Application Layer

Question 1

What are the most widely used concrete applications used on the Internet?

Answer 1

The World Wide Web and electronic mail

Question 2

How does the Application Layer take full advantage of the virtualisation of the network?

Answer 2

All the different application structures are implemented on this layer. The application layer builds on top of all the other layers

Question 3

URL

Answer 3

Uniform Resource Locator. Address of a document on the WWW. An image, webpage, audio file, a program, an app.

Question 4

HTML

Answer 4

Hypertext Markup Language. The document format for web pages

Question 5

HTTP

Answer 5

Hypertext Transfer Protocol. Standard set of commands understood by tall web browsers and servers. Browsers can sed a HTTP command to a server to request a certain doc . based on its URL and the same protocol will be used to send the document back

Question 6

Three components of a URL

Answer 6

Scheme (http/https)
-What protocol must be used to retrieve the document
Host (monash.edu)
- Identifies the server
Path(/authentication/adfs)
- identifies particular document on the server

Question 7

Explain the request-response cycle for http://www.monash.edu/FIT1047/

Answer 7

The browser first notices the scheme and opens a connection with the HTTP server www.monash.edu, then sending a request for the FIT1047 document. The server responds by sending the document until all assets have been loaded

Question 8

Explain what this is:

GET /fit1047.html HTTP/1.1
Host: www.monash.edu

Answer 8

The HTTP request sent from the client to the server.

Question 9

Explain what this is:

HTTP/1.0 200 OK
Date: Fri, 21 Apr 2017 05:30:10 GMT
Content-type: text/html
Content-Length: 463
Last-Modified: Fri, 21 Apr 2017 04:39:52 GMT

Answer 9

This is the HTTP response sent back by the server. The browser will read what is in the HTML file and if there are images, another request is made to the server for the image. The cycle restarts until the entire page is rendered

Question 10

Name 2 HTTP methods

Answer 10

GET

POST

Question 11

HTTP request (structure)

Answer 11

Consists of request line.

• Method
• Path
• Protocol version used

Followed by request header.
-Host……. line is mandatory
other additional information as well like files of a certain language or types of files.

The request header needs to be followed by a blank line followed by the request body

Question 12

HTTP response (structure)

Answer 12

The first line is the response status( protocol version and two status codes. 200 and OK or 404 Not found)

Followed by response header. Contains meta data(what type of document it is, last modified date.

Ends with a blank line followed by a response body

Question 13

What is the state of HTTP?

Answer 13

HTTP is stateless, meaning that every request is sent independently and the server does not know if consecutive requests are form the same user or different users.

Question 14

What is the problem with the state of HTTP?

Answer 14

If you’re shopping, you want the server to remember whether or not you put an item in the cart or not. You want the data saved and kept consistent within a session.

Question 15

How does the server know information about a users session?

Answer 15

The information is kept somewhere else and is transmitted as part of requests and responses with a sessionID. The browser sends that sessionID as part of every single future request. The sessionIDs are embedded in the HTML file and the ID is sent as part of every request.

Question 16

What is a cookie?

Answer 16

A small piece of data that is returned as part of the HTTP response header.

Question 17

How do cookies work?

Answer 17

The browser stores the cookie sent by the server, and every time the browser sends a request to the server, the cookie is in the request header. They allow login
information, preferences and user habits to be saved onto the browser.

Question 18

What is the traditional email setup?

Answer 18

Classic two-tier client server application using SMTP (Simple mail transfer protocol) to send a message to the mail server, which forwards the message to the receivers’ mail server. The receiver accesses their message using POP (post office protocol) or IMAP (Internet Mail access protocol)

Question 19

Why do we use different protocols to send and receive emails?

Answer 19

Servers are available 24/7 whilst clients are not, and also users may want to access their emails from different clients like phones or a separate computer. IMAP and POP allow emails to be pulled on demand, instead of SMTP continuously pushing to an unavailable client.

Question 20

What is the difference between POP and IMAP?

Answer 20

POP downloads messages onto the client and deletes them from the server
IMAP means that the messages stay on the sever, which allows simultaneous access to the email account at the same time from multiple clients making changes at the same time

Question 21

What is the MIME format?

Answer 21

The Multi-Purpose Internet Mail Extensions is a way of encoding( and decoding) binary data into plain text, and specifying how emails with multiple documents are sent

Question 22

Explain how web mail services work

Answer 22

The user is using a browser to compose an email, and as they send the email, a HTTP POST request is sent to the web server. The web server starts an SMTP session to deliver the email with the traditional mail service (client-server)