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VELAMMAL INSTITUTE OF TECHNOLOGY

DEPARTMENT OF COMPUTER SCIENCE & ENGINEERING

IT6601 – MOBILE COMPUTING

UNIT III

TELECOMMUNICATION SYSTEMS

1. Define GSM. MAY!"UN #00$%

GSM (Global System for Mobile communication) is a digital mobile telephony system that is

widely used in Europe and other parts of the world. GSM uses a variation of time division

multiple access (TDM) and is the most widely used of the three digital wireless telephony

technologies (TDM! GSM! and "DM).

GSM digiti#es and compresses data! then sends it down a channel with two other streams of user data! each in its own time slot. $t operates at either the %&& M'# or && M'# fre*uency

 band.

#. Li' '(e '()ee *iffe)en' +,'e-)ie f e)/i+e f GSM. NOV!DEC #00$%

)

2(,' ,)e '(e '34e f e)/i+e in GSM5 MAY!"UN #01%

+earer services

Tele services

Supplementary services

7. 2(,' ,)e '(e '8 9,i+ +:,e f (,n*/e)5 APR!MAY #011%

There are two basic classes in handover,

H,)* (,n*/e); Switching between different antennas or different system is performed at a

certain point in time.Sf' (,n*/e); This is a new real mechanism in -MTS compare to GSM and this only available

in DD mode.

. Di'in-

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hard handover   is one in which the channel in the source cell is released and only then the

channel in the target cell is engaged. Thus the connection to the source is bro/en before or 0as0 the

connection to the target is made1for this reason such handovers are also /nown as break-before-

make.

 soft handover  is one in which the channel in the source cell is retained and used for a while in

 parallel with the channel in the target cell. $n this case the connection to the target is established

 before the connection to the source is bro/en! hence this handover is called make-before-break .

H,)* H,n* = Off

2ccurs in GSM

vailable in DD 3 TDD modes

$nter fre*uency handover! $nter system handover 

Sf' H,n* = Off 

2ccurs in -MTS

vailable only in DD mode

Macro diversity

>. 2(,' ,)e '(e *iffe)en' +n'): +(,nne:

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needed. This hides the identity of a user. The TMS$ is not forwarded to the '78. +ut instead

another temporary number reflects the location and any roaming re*uired is the MS89 is used

internally by the system.

@. 2(,' ,)e '(e e+

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Di,*/,n',-e

 9o end:to:end encryption of user data

8educed concentration while moving

Electromagnetic radiation

'igh comple?ity of system

Several incompatibilities within the GSM standards

11. 2(,' ,)e '(e e)/i+e 4)/i*e* 93

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1>. 2(,' ,)e '(e ne8 +?4nen' ,**e* ' GPRS ne'8)5 MAY!"UN #01#%

Two new components! called Gateway GB8S Support 9odes (GS9s) and! Serving GB8S Support

 9ode (SGS9) are added.

16. S4e+if3 '(e f

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  lways online devices F

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'34i+,: i-n,: ,n* , ?e,-e e

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guarantees. There is not even a IoS guarantee for a voice call F if the ne?t cell is already completely

 boo/ed the connection will brea/ upon entering this cell. (; mar/s)

>. H8 i 3n+()ni,'in ,+(ie/e* in GSM ,n* 8(3 i' i i?4)',n'5 H8 3'e? e+ithin each time:slot during transmission

a mid ample further improves synchronisation. The terminal itself is responsible for precise

synchronisation within the cell. This is very important in TDM systems as otherwise neighbouring

data may be destroyed.( < mar/s)

rame structure ( mar/)

Security mechanisms ( mar/)

ccess control and authentication. "onfidentiality

nonymity

Description of each mechanism ( < < 5 % mar/s)

Diagram ( mar/ 6 mar/)

UNIT IV

PART A

1. 2(,' ,)e '(e *iffe)en+e 9e'8een AODV ,n* '(e ',n*,)* *i',n+e /e+') ,:-)i'(?5 2(3 ,)e

e'enin nee*e*5 APR!MAY #00@%

2DA is capable of both unicast and multicast routing. $t is a reactive routing protocol! meaning that

it establishes a route to a destination only on demand 8outers use distance vector based routing

 protocols to periodically advertise the routes in their routing tables. 8outing information e?changed

 between typical distance vector based routers is unsynchroni#ed and unac/nowledged.

2DA is a reactive protocol. 8oute calculation is only performed if necessary. This improves

scalability under light load! but causes a higher initial latency.

#. 2(,' ,)e '(e *),89,+ f 8i)e* ne'8)5 APR!MAY #010% 8unning the wires from each room within the home can be a difficult tas/.

 9etwor/ cables can loo/ disorgani#ed.

 9etwor/ cables can disconnect or become faulty conse*uently causing the connection to fail.

dding more computers to a wired networ/ may result in une?pected e?pense if you run out of 

connections on your networ/ and could slow down the networ/.

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ll wired networ/s differ from each other. The most familiar type of wired networ/ is an Ethernet

networ/.

7. Di'in-

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S.

N

F,+') 2i)e* Ne'8) 2i)e:e Ne'8)  

A3??e')i+

:in

8outing algorithm asymmetric 8outing algorithm symmetric

;

Re*

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infrastructure). Multi:hop ad:hoc networ/s additionally do not re*uire that all nodes can receive each

other. 9odes may forward transmissions for other nodes. dvantages are the lower re*uired

transmission power (itKs Lust li/e whispering into the neighbourKs ear instead of shouting out loud)

and the increased robustness (failure of single nodes can be tolerated).

The topology of ad:hoc networ/s is dynamic in nature and changes in their topology are possible.

+ut to attain a reliable outptut *uality fre*uent changes can be avoided.

Due to wireless transmission their physical security is limited.

The capacity of these networ/s is lower when compared with wired networ/s.

They e?perience higher loss rates! higher delays and also the Litter than the fi?ed type of 

networ/s.

They use either e?haustible power supplies or batteries for getting energy. $n networ/ design it is

very important to consider power saving.

$n a perfect ad:hoc networ/K it has all the seven layers from physical layer to application layer.

$n designing an ad:hoc networ/ their e?ists high comple?ity with physical layer setups but in case

of mobile networ/s it will be ta/en care by their base stations.

The information related to networ/ density! lin/ failures! node distribution has to be clearly

defined for adhoc networ/s.

To obtain a better networ/ structure it is important that the M" layer and networ/ layer should

collaborate with each other.

The ad:hoc networ/ is independent of any central control or infrastructure.

7. Given the networ/ topology below! use the dynamic source routing algorithm to compute the shortest

 path from to all other nodes. Ma/e sure to show the results of the computation at each step.

() APR!MAY #00@%

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. >ith a suitable e?ample compare the behaviour of DSDA and DS8 algorithms with their routing

table or cache contentsJ(). NOV!DEC #00@%