802.11 STA-driven / AP-assisted handover

1. 802.11 STA-driven / AP-assisted handover Marian Rudolf, Juan-Carlos Zuniga InterDigital Marian.Rudolf@InterDigital.com JuanCarlos.Zuniga@InterDigital.com Marian Rudolf, Juan-Carlos Zuniga, InterDigital

2. Key events in roaming • Discovery phase • STAs builds database about neighboring APs from • Scanning • Information from Candidate lists obtained from serving AP • Handover is triggered • To maintain connectivity and desired QOS in mobile environment • For load balancing & congestion control • Performing the handover • Authentication/pre-authentication with new AP • Security key management with new AP • QOS negociations with new AP • Reassociation • Redirecting buffered traffic from old to new AP Marian Rudolf, Juan-Carlos Zuniga, InterDigital

3. Triggering handover • Maintain connectivity and QOS with mobility • STA would appear to be the natural choice as it directly perceives the RF environment • AP could also do it assuming enough close-to-real-time measurement reporting from the STAs • For load balancing & congestion control • AP would appear to be the natural choice has it is more susceptible of having an holistic view of the whole system. • AP-driven load balancing handover are outside the scope of 802.11r STA seems to be the preferred choice for triggering the handover in 802.11r Marian Rudolf, Juan-Carlos Zuniga, InterDigital

4. Performing handover • AP has a privileged link (wired) to communicate with other APs and could perform: • Authentication/pre-authentication with new AP • Security key management with new AP • QOS negociations with new AP • Reassociation • Redirecting buffered traffic from old to new AP • STA can do some of these things but it faces many roadblocks: • Has to change channels when communicating with candidate AP; cannot be expected to listen to both serving and candidate channels simultaneously • A STA in handover situation runs the risk of having precarious link with either the old and/or the new AP (cell border or corner effect). • It can only be associated with one AP at a time AP is the natural choice for performing handover Marian Rudolf, Juan-Carlos Zuniga, InterDigital

5. STA-driven / AP-assisted handover • STA has the capability of triggering the handover. It is the one driving the handover • AP is responsible for much of the mechanics during the handover (signalling, negotiations, etc.). It is assisting the STA in the execution of the handover Marian Rudolf, Juan-Carlos Zuniga, InterDigital

6. What does the AP need to assist in executing handover? • The serving AP is already aware of numerous parameters related to the STA and its on-going connection. • STA multiple Ids and addresses • Requirements in terms of supported services, capabilities, security, QOS, etc. • Additional handover information have to be supplied to the AP • An example of such information is anything related to the RF conditions perceived by the STA for the different neighboring APs such as SNR, received power, etc. • This info can be complemented by any information that is felt to be non-portable from the serving AP to the candidate AP. • We will refer to this information set as handover information set • STA should then send the AP its handover information set where the candidate APs would be sorted using any metric chosen by STA • This handover information set should be sent: • Periodically: This allows (not forces) serving AP to make preparatory handover arrangements (e.g. pre-authentification). • At the time an handover is requested by the STA, I.e. as part of the handover request. Marian Rudolf, Juan-Carlos Zuniga, InterDigital

7. How can the STA trigger the handover? • By sending an handover request to the serving AP • Reasons for sending this handover request are outside scope of 802.11r • The handover information set from the STA could also be appended to the handover request to allow for most-up-to-date handover preferences and information Marian Rudolf, Juan-Carlos Zuniga, InterDigital

8. Summary • STA is the best suited for deciding and triggering handover • AP is the best suited for executing much of the handover mechanics • To reconcile the two, the STA has to be able to: • Tell the AP to initiate the handover (handover request) • Provide the AP with key and information such as the preferred candidates from its point of view (handover information set) • This proposal allows for robust and fast handovers by: • Providing the APs with periodic and event-driven info allowing it to make arrangements that facilitate eventual handovers (e.g. pre-authentification) • Having the bulk of the handover exchanges over the wired distribution system rather than over the somewhat precarious wireless medium characterizing handover situations. Marian Rudolf, Juan-Carlos Zuniga, InterDigital