Chapters 3 and 4 Flashcards
URL
Uniform Resource Locator
Representation standard that specifies the format and meaning of web page addresses
HTTP
Hypertext Transfer Protocol
Primary Web’s application layer protocol. Transfer protocol that specifies how a browser interacts with a web server to transfer data
Uses client/server model
Browser extracts the address of a server from a URL and contacts the server
HTML
Hypertext Markup Language
Representation standard used to specify the content of a webpage. The language of the Web.
HTML 5 is what we use, newest
client
browser that requests, receives, “displays” Web objects (files, images, video, etc.)
server
Web server sends objects in response to requests
GET message
browser (client) requests a page from server by sending this
RESPONSE message
Server responds by sending this message with a header, blank line, and requested document
POST request
Sends data to a server; the server appends the data to a specified item (e.g. a message is appended to a list)
HEAD request
Requests status information; server responds by sending status information, but does not send a copy of the document
PUT
Sends data to a server; the server uses the data to completely replace the specified item (i.e., overwrites the previous data)
Status code
appears in first line in server to client response
Status Code: 200
OK
request succeeded, requested object later in this message
Status Code: 301
Moved Permanently
requested object moved, new location specified later in this message (location)
Status Code: 400
Bad Request
request message not understood by server
Status Code: 404
Not Found
requested document not found on this server
Status Code: 505
HTTP Version not supported
Cashing: Conditional GET
Goal: Server doesn’t send object if browser’s cache has up-to0date cached version
Browser Cache: HTTP requests specifies date of cached copy in header
Server: Response contains no object if cached copy is up to date.
Cascading Style Sheets (CSS)
Features like background, color, font, layout
JavaScript
used to make HTML pages interactive
Singleton Tags:
<hr></hr>
produces a horizontal line
<br></br> line break, continues text on next line
HTML tags…
define structure and content of a page, but don’t define the style of a page (styling uses CSS)
Each tag defines an…
element of a page.
- Some elements are like boxes
- Some elements are block elements
- Others are inline elements
Required Tags
<!DOCTYPE htmtl>
<html>
<head>
</head>
<body>
</body>
</html>
<head>
</head>
contains the beginning info (title, link to CSS or JavaScript file, etc) that applies to the whole page
this part is not visible on the actual web page
Domain Name System (DNS)
Client-server application
Core internet application, provides rules for giving names to computers on the internet. System to translate between human readable names of computers and the IP addresses used by the Internet protocol
“phone book” for the internet
protocol
the name of the protocol used to access the document
computer_name
“domain name” of the computer storing the document
port
port number at which the server is listening
document
name (or pathname) of the document
parameters
(optional) parameters for the page
Top level domain
e.g., edu
Second level
organization (e.g., “saintmarys”)
Hierarchy of Client-Server DNS Queries
Root “.”
Root -> com -> facebook
Root -> org -> pbs
Root -> edu - > saintmarys -> sites
Name Resolution
obtaining IP addresses for domain name
Reverse DNS resolution
obtaining domain name for IP address
resolver
Sends DNA request to a DNS server when an application needs an IP address of another host (e.g., web server)
Top-Level Domain (TLD) Servers
Resposible for com, org, net, edu, etc, and all top-level country domains uk, fr, ca, jp, etc.
Authoritative DNS Servers
Organization’s DNS servers, providing authoritative hostname to IP mappings for organization’s serves (web, main). Can be maintained by organization or service provider
Local Name Server
Do not strictly belong to hierarchy
Each ISP (residential ISP, company, university) has one (also called default name server)
When a host makes a DNS request, that query is sent to its local DNS name server first
The default name server forwards query, if needed, into hierarchy
ISP
internet service provider
DNS Records
Type = record type (name, value)
Type = A (hostname, IPv4)
Type = AAAA (hostname, IPv6)
Type = NS (domain, hostname for authoritative name server for this domain)
Type = CNAME (canonical, canonical name)
Type = MX (value of mailserver associated with name)
