Homework # 2

bluegooseexchangeNetworking and Communications

Oct 26, 2013 (3 years and 10 months ago)

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Networks


Homework

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H
omework must be printed and solved on the same paper.


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Saturday
,

24
/3/2012

(not late
homework will be accepted)







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2




1.

Write TRUE/FALSE for the following statements :


1
-

( )A property of flooding is that all nodes that are directly or indirectly
connected to the source node are visited.

2
-

( )

Random routing requires the use of network information.

3
-

(

)

A variety of techniques have been developed to cope with congestion and to
give different quality
-
of
-
service guarantees to different types of traffic.

4
-

(
) For the routing function to work, an increased number of routing messages

must be exchanged between nodes to alert each other to areas of congestion; this reduces
the capacity available for data packets.

5
-

( )Congestion control is difficult for a frame relay network because of the limited
tools available to the frame

handlers.

6
-

( )The SAN arrangement improves client
-
to
-
storage access efficiency, as well as
direct storage
-
to
-
storage communications for backup and replication functions.

7
-

( )Switches and hubs form the basic building blocks of most
local area networks.

8
-

( )

Each station attaches to the network at a repeater in the star topology and can
transmit data onto the network through the repeater.

9
-

( ) The choice for transmission medium and topology is critical in LAN
design.

10
-

( ) The bridge provides an extension to the LAN once modifications to the
communications software in the stations attached to the LAN are made.


2.

Choose the correct answer:

1.

The __________ function attempts to find the least cost route
through the network.

a)

ABR

b)

generic flow control

c)

routing

d)

management



2.

The simplest criterion in the selection of a route is to choose the _________ .

a)

maximum nodes available

b)

minimum hop route

c)

network resources

d)

maximum hop route


3.

With _________ the link costs
used in designing routes cannot be based on any dynamic
variable such as traffic.

a)

fixed routing

b)

flooding

c)

random routing

d)

adaptive routing


3


4.

The disadvantage of fixed routing is __________ .

a)

its simplicity

b)

its lack of flexibility

c)

it does not work with
datagrams

d)

it does not work with virtual circuits

5.

"Because all routes are tried, at least one copy of the packet to arrive at the destination
will have used a minimum
-
hop route" is a property of __________ .

a)

fixed routing

b)

random routing

c)

adaptive routing

d)

flo
oding

6.

With __________ , routing decisions that are made change as conditions on the network
change.

a)

fixed routing

b)

random routing

c)

adaptive routing

d)

flooding

7.

The principle conditions that influence routing decisions are _________ .

a)

failure and congestion

b)

route distance and amount of nodes

c)

overhead and bandwidth

d)

complexity and node malfunctions

8.

Which of the following is a drawback associated with adaptive routing?

a)

Because all routes are tried, at least one copy of the packet to arrive at the destination
will
have used a minimum hop route.

b)

Queue is an artificial measure of delay.

c)

All nodes that are directly or indirectly connected to the source node are visited.

d)

It may react too quickly, causing congestion producing oscillation, or too slowly, being
irrele
vant.

9.

Congestion control on the basis of ___________ is the responsibility of end systems and
does not require action on the part of network nodes.

a)

explicit signaling

b)

choke packets

c)

implicit signaling

d)

backpressure

10.

The ___________ specifies the mechanisms
for addressing stations across the medium
and for controlling the exchange of data between two users.

a)

LAN

b)

MAC

c)

LLC

d)

PDU


4



3.

Answer
the following Questions:

1
.

Apply Dijkstra’s routing algorithm and Bellman
-
Ford algorithm to the networks in the
following
Figure:

a)

























































5


b)



























































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2. Consider the problem of transmitting one file of K bits. We are
comparing packet
switching and circuit switching.

For the circuit
-
switched approach, it takes 1 second to set up the circuit. Once the circuit
is set up, the transmission occurs at 1Mbps and the signals take 50ms from the source to
the destination.

For the

packet
-
switched approach, the network transports the information as packets of
1kbits along lines with a transmission rate of 1Mbps; however, each packet must contain
additional information that amounts to 100 bits.

We neglect the packet switching delays.

The signals again take 50ms from the source to
the destination.

(a)

Calcu
late the delays to deliver the fi
le using circuit
-
switching.






(b)

Assume that in packet switching one sends one packet, waits until we get an
acknowledgement (assume that this takes 55ms

after the packet has been completely
received by the destination), then sends the next packet, and so on. Calculate how
long it takes to deliver the file.







(c)

Assume that we use packet switching but that we send all the packets back to back,
without
waiting for

acknowledgments. Calculate how long it takes to deliver the file.







(d) For what values of K is approach (a) faster than approach (c)?














7


3.
Consider sending voice from Host A to Host B over a packet
-
switched network (for
example,

Internet phone). Host A converts analog voice to a digital 64 kbps bit

stream on
the fl
y. Host A then groups the bits into 48
-
byte packets. There is one link between Host
A and B; its transmission rate is 1 Mbps and its propagation delay is 2 ms. As soon
as
Host A gathers a packet, it sends it to Host B. As soon as Host B receives an entire
packet, it converts the packet's bits to an analog signal. What is the maximum time that
elapses from the time a bit is created (from the original analog signal at Host

A) until the
bit is decoded (as part of the analog signal at Host B)?









































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4. Consider two hosts, Hosts A and B, connected by a single link of rate R bps. Suppose
that the two hosts are separated by m meters, and suppose

the propagation speed long the
link is s meters/sec. Host A is to send a packet of size L bits to Host B.

a) Express the propagation delay, d
prop

in terms of m and s ?


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b) Determine the transmission time of the packet, d
trans

in terms of L and R ?


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c)
Ignoring processing and queuing delays, obtain an expression

for the end to end

delay?




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d)
Suppose Host A begins to transmit the packet at time t=0. At time
t= d
trans

, where is
the last bit of the packet?


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e)
Suppose d
prop

is greater than d
trans

.At time t= d
trans

,Where is the first bi
t of the packet ?


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f) Suppose d
prop

is less than d
trans

.At time t= d
trans

,Where is the first bit o
f the packet ?


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g)Suppose s=2.5*10
8
,L=100 bits and R= 28kbps.Find the distance m so that d
prop
equal
d
trans
?


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h)
Suppose s=2.5*10
8
,L=100 bits and R= 28kbps.Find the distance m so that d=250 ms
and there is three identical routers t
hat each has 0.25 us processing?


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