Wireless Networks.ppt- overview of Wireless LANS
- 1. Wireless Networks Authors: Marius Popovici Daniel Crişan Zagham Abbas Cluj-Napoca, 24 Nov. 2003 Technical University of Cluj-Napoca Group 3250
- 2. Presentation Outline • Wireless Technology overview • The IEEE 802.11 WLAN Standards • Secure Wireless LANs • Migrating to Wireless LANs (Cutting the cord)
- 3. Wireless? • A wireless LAN or WLAN is a wireless local area network that uses radio waves as its carrier. • The last link with the users is wireless, to give a network connection to all users in a building or campus. • The backbone network usually uses cables
- 4. Common Topologies The wireless LAN connects to a wired LAN • There is a need of an access point that bridges wireless LAN traffic into the wired LAN. • The access point (AP) can also act as a repeater for wireless nodes, effectively doubling the maximum possible distance between nodes.
- 5. Common Topologies Complete Wireless Networks • The physical size of the network is determined by the maximum reliable propagation range of the radio signals. • Referred to as ad hoc networks • Are self-organizing networks without any centralized control • Suited for temporary situations such as meetings and conferences.
- 6. How do wireless LANs work? Wireless LANs operate in almost the same way as wired LANs, using the same networking protocols and supporting the most of the same applications.
- 7. How are WLANs Different? • They use specialized physical and data link protocols • They integrate into existing networks through access points which provide a bridging function • They let you stay connected as you roam from one coverage area to another • They have unique security considerations • They have specific interoperability requirements • They require different hardware • They offer performance that differs from wired LANs.
- 8. Physical and Data Link Layers Physical Layer: • The wireless NIC takes frames of data from the link layer, scrambles the data in a predetermined way, then uses the modified data stream to modulate a radio carrier signal. Data Link Layer: • Uses Carriers-Sense-Multiple-Access with Collision Avoidance (CSMA/CA).
- 9. Integration With Existing Networks • Wireless Access Points (APs) - a small device that bridges wireless traffic to your network. • Most access points bridge wireless LANs into Ethernet networks, but Token-Ring options are available as well.
- 10. Integration With Existing Networks
- 11. Roaming • Users maintain a continuous connection as they roam from one physical area to another • Mobile nodes automatically register with the new access point. • Methods: DHCP, Mobile IP • IEEE 802.11 standard does not address roaming, you may need to purchase equipment from one vendor if your users need to roam from one access point to another.
- 12. Security • In theory, spread spectrum radio signals are inherently difficult to decipher without knowing the exact hopping sequences or direct sequence codes used • The IEEE 802.11 standard specifies optional security called "Wired Equivalent Privacy" whose goal is that a wireless LAN offer privacy equivalent to that offered by a wired LAN. The standard also specifies optional authentication measures.
- 13. Interoperability • Before the IEEE 802.11 interoperability was based on cooperation between vendors. • IEEE 802.11 only standardizes the physical and medium access control layers. • Vendors must still work with each other to ensure their IEEE 802.11 implementations interoperate • Wireless Ethernet Compatibility Alliance (WECA) introduces the Wi-Fi Certification to ensure cross- vendor interoperability of 802.11b solutions
- 14. Hardware • PC Card, either with integral antenna or with external antenna/RF module. • ISA Card with external antenna connected by cable. • Handheld terminals • Access points
- 15. Hardware CISCO Aironet 350 series Wireless Handheld Terminal Semi Parabolic Antenna BreezeCOM AP
- 16. Performance • 802.11a offers speeds with a theoretically maximum rate of 54Mbps in the 5 GHz band • 802.11b offers speeds with a theoretically maximum rate of 11Mbps at in the 2.4 GHz spectrum band • 802.11g is a new standard for data rates of up to a theoretical maximum of 54 Mbps at 2.4 GHz.
- 17. What is 802.11? • A family of wireless LAN (WLAN) specifications developed by a working group at the Institute of Electrical and Electronic Engineers (IEEE) • Defines standard for WLANs using the following four technologies • Frequency Hopping Spread Spectrum (FHSS) • Direct Sequence Spread Spectrum (DSSS) • Infrared (IR) • Orthogonal Frequency Division Multiplexing (OFDM) • Versions: 802.11a, 802.11b, 802.11g, 802.11e, 802.11f, 802.11i
- 18. 802.11 - Transmission • Most wireless LAN products operate in unlicensed radio bands • 2.4 GHz is most popular • Available in most parts of the world • No need for user licensing • Most wireless LANs use spread-spectrum radio • Resistant to interference, secure • Two popular methods • Frequency Hopping (FH) • Direct Sequence (DS)
- 19. Frequency Hopping Vs. Direct Sequence • FH systems use a radio carrier that “hops” from frequency to frequency in a pattern known to both transmitter and receiver • Easy to implement • Resistance to noise • Limited throughput (2-3 Mbps @ 2.4 GHz) • DS systems use a carrier that remains fixed to a specific frequency band. The data signal is spread onto a much larger range of frequencies (at a much lower power level) using a specific encoding scheme. • Much higher throughput than FH (11 Mbps) • Better range • Less resistant to noise (made up for by redundancy – it transmits at least 10 fully redundant copies of the original signal at the same time)
- 20. 802.11a • Employs Orthogonal Frequency Division Multiplexing (OFDM) • Offers higher bandwidth than that of 802.11b, DSSS (Direct Sequence Spread Spectrum) • 802.11a MAC (Media Access Control) is same as 802.11b • Operates in the 5 GHz range
- 21. 802.11a Advantages • Ultra-high spectrum efficiency • 5 GHz band is 300 MHz (vs. 83.5 MHz @ 2.4 GHz) • More data can travel over a smaller amount of bandwidth • High speed • Up to 54 Mbps • Less interference • Fewer products using the frequency • 2.4 GHz band shared by cordless phones, microwave ovens, Bluetooth, and WLANs
- 22. 802.11a Disadvantages • Standards and Interoperability • Standard not accepted worldwide • No interoperability certification available for 802.11a products • Not compatible or interoperable with 802.11b • Legal issues • License-free spectrum in 5 GHz band not available worldwide • Market • Beyond LAN-LAN bridging, there is limited interest for 5 GHz adoption
- 23. 802.11a Disadvantages • Cost • 2.4 GHz will still has >40% cost advantage • Range • At equivalent power, 5 GHz range will be ~50% of 2.4 GHz • Power consumption • Higher data rates and increased signal require more power • OFDM is less power-efficient then DSSS
- 24. 802.11a Applications • Building-to-building connections • Video, audio conferencing/streaming video, and audio • Large file transfers, such as engineering CAD drawings • Faster Web access and browsing • High worker density or high throughput scenarios • Numerous PCs running graphics-intensive applications
- 25. 802.11a Vs. 802.11b 802.11a vs. 802.11b 802.11a 802.11b Raw data rates Up to 54 Mbps (54, 48, 36, 24,18, 12 and 6 Mbps) Up to 11 Mbps (11, 5.5, 2, and 1 Mbps) Range 50 Meters 100 Meters Bandwidth UNII and ISM (5 GHz range) ISM (2.4000— 2.4835 GHz range) Modulation OFDM technology DSSS technology
- 26. 802.11g • 802.11g is a high-speed extension to 802.11b • Compatible with 802.11b • High speed up to 54 Mbps • 2.4 GHz (vs. 802.11a, 5 GHz) • Using ODFM for backward compatibility • Adaptive Rate Shifting
- 27. 802.11g Advantages • Provides higher speeds and higher capacity requirements for applications • Wireless Public Access • Compatible with existing 802.11b standard • Leverages Worldwide spectrum availability in 2.4 GHz • Likely to be less costly than 5 GHz alternatives • Provides easy migration for current users of 802.11b WLANs • Delivers backward support for existing 802.11b products • Provides path to even higher speeds in the future
- 28. 802.11e Introduces Quality of Service • Also know as P802.11 TGe • Purpose: • To enhance the 802.11 Medium Access Control (MAC) to improve and manage Quality of Service (QoS) • Cannot be supported in current chip design • Requires new radio chips • Can do basic QoS in MAC layer
- 29. 802.11f – Inter Access Point Protocol • Also know as P802.11 TGf • Purpose: • To develop a set of requirements for Inter-Access Point Protocol (IAPP), including operational and management aspects
- 30. 802.11b Security Features • Wired Equivalent Privacy (WEP) – A protocol to protect link-level data during wireless transmission between clients and access points. • Services: • Authentication: provides access control to the network by denying access to client stations that fail to authenticate properly. • Confidentiality: intends to prevent information compromise from casual eavesdropping • Integrity: prevents messages from being modified while in transit between the wireless client and the access point.
- 31. Authentication Means: • Based on cryptography • Non-cryptographic • Both are identity-based verification mechanisms (devices request access based on the SSID – Service Set Identifier of the wireless network).
- 33. Privacy • Cryptographic techniques • WEP Uses RC4 symmetric key, stream cipher algorithm to generate a pseudo random data sequence. The stream is XORed with the data to be transmitted • Key sizes: 40bits to 128bits • Unfortunately, recent attacks have shown that the WEP approach for privacy is vulnerable to certain attack regardless of key size
- 34. Data Integrity • Data integrity is ensured by a simple encrypted version of CRC (Cyclic Redundant Check) • Also vulnerable to some attacks
- 35. Security Problems • Security features in Wireless products are frequently not enabled. • Use of static WEP keys (keys are in use for a very long time). WEP does not provide key management. • Cryptographic keys are short. • No user authentication occurs – only devices are authenticated. A stolen device can access the network. • Identity based systems are vulnerable. • Packet integrity is poor.
- 36. Other WLAN Security Mechanisms • 3Com Dynamic Security Link • CISCO LEAP - Lightweight Extensible Authentication Protocol • IEEE 802.1x – Port-Based Network Access Control • RADIUS Authentication Support • EAP-MD5 • EAP-TLS • EAP-TTLS • PEAP - Protected EAP • TKIP - Temporal Key Integrity Protocol • IEEE 802.11i
- 37. WLAN Migration – Cutting The Cord • Essential Questions • Choosing the Right Technology • Data Rates • Access Point Placement and Power • Antenna Selection and Placement • Connecting to the Wired LAN • The Site Survey
- 38. Essential Questions • Why is the organization considering wireless? Allows to clearly define requirements of the WLAN -> development plan • How many users require mobility? • What are the applications that will run over the WLAN? Helps to determine bandwidth requirements, a criteria to choose between available technologies. Wireless is a shared medium, not switched!!!
- 39. Choose the right technology • Usually IEEE 802.11b or 802.11a • 802.11b offers interoperability (WECA Wi-Fi Certification Program) • 802.11a offers higher data rates (up to 54 mbps) -> higher throughput per user. Limited interoperability.
- 40. Data rates • Data rates affect range • 802.11b 1 to 11 Mbps in 4 increments • 802.11a 6 to 54 Mbps in 7 increments • The minimum data rate must be determined at design time • Selecting only the highest data rate will require a greater number of APs to cover a specific area • Compromise between data rates and overall system cost
- 41. Access Point Placement and Power • Typically – mounted at ceiling height. • Between 15 and 25 feet (4.5m to 8m) • The greater the height, the greater the difficulty to get power to the unit. Solution: consider devices that can be powered using CAT5 Ethernet cable (CISCO Aironet 1200 Series). • Access points have internal or external antennas
- 42. Antenna Selection and Placement • Permanently attached. • Remote antennas connected using an antenna cable. • Coax cable used for RF has a high signal loss, should not be mounted more than a 1 or 2 meters away from the device. • Placement: consider building construction, ceiling height, obstacles, and aesthetics. Different materials (cement, steel) have different radio propagation characteristics.
- 43. Connecting to the Wired LAN • Consider user mobility • If users move between subnets, there are challenges to consider. • OSes like Windows XP and 2000, Linux support DHCP to obtain the new IP address for the subnet. Certain applications such as VPN will fail. • Solution: access points in a roaming area are on the same segment.
- 44. The Site Survey • Helps define the coverage areas, data rates, the precise placement of access point. • Gather information: diagramming the coverage area and measuring the signal strength, SNR (signal to noise ratio), RF interference levels
- 45. Site Survey
- 46. Vendor Information • CISCO Systems Wireless http://www.cisco.com/warp/public/44/jump/wireless.sh tml • 3Com Wireless http://www.3com.com/products/en_US/prodlist.jsp? tab=cat&pathtype=purchase&cat=13&selcat=Wireless+P roducts • Breeze Wireless Communications http://www.breezecom.com • Lucent Technologies http://www.wavelan.com • Symbol Technologies http://www.symbol.com
- 47. References • CISCO Packet Magazine, 2nd Quarter 2002 http://www.cisco.com/en/US/about/ac123/ac 114/ac173/ac168/about_cisco_packet_issue_ home.html • 3Com University – Wireless LANs A Technology Overview www.3com.com/3comu • National Institute of Standards and Technology Wireless Network Security http://csrc.nist.gov/publications/drafts/draft- sp800-48.pdf