MOBILE COMPUTING
UNIT I WIRELESS COMMUNICATION FUNDAMENTALS
Part- A
1.
Define
SAMA.
Spread Aloha Multiple Access is a combination
of CDMA and TDMA. The
CDMA better suits for connection oriented
services only and not for connection less
bursty data traffic because it requires to
program both sender and receiver to access
different users with different codes.
2. Define CDMA.
Code Division Multiple Access systems use
codes with certain characteristics to separate different users. To enable
access to the shared medium without interference. The users use the same
frequency and time to transmit data. The main problem is to find good codes and
to separate this signal from noise. The good code can be found the following 2
characteristic 1.Orthogonal, 2.AutoCorrelation.
3. What are the several versions in CSMA?
There are several versions in CSMA, they are
as follows
a) Non-persistent CSMA
b) p-persistent CSMA
c) 1-persistent CSMA
4.
What is meant by non-persistent CSMA?
In, non-persistent CSMA, stations sense the
carrier and start sending immediately
if the medium is idle., if the medium is
busy, the station pauses a random amount of time
before sensing the medium again and repeating
this pattern.
5. What is meant by p-persistent CSMA?
In p-persistent CSMA system nodes also sense
the medium, but only transmit with a
probability of p. With the station deferring
to the next slot with the probability 1-p,
i.e. access is slotted in addition.
6. What is SDMA?
Space Division Multiple Access (SDMA) is used
for allocating separated spaces to users
in wireless networks. The basis for the SDMA
algorithm is formed by cells and
sectorized antennas which constitute the
infrastructure implementing space division
multiplexing (SDM)
7. What is FDD?
In FDMA, the base station and the mobile station
establish a duplex channel. The two
directions, mobile station to base
station and vice versa are separated using different
frequencies. This Scheme is called Frequency
Division Duplex (FDD)
8. What are the 2 sub layers in DLC?
Logical Link Control (LLC)
Media Access Control (MAC)
9. List out the advantages of frequency division
multiplexing.
·
no dynamic coordination necessary
·
works
also for analog signals
10. List out the disadvantages of frequency
division multiplexing.
- waste of bandwidth if the traffic is
distributed unevenly
- inflexible
- guard spaces
A channel gets the
whole spectrum for a certain amount of time
12. List out the advantages of time division
multiplexing.
- only one carrier in the
medium at any time - throughput high even
for many users
- precise
- synchronization
- necessary
14. Define
code division multiplexing.
àEach channel has a unique code
à
All channels use the same spectrum at
the same time
15. Define Signal
physical representation of data
function of time and location
signal parameters: parameters representing
the value of data
16. Define Analog modulation.
shifts center frequency of base band signal up
to the radio carrier
What is Quadrature Amplitude Modulation?
Quadrature Amplitude
Modulation (QAM): combines amplitude and phase modulation
it is possible to code n bits using one
symbol
2n discrete levels, n=2 identical to QPSK
bit error rate increases with n, but less
errors compared to comparable PSK schemes
18. What is
digital modulation?
* Digital data is
translated into an analog signal (baseband)
* ASK, FSK, PSK -
main focus in this chapter
* Differences in spectral efficiency, power
efficiency, robustness
UNIT II TELECOMMUNICATION SYSTEMS
Part
A
1) What are the four types of handover
available in GSM?
1. Intra cell Handover
2. Inter cell Intra BSC Handover
3. Inter BSC Intra MSC handover
4. Inter MSC Handover
2) What are the categories of Mobile services?
• Bearer services
• Tele services
• Supplementary services
3)
What are the services provided by supplementary services?
• User identification
• Call redirection
• Call forwarding
• Closed user groups
• Multiparty Communication
4) What are types of Handover?
Intra-cell handover
Inter-cell, intra- BSC handover
Inter-BSC, intra-MSC handover
Inter MSC handover
5) What is meant by GPRS?
The General Packet Radio Service provides
packet mode transfer for applications
that exhibit traffic patterns such as frequent
transmission of small volumes.
6) What are subsystems in GSM system?
• Radio subsystem (RSS)
• Network & Switching subsystem (NSS)
• Operation subsystem (OSS)
7) What is the information in SIM?
• Card type, serial no, list of subscribed
services
• Personal Identity Number (PIN)
• Pin Unlocking Key (PUK)
• An Authentication Key (KI)
8) Define Normal
Burst?
The frame used for normal data transmission
within a time slot is called Normal Burst.
9) What are the logical channels in GSM?
• Traffic channel(TCH) • Control channel(CCH)
10) What is the function of Medium Access
Control Layer?
The functions of Medium Access Control Layer
is responsible for establishes,
maintains, and releases channels for higher
layers by activating and deactivating physical channels.
11) What is Handover?
The satellite is the base station in
satellite communication systems and that itself is moving. So, additional
instance of handover are necessary due to the movement of the satellite
1. Intra Satellite handover:
2. Inter Satellite handover.
3. Gateway handover.
4. Inter System handover.
12) What is MSC?
Main Service Channel (MSC) carries all user
data.
eg. audio, multimedia data.
13) What is FIC?
The Fast Information Channel (FIC) contains
Fast Information Block (FIB) with 256bits each(16 bit checksum). An FIC carries
all control information which is required for interpreting the configuration
and content of the MSC.
14) What are the different types of disk?
• A flat disks
• Skewed disks
• Multi disks
15) What are the goals of DVB?
The goal of DVB is to introduce digital TV
broadcasting using satellite transmission (DVB-5) cable technology (DVB-c) and
terrestrial transmission (DVB-7).
16) Name some of the formats supported by
MOT?
• Multimedia and Hypermedia information coding
experts group (MHEG)
• Join photograph’s experts group (JPEG)
• American standard code for information
interchange (ASCII)
• Moving pictures expert group (MPEG)
• Hypertext markup language (HTML)
• Hypertext transfer protocol (HTTP)
• Bitmap (BMP)
• Graphics interchange format (GIF)
17) Give structure MOT object.
7bytes
variable size
variable size
Header core
Header Extension Body
Header core: contain the size of the header
and body and the content type of the object.
Header Extension: contains additional object
handling data such as repetition distance to support caching, segmentation
information and priority of the data.
Body: contains arbitrary data to be
transmitted.
18) What are different interleaving and
repetition schemes applied by DAB to objects and
segments?
1. Object Repetition.
2. Interleaved Objects.
3. Segment repetition.
4. Header repetition.
19) What are the advantages of DAB?
1. DAB can offer sound in CD like quality.
2. DAB can use single frequency network where
all senders transmitting the same radio program can operate at the same
frequency.
3. DAB use VHF and UHF frequency bands.
4. DAB uses DQPSK modulation scheme.
5. DAB user COFDM and FEC.
6. DAB can transmit up to six stereo audio
programmes with a data rate of 192kbit/s each.
20) What is object repetition?
DAB can repeat objects several times. If an
object A consists of four segments (A1,A2,A3,A4) a single repetition pattern
would be A1A2A3A4A1A2A3A4A1A2A3A4……..
21) What is EIT?
Event Information Table (EIT) contains status
information about the current transmission and some additional information for
set-top boxes.
22) What is the service information sent by
DVB?
Digital Video Broadcast Containers are
basically MPEG-2 frames. DVB sends service information. This information is,
1. Network information table (NIT).
2. Service Description Table (SDT).
3. Event Information Table (EIT).
4. Time and Date Table (TDT)
23) What are the advantages of DVB?
1. Data rates planned for users are
6-38mbit/s for the downlink and 33-100kbit/s for the uplink.
2. Transmitted along with TV programmes and
doesn’t require additional lines or hardware per customer.
3. Can be used in remote areas and developing
countries where there is no high bandwidth wired network.
24) What is meant by beacon?
A beacon contains a timestamp and other management
information used for power management and roaming.
e.g., identification of the base station subsystem
(BSS)
25) What is Active scanning?
Active scanning comprises sending a probe on
each channel and waiting for response. Beacon and Probe response contain the
information necessary to join the new BSS.
26) What is Passive Scanning?
Passive Scanning Simply means listening into
the medium to find other networks, i.e. receiving the beacon of another network
issued by the synchronization function within an access point.
UNIT III WIRELESS NETWORKS
Part A
1) What is the primary goal of IEE 802.11?
The primary goal of the standard was the
specification of a simple, robust, WLAN which offers time bounded and
asynchronous services also it should be able to operate with multiple physical
layers.
2) What is meant by SIFS?
SIFS means Short Inter Frame Spacing. The
shortest waiting time defined for short control message such as
acknowledgements or polling response.
3) What are Advantages of wireless LAN?
Flexibility, Planning, Design, Robustness,
Quality Service, Cost, Proprietary Solution, Restriction, Safety and Security
4) What are Design Goals of Wireless LAN?
Global Operation
Low Power
License-free Operation
Robust transmission technology
Simplified spontaneous co-operation
Easy to use
Protection of investment
Safety and Security
Transparency for application
5) What are the three Low Power States
provided by Bluetooth?
PARK state
HOLD state
SNIFF state
6) What is SCO?
SCO-stands for Synchronous Connection
Oriented Link
Standard telephone (voice) connection
requires symmetrical, circuit-switched, point-to point connections. For this
type of link, the master reserves two consecutive slots at fixed intervals.
7) What are the three phases in EY-NPMA?
i. Prioritization: Determine the highest
priority of a data packet ready to be sent on
competing nodes.
ii. Contention: Eliminate all but one of the
contenders, if more than one sender has
the highest current priority.
iii. Transmission: Finally, transmit the
packet of the remaining node.
8) What are Advantages and Disadvantages of
Infrared?
Advantages:
i. Simple & extremely cheap senders and
receivers which integrated in almost all mobile devices
ii. No licenses are needed for infrared
technology and shielding is very simple.
iii. Electrical devices do not interfere with
infrared transmission.
Disadvantages:
i. Low bandwidth
ii. Quite easily shielded
iii. Cannot Penetrate
9) What are the system integration functions
of MAC management?
• Synchronization
• Power management
• Roaming
• Management information base (MIB)
10) What do you meant by roaming?
Moving between access point is called
roaming. Even wireless networks may require more than one access point to cover
all rooms. In order to provide uninterrupted service, we require roaming when
the user moves from one access point to another.
11) What is mobile routing?
Even if the location of a terminal is known
to the system, it still has to route the traffic through the network to the
access point currently responsible for the wireless terminal.
Each time a user moves to a new access point,
the system must reroute traffic. This is known as mobile routing.
12) What are the functions which support
service and connection control?
>Access point control function
>Call control and connection control
function
>Network security agent
>Service control function
>Mobility management function
13) What are the examples for service
scenarios identified in WATM ?
>Office environments
>Universities, schools, training, centres
>Industry
>Hospitals
>Home
>Networked vehicles
14) What is BRAN?
The broadband radio access networks (BRAN)
which have been standardized by
European Telecommunications Standard
Institute( ETSI) are a possible choice for an RAL
for WATM. Although BRAN has been standardized
independently from WATM, there is
co-operation between the two to concentrate
the common efforts on one goal. The main
motivation behind BRAN is the deregulation
and privatization of the telecommunication
sector in Europe .
15) What are the different network types of
BRAN?
>Hyperlan1
>Hyperlan2
>Hyper access
>Hyperlink
16) What is the main problem for WATM during
handover?
The main problem for WATM during the handover
is rerouting of all connections and maintaining connection quality.
17) What are the different segments in ATM
end-to-end connection?
An ATM end-to-end connection is separated
into different segments.
>A fixed segment is a part of the
connection that is not affected by the handover
>Handover segment is affected by the
handover and is located completely within a handover domain.
18) What is anchor point?.
The Anchor point is the boundary between a
handover segment and a fixed
segment.
19) What are different types of handover?
>Hard handover
>Terminal initiated
>Network initiated
>Network initiated, terminal assisted
>Network controlled
>Backward handover
>Forward handover
20) What is mobile terminal and wireless
terminal?.
Mobile terminal is a standard ATM terminal with the additional capability of
reconnecting after access point change. the terminal can be moved between
different access point within a certain domain. Wireless terminal is accessed
via a wireless link, but the terminal itself is fixed,
i.e., the terminal keeps its access point to
the network.
UNIT 4 - NETWORK LAYER
1) What is generic routing encapsulation?
Generic routing encapsulation (GRE) is an
encapsulation scheme which supports other network protocols in addition to IP.
It allows the encapsulation of packets of one protocol suite into the payload
portion of a packet of another protocol suite.
2) Define COA.
The COA (care of address) defines the current
location of the MN from an IP point of view. All IP packets sent to the MN are
delivered to the COA, not directly to the IP address of the MN. Packet delivery
toward the MN is done using the tunnel.
3) What is meant by Transparency?
Mobility should remain invisible for many
higher layer Protocols and applications. The only affects of mobility should be
a higher delay and lower bandwidth which are natural in the case of mobile networks.
4) What is Generic Routing encapsulation?
Generic Routing encapsulation (GRE) allows
the encapsulation of packets of one protocol suite into the payload portion of
a packet of another protocol suit.
5) What is Binding Request?
Any node that wants to know the current
location of an MN can send a binding request to the HA. The HA can check if the
MN has allowed dissemination of its current location.
6) What are the possibilities for the
location of care-of-address (COA)?
The two possibilities for the location of
care-of-address are:
i. Foreign agent COA
ii.Co-related COA
7) What are the requirements for the
development of mobile IP standard?
The requirements are:
a.Compatibility
b.Transparency
c.Scalability and efficiency
d.Security
8) What is Dynamic source Routing?
Dynamic Source Routing eliminates all
periodic routing updates. If a node needs to discover a route, it broadcast a
route request with a unique identifier and the destination address as
parameters. Any node that receivers a route request gives a list of addresses representing
a possible path on its way toward the destination.
9) Why is need of routing?
Routing is to find the path between source
and destination and to forward the packets appropriately.
10) Define Mobile node:
Mobile node:
A mobile node is an end-system or router
that can change its point of attachment to the Internet using mobile IP.
The MN keeps its IP address and can continuously with any other system in the
Internet as long as link layer connectivity is given.
11) What is Encapsulation and Decapsulation?
Encapsulation is the mechanism of taking a
packet consisting of packet header and data and putting it into the data part
of a new packet. The reverse operation, taking a packet out of the data part of
another packet, is called decapsulation.
12) Define Dynamic source routing.
In an adhoc networks where nodes exchanges
packets from time to time. Dynamic Source routing divides the task of routing
into two separate problems:
i) Routing Recovery: A node only tries to
discover a route to destination if it has to send something to this destination
and there is currently no known route
ii) Route Maintenance: If a node is
continuously sending packets via route, it has to make sure that the route is
held urgent. As soon as a node detects problem with the current route it has to
find an alternative node.
13)
Define Compatibility.
Ø support of the same layer 2 protocols as IP
Ø no changes to current end-systems and routers
required
Ø mobile end-systems can communicate with fixed
systems
14) What is Home Agent (HA)?
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
15) Define 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
16) Define Agent Advertisement.
HA
and FA periodically send advertisement messages into their physical subnets
MN
listens to these messages and detects, if it is in the home or a foreign network
MN
reads a COA from the FA advertisement messages
17) Define Registration.
MN
signals COA to the HA via the FA, HA acknowledges via FA to MN
these
actions have to be secured by authentication
18) Define Key distribution
Home agent distributes session keys
·
foreign
agent has a security association with the home agent
·
mobile
host registers a new binding at the home agent
·
home
agent answers with a new session key for foreign agent and mobile node
19) Applications of Dynamic Host
Configuration Protocol.
simplification
of installation and maintenance of networked computers
supplies
systems with all necessary information, such as IP address, DNS server address,
domain name, subnet mask, default router etc.
enables
automatic integration of systems into an Intranet or the Internet, can be used
to acquire a COA for Mobile IP
20)
Define DSDV (Destination Sequenced Distance Vector).
Expansion of distance vector routing
Sequence numbers for all routing updates
assures
in-order execution of all updates
avoids
loops and inconsistencies
21) List the examples for interference
based routing.
Least
Interference Routing (LIR)
calculate
the cost of a path based on the number of stations that can receive a
transmission
Max-Min Residual Capacity Routing (MMRCR)
calculate
the cost of a path based on a probability function of successful transmissions
and interference
Least
Resistance Routing (LRR)
calculate
the cost of a path based on interference, jamming and other transmissions
LIR is very simple to implement
UNIT 5 - TRANSPORT AND APPLICATION LAYERS
Part A
1) What are the two functions of the
transport layer in the internet?
The two functions of the transport layer in
the internet are check summing over user data and multiplexing/ demultiplexing
of data from applications.
2) What is called the exponential growth of
the congestion window?
The senders always calculate congestion
window for a window start size of the congestion window is one segment. Sender
sends one packet and waits for acknowledgement. If acknowledgement arises it
raises the level of congestion window by one. If sender sends two packets if
acknowledgement arises it raises the level of congestion window by two. This
scheme raises the level of congestion window every time the acknowledges come back,
which takes round trip time (RTT).This is called the exponential growth of the
congestion window
3) Advantages of I-TCP:
•I-TCP does not require any changes in the
TCP protocol as used by the hosts in the fixed network or other hosts in a wireless
network that do not use this optimization.
•Without partitioning retransmission of lost
packets would take place between mobile host and correspondent host
across the whole network.
•Optimization of new mechanisms is quite
simple to be done in I-TCP as they only cover a single hop.
•The short delay between the mobile host
and foreign agent can be determined and is independent of other traffic
streams. Therefore an optimized TCP can use precise time-outs to guarantee
retransmission as fast as possible.
•Partitioning into two connections also
allows the use of a different transport layer protocol between the foreign
agent and the mobile host or the use of compressed headers etc. The
foreign agent can act as a gateway to translate between different protocols.
4) Disadvantages of I-TCP:
• The loss of the end to end semantics of TCP
cause problems if the foreign agent portioning the TCP connection crashes.
• An increased handover latency is more
problematic in practical use
• The foreign agent must be a trusted entity because
the TCP connections end at this point.
5) Define Slow Start?
TCP’s reaction to a missing acknowledgement
is quite drastic, but necessary to get rid of congestion. The behaviour TCP
shows after the detection of congestion is called Slow start.
6) How does data transmission takes place?
Data transmission takes place using network
adapters, fibre optics, copper wires, special hardware for routers etc.
7) What is mean by SCPS-TP?
The set of protocols developed for space communication
is known as space communications protocol standards (SCPS), the extended TCP is
called SCPS-transport protocols.(SCPS-TP).
8) What are Advantage and Disadvantage of
MobileTCP?
Advantage:
i. M-TCP maintains the TCP end-to-end
semantice. The SH does not send any ACK itself but forwards the ACKs from the
MH.
ii.If the MH is disconnected, M_TCP avoids
useless retransmissions, slow starts or breaking connections by simply
shrinking the sender’s window to 0;
iii. 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. Lost
packets will be automatically retransmitted to the new SH.
Disadvantage:
i. As the SH does not act as proxy as in
I-TCP, packet loss on the wireless link due to bit errors is propagated to the
sender. M-TCP assumes low bit error rates, which is not always a valid assumption.
ii. A modified TCP on the wireless link not
only requires modification to the MH protocol software but also new network
elements like the bandwidth manager.
9) What is fast retransmit?
In TCP, a receiver sends acknowledgements
only if it receive any packets from the sender. Thus receiving acknowledgements
from a receiver shows additionally that the receiver continuously receives
something from the sender. Therefore, the gap in the packet stream is not due
to severe congestion, but a simple packet loss due to a transmission error. The
sender can now retransmit the missing packets before the timer expires. This
behaviour is called fast retransmit.
10) What is fast recovery?
The receipt of acknowledgement shows that
there is no congestion justifying a slow start. The sender can continue with
the current congestion window. The sender performs a fast recovery from the
packet loss. This mechanism can improve the efficiency of TCP dramatically.
11) What is HTTP?
The Hypertext transfer protocol is a
stateless, lightweight, application level protocol for data transfer between
servers and clients. An HTTP transaction consists of an HTTP request issued by
a client and an HTTP response from the server. Stateless means that all HTTP
transactions independent of each other.
12) What is image scaling?
If a page contains a true color,
high-resolution picture, this picture can be scaled down to fewer colors, lower
resolution, or finally to only the title of the picture. The user can decide to
download the picture separately. Further one can offer clipping, zooming, or
detail studies to users if they are interested in a part of the picture.
13) What is WAP?
Wireless application protocol (WAP) is a
common effort of many companies and organizations to set up a framework for
wireless and mobile web access using many different transport systems.
Eg. GSM, GPRS, UMTS.
WMLBrowser is a library that provides several
functions typical for a browser, such as prev to go back one card or refresh to
update the context of the user interface.
15) Define Damping
Transient changes in topology that are short
duration should not destabilize the routing mechanism. Advertisements
containing changes in topology currently stored are therefore not disseminated further.
A node waits with dissemination if these changes are most likely not yet
stable.Waitingg time depends on the time between the first and the best
announcement.
