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CS2402 Mobile and Pervasive Computing Anna University question paper , April/May 2008 Seventh Semester

Saturday, August 27, 2011 ·

B.E/B.Tech. Degree Examination, April/May 2008
                                                           Eighth Semester (Regulation 2004) 

Computer Science and Engineering 
IT 1402- Mobile Computing 
Part-A(10*2=20 marks)

1. Assume a receiver is located 10 km from a 150 W transmitter. The carrier frequency is 6 GHz and free space propagation is assumed, Gain at
transmitter is 1 dB and Gain at receiver is 1 dB.

(a) Calculate the transmit power in dBW.

(b) Find the power at the receiver in Watts.

2. What limits the number of simultaneous users in a TDM/FDM system compared
to a CDM system ? What happens to the transmission quality of connections
if the load gets higher on the cell ?

3. Consider the handoff procedure in GSM system that is based on relative
signal strength with threshold; that is, a mobile switches from one cell
to another if (a) the signal at the current BS is sufficiently weak (less
than a predefined threshold) and (b) the other signal is stronger than
the two. What are the drawbacks of this scheme, when the threshold is
too low or too high ?

4. State the different types of transport modes and channels used to carry
packets in Digital Audio Broadcasting.

5. In the Distributed Coordination Function(DCF) protocol of IEEE 802.11,
why does a Node wait only SIFS time units (after the last data packet
reception) before sending an ACK, while waiting DIFS time units before
attempting a data transmission ?

6. What are the advantages and problems of forwarding mechanisms in Bluetooth networks regarding security and power saving ?

7. How can DHCP be used for mobility and support of Mobile IP ?

8. What are the differences between AODV and the standard distance vector  algorithm ? Why are extensions needed ?

9. How and why does I-TCP isolate problems on the wireless link ? What are
the main drawbacks of this solution ?

10.Mention two WAP service providers. Find two cell phones supporting WAP and identify which WAP version they support.

                                                                  Part-B(5*16=80 marks)
11. (a) How does frequency reuse enhance cellular network capacity ? Besides
the number of users, what other major factor influences the decision
on cluster size ? A cellular system uses frequency spectrum 1800 MHz
to 1840 MHz for uplink channels and 1860 MHz to 1900 MHz for downlink
channels respectively. Each channel takes 200 KHz and can be shared
by 8 users. Each user needs one uplink and one downlink channel. How
many users can be supported without frequency reuse in this cellular
system ? [16]


(b) What is the use of spread spectrum ? Sketch the block diagram of the
Transmitter and Receiver of DSSS. Explain what each block does and
what the signal looks like (in time and/or frequency domains) at each
location in the block diagram with an example.[16]

12. (a) Name the main elements of GSM system architecture and describe their
functions. What are the advantages of specifying not only the radio
interface but also the internal interfaces of the GSM system ?
Explain the inter-BSC,intra-MSC handover process in the GSM system
using typical signals and a message sequence chart. Explain the
decision points and the resource allocation steps,if they exist.[16]


(b) What is DAB ? Explain the components,frame format and the protocol
used by DAB to access different formats of data also describe how
DVB is used for data broadcasting and to access high speed internet.

13. (a) (i) Using IEEE 802.11 (DCF): S1 and S2 send CBR/UDP traffic to the
common destination D. Consider S1,S2 and D all within receive
range of each other when the basic scheme is used (no RTS/CTS):
Describe a collision (what happens before,during and after).What
does the collision probability depend on ? When RTS/CTS is used:
What are the changes to the previous answers ? comment also on
the throughput and fairness. [16]


(b) (i) Describe the briefly how collision is avoided in HIPERLAN-1. [8]

(ii)Draw the protocol architecture of Bluetooth and explain briefly
the Base band layer and L2CAP of Bluetooth. [8]

14. (a) Given the network topology below, use the dynamic source routing
algorithm to compute the shortest path from A to all other nodes.
Make sure to show the results of the computation at each step.[16]

B --- D
|\ 1/ |
| \ / |
12| /\ |1
| /10\ |
A --- C -------- E
3 1


(b) Consider a mobile node MN from network X. The user of MN wishes to
communicate with a corresponding node CN in network Y. The node MN
moves from X to a foreign network A. Describe the sequence of
messages that are required in Mobile IPv4 so that MN and CN can
continue to communicate. Include both the user data messages and the
Mobile IP control messages. Now, consider the case where CN moves to
foreign network B while MN is still in the foreign network A. Can
CN and MN still communicate ? (Does Mobile IP support both endpoints
moving? ) Show the message flow to indicate how it will succeed or
fail in this case. [16]

15. (a) As a transport layer protocol, TCP uses a window mechanism to
exercise flow control over the best effort IP in the internet.
Flow control is exercised by the edge router based on congestion
status encountered in the core routers between teh TCP sender and
TCP receiver.

(i) Describe the operation of the window flow control mechanism. [8]

(ii)ACKs from the TCP receiver are the basis that the TCP sender
uses to adjust the sending window size. Describe and discuss
how ACKs are used for this purpose. [8]


(b) Specify the enhancements made to the basic client server architecture
of the web to suit a mobile wireless user ? Briefly discuss the main
goals of WAP. Expain the layers of WAP protocol used to achieve the
following : A client wants to have a shared state with the server
for transferring the content. [16]


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