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Metro-Scale Wi-Fi Networks

Metro-Scale Wi-Fi Networks. Emerging Technologies in Wireless LANs. Introduction. Replacement for traditional Ethernet LANs Several Municipalities Portland, OR Philadelphia, PA San Francisco, CA Thornton, CA Rockville, MA New Orleans, LA Anaheim, CA Built-out Plan of the Network.

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Metro-Scale Wi-Fi Networks

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  1. Metro-Scale Wi-Fi Networks Emerging Technologies in Wireless LANs

  2. Introduction • Replacement for traditional Ethernet LANs • Several Municipalities • Portland, OR • Philadelphia, PA • San Francisco, CA • Thornton, CA • Rockville, MA • New Orleans, LA • Anaheim, CA • Built-out Plan of the Network

  3. Network Use Cases & Performance • Virtual Private Network (VPN) Technology • Network Security Mechanisms • 802.11-based Device Support • QoS Capabilities • Access Levels • Free • Premium • Business • Network Operations Centers(NOC) & Authentication, Authorization and Accounting (AAA)

  4. Multi-Tier Network Design • Access Tier • Client Connection Tier • 802.11 b/g • Ad-hoc Mode • Infrastructure Mode • Handoff Delay • Offering an AP for potential handoff. • Continuously update routing information to the client device’s point of attachment. • VoIP Latency Limit of 50ms

  5. Distribution Tier • Mesh Tier • Path Redundancy • Inefficiencies • Hidden Station Phenomenon • CSMA/CA MAC Protocol at high capacity • Injection Tier • Extends existing wired network at low cost. • Connects Mesh Tier to Backhaul Tier • Backhaul Tier

  6. Network Operations Center (NOC) • Aggregates user traffic and responsible for routing, subscriber-related administration functions. • Access Controller (AC) acts as the layer 3 router. • AAA • Operates on a per-subscriber QoS policies. • Network performance monitoring. • Bottleneck Possibilities • Access Controller • Backhaul PoP

  7. WiFi Tier Design • Design Problems • Coverage, RF propagation, and interference require detailed site surveying. • AP placement dependant on scale and cost. • Must interoperate with existing 802.11 devices. • Authentication • Encryption • 802.11 b/g Compatibility • Handoff and Dynamic IP Addressing • Multi-story buildings require AP cells that extend into the third dimension.

  8. Mesh Tier Design • Operate in Ad-Hoc Mode. • Efficient Path Selection • It maximizes the throughput for the current flow as well as the aggregate throughput of the mesh. • It minimizes the delay and jitter imposed on packets of the current flow as well as other flows in the mesh. • Throughput issues • Hidden Station Phenomenon • Transmission Range < Interference Range

  9. Injection Tier Design • Connects wireless mesh network to a wired backhaul. • Drastically reduces throughput. • 1.544 MBps down to 3 Mbps (T1) • Potentially a bottleneck. • Opportunity for high cost.

  10. Frequency Ranges • 900 MHz • Preferred in areas with high foliage. • Long Ranges and/or no LOS • Low Data Rates • 2.4 GHz • Co-channel Interference • the access tier • third-party 802.11 b/g devices • non-802.11 interferers • 5 GHz • Preferred when no subject to obstructions.

  11. Network-wide Seamless Mobility • 802.11r Standard • Alternative for existing cellular networks • Needed capability of efficient handoffs. • Low signaling overhead, packet loss and latency. • Principle Problems • Custom protocols not on standard 802.11 devices. • Non-standard software needed. • RFC 2002 standards designed with low mobility in mind. • Inefficient bandwidth usage.

  12. Metro-Scale Wi-Fi Networks • Conclusion

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