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Introduction to Computer Networks and
Data Communications
Chapter 11
Learning Objectives
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Define the basic terminology of computer networks
Recognize the individual components of the big picture of computer networks
Outline the basic network configurations
Cite the reasons for using a network model and how those reasons apply to current
network systems
List the layers of the OSI model and describe the duties of each layer
List the layers of the Internet model and describe the duties of each layer
Compare the OSI and Internet models and list their differences and similarities

Lecture Notes
The Language of Computer Networks
To better understand the area of computer networks, you should understand the basic
broad categories of computer networks and data communications
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Computer Networks - Basic Configurations
Understand each of the following configurations
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Describe how this configuration works
in simple terms
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Know the OSI Model and its 7 layers including the basic functions performed at each
layer: Physical, Data Link, Network, Transport, Session, Presentation, and Application
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It is also important to learn the Internet Model (or DoD model or TCP/IP model) and its 4
layers: (Network) Interface, Network, Transport, and Application
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Logical and Physical Connections
To avoid future confusion, you must know the difference between a logical connection
and a physical connection
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Basics of transmission
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Analog versus digital
b
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Loss of signal strength
3
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Transmitting digital data with digital signals: digital encoding schemes
• Non-return to zero digital encoding schemes
• Manchester digital encoding schemes
• 4B/5B digital encoding scheme
b
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• Amplitude modulation
• Frequency modulation
• Phase modulation
c
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Transmitting analog data with analog signals
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Data Codes
a
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ASCII

Lecture Notes
Data and Signals
Information that is stored within computer systems and transferred over a computer
network can be divided into two categories: data and signals
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If you want to transfer this data
from one point to another, either by using a physical wire or by using radio waves, the
data has to be converted into a signal
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Converting Data into Signals
Like data, signals can be analog or digital
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However, you can use analog signals to convey
digital data and digital signals to convey analog data
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There are four combinations of data and
signals: digital data transmitted using digital signals, digital data transmitted using analog
signals, analog data transmitted using analog signals, and analog data transmitted using
digital signals
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Spread Spectrum Technology
Using a spread spectrum transmission system, it is possible to transmit either analog or
digital data using an analog signal
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The idea behind spread spectrum transmission is to
bounce the signal around on seemingly random frequencies rather than transmit the signal
on one fixed frequency
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Data Codes
One of the most common forms of data transmitted between a sender and a receiver is
textual data
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To
distinguish one character from another, each character is represented by a unique binary
pattern of 1s and 0s
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Two important data codes are EBCDIC and ASCII
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The Media: Conducted and Wireless
Chapter 31
Learning Objectives
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Outline the differences between Category 1, 2, 3, 4, 5, 5e, 6, and 7 twisted pair wire
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Outline the characteristics of fiber optic cable including the advantages and
disadvantages
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Outline the characteristics of satellite microwave systems including the advantages
and disadvantages as well as the differences between low earth orbit, middle earth
orbit, geosynchronous earth orbit, and highly elliptical earth orbit satellites
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Outline the characteristics of pager systems including the advantages and
disadvantages
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Apply the media selection criteria of cost, speed, distance and expandability,
environment, and security to various media in a particular application
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What is a transmission media
2
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Twisted pair wire
b
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Fiber optic cable
3
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Terrestrial microwave transmission
b
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c
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Cellular digital packet data
e
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Infrared transmissions
g
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Wireless application protocol
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Media Selection Criteria
a
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Speed
c
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Environment
e
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Conducted
media include twisted pair wire, coaxial cable, and fiber optic cable
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This chapter examines seven basic groups of wireless media used for the
transfer of data: terrestrial microwave transmissions, satellite transmissions, cellular radio
systems, personal communication systems, pagers, infrared transmissions, and
multichannel multipoint distribution service
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Twisted pair is almost a misnomer, as one rarely encounters a single pair of wires
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While still a little away from being a published specification,
Category 6 twisted pair should support data transmission as high as 200 Mbps for 100
meters while Category 7 twisted pair will support even higher data rates
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The braided metal
shield is very good at blocking electromagnetic signals from entering the cable and
producing noise
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There are two major coaxial
cable technologies, depending on the type of signal each carries: baseband or broadband
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Fiber Optic Cable
Fiber optic cable (or optical fiber) is a thin glass cable approximately a little thicker than
a human hair surrounded by a plastic coating
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The light pulses travel
down the glass cable and are detected by an optic sensor called a photo receptor on the
receiving end
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In addition to having almost errorfree high data transmission rates, fiber optic cable has a number of other advantages over
twisted pair and coaxial cable
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Wireless Media
All wireless systems employ radio waves at differing frequencies
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The services
covered in this section will include terrestrial microwave transmissions, satellite
transmissions, cellular radio systems, personal communication systems, pagers, infrared
transmissions, and multichannel multipoint distribution service Terrestrial microwave
transmission systems transmit tightly focused beams of radio signals from one groundbased microwave transmission antenna to another
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Satellites orbit the earth
from four possible ranges: low earth orbit (LEO), middle earth orbit (MEO),
geosynchronous earth orbit (GEO), and highly elliptical earth orbit (HEO)
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Cellular digital packet data (CDPD) technology supports
a wireless connection for the transfer of computer data from a mobile location to the
public telephone network and the Internet
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Infrared
transmission is a special form of radio transmission that uses a focused ray of light in the
infrared frequency range
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delivering Internet services into homes and businesses
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Media Selection Criteria
When designing or updating a computer network, the selection of one type of media over
another is an important issue
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Recognize the uses of a modem pool and its advantages and disadvantages
List the four components of all interface standards
Discuss the basic operations of the EIA-232F interface standard
Cite the advantages of FireWire and Universal Serial Bus interface standards
Outline the characteristics of asynchronous and synchronous data link interfaces
Recognize the difference between half duplex, full duplex, and simplex connections
Identify the operating characteristics of terminal- to-mainframe connections and why
they are unique from other types of computer connections

Chapter Outline
1
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Basic modem operating principles
b
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Standard telephone operations
d
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Compression and error correction
f
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Security
h
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Internal versus external models
j
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The 56K Digital Modem
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Channel Service Unit / Data Service Unit (CSU/DSU)
b
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ISDN modems
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DSL modems

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FireWire
b
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Data Link Connections
a
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Synchronous connections
c
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Interfacing a device to a
computer is considered a physical layer activity since it deals directly with analog signals,
digital signals, and hardware components
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Modems
Today’s modems are complex and offer so many functions and features that the user
manuals accompanying them are sometimes hundreds of pages long
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Modems can also be physically
characterized by whether they are internal or external models and whether they are
suitable for use with a laptop computer
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Did something change to allow the faster transmission speed, or
were the industry experts wrong? The experts were correcttwo important facts
changed with the 56,000 bps modems: digital signaling was introduced, and the signal
power level was increased
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Alternatives to Traditional Modems
There are four alternative transmission technologies available, other than the traditional
telephone line, that can be used to connect a computer into a remote network system: T-1
digital telephone lines, cable television networks, Integrated Services Digital Network
(ISDN), and Digital Subscriber Line (DSL)
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Modem Pools
A modem pool is a relatively inexpensive technique that allows multiple workstations to
access a modem without placing a separate modem on each workstation
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Interfacing a Computer to Modems and Other Devices
Interfacing is a complex area of study
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Various organizations set about creating a standard
interface between devices such as computers and modems
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High-speed Interface Protocols
Interface standards such as EIA-232F, X
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They were
designed primarily to support modems
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Two new interface standards that have great potential are FireWire and
Universal Serial Bus
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What is multiplexing
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Time Division Multiplexing
a
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T-1 multiplexing
c
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SONET multiplexing
e
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Dense Wavelength Division Multiplexing
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Comparison of Multiplexing Techniques

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Many times, however, we want a medium to carry multiple signals at the same
time
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Multiplexing is a technique performed at the physical layer of the OSI
model or the interface layer of the Internet model
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So that multiple users can share a single medium, each user
is assigned a channel
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Time Division Multiplexing
Time division multiplexing directly supports digital signals
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Since time division multiplexing was introduced in
1960s, it has split into two roughly parallel but separate technologies: synchronous time
division multiplexing and statistical time division multiplexing
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Unlike frequency division
multiplexing, which assigns input sources to separate sets of frequencies, and time
division multiplexing, which divides input sources by time, wave division multiplexing
uses different wavelength lasers to transmit multiple signals
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Code Division Multiplexing
This multiplexing technique assigns a multiple-bit sequence to each transmitter’s binary 1
and binary 0
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Comparison of Multiplexing Techniques
Frequency division multiplexing relies on analog signaling and is the simplest and most
noisy of all the multiplexing techniques
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The big advantage of
synchronous TDM is the lower noise during transmission
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Thus, statistical TDM wastes less bandwidth on the transmission
link
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Noise, errors, error prevention, detection and control
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White noise
b
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Crosstalk
d
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Jitter
f
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Attenuation
3
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Error Detection Techniques
a
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Cyclic redundancy checksum

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Error Control
a
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Return a message
• Stop and wait ARQ
• Sliding window protocol
• Go-back-N ARQ
• Selective-reject ARQ
c
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This chapter examines some of the more common error detection
methods and compares them in terms of efficiency and efficacy
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Noise and Errors
Transmitted data—both analog and digital—are susceptible to many types of noise and
errors
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Satellite, microwave, and radio networks are also prone to
interference and crosstalk
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Error Prevention
Since there are so many forms of noise and errors, and since one form of noise or another
is virtually a given, every data transmission system must include precautions to reduce
noise and the possibility of errors
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With proper error prevention techniques, many types of errors can be reduced
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If an error is detected, it is
typical to perform some type of request for retransmission
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themselves can be relatively simple or relatively elaborate
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For
example, the simplest error detection technique is simple parity
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At the other end of the
spectrum is the most elaborate and most effective technique available today: cyclic
redundancy checksum
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Error Control
Once an error is detected in the received data transmission stream, what is the receiver
going to do about it? The receiver can do one of three things: nothing, return a message to
the transmitter asking it to resend the data packet that was in error, or correct the error
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Local Area Networks: The Basics
Chapter 71
Learning Objectives
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State the definition of a local area network
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Cite the advantages and disadvantages of local area networks
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Cite the characteristics of wireless local area networks and their medium access
control protocols
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Recognize the different IEEE 802 frame formats
Describe the common local area network systems

Chapter Outline
1
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Primary Function of Local Area Networks
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Basic Local Area Network Topologies
a
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Star-wired bus topology
c
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Wireless LANs
e
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Medium Access Control Protocols
a
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Round robin protocol
c
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Medium Access Control Sublayer
a
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Ethernet
b
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Fiber data distributed interface (FDDI)
d
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Since the local area network first appeared in
the 1970s, its use has become widespread in commercial and academic environments
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This chapter begins
by discussing the basic layouts or topologies of the most commonly found local area
networks, followed by the medium access control protocols that allow a workstation to
transmit data on the network
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Primary Function of a Local Area Network
The majority of users expect a local area network to perform the primary function of
sharing resources
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Disadvantages include complexity, maintenance costs, and the
network is only as strong as the weakest link
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The choice of topology
is occasionally dictated by the physical environment in which the local area network is to
be placed
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Let’s examine each
of the four topologies, paying special attention to advantages and disadvantages
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Depending on the network’s topology, several types
of protocols may be applicable
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In the
case of a broadband local area network, which can support multiple channels at the same
time, it is imperative that only one workstation at a time be allowed to transmit its data
onto a channel on the network
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Medium Access Control Sublayer
Although the seven- layer OSI model was designed to support most typ es of
communication systems, it fell short in several areas
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Thus, the data link layer has been split into two sublayers: the medium access
control sublayer and the logical link control sublayer
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The
logical link control (LLC) sublayer is primarily responsible for logical addressing and
providing error control and flow control information
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IEEE 802 Frame Formats
To standardize many of the local area network protocols, IEEE created a series of
protocols called the IEEE 802 suite of protocols
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Thus,
as data comes down from the application layer through the lower layers of the
communications model and arrives at the MAC sublayer, MAC software places the data
into a unique frame format, ready for transmission across the medium (the physical
layer)
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Then the three major categories of
medium access control protocols that can operate on these different topologies were
introduced: CSMA/CD, token passing, and demand priority
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Four of the most
popular local area network systems are Ethernet, IBM token ring, fiber data distributed
interface, and 100VG-AnyLAN
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HomeRF vs Bluetooth vs WiFi
Bluetooth – piconets and scattenets
• Bluetooth issues:
Cost
Limited support
Shortcomings in protocol itself
Positioning in marketplace
Conflicts with other devices in radio spectrum
802
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11b uses Distributed Coordination Function (DCF) with modified procedure
known as Carrier Sense Multiple Access with Collision Avoidance (CSMA/CA)

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