IT220 Network Standards & Protocols Unit 6: Chapter 6 Wireless LANs
2 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.
3 Objectives Analyze network components and their primary functions in a typical data network from both logical and physical perspectives. 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.
4 Objectives Use network tools to monitor protocols and traffic characteristics. Use preferred techniques and necessary tools to troubleshoot common network problems. 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.
5 Objectives 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.
6 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
Defining Wireless LANs 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 7 Figure 6-1
Wireless Distances UTP 100m Maximum Length Vs. WLAN Range / Coverage Area 8 Figure 6-2
9 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? Test to determine distances : Wireless site survey AP installed in wiring closet, then tester walks around to different locations with wireless testing tool to determine bandwidth capabilities at different distances from AP After testing, might discover need to add more APs
Wireless Bit Rates 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/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 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
Wireless Bit Rates Example Example of Using Speeds Slower than the Maximum, 802.11b 11 Figure 6-4
Wireless Bandwidth Bandwidth usually refers to link speed (bit rate) Each 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
Wireless Bandwidth Increasing Capacity 4X by Adding 4X Access Points 13 Figure 6-6
Wired vs. Wireless 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
IEEE Wireless Standards WLAN standards follows story similar to Ethernet Before standards existed, vendors created products IEEE created 802.11 working group to define WLAN standards First 802.11 standard ratified in 1997; 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
16 WiFi 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
Wireless Standards Interoperability Interoperability happens 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
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
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
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. Wired-only Versus WLAN Only Small Office, with Combined Devices 20 Figure 6-11
LAN Edge Examples of different SOHO sites: 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 21 Figure 6-11
WLAN Hotspots Wireless hotspot: Area in (usually) retail store to encourage their customers to spend more time in the store Allows strangers to use company s network Single-Site WLANs (Protected and Unprotected) and Public Hot Spot 22 Figure 6-12
WLAN Ad-Hoc Network Provides very basic WLAN service by letting two (or more) WLAN devices send data directly without AP Known formally as Independent Basic Service Set (IBSS) No AP needed for connectivity Ad-hoc Wireless LAN: Independent Basic Service Set (IBSS) 23 Figure 6-13
WLAN 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) 24 Figure 6-14
WLAN Extended Service Set (ESS) Extends wireless functions of BSS Allows more than 1 AP on WLAN Service Set Identifier (SSID): Identifies each BSS or ESS defines as name 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) 25 Figure 6-15
WLANs Compared 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 26 Table 6-3
WLAN 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 27 Figure 6-16
WLAN Antennas Coverage by Design 28 Figure 6-17
WLAN Antennas 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 29 Figure 6-19
WLAN Radio Frequency Electromagnetic spectrum review A Partial Electromagnetic Spectrum, for Perspective 30 Figure 6-20
WLAN Radio Frequency Frequency Bands and Government Regulation In U.S., FCC designates some licensed frequency bands and some unlicensed frequency bands Licensed frequency bands: No one can use these frequencies without getting license FCC subdivides licensed frequency bands into smaller subsets (frequency channels or frequency spectrums) and sells licenses for these sub frequencies 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 31 Figure 6-21
WLAN Radio Frequency: Microwaves WiFi/Bluetooth operates at 2.4 GHZ frequency (almost same as microwave ovens) Difference is power output: WiFi 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 32
WLAN Frequency Channels Set of consecutive frequencies that is subset of frequency band defined by regulators ISM frequency band (industial, scientific and medical (ISM) 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 33 Figure 6-22
WLAN Radio Frequency 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 34 Figure 6-23
WLAN Non-overlapping Channels 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 35 Figure 6-24
WLAN Non-overlapping Channels 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 36 Figure 6-25
WLAN Physical Layer Features Summary 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 37 Table 6-4
38 Associating to an AP 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
Associating to an AP 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 39 Figure 6-26
Associating to an AP Beacon frames: Used to discover existing wireless LANs sent by APs announcing its existence Includes name of Wireless LAN 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 40 Figure 6-27
Associating to an AP An Example of Probe, Authenticate, Associate 41 Figure 6-29
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
Queuing and Buffering AP Operation AP Queuing 802.11 Frames While Waiting for a Turn to Send with CSMA/CA 43 Figure 6-31
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 46 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.
Summary, This Chapter 47 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.
Questions? Comments? 48