Transcript Introduction to Networking ITT Version

NT1210 Introduction to Networking
Unit 6:
Chapter 6, Wireless LANs
Objectives
 Identify the major needs and stakeholders for computer
networks and network applications.
 Identify the classifications of networks and how they are
applied to various types of enterprises.
 Compare and contrast the OSI and TCP/IP models and
their applications to actual networks.
 Explain the functionality and use of typical network
protocols.
 Analyze network components and their primary functions in
a typical data network from both logical and physical
perspectives.
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Objectives
 Differentiate among major types of LAN and WAN
technologies and specifications and determine how each is
used in a data network.
 Explain basic security requirements for networks.
 Install a network (wired or wireless), applying all necessary
configurations to enable desired connectivity and controls.
 Use network tools to monitor protocols and traffic
characteristics.
 Use preferred techniques and necessary tools to
troubleshoot common network problems.
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Objectives
 Assess a typical group of devices networked to another
group of devices through the Internet, identifying and
explaining all major components and their respective
functions.
 Identify devices required in wireless networks.
 Differentiate between Layer 1 and Layer 2 concepts in
wireless networks.
 Analyze wireless standards.
 Design a basic small business wireless Ethernet network.
 Troubleshoot wireless LANs for connectivity and
performance.
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Defining Wireless LANs: Wireless vs. Wired
 Both described as LANs
 Both typically support devices close by
 Both provide LAN edge connection in Enterprise LANs
 WLAN headers differ from Ethernet LAN headers, but
both use same MAC addresses with same format and
size
 Wired and wireless LANs can be combined into single
design
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Defining Wireless LANs: Wireless vs. Wired
LAN edge: Refers to the part
of any network where the
user devices sit.
The LAN edge includes each
user device, each device’s
link to the network, along with
the network device on the
other end of that link (usually
a LAN switch or wireless
Access Point [AP]).
Typical Campus LAN with Wired and Wireless LAN Edge
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Figure 6-1
Defining Wireless LANs: Wireless Distances
 “Run” distances from user device to switch/AP
UTP 100m Maximum Length Vs. WLAN Range / Coverage Area
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Figure 6-2
Defining Wireless LANs: Wireless Distances
 Rules for planning distances in wired Ethernet LANs
much more objective than those for WLANs
 Will a device work well 50 feet from the AP? 150 feet?
 Network engineer needs to do test called wireless site
survey
 Engineer installs AP in wiring closet and then walks around to
different locations with wireless testing tool to determine
bandwidth capabilities
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Defining Wireless LANs: Wireless Distances
 Example site survey results





In conference Room 1, wireless works great
In conference Room 2, wireless fails to work
At user A’s cubicle, wireless works great
At user B’s cubicle, wireless works, but little slowly
At user C’s cubicle, wireless fails completely
 After testing, might add second AP somewhere nearer to
opposite end of building
 Building has width of around 300 feet, so that would put most
devices around 100 feet of one AP or another
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Defining Wireless LANs: Bit Rates
IEEE
IEEE WLAN
Standard
Standard
Ratified in this
Year
802.11b
1999
802.11a
1999
802.11g
2003
802.11n (20 MHz)
2009
802.11n (40 MHz)* 2009
802.11ac (80 MHz)* 2011
802.11ad (80 MHz)* 2012
Maximum
Stream Rate
(Mbps)
Maximum Theoretical
Rate, One Device,
Maximum Streams
11
54
54
72
150
1.2Gbps
60 Gbps
N/A
N/A
N/A
288
600
5Gbps
5Gbps
* 802.11n, ac & ad allow the use of multiple channels bonded together
which allows for their faster speeds.
WLAN Standards and Speeds
Table 6-1
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Defining Wireless LANs: Bit Rates
Devices A and C both sit within range of the WLAN AP; however, some
radio noise exists between device C and the AP, resulting in some lost
frames. The figure shows the speeds of the
most recent transmissions. Device A sent
at the maximum speed for 802.11b,
11 Mbps, and device C slowed down
to 2 Mbps to overcome the radio
noise.
Example of Using Speeds Slower than the Maximum, 802.11b
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Figure 6-4
Defining Wireless LANs: Bandwidth
 Bandwidth means different things in networking, but usually
refers to link speed (bit rate)
 Each Ethernet link between
nodes either shares or
dedicates bandwidth
 If nodes use half-duplex logic
(and CSMA/CD), they take turns
sending (shared bandwidth)
 If nodes use full duplex, switch
can use that speed at any time
without waiting (dedicated
bandwidth)
Dedicated Bandwidth and Shared Bandwidth and the Effect on LAN Capacity
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Figure 6-5
Defining Wireless LANs: Bandwidth
The WLAN has 20 end
user devices, but it has
four APs placed around
the floor of the building.
As a result, four devices
at a time can send or
receive data at the
same time to a nearby
AP without interfering
with each other.
Increasing Capacity 4X by Adding 4X Access Points
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Figure 6-6
Defining Wireless LANs: Comparing
Topic
Wired
Uses cables
UTP cable distance/wireless range is defined by the
standard, and not significantly affected by local site
conditions
A single LAN standard specifies a single speed,
rather than a set of allowed speeds
Allows Full Duplex on each link, rather than
sharing bandwidth among all devices using Half
Duplex
Comparing 802.3 Wired LANs with 802.11 Wireless LANs
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Wireless
Yes
No
Yes
No
Yes
No
Yes
No
Table 6-2
Defining Wireless LANs: IEEE Standards
 WLAN standards follows story similar to Ethernet
 Before standards existed, vendors created products
 Eventually, IEEE created 802.11 working group to define WLAN
standards
 802.11 working group ratified first standard (802.11) in 1997
that used frequencies around 2.4 GHz and maximum speed of
2 Mbps
Timeline of IEEE 802.11 WLAN Standards and Max Single Stream Bit Rates
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Figure 6-7
Defining Wireless LANs: Standards
 The Wi-Fi Alliance (WFA): Vendor Group standardssetting process
1. Vendor develops new wireless LAN product
2. Before selling product, vendor sends product to WFA for testing
3. WFA puts product through pre-defined set of tests
4. WFA also tests if new product works with existing approved
wireless products
5. Once product passes tests, WFA certifies product as having
passed; vendor can claim it is certified, and use WFA logos on
product packaging and advertising
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Defining Wireless LANs: Standards
 Degree of interoperability in wireless networking
happens in part because of cooperation between
vendors, IEEE, and WFA
 WFA helps vendors deal
with product testing task by
building formal set of
interoperability tests
 Vendors working with WFA,
as well as cooperate with
IEEE
 IEEE and WFA also cooperate as WFA wants Wi-Fi vendors to
be successful
Some Relationships and Results: Vendors, Wi-Fi Alliance, and IEEE
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Figure 6-8
Defining Wireless LANs: LAN Edge
 Example 1: Business that has a
large number of small remote
offices, plus a small number of
large sites; like a bank or an
insurance company.
 At both the small offices and the
large main sites, these companies
could use a wireless-only LAN
edge.
 All user devices use WLAN
technology to connect to the Enterprise network.
Enterprise Branch Office with Wireless LAN Edge
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Figure 6-9
Defining Wireless LANs: LAN Edge
 Example 2: Those same
companies could use a combined
wired and wireless LAN edge.
 Essentially, the company creates
a wired Ethernet LAN for every
location where a device might
need to connect to the network.
 This design also creates WLAN
coverage for the exact same
space, and possibly some spaces the Ethernet cables cannot reach.
Wired and Wireless LAN Edge
Figure 6-10
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Defining Wireless LANs: LAN Edge
 Small Office / Home Office WLANs:
The networking industry uses the
term small office / home office
(SOHO) to refer to smaller sites
that use the types of technology
and devices that you might find at
someone’s home office.
 Examples of different SOHO sites
(left): Each is at the home of a
different employee of the same
company.
 SOHO networks often use integrated networking devices (e.g., router,
switch, AP, modem).
Wired-only Versus WLAN Only Small Office, with Combined Devices
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Figure 6-11
Defining Wireless LANs: WLAN Roles
 For retailers who want their
customers to spend more time in
the store, the wireless hotspot
concept has become pretty
popular as well.
 The hotspot allows strangers to
use the company’s network.
Single-Site WLANs (Protected and Unprotected) and Public Hot Spot
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Figure 6-12
Exploring WLAN Physical Layer Features
 Ad-hoc wireless LAN: Provides very basic WLAN
service by letting two (or more) WLAN devices send
data directly without AP
 Two wireless devices connect directly
via their WLAN NICs to send data to
one another
 Known formally as Independent Basic
Service Set (IBSS)
 Gives users flexibility as no AP is needed for
connectivity
Ad-hoc Wireless LAN: Independent Basic Service Set (IBSS)
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Figure 6-13
Exploring WLAN Physical Layer Features
 Basic Service Set (BSS): Offers basic wireless service
with one—and only one—AP
to create wireless LAN
 Each wireless client connects
to network through AP
 AP controls BSS, with all
wireless frames flowing either
to AP from user devices
or from AP back to user
devices
Single AP Wireless LAN: Basic Service Set (BSS)
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Figure 6-14
Exploring WLAN Physical Layer Features
 Extended Service Set (ESS): Extends wireless
functions of BSS
 Each BSS and ESS defines
WLAN name as
Service Set Identifier—
SSID
 In BSS, AP defines
SSID
 In ESS, all APs use
same SSID and
cooperate to create WLAN
Multiple AP Wireless LAN: Extended Service Set (ESS)
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Figure 6-15
Exploring WLAN Physical Layer Features
IBSS
(ad-hoc)
BSS
ESS
Number of APs Used
Data Frame Flow
0
Device to device
1
Device to AP
>1
Device to AP
Connects Clients to
Some Other Network?
No
Yes
Yes
Allows Roaming?
No
No
Yes
Feature
Comparisons of Wireless LAN Topologies
Table 6-3
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Exploring WLAN Physical Layer Features:
Antennas
 Omnidirectional Antenna
 Coverage area of AP creates
layered coverage
 Closer parts of coverage area can
run at faster speeds and still work
because greater signal strength
 Further parts of coverage area
run at slower speeds
 Coverage area looks like set of
concentric circles
Coverage Area for an Omnidirectional Wireless LAN AP
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Figure 6-16
Exploring WLAN Physical Layer Features:
Antennas
Coverage by Design
Figure 6-17
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Exploring WLAN Physical Layer Features
 Antenna gain (power) and direction example
 4 APs sit in corners of floor, each using directional antenna
sending out signal for 90 degrees (quarter circle)
 Quarter circle patterns
extend further from
AP than omnidirectional
antennas’ signals would
 In middle of floor, along
walls, two APs each
use antennae with
180-degree pattern
Four 90 Degree and Two 180 Degree Direction Antennae Cover the Floor
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Figure 6-19
Exploring WLAN Physical Layer Features: RF
 Electromagnetic spectrum review
A Partial Electromagnetic Spectrum, for Perspective
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Figure 6-20
Exploring WLAN Physical Layer Features: RF
 Frequency Bands and Government Regulation
 FCC designates some licensed frequency bands and some
unlicensed frequency bands
 Licensed frequency bands: No one can use these frequencies
without getting permission (license)
 FCC subdivides licensed frequency
bands into smaller subsets
(frequency channels
or frequency spectrums) and sells
license for these “sub” frequencies
 National regulators in countries
around world define two major unlicensed frequency bands for
WLAN communications: 2.4GHz or 5GHz
Unlicensed Radio Frequency Bands Used for WLANs
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Figure 6-21
Exploring WLAN Physical Layer Features: RF
 Wi-Fi/Bluetooth operate 2.4 GHZ frequency (almost same
as microwave ovens)
 Difference is power output: Wi-Fi and Bluetooth use much smaller
wattage output making them safer
 Microwave oven works by passing microwave radiation
through food
 Usually operates at 2.45 GHz—wavelength of 122 millimeters;
falling between common radio and infrared
 Ovens use dielectric heating: Water, fat, etc., in food absorb
energy from microwaves and begin rotating
 Rotating molecules then hit other molecules and put them
into motion, dispersing energy
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Exploring WLAN Physical Layer Features: RF
 Wireless LAN radio frequency channels:
 WLAN devices use wireless frequency channel: Set of consecutive
frequencies that is subset of frequency band defined by regulators
 ISM frequency band (regulated by FCC) lists frequencies around 2.4
GHz with total frequency range of about 70 MHz
 Some 802.11
standards use
22-MHz
frequency
channel for
transmissions
in the ISM band
Government Regulated Frequency Bands Compared to 802.11 Transmission Channels
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Figure 6-22
Exploring WLAN Physical Layer Features: RF
The IEEE 802.11 standards do not allow WLAN devices to use just any
22 MHz subset of the ISM frequency band; they define specific
channels. For instance, 802.11b and 802.11g use a channel width of 22
MHz, and they all define 11 channels, which fit into the FCC’s definition
of the ISM frequency band. Each of the eleven channels has a defined
low- and high-end frequency.
802.11b and 802.11g Frequency Channels
Figure 6-23
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Exploring WLAN Physical Layer Features: RF
 Non-overlapping channels: In USA, FCC sets aside 73
MHz of bandwidth for ISM frequency band
 Some IEEE standards use 22-MHz channel for
transmission, so three of these channels (total of 66
MHz worth of frequencies) should fit within 73 MHz
Three Non-Overlapping 22 MHz 802.11 Channels inside 73 MHz ISM Band
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Figure 6-24
Exploring WLAN Physical Layer Features: RF
 With multiple APs in same space, multiple transmissions
can occur at same time
 Example: Each AP uses one of 3
non-overlapping channels
 Result: Even though coverage areas
overlap, each AP can send or
receive at same time as other two
APs
 If using 802.11g standard,
then capacity of WLAN increases
to 3 * 54 Mbps = 162 Mbps
Using Non-Overlapping 802.11 Channels to Increase Capacity, Performance, and Coverage
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Figure 6-25
Exploring WLAN Physical Layer Features
Year Ratified
Channel Width (MHz)
802.11a
802.11b
802.11g
802.11n
1999
1999
2003
2009
2009
2012
20
22
22
20
40
60
DSSS
DSSS
ISM
ISM
Both
Both
3
3
21
9
7
11
54
72
150
?
No
No
Yes
Yes
Yes
Encoding Class
OFDM
Frequency Band (ISM at
UNII
2.4 GHz, UNII at 5 GHz)
Non-overlapping
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Channels, USA (FCC)
Maximum Bit Rate, 1
54
Stream (Mbps)
Supports up to 4 streams
No
on 1 device
Summary of 802.11 Standards and Differences
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802.11n 802.11ac
OFDM OFDM
OFDM
Up to 60
Gig
Table 6-4
Exploring WLAN Common Features:
Associating
 Series of 802.11 management and control frames
associates new wireless client with AP to allow it access
to WLAN
 To associate, wireless clients follow process:
1. Client discovers all nearby APs
2. Decides which one to use
3. Passes any security processes
4. Gets AP to agree to allow it to be used
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Exploring WLAN Common Features:
Associating
 WLAN frames and addresses
 802.11 standard defines frame format used by all physical layer
standards
 Several 802.11 frame fields work same way as in 802.3
 Both have 6-byte destination MAC address in header
 Both have 6-byte source MAC address field in header
 Both have 4-byte FCS in trailer
IEEE 802.11 Frame Format
Figure 6-26
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Exploring WLAN Common Features:
Associating
 Discovering existing wireless LANs uses beacon
frames sent by APs send that announce its existence
 Includes name of Wireless LAN
(Service Set ID [SSID])
 Client listens for beacon frames
to learn of new APs and WLANs
 Example: Coverage areas of two
WLANs overlap, so all WLAN
clients in both locations
discover SSID of both wireless LANs
Learning about Multiple WLANs through 802.11 Beacon Frames
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Figure 6-27
Exploring WLAN Common Features:
Associating
Example of Discovered WLAN List (Mac OS X)
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Figure 6-28
Exploring WLAN Common Features:
Associating
An Example of Probe, Authenticate, Associate
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Figure 6-29
Exploring WLAN Common Features:
AP Operation
 AP must translate
between 802.11 and
802.3 frame formats
when both wired
and wireless used
in same LAN
 Both frame formats
have 6-byte source and destination MAC addresses
 But frame formats also have differences
Conceptual Drawing of WLAN AP Translating from 802.11 Frame to 802.3 Frame
42
Figure 6-30
Exploring WLAN Common Features:
AP Operation
 Queuing and Buffering
AP Queuing 802.11 Frames While Waiting for a Turn to Send with CSMA/CA
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Figure 6-31
Exploring WLAN Common Features:
AP Operation
 AP Switching Logic: MAC address table stored on AP
so if AP has more than one WLAN devices associated
with it, uses “shorthand” MAC addresses for easier
reference
 Example AP has
also learned
MAC addresses of
two wired Ethernet
devices (F1)
AP MAC Address Table
Figure 6-32
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Summary, This Chapter…
 Gave a to-scale drawing of a wired and wireless LAN,
compare the distance and coverage limitations of user
devices connected via both wired UTP Ethernet and
wireless 802.11 standards.
 Gave a to-scale drawing of a wired and wireless LAN,
compare the maximum bit rates of user devices
connected via both wired UTP Ethernet and wireless
802.11 standards.
 Explain the difference in the capacity to send bits in two
LANs, each with the same number of user devices, one
with an Ethernet switch and one with a wireless AP.
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Summary, This Chapter…
 Listed IEEE 802.11 wireless LAN standards and their
ratification order.
 Made simple line drawings with basic descriptions of 34 typical use cases for wireless LANs.
 Listed and illustrate the most important difference
between three WLAN topologies: IBSS, BSS, and ESS.
 Explained the concept of non-overlapping wireless LAN
channels and the importance of these channels in
WLAN operation and design.
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Summary, This Chapter…
 Listed three 802.11 frame fields with the same size,
format, and purpose as an 802.3 frame.
 Paraphrased the process that a WLAN client device
goes though when a user moves to a new WLAN to
discover and start using a new WLAN.
 Listed three functions performed by WLAN APs under
normal operating conditions when the AP connects to
both a wireless LAN and wired LAN.
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Questions? Comments?
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