NT1210 Introduction to Networking Unit 6: Chapter 6, Wireless LANs

NT1210 Introduction to Networking

Unit 6:

Chapter 6, Wireless LANs

Class Agenda 10/23/15

• Learning Objectives

• Midterm Exams.

• Lesson Presentation and Discussions

• Lab Activities will be performed in class.

• Assignments will be given in class.

• Break Times. 10 Minutes break in every 1 Hour.

• Note: Submit all Assignment and labs due today.

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.

3

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.

4

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.

5

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

6

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]).

7

Defining Wireless LANs: Wireless Distances

“Run” distances from user device to switch/AP

Figure 6-2UTP 100m Maximum Length Vs. WLAN Range / Coverage Area8

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

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)*

2011

2012

1.2Gbps

60 Gbps

5Gbps

5Gbps* 802.11n, ac & ad allow the use of multiple channels bonded together which allows for their faster speeds.

10

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)

Figure 6-5Dedicated Bandwidth and Shared Bandwidth and the Effect on LAN Capacity11

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.

12

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

13

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 Rates14

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

15

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 IEEE16

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 Edge17


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 Edge18


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 Devices19

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 hotspot concept has become pretty popular as well.

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

20

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)21


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)22


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)23


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

24

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 AP25

Exploring WLAN Physical Layer Features: Antennas

Figure 6-17Coverage by Design26


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 Floor27

Exploring WLAN Physical Layer Features: RF

Electromagnetic spectrum review

Figure 6-20A Partial Electromagnetic Spectrum, for Perspective28

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

Figure 6-21Unlicensed Radio Frequency Bands Used for WLANs29

29


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 2012Channel Width (MHz) 20 22 22 20 40 60

Encoding Class OFDM DSSS DSSS OFDM OFDM OFDM

Frequency Band (ISM at 2.4 GHz, UNII at 5 GHz)

UNII ISM ISM Both Both Up to 60

Gig

Non-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

30

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

31


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 Format32


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 Frames33

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

34

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.

35

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.

36

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.

37

Unit 6 Assignment

• Unit 5 Assignment will be given in Class.

• Reading Assignment. Read Chapter 7

Unit 5 Lab

• Complete all Labs in Chapter 6 of the lab book.

• Lab should be completed in class.

• Uncompleted Lab must be submitted in the next class.

Documents

NT1210 Introduction to Networking Unit 6: Chapter 6, Wireless LANs