// reference · bss transition timing
BSS Transition Timing
The full 802.11k/v/r roaming sequence - from Neighbor Report Request to first encrypted data frame on the new AP. Each phase has a WARN and FAIL SLA threshold. Source: wlanpi-profiler FT_CAPABILITIES_IE_TAG + RM_CAPABILITIES_IE_TAG, IEEE 802.11-2020.
— Shankar K. · Source: IEEE 802.11r §12.11, §11.4.4 (802.11k), §11.22 (802.11v), wlanpi-profiler IE timing gates
// roaming sequence swimlane - click any phase to expand
// sla thresholds per phase
| Phase | Amendment | WARN | FAIL | Standard |
|---|---|---|---|---|
| Neighbor Report Req → Resp | 802.11k | >200ms | >500ms | IEEE 802.11-2020 §11.4.4 |
| BTM Request → Response (client accept) | 802.11v | >1000ms | >3000ms | IEEE 802.11-2020 §11.22 |
| FT Auth Request → Response | 802.11r | >50ms | >100ms | IEEE 802.11-2020 §12.11 |
| FT Reassoc Request → Response | 802.11r | >50ms | >100ms | IEEE 802.11-2020 §12.11 |
| Full FT roam (Auth + Reassoc) | 802.11r | >80ms | >150ms | IEEE 802.11-2020 §12.11 |
| Full reassoc without FT | 802.11 base | >100ms | >300ms | IEEE 802.11-2020 §11.3.5 |
| 4-Way Handshake after reassoc | 802.11i | >500ms | >2000ms | IEEE 802.11i §8.5.3 |
| DHCP after roam (L3 roam only) | RFC 2131 | >500ms | >2000ms | RFC 2131 §3.1 |
| Full VoIP-grade roam (FT, no DHCP) | 802.11kvr | — | >150ms | Industry SLA - VoIP requires <150ms |
// field note
The 150ms VoIP ceiling
G.711 voice tolerates up to 150ms one-way delay before noticeable degradation. The 802.11 roam time is just one component - add AP processing time, RADIUS latency (if no FT), and DHCP (if L3 roam). A 150ms ceiling leaves very little room for a slow RADIUS server. FT eliminates RADIUS on roam entirely.
// field note
Sticky client vs BTM rejection
A BTM Reject (client refuses AP's steering request) shows as action code 7 in Wireshark with status=1. Some enterprise systems deauth the client after N rejections. Others log and wait. The roam that eventually happens (usually triggered by signal drop) is slow and poorly timed. Confirm client 802.11v capability via wlan_mgt.rsn.capabilities before blaming the AP.
// field note
FT over-air vs over-DS
FT over-the-air (OTA): FT Auth frames fly directly between client and target AP. FT over-the-DS (OtDS): the current AP proxies FT Auth to the target AP via the distribution system before the client disassociates. OtDS is marginally faster because PMK-R1 distribution completes before the client moves -- but not all APs support it.
Measure roam timing in your own PCAP
WiFi Analyser calculates each roaming phase timing and flags WARN/FAIL against these SLA thresholds automatically.