8 Content Distribution

Question 1

What is HTTP

Answer 1

HyperText Transfer Protocol
Request/Response
Layered over byte stream protocol (typically TCP)
Server is stateless

Question 2

HTTP Response Headers

Answer 2

Location
Server
Allow
Content-encoding (compression)
Content length
Expires (cached)
Last modified

Question 3

Problem with early HTTP

Answer 3

One request/response per TCP connection

3-way handshake, slow start

Question 4

What are persistent connections

Answer 4

multiple request/response on a single TCP connection
delimiters indicate the ends of requests
content-length

Question 5

What is pipelining

Answer 5

client sends request as soon as it encounters referenced object

Question 6

Two types of caching for clients

Answer 6

Browser config

Server directed

Question 7

What is a CDN

Answer 7

content distribution network

• overlay network of web caches
• typically geographically disparate servers

Question 8

Who owns CDNs

Answer 8

Content providers

Networks/ISPs

Question 9

How to choose CDN/server replica?

Answer 9

server selection

Question 10

How to direct clients?

Answer 10

content routing

Question 11

Options for server selection

Answer 11

• Lowest load
• Lowest latency
• Any alive server

Question 12

Options for content routing

Answer 12

• Routing (e.g. any cast) : + simple - coarse
• Application-based (e.g. HTTP redirect): - delays
• Naming-based (e.g. DNS): + fine grained controls + fast

Question 13

CDNs and ISPs

Answer 13

symbiotic relationship

Question 14

Benefits of CDN with ISP

Answer 14

+ better throughput (lower latency)
+ redundancy
+ less burstiness

Question 15

Benefits of ISP with CDN

Answer 15

+ good performance for customers

+ lower transit costs

Question 16

What is a seeder

Answer 16

create initial copy

Question 17

What is a leecher

Answer 17

client without complete copy

Question 18

Solution to freeloading

Answer 18

“choking” (aka tit for tat)

temporary refusal to upload

Question 19

What is repeated prisoners dilemma

Answer 19

ensures cooperation among distrustful parties

Question 20

Strategy for BitTorrent clients chunks

Answer 20

Get rarest pieces first (from seeder) or random piece first

End-game: request missing pieces from all peers

Question 21

What is chord

Answer 21

scalable, distributed “lookup service” or distributed hashtable