Notes de cours

Cisco Netacad Module 4-7 Notes

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ITCC 1414

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San Antonio College

A document containing notes about modules 4-7, includes screenshots of important images—mostly bullet points.

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Publié le 24 novembre 2024
Nombre de pages 49
Écrit en 2024/2025
Type Notes de cours
Professeur(s) Shen jiang
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4. Physical Layer
Purpose of the Physical Layer
Before any network connections can happen, a physical connection to a local
network must be established

 Can be a wired connection with a cable or a wireless connection with
radio waves

The type of physical connection depends on the network

 Ex. In corporate offices, employees have computers that are physically
connected to a shared switch
o This is a “Wired Network” with data being transmitted through a
physical cable

Many businesses also offer wireless connections for laptops, tablets, and
phones

 With wireless, data is transmitted with radio waves
 Devices on a wireless network must have access to a wireless Access
Point (AP) or a wireless router

Components of an AP

1. The wireless antennas
a. Sometimes embedded in the router like shown above
2. Several Ethernet switchports
3. An internet port

,Most homes offer both wired and wireless connections options

A home router and a laptop connection to the LAN (Local Area Network)

NICs – Network Interface Cards, connect a device to a network

 Ethernet NICs are used for a wired connection
 WLAN NICs are used for wireless

An end-device may include one or both types of NICs

OSI Layer – Provides the means to transport the bits that make up a data link
layer frame across the network media

 Accepts a complete frame from the data link layer and encodes it as a
series of signals that are transmitted to the local media
 The encoded bits that comprise a frame are received by either an end
device or an intermediate device

The physical layer encodes the frames and creates the electrical, optical, or
radio wave signals that represent the bits in each frame

 The signals are then sent over the media one at a time

The destination node physical layer retrieves the signals from the media,
restores them to bit representations, and passes the bits up to the data link
layer as a complete frame

4.2 Physical Layer Characteristics
The physical layer consists of:

 Electronic circuitry
 Media
 Connectors

,The standards governing the hardware are defined by the relevant
engineering organizations

The Physical Layers standards are defined by these organizations:

 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)
o in the USA and the European Telecommunications Standards
Institute (ETSI)

There are often also regional cabling standards groups who develop local
specifications

 Ex. Canadian Standards Association (CSA), European Committee for
Electrotechnical Standardization (CENELEC), and Japanese Standards
Association (JSA/JIS)

The physical layer standards address 3 functional areas:

 Physical components
 Encoding
 Signaling

The physical components:

 Electronic hardware devices

,  Media
 Other connectors that transmit the signals that rep. bits
o Hardware components like NICs, interfaces and connectors, cable
materials, and cable designs are all specified in standards
associated with the physical layer

Encoding – A method of converting a stream of data bits into a predefined
“code”; the method or pattern used to rep. digital information

 Also called: Line Encoding
 Ex. Manchester encoding reps. a 0 by a high to low transition, and a 1
as a low to high transition

Code – Groupings of bits used to provide a predictable pattern that can be
recognized by both the sender and the receiver

An example of Manchester encoding

The transition occurs at the middle of each bit period

This encoding type is used in 10 Mbps (Mega bits per second) Ethernet

 Faster data rates require more intense encoding
 Manchester is used in older Ethernet standards

The physical layer must generate the signals that rep. the “1” or the “0” on
the media

Signaling Method – The way bits are represented

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