Page 39 - Fundamentals of Communications Systems

Introduction 1.5

Application 1 Application 2

Application Layer Application Layer
Presentation Layer Presentation Layer
Session Layer Session Layer

Transport Layer Transport Layer
Network Layer Network Layer Network Layer Network Layer
Data Link Layer Data Link Layer Data Link Layer Data Link Layer

Physical Layer Physical Layer Physical Layer Physical Layer
The Communication Network
Figure 1.1 The OSI reference model.

copper wire pairs (telephony), coaxial cables, radio channels (mobile telephony),
or optical fibers. It is interesting to note that wireless computer modems for local
area networking are typically referred to as WiPhy in popular culture, which is
an acronym for wireless physical layer communications. The engineering tools,
the technology, and design paradigms are significantly different at the physical
layer than at the higher layers in the stack. Consequently, systems engineer-
ing expertise in practice tends to have the greatest divide at the boundary to
the physical layer. Engineering education has followed that trend and typically
course work in telecommunications at both the undergraduate level and the
graduate level tends to be bifurcated along these lines. To reflect the trend in
both education and in industrial practice, this book will only try to educate in
the area of physical layer communication systems. To reflect this abstraction
the perspective in this text will be focused on point-to-point communications.
Certainly multiple-access communications is very important in practice but it
will not be considered in this text to maintain a consistent focus. Students who

Digital or Analog Digital or
Analog Analog
Information Waveforms Information

Modulator Channel Demodulator
Information to Decoded
be Sent Information
Figure 1.2 The physical layer model.