Q$1)(5$ Points$)$ Multiple Choice:

The internet model consists of the following layers:

a Application, Transport, Network, Link, and Physical.

b$.$ Application, Presentation, Transport, Network, Link, and Physical.

c$.$ Application, Presentation, Session, Transport, Network, Link, and Physical.

d$.$ None of the above

Local DNS name servers:

a Obtain resource records from Web caches

b$.$ Cache resource records and never discard them $x$

c$.$ Never cache resource records $x$

d$.$ Cache resource records, but discard them after a period of time that could be on the order of a few days

SMTP is used to:

a$.$ Define the format of message headers

B$.$ Transfer messages from one mail server to another

c$.$ Transfer messages from mail server to user agent

d$.$ All of the above

For BitTorrent, which of the following is true:

a$.$ Although a peer may have $50$ concurrent TCP connections with other peers, at any given instant of time it sends data to less than $10$ other peers

Among the chunks that a peer does not have, the peer will request chunks that appear to be relatively rare in the torrent

c$.$ At a given instant of time, a peer A may upload to a peer B$,$ even if peer $B$ is not sending anything to $A$

d$.$ All of the above

Consider the minimum time for P$2$P file distribution. Suppose the upload rate of the server is $10$ Mbps $,$ the upload rates of all peers is $1$ Mbps $,$ and the download rates of all peers is $10$ Mbps $.$ Further suppose that there are $100$ peers and the file is $100$ million bits. The minimum distribution time is:

a$.$ Approximately $1$ second

b$.$ Approximately $100$ second

c$.$ Approximately $1000$ second

d$.$ Approximately $10$ second