data transfer, throughput, timing, and security.
    • TCP and UDP are common transport protocols.

    HTTP (HyperText Transfer Protocol)

    • Web's application-layer protocol.
    • Client-server program exchange HTTP messages.
    • HTTP/1.0 (RFC 1945), HTTP/1.1 (RFC 7230), and HTTP/2 (RFC 7540) are common versions.
    • Web pages consist of base HTML files and referenced objects (e.g., images, JavaScript, CSS).
    • Each object has a unique URL.
    • HTTP uses TCP as its underlying transport protocol.
    • The server sends requested files without storing client state (stateless protocol).

    TCP Connections

    • Request/response pairs can be sent over separate TCP connections (non-persistent) or a single TCP connection (persistent).
    • HTTP defaults to persistent connections.
    • Non-persistent connections impose additional delay per object.

    HTTP Request Message

    • Written in ASCII text.
    • Components: request line (method, URL, HTTP version); header lines (Host, Connection, User-Agent, Accept-Language); entity body (often empty for GET requests).
    • Common methods: GET, POST, HEAD, PUT, DELETE.
    • Most HTTP requests use the GET method.

    HTTP Response Message

    • Three sections: status line (protocol version, status code, status message), header lines (Date, Last-Modified, Content-Type), entity body (requested object).
    • Status codes like 200 OK, 301 Moved Permanently, 404 Not Found, indicate successful or failed requests.

    User-Server Interaction: Cookies

    • HTTP is stateless, making user identification challenging.
    • Cookies are used to maintain user session state.
    • Four components: cookie header in HTTP response, cookie header in HTTP request, browser-managed cookie file, database on the Web site.

    Web Caching

    • Proxy servers that act as intermediaries between clients and origin servers.
    • Caching reduces response time for frequently accessed objects.
    • Reduces traffic on the access links and improves overall Internet performance.
    • Uses conditional GET requests to avoid unnecessary data transfers (when objects in the cache are up-to-date).

    HTTP/2

    • Aims to reduce latency by enabling request/response multiplexing over a single TCP connection, prioritizing requests, and compressing HTTP headers.
    • Solves HEAD of Line (HOL) blocking by breaking messages into frames and interleaving them.
    • Improves efficiency and reduces perceived latency.

    DNS (Domain Name System)

    • Translates hostnames to IP addresses.
    • Hierarchical distributed database with root servers, top-level domain (TLD) servers, and authoritative servers.
    • Local DNS servers act as proxies for resolving queries.
    • Uses UDP (port 53) for communication.
    • Offers services like host aliasing, mail server aliasing, load distribution.

    DNS Caching

    • Improves DNS performance and reduces message delays.
    • DNS servers cache mappings in local memory for faster lookups.
    • Cached information is discarded after a period.

    DNS Records and Messages

    • Resource records (RRs) contain information to map hostnames to IP addresses.
    • Records have fields like name, value, type, and time to live (TTL).

    DNS Message Format

    • Query and reply messages share the same format with a header section and data sections.
    • Types of data fields (question, answer, authority, additional).

    nslookup

    • A program for querying DNS servers to translate hostnames.

    ICANN

    • Accredits domain registrars, verifying uniqueness of domain names.

    Socket Programming

    • Programming network applications with sockets to communicate between processes.
    • Two main types: client-side program, server-side program.
    • Socket programs can use UDP (connectionless) or TCP (connection-oriented) protocol.

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    Computer Networks Lecture 02: Application Layer PDF

    Description

    This quiz covers the Application Layer in computer networks, focusing on key topics such as web technologies, email, DNS, and socket programming. Presented by Dr. Sahar M. Ghanem from the Faculty of Engineering, Alexandria University, this lecture explores the historical evolution of network applications to modern usage. Test your knowledge on the principles of network applications and their various real-world applications.

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