Transcript Metro-Scale Wi

Emerging Technologies in Wireless LANs
 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
Virtual Private Network (VPN) Technology
Network Security Mechanisms
802.11-based Device Support
QoS Capabilities
Access Levels
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Free
Premium
Business
Network Operations Centers(NOC) &
Authentication, Authorization and Accounting
(AAA)
 Access Tier
 Client Connection Tier
 802.11 b/g
 Ad-hoc Mode
 Infrastructure Mode
 Handoff Delay
1. Offering an AP for potential handoff.
2. Continuously update routing information to the client
device’s point of attachment.
 VoIP Latency Limit of 50ms
 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
 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
 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.
 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.
2. It minimizes the delay and jitter imposed on packets of
the current flow as well as other flows in the mesh.
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Throughput issues
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Hidden Station Phenomenon
Transmission Range < Interference Range
 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.
 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.
 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.
 Conclusion