11. P2P Flashcards
P2P is an example of an overlay network. What does this mean? Why use an overlay network?
Creates a service that is either not provided or cannot be provided at the native network layer. Built on top of an existing network.
What is P2P networking?
Network made up of peers, who are both clients are servers, which form an overlay network.
What are 4 issues with P2P?
- getting started, you need to find peers in the beginning
- how to find out who has what
- how to prevent anti-social behaviour
- how to make sure it scales
What is the certralised directory model? what problem does it solve? what are it’s drawbacks?
Peers connect and inform a central server of their IP and content. Solves the problem of not knowing who has what. Peers then ask the server who has the files they want, which directs them to the other peer. Drawbacks: limited scalabilty, single point of failure, easy to sue
What is a torrent?
A group of peers exchanging chunks of a file.
Describe how BitTorrent works.
File is divided into 256Kb chunks, peers in the torrent send and receive file chunks. Peers register with a tracker to get a list of peers. While downloading the peer is also uploading to other peers. Once the peer has the entire file, they may leave or stay.
What is “optimistically unchoking”?
Other peers that a client is not sending chunks to are “choked”, because they did not make the top 4. To prevent newcomers from being ignored, every so often the client selects a random peer to also send chunks to.
How does the time taken by client server systems and P2P systems scale with more clients?
C-S system scales linearly, p2p is logarithmic, scales much better
