IT1402 Nov Dec 2009 Answer
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Transcript of IT1402 Nov Dec 2009 Answer
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Nov/Dec 2009
Part-A
1. What are the main problems of signal propagation?
Ans:Power additionally influenced by
o fading (frequency dependent)o shadowingo Reflection at large obstacleso Refraction depending on the density of a mediumo scattering at small obstacleso Diffraction at edges
2. Give the use of SDMA.
Ans: Space Division Multiple Access (SDMA) is used for allocating separatedspaces to users in wireless networks. The basis for the SDMA algorithm is
formed by cells and sectorized antennas which constitute the infrastructure
implementing space division multiplexing (SDM)
3. Define GPRS.
Ans: The General Packet Radio Service provides packet mode transfer forapplications that exhibit traffic patterns such as frequent transmission of small
volumes.
4. What do you mean by DAMA?Ans:Demand Assigned Multiple Access Channel efficiency only 18% for Aloha,36% for Slotted Aloha (assuming Poisson distribution for packet arrival andpacket length).Reservation can increase efficiency to 80%
5. What are the various versions of a physical layer defined in IEEE 802.11
standards?
Ans: IEEE 802.11-83.5 MHz
IEEE 802.11a -300 MHz
IEEE 802.11b 83.5 MHzIEEE 802.11g - 83.5 MHz
6. List the three low power states to save battery power in a Bluetooth device.
Ans: PARK state
HOLD state
SNIFF state7. What are the two kinds of entities in mobile IP?
Ans: Two kinds of entities
Foreign network
Home network
8. Define Generic Routing Encapsulation.
Ans: GRE allows the encapsulation packets of one protocol suite into the payload
portion of another protocol suite.
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9. What are the key elements of the WAP specification?
Ans:
Networks and Network Bearers
TCP/IP as Transport Protocol
Processors
10.What are the goals of WTLS layer?
Ans: It provides the upper-level layer of WAP with a secure transport service
interface that preserves the transport service interface below it. In addition, WTLS
provides an interface for managing (e.g., creating and terminating) secureconnections. It provides functionality similar to TLS 1.0 and incorporates
additional features such as datagram support, optimized handshake and dynamic
key refreshing.
Part-B
11.a) i) Discuss the advantage and disadvantage of cellular system with small
cells.[6 Marks]
Ans: Cellular Network Organization
Areas divided into cells
Each served by its own antenna(s)
Band of frequencies allocated
Neighbors are equidistant
Architecture
PSTN
MTSO
Base Station and AntennaCellular Concept
Limited number of frequencies => limited channels
Single high power antenna => limited number of users
Smaller cells => frequency reuse possible => more number of
users
Base stations (BS): implement space division multiplex
Each BS covers a certain transmission area (cell)
Each BS is allocated a portion of the total number of channels
available
Cluster: group of nearby BSs that together use all available
channels
Mobile stations communicate only via the base station
FDMA, TDMA, CDMA may be used within a cell
As demand increases (more channels are needed)
Number of base stations is increased
Transmitter power is decreased correspondingly to avoidinterference
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Advantages:
Higher capacity, higher number of users
Less transmission power needed
More robust, decentralized
Base station deals with interference, transmission area etc. locally
Disadvantages:Fixed network needed for the base stationsHandover (changing from one cell to another) necessaryInterference with other cells: co-channel, adjacent-channelCellular Architecture
Each tower serves one cell Different frequencies
Handoff calls
Each cell is served by a base station (BS)
Each BS is connected to a mobile switching center (MSC)through fixed links
Each MSC is connected to other MSCs and PSTN
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11.a) ii) Explain briefly the types of spread spectrum techniques. [10 Marks]
Ans:
Types of spread spectrum
DSSS (Direct Sequence Spread Spectrum) IFHSS (Frequency Hopping Spread Spectrum) I
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11.b) i) Compare TDMA, FDMA and CDMA. [6 Marks]
Ans:
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11.b) ii) Explain the different types of phase shift key modulation. [10 Marks]
Ans:
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12)a) Describe the system architecture of a GSM. [16 Marks]
Ans:
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12)b) i) Write a note on LEO satellite system. [8 Marks]
Ans: Leo circulate on a lower orbit
It exhibit a much shorter period
It will only be visible from the earth for around ten minutes.Used for low bandwidth services.
Advantage:
Using advanced compression scheme.For voice communication.
Using low transmit power in the range of 1W
Smaller footprint for better frequency reuse.Disadvantage:
Need for many satellites if global coverage is to be used.
More satellites in orbit.Short life time (5 8 years)
12)b) ii) Explain the transport mechanism of DAB [8 Marks].
Ans:
Digital Audio Broadcasting:
Introduction (2)
Two basic transport mechanism (2)
Main service channel
Fast information channelProgram associated data (1)
DAB frame structure (2)Each frames are divided into three frames (3)
Synchronization channelFast information channel
Main service channelComponents of a DAB senderMultimedia object transfer protocol
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13 a) i) Explain the basic architecture of an IEEE 802.11 MAC data frame.
[8 Marks]
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13)a) ii) Discuss briefly the HyperLAN2. [8 Marks]
Ans:
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13)b) Explain about the IEEE 802.11b standard. [16 Marks]
Ans:
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14)a) i) Discuss about the IP in IP encapsulation. [8 Marks]
Ans: IP in IP Encapsulation:Encapsulation format (4)Fields are, (4)
Version
Internet Header LengthLength
IP Identification
Fragment offset
Time to Live
IP checksum
IP address of HA
Care of Address of COA
IP address of CN
IP address of MN
14 a) ii) Explain the Dynamic Source Routing. [8 Marks]Ans: Split routing into discovering a path and maintaining a path
Discover a path:
Only if path for packets to a certain destination is needed and no path
available
maintaining a path:Only while path is in use one has to make sure that it can be used
continuously
No periodic updates needed!
Path discovery:
Broadcast a packet with destination address and unique ID
If a station receives a broadcast packet If the station is the receiver (i.e., has the correct destination
address) then return the packet to the sender (path was collected in
the packet)
Ifthe packet has already been received earlier (identified via ID)then discard the packet Otherwise, append own address and
broadcast packet Sender receives packet with the current path
(address list)
Optimizations:
Limit broadcasting if maximum diameter of the network is known
Caching of address lists (i.e. paths) with help of passing packets:
Stations can use the cached information for path discovery (ownpaths or paths for other hosts)
Maintaining paths:
After sending a packet:
Wait for a layer 2 acknowledgement (if applicable)
Listen into the medium to detect if other stations forward the
packet (if possible)
Request an explicit acknowledgement
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If a station encounters problems it can inform the sender of apacket or look-up a new path locally
14 b) Explain the Dynamic Host Configuration Protocol. [16 Marks]
Ans:
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15)a) i) Explain the concept of Snooping TCP. [8 Marks]
Ans:
15 a) ii) Explain the WAE logical model. [8 Marks]
Ans: 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)
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Integrated Internet/WWW programming modelHigh interoperability
WAE Logical mode:
15 b) Explain the architecture of WAP 2.0 [16 Marks]
Ans: Wireless Application Protocol (WAP)_ Empowers mobile users with wireless devices
_ A standard created by wireless and Internet companies
wapforum.org:
Co-founded by Ericsson, Motorola, Nokia, Phone.com
Goals
Deliver Internet services to mobile devices
Enable applications to scale across a variety of transportoptions and device types
Independence from wireless network standards
GSM, CDMA IS-95, TDMA IS-136, 3G systems (UMTS,WCDMA)
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