Question 1. What Is Bluetooth?
- Bluetooth is a wireless technology standard used to exchange data over short distances.
- The data is exchanged from fixed and mobile devices by creating Personal Area Network with security at high level.
- Bluetooth was originally conceived as a wireless alternate to RS-232 cables.
- It resolves the problems synchronization by connecting several devices.
- It requires a low-cost transceiver chip that needs to be included in all the devices.
- The connections can be point to point or multipoint.
- A built in verification and encryption is also provided.
Question 2. Bluetooth Is Called A Cable Replacement Technology. Explain.
- Bluetooth allows Personal Area Networks without the cables.
- It provides connectivity to many mobiles users at a time for sharing without wires.
- Bluetooth chip is designed for replacing cables by transmitting the information at a special frequency from sender to receiver.
- Bluetooth is an inexpensive,low-power, short range radio based technology.
- Cabling involves a lot of cost foe execution.
- Bluetooth is much more flexible and robust than cabling.
- They even require a very low bandwidth of data transfer.
Question 3. Explain About Tcp Flow Control?
TCP utilizes a flow control protocol from one end to another end for avoiding the sender to send data too quickly for the TCP receiver to receive and process it in a reliable manner. Machines of diverse network can communicate quickly by having the flow control mechanism.
TCP utilizes a sliding window flow control protocol. In every TCP segment, the receiver is specified in a receive window field, the additional received data that is to buffer for the connection. When a window of size 0 is advertised by a receiver, the data sending is stopped by the sender and starts the persist timer. The TCP dead lock situation is protected by the persist timer. The TCP sender sends the packet and the receiver sends the acknowledgement with the new size of window, at the time of expiring the persist timer.
Question 4. Explain The Working Of Trace Route?
Trace route works by increasing the time-to-live value of every successive packets sent in batch. Every three packets that were sent first, have a time-to-live value 1. The next three packets have a TTL value of 2 and so on. The host decrements the TTL value by one and the packet is forwarded to the next host, when a packet passes through a host.
When a packet (with a time-to-live value of 1) reaches a host, the packets will be discarded by the host, and an ICMP time exceeded packet is sent to the sender. A list of hosts, whose packets have traversed enrouted to the destination, is utilized by the trace route utility.
Question 5. What Is Piconet?
Piconet is an ad-hoc network by linking a group of users which uses blue tooth technology protocols for allowing one ‘master’ device to interconnect with up to seven active ‘slave’ devices. Further, up to 255 slave devices could be inactive or packed and the master device can bring into active status at any given point of time.
The range of Piconet will vary based on the blue tooth device class. The data transfer rate varies around 200 to 2100 KB/S, depending upon the synchronous or asynchronous connection usage, and the number of devices connected in the piconet.
Question 6. Explain The Following Terms: Icmp, Arp, Multicast, Broadcast
- Internet Control Message Protocol: This protocol is used for while checking the connectivity using ping command
- Address Resolution Protocol: This protocol is used to know about the properties of TCP/IP. For example, to know other system MAC addresses.
- Multicast: Communication between single sender and a list of select recipients in a network.
- Broadcast: To send messages to all the recipients simultaneously in a network.
Question 7. List Out The Differences Between Udp And Tcp?
- TCP is connection oriented protocol, where as UDP is connection less protocol.
- In TCP, information is sent after establishing the connection from client to server, where as data is sent in chunks in UDP.
- TCP is reliable – unless the connection fails completely, the message will be reached to the destination.
- UDP is unreliable – there are chances to lose the data sent on the way.
- TCP is an ordered protocol – when messages are sent one after other, the first message will be received first.
- UDP is an unordered protocol – when two messages are sent, the order of their arrival at the destination is unknown.
Question 8. What Is Meant By The Term ‘ip Spoofing’?
IP Spoofing: Sending messages by intruder to a computer system with an IP address that indicates the message is sent from a trusted host, for gaining unauthorized access to computer systems. The hacker / intruder first utilize a variety of techniques for finding an IP address of a trusted host. Later he modifies the packet headers, in order to give an illusion that the packets are sent from the host.
Question 9. What Is Rj-45?
- RJ-45 stands for Registered Jack – 45.
- It is an 8-wire connector for connecting computer systems on to a LAN, especially Ethernets.
- These connections are similar in appearance to the ubiquitous RJ-11, which are used in connecting telephone equipment, with little more width.
- It is one of the most commonly used connectors.
- Two wiring schemes like T568A and T568B are used to terminate the twisted-pair cable to the connector interface.
- They look similar to the RJ-11 connectors which are used for connecting the telephone equipments but are wider then them.
Question 10. Which Technology Is Used To Avoid Interference In Bluetooth?
Blue tooth uses frequency hopping technology. In this technology, 79 hop frequencies are transmitted and received from 2402 to 2480 mhz. hopping in a pseudo random sequence at a rate of 1600 times in a second. Guassian frequency shift keying modulation is utilized with a maximum data transfer rate of 721 kbps. Bluetooth protocol stack is developed and TCP/IP imported layers are used in this technology.
Interference is being avoided by utilizing the frequency-hop(FH) spread spectrum technology. It is adaptable for low-power, low-cost radio implementations and also used in certain wireless LAN products.
The major advantage with this technology transmission is the high rate of 1600 hops / ps. Another advantage is, short packet length is also used by Bluetooth.
Question 11. What Is Tcp Connection Establishment And Tear Down?
The following is the process for TCP connection:
- As connection is made by synchronizing sender and receiver and the OS is informed about the connection establishment.
- Sender starts sending information and gets acknowledged. Soon after the sender sends the data, a timer is started.
- When the sender is not received any acknowledgement ever after exceeding the timer’s limit, the data is transmitted.
- If windowing occurs, buffer on the receiver is full, then a stop signal is sent by the sender and stops sending information.
- Soon after processing all data, a go signal is sent by the sender, followed by transmitting data again.
Question 12. What Is The Signal Strength Transmitted By Cell Phones?
The magnitude of the electric field at a reference point, which is significant distance from the transmitting antenna, is known as signal strength. Signal strength is expressed in voltage/length or signal power received by the antenna. In mobile phones, the signal strength is usually expressed in dB-microvolts per meter or in decibels above a reference level of one milliwatt.
Question 13. What Method Is Used For Voice Transfer? Brief About The Method Used?
For Voice transfer, SCO (Synchronous Connection Oriented) links are used for good synchronization and reliability.
Question 14. Explain The Modulation Techniques Used In Bluetooth Technology?
Blue tooth uses Frequency Hopping Spread Spectrum technique which is used in spread spectrum signal transmission. During radio transmission, frequencies are switched repeatedly, to help reducing unlawful access to cross paths which causes interruptions. FHSS makes Bluetooth communication more robust and secure. The speed of interferences from other devices will be reduced, though it will not cause the transmission to stop.
Adaptive modulation and coding methods, OFDM, GMSK, QAM, CDMA, DMT and similar methods are utilized in the areas of wireless, cellular and satellite communication systems. These modulations are used in wireless, cellular, wired line and satellite communication systems.
New technologies such as MIMO, BLAST and space-time coding are used in transmission data communication systems.
Question 15. What Are The Technical Characteristics Of Bluetooth?
The following are the technical characters of a Bluetooth device:
The devices are either a one chip solution or multiple chips in general. Blue tooth device has three main parts – RF, baseband processor and link manager (could be a CPU core like 8 or 16 bit Reduced Instruction Set Computer. A BT module in multiple chips, usually 2 or 3 chip, like RF on a chip are produced by certain vendors.
For a single chip solution, the following information can be used for referencing from a particular vendor.
- Package : 81 ball BGA, 8mm x 8mm
- Supply Voltage : 2.7 – 3.3v
- Power Consumption : Data transmitting @ 4dBm – type 41mA
- Voice Only Connection : 15mA for HV3 packets, 30mA for HV1
- RI Page Scanning : 420uA
- Inquiry Scanning + RI Page Scanning : 560uA
- Park mode (1 second interval) : 120uA
- Standby state : 10uA
The components, the chip, memory and the crystal, antenna could be placed on a PCB about 20mm x 15mm. The thickness of the chip is about 1.25mm or 1.55 mm..
Question 16. Explain The Term ‘airport’ In Bluetooth?
Airport is standard (802.11) and has a faster transfer rate. Technologically it is more advanced, more rugged and smaller and capable of being used anywhere. It is 10mb/sec, 50 meters, 10 active devices. Apparently, Bluetooth is 1mb/sec, 10 meters and 7 active devices.
Question 17. What Does Fec Mean In Bluetooth?
- FEC stands for Forward Error Correction. On the data payload, FEC reducing the number of retransmissions.
- Within blue tooth, there are 2 versions namely, 1/3 FEC and 2/3 FEC.
- The 1/3 version is 3 times repetition of each information bit.
- The 2/3 version is a shortened Hamming code.
- It is known as a method of obtaining error control in data transmission in which the source sends redundant data and the destination will recognize it without the errors.
- They are used for broadcasting to many destinations from a single source.
Question 18. How Frequency Hopping Is Used For Security In Bluetooth?
Blue tooth technology uses Adaptive Frequency Hopping and capable to reduce interference between wireless technologies with the help of 2.4 GHz spectrum. In order to take the advantage of the available frequency, Blue tooth’s AFH works within the spectrum and is performed by the technology detecting other devices in the spectrum and avoiding the used frequencies. Efficient transmission within the spectrum at high degree of interference immunity is achieved by adapting hopping among 79 frequencies at 1 MHz intervals.
Question 19. What Is 3g?
Definition: 3G, known as 3rd Generation, is a standard for mobile / cellular phones. It provides the services that fulfill the International Telecommunication Union specifications.
The application services of 3G include wireless voice telephone, mobile internet access, video calls and mobile television – all in a mobile environment.
- 3G allows simultaneous use of speech and data services
- 3G provides peak data rates of at least 200 KBits according to the IMT-2000 specification.
- Mobile broadband access of several MBits to laptop computer systems, smart phones is provided by latest 3.5G, 3.75G versions.
Question 20. What Are 3g Standards?
- Universal Mobile Telecommunications System – One of the 3G mobile telecommunications technologies, also being developed into a 4G technology.
- Most common form of UMTS uses W-CDMA as an underlying air interface.
- UMTS also covers Radio Access Network – UMTS Terrestrial Radio Access Network (UTRAN), and Mobile Application Part (MAP).
- Users are authenticated via USIM cards (Universal Subscriber Identity Module).
- Also known as IMT Multi-Carrier (IMT-MC), uses CDMA channel access for sending voice, data and signaling data between mobile phones and cell sites.
- The standards are CDMA2000 IX, CDMA2000 EV-DOR Rev.0, CDMA2000 EV-DO Rev.A and CDMA2000 EV-Rev.B. They are approved radio interfaces for the ITU’s IMT-2000.
Question 21. What Are The Advantages And Disadvantages Of 3g?
Advantages of 3G:
- Overcrowding is relieved in existing systems with radio spectrum
- Bandwidth, security and reliability are more
- Provides interoperability among service providers
- Availability of fixed and variable rates
- Support to devices with backward compatibility with existing networks
- Always online devices – 3G uses IP connectivity which is packet based
- Rich multi media services are available
Disadvantages of 3G:
- The cost of cellular infrastructure , upgrading base stations is very high
- Needs different handsets.
- Roaming and data/voice work together has not yet been implemented
- Power consumption is high
- Requires closer base stations and are expensive
- Spectrum-license costs, network deployment costs and handset subsidies subscribers are tremendous.
Question 22. How Is 3g Different From 2g?
- Packet data speed is higher in 3G, and it is up to 384 KBPS
- Voice and sms speed is also 384 KBPS in 3G
- 2G utilizes different switching techniques for voice and data, where as 3G uses single switching, irrespective of data
- 3G has at least 2MB of data link of a mobile, where in 2G the data rate is in KBPS
- 3G has WiMAX facility for faster VOIP and internet
- 2G uses GSM TDMA technology with narrowband 200Khz.
- 3G uses CDMA technology with broadband 5Mhz, with same frequency carrier and time.
Question 23. Explain Gprs ( General Packet Radio Service)?
GPRS ( General Packet Radio Service) :
- Packet oriented mobile data service available to the users of 2G cellular systems.
- It is global system for communicating through mobile phones using GSM as well as in 3G systems.
- GPRS data transfer is charged per MB of traffic transferred, where as in circuit switching, data transfer is charged per minute of connection time
- GPRS is better packet switching service, as opposed to circuit switching.
- 2G cellular systems are combined with GPRS and known as 2.5G.
- Provides moderate speed data transfer by using unused TDMA channels, such as GSM.
Question 24. Explain Gsm (global System For Mobile Communications)?
GSM (Global System for Mobile Communications):
- GSM (Global System for Mobile Communications).
- Most popular standard for mobile telephony systems, originated from Groupe Special Mobile.
- The ubiquity of GSM enables the international roaming arrangements among mobile phone operators.
- Both signaling and speech channels are digital, and thus GSM is considered as 2G mobile phone system.
- GSM standard benefited customers the ability to roam and switch carriers without replacing the hand sets and network operators.
- GSM implements low-cost implementation of Short Message Service.
Question 25. Explain Hlr (home Location Register) , Iden(integrated Digital Enhanced Network), I-appli ?
HLR (Home Location Register) :
- For GSM and CDMA wireless networks
- It’s responsibility is to authenticate and authorize subscribers and their services.
iDEN (Integrated Digital Enhanced Network) :
- A wireless technology for Motorola
- It has the capabilities of digi-cellular phone, 2 way radio, alphanumeric pager and data modem / fax modem in a single network
- Operational bands are 800 MHz, 900 MHz and 1.5 GHz
- iDEN is based on TDMA (Time Division Multiple Access) and GSM architecture
- For voice compression it uses Motorola’s Vector Sum Excited Linear Predictors vocoder.
- For delivering 64KBPS over a 25 KHz channel, it uses QAM modulation.
- iDEN is designed to serve the mobile user for accessing information quickly without carrying several devices.
- i-appli is a Java environment based on CLDC.
- Handsets of NTT DoCoMos are utilizing i-appli
- It is similar to MIDP, however both APIs are incompatible.
Question 26. Explain Umts?
- UMTS stands for Universal Mobile Telecommunications Systems
- One of the emerging mobile technologies for 3G mobile phones.
- The main benefit of UMTS is, undoubtedly, its speed
- Current rates of broadband data transfer is 2MBits / second
- The speed of UMTS makes it possible to stream video that supports movie downloads and video conferencing.
- In a nut shell, UMTS provides almost all the facilities of a home computer system while on the move.
- UMTS combines the technologies like wireless, satellite which provides seamless transitions between Wi-Fi and satellite.
Question 27. What Is 4g?
- A short name for Fourth Generation
- A stage of broadband mobile communications that supersede 3G
- 4G is expected to use radio spectrum in an efficient manner, and as a result, provides cable-modem transmission speeds to the end users.
- This feature enables high-quality streaming video
- Simultaneous connections to multiple high-speed networks, known as pervasive computing, are expected by 4G.
- Thus seamless handoffs are provided throughout a geographical area.
- Coverage enhancement technologies, like femtocell and picocell are expected to develop for addressing various needs of mobile users in homes, public buildings etc.
Question 28. What Is International Telecommunications Union And What Are Its Functions?
- ITU is an intergovernmental organization
- Telecommunications are developed by using ITU by public and private organizations.
- ITU is responsible for adopting regulations, international treaties and standards that governs telecommunications
Functions of International Telecommunications Union:
- Maintaining and extending the international cooperation for the improvement
- Rational usage of telecommunications, for promoting efficient use of technical facilities
- To harmonize the actions of nations.
Question 29. What Is Cdma2000?
- CDMA2000 is a Multi-carrier code-division multiple access version of IMT-2000 standard
- CDMA2000 is a 3G wireless technology.
- World’s first 3G commercial system was launched by SK Telecom of South Korea using CDMA2000 1X
- CDMA 2000 supports mobile data communications at speeds from 144KBPS to 3MBPS
- The versions of CDMA2000 have been developed by Qualcomm and Ericsson
- There were 250,300,000 subscribes world for CDMA by March 2006.
Question 30. What Is Cdma? Explain The Technology.
- CDMA stands for Code Division Multiple Access
- CDMA is a wireless technology used in transmission of signal from places with high Security and noise reduction.
- The principle of Spread Spectrum is used to work with CDMA.
- Spread signal is below the noise level noise and has no effect on the signal.
- CDMA does not frequency specific to each user. Instead, every channel uses the full available spectrum.
- Individual conversations are encoded with a pseudo-random digital sequence.
- CDMA always provides better capacity for voice and data communications
- CDMA is a common platform for 3G technologies
- Analog radio transmission technologies like Advanced Mobile Phone System were used in CDMA at the time of its inception
- A unique code is received by all mobile network users and is allowed continuous network access instead of intermittent and timed access.
Question 31. Explain Cdma One And Cdma2000?
CDMA One :
- CDMA one refers original ITU IS-95 CDMA wireless interface protocol. It is considered as a 2G mobile wireless technology
- The version IS-95A protocol employs a 1.25 Mhz carrier and data speeds up to 14.4 Kbps
- The version IS-95B support data speeds up to 115 kbps by employing 800 MHz / 1.9 GHz.
- Also known as IMT Multi-Carrier, a family of 3G mobile technology standards.
- Used for sending voice, data and signaling between cell sites and mobile pones
- The standards such as CDMA2000 1X, CDMA2000 EV-DO Rev. 0, are approved radio interfaces for ITU IMT-2000
- CDMA 2000 is backward compatible with its previous 2G iteration IS-95
Question 32. Explain Edge?
- EDGE is an acronym for Enhanced Data GSM Environment
- An improved wireless technology over GSM
- A 2nd generation cell phone technology
- EDGE is used for wireless data transfer via mobile phone connection
- Data transfer rates up to 4 times more than GSM networks
- With the advent of Blackberry and iPhone, faster data transfer is sought
- Using more sophisticated coding, usually without high end hardware, wireless carrier’s base stations are supported for data transfer speeds up to 384 KBPS
- EDGE is an alternative to replacing wireless technology, such as GPRS
- EDGE will eventually be replaced by 3G technology such as WCDMA.
Question 33. Explain Dect?
- DECT is one of the wireless technologies, originated in Europe
- DECT was designed to interwork with various networks such as PSTN, ISDN, GSM etc.
- The initial standard. of DECT focused on developing air interface which is a radio link between cordless telephone and the base stations
- This standard plugged into the telephone socket and the standard protocols for handover between several base stations
- All these are connected to the same office switchboard, typically a PABX
- The first product of its kind was from Olivetti, was a wireless LAN type product, known as NET3.
Question 34. Explain High Speed Packet Access?
- HSPA is a combination of 2 mobile telephony protocols – High Speed Downlink Packet Access and High Speed Uplink Packet Access
- HSPA improves the performance of existing WCDMA protocols.
- HSPA provide increased performance by utilizing schemes of modulation and refining the protocols, through which the base stations and handsets communicate
- HSPA is used for better usage of the available bandwidth provided by WCDMA
- HSPA supports data rates of up to 14 MBit / s in the downlink
- HSPA supports data rates of up to 5.8 MBit / s in the uplink
- HSPA reduces the latency and increases up to 5 times more system capacity during downlink and twice more system capacity during uplink
- HSPA uses 16QAM for yielding higher bit rates
- HSPA rollouts are achieved by implementing software upgrades to existing 3G networks. This gives HSPA a head start over WiMax.
Question 35. Explain Ev-do/ Evdo?
- EVDO stands for Evolution Data Optimized
- EVDO is a 3G broadband technology used by Verizon, Spring, Alltel
- It provides typical download speeds of 600 to 1400 KBPS
- A personal broadband service for wide range of customers
- It is always On
- EVDO utilizes CDMA signals
- Users can be connected remotely for using email, downloading large files, spreadsheets etc.
- EVDO is relatively low cost with high capacity
- Allows rich web browsing and application usage
- Seamless roaming, internal internet connectivity without relying on other’s connection, accessibility to the corporate Virtual Private Network by customers are some of the advantages over WiFi.
Question 36. What Is The Difference Between Cdma And Gsm?
The important differences are:
Data Transfer Speed:
- CDMA is faster than GSM.
- CDMA2000 downstream rate is 2 megabits / second, through EVDO, where GSM downstream rate is up to 384 kilobits / second, through EDGE technology
Subscriber Identity Module (SIM) cards:
- SIM is tied to the network, rather than the actual phone. Phones with card-enabled can be used with any carrier of GSM
- Proprietary handsets are linked to one carrier only and not card-enabled in CDMA
- GSM carriers have wider coverage of more rural areas, where as CDMA may not cover rural areas compared to GSM carriers
- GSM has facility to offer more international roaming, as the number of connections in world market dominate GSM network.
- CDMA phones do not have the capacity; however, there are more countries that use CDMA networks.
Question 37. What Is The Importance Of Cdma In Today’s Cellular World?
- The transition to digital radio through the process of defining standards is implementing about 90% in the cellular industry.
- Smooth transition to digital standards is involved in CDMA technology.
- Most often, it can be viewed as improved and replacement technology of TDMA
- Moving towards 4G technology is compatible with CDMA technology.
Question 38. What Is The Differentiate Between Cdma And Fdma ?
CDMA and FDMA
- Same frequency is used by every user and simultaneous transmission occurs
- Every narrowband signal is multiplied by wideband spreading signal, usually known as codeword
- Every user has a separate pseudo-codeword, i.e., orthogonal to others
- Only the desired codeword is detected by the receivers and others appear as noise
- It is mandatory for the receivers to know about the transmitter’s codeword
- When the channel is not in use, it sits simply idle.
- Bandwidth of Channel is relatively narrow (30 KHz), known as narrowband system.
- Little or no equalization is needed for spreading symbol time.
- Analog links are suitable for FDMA.
- Framing or synchronization bits are not needed for continuous transmission.
- Tight filtering is needed to minimize interference.
Question 39. What Are The Difference Between Tdma?
CDMA and TDMA :
- Power limited system
- While people talking, random noise band playing occurs
- Conversation need to be extracted from the background din
- GP is high when people speak different languages, which is easier to distinguish individual speakers
- It is difficult for distinguishing individuals, when GP is low.
- The system performance will be degraded for every user when the number of users increases.
- Fading would be reduced with wide frequency spectrum
- Need to have separate multipath signals with different delays by “chip” unit.
- Receiving or transmission is allowed for only one user in a given slot
- All slots are assigned cyclically
- The transmission is non-continuous
- It is essential to use digital data and modulation
- Data rate overhead is between 20% – 30%
- Overhead tradeoffs are size of data payload and latency
- Multiple users are shared with single carrier frequency
- Handoff is made simpler by using non-continuous transmission
- All slots are assigned on demand
- Due to reduced inter user interference, the power control is less stringent.
Question 40. What Is The Difference Between Cdma And Gprs? Which Of Them Is Better? Why?
- CDMA is one of the types of mobile connections for making calls where as GPRS is a technology for internet connections through a mobile phone.
- GPRS enables to surf the internet from a mobile phone. GPRS technology is used in other gadgets apart from mobile phones.
- W-CDMA technology is faster than GPRS, since the user cares about the technology that is applied for air interface.
- Average latency on GPRS is around 1.3 seconds, where as on CDMA is around 400 milli second
- GPRS supports only User Datagram Protocol, where as CDMA supports both UDP and TCP
- GPRS relies on Network Address Translation and a private IP address is assigned to it. On the other hand CDMA assigns a public IP address CDMA is better because:
- E-mail is pretty light, until you enter MS-Office.
- Pocket PC’s support for office documents with similar functionality which can be had on Palm OS and Symbian
- Upon availability of APIs, a software developer could write various applications, like voice transfer, data transfer to client’s account, integrating billing amount etc.
- Web services could be utilized.
Question 41. Explain Following Forward Link Channels In Cdma System: A.) Pilot Channel B.) Sync. Channel
Pilot Channel :
- A forward link channel which is a base to mobile that modulates only by the pilot PN. It spreads common codes to all signals transmitted from a given base station.
- Several critical important functions are provided by the pilot channel for forward links in IS-95 systems
- The pilot channel modulation facilitates the process of time synchronized replica generation at the receiver of the PN spreading sequences. These are utilized at the transmitter for modulating the synchronization, paging and traffic channels. These are transmitted from the same base station.
- A base station transmits a Sync-Channel that spreads with Walsh code 32.
- The frame of synch channel is 80/3ms long with frame boundary is aligned to the pilot.
- Sync channel transmits a single message continually, called Sync Channel Message.
- The Sync Channel Message contains network information, including the PN offset that is used by the Base Station sector.
- The length and content of the message is dependent on the P_REV.
- The message transmission rate is 32 bits / frame.
- The message is encoded to 128 symbols
- The message yielding rate is 1200 bits / s.
Question 42. Explain The Following Two Types Of Hand Off In Cdma System: A.) Soft Handoff B.) Softer Handoff
Soft handoff :
- Soft handoff is a feature in which a cellular phone is simultaneously connected to two or more cellular phones during a single call
- It is he overlapping of repeater coverage ones, which enables every cell phone set is always well within the range of a specific repeater.
- More than one repeater can send and receive signals to transmit signals to and from mobiles.
- All repeaters are used with the same frequency channel for each mobile phone set.
- Practically no dead zones and as result, the connections seldom interrupted or dropped.
Softer handoff :
- Softer handover is a significant soft handover in which the added and removed links belong to the same node.
- Macro diversity with maximum ratio combining could be performed in the same node.
- The movement of handoff, when a user can be served in another cell more efficiently (less power emission, less interference), is the most obvious cause for better performance.
Question 43. What Is Gsm?
- Short form of Global System for Mobile Communications, is a wireless network system
- A standard for digital cellular mobile communications
- International roaming arrangements are enabled among mobile network operators, by providing the subscribers to use their personal mobile phones anywhere in the world.
- GSM is considered as second generation mobile, as signaling and speech channels are digital
- The carriers can be replaced without replacing mobile phones.
- The ubiquity of GSM implementations is also enabling the switching between network operators, who can choose equipment from many GSM equipment vendors.
- GSM pioneered low cost SMS implementation.
- The GSM standard includes a worldwide emergency telephone number feature.
Question 44. Explain The Services Offered By Gsm.
- The services offered by GSM are ISDN compatible
- GSM allows synchronous data and asynchronous data to be transported as bearer service, one of the telecommunication services offered by GSM, and forms ISDN terminal
- The data could be either transparent service or nontransparent service
- Telephony is one of the services offered by GSM, which an emergency and the service provider is notified by dialing 3 digits
- By using appropriate fax adaptor, G3 fax service is supported
- One of the features of GSM is Short Messaging Service
- Certain services, namely supplementary services are provided on top of teleservices or bearer services by GSM, such as, caller identification, call forwarding, multiparty conversations, barring outgoing calls and call waiting.
Question 45. What Is The Maximum Data Rate Supported By A Gsm System?
- The maximum data rate supported by a GSM system is 9.6 kbps.
- However there are extensions to GSM standard to improve throughput.
- GPRS is one of the extended GSM service.
- The extended standards of GSM allows theoretical data rates on the order of 114 Kbit/s, but with throughput closer to 40Kbit/s in practice.
Question 46. Explain The Following Techniques In Gsm: A.) Sectorization Of A Cell B.) Frequency Re-use C.) Transmitted Power Control D.) Discontinuous Transmission
Sectorization of a cell :
- Sectorization is a process to cut down equipment costs in a cellular network. It influences in traffic load and cell size
- Sectorization reduces co-channel interference, when applied to clusters of cells
- The maximum traffic capacity of sectored antennas is more than omnidirectional antennas.
Frequency Re-use :
- Frequency re-use is the key factor of cellular network ability for increasing both coverage and capacity.
- Different frequencies are utilized by adjacent cells; however problem does not arise to determine the cell sufficiently far apart using the same frequency.
- Reuse distance and the reuse factor are the two elements that influence frequency reusability
- The frequency is 1/K, where K is the number of cells that cannot use the same frequencies for transmission.
Transmitted Power Control :
- Transmitted power control is one of the technical mechanism used within some networking devices
- TPC is used for preventing too much unwanted interference among wireless networks
- The central idea is to automatically reduce the transmission output power used, when other networks are within the same range.
- TPC reduces interference problems and increases the battery capacity
- The power levels of a single mobile device can be reduced by 6dB
Discontinuous Transmission :
- Discontinuous Transmission, also known as DTX in short is a method of momentarily powering down a mobile set when there is no voice input to the set.
- The overall efficiency of a wireless voice communication system is optimized by DTX.
- Each speaker in a two way conversation speaks slightly less than half of the time.
- The workload of the components in the transmitter amplifiers are made easy and reduces interference.
Question 47. Which Uplink/ Downlink Spectrum Is Allocated To Following? A.) Gsm – 900 B.) Dcs – 1800
GSM – 900: Uplink spectrum is 890.2–914.8 and downlink spectrum is 935.2–959.8
DCS – 1800: Uplink spectrum is 1710.2–1784.8, and downlink spectrum is 1805.2–1879.8
Question 48. Explain Equalisation?
- An adaptive equalizer is employed by a GSM receiver for overcoming the impact of non-ideal channel characteristics which are caused by multipath propagation.
- Adaptive equalizer is required because the channel characteristics are often changing fast.
- Tuning the for each time slot is done by the equalizer.
Question 49. Explain Interleaving?
- Time diversity in a signal communication system is obtained by using Interleaving.
- The possibility of losing whole bursts will be decreased by interleaving.
- Total 456 bits from convolution encoder, including 20ms of speech, is subdivided into eight blocks. Each block consists of 57 bits.
- All these blocks are transmitted in consecutive time slots.
- Enough information is available in 7 blocks, in case one of the blocks is lost due to burst errors. This enables whole segment recovery by using error correction.
Question 50. Explain Speech Coding?
- Speech coding is all about turning voice into digital form.
- Speech is inherently analog, as GSM is a digital system.
- The digitization is employed by ISDN, and the current telephone systems that are used for multiplexing voice lines, with high speed trunks, optical fiber lines is done by Pulse Code Modulation(PCM).
- The PCM output is 64 kbps, which is too high over a radio link in feasibility.
- The 64kbps signal is redundant.
- The algorithm used in conventional cellular is Vector Sum Excited Linear Predictive speech compression.
Question 51. Explain Channel Coding?
Channel coding :
- The data rate for the radio channel is 270 kbps.
- The data rate is split into 8 full rate or 16 half rate traffic channels, along with signaling channels
- In order to have the maximum chance for detecting and correcting errors, the code is complex in a typical propagation path
- Forward Error Correction is applied in order to get the speech coder encryption, coding and interleaving in a sophisticated way
- The data is sent as bursts in 577 mus time slots. Each contains 116 encrypted bits
- Every TDMA frame consists of 8 or 16 time slots
- Transmit time slots are staggered, so that at some instant the mobile station will not receive the same instants while transmitting, which enables the simplifying the filtering requirements
- At least one spare slot between transmit and receive is available with this scheme.
Question 52. What Is Frequency Re-use?
- Frequency re-use is one of the techniques for improving capacity and spectral efficiency.
- Commercial wireless systems are based on Frequency Reuse, that involves the partitioning of an RF radiation area into cell segments.
- A frequency that is far enough away from the frequency in the bordering segment is used by one segment of the cell.
- Similar frequency is used at least two cells apart from each other.
- This practice enables various cellular providers to have several customers for a given site license.
Question 53. Explain Gprs?
- Short form of General Packet Radio System.
- GPRS is the next generation of GSM, and the basis of the 3G networks.
- A packet oriented data service available to users of GSM and IS-136 type mobile phones.
- It complements the existing services like circuit-switched cellular phone connections and the SMS.
- Shortest set-up time is added for ISP connections.
- An optimized mobile service for sending and receiving information across a mobile telephone network, with less cost.
- GPRS provides data rates of mobile telephony and moderate speed data transfer, using unused TDMA channels.
- GPRS does not need dial-up modem connection.
- Sending and receiving e-mails, surfing internet are among the features of GPRS.
Question 54. What Signals Are Transferred In Gprs?
- GPRS uses 2.5 generation of GSM signals.
- The radio interface is the same that of GSM.
- GPRS uses 900 / 1800 Mhz, frequency band and GMSK modulation.
- The bit rates are EGPRS, similar to EDGE.
- Separate hardware and ports need to be added and availed.
Question 55. How Are Gprs Terminals Classified?
- The GPRS services are classified into 12 service classes as per the duration of the time slots occupied / frame.
- Usually 5 time slots per frame are occupied including transmission time slots and reception time slots.
- Increase in the number of occupied time slots certainly causes the increase in the entire duration of the occupied time slots, so that increased amount of data transmission and receipt are enabled.
- All the 12 service classes are further classified into higher and lower classes as per the relative duration of time slots.
- Higher speed data communication can be transmitted with high-class GPRS service by setting high transmission power and setting the duration of the time slots long.
Question 56. What Gross Data Rate Does Gprs Provide?
- GPRS is a packet oriented mobile data service.
- The data transfer is charged per megabyte of traffic.
- GPRS provide gross data rate of 22.80 KBPS / time slot.
- Voice uses only 13KBPS/ time slot and the rest is consumed by Error Correction Code.
- Error connection code is utilized for detecting and correcting the transmission errors.
- As voice is compressed, the usage of Error connection code is mandatory.
- In the 2G systems it provides a rate from 56 up to 114 kbits/s.
Question 57. What Is Piggybacking In Context To Wi-fi?
Piggybacking is a term which states that something that is riding on the back of something else to complete his/her motive, just like similar to an idiom putting gun to another’s shoulder and performing Hunting, so piggybacking is a term used to refer to access of a wireless internet connection by bringing one’s own computer within the range of another’s wireless connection, and using that service without the subscriber’s explicit permission or knowledge. It is a legally and ethically controversial practice, with laws that vary in jurisdictions around the world. Piggybacking is an unauthorized tapping into another’s connection with a public utility.
For e.g.- So piggybacking can take place like when I am accessing the wireless connection of my neighbour Wi-Fi without his/her knowledge by hacking his static ip address, then it would be possible for me to access the Wi-Fi connection of others.
Question 58. What Are The Recommended Channels If You Are Setting Up Three Wlans And Want Minimum Interference Over There?
There is a need of selecting the channels for setting up WLANs, to communicate; all the components of a Wi-Fi network must use the same channel. In the Wi-Fi network in infrastructure mode (using an access point), it depends on the channel set at the access point.
For better results when using Wi-Fi, it is necessary to adjust the channel on the access point as well as configured on the client, to take the least use channel in your neighbourhood.
To do this you can use software such as NetStumbler, which will list the neighbourhood Wi-Fi networks and channels used.
Note:- The channels most frequently used to select one as free as possible.
So the recommended channels are as follows:-
- Channel 1: 2.412 MHz
- Channel 2: 2.417 MHz
- Channel 3: 2.422 MHz
- Channel 4: 2.427 MHz
- Channel 5: 2.432 MHz
- Channel 6: 2.437 MHz
You can choose from these channels while setting up the WLANs.
Question 59. How To Crack Wi-fi Network, If You Are Using Wep (wired Equivalent Privacy) Password With Backtrack?
- The first line of defense of your Wi-Fi network is encryption, which encodes the data transmitted between your PC and your wireless router.
- WEP abbreviates (Wireless Encryption Protocol). It is a less-secure protocol than WPA (Wireless Protected Access). Since WEP is relatively easy to crack, so you have to use the same form on all devices on your network. If you have an older router that supports WEP only you’ll be best safest if you use 128-bit bit WEP keys but also check the manufacturer’s Web site for a firmware update that will add WPA support.
- Two of the most popular programs used for actually cracking the WEP key are Airsnort and Aircrack. Airsnort can be used with the .dump files that Kismet provides; and Aircrack can be use with .cap files that Airodump provides
Question 60. Differentiate Between Ad-hoc And Infrastructure Topology And Also Explain With Their Advantages And Disadvantages?
Wireless networks typically work in one of two configurations: Ad-Hoc or Infrastructure.
- Ad-Hoc is Latin meaning “for this purpose” so these are the networks which are basically created for some purpose. So these are the group of workstations which communicate directly witch each other to exchange information. An Ad-Hoc network is also called as a peer to peer network.
Here are some benefits of an Ad-Hoc network are:-
- The possibilities with Ad-Hoc network are quite endless.
- Ad-Hoc networks are simple to set up.
- Ad-Hoc networks are inexpensive.
- Ad-Hoc networks are fast.
Disadvantages of an Ad-Hoc network are as follows:-
- It is not able to get into the mainstream wired local area network.
- It needs more technology to support their reliability.
- As the network increases its speed slows down considerably.
- In Infrastructure mode, network includes an access point when the wireless clients connect to an access point, which in turn bridges to a network. Infrastructure network can pass information through a central information hub which can be both, hardware or software device on a computer. So under this devices in a wireless network are set up to communicate through an access point.
An infrastructure network enables you to:-
- a) In this you do not have to control over the path your data takes.
- b) Connect to a wired network.
- c) Extend your wireless network’s range.
- d) Utilize roaming ability.
Disadvantages for Infrastructure network are:-
- 1. Use of more wireless access points.
- 2. This increase the cost of implementing a wireless network solution.
Question 61. How Do You Secure A Wireless Network?
Key points for securing a wireless network are as follows:-
- Verify that your PC’s software firewall is turned on, and that Window’s file-sharing feature is off; it’s off by default in Window’s XP with Service Pack 2.
- Never send bank passwords, credit card numbers, confidential e-mail, or other sensitive data unless you’re sure you’re on secure site: Look for the lock icon in the bottom-right corner of your browser, as well as a URL in the address bar that begins with https. Such sites build in their own encryption.
- Always turn your Wi-Fi radio off when you’re not at a hotspot: Hackers can use it to create peer-to-peer Wi-Fi connections with your computer and access it directly.
- For better security, consider signing up for a paid subscription to a hotspot network such as Boingo or T-Mobile. Both companies provide connection software that encrypts your sessions automatically.
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