1. doc.: IEEE 802.11-04/0719r0 Submission July 2004 Marian Rudolf, Juan-Carlos Zuniga, InterDigitalSlide 1 802.11 STA-driven / AP-assisted handover Marian Rudolf, Juan-Carlos Zuniga InterDigital Marian.Rudolf@InterDigital.com JuanCarlos.Zuniga@InterDigital.com

2. doc.: IEEE 802.11-04/0719r0 Submission July 2004 Marian Rudolf, Juan-Carlos Zuniga, InterDigitalSlide 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

3. doc.: IEEE 802.11-04/0719r0 Submission July 2004 Marian Rudolf, Juan-Carlos Zuniga, InterDigitalSlide 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

4. doc.: IEEE 802.11-04/0719r0 Submission July 2004 Marian Rudolf, Juan-Carlos Zuniga, InterDigitalSlide 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

5. doc.: IEEE 802.11-04/0719r0 Submission July 2004 Marian Rudolf, Juan-Carlos Zuniga, InterDigitalSlide 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

6. doc.: IEEE 802.11-04/0719r0 Submission July 2004 Marian Rudolf, Juan-Carlos Zuniga, InterDigitalSlide 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.

7. doc.: IEEE 802.11-04/0719r0 Submission July 2004 Marian Rudolf, Juan-Carlos Zuniga, InterDigitalSlide 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

8. doc.: IEEE 802.11-04/0719r0 Submission July 2004 Marian Rudolf, Juan-Carlos Zuniga, InterDigitalSlide 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.