SECTION – A ( 8 x ½ = 4 Marks)
Answer ALL questions. Each question carries HALF mark
Choose the correct answer:
The second generation of mobile communication phones was ________.
digital
analog
semi analog
radio frequency
Enhance data rate for GSM evolution (EDGE) is a ______ system, with a data rate of 384kbps.
1 G
2.5 G
3.5 G
4 G
This is due to reflection of radio signals by solid objects, which results in signals being received along multiple paths.
Infrared systems
Carrier sense multiple access
Multipath fading
Orthogonal frequency division multiplexing
Which of the following is the IEEE standard for Wi Max?
802.3
802.11
802.15
802.16
_____________ has a data rate of 23.5 mbps, with coverage of 50 m and low mobility of <10 m/s.
HiperLAN/1
HiperLAN/2
IrDA
Bluetooth
Wireless communication suffers from frequent disconnection and slow speeds, as compared with wired communication due to _______.
Ubiquitous computing
Wireless connectivity
Weak connectivity
Pervasive Computing.
_______ cellular systems were the first generation of mobile telephone communication systems.
Analog
Digital
Semi analog
Radio frequency
MAC sub layer of 802.11 supports two modes of operation.
Association & Disassociation
Distributed & Point Coordination Function
IEEE 802.3 & IEEE 802.16
Infrared System & HyperLAN
SECTION – B (5 x 1 = 5 Marks)
Explain FDMA – TDMA – OFDM.
1-(FDMA) - Frequency division multiple access
- channel spectrum divided into frequency bands.
- each station assigned fixed frequency band.
-unused transmission time in frequency bands go idle.
-The sender and the receiver agree on a hopping pattern, so that the receiver can tune to the right frequency.
-Example: 6-station LAN, 1,3,4 have pkt, frequency bands 2,5,6 idle.
2-(TDMA) –Time division multiple access
-access to channel in "rounds"
- each station gets fixed length slot (like one packet in each round)
-unused slots go idle
-example: 6-station LAN, 1,3,4 have pkt, slots 2,5,6 idle
3-OFDM
(orthogonal frequency division multiplexing), which uses the wider 5 GHz ISM ( Industrial, Scientific and Medical) frequency band to deliver up to 54 Mbps.
What is hard and soft handoff?
- In a Hard Handoff, the old BS drops the mobile before the new one acquires it. The call is disconnected abruptly if there is no available frequency with the new BS, or there is a call drop till the new frequency is received. This is noticeable by the user but is typically of very short duration of about 60 ms in GSM systems.
- In a Soft Handoff, the mobile is acquired by the new BS before the old one signs off. Thus, there is no loss of continuity. But it requires the mobile to be able to tune to two frequencies at the same time. Neither first- nor second-generation devices can do this. 3GCDMA systems provide soft handover.
Define mobile computing and Process migration?
- Mobile computing is computing that allows continuous access to remote resources, even to small computing devices such as laptops, palmtops and other handheld devices like personal digital assistants (PDAs) and digital cell phones.
- Process migration is the act of transferring a process between two computers connected through a wired or wireless medium.
Name the nine of distribution and station services provided by WLAN.
-Distribution
1. Association.
2. Disassociation.
3. Re-association.
4. Distribution.
-Process migration
1. Authentication
2. De-authentication.
3. Privacy.
4. Data delivery.
What are MAC sublayer operations?
MAC sub layer of 802.11 supports two modes of operation. these are the DCF and the PCF.
SECTION C ( 1 x 8 = 8 Marks)
Answer the following questions.
Explain the three technical issues of mobility.
-Security: is the biggest challenge for mobility. Security includes user authentication, data integrity and privacy, prevention of denial of service and etc. It is easier to provide security for a stationary system as compared to a mobile one, since the former can be guarded by intrusion detection systems and firewalls. The existing security infrastructure is designed only to protect stationary systems and thus needs to be adapted or modified for use in mobile systems.
-Reliability: in terms of availability of resources, in the presence of disconnection, is also a major issue for mobile systems. Reliability can be improved by mobility but needs additional support in the form of caching and loading of state.
-Naming and locating: are common issues for all forms of mobility. Without locating a mobile object, communication with it or its control is not possible. Communication channels must be reconstructed after every movement. Naming is to be associated with authentication, and all recycling is to be done with great care.
Briefly discuss the 1G,2G,3G and 4G technologies
-The first generation (1G): 1980
-Analog cellular systems were the first generation of mobile telephone communication systems. They used analog frequency modulation for only voice (speech) transmission.
The various systems that fall in this category are:
- AMPS (Advanced Mobile Phone Service) (USA)
- Nordic Mobile Telephone (NMT)-900 (Sweden)
- Cellular Digital Packet Data (CDPD)
-The second generation (2G):1992
- the second generation was digital.
The various advantages of digital cellular are as follows:
1. It is more robust as it displays resistance to noise and has efficient error correction.
2. It exhibits the intelligence of the digital network.
3. It is more flexible and can be integrated with the wired digital network.
4. Reduced RF transmission power is needed.
5. Encryption can be provided for communication privacy.
6. System complexity is reduced.
7. User capacity is increased.
-The second generation (2.5G):1996
-Enhanced data rates for GSM evolution (EDGE) is a 2.5G system, with a data rate of 384 kbps, which is higher than GSM.
-GPRS (general packet radio service) is another 2.5G scheme.
-The third generation (3G): 2000+
- The objective of the third generation of wireless communication is to provide fairly high-speed wireless communications to support multimedia, data, and video in addition to voice. Its goals:
1. Support high mobile velocity (300–500 km/hour), compared with less than 100 km/hour in GSM.
2. Support global roaming, as opposed to district and country in GSM.
3. More efficient use of the available spectrum in general.
-The fourth generation (4G):2002+
- 4G networks support Mobile Web access and high bandwidth applications such as high-definition mobile TV, mobile video conferencing, and gaming services.
- Be based on an all-IP packet-switched network.
- Support data rates of up to 100 Mbps for high-mobility mobile access and up to 1 Gbps for low-mobility access such as local wireless access.
- Dynamically share and use the network resources to support more simultaneous users per cell.
Discuss the three satellite systems with the help of examples.
A communication satellite is like a big microwave repeater in the sky.
- Mobile satellite services allow global coverage, because in these systems satellites play the role of mobile base stations (BSs). Satellite-based systems are categorized according to the orbital altitude of the satellite.
Two Stations on Earth want to communicate through radio broadcast but are too far away to use conventional means.
- The two stations can use a satellite as a relay station for their communication --One Earth Station sends a transmission to the satellite. This is called a Uplink.
-The satellite Transponder converts the signal and sends it down to the second earth station. This is called a Downlink.
Explain the mobile agents.
-A mobile agent is a program that can move through a network and autonomously execute tasks on behalf of the users. An agent is different from a user application, as it represents and acts on the owner’s behalf by inheriting the owner’s authority.
-Some of the more well-known systems are Aglets, Agent Tcl and PMADE .
- Since mobile agents also migrate towards a source of information or towards a computer that they manage, they provide great flexibility and can mean easier reconfiguration or improved reliability.
Discuss the Bluetooth technology and its advantages
It connecting mobile phones or computing and communication devices without the use of cables. It is a short-range, low-cost and power-efficient radio-frequencybased wireless technology that supports both point-to-point and point-to-multipoint connections.
Advantages of Bluetooth
1. Non-cable connections.
2. File sharing.
3. Wireless synchronization.
4. Wireless Internet connectivity.
Illustrate the layers of IrDA protocol stack
-The infrared link access protocol (IrLAP) provides connectionless (UDP) and connection –oriented (TCP) transport services to the upper layer.
-The infrared link management protocol (lrLMP) supports ad hoc connections with peer devices.
The main reason for using the IrDA protocols had been wireless data transfer over the "last one meter" using point-and-shoot principles.
Communications protocols deal with many issues, and so are generally broken into layers, each of which deals with a manageable set of responsibilities and supplies needed capabilities to the layers above and below. When you place the layers on top of each other, you get what is called a protocol stack, rather like a stack of pancakes or a stack of plates. An IrDA protocol stack is the layered set of protocols particularly aimed at point-to-point infrared communications and the applications needed in that environment.
• Physical Layer: Specifies optical characteristics, encoding of data, and framing for various speeds.
• IrLAP: Link Access Protocol. Establishes the basic reliable connection.
• IrLMP: Link Management Protocol. Multiplexes services and applications on
the LAP connection.
• IAS: Information Access Service. Provides a “yellow pages” of services on a
device.
Difference between CSMA/CD and CSMA/CA.
-Ethernet uses carrier sense multiple access with collision detection (CSMA/CD). An Ethernet station just waits until the ether is idle and starts transmitting.
-Distributed Coordination Function (DCF): It uses (CSMA/CA). that is, CSMA (carrier sense multiple access ) with collision avoidance, which itself supports two methods of operation.
Name the three modulation techniques of IEEE 802.11 standard used for sending MAC frames.
1. 802.11: Infrared, which uses diffused .transmission at 0.85 or 0.95 microns. Infrared signals do not penetrate walls, so cells in adjacent rooms are well insulated from each other
2. 802.11: FHSS (frequency hopping spread spectrum), in which the transmitter hops from frequency to frequency hundreds of times per second
3. 802.11: DSSS (direct sequence spread spectrum) is like CDMA. It is also restricted to 1 or 2 Mbps.
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