2.2 Web and HTTP Flashcards
object definition
what makes up a web page
can be a JPEG image, HTML file, Java applet, audio file
webpage definition
consists of a base HTML-file that includes several referenced objects
each object is addressable by a URL
name the parts of this URL: https://www.psu.edu/news/academics/featured-courses
host name:
www.psu.edu
path:
name/news/academics/featured-courses
HTTP definition
Hypertext Transfer Protocol
protocol = defines format and order of messages sent/received
HTTP = the web browser’s language; allows web browsers to communicate with servers for loading websites
What type of architecture does HTTP use and how does HTTP use it?
client/server
client = a browser that requests, receives, and displays web objects
server = a Web server that, using HTTP, sends objects in response to requests
Does HTTP use TCP or UDP?
TCP; more reliable
What are the steps of opening and closing a TCP connection with HTTP
- client opens a TCP connection to a web server (creates a socket)
- server accepts TCP connection from client
- HTTP messages are exchanged between the browser (the HTTP client) and the Web server (the HTTP server)
- the TCP connection is closed
What are the two types of HTTP connections and how do they compare?
Non-persistent HTTP:
downloading multiple objects requires multiple connection
1. TCP connection is opened
2. at most 1 object is sent over the connection
3. TCP connection is closed
Persistent HTTP:
most common form of HTTP, cuts RTT in hlad
1. TCP connection is opened to a server
2. multiple objects can be sent over a single TCP connection between client and that server
3. TCP connection is closed
most common form of HTTP
What does it mean that HTTP is stateless?
Each request sent by a client to the HTTP server is independent and not remembered by the server
Features like cookies are used to maintain state when needed, like for authentication (keep you sign in)
RTT meaning
Round-Trip Time: how long it takes for a small packet to travel from the client to the server and back again
Non-persistent HTTP
Formula to calculate non-persistent HTTP response time
2 * RTT + file transmission time
Non-persistent HTTP issues
Requires 2 RTTs per object
OS overhead (operating system processing time)
HTTP request message format and its methods
the first line is called the request line, which starts with method name (e.g. “GET”), followed by a URL, followed by HTTP
the 4 methods:
1. POST - for form input
2. GET - for sending data to server
3. HEAD - requests headers
4. PUT - uploads new file (object) to server
How many types of messages does HTTP have?
Two: response and request
HTTP response message format and its status codes
the first line is called the status line, which starts with HTTP version number, followed by status code and a status phrase
Some status codes:
200 OK = request succeeded
301 Moved Permanently = request object has moved, its new location is later in this message
400 Bad Request = request message not understood by the server
404 Not Found = requested document not found on this server
505 HTTP Version Not Supported = what the title says
HTTP cookie definition
code used by the server to access information about earlier interactions with the browser
makes web browsing faster
though HTTP is technically a “stateless” protocol, a web server can maintain some user state (remember user’s past)
cookies’ use cases
authorization (keeping you logged in)
shopping carts
recommendations
email
proxy server definition
proxy server - a middle server between host and the internet
acts as both a client and a server
gives the client (the host) web access via cache
proxy server benefits
saves bandwidth for the host
privacy - hides IP address
can block certain websites
faster browsing–stores copies of popular websites to load them quicker
security
filters out malware
web server definition
computer/software that stores and delivers websites to users when they request them through a browser
HOSTS websites
It’s like a restaurant: you (the browser) order food (a webpage), the kitchen (web server) prepares it, and the waiter (internet) delivers it to you!
How is a web server related to HTTP?
web server uses HTTP to communicate with clients
HTTP is the protocol that defines how the server and client communicate
‘conditional’ HTTP GET command meaning
This command only allows the server to send the requested object if it changed since last time
purpose of HTTP GET command
used by the client to request a Web server to send an object
