1 / 14

Proposal for Fast Inter-BBS Transitions

This proposal focuses on QoS aspects of fast inter-BSS transitions, expediting packet delivery for hand-off packets using innovative methods. It is designed for seamless integration with other security-focused proposals.

bbaron
Download Presentation

Proposal for Fast Inter-BBS Transitions

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Proposal for Fast Inter-BBS Transitions Hui Tang CNC Broadband, Inc. Beijing, China Jie Liang, Gang Wu, Xiaoning He Paragon Wireless, Inc. San Jose, CA Contact: liang@parawireless.com Liang et al

  2. Executive Summary • This proposal is focused on QoS aspects of fast inter-BSS transitions • More specifically, 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 (HCCA and EDCA) • 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 (proposed faster handshake, normal 4-way handshake, full 802.1x authentication, etc), and is designed also for seamless integration with other security-focused proposals (it does not affect key hierarchy or packet exchange sequence) Liang 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 other contention based 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. Liang et al

  4. Packet Delivery Latencies AP VoIP Phone Roaming STA High Priority AC Regular Data Users: BE packets, 1000 bytes nominal packets Liang et al

  5. Packet Delivery Latencies • Assumptions: • N: number of active users, CW-BE: contention window size for BE data, FrameSize: norminal BE MPDU size, R: PHY rate, Td: packet delivery delay • CW-VO: contention window size for high priority AC, α: CW-VO/CW-BE ratio of CW-VO and CW-BE • 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: Td ≧ α2·CW-BE/2 · min(1, N/CW-BE) · (DIFS+PreambleTime+FrameSize*8/PhyRate) +CW-VO/2 ·aSlotTime Liang et al

  6. Expedited Delivery Sequence: HCCA based Proc. delay Proc. delay AP Proc. delay AP Proc. delay P+ F P+ X D P B P P ● ● ● AP scheduled G+ A A C E ● ● ● Ack SIFS STA PIFS 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 Liang et al

  7. 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): handoff admission policy • 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 Liang et al

  8. 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 (STA processing delay): • 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) Liang et al

  9. 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 Liang et al

  10. 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) Liang et al

  11. EDCA Controlled Handoff • After the initial setup period (T1), the STA is assigned a Priority to use for subsequent handoff packets (management frames and data frames such as the 802.1x frames and 4-way handshake frames) • The EDCA based signaling also allows the flexibility of protecting existing sessions (such as VoIP) from a flood of handoff management frames • In normal cases when the highest priority Access Category (AC) has excess bandwidth left, the highest priority AC (3) will be assigned • All uplink handoff 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/RADIUS 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) Liang et al

  12. 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 Liang et al

  13. 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 Liang et al

  14. 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 when 802.1x data frames are involved. It also allows better control of the handoff process (priority of the handoff frames vs. current active high-priority sessions) • 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. Liang et al

More Related