Wlan Fundamentals - Le Site De Marc

Transcript

WLAN Fundamentals By Marc-André Léger DESS, MASc, PHD(candidate) Fall 2007 Save the forest • Please do not print out more than one module at a time as it may evolve… Module 2 Session objectives • Description and review of the various components which make up a wireless network. WLAN Design Issues • THROUGHPUT: Factors that affect throughput include airwave congestion (number of users), range, the type of WLAN system used, as well as bottlenecks on the wired portions of the WLAN. • COVERAGE: Function of product design including transmitted power and receiver design and the propagation path, especially in indoor environments. • INTEROPERABILITY: Interconnection with wired systems. • RELIABILITY: Radio interference can cause degradation. Costs issues of WLAN implementations • Initial investment • • • • Network Interface Cards Access Points WLAN Management Software Test and Evaluation Costs • On-going operation & Support • User Training, guides and policies • On-going IT training • License and Service Contract Fees (Hardware & Software) • Infrastructure maintenance • Network and Security monitoring Six critical planning challenges 1. Defining data needs, capacity and coverage requirements 2. Service Levels and Quality 3. Threats and Risk 4. Project planning 5. Choosing the right standard and vendor 6. Educating users WLAN Applications • Home Usage: Wireless networks save time and money. • Small business: entrepreneurs focus on growing their businesses, the WLAN can grow with them. • Services industry: Wireless internet access for customers • Enterprise: Larger corporations and manufacturing facilities find benefits in having a portion of their network wireless, combined with RFID and GPS it can be an agent of change. • Urban access: Wireless hotspots create a public space. • LAN to LAN Bridging: WLAN are a quick and reliable solution to link a campus WAN. WLAN infrastructure networks infrastructure network AP AP wired network AP= Access Point AP Infrastructure-based networks • Infrastructure networks provide access to other networks. • Communication typically takes place only between the wireless nodes and the access point, but not directly between the wireless nodes. • The access point does not just control medium access, but also acts as a bridge to other wireless or wired networks. • Several wireless networks may form one logical wireless network: – The access points together with the fixed network in between can connect several wireless networks to form a larger network beyond actual radio coverage. Infrastructure-based networks (cont) • Network functionality lies within the access point (controls network flow), whereas the wireless clients can remain quite simple. • Use different access schemes with or without collision. – Collisions may occur if medium access of the wireless nodes and the access point is not coordinated. • If only the access point controls medium access, no collisions are possible. – Useful for quality of service guarantees (e.g., minimum bandwidth for certain nodes) – The access point may poll the single wireless nodes to ensure the data rate. • Infrastructure-based wireless networks lose some of the flexibility wireless networks can offer in general: – They cannot be used for disaster relief in cases where no infrastructure is left. Ad hoc networks Ad Hoc network definition • A network made up exclusively of wireless nodes without any access points operating in peer-to-peer configuration, grouped together in a temporary manner. Ad hoc WLAN networks • No need of any infrastructure to work – greatest possible flexibility • Each node communicate with other nodes, so no access point controlling medium access is necessary. – The complexity of each node is higher • implement medium access mechanisms, forwarding data • Nodes within an ad-hoc network can only communicate if they can reach each other physically – if they are within each other’s radio range – if other nodes can forward the message Sensor network definition • A sensor network is a collection of collaborating sensor nodes (ad hoc tiny nodes with sensor capabilities) forming a temporary network without the aid of any central administration or support services. • Sensor nodes can collect, process, analyze and disseminate data in order to provide access to information anytime and anywhere. Sensor network features • • • • • • • Large number of sensors Low energy use Efficient use of the small memory Data aggregation Network self-organization Collaborative signal processing Querying ability Wireless LAN Topologies Wireless LAN Topologies • • • Without a wireless alternative, organizations frequently resort to wide area networking (WAN) technologies to link together separate facilities. Contracting for leased-line or other wide-area services often presents a variety of drawbacks: • Installation is typically expensive and rarely immediate • Monthly fees are often quite high for bandwidth A wireless bridge can typically be purchased and installed in a day with no recurring charges. WLAN Devices WLAN Devices • • • • • • • • • Access points Wireless bridges Wireless Workgroup bridges Wireless routers WLAN Client devices Wireless Gateways Enterprise gateways WLAN Switches WLAN Mesh routers PoE Access points (CWNA Ch7-p220) Access Point Different vendors • Cisco • D-Link • Linksys • Nortel • Symbol • and more… Access Point Different shape and size but all share similar options • Fixed or detachable antennas • Advanced filtering capabilities • Removable radio cards • Variable output power • Variable types of wired connectivity – 10BaseTx, 10/100BaseTx, 100BaseTx, 100BaseFx, and more Typical Application of AP Wireless Laptop Access Point PC with Wireless Card Wireless Laptop Wireless Router Wired Infrastructure Backbone Wireless Laptops Access Point PC with Wireless Card AP Modes – Root mode – Repeater Mode – Bridge Mode • • • • Root Non-root Repeater Access-point – Additional topologies • • System redundancy Added bandwidth AP Wireless root mode CHANNEL 1 CHANNEL 6 AP AP LAN Backbone Root Mode Root Mode AP Wireless Repeater Mode • • • • The repeater’s Ethernet port does not forward packets The repeater must be within reach of the root The repeater is a client to the root like any other STAs Reduction of throughput !!! CHANNEL 1 CHANNEL 1 LAN Backbone Root Mode Repeater Mode AP Wireless Bridge Mode – 4 modes supported • Root, Non-Root, Repeater, Access-Point – In bridge mode no STAs are allowed • Except in Access-Point mode tA N LA n me g se tB N LA Bridge Mode (Access-Point) Bridge Mode (Root) N LA Bridge Mode (Repeater) Bridge Mode (Non-root) se n me g se en gm tC Wireless Workgroup Bridge • Aggregates multiple wired clients over a common wireless link – Clients’ MAC will not be seen behind the workgroup bridge • The workgroup bridge is a client to the AP • The AP can associate with other STAs • Useful for mobile setups tB tA Ns A L n me eg Root Mode N LA Workgroup Bridge Mode se g n me AP Modes (cont’d) Distances Limited by the 802.11 Specification 1.6km @ any Data Rate AP to any client 40km @ 2Mbps 18km @11Mbps Bridge to any client Hot standby Redundancy Topology • • • • One AP acts as a backup for a root AP Provides redundancy when one AP fails Standby AP must associate to the Root AP as a client Root and Standby APs communicate through radio and Ethernet interfaces LAN Backbone Active AP Standby AP Added Bandwidth Topology • Used in crowded workplace • More than 1 channel (3 maximum) covering an area • Provides different AP to associate with LAN Backbone CHANNEL 1 CHANNEL 6 Wireless bridges (CNWA Ch7-p243) Wireless Bridge Applications Wireless Bridge Types of WLAN Bridges • Basic Ethernet-to-Wireless • Workgroup Bridges • Access Point / Wireless Bridge Combos Wi-Fi bridge •A device used to add desktop computers and printers in remote locations to the network without having to string cables and without having to equip each one with a WiFi adapter. •Has a built-in LAN switch for plugging in several devices, and does not require line-of-site. •Can be set up almost anywhere and transmit over the air to another Wi-Fi bridge or access point that is wired to the main network. Wireless Bridge A wireless bridge is used to span buildings or areas where laying cable or leasing lines is prohibitive. Wireless Workgroup bridges • A Wireless bridge + an AP in a box (CNWA Ch7-p253) Wireless routers WLAN products See also • http://www.tigerdirect.ca/ • http:// www.cdw.com/webcontent/promos/coops/cisc WLAN Client devices (CNWA Ch7-p257) Client Adapters • For all types of computer in all WLAN standards… Antennas • External or directional antennas can provide extra distance, special applications • This is covered in-depth in the RF course… WLAN Switch • Wireless vendors such as Airespace (now Cisco) offer an alternative wireless LAN infrastructure that includes a wireless switch in addition to the access points. • In this case, a company installs the wireless switch instead of using existing infrastructure. The switch concentrates the intelligence of the wireless network, enabling the access points to be less intelligent ("thin"). WLAN Switch • The WLAN switch offers a centralized hardware platform for supporting the access points without tying up an existing wired network. • The WLAN switch continually monitors the access points and physically disables an access point if it doesn't have a configuration that matches the company's security WLAN Switch • The switch is smart enough to shut off the electrical power to suspicious access points via a power-overEthernet (PoE) connection. • In addition, wireless switches incorporate designs that offer very fast handoffs as users roam from one access point to another. This results in smooth operation of Voip WLAN systems. Cable and Accessories Low Loss Cable Antenna Mounts Lightening Arrestor Wireless IP Phone Consumer wireless products • There is a real difference in functionality and administrative capabilities between Business-class and Consumer wireless products. Wireless Gateways (CNWA Ch7-p271) WLAN Residential Gateways • ‘All-in one’ single device solution • Built to connect a small number of STAs to a single device offering more than WLAN connectivity. WLAN Residential Gateways • They generally offer: • Ethernet connectivity both wired and wireless. • Built-in hub or switch • WAN port facing the Internet that may be connected through one of the following: Cable modem, xDSL modem, Analog modem, Satellite modem • Point-to-Point Protocol over Ethernet (PPPoE) • Network Address Translation (NAT) • Port Address Translation (PAT) • Ethernet switching • Print Services • Routing • Virtual Private Networks (VPNs) • Dynamic Host Configuration Protocol (DHCP) Server • Firewall Linksys - SOHO Wireless Devices WAP54G Wireless-G Access Point WMP54G Wireless-G PCI Adapter WRT54G Wireless-G Broadband Router WRT300N Wireless-N Broadband Router WAP4400N Wireless-N Access Point with Power Over Ethernet WUSB54GC Compact Wireless-G USB Adapter WPC54G Wireless-G Notebook Adapter WPC300N Wireless-N Notebook Adapter Enterprise gateways WLAN Enterprise Gateways • Supports: – many APs – a variety of WLAN and WPAN technologies such as: • 802.11 standard, Bluetooth, HomeRF and more – SNMP and allow enterprise-wide simultaneous user profiles upgrades – RADIUS, LDAP, Windows NT authentication databases, and data encryption using industrystandard VPN tunnel types WLAN Enterprise Gateways • Provides specialised authentication and connectivity for wireless clients Enterprise Gateway Cisco Wireless Devices Aironet 1200 Series Access-Point Aironet 1100 Series Access-Point Aironet 1300 Series Bridge Diversity omnidirectional ceiling mount Antenna Cisco Client Adapters 2.2-dBi dipole antenna Yagi mast or wall mount Antenna Omnidirectional mast mount Antenna WLAN Switches (CNWA Ch7-p280) WLAN Switches • Creates virtual or logical WLANs • Can segregate WLAN for security • Still evolving – bleeding edge WLAN Mesh routers Wireless Mesh Networks are anticipated to resolve the limitations and to significantly improve the performance of ad hoc networks, wireless local area networks (WLANs), wireless personal area networks (WPANs), and wireless metropolitan area networks (WMANs). (CNWA Ch7-p286) Mesh routers • Wireless mesh networks (WMNs) consist of mesh routers and mesh clients, where mesh routers have minimal mobility and form the backbone of WMNs. • They provide network access for both mesh and conventional clients. • The integration of WMNs with other networks such as the Internet, cellular, IEEE 802.11, IEEE 802.15, IEEE 802.16, sensor networks, etc., can be accomplished through the gateway and bridging functions in the mesh routers. Mesh routers • Mesh clients can be either stationary or mobile, and can form a client mesh network among themselves and with mesh routers. • They are undergoing rapid progress and inspiring numerous deployments. • WMNs will deliver wireless services for a large variety of applications in personal, local, campus, and metropolitan areas. Wireless Mesh backbone PoE (CNWA Ch7-p290) Power over Ethernet (PoE) • Use to place radio near antenna to avoid cost and loss of a long antenna cable – PoE injector at base – Run Cat 5E Ethernet cable to 24 VDC conditioned power tap by radio • Can be means to meet specifications requiring PoE support – PoE injectors / taps not too costly PoE Regulated Tap Diagnostics devices Handheld Spectrum Analyzer & 802.11 Analyzers Key terms • • • • • Bridge mode Mesh router PoE Root mode Wireless routers (CNWA Ch7-p297) 802.11 Alphabet Soup 802.11a & b – 802.11a    High rate PHY, 6 to 54 Mb/s 5 GHz UNII band OFDM (Orthogonal Frequency Division Multiplexing) – 802.11b    High rate PHY, 5.5 and 11 Mb/s 2.4 GHz ISM band (83 MHz, 22 MHz channel) CCK (Complementary Code Keying) 802.11c & d – 802.11c • • • Bridging operation procedures between APs Used by AP manufacturers to insure interoperability Approved in 1998 – 802.11d • • Extending operations to new regulatory domains Specifically 5 GHz 802.11e - QoS – QoS and improved efficiency of 802.11 MAC – 8 priority levels – Remember 802.11 as media access control protocol defined: • • DCF based on CSMA/CA PCF based on polling – Problem: DCF and PCF don’t differentiate traffic types 802.11e – QoS – Enhanced DCF (EDCF) • Arbitration Interframe Space (AIFS) – High priority traffic have a shorter AIFS – STA’s with lower priority wait longer before accessing the medium • To avoid collision within a traffic category • STA’s countdown additional random number of time slots (contention window) • If STA 1 transmit before countdown ended, STA 2 waits next idle period and continues countdown where it left off – NO guarantees of service are provided, just a mechanism to allocate bandwidth based on traffic categories 802.11f & g – 802.11f - Inter AP Protocol • • • • Higher layer protocol Communication between APs Roaming between multi vendor APs Fast hand off – 802.11g – 54Mbps for 2.4 GHz ISM band • • • • > 20 Mb/s (max 54 Mb/s) Backward compatibility with 802.11b (through CCK and RTS/CTS) CCK and OFDM mandatory Other optional modulation schemes 802.11h, i & j – 802.11h • • – Use of 802.11a in 5 GHz band in Europe Include dynamic frequency selection (DFS) and transmit power control (TPC) 802.11i • • • Enhanced security and authentication in 802.11 WEP not enough Solution leveraging existing 802.1x standard – 802.11j • Use of 802.11a in the Japanese 4.9 GHz band 802.11n     High throughput PHY and MAC 108 to 320 Mb/s Reduced overhead Year 2005/2006 Acronym List •16QAM 16 Level Quadrature Amplitude Modulation •2GFSK 2nd Gaussian Frequency Shift Keying •3G Third Generation Cellular Mobile Communications •4GFSK 4th Gaussian Frequency Shift Keying •64QAM 64 Level Quadrature Amplitude Modulation •AC Alternating Current •ACK Acknowledgement •ADSL Asymmetric Digital Subscriber Loop (Line) •AIFS Arbitration Interframe Space •AM Amplitude modulation •AP Access Point •ARS Adaptive/Automatic Rate Shifting •ATIM Adhoc Traffic Indication Map •ATM Asynchronous Transfer mode •BPSK Binary Phase Shift Keying •BSS Basic Service Set •CCA Clear Channel Assessment •CCK Complementary Code Keying •CDMA Code Division Multiple Access •CP Contention Period •CRC Cyclic Redundancy Check •CRTC Canadian Radio Television Committee •CSMA Carrier Sense Multiple Access •CSMA/CA Carrier Sense Multiple Access/Collision Avoidance •CSMA/CD Carrier Sense Multiple Access/Collision Detection •CTS •DBPSK •DA •DC •DCF •DFS •DHCP •DIFS •DQPSK •DRS •DS •DSSS •EDCF •ESS •FAQ •FCC •FCS •FHSS •FM •FSK •GHz •GPS •HCF •HEC •IBSS Clear To Send Differential Binary Phase Shift Keying Destination Address Direct Current Distribution Coordination Function Dynamic Frequency Selection Dynamic Host Configuration Protocol Distributed Coordination Function Interframe Space Differential Quadratic Phase Shift Keying Dynamic Rate Shifting Distribution System Direct Sequence Spread Spectrum Enhanced Distribution Coordination Function Extended Service Set Frequently Asked Question Federal Communications Commission Frame Check Sequence Frequency Hopping Spread Spectrum Frequency Modulation Frequency Shift Keying Gigahertz Global Positioning System Hybrid Coordinator Function Header Error Check Independent Basic Service Set Acronym List •IEEE •IFS •IIT •IP •IR •ISM •ISP •LAN •LBT •LEN •LLC •MAC •Mbps •MHz •NAV •NetBIOS •NIC •OFDM •OSI •PAD •PAN •PAR •PCF •PCS •PDA Institute of Electrical and Electronic Engineers Interframe Space International Institute of Telecommunications Internet Protocol Infra Red Industrial Scientific Medical Internet Service Provider Local Area Network Listen Before Talk Length Logical Link Control Media Access Control Mega Bits per Second Mega Hertz Network Allocation Vector Network Adapter Basic Input Output System Network Interface Card Orthogonal Frequency Division Multiplexing Open System Interconnection Padding Personal Area Network Project Authorisation Request Point Coordination Function Personal Communication Services Personal Digital Assistant •PHY •PIFS •PLCP •PMD •PPDU •PRE •PSDU •PSK •PSP •PTMP •PTP •QAM •QoS •QPSK •RF •RTS •SA •SDLC •SFD •SIFS •SOHO •SSID •STA •SYNC •TG Physical Point Coordination Function Interframe Space Physical Layer Convergence Procedure Physical Medium Dependent PLCP Protocol Data Unit Preamble Physical Layer Service Data Unit Phase Shift Keying Power Save Polling Point To Multipoint Point To Point Quadrature Amplitude Modulation Quality of Service Quadratic Phase Shift Keying Radio Frequency Request To Send Source Address Synchronous Data Link Control Start Frame Delimiter Shortest Interframe Space Small Office Home Office Service Set IDentification Station Synchronisation Task Group Acronym List •TIM •UNII •VLAN •VoIP •VPN •WECA •WEP •WG •Wi-Fi •WISP •WLAN •WLANA •WLIF •XOR Traffic Indication Map Unlicensed National Information Infrastructure Virtual Local Area Network Voice over IP Virtual Private Network Wireless Ethernet Compatibility Alliance Wired Equivalency Privacy Working Group Wireless Fidelity Wireless Internet Service Provider Wireless Local Area Network Wireless Local Area Network Association Wireless LAN Interoperability Forum eXclusive OR •For more Acronyms •http://www.csrstds.com/ Questions ? End of Module 2 Please note • These slides are produced as presentation material for a technical college course, all references, sources and bibliographical information is available in the commentaries section of the PowerPoint presentation and may not be visible to viewers of PDF versions. • The course instructor has no pretensions to be the original author of any of the material.