Radio Measurement Actions

1. Radio Measurement Actions Daryl Kaiser (Cisco Systems) 12 November 2002 Daryl Kaiser, Cisco Systems

2. Where do radio measurement actions fit intothe proposed RRM framework? • First, Define and Add Passively Observable Parameters to 802.11 MIB • Standard Impact Minimal • While the above is being balloted • Transfer of Parameters between STA to AP • Actively Measured Parameters: extend TGh? • May Need some architectural thinking • While the above is being balloted • Work on Control Issues: Maybe a next TG • Definitely Need some architectural thinking Daryl Kaiser, Cisco Systems

3. Defining the focus of this presentation • What it addresses: Measurements that require specific action • Measurements that are not part of normal processing, or • Measurements that make sense to perform in “snapshots” • Suggests measurement contents for further discussion • Not addressed: Status and statistics requiring no specific action • E.g., authentication/association status, link counter statistics • Can populate MIB objects for these without measurement action Daryl Kaiser, Cisco Systems

4. Specific RRM goals that require radio measurement action • Detect possible rogue APs to help the WLAN administrator plug security holes • Quantify WLAN radio topology to facilitate automatic frequency selection and AP/client power limits • Measure BSS overlap to help balance coverage, capacity and QoS (current topic in TGe) • Quantify each station’s local performance for better network visualization and to facilitate roaming and load balancing • Detect non-802.11 interference and quantify noise to facilitate adjustments in WLAN configuration Daryl Kaiser, Cisco Systems

5. Define a request/report mechanism • Requests • Set through measurement action table in MIB • Include any required measurement parameters • May pertain to AP radio and/or client radios • Measurements • Serving channel is measured without disrupting traffic • Off-channel measurements temporarily disrupt traffic • Station’s traffic is buffered if it measures off-channel • Station may decline if measurement poses undue burden • Reports • Reports communicated through new MIB tables Daryl Kaiser, Cisco Systems

6. Action #1 =Beacon Report (and probe responses, too) • Purpose: • Detects possible rogue APs • Quantifies WLAN radio topology • Measures BSS overlap • How it works: • Each request specifies channels or asks for current beacon table • Measure at AP radio and/or client radios • Measure on serving channel or off-channel • For each detected beacon and probe response, • Always report channel, BSSID, RSSI and time of detection • Optionally report other fixed fields and information elements Daryl Kaiser, Cisco Systems

7. Diagram of Beacon Request/Report External Network Manager One request Periodic requests Access Point Client Station Periodic poll/trap One report per request MIB MIB Request via MIB • Scan interval and channels • Active and/or passive scan • AP and/or client stations Schedule radio measurements • AP follows scan parameters • Trigger measurements on schedule • Measure locally and request of clients Send one report per request • Passive co-channel scan • Active off-channel scan • Accumulated beacon table Write beacon reports to MIB • Detected BSSID, SSID, channel • Other detected beacon parameters • TSFTIMER offset versus serving AP • Detected signal strength per STA Retrieve reports • Poll or trap (TBD) Local measurement access • Client saves in MIB • Available via MLME-SAP • Need SME vendor support Issues • How should this work in IBSS? • When is STA allowed to decline? • How to enforce minimal disruption? Daryl Kaiser, Cisco Systems

8. Action #2 =Extended CCA Report • Purpose: • Quantifies each station’s current local performance • How it works: • Measure at AP radio and/or client radios • Measure on serving channel only • Measured parameters • CCA busy fraction indicates degree of local contention at STA • Histogram of recent backoff translates to radio-related jitter at STA Daryl Kaiser, Cisco Systems

9. Action #3 = Non-802.11 RPI Histogram Report • Purpose: • Detects non-802.11 interference and quantifies noise • How it works: • Measure at AP radio and/or client radios • Measure on serving channel only • Measured parameters • Received power indicator (RPI) is a quantized measure of received power • TGh defines eight RPI levels with 5-dB ranges for inner levels • RPI Histogram measures occurrences of each RPI level • RPI Histogram in TGh does not distinguish non-802.11 energy Daryl Kaiser, Cisco Systems

10. What could external management entity do if AP detects acceptable CCA, but station detects unacceptably high CCA ? • With just CCA information…not much could be done • Need to know which stations are causing the contention • Define one more radio measurement action for this case: Action #4 = Frame Report Daryl Kaiser, Cisco Systems

11. Action #4 =Frame Report • Purpose: • Identifies a station’s local contending stations • How it works: • Measure at AP radio or client radios, but typically client • Measure on serving channel only • Report one sub-element for each detected contending station • Transmitter MAC address • BSSID to which contending STA belongs • Number of frames decoded from STA • Average signal strength of frames from STA Daryl Kaiser, Cisco Systems

12. Store the reported measurement table in MIB under SMT Measurements taken by other STAs and reported back dot11reportedStatsTable Measurements taken at STA itself Daryl Kaiser, Cisco Systems

13. Summary of proposed radio measurement actions • Beacon report detects possible rogue APs, quantifies WLAN radio topology and measures BSS overlap • Extended CCA report quantifies each station’s current local performance in terms of CCA busy fraction and backoff experience • Non-802.11 RPI histogram report detects non-802.11 interference and quantifies noise • Frame report identifies a station’s local contending stations Daryl Kaiser, Cisco Systems