NT1210 Introduction to Networking - · PDF fileChapter 6, Wireless LANs ... WLAN standards...

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.

2

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.

3

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.

4

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

5

Defining Wireless LANs: Wireless vs. Wired

Figure 6-1Typical Campus LAN with Wired and Wireless LAN Edge

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]).

6

Defining Wireless LANs: Wireless Distances

“Run” distances from user device to switch/AP

Figure 6-2UTP 100m Maximum Length Vs. WLAN Range / Coverage Area7


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

8


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

9

Defining Wireless LANs: Bit Rates

Table 6-1WLAN Standards and Speeds

IEEE WLAN Standard

IEEE Standard Ratified in this Year

Maximum Stream Rate (Mbps)

Maximum Theoretical Rate, One Device, Maximum Streams

802.11b 1999 11 N/A802.11a 1999 54 N/A802.11g 2003 54 N/A802.11n (20 MHz) 2009 72 288802.11n (40 MHz)* 2009 150 600802.11ac (80 MHz)*802.11ad (80 MHz)*

20112012

1.2Gbps60 Gbps

5Gbps5Gbps

* 802.11n, ac & ad allow the use of multiple channels bonded together which allows for their faster speeds.

10

Defining Wireless LANs: Bit Rates

Figure 6-4Example of Using Speeds Slower than the Maximum, 802.11b

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.

11

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 (dedicatedbandwidth)

Figure 6-5Dedicated Bandwidth and Shared Bandwidth and the Effect on LAN Capacity12

Defining Wireless LANs: Bandwidth

Figure 6-6Increasing Capacity 4X by Adding 4X Access Points

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.

13

Defining Wireless LANs: Comparing

Table 6-2Comparing 802.3 Wired LANs with 802.11 Wireless LANs

Topic Wired WirelessUses cables Yes No UTP cable distance/wireless range is defined by the standard, and not significantly affected by local site conditions Yes No A single LAN standard specifies a single speed, rather than a set of allowed speeds Yes No Allows Full Duplex on each link, rather than sharing bandwidth among all devices using Half Duplex Yes No

14

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

Figure 6-7Timeline of IEEE 802.11 WLAN Standards and Max Single Stream Bit Rates15

Defining Wireless LANs: Standards

The Wi-Fi Alliance (WFA): Vendor Group standards-setting 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

16

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

Figure 6-8Some Relationships and Results: Vendors, Wi-Fi Alliance, and IEEE17

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.

Figure 6-9Enterprise Branch Office with Wireless LAN Edge18


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.

Figure 6-10Wired and Wireless LAN Edge19


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).

Figure 6-11Wired-only Versus WLAN Only Small Office, with Combined Devices20

Defining Wireless LANs: WLAN Roles

Figure 6-12Single-Site WLANs (Protected and Unprotected) and Public Hot Spot

For retailers who want their customers to spend more time in the store, the wireless hotspotconcept has become pretty popular as well.

The hotspot allows strangers to use the company’s network.

21

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

Figure 6-13Ad-hoc Wireless LAN: Independent Basic Service Set (IBSS)22


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

Figure 6-14Single AP Wireless LAN: Basic Service Set (BSS)23


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

Figure 6-15Multiple AP Wireless LAN: Extended Service Set (ESS)24


Table 6-3Comparisons of Wireless LAN Topologies

FeatureIBSS

(ad-hoc)BSS ESS

Number of APs Used 0 1 >1 Data Frame Flow Device to device Device to AP Device to AP Connects Clients to Some Other Network?

No Yes Yes

Allows Roaming? No No Yes

25

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

Figure 6-16Coverage Area for an Omnidirectional Wireless LAN AP26

Exploring WLAN Physical Layer Features: Antennas

Figure 6-17Coverage by Design27


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

Figure 6-19Four 90 Degree and Two 180 Degree Direction Antennae Cover the Floor28

Exploring WLAN Physical Layer Features: RF

Electromagnetic spectrum review

Figure 6-20A Partial Electromagnetic Spectrum, for Perspective29

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 channelsor 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

Figure 6-21Unlicensed Radio Frequency Bands Used for WLANs30

30


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

31


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

Figure 6-22Government Regulated Frequency Bands Compared to 802.11 Transmission Channels32


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.

Figure 6-23802.11b and 802.11g Frequency Channels33


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

Figure 6-24Three Non-Overlapping 22 MHz 802.11 Channels inside 73 MHz ISM Band34


With multiple APs in same space, multiple transmissions can occur at same time

Example: Each AP uses one of 3non-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

Figure 6-25Using Non-Overlapping 802.11 Channels to Increase Capacity, Performance, and Coverage35


Table 6-4Summary of 802.11 Standards and Differences

802.11a 802.11b 802.11g 802.11n 802.11n 802.11ac

Year Ratified 1999 1999 2003 2009 2009 2012

Channel Width (MHz) 20 22 22 20 40 60Encoding Class OFDM DSSS DSSS OFDM OFDM OFDMFrequency Band (ISM at 2.4 GHz, UNII at 5 GHz)

UNII ISM ISM Both Both Up to 60

GigNon-overlapping Channels, USA (FCC)

23 3 3 21 9 7

Maximum Bit Rate, 1 Stream (Mbps)

54 11 54 72 150 ?

Supports up to 4 streams on 1 device

No No No Yes Yes Yes

36

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

37

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

Figure 6-26IEEE 802.11 Frame Format38

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

Figure 6-27Learning about Multiple WLANs through 802.11 Beacon Frames39

Exploring WLAN Common Features: Associating

Figure 6-28Example of Discovered WLAN List (Mac OS X)40

Exploring WLAN Common Features: Associating

Figure 6-29An Example of Probe, Authenticate, Associate41

Exploring WLAN Common Features:AP Operation

Figure 6-30Conceptual Drawing of WLAN AP Translating from 802.11 Frame to 802.3 Frame

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

42

Exploring WLAN Common Features:AP Operation Queuing and Buffering

Figure 6-31AP Queuing 802.11 Frames While Waiting for a Turn to Send with CSMA/CA43

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)

Figure 6-32AP MAC Address Table44

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.

45

Summary, This Chapter… Listed IEEE 802.11 wireless LAN standards and their

ratification order.

Made simple line drawings with basic descriptions of 3-4 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.

46

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.

47

Questions? Comments?

48

NT1210 Introduction to Networking - · PDF fileChapter 6, Wireless LANs ... WLAN standards...

Documents

Transcript of NT1210 Introduction to Networking - · PDF fileChapter 6, Wireless LANs ... WLAN standards...