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Wireless LANs: Different, Slower, Kinda Cheaper

Wireless LANs: Different, Slower, Kinda Cheaper. Jim Gogan Director, ITS - Networking jim_gogan@unc.edu. What They Are Not. Not wireless MANs (but…) Not wide-area data transmissions over cellular or packet radio Overlap with point-to-point LAN-LAN bridging

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Wireless LANs: Different, Slower, Kinda Cheaper

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  1. Wireless LANs:Different, Slower, Kinda Cheaper Jim Gogan Director, ITS - Networking jim_gogan@unc.edu

  2. What They Are Not • Not wireless MANs (but…) • Not wide-area data transmissions over cellular or packet radio • Overlap with point-to-point LAN-LAN bridging • Overlap with PANs (the few feet surrounding a user’s workspace) • NOT a substitute for wired LANs!!!

  3. How They Are Connected • Configured with transmitter/receiver (“access point”) that is usually connected to the “wired” network • Accessed by end users with wireless LAN adapters (usually built-in to newer laptops or PCMCIA cards for older notebook computers)

  4. 802.11 Evolution • Sept. 1999 - 802.11b (“Wi-Fi”) extension standardized by IEEE; provides for 11 Mb/sec using DSSS technology in 2.4 GHz band • IEEE also ratified 802.11a: uses 5 GHz band to support data rates from 6 Mb/sec to 54 Mb/sec; shares the same wireless LAN MAC protocol as Wi-Fi, but equipment not compatible. • Other standards enhancements completed or underway (more later)

  5. Issues: Coverage • Distance: • function of product design and propogation path (radius: less than 100 ft - more than 300 ft) • Throughput: • 802.11b: 1, 2, 5.5, 11 Mb/sec (highest throughput we’ve seen 4-6 Mb/sec) • SHARED bandwidth! • Scalability: • number of clients on each access point depends on number and nature of transmissions (between 15-50 clients)

  6. Roaming • microcells: similar to cellular telephone system; users get “handed off” thru wired net as they roam • limited part of 802.11 standard

  7. Issues: Interoperability • 802.11 goal is to allow interoperability at Physical layer • Roaming still an issue • Interference from/coexistence with other WLANs (implications of Bluetooth)

  8. Issues: Other • Security: • many security options/provisions included by vendors • 802.11 provides for optional encryption feature (WEP: Wired Equivalent Privacy - encrypts data portion of packet) • Cost: • varies - wildly

  9. Issues: Other (cont.) • Battery life on notebooks: • at present, can reduce 3 hour battery life to 2 hours • special techniques from different vendors to maximize battery life • Issues with “stand-by”/hibernate power saving • Safety: • less output power than cell phone

  10. Organizations • WLANA - Wireless LAN Alliance • www.wlana.com • includes all previous vendors plus a few others • WECA - Wireless Ethernet Compatibility Alliance • www.wirelessethernet.org

  11. Newer/Developing Standards • majority of stuff to-date: 802.11b • 802.11a – different frequency (5GHz band); 54 Mb/sec (27 Mb/sec?) • 802.11g – 2.4GHz range/compatible with 802.11b; 54 Mb/sec (27 Mb/sec? 8 Mb/sec?) • 802.11e – traffic prioritization and bandwidth provisioning (coming) • 802.11i – security (ties in with WPA – Wi-Fi Protected Access) • 802.11r – non-proprietary roaming (2006) • 802.11n – 100 Mb/sec (MIMO)

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