WLAN Basics. 2001, Cisco Systems, Inc. All rights reserved.

Transcription

2 Wireless Technologies WAN (Wide Area Network) MAN (Metropolitan Area Network) LAN (Local Area Network) PAN (Personal Area Network) PAN LAN MAN WAN Standards Bluetooth a,11b,11g HiperLAN MMDS, LMDS GSM, GPRS, CDMA, 2.5-3G Speed < 1Mbps 2 to 54+ Mbps 22+ Mbps 10 to 384Kbps Range Short Medium Medium-Long Long Applications Peer-to to-peer Device-to to-device Enterprise networks Fixed, last mile access PDAs, Mobile Phones, cellular access 2001, Cisco Systems, Inc. All rights reserved. 2

3 Bluetooth , King of Danmark 2,4 Ghz FH mit 1600 per sec 1 Mbit/sec.,10 Meter max. 8 devices Notebooks, Printer, Mouse, Keyboard, Handy, 2001 wurden 33 Million Geraete erwartet consortium mit > 1200 Mitgliedern , Cisco Systems, Inc. All rights reserved. 3

4 ISM Unlicensed Frequency Bands Audio Short-Wave Radio AM Broadcast FM Broadcast Infrared Wireless LAN Television Cellular 840 MHz NPCS 1.9 GHz Extremely Low Very Low Low Medium High Very Ultra High High Super High Infrared Visible Light Ultraviolet X-Rays MHz 26 MHz GHz 83.5 MHz IEEE b 5 GHz IEEE a HyperLAN HyperLAN2 2001, Cisco Systems, Inc. All rights reserved. 4

5 900 MHz vs. 2.4 GHz vs. 5GHz 900 MHz 2.4 GHz 5 GHz Globaler Markt Globaler Markt PROs Groessere Reichweite als 2.4 GHz (Fuer in-gebaeude LANs) IEEE Hoehere Datenrate (10+ Mbps) IEEE Hoehere Datenrate (20+ Mbps) CONs Maximale Datenrate 1 Mbps Begrenzte Bandbreite stark genutztes Band Geringere Reichweite als 900 MHz (Fuer in-gebaeude LANs) Geringere Reichweite als 900 MHz oder 2.4GHz Hoehere Kosten als RF KOmponenten (Handy) Groessere Antennen erforderlich 2001, Cisco Systems, Inc. All rights reserved. 5

6 Wireless LAN Technologies b g a HiperLAN2 Freq. Band 2.4 GHz 2.4 GHz 5 GHz 5 GHz Coverage Worldwide Worldwide (subject to approval) US/AP (initially) Europe Data Rate 1-11 Mbps (now) <54 Mbps (?? mths) Mbps (now) 100+Mbps (future) Mbps (??) The Laws of Radio Dynamics: Higher data rates = shorter transmission range Higher power output = increased range, but lower battery life Higher frequency radios = higher data rates, shorter ranges 2001, Cisco Systems, Inc. All rights reserved. 6

7 Characteristics of a Orthogonal Frequency Division Multiplexing (OFDM) Data rates supported: 54, 48, 36, 24, 12 and 6Mbps Can downshift to lower data rates for longer range Compliant with FCC and Japanese regulations Only available in some European countries under local regulations 5GHz band has more channels than 2.4GHz band UNII-1 + UNII-2 = 8 non-overlapping channels (vs. 3 channels for 2.4GHz) 2001, Cisco Systems, Inc. All rights reserved. 8

8 IEEE802.11g Standard for Higher Rate (20+ Mbps) Extensions in the 2.4GHz Band Working on draft for letter ballot Passed the task group committee only in November Provides higher data 2.4 GHz Similar speeds as a Backward compatible with 11 Mbps (802.11b) Same modulation as a OFDM Estimated to complete specification in Spring g MB 11 MB g b 2001, Cisco Systems, Inc. All rights reserved. 10

9 Positioning Both Frequency Bands Will Be Successful! 5GHz a Maximum Wireless LAN performance: 54Mbps Higher expected throughput than g 8 channels Works only in U.S., Japan, and some other selected countries 5 GHz band has less interference 2.4GHz b and g 11Mbps 36Mbps 54Mbps 3 channels Worldwide compatibility Compatibility with installed base of b products Easy upgrade path to highspeed g Wide selection of client devices Lower cost products Lower power products (important for handhelds) 2001, Cisco Systems, Inc. All rights reserved. 11

10 Wi-Fi Certification WECA certifies interoperability between products Provides assurance to customers of migration and integration options Cisco is a founding member of WECA Certified products can be found at New WPA (security features) 2001, Cisco Systems, Inc. All rights reserved. 13

12 FH vs. DS: Zusammenfassung von Stoerungsbehandlung Frequency Hopping Direct Sequence 2.4 GHz GHz Frequenz Time FH springt um Stoerungen herum Verlohrene Packete werden beim next hop neu uebermittelt 2001, Cisco Systems, Inc. All rights reserved GHz GHz Frequenz Channel 1 Channel 2 Channel 3 Daten koennen von redundaten Bits entschluesselt werden Kann auf einen alternativen Kanal geaendert werden um Stoerungen zu vermeiden

14 Channels DS (13) 22-MHz-wide stationary channels x chips per bit, means each bit is sent redundantly 11-Mbps data rate 3 non-overlapping channels (1, 6, and 11, 1/7/13) 3 Access Points can occupy same area 2001, Cisco Systems, Inc. All rights reserved. 18

16 Diversity and Multipath In a multipath environment, signal null points are located throughout the area. Moving the antenna slightly will allow you to move out of a null point and receive the signal correctly. TX Obstacle Dual diversity antennas typically mean if one antenna is in a null, the other one will not be, therefore providing better performance in multipath environments. 2001, Cisco Systems, Inc. All rights reserved. 20

17 Multipath (cont.) Multipath signals can cause high RF signal strength, but poor signal quality levels Bottom line- Low RF signal strength does not mean poor communications Low signal quality DOES mean poor communications 2001, Cisco Systems, Inc. All rights reserved. 21

27 Current security methods Standard Wi-Fi methods for authentication and data encryption SSID : Service Set Identifier WEP : Wired Equivalent Privacy (40bit, 128bit) MAC address filtering Early WLAN applications were primarily in the vertical industries (e.g., bar code scanning) and security was not the major driver. Mobility was. 2001, Cisco Systems, Inc. All rights reserved. 32

28 WEP for encryption WEP : Wired Equivalent Privacy encryption scheme choosen by IEEE based on RC4 algorythm IV base key RC4 64 bits encryption key optional (several vendors propose 128) to be Wi-Fi compliant, 64 bits has to be supported stream cipher i task group is working on improving WEP to fix current flaws 2001, Cisco Systems, Inc. All rights reserved. 33

29 Weaknesses of WEP Stateless Protocol weakness to replay attacks WEP Encrypted Linear Checksum DA SA IV Data ICV packet can be modified and checksum re-calculated Re-use of the same Initialization Vector (IV) Wep key can be stasticaly calculated (15 mn can be enough) Client cards hard to manage (stolen( or lost card) )!! 2001, Cisco Systems, Inc. All rights reserved. 34

30 Limitations of Security Shared, static WEP keys No centralized key management Poor protection from variety of security attacks No effective way to deal with lost or stolen adapter Possessor has access to network Re-keying of all WLAN client devices is required Lack of integrated user administration Need for separate user databases; no use of RADIUS Potential to identify user only by device attribute like MAC address 2001, Cisco Systems, Inc. All rights reserved. 35

31 End of the story? No Security No WEP and Broadcast Mode Basic Security Wi-Fi 40-bit, 128-bit, and Static WEP Enhanced Security i EAP over 802.1x Dynamic Key Management, Mutual Authentication Public Access Telecommuter and Small Business Enterprise class 2001, Cisco Systems, Inc. All rights reserved. 36

32 The VPN? What about VPN? Isn t it simpler? It s also a solution : but that will hit the performances of your WLAN by 20 to 30% it s more expensive and more complicated! Basically VPN over wireless is excellent for public access hot spot, where the infrastructure is open and the environment heterogeneous!! 2001, Cisco Systems, Inc. All rights reserved. 40

33 Enhanced Security x Overview Centralized, scalable, user based authentication Mutual (2way) authentication Various authentication types Dynamic WEP key support WEP key refresh 2001, Cisco Systems, Inc. All rights reserved. 41

34 Advantages of 802.1x for Wireless LAN Security Improved user authentication: username and password Dynamic, session-based encryption keys Centralized user administration RADIUS support (RFC 2138, 2139) for centralized authentication, authorization, and accounting RADIUS/EAP (draft-ietf-radius-ext-07.txt) for forwarding of EAP packets within RADIUS 2001, Cisco Systems, Inc. All rights reserved. 43

35 802.1X Protocol in WLAN Environment 4 Encrypted WEP 5 Other network servers And services Very scalable Supports a variety of authentication types (EAP-TLS, EAP-LEAP, biometrics, etc.) Standards based solution Centralized policy control ~ Very scalable Wireless Client 1 Access Point 3 Strong Authentication 2 Authentication Server 1) User requests access. AP prevents network access. 2) Encrypted credentials sent to authentication server. 3) Authentication server validates user, grants access rights. 4) AP Port enabled and dynamic WEP keys are assigned to client (encrypted). 5) Wireless client can now access general network services securely. 2001, Cisco Systems, Inc. All rights reserved. 44 ~ Transparent Roaming Better multicast capability Standards based solution

36 802.1X for Benefits Is very scalable Supports a variety of authentication types EAP-Cisco Wireless, or LEAP EAP-TLS with Windows XP and other Windows versions Others, as they are developed Is a standards-based solution Enables centralized policy control Session timeout triggers reauthentication and new WEP key 2001, Cisco Systems, Inc. All rights reserved. 45

37 Publicly Secure Packet Forwarding Prevents WLAN inter-client communication Clients cannot ARP for each other Client can communicate out through the AP 2001, Cisco Systems, Inc. All rights reserved. 63

46 Fresnel Zone Fresnel zone- is an elliptical area immediately surrounding the visual path. It varies depending on the length of the signal path and the frequency of the signal. The Fresnel zone can be calculated, and it must be taken into account when designing a wireless link. Fresnel Zone 2001, Cisco Systems, Inc. All rights reserved. 85

48 Antenna Concepts Directionality- Gain Omni (360degree coverage) directional Directional (limited range of coverage) Measured in dbi and dbd. (0dBd = 2.14dBi) More gain means more coverage - in certain directions! Polarization Antennas are used in the vertical polarization 2001, Cisco Systems, Inc. All rights reserved. 87

49 Antenna theory A theoretical antenna (Isotropic) has a perfect 360 degree vertical and horizontal beamwidth. This is a reference for ALL antennas Side View (Vertical Pattern) Top View (Horizontal Pattern) 2001, Cisco Systems, Inc. All rights reserved. 88

50 High Gain Omnidirectionals High gain omnidirectional antennas will create more coverage area in far distances, but the energy level directly below the antenna will become lower, and coverage here may be poor Area of poor coverage directly under the antenna Beamwidth 2001, Cisco Systems, Inc. All rights reserved. 90

51 Directional Antennas For directional antennas the lobes are pushed in a certain direction, causing the energy to move be condensed in a particular area. Very little energy is in the back side of a directional antenna. Side View (Vertical Pattern) Top View (Horizontal Pattern) 2001, Cisco Systems, Inc. All rights reserved. 91

52 Wireless Antennas - Bridges Type Patch Wall Directional Mast Mount Mast Mount Yagi Mast Solid Dish High Gain Omni Omni Directional Directional Gain 8 dbi 5.2 dbi 12 dbi 13.5 dbi 21 dbi Beam Width 60 H 55 V 360 H 75 V 360 H 7 V 30 H 25 V 12.4 H 12.4 V Approximate Range at 2 Mbps 2.0 Miles Miles 6.5 Miles 25 Miles Approximate Range at 11 Mbps Miles 2 Miles 11.5 Miles Cable Length , Cisco Systems, Inc. All rights reserved. 92

54 Hitches/Trailers Performing Site Surveys O Haras World of Golf Outlet Store Stock Room- Metal shelves Offices Large industrial equipment Microwave ovens Office Preparation, customer interviews and a Site Survey is the ONLY way to have a successful installation! 2001, Cisco Systems, Inc. All rights reserved. 94

55 Hitches/Trailers Performing A Survey- From the outside looking in. E O Haras World of Golf Outlet Store Stock Room- Metal shelves F H Offices G D B Office C A 2001, Cisco Systems, Inc. All rights reserved. 96

56 Wireless LANs Competitive Landscape Gartner Vendor Ratings: Magic Quadrant 15 July 2002 Gartner believe Cisco is ahead: From a technology perspective From a sales, marketing, operations and finance perspective We estimate that 9 out of 10 of our conversations with clients deploying WLANs as an enterprise initiative only consider Cisco or strongly consider Cisco 2001, Cisco Systems, Inc. All rights reserved. 97

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