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Submission
doc.: IEEE 11-13/0995r1Sep 2013
Broadcom / IntelSlide 1
802.1AS Synchronization Servicesfor 802.11ak Links
Date: 2013-09-09
Name Affiliations Address Phone email Philippe Klein Broadcom Golan Building
Airport City, Israel +972 54 3134500 [email protected]
David Goodall Broadcom 24 Campbell Street Haymarket, Sydney, NSW, 2000
+61-2-8030-7452 [email protected]
Kevin Stanton Intel 2111 NE 25th Ave Hillsboro OR 97124
+1 (503)712-1888 [email protected]
Authors:
Submission
doc.: IEEE 11-13/0995r1
Broadcom / Intel
Abstract
This presentation describes 802.1AS synchronization services for 802.11ak links
Slide 2
Sep 2013
Submission
doc.: IEEE 11-13/0995r1
Broadcom / Intel
802.1AS for 802.11 Links (1)
• Specified in IEEE Std 802.1AS-2011 Clause 12
• Path Delay measurement + time propagation- Peer delay mechanism
- Use the Timing measurement procedure defined in IEEE 802.11v specified in IEEE 802.11-2012 Section 10.23.5- MLME-TIMINGMSMT Primitives
- Messages are the “timing measurement action frame” and its corresponding “ACK”
- Vendor Specific (OUI of 802.1) information element contains various time-synchronization parameters, including an entire Follow_Up message
Slide 3
Sep 2013
Submission
doc.: IEEE 11-13/0995r1
Broadcom / Intel
802.1AS for 802.11 Links (2)
• Messages - All media-dependent frames are generated and consumed by the lower-
layer 802.11 MLME
- Messages are timestamped by the MAC/PHY
• Determination of “asCapable”- Per-port global variable
- Set to FALSE if the timing measurement bit in the ExtendedCapabilities information element indicates that the peer IEEE 802.11 station is incapable of participating in the timing measurement protocol
- Otherwise, may be set to TRUE
Slide 4
Sep 2013
Submission
doc.: IEEE 11-13/0995r1
Broadcom / Intel
Timing Measurement Procedure for 802.11 Links
Slide 5
Sep 2013
Submission
doc.: IEEE 11-13/0995r1
Broadcom / Intel
Propagation of Sync and Follow_Up Messages on 802.11ak Links (1)
Slide 6
Sep 2013
802.11ak Requester STA
802.11ak Responder STA
Sync (i)Follow_Up (i)
Time Aware System
Port
Sync Interval
Time Measurement Action Frame
Sync (i+1)Follow_Up (i+1)
[Follow_Up (i)]
Time Measurement Action Frame[Follow_Up (i-1)]ACK
ACK
Sync (i)
Follow_Up (i)
Time Aware System
Port
Follow_Up (i-1)
Sync (i+1)
Delayed FollowUp
• Timing measurement procedure for 802.11 links introduces a one Sync_interval delay per 802.11ak link to the propagation of the Sync message
Submission
doc.: IEEE 11-13/0995r1
Broadcom / Intel
Sync Msg Propagation for .11ak LinksOption #1
Slide 7
Sep 2013
• Same procedure as for .11 links
• Pros:- No change to 802.1AS
• Cons:- Sync msg propagation is delayed by one Sync_interval per .11ak link (the
default Sync_interval for 802.11 link is 1/8 sec)
- This delay is accumulative per 802.11ak hop
- The “maximum_time_accumulation” that could be sustained by the sync msg propagation is a function of the clock frequency stability (values will be provided by the 802.1AS experts)
- Max nbr of 11ak hops = fct (maximum_time_accumulation, Sync_interval)
Submission
doc.: IEEE 11-13/0995r1
Broadcom / Intel
Sync Msg Propagation for .11ak LinksOption #2
Slide 8
Sep 2013
• For .11 links, two consecutive Time Measurement Action Frames are generated for the Sync and Follow_Up messages
• Pros:- Eliminates the one Sync_interval delay
• Cons:- Makes the protocol more “chatty” (but fewer packets than on Ethernet)
- Requires a Modification of the MD State Machine (and the 802.1AS Specs for .11ak links)
Submission
doc.: IEEE 11-13/0995r1
Broadcom / Intel
Fine Timing Measurement 802.11mc (1)
• New MLME primitive MLME-FINETIMINGMSMTRQ to provide improved timing measurement accuracy included in IEEE P802.11-REVmc/D1.5, June 2013
Slide 9
Sep 2013
Submission
doc.: IEEE 11-13/0995r1
Broadcom / Intel
Fine Timing Measurement 802.11mc (2)
• Almost the same syntax as MLME-TIMINGMSMTRQ - timestamp precision of 0.1ns
• Issue: An STA supporting MLME-FINETIMINGMSMTRQ does not support MLME-TIMINGMSMTRQ- as currently defined in IEEE Std 802.1AS this STA will not be “asCapable” (cf
slide 4 - the timing measurement bit in the ExtendedCapabilities information will be different…)
• Solution: Support for Fine Timing Measurement could be added to P802.1ASbt - as IEEE Std 802.1AS describes the .11v’s MLME-TIMINGMSMTRQ primitive
only- **if** the 802.11mc timeframe could match the P802.1ASbt timeframe
Slide 10
Sep 2013
Submission
doc.: IEEE 11-13/0995r1
Broadcom / Intel
Fine Timing Measurement 802.11mc (2)
• Almost the same syntax as MLME-TIMINGMSMTRQ - timestamp precision of 0.1ns
• Issue: An STA supporting MLME-FINETIMINGMSMTRQ does not support MLME-TIMINGMSMTRQ- this STA will not be “asCapable” as currently defined in IEEE Std 802.1AS (cf
slide 4 - the fine timing measurement bit in the ExtendedCapabilities will be a different bit …)
• Solution: Support for Fine Timing Measurement could be added to P802.1ASbt - as IEEE Std 802.1AS describes the .11v’s MLME-TIMINGMSMTRQ primitive
only- **if** 802.11mc is completed in a timeframe compatible with the P802.1ASbt
timeframe
Slide 11
Sep 2013
Submission
doc.: IEEE 11-13/0995r1
Broadcom / Intel
Timestamping of 802.1AS Sync Messages over 802.1Qbz Bridge and 802.11ak Link
• Disclaimer:• The three following slides are INFORMATIVE only and
implementation related.
• Their aim however is to raise the awareness of the needed synchronization between the 802.1Qbz Bridge and 802.11ak time domains
Slide 12
Sep 2013
Submission
doc.: IEEE 11-13/0995r1
Broadcom / Intel
Timestamping of 802.1AS Sync Messages over 802.1Qbz Bridge and 802.11ak Link
• Residence time of the 802.1Qbz bridge includes 2 time domains: 802.1Qbz bridge and 802.11
• Two mutually exclusive options:• Option 1: Bridge and STA clocks are synchronized
• Option 2: Bridge and STA clocks are independent free running clocks. In this case:
- Sync messages must be timestamped at the “Infrastructure” and “STA/Bridge” interfaces
- The Timestamping is identical to the timestamping at the portal interface in a Time Aware 802.11 AP STA
Slide 13
Sep 2013
Submission
doc.: IEEE 11-13/0995r1
Broadcom / Intel
802.1Qbz / 802.11ak Sync Msg Timestamping (1)
• Option#1 : Bridge & STA free running clocks
Slide 14
Sep 2013
Time AwareBridgeport
Time Aware802.11ak
infrastructure interface
802.11ak link
Time Aware802.11 AP
station
Time AwareBridgeport
Time Aware802.11ak
STA/bridgeinterface
Time Aware802.11 non-AP
station
tib1 tib2
tes2
tis1tis2
teb1 teb2
tes1
Bridgeresidence time
AP residence time
Bridgeresidence time
Non-AP STA residence time
802.11aklink delay
ingress Bridge free running clock
ingress STAfree running clock
egress Bridge free running clock
egress STAfree running clock
freq rate ratio
freq rate ratio
tis3tes2
Submission
doc.: IEEE 11-13/0995r1
Broadcom / Intel
802.1Qbz / 802.11ak Sync Msg Timestamping (2)
• Option#2 : Bridge & STA clocks are synchronized
Slide 15
Sep 2013
Time AwareBridgeport
Time Aware802.11ak
infrastructure interface
802.11ak link
Time Aware802.11 AP
station
Time AwareBridgeport
Time Aware802.11ak
STA/bridgeinterface
Time Aware802.11 non-AP
station
tib1
tis2
teb2
tes1
Bridgeresidence time
AP residence time
Bridgeresidence time
Non-AP STA residence time
802.11aklink delay
ingress Bridge free running clock
ingress STAclock
egress Bridge free running clock
egress STA clock
syncsync
tis3tes2
Submission
doc.: IEEE 11-13/0995r1
Broadcom / Intel
Questions ?
Sep 2013
Slide 16
Submission
doc.: IEEE 11-13/0995r1
Broadcom / Intel
Thank you
Sep 2013
Slide 17
