Mobile network and wireless communication.1

Mobile network and wireless communication
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Part A
Solution 1: Access to Wireless Network ( e.g. Wifi)
a) Media Access Control
MAC ( media access control ) is a layer present in the DLL ( data link layer ) of the
OSI reference model ( which consists of 7 layers). It controls when the computers can
transmit. It helps to transmit the packets of data to the NIC ( network interface card )
and a remote shared channel and also from both of them. MAC sub layer can control
the hardware which helps to interact to various types of transmission media ( like
wired , wireless , optical etc. )
Importance :
It is important because it performs various functions like delimitation and recognising
the frame, destination station addressing, source station addressing, protects from
errors ( by generation as well as frame check sequence) , controls interaction with
transmission media and leads to transparent data transfer.
b) Example of controlled access methods :
Reservation, Polling , Token Passing.
Example of Contention based media access methods :
Ethernet uses the scheme CSMA/CD.
c) Preference of 1 access method over another in a network :
The method which is better depends on certain conditions of the network. Contention
based media access methods are preferred as compared to controlled access methods.

In this method , any of the computers present within a network has the capability of
data transmission at any given time. There is mechanism for collision detection ,
recovery and avoidance.
d) Contention based media access control techniques can outperform controlled access
techniques. It means they have lower response time. This happens under certain
conditions. It works better for small networks having small value of usage. In this
case, the collision probability is less. But incase of higher volume, the performance
can degrade.
Solution 2 :
U1
CODE 1111 1111 1111
DATA 0000 0000 0000
XOR 1111 1111 1111
U2
CODE 0011 0011 0011
DATA 1111 0000 0000
XOR 1100 0011 0011
U3
CODE 1001 1001 1001
DATA 0000 0000 1111
XOR 1001 1001 0110
U4
CODE 1010 1010 1010
DATA 1111 1111 1111
XOR 0101 0101 0101