1. 802.11 Networks Olga Agnew Bryant Likes Daewon Seo

2. Agenda  Bryant:802.11 Overview  Bryant:802.11b  Olga:802.11a  Olga:Comparison - 802.11b and 802.11a  Daewon:Security

3. Why wireless?  Mobility  Flexibility  Can be more cost effective

4. 802.3 Ethernet Networks  Ethernet networks make up 95% of LANs  Ethernet  Network Interface Cards (NIC)  Network Cables  Hubs

5. 802.11 Wireless Networks  802.11 builds on Ethernet  802.11  Network Interface Cards (NIC)  Air  Access Points

6. 802.11 Components  Distribution System  Access Points  Wireless Medium  Stations Distribution System Access Point Station Wireless Medium

7. 802.11 Topologies  Independent networks  Infrastructure networks Access Point

8. Wireless Bridging  Can also be setup as a bridge (Yagi directional antenna) Access Point

9. 802.11 Media Access Control  Ethernet uses CSMA/CD  802.11 uses CSMA/CA  Distributed Coordination Function (DCF)  Low overhead  Point Coordination Function (PCF)  Avoids the hidden node problem

10. 802.11 Network Operations  Distribution  Deliver messages to their destination  All messages use this service  Integration  Connects the wireless network to the wired network

11. 802.11 Network Operations  Association  “Plugs” stations into the network  Reassociation  Switching to another AP with better service  Disassociation  Association no longer needed

12. 802.11 Network Operations  Authentication  Prevents unauthorized use  Deauthentication  Terminates authenticated relationship  Privacy  Wired Equivalency Privacy (WEP)  MAC Service Data Unit (MSDU) Delivery  Destination delivery

13. 802.11b

14. 802.11b - Data Transmission  Transmit 300 to 500 feet  Frequency-hopping spread-spectrum (FHSS)  1 or 2 Mbps  Direct-sequence spread-spectrum (DSSS)  1, 2, 5.5, or 11 Mbps

15. 802.11b – Frequencies and Bandwidth  2.4000 to 2.4835 GHz frequency  22 MHz bandwidth per channel  3 MHz guardbands  Analog radio signal (NIC is modem)

16. 802.11b - Transmission  1 and 2 Mbps speeds  Use 11-bit Barker sequence  5.5 and 11 Mbps speeds  Use complementary code keying (CCK)

17. 802.11a

18. 802.11a  Why did ‘a’ come before ‘b’?  Is it different?  Is it better?  Is it faster?

19. 802.11a - Data Transmission  Transmit 100 to 150 feet  Orthogonal Frequency-Division Multiplexing (OFDM)  6 to 54 Mbps

20. 802.11a - Frequencies and Bandwidth  5 - GHz frequency  12 channels  20 MHz bandwidth per channel  Broken into 52 separate channels  48 transmit, 4 used for control

21. 802.11a - Transmission  6 and 9 Mbps speeds  Use 24-bit Barker sequence  Converted to 1 OFDM symbol of 48 bits  12, 24 and 48 Mbps speeds  Use binary phase shift keying (BPSK)

22. Comparison  Physical Layer 802.11b802.11a DSSS  3 - 22 MHz channels  Data Rates: up to 11 Mbps (5.5 is norm) Mbps (5.5 is norm)OFDM  12 – 20 MHz channels  Data rates: up to 54 Mbps (12-24 is norm) Mbps (12-24 is norm)

23. Comparison (cont’d)  Physical Layer 802.11b802.11a DSSS (cont’d)  Frequency Range up to 300 Feet up to 300 Feet OFDM (cont’d)  Frequency Range: up to 150 Feet up to 150 Feet

24. Conclusion  Is faster really better?  What are the application needs?  Better for higher end apps  Video, Voice, transmission of large image or large files, etc.  Shorter distance  Remember…“There’s always a trade-off”

25. Conclusion (Cont’d)  Additional factors to consider:  2.4 GHz frequency shared by:  wireless phones, microwave ovens  Bluetooth devices, others…  Combo-cards now available  Proxim’s

26. 802.11 Security Overview

27. Overview of 802.11 Security  Not long ago  Wireless security was an afterthought (new and rare)  Now  Security issues became more vital (available for anyone and cheap)

28. Same risks as Wired-LANs?  Threat to physical security of a network  Denial of service and sabotage  Unauthorized access and eavesdropping  Attacks form within the network’s user community  Employees have been known to read, distribute, and alter valuable company data

29. 802.11 Security Mechanisms  Authentication through…  Open system  Shared key authentication  Data confidentiality through…  Wired Equivalent Privacy (WEP)

30. Authentication  Open systems  Do not provide authentication  Only identification using the wireless adapter’s MAC address  Access can be based on MAC address  MAC address of wireless client can be spoofed Overall, the open system is not secure.

31. Authentication (Continued)  Shared key authentication

32. Authentication (Continued)  Shared key authentication…  It is delivered to participating station through a secure channel that is independent of IEEE 802.11  The secret of shared key is manually configured for both the wireless AP and client  Securing physical access to the network is difficult  Anyone within range of wireless AP can listen other users’ data  In the overall, this authentication is not secure and is not recommended for use

33. WEP Encryption  802.11-Level of data confidentiality is equivalent to a wired network  Use-RC4 symmetrical stream cipher(40-bit or 104-bit encryption key)

34. WEP Encryption (Cont)  Provide data integrity from random errors (Integrity Check Value)  The determination and distribution of WEP keys are not defined text string must be manually configured  There is no defined mechanism to change the WEP key

35. WEP Encryption (Cont)  All wireless APs and Clients use the same configured WEP key for multiple connection and authentication-it is possible for a malicious users to remotely capture WEP cipher text- problem of security  The lack of WEP key management – cause change in WEP key frequently

36. Security Summary  The lack of automated authentication and key determination cause problems in shared communication  WEP never be totally secure, and 802.11 security will not be secure either  New versions of 802.11 is focus on new encryption, authentication and key exchange algorithm for better security  802.11 security is being investigated for better protection from all attacks

37. Questions?