1. Providing Faster GAS Response
March 2014
doc.: IEEE /0216r0
Providing Faster GAS Response
Date:
Authors:
Yunsong Yang, Huawei
Stephen McCann, Blackberry

2. March 2014
doc.: IEEE /0216r0
Abstract
This contribution presents a mechanism for potentially providing faster GAS response to a requesting STA and with less GAS signaling overhead.
Yunsong Yang, Huawei
Stephen McCann, Blackberry

3. March 2014
doc.: IEEE /0325r0
Background
During WG LB process, service query using Probe Request and Probe Response frames was replaced by GAS frames based service query, where the query response comes from an ANQP server and based on information from a service information registry (SIR), both of which are typically centrally located, therefore resulting in a longer latency.
During Initial Sponsor Ballot, GA GAS frame and GAS Extension element were introduced in 11aq to address the issue of slow service query using unicast GAS frames (SB0 CIDs 6050 and 6053).
Yunsong Yang, Huawei
Stephen McCann, Blackberry

4. Review of CAG in 802.11ai-2016 (1) CAG CAG ANQP-element
March 2014
doc.: IEEE /0325r0
Review of CAG in ai-2016 (1)
CAG
“The Common Advertisement Group (CAG) is a group of elements that are defined by the same advertisement protocol and that do not change on a rapid basis within an AP.”
CAG ANQP-element
“The CAG ANQP-element provides the info IDs for the ANQP-elements contained within a CAG associated with ANQP and the current value of the ANQP CAG version, indicating the version of information within the CAG associated with ANQP.”
Yunsong Yang, Huawei
Stephen McCann, Blackberry

5. Review of CAG in 802.11ai-2016 (2) CAG Number element
March 2014
doc.: IEEE /0325r0
Review of CAG in ai-2016 (2)
CAG Number element
“The CAG Number element provides one or more current version numbers of the CAG (CAG Version) associated with the AP, where each version number is associated with a specific advertisement protocol. The CAG Number element is optionally present in the Beacon or Probe Response frame to reduce GAS frame exchanges.”
Yunsong Yang, Huawei
Stephen McCann, Blackberry

6. Can 11aq use CAG as defined in 11ai?
March 2014
doc.: IEEE /0325r0
Can 11aq use CAG as defined in 11ai?
If a service information is considered as a CAG or a part of a CAG, by comparing the CAG Version of a stored service information with the last CAG Version at the AP, a requesting STA may be able to reuse the stored service information to decide if to associate with the AP or not.
Resulting in faster service discovery and less GAS signaling.
However, two issues may stand in the way:
Both 11aq and 11ai use ANQP protocol, but the CAG Number element supposedly supports only one CAG Version per advertisement protocol. So, there may be an issue if the AP supports both 11ai and 11aq.
Signaling overhead for broadcasting CAG Number element in the Beacons may not be so justified, considering that service query may not happen as frequently as the Beacon transmissions.
Yunsong Yang, Huawei
Stephen McCann, Blackberry

7. Proposal of using CAG (or similar) in 11aq
March 2014
doc.: IEEE /0216r0
Proposal of using CAG (or similar) in 11aq
The SIR considers one or more service information as a CAG (or a similar term such as a Service Group) and maintains a CAG Version for the CAG so that the CAG Version is incremented by 1 if a service information within the CAG changes.
The SIR provides the CAG Version along with the service info to the advertisement server (AS), which generates the query response. The AS provides the query response and the CAG Version to the AP, which generates the GAS response frame. The CAG Version can be included:
Option 1: in a modified GAS Extensions element in the GAS response frame;
Option 2: in an (11ai) CAG Number element in the GAS response frame;
Option 3: in a new Service Number element in the GAS response frame; or
Option 4: in an (11ai) CAG ANQP-element in the Query Response field of the GAS response frame. (Note: Options 1-3 can directly benefit other advertisement protocols, such as RLQP, but Option 4 won’t benefit protocols other than ANQP without defining similar protocol-element in the other protocols.)
The SIC of the requesting STA caches the service information and the associated CAG (or Service) Version for future use.
Yunsong Yang, Huawei
Stephen McCann, Blackberry

8. Proposal of using CAG (or similar) in 11aq – cont’d
March 2014
doc.: IEEE /0216r0
Proposal of using CAG (or similar) in 11aq – cont’d
When the requesting STA visits the same BSS/ESS later and is interested in the same service, the STA sends a GAS Initial Request or GA GAS Request frame containing a Service Hash Request or Service Information Request ANQP-element to discover if the service parameter is the same as before, by including, in the GAS request frame: a) a GAS Extension element; b) an (11ai) CAG Number element; or c) a new Service Number element, which includes the CAG (or Service) Version cached at the SIC.
Meanwhile, as the AP maintains the latest CAG (or Service) Version from the AS/SIR, which is out of the scope of 11aq, the AP compares the latest Version from the AS/SIR with the Version from the requesting STA:
If the two Versions match, the AP sends a GAS Initial Response frame to the requesting STA with the Status Code field indicating that the two Versions match. Then, the requesting STA may decide whether to associate with the AP based on its cached service information.
If the two Versions don’t match, the AP posts the query request to the advertisement server as usual, and so are the following steps.
Yunsong Yang, Huawei
Stephen McCann, Blackberry

9. An Example Message Flow
March 2014
doc.: IEEE /0216r0
An Example Message Flow
Notice that AP doesn’t need to broadcast the CAG (or Service) Version in Beacons.
Yunsong Yang, Huawei
Stephen McCann, Blackberry

10. Benefits of the Proposal
March 2014
doc.: IEEE /0216r0
Benefits of the Proposal
When CAG (or Service) Versions match, the AP can respond
more quickly without posting the query to the advertisement server thus the requesting STA can make a decision on association more quickly.
with the status code without the Query Response field (i.e., without repeating the service information that the requesting STA already has).
When the two Versions don’t match, the query proceeds as usual and no extra delay is incurred to the service discovery.
Having little to lose, vendors may be more motivated to have the STA including the CAG (or Service) Version in the GAS request than to have the AP broadcasting the CAG (or Service) Version in the Beacons.
If using options 1-3 as discussed in slide 7, the proposal can also benefit other advertisement protocols, such as RLQP, without the need of additional standardization efforts in beyond what is being proposed to 11aq.
Yunsong Yang, Huawei
Stephen McCann, Blackberry

11. Comparing 4 Options Option Support of GAS request
March 2014
doc.: IEEE /0216r0
Comparing 4 Options
Option
Support of GAS request
Support of GAS response
Support Ad. Protocol(s)
1: GAS Extension
element
Support both GAS request and GAS response. Having same advantage as Option 3 when comparing to Option 2.
All
2: CAG Number element
Support both GAS request and GAS response.
Potential issues: 11ai-defined CAG is managed by the advertisement server, but the service information is managed by the SIR.
3: Service Number element
Advantage: Service Number is separate from 11ai CAG and is managed by the SIR.
4: CAG ANQP-element
Being inside the Query Request field, this requires the AP to process the Query Request field.
Support (as the end recipient of query response is the SME/SIC of the STA)
ANQP only
Yunsong Yang, Huawei
Stephen McCann, Blackberry

12. Changes needed to 11aq D8.0 (1)
March 2014
doc.: IEEE /0216r0
Changes needed to 11aq D8.0 (1)
If based on Option 1, modify Clause GAS Extensions element:
Insert a CAG (or Service) Version field, which is optionally present in the GAS Extensions element. The CAG (or Service) Version field,
when present in a GAS Initial Request or GA GAS Request frame, carries the CAG (or Service) Version) associated with the cached service information of the service being queried in the GAS request frame, and
when present in a GAS Initial Response, GAS Comeback Response, or GA GAS Response frame, carries the latest CAG (or Service) Version at the SIR associated with the service information in the GAS response frame.
Insert a CAG (or Service) Version Flag subfield in the GAS Flags field to indicate the absence/presence of the CAG (or Service) Version field.
If based on Option 2, modify Clause CAG Number element to allow it to be optionally present in a GAS request or GAS response frame.
If based on Option 3, define a new Service Number element similar to CAG Number element (can debate if we need the protocol ID or not) and optionally present in a GAS request or GAS response frame.
Yunsong Yang, Huawei
Stephen McCann, Blackberry

13. Changes needed to 11aq D8.0 (2)
March 2014
doc.: IEEE /0216r0
Changes needed to 11aq D8.0 (2)
Clause MLME-GAS.confirm
Add GASExtensions, CAGNumber, or ServiceNumber (depending on which of the 3 options is adopted) parameter in the MLME-GAS.confirm primitive.
If Option 2 or 3 is adopted, CAGNumber, or ServiceNumber is also needed in MLME-GAS.request, MLME-GAS.indication, and MLME-GAS.response.
Clause Status Code field
Add a new Status Code value for “VERSIONS_MATCH”.
Clause GAS Initial Response frame format
Add GAS Extensions, CAG Number, or Service Number element (depending on which of the 3 options) as an optionally present element in the frame.
Clause General (under GAS Protocol)
Add a flow diagram similar to the one in slide 9 and add related text description.
Clause STA procedures to transmit a GAS Query
Add text describing a requesting STA may submit the cached CAG Version in a GAS Query if the STA has cached the service information and the CAG Version.
Yunsong Yang, Huawei
Stephen McCann, Blackberry

14. Changes needed to 11aq D8.0 (3)
March 2014
doc.: IEEE /0216r0
Changes needed to 11aq D8.0 (3)
Clause STA procedures to post a GAS Query to an AS
Add text describing when the two Versions match, the AP may respond to the requesting STA without posting the GAS Query to the advertisement server.
Clause STA procedures for transmitting the GAS Query Response
Add text describing when receiving the Query Response with the CAG (or Service) Version from the AS, how the AP maps the CAG (or Service) Version into the GAS Extensions, CAG Number, or Service Number element (depending on which of the 3 options is adopted) in the GAS response frame.
Yunsong Yang, Huawei
Stephen McCann, Blackberry

15. March 2014
doc.: IEEE /0325r0
Summary
An mechanism is provided for opportunistically providing faster GAS response to a requesting STA with less GAS signaling overhead.
Changes to 11aq D8.0 to support the enhancement are identified and listed.
The enhancement can also benefit other advertisement protocols, such as RLQP, without the need of additional standardization efforts in beyond what is being proposed to 11aq.
Additional standardization efforts that are out of the scope of may be carried out in the Wi-Fi Alliance.
Yunsong Yang, Huawei
Stephen McCann, Blackberry

16. March 2014
doc.: IEEE /0216r0
Straw Poll 1
Do you support the concept proposed in slides 7-9 for opportunistically providing faster GAS response?
Yes:
No:
Abstain:
Yunsong Yang, Huawei
Stephen McCann, Blackberry

17. March 2014
doc.: IEEE /0216r0
Straw Poll 2
Which option below do you support to include the (cached) CAG (or Service) Version in the GAS request frame?
Option 1: in a modified GAS Extension element in the GAS request frame.
Option 2: in an (11ai) CAG Number element in the GAS request frame.
Option 3: in a new Service Number element in the GAS request frame.
Option 1:
Option 2:
Option 3:
Abstain:
Yunsong Yang, Huawei
Stephen McCann, Blackberry

18. March 2014
doc.: IEEE /0216r0
Straw Poll 3
Which option below do you support to include the CAG (or Service) Version in the GAS response frame?
Option 1: in a modified GAS Extension element in the GAS response frame.
Option 2: in an (11ai) CAG Number element in the GAS response frame;
Option 3: in a new Service Number element in the GAS response frame;
Option 4: in an (11ai) CAG ANQP-element in the Query Response field of the GAS response frame.
Option 1:
Option 2:
Option 3:
Option 4:
Abstain:
Yunsong Yang, Huawei
Stephen McCann, Blackberry