Time Features Date: 2009-05-11 Authors: May 2009 Month Year doc.: IEEE 802.11-yy/xxxxr0 May 2009 Time Features Date: 2009-05-11 Authors: Allan Thomson, Cisco Systems John Doe, Some Company

Month Year doc.: IEEE 802.11-yy/xxxxr0 May 2009 Abstract TGp LB144 CID#110 raised an issue around the introduction of time advertisement features in TGp that overlaps somewhat with similar features in TGv and TGu This presentation attempts to provide an overview of each of the features to facilitate further discussion on how to possibly align these features Allan Thomson, Cisco Systems John Doe, Some Company

May 2009 Summary TGv – Provides general scheme to distribute external time reference (UTC) wrt TSF to non-AP STAs Motivated by timestamping of events but is a general scheme TGu – Provides scheme to distribute external timestamp (UTC & Time Zone) for local time at the AP TGp – Provides scheme to distribute external time reference wrt TSF between STAs Allan Thomson, Cisco Systems

TGp – Additional Information May 2009 TGp – Additional Information Courtesy Richard Roy: “In a mobile environment where one might want to coordinate switching of physical channels so that the STAs were on the same RF channel at the same time, one could use GPS UTC time as the “external clock” that everyone would use for aligning channel switches.  Now imagine that NOT all STAs have a source of UTC time.  How should they get such a reference.  Answer: the TA frame with a TIE provides, in a single frame, information from a STA with UTC time to a STA w/o UTC time that allows the second STA to align an “external” clock to UTC and then can proceed to engage in aligned channel switches.  Note the big difference between this mechanism and the one in TGu. The extension of 1) is for deployment of a TDMA scheme for channel assignments, eg. a logical MESH channel mapped to a physical channel which is a time slot on a given RF carrier … you get the idea.  Note that in highly mobile environments, alignment (i.e., TSF synchronization) using beacons is not viable for many reasons.  An external well-defined source of time is required. Higher layer security mechanisms often use accurate time to prevent replay and other similar attacks on the system.  The higher layer protocols the ITS community is developing (IEEE 1609, ETSI TC ITS WG5) are examples of such use of accurate time. Generally, any scenario one can dream up that makes use of/relies on “aligned time sources/clocks” on distinct (i.e., physically separate) physical devices (STAs)  can make use of the TA frame to distribute time to those STAs that don’t have  the agreed upon external time reference. “ Allan Thomson, Cisco Systems

May 2009 TGv – UTC TSF Offset Provides an offset between the AP’s TSF counter and UTC to non-AP STAs Distributed via an IE in Probe Response and Beacon frames Two fields UTC TSF Offset & UTC TSF Offset Accuracy UTC Time is represented as follows: Same format is used by TGu Allan Thomson, Cisco Systems

TGu – AP Date, Time and Time Zone Information May 2009 TGu – AP Date, Time and Time Zone Information Provides the AP Date, Time and Time Zone for the AP to non-AP STAs Distributed via an IE in Native GAS Query Response Two fields Timestamp & Time Zone Timestamp uses TGv format without millisecond granularity Time Zone specified using Allan Thomson, Cisco Systems

TGp – Timing Advertisement May 2009 TGp – Timing Advertisement Provides a method for a STA to synchronize to an external time standard distributed by another STA Introduces a new management frame, Timing Advertisement, frame containing the following elements Allan Thomson, Cisco Systems

TGp – Timing Advertisement Cont’d May 2009 TGp – Timing Advertisement Cont’d Timing IE defined as: Timing Capabilities defined as a set of bits that indicate whether the external time source is available…etc TTOE (TSF Timer Offset Estimate) TTOE-STD (TTOE Standard Deviation) Allan Thomson, Cisco Systems

Observations May 2009 TGv TGu TGp On Demand Distribution Periodic Update of time Distribution of time from AP to non-AP STA Distribution of time from any STA to any STA Distribution of external time pre-association Distribution of external time post-association Defines offset between TSF and external time Defines time zone Granularity mSec Sec nSec Allan Thomson, Cisco Systems

May 2009 Straw Poll Do you agree the time advertisement features in TGv, TGu and TGp should be aligned? Yes (all or part of): 18 No: 1 Don’t Care: 4 Allan Thomson, Cisco Systems

Solutions Proposed Solution #1: Combine TGv &TGu May 2009 Solutions Proposed Solution #1: Combine TGv &TGu Proposed Solution #2: Modify TGv and combine with TGu Proposed Solution #3: Add TGp missing items to Solution #1 or Solution #2 Allan Thomson, Cisco Systems

Proposed Solution #1: Combine TGv &TGu May 2009 Proposed Solution #1: Combine TGv &TGu TGv - Add Time Zone field to UTC TSF Offset IE TGu - Remove AP Date, Time & Time Zone from Native GAS Query TGp – leave as is Continue to use Probe Response and Beacon frames to communicate time advertisement Allan Thomson, Cisco Systems

Proposed Solution #2: Modify TGv & combine with TGu May 2009 Proposed Solution #2: Modify TGv & combine with TGu TGv - Add Time Zone field to UTC TSF Offset IE TGv – Remove IE from Beacon and add to (Re)association response frames TGu - Remove AP Date, Time & Time Zone from Native GAS Query TGp – leave as is Use Probe Response & (Re)Association Response frames to communicate time advertisement Allan Thomson, Cisco Systems

May 2009 Proposed Solution #3: Add TGp missing items to Solution #1 & Solution #2 TGp – Remove Timing Advertisement frame TGp - Add new combined UTC TSF Offset (and associated frames) including Timing Capabilities to TGp TGv – Remove UTC TSF Offset Allan Thomson, Cisco Systems

Proposed Solution #4: Combine TGp, TGv & TGu fields into a single IE May 2009 Proposed Solution #4: Combine TGp, TGv & TGu fields into a single IE TGp – Keep Timing Advertisement frame TGp/TGv/TGu - Combine new combined UTC TSF Offset including Timing Capabilities from TGp TGv – Refer to new IE TGu – Remove Native GAS Query Response, Rely on TGv frames Allan Thomson, Cisco Systems

May 2009 Straw Poll If you agreed that time advertisement should be aligned what is your preferred solution? Solution #1: 0 Solution #2: 0 Solution #3: 0 Solution #4: 14 Other: 2 Allan Thomson, Cisco Systems

May 2009 Straw Poll Summary Do you agree the time advertisement features in TGv, TGu and TGp should be aligned? Yes (all or part of): 18 No: 1 Don’t Care: 4 If you agreed that time advertisement should be aligned what is your preferred solution? Solution #1: 0 Solution #2: 0 Solution #3: 0 Solution #4: 14 Other: 2 Allan Thomson, Cisco Systems

Proposed Solution #4 Summary May 2009 Proposed Solution #4 Summary Strategy: Step 1: TGp used as the baseline for these changes Step 2: TGv builds on TGp Step 3: TGu builds on TGv and TGp Step 1: TGp 09/0482r4 (Group Reviewed Tue PM) Define TGp Time Advertisement IE to enable 3 amendment adoption Retain TGp Timing Advertisement frame use Step 2: TGv 09/0592r0 (Group Reviewed Tue Eve) Add TGv specific updates to Time Advertisement IE Update TGv to refer to new combined IE Retain TGv Probe Response and Beacon frame use Step 3: TGu 09/0593r0 (Group Reviewed Wed AM) Update TGu to refer to new combined IE Change TGu from GAS Query Response to use Probe Response frame Allan Thomson, Cisco Systems

May 2009 TGp Details Retains the Timing Advertisement frame that includes the Timestamp and Time Advertisement information element Time Advertisement information element is basis for all 3 amendments Timing capabilities field defines how the remaining contents are defined 0 = Arbitrary time base (no time value or time error included) 1 = Time Value field specifies the time offset estimate between UTC UT0 and the Timestamp transmitted in the Timing Advertisement frame Time Error field specifies the standard deviation of time error 2 to 255 – Reserved Nanoseconds are units of standard deviation of time error Element ID Length Timing Capabilities Time Value Time Error Octets: 1 9 5 Allan Thomson, Cisco Systems

May 2009 TGv Details Continued support of time advertisement in the Beacon frame and Probe Response frame Defines new Timing Capabilities field value (2) in Time Advertisement IE Value 2 = Time Value field defines as UTC UT0 estimate is referenced to the TSF timer at TSF time 0 Time Error field same definition as 802.11p Time Value as per previous TGv that defines UTC down to milliseconds granularity Adds Time Zone information element to probes and beacons Allan Thomson, Cisco Systems

TGu Details Eliminate GAS Query Response use of AP Date, Time…etc May 2009 TGu Details Eliminate GAS Query Response use of AP Date, Time…etc Instead use TGv approach of Probe Response frames with Time Advertisement IE Allan Thomson, Cisco Systems