CNT 4704: Analysis of Computer Communication Networks
Fall 2011
Homework 2
(assigned 10/11; due: 10/18 midnight, submitted via webcourse;
No late
submission allowed)
1. Chapter 3, problem 1.
Suppose Client A initiates a Telnet session
with
Server S. At about the same time, Client B also initiates a
Telnet
session with Server S. Provide possible source and destination
port
numbers for
a). The segments sent from A to S.
b). The segments sent from B to S.
c). The segments sent from S to A.
d). The segments sent from S to B.
e). If A and B are different hosts, is
it
possible that the source port number in the segments from A to S
is the
same as that from B to S?
f). How about if they are the same
host?
2. Chapter 3, problem 4.
a). Suppose you have the following 2 bytes:
00110100
and 01101001. What is the 1s complement of these 2 bytes?
b). Suppose you have the following 2 bytes:
11110101
and 00101001. What is the 1s complement of these 2 bytes?
c). For the bytes in part (a), give an
example where
one bit is flipped in each of the 2 bytes and yet the 1s
complement
doesn't change.
3. Chapter 3, problem 12.
Consider the rdt 3.0 protocol. Draw a diagram
showing that if the network connection between the sender and
receiver
cna reorder messages (that is, that two messages propagating in
the
medium between the sender and receiver can be reordered), then
the
alternating-bit protocol will not work correctly (make sure you
clearly
identify the sense in which it will not work correctly). Your
diagram
should have the sender on the left and the receiver on the
right, with
the time axis running down the page, showing data (D) and
acknowledgement (A) message exchange. Make sure you indicate the
sequence number associated with any data or acknowledgement
segment.
4. Chapter 3, problem 22 (Problem 21 in 4th
edition).
Justify your answer even if
the answer is true. For statement (a), you should justify it by
drawing
a
protocol running example.
Answer true or false to the following
statements and
briefly justify your answer:
a). With the SR protocol, it is
possible fo
rthe sender to receive an ACK for a packet that falls outside of
its
current window.
b). With GBN, it is
possible fo
rthe sender to receive an ACK for a packet that falls outside of
its
current window.
c). The alternating-bit protocol is the
same
as the SR protocol with a sender and receiver window size of 1.
d). The alternating-bit
protocol
is the same as the GBN protocol with a sender and receiver
window size
of 1.
5. Chapter 3, problem 24 (Problem 23 in 4th
edition).
For qustion (b), assume that the
network is perfect and there is no error or retransmissions.
Consider transferring an enormous file of L
bytes
from Host A to Host B. Assume an MSS of 1,460 bytes.
a). What is the maximum value of L such that
TCP
sequence numbers are not exhausted? Recall that the TCP sequence
number
field has 4 bytes.
b). For the L you obtain in (a), find how
long it
takes to transmit the file. Assume that a total of 66 bytes of
transport, netowrk and data-link header are added to each
segment
before the resulting packet is sent out over a 10Mbps link.
Ignore flow
control and congestion control so A can pump out the segments
back to
back and continuously.
6. Chapter 3, problem 37 (Probelm 33 in 4th
edition).
7. Consider the cross-country example shown in lecture notes Chapter3-part2.ppt (page 10-12). How big would the window size have to be for the channel utilization to be greater than 90 percent?