Application Layer Protocol

Question 1

How does peer-to-peer architecture work?

Answer 1

No always on server

Peers intermittently connected

Question 2

Why do we use hash tables?

Answer 2

Convenient to store and search

Question 3

How do we get a hashed key?

Answer 3

Hash(original key)

Question 4

How does a distributed hash table work?

Answer 4

Assign each peer identifier
Any number stored in n bits
Define hash function
Make hash available to every peer

Question 5

What is a circular hash?

Answer 5

Each peer only aware of immediate successor/predecessor

Question 6

What is peer churn?

Answer 6

Peers may come and go

Each peer periodically pings successors

Question 7

What is a torrent file?

Answer 7

Calculates hash code

Question 8

What is a magnet link?

Answer 8

Use distributed hash table

Question 9

What is a tracker in a BitTorrent?

Answer 9

Tracks peers participating in torrent

Question 10

What is a torrent in a BitTorrent?

Answer 10

Group of peers exchanging chunks of file

Question 11

How does the tit-for-tat approach for a BitTorrent work?

Answer 11

Peers join network and register with tracker
Tracker sends list of IPs of S out of N peers
Peer establishes concurrent TCP connections with each node in S
Peer periodically requests neighbours send chunk lists
Rarest chunk is 1st
Peers track neighbourhood that transmit fastest (unchoked = send 1st)
Neighbours are choked
Once peer has file, selfish leave or altruistically remain