IMPORTANT QUESTIONS

ECS-087 Mobile Computing

YEAR / SEM: IV/VIII

Dronacharya Group of Institutions Department of Information

Technology

Short Answer Type Questions

Q1. Differentiate between signal and data.

Ans. The term ‘data’ represents message or information where the signal is the representation of the

data, and it is also termed as information bearing signal.

Q2. What is a periodic signal?

Ans. In a signal if a particular signal pattern repeats over a time period systematically it is a periodic signal.

Q3. What is a “Aperiodic” signal?

Ans. In a signal if the same signal pattern does not repeat itself over a time period it is known as

‘Aperiodic’ signal.

Q4. Give an example for periodic and aperiodic signals.

Ans. a. periodic signal x (t + T) = x(t).

where - ∞ < t < + ∞

b. Aperiodic signal x (t + T) ≠ x(t).

Q5. Define wavelength.

Ans.The wavelength of a signal represents its distance or range it takes for one cycle. It is denoted as ‘λ’.

Wavelength λ = c/f

Q6. What is a bandwidth?

Ans. Bandwidth is the range of frequencies and represented as BW = f2 – f1, where f1 – f2 are the first and

last frequencies of the signal graph.

Q7. Define attenuation.

Ans. It is nothing but reduction in signal strength mainly at higher frequency ranges, and at receiving end

this attenuated signal has reduced voltage levels.

Q8. Draw the diagram of multiplexing.

Ans.

M D

U One link E

Input X M Outputs

U

X

Q9. What is the principle used in multiplexers?

Ans. The principle used in multiplexer is ‘many to one’ concept. Many inputs are combined as one link or

one output from a MUX unit where a DEMUX unit at the receiver reproduces the same many units

at the end entity.

Q10. What are the important multiplexing schemes?

Ans.

Multiplexing

Frequency Division Time Division Code Division

Multiplexing (FDM) Multiplexing (TDM) Multiplexing (CDM)

Q11. What are the multiple access schemes?

Ans. a) FDMA b) TDMA c) CDMA

Q12. What is personal communication?

Ans The vision for the emerging mobile and personal communication services and system is to enable

communication with a person, at any time, at any place, and in any form. Besides providing

unlimited reach ability and accessibility, this vision for personal communication is also underlines

the increasing need for users of communication services to be able to manage their individual calls,

and services according to their real time needs.

Q13. What are the different kinds of mobility?

Ans. Terminal mobility: Terminal mobility systems are characterized by their ability to locate and identify

mobile terminals as it moves, and to allow the mobile terminal to access telecommunication

services from any location-even while it is in motion. Terminal mobility is associated with wireless

access and requires that the user carry a wireless terminal and be with in a radio coverage area.

Personal mobility: personal mobility on the other hand , relies on a dynamic association between

the terminal and the user, so that the call delivery and billing can be based on a personal identity

assigned to a user. Personal mobility systems are therefore characterize by their ability to identify

end users as they move, and allow end users to originate and receive calls, and to access subscribed

telecommunication services on any terminal, in any location.

Service portability: it refers to the capability of a network to provide subscribed services at the

terminal or location designated by the user. The exact services the user can invoke at the designated

terminal, of course, depend on the capability of the terminal and the network serving the terminal.

Q14 . Define guard band.

Ans. It is unused (dummy) frequency inserted with actual spectrum to reduce adjacent channel

interference to enhance accuracy.

Q15. What are the types of spread spectrum and differentiate them?

Ans. a) FHSS - Frequency Hopping Spread Spectrum

b) DSSS – Direct Sequence Spread Spectrum..

DSSS FHSS

Each bit in transmission can be

represented as multiple bits.

Signal is transmitted in random series at

fixed time intervals. Synchronization

between transmitter and receiver is a

must.

Q16. Define a cell.

Ans. The smallest geographical area covered by wireless communication is said to be a cell.

Q17. What are the shapes related to a cell?

Ans. In early days three shapes namely.

a. Circle b. Square c. Hexagon

were suggested for a cell. But coverage of signal was very accurate with hexagonal shaped cells and

in later stage it was taken as standard.

Q18. Define BTS.

Ans. BTS is the base transceiver station available in each cellular region.

Q19. What is a MSC? What are the functions of MSC in network and switching subsystem?

Ans. It is mobile switching center and it enables connectivity between BTS and PSTN.

(i) It is like a normal switching node for PSTN fixed telephone and for cellular subscribers of the same network.

(ii) It is possible to have functions like registration, location updating, and authentication, call routing etc.

Q20.What is known as ‘handoff' ?

Ans. Handoff is a principle used to continue the call established in mobile communication. When the

subscriber is towards the cell boundary the signal strength reduces by which the BTS of that cell hand over the call to the next BTS of another cell where the subscriber enters.

Q21. What are the types of handoff?

Ans. a) Hard hand off.

b) Soft handoff.

Q22. What is mobility management?

Ans. Mobility management is one of the major functions of a GSM or a UMTS network that allows mobile phones to work. The aim of mobility management is to track where the subscribers are, allowing calls, SMS and other mobile phone services to be delivered to them.

Q 23.What is frequency reuse in cellular systems?

Ans. The key characteristic of a cellular network is the ability to re-use frequencies to increase both coverage and capacity. As described above, adjacent cells must utilize different frequencies, however there is no problem with two cells sufficiently far apart operating on the same frequency. The elements that determine frequency reuse are the reuse distance and the reuse factor.

The reuse distance, D is calculated as

where R is the cell radius and N is the number of cells per cluster. Cells may vary in radius in the ranges (1 km to 30 km). The boundaries of the cells can also overlap between adjacent cells and large cells can be divided into smaller cells.

The frequency reuse factor is the rate at which the same frequency can be used in the network. It is 1/K (or K according to some books) where K is the number of cells which cannot use the same frequencies for transmission. Common values for the frequency reuse factor are 1/3, 1/4, 1/7, 1/9 and 1/12 (or 3, 4, 7, 9 and 12 depending on notation).

In case of N sector antennas on the same base station site, each with different direction, the base station site can serve N different sectors. N is typically 3.

A reuse pattern of N/K denotes a further division in frequency among N sector antennas per site. Some current and historical reuse patterns are 3/7 (North American AMPS), 6/4 (Motorola NAMPS), and 3/4 (GSM).

If the total available bandwidth is B, each cell can only utilize a number of frequency channels corresponding to a bandwidth of B/K, and each sector can use a bandwidth of B/NK.

Cells with the same number have the same set of frequencies. Here, because the number of available frequencies is 7, so the frequency reuse factor is 1/7. That is each cell is using 1/7 of available cellular channels.

Q 24. What is cluster?

Ans. A cluster is a group of cells. No channels are reused with in a cluster. Figure shows 7-cell cluster.

Q25. List all the services provided by GSM.

a) Tele services. b) Bearer services. c) Supplementary services.

Q26. What are the services provided by supplementary services?

Ans. · User identification

· Call redirection

· Call forwarding

· Closed user groups

· Multiparty Communication

Q27. What are the different managements under GSM protocol architecture?

Ans. (i) Mobility management (ii) Connection management

(iii) Radio resource management (iv) Message transfer

Q28. What is a TCH/H GSM channel?

Ans. It is half rate traffic channel that supports traffic channels with half-rate speech coding. It can use up to 16 slots in one frame with a data rate of 11.4 kbps/sec.

Q29. What are the common control channels?

Ans.The common control channels (CCCH) are used for call establishment and they are basically one way channels.

Q30. What are types of CCCH ?

Ans. (i) Random access channel (RCH) (ii) Paging channel (PCH)

(iii) Access grant channel (AGCH)

Q31. What is a RCH?

Ans. For establishing a call RCH (Random access channel) is used by mobile station to access the base station involved.

Q32. What is DCCH? What are the types of DCCH?

Ans. It is duplicated control channels known as two way channels and it is useful for signaling and control operations for individual subscribers.

DCCH types:

(i) Stand alone dedicated control channel (SDCCH) (ii) The slow associated control channel (SACCH) (iii) The fast associated control channel (FACCH)

Q33. What are the four types of handover available in GSM?

Ans. (i) Intra cell Handover

(ii) Inter cell Intra BSC Handover

(iii) Inter BSC Intra MSC handover

(iv)Inter MSC Handover

Q34. What are subsystems in GSM system?

Ans. · Radio subsystem(RSS)

· Network & Switching subsystem(NSS)

· Operation subsystem(OSS)

Q35.What are the information in SIM?

Ans. · card type, serial no, list of subscribed services

· Personal Identity Number(PIN)

· Pin Unlocking Key(PUK)

· An Authentication Key(KI)

Q36. What is meant by GPRS?

Ans. The General Packet Radio Service provides packet mode transfer for applications

that exhibit traffic patterns such as frequent transmission of small volumes.

Q37. What is the function of an AuC?

Ans.The authentication center (AuC) maintains copy of secret key that is stored in each and every subscribers SIM card. It is used to protect user’s database.

Q38. What are the three types of switching methods?

Ans. a. Circuit switching

b. Message switching

c. Packet switching

Q39. What is QoS in GPRS.

Ans. In GPRS the users can specify the QoS profile where the profile determines

important things like reliability class, delay class and service precedence.

Q40. What is the use of SS7?

Ans. (a) In network subsystem the SS7 (signaling system number 7) is used for signaling between different functional entities.

(b) SS7 is used for SMS, roaming prepaid network functions.

(c) SS7 is also used for trunk signaling.

Q41. What are the parameters considered for defining QoS in GPRS technology?

Ans. (i) Service precedence (ii) Delay

(iii) Throughput (iv) Reliability

Q42. A certain city has an area of 1300 square miles and is covered by a cellular system using a seven cell

reuse pattern. Each cell has a radius of 4 miles and the city has 40 MHz spectrum with a full duplex channel bandwidth of 60KHz. Find:

(i) The number of cells in the service area. (ii) The number of channels per cell. (iii) Total number of subscribers that can be served.

Ans. (i) Radius of a cell = 4 miles

Area covered by cell = 50 square miles.

For 7 cell reuse pattern

Area covered by cluster = 7*50 = 350 square miles.

So, no. of cells required to cover 1300 square miles is 28.

(ii)No. of channels per cell = total no. of channels/no. of cells in a cluster

Available frequency = 40MHz Channel bandwidth = 60 KHz

No. of channels available = 40 MHz/60KHz = 666 channels No. of channels per cell = 666/7= 95 channels per cell.

(iii)total number of subscriber that can be served =666*4 = 2664 subscribers. Q43. If a total of 33 MHz of bandwidth is allocated to a particular cellular system which uses two 25 KHz

Simplex channels to provide full Duplex voice. Compute the number of channels available per cell if the system uses:

(i) 4 cell reuse (ii) 7 cell reuse

Ans. Available bandwidth = 33 MHz

Channel bandwidth = 25 KHz

Total no. of channels available = 1320 simplex channels.

(i) For 4 cell reuse No. of channels per cell = 1320/4 = 330 channels

(ii) For 7 cell reuse No. of channels per cell = 1320/7 = 188 channels

Q44. What are the functions of MSC in network and switching subsystem?

Ans. (i) It is like a normal switching node for PSTN fixed telephone and for cellular subscribers of the same network.

(ii)It is possible to have functions like registration, location updating, and authentication, call routing etc.

Q45. State the requirements of mobile IP.

Ans. i. Compatibility ii. Transparency iii. Scalability and efficiency

iv Security

Q46. What is COA? How is it assigned?

Ans. Care-or address (COA): The COA defines the current location of the MN from an IP point of view.

There are two different possibilities for the location of the COA:

• Foreign agent COA • Co-located COA

Q47. How does a MN identify that it has moved?

Ans. Mobile IP describes two methods: agent advertisement and agent solicitation, which are in fact router discovery methods plus extensions.

Q48. What are the contents of mobility binding?

Ans. Mobility binding containing the mobile node’s home IP address and the current COA. Additionally, the mobility binding contains the lifetime of the registration which is negotiated during the registration process.

Q49. Define encapsulation. List the types of encapsulation.

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

• IP-in-IP encapsulation • Minimal encapsulation • Generic routing encapsulation

Q50. State any 4 features of IPv6.

Ans.

• No special mechanisms as add-ons are needed for securing mobile IP registration. Every IPv6 node masters address auto configuration – the mechanisms for acquiring a COA are already built in.

• Neighbor discovery as a mechanism mandatory for every node is also included in the specification; special foreign agents are no longer needed to advertise services.

• Combining the features of auto configuration and neighbor discovery means that every mobile node is able to crate or obtain a topologically correct address for the current point of attachment.

• Every IPv6 node can send binding updates to another node, so the MN can send its current COA directly to the CN and HA.

Q51. State the layers in WAP architecture. Ans.

• Transport layer • Security layer • Transaction layer • Session layer • Application layer

Q52. What are the different security levels offered by WTLS?

Ans. (i) Privacy (ii) data integrity (iii) authentication

Q53. How is reliability achieved in WTP?

Ans. (i) duplicate removed (ii) retransmission

(iii) acknowledgements (iv) unique transaction identifier.

Q54. What are the functions of WSP?

Ans.

(i) session management (ii) Capability negotiation

(iii)content encoding

Q55. List any 4 basic features of WML.

Ans.

(i) Text and images representation. (ii) User interaction

(ii) Navigation (iv) Context management.

Q56. List any 4 capabilities of WML script.

Ans.

(i) Validity check of user input (ii) Access to device facilities

(iii) Local user interaction (iv) Extension to the device software.

Q57. What are the benefits of IMT-2000 over 2G systems?

Ans.

(i) Circuit and packet bearer capability up to 144 kbps. (ii) User authentication and ciphering. (iii) Multimedia services. (iv) Emergency and priority calls.

Q58. Compare MEO and LEO satellite types.

Ans.

Characteristics MEO LEO

Satellite lifetime 10 to 15 years 4 to 8 years

Altitude range 10,000 to 20.000 km 500 to 2000 km

Round - trip delay 40 to 80 msec 5 to 10 msec

Q59. What is a GEO?

Ans. The communication satellite (GEO) orbits in geo stationary orbit which is at 36000 km above earth's surface. The satellite revolves with same speed as that of the earth (1 Rev / day) that revolves around sun.

Q60. What are examples of global mobile satellite system?

Ans.

(i) Iridium (ii) Teledesic (iii) Global star

Q61. Give three specifications of Global star and Iridium systems.

Ans.

Characteristic Global star Iridium

System type LEO LEO

Data speed 7.2 kbps 2.4 kbps

Launched year 1999 1998

Q62. What are the advantages of Iridium satellite system?

Ans.

(i) Inter-satellite links are possible. (ii) Number of satellites possible is 66 and 6 numbers of satellites can be maintained as spares. (iii) The terminal types can be of dual mode, mobile or handheld.

Q63. Give few advantages of GEO satellites.

Ans.

(i) They have large footprints and provide large coverage.

(ii)Used for communication related applications.

Q64. What is the demerit of GEO satellite?

Ans.

Their round trip time delay is long due to high altitudes, and it results in qua1ity degradation.

Q65. What are the advantages of LEO satellites?

Ans.

(i) LEO satellites provide higher global coverage. (ii) High spectrum utilization. (iii) The propagation delay is lower (say ≈5 to 10 msec).

Q66. What are the demerits of LEO system?

Ans.

(i) The network architecture is complex. (ii) Satellite movement is rapid and analysis is tough.

(iii) Routing mechanism is difficult. (iv) Long period of deployment.

Q67. What is IEEE 802.11? Explain 802.ii family.

Ans. IEEE 802.11 is a set of standards for implementing wireless local area network (WLAN) computer communication in the 2.4, 3.6 and 5 GHz frequency bands. They are created and maintained by the IEEE LAN/MAN Standards Committee (IEEE 802).

IEEE 802.11 Family

Q68. What is

WLL? Draw

the WLL setup

diagram.

Ans. WLL is a system that connects subscribers to the local telephone station wirelessly.

It is based on:

– Cellular – Satellite (specific and adjunct) – Microcellular

Its Other names:

– Radio In The Loop (RITL) – Fixed-Radio Access (FRA).

802.11 protocol

Freq. (GHz)

Bandwidth (MHz)

Data rate per stream (Mbit/s)

Allowable MIMO streams

Modulation

----- 2.4 20 1,2 1 DSSS,FHSS

a 5 20 6,9,12,18,24,36,48,54 1 OFDM

b 2.4 20 5.5,11 1 DSSS

g 2.4 20 6,9,12,18,24,36,48,54 1 OFDM,DSSS

n 2.4/5 20/40 7.2, 14.4, 21.7, 28.9, 43.3, 57.8, 65, 72.2/ 15, 30, 45, 60, 90, 120, 135, 150

4 OFDM

A general WLL Setup

Q69. State the modes possible when the slave is in connection state in Bluetooth.

Ans. (i) Active (ii) Sniff (iii) Hold (iv) Park

Q70. What are elements available under link security of Bluetooth technology?

Ans. (i) Authentication (ii) Key management (iii) Encryption

Q71. What is a LMP? List three security services under LMP.

Ans. It is “link manager specification” that is responsible for radio link between the master and slave in Bluetooth. This protocol also involves message exchanges in the form of LMP-PDU’s.

a) Authentication b) Change link key c) Encryption

Q72. What is Bluetooth? List few functions of Bluetooth.

Ans. It is a low power short range wireless standard and it can operate in situations where several users are involved. At the maximum eight different devices can communicate in a network using this standard.

(i) It can make call from a headset (wireless) to a mobile phone which is at a distant place.

(ii) It can trigger MP3 players on some other machines to download audio signals like music in wireless environment.

(iv) It mainly eliminates cables in many user applications.

Q73. Differentiate piconet and scatternet in Bluetooth technology.

Ans.

(i) Piconet – It is a basic network supported by Bluetooth standard where one master and seven slaves (total eight devices) can interact.

(ii) Scatternet – A device in one piconet either a master or slave can interact with other device that is overlapping of one piconet on other piconet is possible and termed as a “Scatternet”.

Q74. What is an ‘IrDA’ standard?

Ans. ‘IrDA’ is a standard that is specified by Infrared Data Association formed in the year 1993. It was developed mainly to enhanced point-to-point or point-to-multipoint communication. It is dependant on line of sight (LOS) operation.

The infrared rays can be used wherever LOS is preferred and useful for this indoor consumer applications.

Q75. What are the specifications of ‘IrDA’?

Ans. The IrDA standard 1.0 supports the data rate up to 115.2 kb/sec. for the range up to 1m and next version ‘IrDA 1.1” developed later supports data transfers up to 35 times faster when compared to “IrDA 1.0”.

Q76. What are the new specifications supported by current Bluetooth?

Ans. The short range Bluetooth technology is improved for meeting the distance of 100m in open air and 30 m within building infrastructures for it’s operation. It works with data rate of 1 Kbps.

Q77. What re the two kinds of profiles in Bluetooth 1.1 version?

Ans. The two main profile classification is nine application profiles and four system profile and as a whole thirteen profiles are supported by Bluetooth 1.1 version.

Q78. What are the system profiles used in Bluetooth 1.1 version?

Ans. The system profiles are generic object exchange, object push, file transfer and synchronization profiles.

Long Answer Questions

Q.1. What is WAP?

WAP stands for Wireless Application Protocol is a set of standard protocols which provide wireless internet services on digital mobile phones, pagers, PDAs and other wireless devices. WAP extends the Internet by addressing the unique requirements of the wireless network environment and the unique characteristics small handheld devices. The WAP specifications leverages existing technologies, like digital data networking, and the Internet technologies, such as HTTP, XML, SSL, URLs, and developing new extensions when needed. It helps developers and industry to develop solutions that are air- interface independent, device independent, and that are fully interoperable. The WAP specifications ensure that the solutions are secure, fast and reliable. The WAP standard provides the necessary network protocols, content types, and run-time application environments to deliver a broad set of new and existing services.

Q.2. What are the factors enabling the convergence of wireless and wired world?

Today Internet allows people to exchange message at the speed of light and access information from any source around the globe, thereby enriching people’s personal lives and reducing costs for business. At the same time people have jumped to wireless communications. Cellular telephones are critical companions for active consumers and mobile professionals. It is easier to deploy cellular infrastructure than traditional phone infrastructure where we have insufficient telephone infrastructure.

These two trends – ‘the expansion of the Internet ‘s reach and burgeoning of the mobile

Internet’ extends the traditional Internet to wireless devices such as cellular phones, PDAs, and even automobiles.

Q.3. What is mobile Internet?

The convergence of Internet and wireless communication has given rise to mobile Internet. Where users can access Internet and World Wide Web anywhere and anytime and wide range of wireless devices such as mobile phones, PDAs, etc. WAP (wireless application protocol) has enabled the use of Internet

over high latency and low bandwidth cellular networks. The mobile Internet users want personalized services that match their individual preference and

needs. Services should be tailored to suit the user’s current physical location. The mobile Internet combines data and voice, information and communication, and global reach and personalization. The mobiles applications deliver data that is currently available on enterprise intranets, the World Wide Web to devices in mobile context which may be time-sensitive, location-sensitive, or secure in nature.

Q.4. List some productivity application services provided by mobile Internet.

Some of the productivity applications provided by mobile Internet are as follows: > Email/Text Messaging > Personal Information Management

> Unified messaging and Universal Mailbox > Instant Messaging

Q.5. How Mobile Internet is helping us to improve our productivity?

Productivity applications enable the user to manage information and enhance their day-to-day communications with friends and colleagues.

Email/Text Messaging: They improve speed and quality of business decision making by facilitating communication with the external clients and vendors, and enabled collaboration. It allows to keep I touch with family and friends easily and eliminates the barrier posed by long distances.

Wireless e-mail makes traditional e-mail even more powerful by allowing users to read and reply to email messages from anywhere, without being chained to home or office. Mobile Internet as enabled by WAP, allows for native(live) access to the original copy of the information residing on an enterprise or web based email server.

Personal Information Management: This application suite includes tools such as calendar, scheduling, contact lists or address books, and to-do lists. It allows users to schedule meetings and maintain a directory of contacts while on the road.

WAP enabled PIM solutions allows the user to download and synchronize databases over the air, giving the user access to a global phone book, the organizational diary database, and other information at all times.

Unified Messaging and Universal: The Unified Messaging Consortium(UMC) defines messaging as the ability to users to respond to multimedia messages without concern for the sender’s message format. Unified messaging enables the integration of voice, e-mail, and fax into a single inbox that can be accessed by the user.

With the advent of several communication technologies such as voice mails, text messages, emails the users are forced to deal with several mailboxes and corresponding devices. Unified messaging allows the user to user a variety of devices to not only access a single message store containing multiple messages types but also respond to those messages in a format that is acceptable to the original sender. It is a key application that streamlines and simplifies messaging in both the voice and data worlds.

Instant Messaging: permits two or more people to carry on a private conversation online. Unlike with email, the interaction is instantaneous. It allows users to create a personalized directory of people with whom to converse and determine whether those people are online. The instant messaging services allows users to exchange instant messages, pictures, and documents, and ability to participate in group chat rooms and also offers voice capabilities.

Corporate call centers, customer-support operations, and supply chains are benefiting using real-time IM to improve customer relations and boost business. It also enables real-time transactions in business-to-business online marketplaces and digital exchanges.

Q.6. Name and explain the key services for the mobile Internet.

The key applications for mobile Internet as follows:

Productivity Applications: enable the user to manage information and enhance their day-to- day communications with friends and colleagues.

o Email/Text Messaging: Native access to electronic mail, with features such as reading message, replying to it.

o Personal Information Management: Access to calendar for schedule and appointments, reminders and notifications, address book, and contacts, and to-do lists.

o Unified Messaging and Universal Mailbox: Integration of voice mail, e-mail, and fax into the same inbox that can be accessed by the user by various means.

o Instant Messaging: Awareness of online users and instant messaging with them.

Information and Transaction Services: o Kiosk to content o E-commerce

Life-enhancing applications o Telematics o Entertainment services o Multimedia Services o Enhanced telephony applicatios

Telephony, account and subscription, Vertical Services o E-care o Fleet Management and dispatch o Sales force automation

Q.7. What is the role of Mobile Internet Access provider?

The wireless operator or carrier enables seamless coverage and connectivity to both voice and data applications, regardless of the location from which the services are accessed. To support WAP, the carrier implements, maintains, and upgrades the necessary wireless network and data (ISP) infrastructure; it also ensures high availability of the network at all times. The operator has access to a large subscriber base from the voice world, and also has the infrastructure needed for billing and payment collection, so the portals and content providers can partner and obtain access to customers and infrastructure. The operator would act as the primary interface to the subscriber and function like a service bureau. Some carriers might implement a revenue-sharing business model with the content providers, others may function as a simple transport or access provider. Some might develop a strategic collaboration with the content providers to support private-labeled or co-branded WAP sites or instead opt to earn a small commission from the million of transactions carried out over their wireless networks. It might even extend its role to niche areas such as service hosting, service aggregation, or customization rendering

Q.8. Write all stakeholders of Business Value chain and explain how mobile ISP and Application Service

Providers are generating revenues?

The key components for engaging the wireless Internet are

the device the network access and infrastructure the service subscription the application and its development the server that hosts the applications.

Collectively, the businesses that will play a part in providing one or more of these components, define a value chain for delivering services to end users. Each member of the value chain offers a specific revenue-generating value proposition either to end users or to other businesses within the value chain.

The stakeholders of the Business Value Chain are as follows:

Stakeholder Function Examples End User Is the primary consumer of the service. You and Me Handset Manufacturer

Manufactures the terminal device and the micro-browser or other user agents running on it.

Ericsson, Nokia, Motorola,Panasonic, Sharp

Wireless Network Operator and ISP

Operates the wireless network; may implement the WAP capability and provide connectivity between the device and the internet

AT&T, NTT, DoCoMo, SBC, Vodafone Airtouch

Infrastructure Vendor

Manufactures gateways, switches, servers, and tools that implement WAP technology and allow WAP applications to be built and hosted

Ericsson, IBM, Nokia, Phone.com

Content Aggregator or content portal

Aggregates and packages a variety of content offered by various content providers; may implement the WAP capability and provide connectivity between the device and the Internet

Excite, Infospace, Nokia, Phone.com

Application Service Provider/Service Bureau

Provides and aggregates services such as e-mail, PIM and enterprise application access

Aether, AOL, Concentric, IBM

Content Provider Owns the specialized content and makes it available to end users by hosting it on the Internet or intranet

CNN, Mapquest, Reuters

Application and content developer/author

Develops the application, service, or content Various ISVs

Application service providers (ASPs) and service bureaus are emerging new channel for applications on the web. These providers host and rent niche applications to ISPs, enterprises, and consumers alike. Service Bureaus generally offer ‘horizontal’ applications such as email, and content hosting, whereas most ASPs also support specialized business software such as ERP or sales force automation.

The value proposition lies in offering economies of scale while hosting applications and servers within virtual domains for multiple small or medium-size businesses. The typical revenue model is based on the number of seats per customer per application per month. The vendors could find opportunities for new horizontal and vertical applications specifically tailored for the mobile data space. The new applications would likely require ASPs to incur only an incremental infrastructure cost because they already operate data and network operations centers. The service bureau would provide the enterprise with secure solutions that enable access to the corporate groupware application from any device over any network at any time. Other integrated access scenarios could include web hosting, supply chain management, sales force automation, and field service dispatch services. In the area of e-business, ASPs would host managed security offerings, audio and video streaming, and e-commerce transaction and fulfillment capabilities.

Q.9. Explain wireless device constraints.

The portable devices have a limited amount of processing power available, so the application which require large caches of data or complex calculation will perform poorly.With improvements happening regularly in the processing power we also require more data storage and battery power. However, the user interface is still limited to a handful of keys, low-definition displays and small form factors. The constrained user interface implies the need for new usability and design paradigm. Also, the application must be tailored toward specific devices and even may need to change its behavior dynamically based on how the device is currently being used. Eg. Sound may be turned on or off.

Q.10. What is latency? How TCP behaves in high latency environment?

Network latency or delay is the amount of time required for a message to travel between two points in the network. The latency, once established, will remain reasonably constant for each byte sent via connection. Wireless networks typically have considerably longer latencies than their wired counterparts.

Wireless network latency also effects the underlying transport protocols. The TCP get into all sorts of trouble if the network latency exceeds what the TCP considers a reasonable time to receive a response. TCP includes a very complex set of rules to ensure that it can handle slow-responding network and it tries to adjust itself to work with the response times discovered. The transport problems arise because of the way that TCP attempts to adjust its transmission speed to account for network congestion and avoid flooding the network. TCP sends two basic acknowledgments from the receiver:

ACK, the normal positive acknowledgment that the data was received correctly and in sequence

order. DUPACK, indicating that the data was received correctly but “out of sequence”.

TCP has two types of triggers for error recovery:

Timeout: If timeout is detected, the sender reduces its transmission speed to one segment per

Round-Trip Time (RTT), in the belief that either serious congestion or link failure has occurred. If this drastic rate reduction is successful, the sender then ramps up the transmission speed exponentially in the “slow start” phase, reaching half of the original transmission rate. Finally, in the “congestion avoidance phase”, the transmission rate is increased linearly.

DUPACK: recovery mechanism begins with the sender halving its data rate (i.e. segments sent per RTT). The rate is then increased in the same way as in the congestion avoidance phase.

Q.11. What is the effect of latency on wireless devices and applications?

A wireless system will need to take account of the network latency to operate effectively, otherwise false errors will be detected. Miscalculations of the expected response time has dire consequences for an application’s behavior. Variable wireless network latencies can introduce other side effects as well. Eg, if each packet incurs a different latency, then packets may be received out of order. Reassembling of the packets in the correct order requires each packet to have some form of sequence identifier and a reassembly software in the device.

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