CS计算机代考程序代写 Chapter 3

Chapter 3

IFN507 – Lecture 2
Network Media
NIC
Ethernet and Wi-Fi

Outline
Network Media
Network Interface Cards (NICs)
Wired network technology – Ethernet
Wireless network technology – Wi-Fi
7. Application
6. Presentation
5. Session
4. Transport
3. Network
2. Data Link
1. Physical

Network Media
2 major categories of media include:
Wired media
Wireless media
2 broad categories of cables
Copper wire
Fiber optic
The main differences between the 2 types:
Composition of signals (electricity or light)
Speed at which signals can be sent
Distance the signals can effectively travel

Criteria for Choosing Network Media
Bandwidth
Distance
Interference
Ease of installation
Total cost
Mobility
Security

Criteria for Choosing Network Media Bandwidth
Network bandwidth (data transfer rate)
The amount of data that can be carried from one point to another for given time period (usually a second).
Expressed in bits per second (bps);
Speeds can be measured in the millions of bits per second (megabits per second, or Mbps) or
billions of bits per second (gigabits per second, or Gbps).
Not to be confused with MB/s (Megabytes per second or GB/s Gigabytes per second
1 Mbps = 0.125 MB/s
100 Mbps = 12.5 MB/s
1 Gbps = 125 MB/s

Criteria for Choosing Network Media Distance
Maximum Segment Length
Maximum length of cable between two network devices (called cable segment)
Each cable type can transport data only so far before its signals begin to weaken (called attenuation)

Criteria for Choosing Network Media
Interference (1)
Physical objects
The density of objects.
Concrete/steel walls are difficult for a signal to pass through
Radio frequency interference
802.11b/g use an RF range of 2.4GHz
Devices that share the channel can cause noise and weaken the signals
Environmental Interference
Computers, refrigerators, fans, lighting fixtures, or any other motorized devices

Criteria for Choosing Network Media
Interference (2)
Electronical interference
Interference to electrical signals on copper media comes in the form of electromagnetic interference (EMI) and radio frequency interference (RFI)
Motors, transformers, fluorescent lights and other sources of intense electrical activity can emit both EMI and RFI.
Weather conditions
on wireless signal integrity, e.g. lightning, fog

Criteria for Choosing Network Media
Security
Copper wire is susceptible to electronic eavesdropping
Fiber-optic media carries light signals and is not susceptible to interference or eavesdropping

Types of Cables

Coaxial Cable
Often called “coax” for short
Once was the predominant form of network cabling
Inexpensive and easy to install
Started to phase out in the early 1990’s
Still used primarily in connecting a cable modem to the wall outlet your cable TV/Internet provider installs

Coaxial Cable

Often called “coax” for short
Once was the predominant form of network cabling
Inexpensive and easy to install
Started to phase out in the early 1990’s
Still used primarily in connecting a cable modem to the wall outlet your cable TV/Internet provider installs

Twisted-Pair Cable
The 2 types of twisted-pair cable
Unshielded Twisted-Pair (UTP)
Shielded Twisted-Pair (STP)

Twisted-Pair Cable
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Twisted-Pair Cable
Twisted pair cable is classified by category.
Twisted pair is currently Category 1 through Category 8, although Categories 1, 2 and 4 are nearly obsolete
Categories 5e, 6 and 7 UTP Cabling are the most popular types of UTP cabling in today’s networks
Twists are necessary to improve resistance to crosstalk from wires and EMI from outside sources
Shielding can further help to eliminate interference
electromagnetic interference (EMI)
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Shielded Twisted-Pair Cable
Includes shielding to reduce crosstalk and interference
Has a wire braid inside the sheath material or a foil wrap
Best to use in electrically noisy environments or very high-bandwidth applications

Shielded Twisted-Pair Cable

Includes shielding to reduce crosstalk and interference
Has a wire braid inside the sheath material or a foil wrap
Best to use in electrically noisy environments or very high-bandwidth applications

Twisted-Pair Cable Plant Components
RJ-45 Connectors – STP and UTP uses registered jack 45 (RJ-45)
Most used in patch cables, which are used to connect computers to hubs, switches, and RJ-45 wall jacks

Twisted-Pair Cable Plant Components

RJ-45 Connectors – STP and UTP uses registered jack 45 (RJ-45)
Most commonly used in patch cables, which are used to connect computers to hubs, switches, and RJ-45 wall jacks

Installing UTP Cabling
Cable termination – putting RJ-45 plugs on the ends of cable or punching down wires into terminal blocks on a jack or patch panel
Some tools
needed:
Wire cutters
Crimping Tool
Cable Tester
Punchdown Tool
Cable Stripper
RJ-45 plugs/jacks

Installing UTP Cabling

Cable termination – putting RJ-45 plugs on the ends of cable or punching down wires into terminal blocks on a jack or patch panel
Some tools
needed:
Wire cutters
Crimping Tool
Cable Tester
Punchdown Tool
Cable Stripper
RJ-45 plugs/jacks

Installing UTP Cabling
When making a cable or terminating a cable at a jack or patch panel
It is important to get the colored wires arranged in the correct order
Two standards: 568A and 568B from the Telecommunications Industry Association (TIA)/ Electronic Industries Alliance (EIA).
The definition of pin/pair assignments for UTP cables

Installing UTP Cabling

When making a cable or terminating a cable at a jack or patch panel
It is important to get the colored wires arranged in the correct order
There are two standards: 568A and 568B

Standard patch cables are called straight-through cables (same wiring standard on both ends)
Crossover cables
Use 568A standard on one side of the cable and 568B standard on the other side
Crosses the transmit and receive wires so that transmit on one end connects to receive on the other
This type of cable is often needed when you connect two devices of the same type to one another, e.g.
PC-to-PC
PC-to-router
Switch-to-switch
router-to-router

Straight-Through vs. Crossover Cable
S
S
R
R
S
R
R
S
Crossover
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Straight-Through Versus Crossover Cable

Standard patch cables are called straight-through cables (same wiring standard on both ends)
Crossover cables – use 568A standard on one side of the cable and 568B standard on the other side
Crosses the transmit and receive wires so that transmit on one end connects to receive on the other
This type of cable is often needed when you connect two devices of the same type to one another
For a 1000BaseT crossover cable, you have to cross the blue and brown pins because they’re used in 1000BaseT

Straight-Through vs. Crossover Cable

Source: https://en.wikipedia.org/wiki/Ethernet_crossover_cable#/media/File:Ethernet_MDI_crossover.svg
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Do we still need a crossover cable?
Nowadays, the need for crossover cables has been eliminated with latest equipment.
G/Ethernet comes with automatic medium-dependent interface crossover (Auto-MDIX).
This technology detects whether you need a crossover cable or a straight-through cable, and it automatically configures the network interface card accordingly.
Yet, we still need to use crossover cables to connect two devices of the same type, e.g.
Router – Router
Switch – Switch

Structured Cabling: Managing and Installing a UTP Cable Plant

Structured Cabling: Managing and Installing a UTP Cable Plant
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Lab S513

Twisted Pair Wire (continued)
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Click to edit Master text styles
Second level
Third level
Fourth level
Fifth level

Twisted Pair Summary
Most common form of wire
Comes in shielded and unshielded forms
Relatively inexpensive
Easy to install
Carries high data rates (but not the highest)
Can suffer from electromagnetic noise
Can be easily wire-tapped
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Fiber-Optic Cable
Composition
A slender cylinder of glass fiber called the core is surrounded by a concentric layer of glass called the cladding
Fiber is then jacketed in a thin transparent plastic material called the buffer

Fiber-Optic Cable
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Fiber-Optic Cable (continued)
Bits are transmitted as pulses of light instead of electricity. Information is sent in a beam of light bouncing down a glass or plastic pipe.
High data capacity
Immune to electrical interference
Less attenuation
It can carry signals over a much longer distance without a repeater compared to copper.
Security
Difficult for eavesdropping

Fiber-Optic Cable

Bits are transmitted as pulses of light instead of electricity
Immune to electrical interference
Highly secure – electronic eavesdropping is eliminated
Composition
A slender cylinder of glass fiber called the core is surrounded by a concentric layer of glass called the cladding
Fiber is then jacketed in a thin transparent plastic material called the buffer

Fiber-Optic (continued)
Installation costs:
More difficult and time consuming than copper media installation
Connectors and test equipment required for termination are still more expensive than copper
Wildlife damage to fiber-optic cables
Birds peck at the fiber cable jackets to use bits of nesting material.
Beavers and mice use exposed fiber cable to sharpen their teeth
Ants like to eat plastic shielding
Sharks have been known to damage fiber cabling when laid underwater

Fiber-Optic Installation

Somewhat more difficult and time consuming than copper media installation
However, advances in connector technology is closing the gap
Connectors and test equipment required for termination are still more expensive than copper
There are many methods for terminating fiber-optic cables because of the many connectors and cable types available
Installation details are beyond the scope of this book
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Fiber-Optic Cable Types
Single-mode fiber (SMF)
Includes a single, small-diameter fiber at the core (8 microns)
Generally uses laser light source
Spans the longest distances
Used in higher-bandwidth applications
Multimode fiber (MMF)
Larger diameter fiber at the core (50 and 62.5 microns)
Costs less than SMF
Use LED for light source
Spans shorter distances

Fiber-Optic Cable Types

Single-mode fiber (SMF)
Includes a single, small-diameter fiber at the core (8 microns)
Generally works with laser-based emitters
Spans the longest distances
Used in higher-bandwidth applications
Multimode fiber (MMF)
Larger diameter fiber at the core (50 and 62.5 microns)
Costs less than SMF
Works with lower-power light emitting diodes (LEDs)
Spans shorter distances

Fiber-Optic Cable Summary
Fiber optic cable can carry the highest data rate for the longest distances
Initial cost-wise is more expensive than twisted pair and coaxial
But when you consider the superiority of fiber, initial costs outweighed by capacities
Not affected by electromagnetic noise
Cannot be easily wiretapped

How are all these technologies used?
NBN Fixed Line Connections
Fibre to the Premises (FTTP)
Fibre to the Building (FTTB)
Hybrid Fibre Coaxial (HFC)
Fibre to the Curb (FTTC)
Fibre to the Node (FTTN)
NBN Fixed Wireless/Satellite
NBN Fixed Wireless
Satellite
Source: https://www.nbnco.com.au/learn/network-technology
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NBN Technology Examples

Source: https://www.draytek.com.au/solutions/nbn-solutions/
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Serial Communications
A serial link is a point-to-point link between two devices
Bits are transmitted sequentially over a single channel
Parallel in theory faster than serial, however, suffers problems with synchronization and higher cost
Original serial standard RS-232 was introduced in the 1960s – Now mostly replaced by USB

Sources: https://en.wikipedia.org/wiki/RS-232, https://www.ciscopress.com/articles/article.asp?p=2202412&seqNum=4,

DTE vs. DCE devices
Devices that communicate over a serial interface are divided into:
Data Terminal Equipment (DTE)
An end instrument that converts user information into signals or reconverts received signals.
Data Communications Equipment (DCE)
Typically, a modem or other piece of data communications equipment.
When connecting two DTE(such as two routers in the lab) devices together without a modem, you require a special type of cable called a null modem
Generally, DCE devices provide the clock rate and the DTE device synchronizes on the provided clock rate

DCE
DTE

Serial link
Router A
Router B

Source: https://www.ciscopress.com/articles/article.asp?p=2202412&seqNum=4
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Cisco Smart Serial Connector

Source: https://www.ciscopress.com/articles/article.asp?p=2202412&seqNum=4
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Wireless Networks

Wireless Benefits
Creates temporary connections to wired networks
Establishes backup or contingency connectivity for existing wired networks
Extends a network’s span beyond the reach of wire-based or fiber-optic cabling, especially in older buildings where rewiring might be too expensive
Allows businesses to provide customers with wireless networking easily, offering a service that gets customers in and keeps them there
Enables users to roam around a corporate or college campus with their machines

Wireless Benefits

Creates temporary connections to wired networks
Establishes backup or contingency connectivity for existing wired networks
Extends a network’s span beyond the reach of wire-based or fiber-optic cabling, especially in older buildings where rewiring might be too expensive
Allows businesses to provide customers with wireless networking easily, offering a service that gets customers in and keeps them there
Enables users to roam around a corporate or college campus with their machines

Wireless Networking
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Wireless Networking

Demand has increased considerably
Many home users have turned to wireless networks
Wireless networks are often used with wired networks to interconnect geographically dispersed LANs or groups of mobile users with wired servers and resources on a wired LAN (sometimes referred to as “hybrid networks”)
Even in small networks with workstations connecting to a wireless AP or router, the AP or router usually connects to the Internet via a wired connection to a cable modem

Wireless LAN Components
Network interface attaches to an antenna and an emitter rather than to a cable
The heart of a wireless network is the wireless access point (AP)
Includes an antenna and a transmitter to send and receive wireless traffic but also connects to the wired side of the network
Shuttles traffic back and forth between a network’s wired and wireless sides
Most small business and home networks use a device typically called a wireless router that combines the functions of an AP, a switch, and a router
Wireless LANs are usually attached to wired networks

Wireless LAN Components

Network interface attaches to an antenna and an emitter rather than to a cable
Transceiver/access point (AP) – a transmitter/receiver device that must be installed to translate between wired and wireless networks
Includes an antenna and a transmitter to send and receive wireless traffic but also connects to the wired side of the network
Shuttles traffic back and forth between a network’s wired and wireless sides

LAN Media Selection Criteria

30.48m – 91.44m
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LAN Media Selection Criteria
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Wireless vs. Wired Networking
Speed
Wired Ethernet is faster than wireless than Wi-Fi,
Wi-Fi is becoming faster over recent years.
Stability
Wireless is susceptible to environmental factors
Radio waves can be blocked by walls and floors
Can interfere with microwaves, cordless phones
Mobility, installation and convenience
E.g. connecting to speakers, Wi-Fi appliances
Security
Wireless transmission can be intercepted more easier than wired transmission
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Network Interface Cards (NIC)
Attaching a computer to a network requires a NIC to create and mediate the connection between a computer and the networking medium
A NIC can be
built into the motherboard
a separate adapter card that slides into one of the motherboard expansion slots

Network Interface Cards

Most NICs are built into a computer’s motherboard
Occasionally fail or additional NICs are needed for an application
It is important to know how to install a new NIC

NICs and MAC Addresses
MAC address is unique and stored in ROM on the NIC.
48-bit address expressed in 12 hexadecimal digits
E.g. 04-40-31-5B-1A-C4
Two 24-bit hexadecimal numbers
24 bits are referred as the manufacturer ID (OUI)
The last 24 bits are the device’s unique serial number, assigned to the device by the manufacturer.
The broadcast address is ff-ff-ff-ff-ff-ff
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NICs and MAC Addresses

NIC manufacturers ensure that every NIC produced has a unique address
Networks won’t function correctly if duplicate MAC addresses exist
MAC address is stored in read-only memory (ROM) on the NIC
Two 24-bit hexadecimal numbers
24-bit manufacturer ID called OUI
24-bit serial number assigned by the manufacturer
48-bit address expressed in 12 hexadecimal digits: 04-40-31-5B-1A-C4

Wireless NICs
Wireless NICs must be chosen according to type of wireless AP being used
Typical are 802.11ac, 802.11ax, 802.11ax-2021 or 802.11 a/b/g/n
The letter a,b,g, n, ac, ax refer to the wireless networking standard the device supports
Wireless NICs connect to network using service set identifier (SSID)
SSID is the name assigned to the wireless network
You may also need to enter a security key or a username and password, depending on the network’s security configuration
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Wireless NICs

Wireless NICs must be chosen according to type of wireless AP being used
Typical are Wireless-n, 802.11ac or 802.11 a/b/g/n
The letter a,b,g, n, and ac refer to the wireless networking standard the device supports
Wireless NICs connect to network using service set identifier (SSID)
SSID is the name assigned to the wireless network
You may also need to enter a security key or a username and password, depending on the network’s security configuration

NIC functions
Incoming messages:
Receives bit signals and assembles them into frames
Verifies the destination address
If the destination MAC address = its own MAC address or broadcast address
Removes frame header and sends the resulting packet to the network protocol
Outgoing messages:
Receive packets from the Network layer
Creates frames by adding MAC addresses/error check
Converts frame into bit signals suitable for the medium and transmits them

NIC Basics

The tasks a NIC and its driver perform:
Provide a connection from computer to medium
Incoming messages: Receives bit signals and assembles them into frames
Verifies the destination address
Removes frame header and sends the resulting packet to the network protocol
Outgoing messages: receive packets from network protocol
Creates frames by adding MAC addresses/error check
Converts frame into bit signals suitable for the medium and transmits them

NIC Basics

Ethernet
Ethernet is used in local area networks (LAN), metropolitan area networks (MAN) and wide area networks (WAN)
Introduced in 1980 and standardized in 1983 as IEEE 802.3
Ethernet has replaced wired LAN technologies (e.g. Token Ring, FDDI) and WAN technologies (e.g. ATM)
The protocol has evolved and improved over time to transfer data. The system now has three main speeds:
10Mbps, 100Mbps and 1000Mbps (Gigabit Ethernet),
Ethernet can support a broad range of speeds:
10 Mbps to 10 Gbps
Most NICs/switches can operate at multiple speeds: 10/100/1000 Mbps

Ethernet Media Access
Media access method:
Rules governing how and when the medium can be accessed for transmission
Ethernet uses Carrier Sense Multiple Access with Collision Detection (CSMA/CD)
Carrier Sense: Listen before send – must hear silence
Multiple Access: If two or more stations hear silence, multiple stations may transmit at the same time
Collision Detection: If two or more stations transmit, a collision occurs and is detected by the NIC; all stations must retransmit

Ethernet Media Access

Media access method: Rules governing how and when the medium can be accessed for transmission
Ethernet uses Carrier Sense Multiple Access with Collision Detection (CSMA/CD)
Carrier Sense: Listen before send – must hear silence
Multiple Access: If two or more stations hear silence, multiple stations may transmit at the same time
Collision Detection: If two or more stations transmit, a collision occurs and is detected by the NIC; all stations must retransmit

Ethernet Error Handling
Ethernet is a best-effort delivery system
Like the post-office; you hope it gets there but there is no acknowledgement either way
Network protocols and applications ensure delivery
Only collisions are automatically retransmitted
Ethernet detects damaged frames
The error-checking code in a frame’s trailer is called a Cyclic Redundancy Check (CRC)
Uses CRC to determine that data is unchanged
If a frame is detected as damaged, it is discarded with no notification

Ethernet Error Handling

Ethernet is a best-effort delivery system
Like the post-office; you hope it gets there but there is no acknowledgement either way
Network protocols and applications ensure delivery
Only collisions are automatically retransmitted
Ethernet detects damaged frames
The error-checking code in an frame’s trailer is called a Cyclic Redundancy Check (CRC)
Uses CRC to determine that data is unchanged
If a frame is detected as damaged, it is discarded with no notification

Ethernet Addressing
Every station has a physical (MAC) address
Each MAC address has 48 bits expressed as 12 hexadecimal digits
Incoming frames must match NIC’s address or broadcast address (FF-FF-FF-FF-FF-FF).
Once processed by NIC, incoming frames are sent to the network protocol for further processing

Ethernet Addressing

Every station has a physical (MAC) address
Each MAC address has 48 bits expressed as 12 hexadecimal digits
Incoming frames must match NIC’s address or broadcast address (FF-FF-FF-FF-FF-FF).
Once processed by NIC, incoming frames are sent to the network protocol for further processing

Ethernet Frames
Four different formats or frame types –depending on the network protocol used to send the frame
Ethernet II frame type used by TCP/IP
TCP/IP has become the dominant network protocol in LANs so supporting multiple frame types has become unnecessary
Frames must be between 64 and 1518 bytes
Destination MAC
Source MAC
Type
Data
FCS

Ethernet Frames

Four different formats or frame types –depending on the network protocol used to send the frame
Ethernet II frame type used by TCP/IP
TCP/IP has become the dominant network protocol in LANs so supporting multiple frame types has become unnecessary
Frames must be between 64 and 1518 bytes
Destination MAC
Source MAC
Type
Data
FCS

Ethernet Standards
Ethernet standards expressed as:
XBaseY – 10Base2, 10BaseT, 100BaseT, 100BaseFX
X – designates the speed of transmission
Y – specifies the type of media (T = twisted-pair, FX = fiber optic)
10BaseT (dated)
Uses two of the four wire pairs
Runs over Category 3 or higher UTP cabling
Highly susceptible to collisions and is obsolete

Ethernet Standards

Ethernet standards expressed as:
XBaseY – 10Base2, 10BaseT, 100BaseT, 100BaseFX
X – designates the speed of transmission
Y – specifies the type of media (T = twisted-pair, FX = fiber optic)
10BaseT
Uses two of the four wire pairs
Runs over Category 3 or higher UTP cabling
Highly susceptible to collisions and is obsolete

Ethernet Standards
100BaseTX
A common variety of Ethernet
Runs over Category 5 or higher UTP
Uses two of four wire pairs
Two types of 100BaseTX hubs
Switches can be used to interconnect multiple hubs

Ethernet Standards

100BaseTX
Most common Ethernet variety
Runs over Category 5 or higher UTP
Uses two of four wire pairs
Two types of 100BaseTX hubs
Class I – can have only one hub between communicating devices
Class II – can have a maximum of two hubs between devices
Switches can be used to interconnect multiple hubs

Ethernet Standards
100BaseFX
Runs over two strands of fiber optic cabling
Typically used as backbone cabling between switches
Also used to connect clients or servers when immunity to noise and eavesdropping is required
1000BaseT Ethernet
Also known as “Gigabit Ethernet”
Runs over Category 5 or higher UTP and uses all four wire pairs

Ethernet Standards

100BaseFX
Runs over two strands of fiber optic cabling
Typically used as backbone cabling between hubs or switches
Also used to connect clients or servers when immunity to noise and eavesdropping is required
1000BaseT Ethernet
Also known as “Gigabit Ethernet”
Runs over Category 5 or higher UTP and uses all four wire pairs

Ethernet Standards
10GBaseT Ethernet
Runs over four pairs of Category 6A or 7 UTP
Operates only in full-duplex mode
Still considered an expensive option
Good for network servers so they can keep up with desktop systems that commonly operate at 1 Gbps

Ethernet Standards

10GBaseT Ethernet
Runs over four pairs of Category 6A or 7 UTP
Operates only in full-duplex mode
No hubs, only switches support 10GBaseT
Still considered an expensive option
Good for network servers so they can keep up with desktop systems that commonly operate at 1 Gbps

Additional Ethernet Standards
100BaseT4
Uses all four pairs of wires in UTP Category 3 cable
Obsolete
1000BaseLX
Uses fiber-optic media
“L” stands for “long wavelength” laser
Supports a maximum cable segment length of 5000 meters

Additional Ethernet Standards

100BaseT4
Uses all four pairs of wires in UTP Category 3 cable
Obsolete
1000BaseLX
Uses fiber-optic media
“L” stands for “long wavelength” laser
Supports a maximum cable segment length of 5000 meters

Additional Ethernet Standards
1000BaseSX
Uses fiber-optic media
“S” stands for “short wavelength” laser
Can’t cover as much distance as long-wavelength lasers, but are less expensive
1000BaseCX
Uses specially shielded, balanced, copper jumper cables
Might also be called “twinax” or “short-haul” copper cables

Additional Ethernet Standards

1000BaseSX
Uses fiber-optic media
“S” stands for “short wavelength” laser
Can’t cover as much distance as long-wavelength lasers, but are less expensive
1000BaseCX
Uses specially shielded, balanced, copper jumper cables
Might also be called “twinax” or “short-haul” copper cables

Additional Ethernet Standards
10 Gigabit Ethernet IEEE 802.3ae
Much like the others in frame formats and media access
Defined to run only on fiber-optic cabling and specifies a maximum distance of 40 kilometers
Primarily used for network backbones
Varieties:
10GBaseSR, 10GBaseLR, 10GBaseER, 10GBaseSW, 10GBaseLW, and 10GBaseEW

Additional Ethernet Standards

10 Gigabit Ethernet IEEE 802.3ae
Much like the others in frame formats and media access
Defined to run only on fiber-optic cabling and specifies a maximum distance of 40 kilometers
Primarily used for network backbones
Varieties:
10GBaseSR, 10GBaseLR, 10GBaseER, 10GBaseSW, 10GBaseLW, and 10GBaseEW

Additional Ethernet Standards
40 Gigabit and 100 Gigabit Ethernet
Fiber-optic cabling is primary medium
Although there are provisions to use special copper assemblies over short distances

Additional Ethernet Standards

40 Gigabit and 100 Gigabit Ethernet
Very high cost is still prohibitive
Adoption has been slow
Fiber-optic cabling is primary medium
Although there are provisions to use special copper assemblies over short distances

Additional Ethernet Standards

Additional Ethernet Standards
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802.11 Wi-Fi
The 802.11 wireless networking standard is also referred to as Wireless Fidelity (Wi-Fi)
In most towns you can usually find a public Wi-Fi network, called a hotspot
802.11 is essentially an extension to Ethernet
Using airwaves instead of cabling as the medium

802.11 Wi-Fi

The 802.11 wireless networking standard is also referred to as Wireless Fidelity (Wi-Fi)
In most towns you can usually find a public Wi-Fi network, called a hotspot
802.11 is essentially an extension to Ethernet
Using airwaves instead of cabling as the medium

Wi-Fi Modes of Operation
Wi-Fi can operate in one of two modes:
Infrastructure
uses central access point (AP)
Ad hoc
Uses no central device
Data travels from device to device like a bus
Sometimes called “peer-to-peer mode”

Wi-Fi Modes of Operation

Wi-Fi can operate in one of two modes
Infrastructure — use central access point (AP)
Ad hoc — no central device; data travels from device to device like a bus
Sometimes called “peer-to-peer mode”
Most of this chapter’s discussion of Wi-Fi focuses on infrastructure mode

Wi-Fi Channels and Frequencies
Wi-Fi can operate: 2.4GHz and 5.0 GHz frequencies
2.4 GHz is actually 2.412 thru 2.484 divided into 14 channels spaced 5 MHz apart

5.0 GHz is actually 4.915 thru 5.825 GHz divided into 42 channels of 10, 20, 40, 80, 160 MHz each

Wi-Fi Channels and Frequencies

Wi-Fi operate at one of two radio frequencies: 2.4GHz and 5.0 GHz
Although this frequency is not fixed
2.4 GHz is actually 2.412 thru 2.484 divided into 14 channels spaced 5 MHz apart
Work like a TV channel – you must tune to the correct channel to connect
Needs 25 MHz to operate spanning 5 channels
Choose channels five apart from other known APs
5.0 GHz is actually 4.915 thru 5.825 GHz divided into 42 channels of 10, 20, or 40 MHz each

Wi-Fi – IEEE802.11standards
Generation/IEEE Standard Maximum Linkrate Adopted Frequency
Wi-Fi 6e (802.11ax-2021) 600–9608 Mbit/s 2021 2.4/5/6 GHz
Wi‑Fi 6 (802.11ax) 600–9608 Mbit/s 2019 2.4/5 GHz
Wi‑Fi 5 (802.11ac) 433–3460 Mbit/s 2014 5 GHz
Wi‑Fi 4 (802.11n) 72–600 Mbit/s 2009 2.4/5 GHz
Wi‑Fi 3 (802.11g) 3–54 Mbit/s 2003 2.4 GHz
Wi‑Fi 2 (802.11a) 1.5 to 54 Mbit/s 1999 5 GHz
Wi‑Fi 1 (802.11b) 1 to 11 Mbit/s 1999 2.4 GHz

Source: https://en.wikipedia.org/wiki/Wi-Fi
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2.4GHz vs. 5GHz
Advantage | Disadvanage
Lower data rate, more susceptible to interference and has more devices using this spectrum
Larger coverage area, better at successfully penetrating solid objects

5 GHz
Higher data rate, less susceptible to interference and usually has fewer devices using this frequency.
Smaller coverage area, less successful at penetrating solid objects.
2.4 GHz
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Wi-Fi Access Methods and Operation
Wi-Fi Access Method
Sending station can’t hear if another station begins transmitting so they cannot use the CSMA/CD access method that Ethernet uses
Wi-Fi devices use carrier sense multiple access with collision avoidance (CSMA/CA)
Optionally be used with request-to-send/clear-to-send (RTS/CTS) packets and acknowledgements

RTS=Request to Send
CTS=Clear to Send
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Wi-Fi Access Methods and Operation

Wi-Fi Access Method
Sending station can’t hear if another station begins transmitting so they cannot use the CSMA/CD access method that Ethernet uses
Wi-Fi devices use carrier sense multiple access with collision avoidance (CSMA/CA)
Uses request-to-send/clear-to-send (RTS/CTS) packets and acknowledgements
With this extra “chatter” actual throughput is essentially cut in half

CSMA/CA protocol steps
Sender node (A) has some data to transmit
A checks if the media is free or not
Optionally, the sending node can send transmits an RTS (Request to Send) packet to the Access Point (AP)
The sending node waits until all nodes have had time to receive the jam signal
AP replies with a CTS (Clear to Send) packet.
During transmission, the node monitors the media for an RTS signal from any other node that may already be transmitting data. If an RTS signal is received, it stops transmitting and retries after a random delay.

Wi-Fi Security
Signals from a Wi-Fi network can travel several hundred feet – Wi-Fi devices outside your home or business can detect your signals
Wi-Fi network should be protected by an encryption protocol that makes data difficult to interpret
Encryption protocols
Wired equivalent privacy (WEP), Wi-Fi Protected Access (WPA), WPA2, WPA3
Not all devices support all three protocols
Very old devices might only support WEP and/or WPA
70

Wi-Fi Security

Signals from a Wi-Fi network can travel several hundred feet – Wi-Fi devices outside your home or business can detect your signals
Wi-Fi network should be protected by an encryption protocol that makes data difficult to interpret
Encryption protocols
Wired equivalent privacy (WEP), Wi-Fi Protected Access (WPA), and WPA2,
Not all devices support all three protocols
Older devices might only support WEP and/or WPA

Lecture 3
IP Addressing
Practical 2
Introduction to Packet Tracer

References
Guide to Networking Essentials, Greg Tomsho, Cengage Learning 2020
Chapter 2: Network Hardware Essentials
Chapter 4 Network Media
Chapter 3: Network Topologies and Technologies

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