Finals-fall02-343-44..

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Computer Networks

COMP 343/443: Fall 2002

Finals






Due in the submit folder 10 am Wednesday, 11
th

Dec. *


1.

Write the steps of the distance
-
vector algorithm. What are the important features
of it?

(15 points)

2.

Suppose there is a TCP/IP network containin
g two hosts A and B and two routers
R1 and R2. Host A with IP Address 141.126.2.9 and Physical Address 5.6 wants
to communicate to Host B with IP Address 202.3.9.15 and Physical Address 9.68.
The port number of Host A is 7000 and the port number of Host
B is 8000.

Host A is directly connected to R1, R1 is directly connected to R2, and R2 is
directly connected to Host B. The Physical Address of R1 is 92.9 and that of R2
is 93.10. The IP Addresses of R1 are 141.126.2.253, and 171.3.9.243. The IP
Address
es of R2 are 171.3.9.200, and 202.3.9.253.

Show how the IP,TCP, Link Layer headers look like on link A to R1, R1
to R2 and R2 to B. You only need to show the relevant field values given
above. If any field value is unknown or is not given, leave it bla
nk.



(15 points)

3.

In CSMA
-
CD exponential back
-
off algorithm, suppose that a host suffers
collision for three consecutive times and chooses values 1,3,6 randomly after first
collision, second collision, and third collision respectively. What are the
ret
ransmission delays? You can assume 10 Mbps Ethernet.

(10 points)

4.

True or False:

(a)

Quality of Service is present in today’s TCP/IP networks

(b)

Sequence number is used in TCP header to detect lost packets

(c)

IP V6 uses segmentation.

(d)

Address Resolution Protocol is u
sed to change IP Address to Physical
address and vice versa.

(e)

It is possible to have a network that does not use TCP/IP.

(f)

Flow control is designed to reduce congestion in a TCP/IP network.

(g)

Each LAN adapter has a unique LAN address.

(h)

The even parity bit scheme

can correct single bit errors.

(i)

Suppose the computer in your office has been configured with an IP
address, and you move (along with your computer) to an office down the
hall. If after the move your computer is connected to the same IP network,
then it is
not necessary to reconfigure the IP address in your computer.

(j)

Single
-
homed hosts have one interface and routers typically have two or
more interfaces.

(k)

Host A is sending host B a large file over a TCP connection. Assume host
B has no data to send A. Host B
will not send acknowledgements to host
A because host B cannot piggyback the acknowledgements on data.

(l)

Consider a HTTP Web server using persistent connections. Suppose the
server spawns a separate process for each client that connects to the
server. Then e
ach of these spawned processes will have different server
port numbers

(m)

The size of the TCP
RcvWindow

never changes throughout the duration
of the connection.

(n)

The TCP segment has a field in its header for
RcvWindow
.

(o)

The MSS is the maximum size of a TCP segm
ent including headers
.

(p)

In TCP, the acknowledgement number that a host puts in a segment is
the sequence number of the next byte the host is expecting from the
sender.

(q)

Suppose host A sends host B one segment with sequence number 38
and 4 bytes of data. Then

in this same segment the acknowledgement
number is necessarily 42
.

(r)

Suppose host A is sending a large file to host B over a TCP connection. If
the sequence number for a segment of this connection is m, then the
sequence number for the subsequent segment wi
ll necessarily be m+1.

(s)

The TCP segment has a field in its header for
RcvWindow
.

(t)

Suppose that the last
SampleRTT

in a TCP connection is equal to 1 sec.
Then
Timeout

for the connection will necessarily be set to a value >= 1
sec.

(40 points)


5.

Write a Java pr
ogram to implement the Link State algorithm with appropriate data
structures. You may use a two
-
dimensional array C[i,j] to store the link costs
from node i to j and an one
-
dimensional array D[v] to store the cost of the path
from the source node to desti
nation v and other arrays as needed. You can also
assume that the source node is always the node numbered 1.

(20 points)