Week 5

Question 1

What are objects of a web page?

Answer 1

a file, like an HTML file, image, CCS file, addressable by a single URL.

Question 2

What is a webpage?

Answer 2

a document that consists of one or more objects

Question 3

What transport protocol does HTTP use? Port Number?

Answer 3

TCP

Port number 80

Question 4

What does it mean that HTTP is “stateless”?

Answer 4

the server keeps no information about the past clients and its reqiuests

Question 5

What are the main components of a URL?

Answer 5

1. the host name of the server
2. the object’s path name

Question 6

What are the 2 types of HTTP connections?

Answer 6

1. Non Persistent HTTP
2. Persistent HTTP

Question 7

What is Non Persistent HTTP?

Answer 7

at most one object is sent over the TCP connection.

TCP connection closes after server sends the object

Question 8

What is Persistent HTTP?

Answer 8

A persistent TCP connection that allows to send multiple objects over a single TCP connection.

Question 9

What is RTT?

Answer 9

Round-Trip Time for Non Persistent HTTP.

The time for a packet for client -> server -> client.Ho

Question 10

How much RTT for non persistent HTTP?

Answer 10

2 RTT

1 RTT to establish connection

1 RTT to send/receive

Question 11

What are the 2 types of HTTP messages?

Answer 11

1. Request
2. Response

Question 12

Format of an HTTP Request message?

Answer 12

1. Request Line
2. Header Lines
3. Blank Line
4. Body

• IN ASCII: human readable format

Question 13

What is in the request line of a HTTP Request message?

Answer 13

Method, URL, HTTP version

Question 14

What is the entity body used for in a HTTP Request message?

Answer 14

Other methods such as POST or PUT

Question 15

What are the methods?

Answer 15

GET, POST, HEAD, PUT, DELETE

Question 16

What is “user-agent”

Answer 16

the browser type making the request to the server

Question 17

Format of an HTTP Response message?

Answer 17

1. Status Line
2. Header Lines
3. Blank Line
4. Entity Body

Question 18

What is “Server” in an HTTP response message?

Answer 18

Like similar agent, the browser type

Question 19

What is “Date” in an HTTP response

Answer 19

time when the server retrieves the object.

Question 20

What is a web cache / proxy server?

Answer 20

An entity that does HTTP request on behalf of an original web server.

Question 21

How does a web cache work?

Answer 21

• web cache has its own storage
• keep copies of recently requested objects
• if it doesn’t have the object it requests a TCP connection to the origin server

Question 22

Is a cache a server or client?

Answer 22

Both.

Question 22

Pros of web caching?

Answer 22

keeps copies of recently requested objects, so it saves response time and reduce costs

Question 22

What is a stale object?

Answer 22

an object that has been modified after it’s been cached.

Question 23

How to solve a stale object in web caching?

Answer 23

Use the conditional GET

Question 24

2 characteristics of a conditional get?

Answer 24

1. request uses the GET method
2. request has an “if-modified-since” header line