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4.1.1
Key points
• Before any network communication can occur, a
physical connection to a local network must be
established.
• Switch devices and wireless access points are
often two separate dedicated devices within a
network implementation
• ISRs allow switching components with multiple
ports, which allows multiple devices to be
connected to a LAN
• ISRs also include an AP which allows wireless
devices to connect
• Network Interface Cards (NICs) connect a
device to the network.
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4.1.1
Key points pt.2
• A wireless device will experience degradation in
performance based on its distance from a
wireless access point.
• Each wired device has a separate
communications channel over its Ethernet
cable.
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The Physical Layer
• The OSI physical layer transports the bits that make up
a data link layer frame across the network media.
• This layer takes a complete frame from the data link
layer and encodes it as a series of signals that are
transmitted onto the local media.
•
The encoded bits that comprise a frame are received by
either an end device or an intermediate device.
• The process that data undergoes from a source node to a
destination node is:
•
•
•
•
The user data is segmented by the transport layer, placed into packets
by the network layer, and further encapsulated into frames by the data
link layer.
The physical layer encodes the frames and creates the electrical,
optical, or radio wave signals that represent the bits in each frame.
These signals are then sent on the media, one at a time.
The destination node physical layer retrieves these individual signals
from the media, restores them to their bit representations, and passes
the bits up to the data link layer as a complete frame.
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Physical Layer Media
• There are three basic forms of network media.
• The physical layer produces the representation and groupings of bits
for each type of media as:
• Copper cable: The signals are patterns of electrical pulses.
• Fiber-optic cable: The signals are patterns of light.
• Wireless: The signals are patterns of microwave transmissions.
• To enable physical layer interoperability, all of the aspects of these
functions are governed by standards organizations.
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Physical Layer Standards
• The protocols and operations of the
upper OSI layers are performed in
software designed by software
engineers and computer scientists.
• The services and protocols in the
TCP/IP suite are defined by the
Internet Engineering Task Force
(IETF).
• The physical layer includes
electronic circuitry, media, and
connectors developed by engineers.
In result it's appropriate that the
standards governing this hardware
are defined by the relevant electrical
and communications engineering
organizations.
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Physical Layer
Functions
The three functions are...
• Physical Components are with
physical connections such as
media and NICs
• Encoding is the method when
you're streaming using bits to
display the data information
• Signaling needs to generate
electrical or wireless signals that
represent 1 and 0
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Bandwidth
Unit of Bandwidth
Abbreviation
Equivalence
Bits per second
b/s
1 b/s = fundamental unit
of bandwidth
Kilovits per second
kb/s
1 kb/s = 1,000 bps= 10^3
bps
Megabits per second
Mb/s
1 Gb/s = 1,000,000,000
bps = 10^9 bps
Tb/s
1 Tb/s +
1,000,000,000,000 bps =
10^12 bps
Terabots per second
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Physical Layer Standards cont.
•
There are many different international and national organizations, regulatory
government organizations, and private companies involved in establishing and
maintaining physical layer standards.
•
The physical layer hardware, media, encoding, and signaling standards are
defined and governed by the:
• International Organization for Standardization (ISO)
• Telecommunications Industry Association/Electronic Industries
Association (TIA/EIA)
• International Telecommunication Union (ITU)
• American National Standards Institute (ANSI)
• Institute of Electrical and Electronics Engineers (IEEE)
• National telecommunications regulatory authorities including the
Federal Communication Commission (FCC) in the USA and the
European Telecommunications Standards Institute (ETSI)
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Throughput
Factors
Latency
• The amount of traffic
• The type of traffic
• Measure of usable data
transferred over a given
period
• Throughput is the measure
of media over a given
period
• The latency created by the
number of network devices
encountering between a
source and destination
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Types of Physical Media
Copper Media
Standards
• Type of copper cabling being
used
• Bandwidth of Communication
• Type of connectors used
• Pinout and color codes of
connections to the media
• Maximum distance of the
media
• Physical
• Electrical
• Mechanical properties of the
media availbel for different
data communications
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4.3.1
Things to know
The data link layer of the OSI model is
responsible for:
• Receiving and directing packets to an upper
layer protocol
• Performing error detection
• The Layer 2 notation for network devices
connected to a common media is called a node.
Nodes build and forward frames. the OSI data
link layer is responsible for the exchange of
Ethernet frames between source and
destination nodes over a physical network
media.
- Data link is here to make
sure your data is at its most
credible state with no errors
or malfunction 
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4.3.1
LLC & MAC
The data link layer is divided into two
sublayers:
• Logical Link Control (LLC) - This upper
sublayer communicates with the network layer.
• Media Access Control (MAC) - This lower
sublayer defines the media access processes
performed by the hardware. It provides data link
layer addressing and access to various network
technologies.
• Layer 2 protocols specify the encapsulation of a
packet into a frame and the techniques for
getting the encapsulated packet on and off each
medium. The technique used for getting the
frame on and off the media is called the media
access control method.
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4.3.1
Extra facts
More about data link
Data link standards
• Router interfaces encapsulate the packet into
the appropriate frame, and a suitable media
access control method is used to access each
link. In any given exchange of network layer
packets, there may be numerous data link
layers and media transitions.
• Engineering organizations that define open
standards and protocols that apply to the
network access layer include:
• At each hop along the path, a router:
• Accepts a frame from a medium
• De-encapsulates the frame
• Institute of Electrical and Electronics Engineers
(IEEE)
• International Telecommunication Union (ITU)
• International Organization for Standardization
(ISO)
• American National Standards Institute (ANSI)
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Launch
Wheel Of Fortune
•
Each game in WOF has a puzzle in a
certain category
•
The game starts up with a tossup round,
revealing letter by letter of a puzzle.
First group to solve the puzzle wins
$1,000
•
In the main puzzle rounds, the first
group can spin the wheel for a certain
amount of money for every letter
guessed correctly. If they're correct, they
can go again, if not, it's the next group's
turn
•
Vowels (a, e, I, o, u) cost $250 and can't
be guessed from the wheel
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