CS2402 MOBILE AND PERVASIVE COMPUTING (2 Marks with Answers)

CS2402                                 MOBILE AND PERVASIVE COMPUTING         L T P C

 3 0 0 3

UNIT I                                                 MOBILE NETWORKS                                            9

Cellular Wireless Networks – GSM – Architecture – Protocols – Connection Establishment – Frequency Allocation – Routing – Mobility Management – Security – GPRS.

UNIT II                                    WIRELESS NETWORKS                                                  9

Wireless LANs and PANs – IEEE 802.11 Standard – Architecture – Services –Network –HiperLAN – Blue Tooth- Wi-Fi – WiMAX

UNIT III                                   ROUTING                                                                              9

Mobile IP – DHCP – AdHoc– Proactive and Reactive Routing Protocols – Multicast Routing.

UNIT IV                                  TRANSPORT AND APPLICATION LAYERS                9

Mobile TCP– WAP – Architecture – WWW Programming Model– WDP – WTLS – WTP – WSP – WAE – WTA Architecture – WML – WMLScripts.

                                   

UNIT V                                   PERVASIVE COMPUTING                                               9

Pervasive computing infrastructure-applications- Device Technology - Hardware, Human-machine Interfaces, Biometrics, and Operating systems– Device Connectivity –Protocols, Security, and Device Management- Pervasive Web Application architecture- Access from PCs and PDAs - Access via WAP

TOTAL: 45 PERIODS

TEXT BOOKS:

1. Jochen Schiller, “Mobile Communications”, PHI, Second Edition, 2003.

2. Jochen Burkhardt, Pervasive Computing: Technology and Architecture of Mobile Internet Applications, Addison-Wesley Professional; 3rd edition, 2007

REFERENCES:

1. Frank Adelstein, Sandeep KS Gupta, Golden Richard, Fundamentals of Mobile and Pervasive Computing, McGraw-Hill 2005

2. Debashis Saha, Networking Infrastructure for Pervasive Computing: Enabling Technologies, Kluwer Academic Publisher, Springer; First edition, 2002

3. Introduction to Wireless and Mobile Systems by Agrawal and Zeng, Brooks/ Cole(Thomson Learning), First edition, 2002

4. Uwe Hansmann, Lothar Merk, Martin S. Nicklons and Thomas Stober, Principles of Mobile Computing, Springer, New York, 2003.

MOBILE AND PERVASIVE COMPUTING

UNIT-I- MOBILE NETWORKS

1.   How to improve signal reception by countered the negative effects of multipath propagation?

            Signal degradations due to multipath are fading and delay spread. Fading can be overcome by diversity reception. Delay spread will result in Inter Symbol Interference which can be compensated by equalizers.

2.   What are the advantages of cellular systems?

The advantages of cellular systems are,

• Higher capacity
• Less transmission power
• Local interface only
• Robustness

3.   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.

4.      What are the three services offered by GSM ?

            Three services offered by GSM are

·        Bearer services

·        Tele services

·        Supplementary services

5.      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

6.      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.

7.      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

8.      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.

9.      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

10.  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.

11.  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.

12.  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

13.  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.

14.  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.

15.  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.

16.  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)

17.  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)

18.  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.

19.  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.

20.  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.

21.  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.

22.  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.

23.  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.

24.  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)

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

            The security services offered by the GSM are,

• Access control and authentication
• Confidentiality
• Anonymity

26.  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.

27.  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.

28.  What is HSCSD ?

            A straightforward improvement of GSM’s data transmission capabilities is high speed circuit switched data (HSCSD). In this system, higher data rates are achieved by bundling several TCHs(Traffic Channel). An MS requests one or more TCHs from the GSM network, i.e., it allocates several TDMA slots within a TDMA frame.

29.  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.

30.  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.

31.  List the three different categories of services of GSM. (Nov/Dec-2007)(Nov/Dec-2013)

Three categories of services of GSM are:

·           Bearer services

·           Tele services

·           Supplementary services

32.  Differentiate symmetric and asymmetrical communication system  (Nov/Dec-2008)

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

33.  Compared in the TCHs offered, standard GSM could provide a much higher data rate(33.8kbits/s) when looking at the air interface. What lowers the data rates available to a user?  (Nov/Dec-2008)

Data transmission in GSM is possible at many different data rates.

Example:          TCH/F4.8 for 4.8 kbps

                        TCH/F9.6 for 9.6 kbps

                        TCH/F14.4 for 14.4 kbps

(OR)

Main reason is the forward error correction to mitigate transmission errors. Furthermore bandwidth is needed for signaling guard spaces

34.  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 SM. 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)

35.  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.

36.  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.

37.  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.

38.  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).

39.  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 type	This is available only in FDD mode
2.	All inter system handovers are hard handovers.	UE receives data from different antennas at the same time makes a handover soft.

40.  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

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

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

42.  Which are the new components added to GPRS networks? (May/Jun-2012)

Serving GPRS Support Node(SGSN),

Gateway GPRS Support Node(GGSN)

43.  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.

44.  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.

45.  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-II-TELECOMMUNICATION NETWORKS

1.      What are the advantages exhibit by WLANs ?

            Advantages

–        Flexible deployment

–        Minimal wiring difficulties

–        More robust against disasters (earthquake etc)

–        Historic buildings, conferences, trade shows,…

2.      What are the disadvantages exhibit by WLANs ?

             Disadvantages

–        Low bandwidth compared to wired networks (1-10 Mbit/s)

–        Proprietary solutions

–        Need to follow wireless spectrum regulations

–        High cost

–        Restrictions

–        Safety and Security

3.      What are the design goals have to taken into account for WLANs to ensure their commercial success ?

·        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

4.      Give the different field names of FHSS PHY frame. (Nov/Dec 2013)

            FHSS PHY packet format

Synchronization

q     synch with 010101... pattern

SFD (Start Frame Delimiter)

q     0000110010111101 start pattern

PLW (PLCP_PDU Length Word)

q     length of payload incl. 32 bit CRC of payload, PLW < 4096

PSF (PLCP Signaling Field)

q     data of payload (1 or 2 Mbit/s)

HEC (Header Error Check)

q     CRC with x16+x12+x5+1

5.      What are the three basic access mechanisms of IEEE 802.11?

            The following three basic access mechanisms have been defined for IEEE 802.11:

• Mandatory basic method – based on a version of CSMA/CA,
• An optional method - avoiding the hidden terminal problem,
• Contention free polling method – for time bounded service.

6.      What are the functional groups of MAC management?

    Synchronization

·        try to find a LAN, try to stay within a LAN

·        timer etc.

    Power management

·        sleep-mode without missing a message

·        periodic sleep, frame buffering, traffic measurements

    Association/Reassociation

·        integration into a LAN

·        roaming, i.e. change networks by changing access points 

·        scanning, i.e. active search for a network

    MIB - Management Information Base

·        managing, read, write

7.      Give the characteristics of HIPERLAN.

     HIPERLAN – High Performance Local Area Network

Data transmission

q     point-to-point, point-to-multipoint, connectionless

q     23.5 Mbit/s, 1 W power, 2383 byte max. packet size

Services

q     asynchronous and time-bounded services with hierarchical priorities

q     compatible with ISO MAC

Topology

q     infrastructure or ad-hoc networks

q     transmission range can be larger then coverage of a single node  („forwarding“ integrated in mobile terminals)

8.      What are the three phases of medium access for EY-NPMA ?

            EY-NPMA (Elimination Yield Non-preemptive Priority Multiple Access) divides the medium access of different competing nodes into three phases.

·        Prioritization : Determines the highest priority of a data packet ready to be sent on competing nodes.

·        Contention : Eliminates all but one of the contenders, if more than one sender has the highest priority.

·        Transmission : Finally, transmit the packet of the remaining node.

9.      State two service primitives offers MAC layer, for data transfer.

            For data transfer, the MAC layer offers two service primitives.

• HM-UNIDATA.req : This primitive can be used to send the MSDU with a certain priority and lifetime to one or more destinations.
• HM-UNIDATA.ind : This primitive indicates an MSDU received and also includes the residual lifetime.

10.  Write a note on Bluetooth .

• Universal radio interface for ad-hoc wireless connectivity
• Interconnecting computer and peripherals, handheld devices, PDAs, cell phones – replacement of IrDA
• Embedded in other devices, goal: 5€/device (2005: 40€/USB Bluetooth)
• Short range (10 m), low power consumption, license-free 2.45 GHz ISM
• Voice and data transmission, approx. 1 Mbit/s gross data rate

11.  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

12.  What are the primary goal of IEEE 802.11 Wireless LAN ?

            The primary goal of the standard was the specifications of a simple and robust WLAN which offers time bounded and asynchronous services.

13.  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.

14.  What are the sub layers of physical layer in 802.11 ?

            There are two sub layers of physical layer in 802.11 are

• PLCP (Physical layer convergence protocol)
• PMD (Physical medium dependent)

15.  What are the functions of MAC management ?

            The MAC management supports the association and re-association of a station to an access point and roaming between different access points.

16.  Define FHSS.

            FHSS (Frequency Hopping Spread Spectrum) is a spread spectrum technique which allows for the coexistence of multiple networks in the same area by separating different networks using different hopping sequence.

17.  What is DIFS, PIFS, SIFS ?

            DCF Interference spacing (DIFS) denotes the longest waiting time and thus the lowest priority for medium access. PCF Interference spacing (PIFS) is the waiting time between DIFS and SIFS is used for a time bounded service. Shortest interference spacing (SIFS) is the shortest waiting time for medium access is defined for short control messages such as acknowledgements for data packets or polling responses.

18.  Write note on problems in the access scheme ?

            The access scheme has the problems under heavy or light load, depending on the size of the contention window(CW), the random values can either be too close together, causing too many collisions and cause unnecessary delay.

19.  What are the fields in the format of an IEEE 802.11 PHY frame using FHSS?

The fields in the frame fulfill the following functions :

·        Synchronization

·        Start frame delimiter (SFD)

·        PLCP-PDU length word(PLW)

·        PLCP signaling field(PSF)

·        Header error check(HEC)

20.  What is the use of sequence control field in IEEE 802.11 MAC data frame ?

            Due to the acknowledgement mechanism it may happen that frames are duplicated. Therefore a sequence number is used to filter duplicates.

21.  What is CRC  & Checksum?

            The cyclic redundancy check is an error detecting code in which the code is the remainder resulting from dividing the bits to be checked by a predetermined binary number. Checksum is an error detecting code based on a summation operation performed on the bits to be checked.

22.  What are the functional groups have been identified in MAC management of IEEE 802.11 ?

            The following functional groups have been identified in MAC management of IEEE 802.11

• Synchronization
• Power management
• Roaming
• Management information base (MIB)

23.  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.

24.  When the station starts scanning in IEEE 802.11?

            A station decides that the current link quality to its access point AP1is too poor. The station then starts scanning for another access point.

25.  Differentiate Passive and Active scanning ?

Passive Scanning :

            Passive Scanning simply means, station 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.

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.  State two service primitives offers CAC sub layer, for data transfer.

            For data transfer, the CAC sub layer offers two service primitives.

• HC-UNITDATA.req (source HCSAP, destination HCSAP, HCSDU, HIPERLAN identifier, channel access priority): This service primitive is used for sending data.
• HC-UNITDATA.ind (source HCSAP, destination HCSAP, HCSDU, HIPERLAN identifier): This service primitive indicates incoming data.

27.  What are the subdivisions of contention phase in HIPERLAN?

            The contention phase is further subdivided into an elimination phase and a yield phase. The purpose of the elimination phase is to eliminate as many contending nodes as possible. The result of the elimination phase is a more or less constant number of remaining nodes, almost independent of the initial number of competing nodes. Finally, the yield phase completes the work of the elimination phase with the goal of only one remaining node.

28.  What are the states a Bluetooth device can go for save battery power?

            To save battery power, a Bluetooth device can go into the one of the three low power states if no data is ready to sent :

• PARK state
• HOLD state
• SNIFF state

29.  What are the services offered by Bluetooth?

            Bluetooth offers two different types of services

• Synchronous connection-oriented link(SCO)
• Asynchronous connectionless link(ACL)

30.  What is scatternet?

            The idea of forming groups of piconets called scatternet.

31.  What are the main security features offered by Bluetooth?

            The main security features offered by Bluetooth include a

• Challenge-response routine for authentication
• A stream cipher for encryption
• Session key generation

32.  What are the functions of LM in Bluetooth?

A Bluetooth system is managed by a link manager (LM0. An LM handles the authentication procedures, negotiates authentication parameters, carries out link setup and release, configures links etc.

33.  What are the two different basic transmission technologies used to setup WLANs? (Nov/Dec-2007)

Three possible transmission technologies used in WLANs are:

(i)                  Infrared communication

(ii)                Spread spectrum communication

(iii)               Narrowband microwave communication

34.  What is WiMax?

            WiMAX(Worldwide Interoperability for Microwave Access) is a communication protocol providing fixed and mobile Internetr access. It is implemented with standards specified in IEEE 802.16.  It currently offers data transfer rate upto 40MB/Sec but with IEEE 802.16m it goes upto 1 GB/sec. It is similar to Wi-Fi but it allows longer distance connections.

35.  Where the WiMAX application is useful?

            It is useful in,

·      Providing portable mobile connectivity across cities.

·      Providing suitable alternative for the ‘lat mile’ connection.

·      Providing three types of services,  namely data, telecommunications and IPTV.

·      Acting as a source of Internet services.

36.  Compare WiMAX with Wi-Fi.

·        WiMAX is a long range system. It can support wireless connectivity over a few kilometers using licensed spectrum for Internet access.

·        Wi-Fi is used to support connectivity to local network in unlicensed spectrum.

·        WiMAX uses a connection oriented MAC whereas Wi-Fi uses a connectionless contention based CSMA/CA protocol for MAC.

·        In WiMAX each connection to base station is based on scheduling algorithm. Wi-Fi uses contention access.

37.  List the different user scenario for wireless piconets. (Nov/Dec-2007)

In scatternet, overlapped piconets can exist. It devices in one piconet can be member in another piconet. There can be two piconets without overlap.

38.  What is HIPERLAN?      (Nov/Dec-2008)

HIPERLAN (High Performance Radio LAN): It is a new standard for radio LAN developed by ETIS. Offers interoperability standard which specifies a common air interface. EITS developed a standard that would be equivalent in performance to wired LAN such as Ethernet.

39.  How is mobility restricted using WLANS?         (Nov/Dec-2008)

WLAN: Mobile restricted with respected to the Access Point. When moving the mobile entity needs to change Network Access Point. Every mobile entity(person,terminal) must have its own identity. An identifier is assigned uniquely to one mobile entity.

40.  Why the PHY layer of IEEE 802.11 is subdivided?(April/May 2008),(Nov/Dec-2008)

Physical layer is subdivided into,

1.PLCP(physical Layer Convergence Protocol):It provides a carrier sense signal, called Clear Channel Assesment(CCA), and provides a common PHY Service Access Point (SAP) independent of transmission technology.

2.PMD(Physical Medium Dependent) sublayer: It handles modulation and encoding/ decoding of signals.

41.  What is the functionality L2CAP? List the different types of logical channels it provides.     (Nov/Dec-2008)

The Logical Link Control and Adaptation Protocol (L2CAP) is a data link control protocol on top of the baseband layer offering logical channels between Bluetooth devices with QoS properties.L2CAP provides three different types of logical channels are,

Connectionless: It is used for broadcasting from a master to its slaves, which is a unidirectional one.

Connection-Oriented: It supports QoS flow specifications for each bidirectional channels.

Signalling: It is used for exchanging signaling messages between L2CAP entities.

42.  How mobility is restricted using WLANs? (April/May 2008)

WLAN: Mobile restricted with respected to the Access Point. When moving the mobile entity needs to change Network Access Point. Every mobile entity (person,terminal) must have its own identity. An identifier is assigned uniquely to one mobile entity.

43.  Why the PHY layer of IEEE802.11 is subdivided? What about HIperLAN2 and Bluetooth? (Nov/Dec 2008)

a.                  PHY layer: To allow coexistence of multiple Network in the same area

b.                  Hiper LAN2: BRAN PHY-1

                              BRAN PHY-2

ü      Bluetooth: One layer based on Infrared

ü      Two layers based  on Radio Transmission (FHSS, DSSS)

ü      Bluetooth Protocol stack divided to a core specification which describe the protocol from physical layer to the data link control together with management function.

ü      Profile Specification

     

44.  Is IEEE802.11 and WiFi same? State the purpose of WiFi. (May/June 2009)

The newest IEEE standard in the Wi-Fi category is 802.11n. It was designed to improve on 802.11g in the amount of bandwidth supported by utilizing multiple wireless signals and antennas (called MIMO technology) instead of one.

Purpose of WiFi:

It is wireless internet. Your laptop has an internal wireless card so you can connect to wireless routers. If you goto a hotel that advertises free wireless internet, you should be able to connect to it. You don't have to have an ethernet cable to connect to the web at home either. You could buy a wireless router, and be able to have internet in most of your house. It also works at school/library/internet cafe, etc.

45.  Why Bluetooth specification  comprises so many protocols and components? (May/June 2009)

Since it is a single chip low cost radio based wireless network technology. It should      be operated within a Personal Operating Space(POS).

46.  State the three phases of the medium access of different competing nodes. (Apr/May 2010)

Ø      State sender has to sense the medium to see if  it is free.

Ø      If the medium is free the sender states for data and continues to listen to medium

Ø      If it is busy the sender waits until if is free

47.  What are the powers saving mechanism in Blue tooth? (Apr/May 2010)

Ø      To save power Bluetooth devices can go into one of 3 low power state

Ø      If sender defects a collision while sending if slops at once and sends a jamming signals

Ø      Sniff  State highest power consumption

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

Ø                  Infra Structure Required.

Ø                  It will not survive disaster

Ø                  It is not flexible.

Ø                  Planning is required to establish a wired network.

Ø                  Additional cabling with the right plugs and probably internetworking units 

Ø                  have to  be  provided.

49.  Mention the features of HIPERLAN. (Nov/Dec 2011)

(i)                  Integration of time sensitive data transfer services.

(ii)                Standardization efforts had lot of impact on QOS suppoting wireless broadband.

(iii)               The current focus is on HIPERLAN2 a standard that comprises many elements from ETSI’s BRAN and wireless ATM activites.

50.  List out the various elements of Bluetooth core protocol. (Nov/Dec 2011)

·                 Radio

·                 Baseband

·                 Link Manager protocol

·                 L2CAP

·                 Service Discovery Protocol

51.  In what situations can collision occur in IEEE802.11? (May/Jun 2012)

            For 802.11 collisions on the MAC layer are nothing unusual. The MAC algorithm with backoff solves this problem. In 802.11 networks MAC collisions are also collisions at PHY layer. Important packets in 802.11 have higher priorities implemented via shorter waiting times(SIFS,PIFS).

52.  What is Adaptive modulation? (May/Jun 2012)

            It is a term used in wireless communications to denote the matching of the modulation, coding and other signal and protocol parameters to the conditions on the radio link. Adaptive modulation systems improve rate of transmission and bit error rates by exploiting the channel information that is present at the transmitter. Especially over fading channels, adaptive modulation system exhibit great performance enhancements compared to systems that do not exhibit channel knowledge at the transmitter.

53.  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 communication between 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-III - ROUTING

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 to 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 understanding Mobile 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 all the areas the Ad hoc networks are used ?

• Instant infrastructure
• Disaster relief
• Remote areas
• Effectiveness

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

Split routing into discovering a path and maintaining a path

            Discover a path:

q     Only if a path for sending packets to a certain destination is needed and no path is currently available

            Maintaining a path:

q     Only while the path is in use one has to make sure that it can be used continuously

25.  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.

26.  What are the fundamental differences between wired networks and  ad hoc networks related to routing ?

• Asymmetric links
• Redundant links
• Interference
• Dynamic topology

27.  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.

28.  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.

29.  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.

30.  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.

31.  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.

32.  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.

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

            Registration can be done in two different ways,

i.                     If the COA is at the FA, and

ii.                    If the COA is co-located.

34.  . What are the advantages does the use of IPv6 offer for mobility?

                 i. COA can be auto configured.

ii. No need for a separate FA instead all the routers perform routing advertisement.

iii.The address are always collocated COA.

iv.Sending a signal via HA not needed.

35.  What are the problems related to the use of DHCP? (Nov/Dec-2007)

i)        Security is a major problem with DHCP. There is no authentication procedure for DHCP messages.

ii)       There is no specific protocol for DHCP server to server communication.

36.  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.

37.  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.

38.  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)

39.  How does registration on layer 3 of a mobile node work?         (Nov/Dec-2008)

Registration can be done in two different ways,

(i)                  If the COA is at the FA, and

(ii)                If the COA is co-located.

Registration request

Registration Request

      MN                             FA                               HA                  MN                             HA

 

      T                                                                                              t

Figure: Registration of a mobile node via the FA or directly with the HA

40.  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.

41.  Why is the basic purpose of DHCP? (April/May 2008)

            The basic purpose of DHCP is to provide an IP address. The Dynamic host configuration protocol (DHCP) is mainly used for the simplification of installation and maintenance of networked computers. The DHCP model is based on a client/server model. DHCP clients send a request to a server to which the server responds. A client sends requests using MAC broadcasts. A DHCP relay might be needed to forward requests to a DHCP server.

42.  Specify the DHCP state transition diagram for acquiring the IP address. (Nov/Dec-2008)

43.  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  

44.  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 a reactive 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

45.  How can DHCP be used for mobility and support of mobile IP? (May/June2009)

It will support the acquisition of care of address for mobile nodes the same holed for all other parameters needed such as the address of default router, DNS server, the time server etc. The DHCP server should be located in the sub net of the access point of the mobile node. Authentication for DHCP messages which is needed to protect mobile nodes from malicious DHCP server.

46.  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.

47.  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.

UNIT-IV-TRANSPORT & APPLICATION LAYERS

1.      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.

2.      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.

3.      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.

4.      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.

5.      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.

6.      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.

7.      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

8.      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.

9.      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.

10.  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.

11.  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.

12.  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.

13.  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.

14.  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.

15.  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.

16.  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.

17.  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.

18.  What are the disadvantages of selective retransmission approach ?

            There might be minor disadvantage of more complex software on the receiver side, because now more buffer is 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.

19.  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.

20.  What is WAP  and what are its key aspects?

•   A standard for bringing Internet content and services to mobile devices.

•   WAP is not a service or a product but a protocol for delivering applications.

               Key aspects:

•   It can run on any network

–                    e.g. GSM, CDMA, 3G networks

•   It can run on any kind of device 

–                    e.g. cell phones, PDAs, and laptops.

–                    achieves device-independence through the Wireless Application Environment (WAE).

•   WAP defines a new format, the Wireless markup Language (WML)

–                    designed for efficient content delivery

21.  Give the protocol stack of WAP.

•                  Five Layers

–        Transport (WDP)

–        Security (WTLS)

–        Transaction (WTP)

–        Session  (WSP)

–        Application(WAE)

22.  Write short note on Wireless Datagram Protocol .

•Offers a consistent datagram transport service independent of the underlying bearer         

  (GSM, CDMA, etc.).

•Offers more or less the same services UDP does.

–                 e.g. application addressing by port numbers.

23.  Write short note on WML.

•A WML document is made up multiple cards.

–                 Each card represents a screen of information.

•Cards can be grouped together in a deck.

–                 A WML deck is similar to an HTML page.

•Web servers deliver web pages one at a time but WAP delivers a deck of related cards.

–                 There is no waiting for the next screen (card) to display, which differs from the web, where clicking on a new link typically means waiting for the server to deliver that page.

24.  Write short note on WML Script.

•A complement to WML

•Provides a general scripting capability (like JavaScript)

–           Example: before user input is sent to a server, WML Script can check the validity and save bandwidth and latency in case of an error.

25.  Say something about the push architecture of WAP.

•WAP 1.2 introduces a push architecture (2000)

•Clients pulling content from servers are typical for today’s web.

•In a push context, the server initiates the message transfer, not the client.

–                 Useful for services such as online auctions or stock trading, where it’s important for users to receive information whenever something interesting happens.

26.  List out main features of WAP. (Apr/May 2010)

§               Browser: “Micro browser”, similar to existing web browsers

§               Markup language: Similar to HTML, adapted to mobile devices

§               Script language: Similar to Javascript, adapted to mobile devices

§               Gateway: Transition from wireless to wired world

§               Server: “Wap/Origin server”, similar to existing web servers

§               Protocol layers: Transport layer, security layer, session layer etc.

§               Telephony application interface: Access to telephony functions

27.  What is WAP Micro browser?

§            Optimized for wireless devices

§            Minimal RAM, ROM, Display, CPU and keys

§            Provides consistent service UI across devices

§            Provides Internet compatibility

§            Enables wide array of available content and applications

28.  Say some WAP “Killer” Applications.

§               Location-based services

–              Real-time traffic reporting, Event/restaurant recommendation

§               Enterprise solutions

–              Email access, Database access, “global” intranet access

–              Information updates “pushed” to WAP devices

§               Financial services

–              Banking, Bill-paying, Stock trading, Funds transfers

§               Travel services

–              Schedules and rescheduling, Reservations

§               Gaming and Entertainment

–              Online, real-time, multi-player games

–              Downloadable horoscopes, cartoons, quotes, advice

§               M-Commerce

–              Shopping on the go

–              Instant comparison shopping

–              Location-based special offers and sales

29.  What are the goals of Wireless Application Environment (WAE) ?

§            Goals

–           device and network independent application environment

–           for low-bandwidth, wireless devices

–           considerations of slow links, limited memory, low computing power, small display, simple user interface (compared to desktops)

–           integrated Internet/WWW programming model

–           high interoperability

30.  What are the things included in the WAP forum solutions ?

·           Interoperable

·           Scaleable

·           Efficient

·           Reliable

·           Secure

31.  What are the functions offered by WTLS ?

            The WTLS – Wireless Transport Layer Security is based on transport layer security. WTLS can offer data integrity, privacy, authentication, and denial-of-service protection.

32.  What are the functions offered by WTP ?

            The Wireless Transaction Protocol offers a lightweight transaction service at the transaction SAP (TR-SAP). A transaction is defined as a request with its response. This service efficiently provides reliable or unreliable requests and asynchronous transactions.

33.  What are the three classes of transaction services in WTP ? (Nov/Dec 2011)

            Three classes of transaction service offered by WTP are

• Class 0 : Unreliable one-way request

o       No retransmission if the sent message is lost.

• Class 1 : Reliable one way request.

o       Message is resent if no ACK received.

• Class 2: Reliable two-way request-response.

o       A data request is sent and a result is received which finally is ACK’ed by the sender.

34.  What are the service primitives offered by WTP?

            The three service primitives offered by WTP are

1. TR-Invoke: to initiate a new transaction.
2. TR-Result: to send back the result of a previously initiated transaction.
3. TR-Abort   : to abort an existing transaction.

35.  What are the PDUs exchanged between two WTP entities?

            The Protocol Data Units exchanged between two WTP entities for normal transactions are the

·                    Invoke PDU

·                    Ack PDU

·                    Result PDU

36.  What are the features offered by WSP?

            Wireless Session Protocol offers the following three general features,]

·     Session Management :

o    Capabilities of suspending and resuming a session.

-                     Assume a mobile device is disconnected. The user is able to continue operation at exactly the point where the device was switched off.

·     Capability negotiation :

o    Clients and servers can agree upon a common level of protocol functionality during session management.

·     Content encoding :

o    Defines the efficient binary encoding for the content it transfers.

37.  What are the features offered by WSP/B adapted to web browsing  ?

            WSP/B – Wireless Session Protocol / Browsing – offers the following features adapted to web browsing:

·  HTTP/1.1 functionality :

           WSP/B supports the functions HTTP/1.1 offers, such as extensible request/reply                            methods, composite objects, and content type negotiation

·  Exchange of session headers :

           Client and server can exchange request/reply headers that remain constant over                         the lifetime of the session.

·  Push and Pull data transfer :

Pulling data from a server is on the basis of client request.

Pushing data transfer means, with out client request the server automatically pushing data to client.

·  Asynchronous request :

WSP/P, supports a client that can send multiple requests to a server simultaneously.

38.  What is T-SAP?

            T-SAP (Transport Layer Service Access Point) is the common interface to be used by higher layers independent of the underlying network.

39.  Mention the components of WAP.

            The various components of WAP are:

• Wireless Datagram Protocol
• Wireless Transport Layer Security
• Wireless Transaction Protocol
• Wireless session Protocol
• Wireless Application Environment
• Wireless Markup Language
• WML Script
• Wireless Telephony Application
• Push Architecture
• Push / Pull Services

40.  Why the TCP protocols used in wired netwoks 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.

41.  Discuss the problems of a file system in mobile environment. (Nov/Dec-2007)

Problems of file system in mobile environment:

(i)         Efficiency of bandwidth is low, protocol overhead must be minimum.

(ii)       Transparency, i.e., file system must support mobility & provide identical views of directories, file names & access rights.

(iii)      Consistency due to replication of data among many mobile clients.

42.  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.

43.  Can the problems using TCP for mobile communication be 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.

44.  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.

45.  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

46.  Name the libraries specified by WML script. (Nov/Dec 2011)

(i)      Lang: provides function closely related to WML script itself

(ii)    Float: Many typical arithmetic floating point operation in this library

(iii)   String: Many string manipulation function are in this library.

(iv)  URL: This library provides many function for handling URLs with the syntax defined inn fielding

(v)    WML Browser: This library provides several function typical for the browser

(vi)  Dialogs: For interaction with the user, this library has been defined.

47.  What are the problem of proactive routing? (May/Jun 2012)

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

48.  Name the advantages and Disadvantages of user acknowledgement in WTP?   (May/Jun 2012)

      Advantage:

      Users can control the acknowledgement process, users may want to know if something went wrong, sometimes it is also possible to slow down a sender by inserting artificial delays in acknowledgement process, the acknowledgement of the user is stronger as it shows the sender that intended receiver and not the WTP process actually got the message.

      Disadvantage:

      Users have to interact, this may take some more time. Classical transactional services typically benefit from user acknowledgement, for most push service user acknowledgement are not necessary, still WTP acknowledgements can improve reliability.

49.  What is hoarding? (Nov/Dec 2013)

            The hoarding is a cache maintenance scheme used for facilitating any disconnected operations

50.  Draw the components and interface of the WAP 1.x architecture. (Nov/Dec 2013)

.

UNIT – V PERVASIVE COMPUTING

1.What is pervasive computing?

            Pervasive computing also called as ubiquitous computing is the trend toward embedding micro processors in everyday objects so that they can communicate information.

2.Discuss the problems of a file system in mobile environment.

Problems of a file system in mobile environment:

Ø Limited resources on portable devices

Ø Low bandwidth of the wireless access

Ø Cannot rely on large caches in the end . system or perform many updates via

the wireless link.

3.What are the three technologies involved in pervasive computing?

i)                       Micro electronic technology.

ii)                      Digital communication technology

iii)                    The international standardization.

4.What are the Key characteristics of pervasive computing?

i)                    Multiple devices are integrated in the system.

ii)                   Devices are used for multipurpose

iii)                 A large no.of different interfaces are used to build an optimized user interface.

iv)                 Security elements are integrated to prevent unauthorized access.

5.   What are application of pervasive devices?

            i) Retail

            ii) Airlines check in and booking

iii)Health care

            iv)car information system

            v)Tracking

6.   What are the technologies that support the evolution of  mobile device in pervasive computing?

            It has three categories,

·     Hardware technologies

·     Software technologies for human-machine interaction

·     Operating systems and Java platforms for PDA

7.   What are the h/w device involved in pervasive computing?

            The hardware components required to be designed especially for mobile applications are,

·     Batteries

·     Diaplays

·     Memory

·     Processors

8.      What are the factors to be considered for device management to incorporate with software?

            The factors are,

·        Hardware capabilities

·        Hardware Version Management

·        Software Version Management

·        Library Management

·        Devices are not connected always

·        Insecure connections

·        Unstable connections

·        Operating Syatem updates

9.      What are the two types of error that may occur in Fingerprint authentication?

·        False Accept Rate(FAR) – It is a rate at which the wrong person is allows access to system

·        False Reject Rate(FRR) – It is the rate at which a genunine person is denied access to system

10.  List the Functions/Features of Palm OS.

·        Task management

·        Power management

·        User management

·        Memory management

·        User Interface

·        OS size

11.  What are the types of protocols used in Device Connectivity?

·        Wireless protocols

·        Mobile Phone technologies

·        Bluetooth

·        Mobile IP

·        Synchronization protocol

·        Transaction Protocol

·        Protocol enabled with distributed services

12.  What is OBEX? What are its two modes?

            OBEX(Object Exchange) is defined for IrDA. It is independent of transport protocol. With Bluetooth, it has become high level protocol to be independent of underlying transport protocol. It is intended to make communication through IrDA as complete as possible. It has two modes.

1.      The Session mode: For structuring the dialogue between two devices. It is based on binary pocket-based client/server request/response model.

2.      The Object mode: It carries the information about the objects or the object themselves. The object is a sequence of header.

13.  Distinguish  the characteristics of Bluetooth and IrDA?

           

Characteristics	Bluetooth	IrDA
Frequency range	2.5 GHz ISM band	Infrared light is the physical medium
Security	Authentication based on private keys and encryption are specified	No inbuilt security
Transmission Capabilities	It has range of 10m supporting isochronous and synchronous transmission	Point to Point connection with a narrow angle between center and receiver is only possible.
Bandwidth	Data rate up to 1Mbps	Data rate  up to  4Mbps
Speech	Three digital speech channels can be supported simultaneously	One digital speech channel is supported

14.  Differentiate the different generations of mobile phone communications.

Characteristics	1G	2G	2+G	3G
Protocol	AMPS,      C-Net	GSM, TDMA, CDMA	GPRS, HSCSD, EDGE	UMTS,    W-CDMA
Technology	Analog, Circuit switched	Digital, Circuit switched	Digital, Circuit or Packet switched	Digital, Packet switched
Speech Quality	Poor	High	High	High
Bandwidth	Low	Low	Medium	High
Security	None	Depending on protocol, Low to High	High	High

15.  What are the steps involved in Mobile Internet Protocol?

1.      Discover the care of address

2.      Register the care of address

3.      Tunnel the care of address

16.  What is Jini and what are the services offered by it?

            Jini is for Java Software systems. The basic requirement is that all devices must be running java. It ensures the uniformity of data types. It is easy to distribute data and code among all systems.The services offered by it is,

·        Discovery

·        Look-Up

·        Leasing

·        Remote events

·        Transactions

17.  What are the services offered by Universal Plug and Play?

·        IP addressing

·        Discovery

·        Description

·        Control

·        Events

·        Presentation

18.  What are the security services offered by Device connectivity in Pervasive computing?

·        Identification

·        Authentication

·        Authorization

·        Transaction authorization

·        Non-repudiation

19.  What are the features contained in Smart card?

            The card contains the following information,

1.      Private key for generating digital signatures

2.      Certificate containing data about the customer

3.      Public key associated with private key of the customer

4.      Signature for all these data

20.  Compare the implementation method in Access from PCS and PDAs

Features	Implementation for synchronized devices	Implementation for intermittently connected devices	Implementation for connected devices
Tools Used	iSilo and iSilo web	Metroworks Code Warrior	KBrowser
Client Data Format	Proprietary document format	Proprietary document format	Not Applicable
Client Application	Special viewer for the relevant PDA  operating system	Native application for the PDA operating system	Standard WAP browser
Data Actuality	Initial replication without enforced updates	Initial replication with regular updates	No replication, but immediate access to data
Connection	One-time connection for the initial replication	Regular connections to synchronize data	Permanent connection during application use

21.  How the security is provided in WAP phones?

            WAP phones allow secured connection to WAP gateways or WAP servers. It allows RSA encryption algorithm. Currently WAP gateway terminate the secure WTLS connection between the WAP phone and the telecommunication company and establish a secure SSL connection instead to the application server.

22.  Give the other terms of pervasive computing.(Nov/Dec 2011)

·        Automobile

·        Workplace

·        Home

·        Personal Communication

·        Location based services

23.  How biometric signals are used in pervasive computing? .(Nov/Dec 2011)

      Personal characteristics such as finger print,iris scan,signatute,hand geometry,face recognition and voice recognition are used for biometric authentication. Since they use small sensors, fingerprint,speaker verification are used in pervasive computing.

     

24.  What is meant by pervasive computing? How is it done? (May/Jun 2012)

            Pervasive computing also called ubiquitous computing which means “exisisting everywhere”. Pervasive computing devices are completely connected and constantly available. It relies on the convergence of wireless technologies, advanced electronics and internet. The goal of researches working in pervasive computing is to create a smart products that communicate unobtrusively. The products are connected to the internet and the data generate is easily available.

25.  What makes Device connectivity possible in pervasive computing? .(Nov/Dec 2011)

            Pervasive devices cannot be used in stand alone mode. They have to be connected to the services and applications through internet. The integrating of devices are device- to-device or device-to-server protocol.             

UNIT- I

BIG QUESTIONS

1.         Explain the wireless cellular system.

2.         Explain GSM architecture?

3.         Explain Protocol architecture of GSM.

4.         Explain the bearer services, tele services and supplementary services of GSM networks.

5.         Discuss the localization and handover features of GSM system.

6.         Explain the security features in GSM.

7.         Explain the GPRS architecture.

UNIT- II

BIG QUESTIONS

1.         Explain the IEEE 802.11 protocol architecture and bridging with other networks.

2.         How do IEEE 802.11 solve hidden terminal problem? Explain with necessary diagrams.

3.         Write notes on IEEE 802.11 focusing on functionalities and also explain the concept of       routing, localization and handover in them.

4.         Present and explain the schematic of Bluetooth protocol architecture.

5.         Compare IEEE 802.11, HiperLAN2, and Bluetooth with regard to their ad-hoc capabilities.

6.         Where is the focus of these technologies?

7.         Explain the concept of Bluetooth architecture.

8.         Explain the concept of IEEE 802.11 medium access control layer.

9.         Explain the fields of IEEE 802.11 MAC packet structure. Compare them with IEEE 802.11          MAC fields.

10.     Explain the handover scenarios of HiperLAN2 in detail.

11.     How is roaming on layer 2 achieved, and how are changes in topology reflected. What are             the different between infrastructure based and ad-hoc networks regarding roaming?

12.     Write short notes on ad hoc networks.

13.     Explain the concept of WiFi.

14.     Explain in detail about the WiMAX.

UNIT- III

BIG QUESTIONS

1.         Explain the following with respect to mobile IP.

(i)            IP packet delivery

(ii)          Agent discovery

(iii)         Registration

(iv)        Tunneling & encapsulation

2.         Write notes on IP packet delivery, Agent Advertisement and Discovery.

3.         Specify the inefficiencies of mobile IP regarding data forwarding from a correspondent node           to a mobile node. State the general problems of mobile IP regarding security  and support of         quality of service.

4.         With a suitable example compare the behavior of DSDV and DSR algorithm with their       routing table or cache contents.

5.         Discuss about tunneling and encapsulation mechanism and reverse tunneling

6.         What is DSDV and explain it in detail.

7.         Explain the approaches of IP micro-mobility support ‘in detail’.

8.         Define DSR, principle of DSR, discuss.

9.         Explain DSR protocol with example. What are the advantage and pitfalls of cache maintenance in DSR?

10.     Explain the role of different entities in mobile IP with an example.    

11.     What are the types of registration in mobile IP? Explain.                  

12.     Explain the different types of encapsulation techniques in mobile IP.    

13.     Explain the different routing techniques available for mobile ad hoc network with an            example.

14.     Explain the agent discovery process in mobile IP.                                     

15.     Explain the different approaches available for IPv6 to support mobility.

16.     Compare the features of wired network with ad hoc network related to routing.                                         

UNIT- IV

BIG QUESTIONS

1.         Explain in detail about classical enhancements to TCP for mobility.

2.         How many types of TCP exist? Explain them in detail.

3.         Compare I-TCP, Snooping and mobile TCP

4.         Compare and contrast I-TCP, Snooping TCP, and Mobile TCP.

5.         What is the reaction of standard TCP in case of packet loss? In what situation does this      reaction make sense and why it is quire problematic in the case of wireless networks and             mobility?

6.         What are the primary goals or objectives of WAP forum efforts and how the effected in the            initial WAP protocol architecture?

7.         Explain a digital video broadcasting scenario.

8.         Explain in detail about traditional TCP.

9.         Explain about indirect and snooping TCP.

10.     Briefly discuss about WAP.

11.     Compare snooping TCP with Mobile TCP with example network scenarios.

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

13.     Explain in detail about the architecture of WAP.

13.     State the features of I-TCP                                                                       

14.     Explain the features of S-TCP.                                                                   

15.     State the features of M-TCP.                                                                   

16.     Explain the architecture of WAP.                                                             

17.     Explain the features of WML.                                                                   

18.     Explain the function of WDP.                                                                    

19.     Explain the services offered by WSP.       

20.     Describe Transaction and Session protocols of wireless.                                       

21.     Explain the services offered by WTA with an example.                              

UNIT- V

1.         Discuss in detail about any two Pervasive Applications of your choice in detail.

2.         Explain about the various hardware components involved in Pervasive Computing Devices.

3.         Write brief notes on the following.
                        a. Speech Recognition
                        b. Handwriting recognition
                        c. Haptic Interfaces
                        d. QWERTY and FITALY keyboards

4.         Explain in detail about Bio-Metrics. List out its merits and demerits.

5.         How is synchronization carried out in a Pervasive Environment? Write brief notes on the                             syncML tool.

6.          What are the various issues related to device management and how are they dealt with?

7.          Explain how a Pervasive Web Application can be secured using an ‘Authentication Proxy’.

8.         How security is achieved in MVC and JSP based applications?

9.         Discuss in detail about the access form PCs.

10.      How is access carried out in case of a PDA?

11.      Explain in detail about access via WAP.

                        B.E/B.Tech Degree Examination APRIL /MAY 2010
Eighth Semester
Computer Science and Engineering
IT1402-MOBILE COMPUTING
(Regulation 2004)

Answer all questions

Part -A(10*2=20)Marks

1 What is spreading factor?
2.What is polling?
3.Distinguish between soft handover& hard Hand over.
4.Define foot print with respect to satellite systems.
5.State the 3 phases of the medium access of different competing nodes.
6.what are the power saving mechanisms in bluetooth?
7.What are the drawbacks of wired networks?
8.Define Dynamic Source Routing.
9.What is the difference between TCP & UDP.
10. Mention any 2 salient features of WAP.

Part-B (5*16=80)Marks

11 (a) i Discuss in detail about the types of antennas with their radiation patterns.(12)
            ii Explain Diversity techniques.(4)
                                                                        [or]
11 (b) Explain space Frequency,code & Time division Multiplexing in detail.(16)

12 (a) Describe Digital Audio Broadcasting.(16)

[or]

(b) Explain routing ,localization and handover in satellite systems.(16)

13 (a) Describe architecture of BLUE TOOTH.(16)

[or]

(b)Explain Channel control sub layer in HIPERLAN.(16)

14 (a) Explain optimization in Mobile IP in detail.(16)

[or]

(b)Explain IPV6 Protocol in detail.(16)

15 (a) Discuss the role of WWW in support for mobility.(16)
[or]

(b) Explain the following:
(i) Indirect TCP. (6)
(ii)Snooping TCP.(6)
(iii)Explain about performance enhancing proxies.(4)

                        B.E./B.Tech. DEGREE EXAMINATION, NOVEMBER/DECEMBER 2011.
                                                                        Seventh Semester
                                                            Computer Science and Engineering
                                                CS 2402 — MOBILE AND PERVASIVE COMPUTING
                                                                        (Regulation 2008)   www.2webworld.com
Time : Three hours                                                                                        Maximum : 100 marks
                                                            Answer ALL questions.
                                                PART A — (10 × 2 = 20 marks)
1. What are the four types of handover available in GSM?
2. Distinguish between mobile terminated call and mobile originated call.
3. Mention the advantages of WLAN?
4. What are the three Low Power States provided by Bluetooth?
5. What are the requirements of mobile IP standard?
6. Differentiate wired networks routing from ad-hoc wireless networks routing.   www.2webworld.c
7. List the advantages and disadvantages of mobile TCP?
8. Define WAE.
9. What is Pervasive Computing?
10. What are the various issues related to device management in pervasive
computing?
                                                PART B — (5 × 16 = 80 marks)
11. (a) (i) Explain the GSM system architecture with a neat diagram. (8)
(ii) Describe the security services provided by GSM. (8)
                                                            Or
(b) (i) Explain the protocol architecture of GSM for signaling. (8)
(ii) Explain the architecture of GPRS with a neat diagram. (8)

12. (a) (i) Describe HiperLAN architectural components and their interactions. (8)
(ii) Explain the architecture of WiFi in detail. (8)
                                                Or
(b) (i) Explain the system architecture of IEEE 802. (8)
(ii) Describe the architecture of WiMAX in detail. (8)

13. (a) (i) List the entities involved in mobile IP and describe the process of data transfer from a mobile node to a fixed node and vice versa. (8)
(ii) Why is conventional routing in wired networks not suitable for wireless networks? Substantiate your answers with suitable examples. (8)
                                                            Or 
(b) (i) Explain in detail Dynamic Host Configuration Protocol. (8)
(ii) Describe how the multicast routing is done in ad-hoc networks. (8)
14. (a) (i) State the requirements of WAP. Explain its architectural components. (8)
(ii) Explain WML and WML scripts with an example. (8)
                                                            Or
(b) (i) What is WTP? Discuss about its classes. (8)
(ii) Explain the architecture of WTA. (8)
15. (a) (i) Describe the various hardware components involved in pervasive computing devices. (8)
(ii) Explain how a pervasive web application can be secured using an ‘Authentication Proxy’. (8)
                                                            Or 
(b) (i) What are the applications of pervasive computing? Discuss any two of them. (8)
(ii) Explain how pervasive web applications can be accessed via WAP.(8)    w