Proposal for Fast Inter-BBS Transitions

1. Proposal for Fast Inter-BBS Transitions Hui Tang CNC Broadband, Inc. Beijing, China Xiaoning He Paragon Wireless, Inc. Sunnyvale, CA He et al

2. Executive Summary • This proposal is focused on QoS aspects of fast inter-BSS transitions. • This proposal deals not only with signaling protocol but also innovative methods for speeding up packet delivery of the handoff signaling protocols using TGe mechanisms • This proposal expedites packet delivery sequence for hand-off packets from security context transfer, to QoS traffic stream setup • HCCA based methods for bounded maxim delay • EDCA based methods for expedited hand-off related packet delivery • This proposal is beneficial for various handoff scenarios (normal 4-way handshake, proposed faster handshake, full 802.1x authentication, etc), and is designed also for seamless integration with other security-focused proposals. He et al

3. Expedited Handoff Packet Delivery - Motivation • Packet delivery latency in a BSS depends heavily on the network load (number of users, traffic pattern, etc.). • Handoff packets must contend for the medium just like best-effort packets. • Due to the variability of the packet delivery delay, even with the proposed shortened handoff signaling protocol sequence, it is very difficult to have a bounded delay for fast BSS handoff. To reach the goal of less than 50ms handoff latency, a method for expediting the delivery of fast BSS handoff protocol packets must be provided by TGr. He et al

4. Packet Delivery Latencies • Assumptions: • N: number of active users, CW: contention window, FrameSize: norminal MPDU size, R: PHY rate, Td: packet delivery delay • Factors considered: • Only considered packet deferment. No collision. No higher priority packets (EDCA) from other STAs. We can derive a lower bound on the average packet delivery latency Td: He et al

5. Expedited Delivery Sequence: HCCA based P+ H+ A PIFS PIFS P+ D P+ F P+ X B P P ● ● ● AP Ack scheduled G+ A A C E ● ● ● Ack SIFS CAP STA PIFS T3 T1 T2 Management or 802.1x data packets QoS Data+CF-Poll P+ X Ack frames G+ X P+ X+ A P QoS Data+CF-Ack + CF-Poll QoS CF-Poll QoS data+CF-Ack T1: fast delivery setup period T2: HCCA controlled handoff period T3: 802.1x port open, payload delivery with TSPEC setup CAP: polled access period Payload packets He et al

6. Fast Handoff Delivery Setup Procedure • Fast handoff delivery is requested by STA through first handoff packet (e.g. open authentication request) • The request is through the inclusion of a Fast Handoff Packet Delivery (FHPD) Request information element • Fast handoff delivery request is granted or denied by AP in the next packet in the handoff sequence (e.g. open authentication response) • The AP indicates to the requesting STA, through the inclusion of Fast Handoff Packet Delivery (FHPD) Status information element, the mode and parameters to be use for the subsequent handoff packets. • Modes supported: HCCA, EDCA • Parameters: • TSID (Traffic Stream ID) to be used for HCCA delivery • UP (user priority) to be used for EDCA delivery He et al

7. Fast Handoff Packet Delivery (FHPD) Request Information Element Length FHPD Control Minimum Response Time Element ID EDCA (1 bit) Preference (2 bits) Reserved (4 bits) HCCA (1 bit) 1 2 1 1 Octects Sent by STA • FHPD control: • - HCCA: HCCA mode is supported for FHPD • - EDCA: EDCA mode is supported for FHPD • - Preference: 10 – HCCA mode is preferred • 01- EDCA mode is preferred • 00 – best effort is preferred • 11 – No preference • Minimum Response Time: • The time that will take the Station to process an incoming handoff frame • T= this field * 32us • The AP can use this information to schedule the separation between a downlink (AP-STA) packet and a uplink CAP (polled access time) He et al

8. Fast Handoff Packet Delivery (FHPD) Status Information Element Length FHPD Control FHPD Parameter Element ID EDCA (1 bit) Mode (2 bits) TID (4 bit) HCCA (1 bit) Reserved (4 bits) Reserved (4 bits) 1 1 1 1 Octects Sent by AP • FHPD control: QoS mode to be used for packet delivery • FHPD Parameter: • TID: • HCCA: TSID to be used in HCCA polling • EDCA: User Priority to be used by the STA for handoff packets He et al

9. HCCA Controlled Handoff • After the initial setup period (T1), the rest of the handoff signaling protocol can be delivered using HCCA mechanism for bounded delay • In HCCA controlled handoff, all downlink packets can be delivered through pre-emption by AP using PIFS after an on-air transmission • All uplink packets can be delivered through polling by AP • AP can schedule handoff exchange sequence around existing admitted TSPEC schedules, as well as considering minimum separation between consecutive handoff signaling frames. • Handoff time can be bounded and is not related to network load • The proposed methods can be applied to various handoff scenarios: • Cached PMK with accelerated handshake • Cached PMK with normal 4-way handshake • Full EAP/RADIUM authentication, 4-way handshake, TSPEC setup • This proposal also applies to the other proposals before TGr (e.g. 802.11-04-1117/r0 , 802.11-04-1127/r0) He et al

10. EDCA Controlled Handoff • After the initial setup period (T1), the STA is assigned a Priority to use for subsequent handoff packets • In normal cases when the highest priority Access Category (AC) has excess bandwidth left, the highest priority AC (3) will be assigned • All uplink packets can be delivered using this high priority queue • AP can still deliver downlink packets using AP preemption if it chooses to do so. • Unlike HCCA controlled handoff where delay can be bounded, EDCA based method will statistically achieve much faster handoff, but no delay bound can be guaranteed. • The EDCA method also can be applied to various handoff scenarios: • Cached PMK with accelerated handshake • Cached PMK with normal 4-way handshake • Full EAP/RADIUM authentication, 4-way handshake, TSPEC setup • The EDCA method also applies to the other proposals before TGr (e.g. 802.11-04/1117r0 , 802.11-04/1127r0) He et al

11. Performance: 802.11i 4-way handshake • Assumptions: 11mbps/1mbps PHY rate, HCCA controlled handoff, real-time response from STA and AP • All packet exchanges are done in one HCCA controlled burst sequence • The results do not change with network load He et al

12. FHPD Capability Announcement • AP indicates its support for Fast Handoff Packet Delivery (FHPD) by including a FHPD Status Information Element in its Beacon Length FHPD Control FHPD Parameter Element ID EDCA (1 bit) Preference (2 bits) Reserved (4 bit) HCCA (1 bit) Reserved (4 bits) Reserved (4 bits) 1 1 1 1 Octects • AP indicates its support for Fast Handoff Packet Delivery (FHPD) by including a FHPD Information Element in its Beacon • HCCA and EDCA bits in FHPD control indicate the modes supported by the AP • Preference bits in FHPD indicate the preferred mechanism in this BSS He et al

13. Conclusions • This proposal addresses a critical missing piece in Fast Inter-BSS handoff: speedy delivery of the handoff packets • Using HCCA mode, a deterministic handoff delay bound can be guaranteed • Using EDCA mode, significant improvement can be obtained in handoff delay • This proposal achieves its benefits for various scenarios that will be encountered in real-world handoff applications: • Cached PMK exists • Full 802.1x authentication is needed • This proposal can be combined naturally with other proposals which try to reduce the number of packets in a handoff process to achieve better results. He et al