Wireless Role in the Open System Interconnection Model

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23 Οκτ 2013 (πριν από 3 χρόνια και 11 μήνες)

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Wireless Role in the Open System Interconnection Model


Today’s public communications networks are complicated systems. Networks such as
the public switched telephone network (PSTN) and the Internet provide seamless
connections between cities, across ocean
s, and between different countries, languages,
and cultures. Wireless is only one component of these complex systems, but there are
three areas or layers where it can affect the design of such systems:


1.

Physical Layer
:

This layer provides the physical mech
anism for transmitting
bits (i.e. binary digits) between any pair of nodes. In wireless systems, it
performs the modulation, demodulation of the electromagnetic waves used for
transmission, and it includes the transmission medium as well.

2.

Data
-
link Layer:

Wireless links can often be unreliable. One purpose of the
data
-
link layer is to perform error correction or detection, although this
function is shared with the physical layer. Often, the data
-
link layer will
retransmit packets that are received in error
but, for some applications, it
discards them. This layer is also responsible for the way in which different
users share the transmission medium. In wireless systems, the transmission
medium is the radio spectrum. A portion of the data
-
link layer called the

Medium Access Control (MAC) sub layer is responsible for allowing frames
to be sent over the shared media without undue interference with other nodes.
This aspect is referred to as multiple
-
access communications.

3.

Network Layer:

This layer has several func
tions, one of which is to
determine the
routing

of the information, to get it from the source to its
ultimate destination. A second function is to determine the
quality of service

(QoS). A third function is
flow Control
, to ensure that the network does not

become congested
. Wireless systems, in which some of the nodes can be
mobile, place greater demands on the network layer, since the associations
among nodes are continually changing.


These are three layers of a seven
-
layer model for the functions that o
ccur in the
communications process. The model is called the
open system interconnection

(OSI)
reference model.




Reference:


Haykin, S. and Moher, M. (2005)
Modern Wireless Communications,

International
Ed., Pearson Education
-

Prentice Hall,
ISBN

0131246
976.