UNIT I

1. What is mobile computing?

Mobile computing is a technology that allows transmission of data, via a computer,
without having to be connected to a fixed physical link.

2. What is Mobility?
• A person who moves
Between different geographical locations
Between different networks
Between different communication devices
Between different applications
• A device that moves
Between different geographical locations
Between different networks

2. What are two different kinds of mobility?

User Mobility: It refers to a user who has access to the same or similar
telecommunication services at different places.
Device Portability: many mechanisms in the network and inside the device have to
make sure that communication is still possible while the device is moving.

3. Find out the characteristics while device can thus exhibit during communication.
1. Fixed and Wired
2. Mobile and Wired
3. Fixed and Wireless
4. Mobile and Wireless

4. What are applications of Mobile Computing?

1. Vehicles
2. Emergencies
3. Business
4. Replacement of wired networks
5. Infotainment
6. Location dependent services
7. Mobile and wireless devices

5. What are the obstacles in mobile communications?

1. Interference
2. Regulations and spectrum
3. Low Bandwidth
4. High delays, large delay variation
5. Lower security, simpler to attack
6. Shared Medium
7. Adhoc-networks
6. Give the information’s in SIM?
1. Card type, serial no, list of subscribed services
2. Personal Identity Number(PIN)
3. Pin Unlocking Key(PUK)
4. An Authentication Key(KI)

7. Describe about MAC layer in DECT architecture.

The medium access control (MAC) layer establishes, maintains and releases channels
for higher layers by activating and deactivating physical channels. MAC multiplexes
several logical channels onto physical channels. Logical channels exist for signaling
network control, user data transmission, paging or sending broadcast messages.
Additional services offered include segmentation/reassembly of packets and error
control/error correction.

8. What are the basic tasks of the MAC layer?

Medium access Fragmentation of user data Encryption

9. What are the basic services provided by the MAC layer?

Asynchronous data service (mandatory)
Time-bounded service (optional)

10. What are the techniques used for MAC management?

Synchronization
Power management
Roaming
Management information base(MIB)

11. Define hidden terminal.

The transmission range of A reaches B but not C. The transmission range of C reaches B
but not A. B reaches A and C. A cannot detect C and vice versa.
A starts sending to B, but C does not receive this transmission. C also wants to send
something to B and senses the medium. The medium appears to be free, the carrier
sense fails. C also starts sending, causing a collision at B. But A can‟t detect this collision
at B and continues with its transmission. A is hidden for C and vice versa.

12.Limitations of Mobile Computing?

i)Resource constraints.
ii)Interface
iii)Bandwidth
iv)Dynamic changes in communication environment.
v)Network issues.
vi)Interoperability issues.
vii)Security Constraints.
13.Give the difference between the network 1G,2G,2.5G,3G mobile communication?
1G - Voice-only communication.
2G – Communicate voice as well as data signals.
2.5G – Enhancements of the second generation and sport data rates up to 100 kpbs.
3G – Mobile devices communicate at even higher data rates and support voice, data ,
and multimedia streams. High data rates in 3G devices enable transfer of video clips
and faster multimedia communication.

14.Agent-based Computing
An agent is any program that acts on behalf of a (human) user. A software mobile agent
is a process capable of migrating from one computer node to another.

15.Ubiquitous computing
Ubiquitous computing enhances computer use by making many computers available
throughout the physical environment, while making them effectively invisible to users.

16.Client-Server Computing
An architecture in which the client is the requesting machine and the server is the
supplying machine. The client contains the user interface and may perform some or all
of the application processing.

17. Define the term wireless?

Wireless telecommunications refers to the transfer of information between two or more
points that are not physically connected. Distances can be short, such as a few meters
for television remote control, or as far as thousands or even millions of kilometers for
deep-space radio communications. It encompasses various types of fixed, mobile, and
portable applications, including two-way radios, cellular telephones, personal digital
assistants (PDAs), and wireless networking.

18. Explain difference between wired and wireless networks

Wired Vs. Wireless Networks
Wired Networks Mobile Networks
- high bandwidth - low bandwidth
- low bandwidth variability - high bandwidth variability
- can listen on wire - hidden terminal problem
- high power machines - low power machines
- high resource machines - low resource machines
- need physical access(security) - need proximity
- low delay - higher delay

19. Types of Wireless Devices

Laptops Cell phones
Palmtops Pagers
PDAs Sensors
20. Why Mobile Computing?
Enable anywhere/anytime connectivity
Bring computer communications to areas without pre existing infrastructure
Enable mobility
Enable new applications
An exciting new research area

21.what are the New Forms of Computing available?.

Wireless Computing
Nomadic Computing
Mobile Computing
Ubiquitous Computing
Pervasive Computing
Invisible Computing

22.Mobile Communication Networks: Examples

GSM (Global System for Mobile Communications): worldwide standard for digital,
cellular Mobile Radio Networks
UMTS (Universal Mobile Telecommunications System): European Standard for future
digital Mobile Radio Networks
AMPS (Advanced Mobile Phone System): analog Mobile Radio Networks in USA
DECT (Digital Enhanced Cordless Telecommunications): European standard for
cordless phones
TETRA (Terrestrial Trunked Radio): European standard for circuit switched radio
networks
ERMES (European Radio Message System): European standard for radio paging
systems (Pager)
802.11: International standard for Wireless Local Networks
Bluetooth: wireless networking in close/local area
Inmarsat: geostationary satellite systems
Teledesic: planned satellite system on a non-geostationary orbit

23.Components of a wireless communication system

Transmitter, receiver, filter, antenna, amplifier, mixers

24.What are the disadvantages of small cells?

a) Infrastructure b) Handover c) Frequency

25. What are the benefits of reservation schemes?

a) Increased no other station is allowed to transit during this slot
b) Avoidance of congestion.
c) Waiting time in clearly known.
26. Define hidden terminal.
The transmission range of A reaches B but not C. The transmission range of C reaches B
but not A. B reaches A and C. A cannot detect C and vice versa. A starts sending to B,
but C does not receive this transmission. C also wants to send something to B and
senses the medium. The medium appears to be free, the carrier sense fails. C also starts
sending, causing a collision at B. But A can‟t detect this collision at B and continues with
its transmission. A is hidden for C and vice versa.

27.Mobile Computing - Characteristics

–Mobile devices –Anytime
•Laptops •Nomadic users
•Palmtops –Constraints
•Smart cell phones •Limited resources
–Requirements •Variable connectivity
•Data access: –Performance
–Anywhere –Reliability

28. What are the different types of modulation ?

The Modulation types are: i).Amplitude Modulation. ii).Frequency Modulation.
iii).Phase Modulation.

29. What are the multiplexing techniques ?

The Multiplexing techniques are: i)Space division multiplexing. ii)Time division
multiplexing. iii)Frequency division multiplexing. iv)Code division multiplexing.

30. Define Space Division Multiplexing Access?

Space division multiple access (SDMA) means division of the available space so that
multiple sources can access the medium at the same time. SDMA is the technique in
which a wireless transmitter transmits the modulated signals and accesses a space slot
and another transmitter accesses another space slot such that signals from both can
propagate in two separate spaces in the medium without affecting each other.

31. Define Code division multiplexing Access?

CDMA(Code Division Multiple Access) is an access method in which multiple users are
allotted different codes (sequence of symbols) to access the same channel (set of
frequencies)

31. Define Time division multiplexing Access?

Time division multiplexing (TDMA) is an access method in which multiple users, data
services, or sources are allotted different time-slices to access the same channel. The
available time-slice is divided among multiple modulated-signal sources. These sources
use the same medium, the same set of frequencies, and the same channel for
transmission of data.
32. Define Frequency division multiplexing Access?
Frequency division multiple access (FDMA) is an access method in which entails
assignments of different frequency-slices to different users for accessing the same
carrier.

33. Difference between Circuit Switching and Packet Switching?

CIRCUIT SWITCHING :
Circuit switching is a method of data transmission in which a circuit (Communication
channel or path) once established, continues to be used till the transmission is complete.
PACKET SWITCHING :
Packet switching is a means of establishing connection and transmitting data in which
the message consists of packets containing the data frames. A packet is a formatted
series of data, which follows a distinct path directed by a router from among a number
of paths, available at that instant.

34.What is the aim of ubiquitous computing? (AUT-NOV/DEC 2012)

• The aim of ubiquitous computing is to design computing infrastructures in such a
manner that they integrate seamlessly with the environment and become almost
invisible.
• Present everywhere bringing mobile, wireless and sensor Ubiquitous computing
(ubicomp) integrates computation into the environment, rather than having computers
which are distinct objects

35. What are the characteristics of mobile computing devices?

• Adaptation Data dissemination and Management
• Heterogeneity Interoperability Context awareness

36. What are the key constraints of mobile computing?

• unpredictable variation in network quality
• lowered trust and robustness of mobile elements

37. Define FDMA?

Frequency division multiple access (FDMA)
This comprises all algorithms allocating frequencies to transmission channels
according to the frequency division multiplexing (FDM).
Frequency can be fixed or dynamic

38. Define CDMA?

An access method in which multiple carriers, channels, or sources are allotted different
codes (Sequences and Symbols) to access the same channel (set of frequencies at the
same time in same space).

39. What is ALOHA?

The ALOHA net used a new method of medium access (ALOHA random access) and
experimental UHF frequencies for its operation, since frequency assignments for
communications to and from a computer were not available for commercial
applications in the 1970s. But even before such frequencies were assigned there were
two other media available for the application of an ALOHA channel – cables and
satellites. In the 1970s ALOHA random access was employed in the widely used
Ethernet cable based network and then in the Marisat (now Inmarsat) satellite network.
In the early 1980s frequencies for mobile networks became available, and in 1985
frequencies suitable for what became known as Wi-Fi were allocated in the US. These
regulatory developments made it possible to use the ALOHA random access techniques
in both Wi-Fi and in mobile telephone networks.

40. What are the advantages of cellular systems?

The advantages of cellular systems are,
Higher capacity
Less transmission power
Local interface only
Robustness

41. List out disadvantages of cellular systems. (Nov/Dec-2008)

(i) Self-jamming: Unless all of the mobile users are perfectly synchronized, the arriving
transmission from multiple users will not be perfectly aligned on chip boundaries. Thus
the spreading sequences of the different users are not orthogonal and there is some
level of cross correlation.
(ii) Near-far problem: Signals closer to the receiver are received with less attenuation
than signals farther away. Given the lack of complete orthogonality, the transmissions
from the more remote mobile units may be more difficult to recover. Thus, power
control techniques are very important in a CDMA system.
(iii) Soft handoff: A smooth handoff from one cell to the next requires that the mobile
unit acquires the new cell before it relinquishes the old. This referred to as a soft
handoff and is more complex than the hard handoff used in FDMA and TDMA
schemes.

42. Write a note on Piconet.

 Collection of devices connected in an ad hoc fashion
 One unit acts as master and the others as slaves for the lifetime of the piconet
 Master determines hopping pattern, slaves have to synchronize
 Each piconet has a unique hopping pattern
 Participation in a piconet = synchronization to hopping sequence
 Each piconet has one master and up to 7 simultaneous slaves (> 200 could be
parked

43. What is station and access point ?

Station :
Several nodes in the network are called stations or terminals with access
mechanisms to the wireless medium and radio contact to access points (AP).
Access Point :
Various stations are connected to Access Points, which connects the WLANs to
other network or to the other WLAN.

44.What is roaming?
Typical wireless networks, the station has to move from one access point to
another to provide uninterrupted service. Moving between access points is called
roaming.

45.State the three phases of the medium access of different competing nodes.
(Apr/May 2010)
 State sender has to sense the medium to see if it is free.
 If the medium is free the sender states for data and continues to listen to medium
 If it is busy the sender waits until it is free

46.What are the draw backs of wired networks? (Apr/May 2010)

 Infra Structure Required.
 It will not survive disaster
 It is not flexible.
 Planning is required to establish a wired network.
 Additional cabling with the right plugs and probably internetworking units have
to be provided.

47. What is difference between Piconet and Scatternet? (Nov/Dec 2013)

A piconet is the type of connection that is formed between two or
more Bluetooth-enabled devices, one device takes the role of 'master', and all
other devices assume a 'slave' role for synchronization reasons.
Scatternet is a number of interconnected piconets that supports
communicationbetween more than 8 devices. Scatternets can be formed when a member
of one piconet (either the master or one of the slaves) elects to participate as a slave in a
second, separate piconet.

UNIT II
1. State the Motivation for Mobile IP.
Routing-
Based on IP destination address, network prefix (e.g. 129.13.42) determines physical
subnet
Change of physical subnet implies change of IP address to have a topological correct
address (standard IP) or needs special entries in the routing tables
Specific routes to end-systems
 Change of all routing table entries to forward packets to the right destination
Does not scale with the number of mobile hosts and frequent changes in the
location, security problems
Changing the IP-address
Adjust the host IP address depending on the current location almost impossible to
find a mobile system, DNS updates take too long time
TCP connections break, security problems

2. What are the requirements for Mobile IP.(Nov/Dec 2013)

· Transparency
· Compatibility
· Security
· Efficiency and scalability

3. What are all the entities and terminologies needed for understandingMobile IP?
· Mobile Node (MN)
· Correspondent Node (CN)
· Home network
· Foreign network
· Home Agent (HA)
· Foreign Agent (FA)
· Care-of Address (COA)

4. Define Mobile Node(MN), Correspondent Node (CN),

A mobile node is an end system or router that can change the point of connection
to the network without changing its IP address. At least one partner is needed for
communication. The CN represents the partner for the MN. The CN can be a fixed or
mobile node.

5. Define Home Network and Foreign Network.

The home network is the subnet the MN belongs to with respect to its IP address.
Within the home network no mobile IP support is needed.
The Foreign Network is the current subnet the MN visits and which is not the
home network.

6. Define Home Agent (HA) and Foreign Agent (FA).

Home Agent (HA):
· System in the home network of the MN, typically a router
· Registers the location of the MN, tunnels IP datagrams to the COA
Foreign Agent (FA):
· System in the current foreign network of the MN, typically a router
· Forwards the tunneled datagrams to the MN, typically also the default router for
the MN
7. Define Care-of Address (COA)
· address of the current tunnel end-point for the MN (at FA or MN)
· actual location of the MN from an IP point of view e.g., via DHCP

8. What are the two different possibilities for the location of the COA?
· Foreign agent COA : The COA is an IP address of the FA.
· Co-located COA : The COA is called co-located if the MN temporarily acquired an
additional IP address with acts as COA.

9. What are the three alternatives exist for the implementation of an HA?
· The HA can be implemented on a router that is responsible for the home network.
· If changing the router‟s software is not possible, the HA could implemented on an
arbitrary node in the subnet.
· Finally, a home network is not necessary al all. The HA could be again on the „router‟
but this time only acting as a manager for MNs belonging to a virtual home network.

10. What is the main purpose of the registration in mobile IP ?

The main purpose of the registration is to inform the HA of the current location
for correct forwarding of packets. Registration can be done in two different ways
depending on the location of the COA.

11. Define Encapsulation and decapsulation.

Encapsulation :
Encapsulation is the mechanism of taking a packet consisting of packet header
and data and putting into the data part of a new packet.
Decapsulation.
The reverse operation, taking a packet out of the data part of another packet, is
called decapsulation.

12. In agent advertisement packet, Lifetime and Registration lifetime denotes what?
Lifetime : Lifetime denotes the length of time the advertisement is valid.
Registration lifetime : By the registration lifetime the agent can specify the
maximum lifetime in seconds a node can request during registration.

13. What is tunnel ?

A Tunnel establishes a virtual pipe for data packets between a tunnel entry and a
tunnel endpoint.

14. Mention different types of encapsulation.

1. IP-in-IP-encapsulation (mandatory)
2. Minimal encapsulation (optional)
3. Generic routing encapsulation
15. What is IP-in-IP-encapsulation ?
IP-in-IP-encapsulation represents tunnel between Home Address (HA) and Care Of
Address (COA).

16. What is Minimal encapsulation ?

 Avoids repetition of identical fields
 e.g. TTL, IHL, version, DS (RFC 2474, old: TOS)
 Only applicable for unfragmented packets, no space left for fragment
identification

17. What is Generic routing encapsulation ?

Generic routing encapsulation allows the encapsulation of packets of one protocol suite
into the payload portion of a packet of another protocol suite.

18. What is the function of recursion control field in generic routing encapsulation?
The recursion control field is an important field that additionally distinguishes
GRE from IP-in-IP and minimal encapsulation. This field represents a counter that
shows the number of allowed recursive encapsulation.

19. What is triangular routing ?

 sender sends all packets via HA to MN
 higher latency and network load

20. What are the additional messages needed by the optimized mobile IP ?
 Binding request
 Binding update
 Binding Acknowledgement
 Binding Warning

21. What is Agent Advertisement in Mobile IP ?

· HA and FA periodically send advertisement message in to their physical subnets.
· MN listens to these messages and detects, if it is in the home or a foreign network.
· MN reads COA from the FA advertisement messages.

22. In what way routing optimization is to be done ?

One way to optimize the route is to inform the CN of the current location of the
MN. The CN can thus learn the location by caching it in a binding cache which is a part
of the local routing table for the CN.

23. What are the severe problems associated with Reverse Tunneling ?
  Firewalls : Firewalls only allow packets with topologically correct addresses to
pass. However, MN still sends packets with its fixed IP address as source which
is not topologically correct in a foreign network.
 Multicast : An MN in the foreign network cannot transmit multicast packets in a
way that they emanate from its home network without a reverse tunnel.
 TTL : The TTL is low enough so that no packet s transmitted outside a
certain region.

24. How does the registration on layer 3 of a mobile node work?

Registration can be done in two different ways,
 If the COA is at the FA, and
 If the COA is co-located.

25. What advantages does the use of IPv6 offer for mobility? (Nov/Dec-2008)
 COA can be auto configured.
 No need for a separate FA instead all the routers perform routing advertisement.
 The address are always collocated COA.
 Sending a signal via HA not needed(Automatic path optimization)

26. Specify the fields of minimal encapsulation method in mobile network layer.
(Nov/Dec-2008)
Minimal encapsulation is an optional encapsulation method for mobile IP, which
comprises the following fields

27. What contains in Mobility binding ? (Nov/Dec 2011)

The Home Agent sets up a mobility binding containing the mobile node‟s IP
address and the current COA. Additionally, the mobility binding contains the lifetime
of the registration which is negotiated during the registration process.

28. What is reverse tunneling? (May/Jun 2012)

A reverse tunnel is a tunnel that starts at the care-of-address of the mobile node
and terminates at the Home Agent. It is a mechanishm, of taking a packet out of the
data part of another packet.

29. What are the two function’s of Transport Layer in the internet ?
The two function‟s of Transport Layer in the internet is checksumming over user
data and multiplexing / de multiplexing of data from/to applications. While the
network layer only addresses a host, ports in UDP or TCP allow addressing of
dedicated applications.

30. Differentiate TCP and UDP. (Apr/May 2010)

 The main difference between UDP and TCP is that TCP offers connections
between two applications. Within a connection TCP can give certain guarantees, such as
in-order delivery or reliable data transmission using retransmission techniques. Further,
TCP has built-in mechanisms to behave „network friendly‟. UDP on the other hand
provides a connectionless and unreliable datagram service. Furthermore, UDP does not
behave network friendly, i.e., does not pull back in case of congestion.

31. What is slow start and Fast retransmit ?

Slow start: TCP‟s reaction to a missing acknowledgement is quite drastic, but necessary
to get rid of congestion fast enough. The behavior TCP after the detection of congestion
is called slow start.
Fast retransmit: While transmission, there is a chance for simple packet loss due
to a transmission error. The sender can now retransmit the missing packet(s) before the
timer expires. This behaviour is called fast retransmit.

32. What are the advantages come with I-TCP ?

· I-TCP does not require any changes in the TCP protocol as used by the hosts in the
fixed network for other hosts in a wireless network that do not use this optimization.
· Due to the strict partitioning into two connections, transmission errors on the
wireless link.
· It is always dangerous to introduce new mechanisms into a huge network such as
the internet without exactly knowing their behaviour.

33. What are the disadvantages come with I-TCP ?

 The loss of the end-to-end semantics of TCP might cause problems if the foreign
agent partitioning the TCP connection crashes.
 In practical use, an increased handover latency may be much more problematic.
 The foreign agent must be a trusted entity because the TCP connections end at
this point.

34. What are the advantages of ‘snooping’ TCP ?

 Preservation of the end-to-end TCP semantic.
 No correspondent host needs to be changed, most of the enhancements are in the
foreign agent.
 It needs no handover of state as soon as the mobile host moves to another foreign
agent.
 It does not matter if the next foreign agent uses the enhancement or not.

35. What are the disadvantages of ‘snooping’ TCP ?

· Snooping TCP does not isolate the behaviour of the wireless link as good as I-TCP.
· Using negative acknowledgements between the foreign agent and mobile hosts
assumes additional mechanisms on the mobile host.
· All efforts for snooping and buffering data may be useless if certain encryption
schemes are applied end-to-end between the correspondent host and mobile host

36. State about M-TCP.

The M-TCP(Mobile TCP) prevent the sender window from shrinking if bit errors
or disconnection but not congestion cause current problems. M-TCP wants to improve
overall throughput, to lower the delay, to maintain end-to-end semantics of TCP, and to
provide a more efficient handover.

37. Why M-TCP needs a bandwidth manager ?

On the wireless side an adapted TCP is used that can recover from packet loss
much faster. This modified TCP does not use slow start, thus, M-TCP needs a
bandwidth manager to implement fair sharing over the wireless link.
38. What are the advantages of M-TCP ? (Nov/Dec-2008)
 M-TCP maintains the TCP end-to-end semantics
 If the MH is disconnected, M-TCP avoids useless retransmissions, slow starts or
breaking connections by simply shrinking the sender‟s window to 0.
 Since M-TCP does not buffer data in the SH AS I-TCP does, it is not necessary to
forward buffers to a new SH.

39. What are the disadvantages of M-TCP ? (Nov/Dec-2008)

· As the SH does not act as a proxy as in I-TCP, packets loss on the wireless link due
to the bit errors is propagated to the sender.
· A modified TCP on the wireless link not only requires modifications to the MH
protocol software but also new network elements like the bandwidth manager.

40. What are the advantages of fast retransmit/fast recovery approach ?

 The advantages of fast retransmit/fast recovery approach is its simplicity.
 Only minor changes in the mobile host‟s software already result in a
performance increase.
 No foreign agent or correspondent host has to be changed.

41. What are the disadvantages of fast retransmit/fast recovery approach ?

 Insufficient isolation of packet losses.
 Forcing fast retransmission increases the efficiency, but retransmitted packets
still have to cross the whole network between correspondent host and mobile
host.

42. What are the advantages of Transmission /time-out freezing approach ?

 It offers a way to resume TCP connections even after the longer interruptions of
the connectivity.
 It is the independent of the any other TCP mechanism.
43. What are the disadvantages of Transmission /time-out freezing approach ?
 Not only the software on the mobile host has to be changed.
 To be more effective, the correspondent node cannot remain unchanged.
 All mechanisms rely on the capability of the MAC layer to detect future
interruptions.

44. What is selective retransmission ?

A very useful extension of TCP is the use of selective retransmission. TCP
acknowledgements are cumulative, i.e, they acknowledge in-order receipt of packets up
to a certain packet. If the single packet is lost, the sender has to retransmit everything
starting from the lost packet.

45. What are the advantages of selective retransmission approach ?

 A sender retransmits only the lost packets.
 This lowers bandwidth requirements and helps especially in case of slow
wireless links.
 The gain in efficiency is not restricted to wireless links and mobile environment.

46. What are the disadvantages of selective retransmission approach ?

There might be minor disadvantage of more complex software on the receiver
side, because now more buffers are necessary to re sequence data and to wait for gaps
to be filled. But while memory sizes and CPU performance permanently increased, the
bandwidth of the air interface remains almost the same.

47. What is Transaction oriented TCP ?

T-TCP can combine packets for connection establishment and connection release
with user data packets. This can reduce the number of packets down to only two
instead of seven.

48.Why the TCP protocols used in wired networks cannot be as such used in wireless
networks? (Nov/Dec-2007)
While it is normal for TCP to assume congestion in the case of non receipt of ACK in a
fixed network. In a wireless network, the non receipt of ACK may be due to other
reasons. Moreover, packet loss in common in wireless networks. To accommodate these
situations, TCP used in wired networks cannot be used in wireless networks.

49. Define fast retransmit. (Nov/Dec-2008)

Fast retransmit: FR is an enhancement to TCP which reduces the time a sender waits
before retransmitting a lost segment. The fast retransmit enhances the works as follows
as follows if a TCP sender receives three duplicated acknowledgement with the
acknowledgement number the sender can be reasonably confident that the packet loss
due to transmission error. The sender now retransmits the missing packets before the
time expires. This behavior is called fast retransmit.
50. Can the problems using TCP for mobile communication is solved by replacing
TCP with snooping TCP? Justify your answer. (Nov/Dec-2008)
Yes.
Drawbacks of I-TCP:
 The one of the demerit of I-TCP is the segmentation of single TCP connection
into two TCP connections.
 This loses the original end-to-end semantic.
 This problem can be solved using snooping TCP.

51. How does I-TCP isolate problems on the wireless link? (April/May
2008),(May/Jun 2012)
(i) It doesn‟t require any changes in the TCP protocol.
(ii) Due to strict partitioning into wireless and fixed networks, transmission errors on
the wireless link cannot propagate into fixed network.
(iii) TCP performance can be improved using new mechanisms, with I-TCP only
between MH and foreign agent allows for testing different solutions without
jeopardizing the stability of the network.
(iv) Partitioning into two connections also allows the use of a different transport layer
protocol between the foreign agent and the MH or the use of compressed headers etc.
(v) Delay on wireless links will be higher than the delay on wired networks it will be
reduced by I-TCP.

52. Compare the different types of transmission errors that can occur in wireless and
wired networks. (May/June 2009)
§ Packet loss due to transmission errors:
Relatively low in fixed networks quit high in wireless networks/ large
variation/typically compensated by FEC/ARQ.
§ Packet loss due to congestion:
No difference between fixed and wireless networks.
§ Packet loss due to mobility:
Happens only in mobile networks

UNIT III
1. What are the three services offered by GSM ?
Three services offered by GSM are
· Bearer services
· Tele services
· Supplementary services
2. What are the tele services of GSM ?
GSM mainly focuses on voice oriented tele services. The main services are
· Telephony
· Emergency number
· Short message service
· Group 3 fax

3. State the three subsystems of GSM.

A GSM system consists of three subsystems,
 Radio Subsystems – it comprises all radio specific entities
· Network and switching subsystems – The NSS connects wireless networks with
standard public networks.
 Operating Subsystem – It contains all functions necessary for network operation
and maintenance.

4. What are the supplementary services offered by GSM ?

Supplementary services offer various enhancements for the standard telephony service.
Typical services are
· User identification
· Call redirection or forwarding of ongoing calls
· Closed user group
· Multiparty communication

5. What are the main task of the physical layer in GSM ?

The main tasks of the physical layer comprise channel coding and error
detection/correction, which is directly combined with the coding mechanisms. Channel
coding makes extensive use of different forward error correction(FEC) schemes. FEC
adds redundancy to user data, thus allowing for the detection and correction of selected
errors.

6. What are the four possible handover scenarios in GSM ?

The following are the four possible handover scenarios in GSM.
 Intra-cell handover
 Inter-cell, intra-BSC handover
 Inter-BSC, intra-MSC handover
 Inter MSC handover

7. What are the two basic reason for handover ?

There are two basic reasons for handover.
1. The mobile station moves out of the range of a BTS or a certain antenna of a BTS
respectively.
2. The wired infrastructure may decide that the traffic in one cell is too high and
shift some MS to other cells with a lower load.

8. State the security services offered by GSM.

The security services offered by GSM are explained in the following.
  Access control and Authentication : Authentication of valid user for the SIM
· Confidentiality : All user-related data is encrypted. After authentication, BTS and
MS apply encryption to voice, data and signals.
 Anonymity : To provide user anonymity, all data are encrypted before
transmission, and user identifiers which would reveal an identity are not used
over the air.

9. What are the channel types of GSM system?

i) GSM traffic channel
ii) GSM control channel
· Broad cost channel
· Common control channel
· Dedicated control channel

10. What is error correction code ?

A code in which each expression conforms to specific rules of construction so that
departures from this construction can be automatically detected and permits the
automatic correction of some or all of the errors.

11. What is Error detecting code ?

A code in which each expression conforms to specific rules of constructions so that if
certain errors occur in an expression, the resulting expression will not conform to the
rules of construction and thus the presence of the errors is detected.

12. What is FEC ?

FEC stands for forward error correction, it is a procedures whereby a receiver, using
only information contained in the incoming digital transmission, a receiver corrects bit
errors in the data.

13. What are the switches and databases consists of NSS ?

The Network and Switching subsystem consists of the following switches and
databases,
 Mobile services switching centre (MSC)
 Home location register (HLR)
 Visitor location register (VLR)

14. What is the function of operation subsystem(OSS) ?

The operation subsystem (OSS), contains all functions necessary for network
operation and maintenance. The OSS possess the following entities;
 Operation and maintenance centre (OMC)
 Authentication centre (AuC)
 Equipment identity register (EIR)
15. What is burst and burst error ?
Burst :Data is transmitted in small portions, called burst.
Burst error :A burst error of length B is a contiguous sequence of B bits in which the
first and last bits and any number of intermediate bits are received in error.

16. What is the use of training sequence field in GSM TDMA frame?
The training sequence in the middle of a slot is used to adapt the parameters of the
receiver to the current pat propagation characteristics and to select the strongest signal
in case of multi path propagation.

17. What is the use of guard space in GSM TDMA frame?

The guard space is used to avoid overlapping with other bursts due to different path
delays and to leave the transmitter time to turn on and off.

18. What is the use of different burst in GSM TDMA frame ?

Frequency correction burst : allows the MS to correct the local oscillator to avoid
interference with neighboring channels.
Synchronization burst : synchronizes the MS with the BTS in time.
Access burst : used for the initial connection setup between MS and BTS.
Dummy burst : it is used if no data is available for a slot.

19. What is the purpose of comfort noise generated by physical layer of GSM ?
In voice data transmission, during periods of silence (e.g., if a user needs time to
think before talking), the physical layer generates a comfort noise to fake a connection
(complete silence would probably confuse a user), but no actual transmission takes
place.

20. What is the use of TMSI ?

TMSI is a temporary mobile subscriber identity, it is used to hide the IMSI, which
would give away the exact identity of the user which is signaling over the air interface.

21. What are the numbers needed to locate and address MS in GSM system ?
To locate an MS and to address the MS, the following numbers are needed,
 Mobile station international ISDN number (MSISDN)
 International mobile subscriber identity (IMSI)
 Temporary mobile subscriber identity (TMSI)
 Mobile station roaming number (MSRN)

22. What are the security services offered by the GSM ?

The security services offered by the GSM are,
 Access control and authentication
 Confidentiality
 Anonymity
23. What are the three algorithms have been specified to provide security services in
GSM?
The three algorithms have been specified to provide security services in GSM
are,
 Algorithm A3 : used for authentication
 Algorithm A5 : used for encryption
 Algorithm A8 : used for generation of a cipher key.

24. What is challenge-response method ?

In GSM, authentication uses a challenge-response method: the access control AC
generates a random number RAND as challenge, and the SIM within the MS answers
with SRES (signed response) as response. Both sides, network and subscriber module,
perform the same operation with RAND and the key Ki called A3. The MS sends back
the SRES generated by the SIM, the VLR can now compare both values. If they are the
same, the VLR accepts the subscriber, otherwise the subscriber is rejected.

25. What is GPRS ?

GPRS stands for general packet radio service, it is a more flexible and powerful
data transmission technique. GPRS provides packet mode transfer for applications.

26. What is the big difference between GSM and DECT ?

A big difference between GSM and DECT exists in terms of cell diameter and cell
capacity. While GSM is designed for outdoor use with a cell diameter of up to 70 km,
the range of DECT is limited to about 300 m from the base station.

27. Differentiate symmetric and asymmetrical communication system (Nov/Dec-

2008)
Sl.No. Symmetrical Communication Asymmetrical Communication
System System
1. Channel characteristics from Refers to any system in which the
one direction to other and vice- data speed or quality differ in one
versa are same. direction as compared with other
direction.
2. Bandwidth , transmission Differences in transmission power,
power, cost factor are same on antenna characteristics.
both direction.

28. How much of the original GSM network does GPRS need? Which elements of
the network perform the data transfer? (Nov/Dec-2008)
GPRS is an enhancement of GSM. It uses same physical channel as GSM and only new
logical GPRS radio channels are defined. Elements needed for data transfer:
¨ GPRS Support Nodes(GSN)
¨ Gate way GPRS Support Node(GSN)
¨ Serving GPRS Support Node(SGSN)
¨ GPRS Register(GR)
29. What are the reasons for delays in GSM for packet data traffic? (April/May 2008)
(i) Different data rates provided by traffic channels are low.
(ii) Authentication and encryption also makes the packet data transmission slow.
(iii)Various interferences and noises from the channel also courses delay.

30. State the objectives of UMTS. (April/May 2008)

One initial enhancement of GSM toward UMTS was Enhanced Data rates for Global
Evolution (EDGE), which uses enhanced modulation (SPSK) and data rates upto
384kbits/s using 200 kHz wider carrier.

31. What are the general problems of satellite signals traveling from a satellite to a
receiver? (Nov/Dec-2008)
Terrestrial object that would block the LOS, may result in attenuation of the signal
absorption or in distortion due to multipath reflection. Atmospheric attenuation is
greater at low elevation angle because the signal traverse the atmosphere for longer
distances. Electrical noise generated by the earth‟s heat near its surface adversely affects
reception.

32. What are the reasons for delays in GSM for packet data traffic? (May/June 2009)
Connection setup(some seconds), FEC coding/decoding and interleaving(about 100
ms), Propagation delay(some ms).

33. Differentiate hard and soft hand-off (April/May 2008), (Apr/May 2010)
Sl.No. Hard Handoff Soft Handoff
1. UTRA TDD can only use this This is available only in FDD mode
type
2. All inter system handovers are UE receives data from different
hard handovers. antennas at the same time makes a
handover soft.

34. What are the two basic classes of handover? (Nov/Dec 2011)
There are two basic classes in handover:
(i)Hard handover: Switching between different antennas or different system is
performed at a certain point in time.
(ii)Soft handover: This is a real mechanism in UMTS compare to GSM and this is
available in FDD mode

35. Define Elevation angle? (Nov/Dec 2011)

The elevation angle is defined as an angle between the centre of satellite beam and the
plane tangential to the earth‟s surface.

36. Which are the new components added to GPRS networks? (May/Jun-2012)
Serving GPRS Support Node(SGSN),
Gateway GPRS Support Node(GGSN)

37. Why are so many different identifiers/addresses needed in GSM? (May/Jun-2012)

Users of GSM systems works with telephone numbers. This phone numbers are
completely independent of the current location of the user. The system itself needs
some additional information. However, it must not reveal the identity of users. The
international identification of users is done with the IMSI. During operation within a
location area, only a temporary identifier, the TMSI is needed. This hides the identity of
user. The TMSI is not forwarded to the HLR. But instead another temporary number
reflects the location and any roaming required is the MSRN is used internally by the
system.

38. What are the effects of multipath propagation?( Nov/Dec 2013)

The effects of multipath include constructive and destructive interference, and phase
shifting of the signal. In digital radio communications (such as GSM) multipath can
cause errors and affect the quality of communications.

39. What is polling? ( Nov/Dec 2013)

Where one station is to be heard by others(Base Station of mobile network or any other
dedicated system) polling scheme can be applied. Polling is a strictly centralized
scheme with one master station and several Slave station.

UNIT IV

1. What are all the areas the Ad hoc networks are used?
 Instant infrastructure
 Disaster relief
 Remote areas
 Effectiveness

2. What is the function of Dynamic Source Routing? (Apr/May 2010)

Split routing into discovering a path and maintaining a path
Discover a path:
Only if a path for sending packets to a certain destination is needed and no path is
currently available
Maintaining a path:
Only while the path is in use one has to make sure that it can be used continuously
3.What are the fundamental differences between wired networks and ad hoc
networks related to routing ?
 Asymmetric links
 Redundant links
 Interference
 Dynamic topology

4.What is the problem of proactive routing? (May/Jun 2012)

Count to infinity problem: It performs extremely poor with certain network
changes.

5. What are the two things DSDV adds to the distance vector algorithm ?
 Sequence numbers : Sequence no. help to apply the advertisement in correct
order.
 Damping : Transient changes in topology that are of short duration
should not destabilize the routing mechanism.

6. What are the work done by a node while it receives a route request ?
 If the node has already received the request, it drops the request packet.
 If the node recognizes its own address as the destination, the request has reached
its target.
 Otherwise, the node appends its own address to a list of traversed hops in the
packet and broadcasts this updated route request.

7. What is Ad hoc networks ?

Ad hoc networks, do not need any infrastructure to work. Each node can
communicate with another node, no access point controlling medium access is
necessary.

8. What is the necessity of routing in infrastructure network ?

The routing is needed to find a path between source and destination and to
forward the packets appropriately.

9. What is distance vector routing ?

 Periodic exchange of messages with all physical neighbors that contain
information about who can be reached at what distance.
 Selection of the shortest path if several paths available.

10. How dynamic source routing divides the task of routing into two separate
problems ?
The Dynamic source routing divides the task of routing into two separate problems :
 Route discovery: A node only tries to discover a route to a destination if it has to
send something to this destination and there is currently no known route.
  Route maintenance: If a node is continuously sending packets via a route, it has
to make sure that the route is held upright. As soon as a node detects problems
with the current route, it has to find an alternative route.
11. Discuss some of the routing metrics to be considered in a mobile network layer.
(Nov/Dec-2007)
(i) Destination Sequence Distance Vector (DSDV).
(ii) Dynamic Source Routing (DSR)
(iii) No. of hops in each route.

12. What could be quick ‘solutions’ and why don’t they work? (Nov/Dec-2008)
 Change of all routing table entries to forward packets to the right destination and
frequent changes in the location, and security problem needs a quick solution by
assigning the computer a new topologically correct IP address.
 Adjust the host IP address depending on the current location.
 Mobile nodes would have to notify all communication parties about new
address.
 Router always chooses the best filling prefix for the routing decision.

13. Why is routing in multi-hop ad-hoc networks complicated? (April/May 2008)

The routing in multi-hop ad-hoc network is complicated because,
(i) Traditional routing algorithms will not work efficiently.
(ii) Routing in wireless ad-hoc cannot rely on layer three knowledge alone.
(iii) Centralized approaches will not work, because it takes too long to collect the
current status.
(iv) Forwarding a packet in the case of unknown topology is flooding.

14. What are the difference between AODV and the standard distance vector
algorithm? (May/June 2009)
Dynamic Source Routing (DSR):
The key distinguishing feature of DSR is the use of source routing. Dynamic DSR is are
active protocol i.e. it doesn‟t use periodic advertisements. It computes the routes when
necessary and then maintains them. Source routing is a routing technique in which the
sender of a packet determines the complete sequence of nodes through which the
packet has to pass, the sender explicitly lists this route in the packet‟s header,
identifying each forwarding “hop” by the address of the next node to which to
transmit the packet on its way to the destination host.
AdHoc On-Demand Distance Vector Routing (AODV):
AODV is essentially a combination of both DSR and DSDV. It borrows the basic on-
demand mechanism of Route Discovery and Route Maintenance from DSR, plus the use
of hop-by-hop routing, sequence numbers, and periodic beacons from DSDV. It uses
destination sequence numbers to ensure loop freedom at all times and by avoiding the
Bellman-Ford ”count-to -infinity” problem offers quick convergence when the ad hoc
network topology changes
15. Define MANET.
MANET - Mobile Adhoc NETworks. Continuously self-configuring, infrastructure-less
network of mobile devices connected without wires.There are several specialized MANETs
such as wireless sensor networks(WSNs) and vehicular adhoc networks(VANETs).

16. Write any two design issues of MANET.

 Network size and node density
 Connectivity
 Network topology
 User traffic
 Operational environment
 Energy constraint

17. Difference between cellular and Ad-Hoc Networks

18. What are the functions of each node in MANET?

a. Forward the packet to the next hop
Before forwarding, Sender has to ensure that the packet moves towards its destination
b. the number of hops(path length) to destination is minimum
c. Delay is minimized
d. Packet loss is minimum through the path
. Path does not have a loop
19. Comparison of Link state and Distance vector.
 20. List the Types of Communications.
Unicast
Message is sent to a single destination node
Multicast
 Message is sent to a selected subset of network nodes
Broadcast
 Broadcasting is a special case of multicasting
 Message is sent to all the nodes in the network
21. Define Proactive (table-driven) protocols.
Also known as table-driven routing protocols. Each node in the routing table maintains
information about routes to every other node in the network.
Tables are updates frequently due to
Changes in network topology
Node Movements
  Nodes shutting down
Nodes can determine the best route to a destination
 Generates a large number of control messages to keep. The routing tables up-to-date
Generates overhead which consumes large part of available bandwidth
22. Compare MANET Vs VANET

23. How security threats in MANET are different from wired network?
Wired intruder is host that is outside the network and can be controlled through firewall
and subjected to access control and authentication
In MANET, intruder is part of network, and therefore much more difficult to detect and
isolate.

24. Why routing in Multi-hop ad hoc network is complicated

25. Compare Proactive and Reactive routing protocols in MANET.
Proactive
Also known as table-driven routing protocols. Each node in the routing table maintains
information about routes to every other node in the network.
Tables are updates frequently due to
Changes in network topology
Node Movements
  Nodes shutting down
 Nodes can determine the best route to a destination
 Generates a large number of control messages to keep. The routing tables up-to-date
Generates overhead which consumes large part of available bandwidth
Reactive
Also called as On-demand routing protocol
Nodes do not maintain up-to-date routing information
New routes are discovered only when required
Uses flooding technique to determine the route
Flooding technique is used when the node does not have routing knowledge

26. Reactive protocols are mostly preferred for MANET-Justify

27. List out the important classes of MANET Routing Protocols (explain)

28. Difference between active and passive attacks in MANET

Page no 140
29. What are the uses of VANET
 The driver can get road condition ahead or a warning about the application of emergency
electronic brake by a vehicle ahead in the lane.
 Drivers may have the opportunity to engage in other leisurely tasks, VoIP with family,
watch news and participate in an office video conference etc
 Two vehicles are involved in a collision. The trailing vehicle get advance notification of
the collision ahead on the road.
30. For every layer of MANET, list out one type of security attack
Page no 141
31. What are the important characteristics of secured ad hoc network
 Availability – able to survive denial of service(DOS)
 Confidentiality- Prevent unauthorized users to access confidential information
 Integrity- no tampering of transmitted messages.
 Authentication – Guarantee about the true identity of peer node
 Non-repudiation- Should ensure that a node having sent a message can not deny it.

UNIT V
1.Define Operating System.
Interface between hardware and user
Manages hardware and software resources of the system
Provides set of services to application programs
2.Name the features of Operating System.
• Multitasking
• Scheduling
• Memory Allocation
• File System Interface
• Keypad Interface
• I/O Interface
• Protection and Security
• Multimedia features
3. How is the operating system structured?
Kernel Layer
Shell Layer
4. Give the types of Operating System.
Monolithic Kernel
Micro kernel
5. Specify the motivation of Monolithic Kernel OS design.
Kernel contains the entire OS operations except shell code
Motivation
o OS services can run more securely and efficiently in supervisor mode
6. Mention the examples of Monolithic Kernel OS design.
Windows
Unix
7. List the Advantages of Monolithic Kernel OS design.
Provides good performance
Always runs in supervisor mode
More efficient and secure
8. List the disadvantages of Monolithic Kernel OS design.
o Makes kernel
• Massive
Non-modular
Hard to tailor
• Maintain
Extend
Configure
9. List the disadvantages of Microkernel OS design.
• Flexible
• Modular
Easier to port
Easy to extend and implement
10. List the disadvantages of Microkernel OS design,
Difficult to debug compared to application programs
Bog in the kernel crashes the system and the debugger
Non- reliable
11. What is Mobile OS?
Facilitate third party development of application software
Allow manufacturers of different brands of mobile devices to build their choice
set of functionalities for the users
12. Give some examples of Mobile OS.
• Windows Mobile
• Palm OS
• Symbian OS
• iOS
• Android
• Blackberry
13. What are the five parts in Android architecture or Android software stack?
Application Layer
Application Framework
Android Runtime
Native libraries (Middleware)
Linux kernel
14. What are the Key services provided in Application Framework?
• Activity Manager
• Content Providers
• Resource Manager
• Notifications Manager
• View System
15. List the Native libraries in Android architecture.
WebKit - web browser engine
OpenGL
FreeType - font support
• . SQLite - SQL database
Media - playing and recording audio and video formats
MP3
MPEG-4 ,
• C runtime library (libc) etc
16.Mention the responsibilities of Linux Kernel.
• Device drivers
• Power management
• Networking Functionalities .
• Memory management
• Device management
• Resource access
17. What is M-Commerce?
• M-Commerce stands for Mobile Commerce
• Buying and selling of goods and services through mobile handheld devices
18. Compare B2C and B2B.