2.2 The Web and HTTP

• The hypertext transfer protocol (HTTP) is a protocol used for communication between web browsers and web servers.
• HTTP is implemented into two programs: a client program and a server program.
• Web pages are made up of HTML files that contain text, images, links, and other content.
• When a user requests a web page, the browser sends HTTP request to the web server.
• HTTP uses TCP as its transport protocol.
• HTTP is a stateless protocol, meaning servers do not retain client state information between requests.
• Non-persistent connections involve separate TCP connections for each request-response pair, resulting in higher overhead and latency.
• Persistent connections keep TCP connections open after sending a response, allowing multiple requests and responses to be sent over the same connection, reducing overhead and latency.
• HTTP messages include request messages sent by clients and response messages sent by servers.
• What are cookies in the context of HTTP?


  Small pieces of data sent from a website and stored on the user's browser, allowing the site to track and identify users.
• How do cookies allow websites to identify users?

  Cookies consist of a cookie header line in HTTP response/request messages, a cookie file on the user's system, and a backend database on the website.
• How does a web server use cookies to track user activity?

  Cookies are used for personalized content, user tracking, shopping carts, and user sessions.
• What role do cookies play in creating a user session layer on top of HTTP?

  They enable websites to identify users across sessions, enhancing functionality like personalized content and targeted advertising.
• Why are cookies controversial in terms of privacy?

  They raise privacy concerns as they can track and collect user data, potentially leading to unauthorized access or data misuse.
• A web cache is a temporary storage of web pages that are frequently requested by users.