Lesson 8 - Content Distribution

Question 1

What does HTTP stand for?

Answer 1

HyperText Transfer Protocol (HTTP)

Question 2

What is a Stateless Server?

Answer 2

A stateless server is a server that retains no information about a client request after it has processed it

Question 3

What is typically is in an HTTP Request?

Answer 3

• method = GET, POST, etc
• URL = index.html
• Version number
• Headers -> Referer, User Agent, etc

Question 4

What does the Referer header do?

Answer 4

Located in the HTTP Request.

It tells what caused the page to be requested.

Question 5

What does the User Agent header do?

Answer 5

Located in the HTTP Request.

It tells what client software (chrome, firefox, etc) the request came from.

Question 6

What is typically in an HTTP Response?

Answer 6

• HTTP Version
• Response Code
• Location (for redirection)
• Server (indicates server software)
• Allow (indicates what HTTP methods are allowed)
• Content Encoding (if it is compressed, etc)
• Content Length (in terms of bytes)
• Expires
• Last Modified

Question 7

What type of response code is 100?

Answer 7

Informational

Question 8

What type of response code is 200?

Answer 8

Success

Question 9

What type of response code is 300?

Answer 9

Redirect

Question 10

What type of response code is 400?

Answer 10

Error

Question 11

What type of response code is 500?

Answer 11

Server Error

Question 12

What are Persistent Connections?

Answer 12

• Allows multiple request/response on single TCP connection
• Delimiters indicate end of request
• Content-length (so server has to know how large the thing is in advance)

Question 13

What is Pipelining?

Answer 13

• The client sends a request as soon as it sees a referenced object
• Often combined with Persistent Connections

Question 14

What two places are caches typically located?

Answer 14

• In the browser

* On a network

Question 15

What are the benefits of caching?

Answer 15

• Reduced transit costs of local ISP

* Improved performance for local clients

Question 16

What is a Content Distribution Network (CDN)? What is the goal of it?

Answer 16

The goal is to replicate content on many servers to keep content close to the clients

We are trying to overlay a network of web caches that deliver content to a client from the optimal location (not necessarily closest)

Question 17

How do we choose what server replica to access?

Answer 17

• Typically the one with the lowest latency

Question 18

What methods exist for Content Routing and how do we direct clients with it?

Answer 18

• Routing based (anycast) - Simple, but coarse
• Application based - causes delays
• Naming-Based system (like DNS) - provides local caches whenever you look up the name

Question 19

In torrents, what is the freerider problem and how is it solved?

Answer 19

Where people download a resource and then don’t seed it.

The problem is resolved by restricting download access next time person tries to download

Question 20

What is Chord?

Answer 20

• It is a scalable, distributed “lookup service” that maps keys to values
• Provable correctness
• Uses consistent hashing

Question 21

What is Consistent Hashing?

Answer 21

• keys and nodes map to the same ID space
• Nodes hash IP address
• Keys hash the Key

Question 22

What 3 ways can consistent hashing be implemented and the associated complexities?

Answer 22

Every node knows location of every other node

* lookups O(1)
* tables O(N)

Every node knows only its sucessor

* lookups O(N)
* table O(1)

Finger Table - Every node knows M other nodes in the ring
* O (log N)