ENVS 1000 Lecture Notes - Lecture 32: Network Interface Controller, Carrier Wave
10 May 2018
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ENVS 1000 Lecture 32 Notes – Physical layer (layer 1)
Introduction
• The medium-access control (MAC) sub layer is responsible for providing orderly access
to the physical medium.
• Because there are a variety of media and signaling techniques in use, the standards
define a number of different protocols and frame headers, each corresponding to a
particular physical medium and signaling method.
• The protocol is responsible for such services as data encoding, collision handling (when
multiple computers try to access a multipoint connection at the same time, for
example), synchronization, and multiplexing.
• The physical layer is the layer at which communication actually takes place.
• Communication at the physical layer consists of a bare stream of bits.
• The physical access protocol includes definition of the medium, the signaling method
and specific signal parameters, voltages, carrier frequencies, lengths of pulses, and the
like
• Synchronization and timing issues.
• The method used to physically connect the computer to the medium.
• An example of a physical access protocol is the specification describing the specifics of
the communication between an 802.11n wireless network card and a corresponding
access point.
• The physical layer protocol defines the frequency of the carrier signal, data modulation
and demodulation technique, bandwidth, strength of the transmitted signal under
different conditions, and more.
• Physical communication between computers, routers, and other devices takes place
only at the physical layer.
• The physical layer is implemented primarily in hardware by a network interface
controller (NIC)4, which generates the particular voltages, light pulses, radio waves,
clock and synchronizing signals, and the like appropriate to a particular specification.
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