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\title{CSc 450/550: Computer Networks (Summer 2006)}
\author{Assignment 2}
\date{To be handed in at the lecture on June 19, 2006}
\maketitle
\begin{enumerate}
\item Computer A and Computer B are interconnected by a
store-and-forward Router C and two 10 Mbps duplex communication
links (i.e., AC and CB) of 1000 km length each. A binary file of 10
MB is to be transferred from A to B. Signal is propagated at $10^8$
m per second in the communication channel.
\begin{enumerate}
\item if the whole file is transferred as one big message (i.e.,
message switching), how long does it take for B to receive the
entire file after A starts to send the file?
\item if the file is transferred in a series of 10 KB packets (i.e.,
packet switching), how long does it take for B to receive the
entire file after A starts to send the file?
\item if it takes 10 ms for C to make the forward decision for a
message or packet, please recalculate the time for B to receive
the file with message or packet switching.
\item please calculate the minimal buffer size required at C to
support message or packet switching without or with the 10 ms
processing time for each message or packet.
\end{enumerate}
\item In a few sentences, please explain and compare frequency
division multiplexing, wavelength division multiplexing, and time
division multiplexing.
\item In a few sentences, please explain the scalability issue of the
client-server model over the Internet and compare the different ways
to improve it.
\item In a few sentences, please explain and compare recursive and
iterative DNS query.
\item A client needs to send a 5-byte request message to a server over
TCP, and the server will respond with a 10-byte reply message.
Assume initial sequence number is 0. Please write down the sequence
of packets exchanged between the client and the server, along with
TCP flag(s), sequence number, and acknowledgment number in each TCP
packet.
\item Please calculate the TCP/IP-style checksum for a 3-byte message
in its hexadecimal representation: AB, CD, EF. Please also explain
when the checksum would fail to detect possible packet errors.
\item Please calculate the TCP timeout value (RTO) for the following
round-trip time (RTT) sequence: 1, 2, 3, 4, 1, 2, 3, 4. The initial
SRTT is 1 and the initial RTTV is 0.5.
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\item For a simplified HTML document with URL {\texttt
http://a.b.com/index.html}
\begin{verbatim}
\end{verbatim}
and for a web browser that loads images (JPEG and GIF files)
automatically, how long (in round-trip time) does it take to display
this Web page properly (DNS overhead is omitted), if all files are
small enough to be accommodated in one packet and:
\begin{enumerate}
\item non-persistent HTTP connections are used, or
\item persistent HTTP connections with non-pipelining are used, or
\item persistent HTTP connections with pipelining are used.
\end{enumerate}
How about if at most two parallel TCP connections per server can be
used by the browser with the above three scenarios?
\end{enumerate}
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