Download Tutorial 3 Selected Answers Question 13

Tutorial 3 Selected Answers
Question 13:
Consider a new peer User1 that joins BitTorrent without processing any
chunks. Without any chunks, he cannot become a top-four uploader for
any of the other peers, since he has nothing to upload. How then will
User1 get his first chunk?
In BitTorrent, a peer picks a random peer and optimistically unchokes the
peer for a short period of time. Therefore, Alice will eventually be
optimistically unchoked by one of her neighbors, during which time she
will receive chunks from that neighbor.
Question 14:
In bitTorrent, suppose Alice provides chunks to Bob throughout a 30second interval. Will Bob necessarily return the favour and provide
chunks to Alice in this same interval? Why or why not?
It is not necessary that Bob will also provide chunks to Alice. Alice has
to be in the top 4 neighbors of Bob for Bob to send out chunks to her; this
might not occur even if Alice provides chunks to Bob throughout a 30second interval.
Question 15:
What is an overlay network? Does it include routers? What are the edges
in the overlay network?
The overlay network in a P2P file sharing system consists of the nodes
participating in the file sharing system and the logical links between the
nodes. There is a logical link (an “edge”) from node A to node B if there
is a semi-permanent TCP connection between A and B. An overlay
network does not include routers.