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 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 6 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 7 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 8
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 9
Defining Wireless LANs: Bit Rates IEEE WLAN Standard IEEE Standard Ratified in this Year Maximum Stream Rate (Mbps) 802.11b 1999 11 N/A 802.11a 1999 54 N/A 802.11g 2003 54 N/A 802.11n (20 MHz) 2009 72 288 802.11n (40 MHz)* 2009 150 600 802.11ac (80 MHz)* 802.11ad (80 MHz)* 2011 2012 1.2Gbps 60 Gbps Maximum Theoretical Rate, One Device, Maximum Streams 5Gbps 5Gbps * 802.11n, ac & ad allow the use of multiple channels bonded together which allows for their faster speeds. WLAN Standards and Speeds 10 Table 6-1
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 11 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 12 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 13 Figure 6-6
Defining Wireless LANs: Comparing Topic Wired Wireless Uses 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 Comparing 802.3 Wired LANs with 802.11 Wireless LANs 14 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 15 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 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 Some Relationships and Results: Vendors, Wi-Fi Alliance, and IEEE 17 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 18 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 19 Figure 6-10
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 20 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 21 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) 22 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) 23 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) 24 Figure 6-15
Exploring WLAN Physical Layer Features Feature IBSS (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 Comparisons of Wireless LAN Topologies 25 Table 6-3
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 26 Figure 6-16
Exploring WLAN Physical Layer Features: Antennas Coverage by Design 27 Figure 6-17
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 28 Figure 6-19
Exploring WLAN Physical Layer Features: RF Electromagnetic spectrum review A Partial Electromagnetic Spectrum, for Perspective 29 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 30 30 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 31
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 32 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 33 Figure 6-23
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 34 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 35 Figure 6-25
Exploring WLAN Physical Layer Features Summary 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 60 Encoding Class OFDM DSSS DSSS OFDM OFDM OFDM Frequency Band (ISM at 2.4 GHz, UNII at 5 GHz) Non-overlapping Channels, USA (FCC) Maximum Bit Rate, 1 Stream (Mbps) Supports up to 4 streams on 1 device UNII ISM ISM Both Both Up to 60 Gig 23 3 3 21 9 7 54 11 54 72 150? No No No Yes Yes Yes 36 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 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 IEEE 802.11 Frame Format 38 Figure 6-26
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 39 Figure 6-27
Exploring WLAN Common Features: Associating Example of Discovered WLAN List (Mac OS X) 40 Figure 6-28
Exploring WLAN Common Features: Associating An Example of Probe, Authenticate, Associate 41 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 43 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 44 Figure 6-32
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