• Roaming occurs when a wireless client moves between access points (APs) while maintaining network connectivity
• Client device (not the network infrastructure) makes the roaming decision based on signal strength, noise levels, and vendor-specific algorithms
• Seamless roaming requires same SSID, security settings, and VLAN configuration across all APs

Common Roaming Problems

• Sticky client syndrome - Client holds onto weak AP signal too long instead of switching to stronger nearby AP
• Authentication delays - Client must re-authenticate with new AP, causing temporary disconnection (especially with WPA2-Enterprise)
• VLAN/subnet changes - Client receives new IP address when roaming between different subnets, breaking existing sessions
• Co-channel interference - Multiple APs on same channel create interference, degrading performance during handoff

Roaming Triggers and Thresholds

• Most clients begin scanning for new APs when RSSI (Received Signal Strength Indicator) drops below -70 dBm
• Hysteresis prevents ping-ponging between APs by requiring new AP signal to be significantly stronger (typically 5-12 dB better)
• Roaming decisions also consider factors like retry rates, data rate capabilities, and load balancing

Solutions and Best Practices

• Wireless LAN Controller (WLC) deployment enables centralized management and faster roaming through tunneling protocols
• 802.11r Fast Transition (FT) pre-authenticates clients with neighboring APs to reduce handoff time
• 802.11k Radio Resource Management helps clients discover nearby APs more efficiently
• 802.11v BSS Transition Management allows network to suggest better AP to client
• Proper cell sizing with 15-25% overlap between coverage areas and -67 dBm minimum signal strength

Configuration Considerations

• Use same channel plan across floors/buildings to avoid interference
• Configure band steering to push dual-band clients to less congested 5GHz band
• Implement load balancing to distribute clients evenly across APs
• Set appropriate power levels - too high causes sticky clients, too low creates coverage gaps
• Enable client isolation only when necessary as it can interfere with some roaming mechanisms

Vocabulary

RSSI (Received Signal Strength Indicator) - Measurement of wireless signal power received by client device, typically expressed in negative dBm values

BSS (Basic Service Set) - Single access point and all associated wireless clients

ESS (Extended Service Set) - Multiple BSSs connected through distribution system, appearing as single network to clients

Fast Transition (FT) - 802.11r standard that reduces roaming time by pre-establishing security keys with neighboring APs

Sticky Client - Wireless device that remains associated with distant/weak AP instead of connecting to closer/stronger AP

Notes

• Roaming issues are often client-dependent - different devices from various manufacturers exhibit different roaming behaviors
• Enterprise wireless surveys should test roaming with actual client devices, not just AP coverage maps
• Voice and video applications require roaming handoff times under 150ms to avoid noticeable interruption
• Consider minimum data rates configuration to encourage clients to roam before connection becomes unusable (disable 1, 2, 5.5 Mbps rates)
• Troubleshoot roaming issues using wireless packet captures and client connection logs rather than just signal strength measurements
• Controller-based solutions generally provide better roaming experience than autonomous AP deployments for enterprise environments