1. TGaq Service Transaction Protocol for ANDSF Discovery Service
July 2013
doc.: IEEE /0158r0
March 2014
TGaq Service Transaction Protocol for ANDSF Discovery Service
Authors:
Date:
Joe Kwak, InterDigital
Joe Kwak, InterDigital

2. July 2013
doc.: IEEE /0158r0
March 2014
Abstract
This is a TGaq Transaction Protocol example showing how a pre-associated STA may access ANDSF Service for WLAN discovery and selection.
This builds upon the 11aq draft text in aq-service-transaction-protocol and is intended to be the basis for an informative annex in our 11aq draft.
Joe Kwak, InterDigital
Joe Kwak, InterDigital

3. Background TGaq develops simple MAC protocol
July 2013
doc.: IEEE /0158r0
Background
March 2014
TGaq develops simple MAC protocol
Defines over-the-air messages only (PAM)
Meets low level requirements of use cases
Other Fora deal with higher layers (L2+)
Liaison to other fora of our use cases
3GPP has developed a discovery service for dual mode smartphones and other dual mode (cell/WLAN) devices that uses assistance data to discover and select WLANs suitable for offload.
Access Network Discovery and Selection Function (ANDSF) has been specified by 3GPP to provide this assistance data.
ANDSF is normally implemented in a server accessible on the internet, and discovered by DNS lookup.
Joe Kwak, InterDigital
Joe Kwak, InterDigital

4. Service Transaction Protocol (STP) Review
July 2013
doc.: IEEE /0158r0
March 2014
Service Transaction Protocol (STP) Review
STP is different from ANQP
STP is not limited to simple Request/Response mechanism.
Using transparent packet containers, STP provides flexible transport for pre-associated STAs to communicate with different existing Upper Layer Protocols (ULPs) for service discovery, bonjour, UPnP, etc.
Service/discovery information is transparently encapsulated for transport to a Service Transaction Proxy (STPxy) which implements this protocol for a particular (or set) of discovery ULP.
Packets are routed from the pre-associated STA, through the AP, to the STPxy, which acts on behalf of the STA to communicate with the intended discovery protocol server.
In other words, STP sets up a short-term tunnel from the STA to the STPxy which proxies for the STA for internet packet exchanges.
Joe Kwak, InterDigital
Joe Kwak, InterDigital

5. Service Transaction Protocol Review
July 2013
doc.: IEEE /0158r0
March 2014
Service Transaction Protocol Review 1
Part of the PAM (Pre-Association Messages)
The TP is implemented as an advertisement protocol enabling it to be carried, over the IEEE air interface, by the existing GAS mechanism.
Use a new advertisement protocol id “STP” – service transaction protocol (e.g. like RLQP). NOTE: TG has decided to change name to PADP in place of STP
Define a new IE for use in Beacon, Probe Response frames to advertise service capabilities.
[1] Transaction Protocol Review (slides 5-10) from
aq-transaction-protocol
Joe Kwak, InterDigital
Joe Kwak, InterDigital

6. Service Transaction Protocol Review
July 2013
doc.: IEEE /0158r0
Service Transaction Protocol Review
March 2014
A mobile device requires service information prior to association.
The mobile device supports one or more ULP’s
The Access Point advertises (in this example using ANQP) service types as well as a list of ULP’s that are supported.
An STP Encapsulation message carries the ULP service information request to the AP, which relays the request to the STPxy.
The STPxy proxies for the STA to exchange service information using the discovery ULP.
The STPxy provides service information in a response that is encapsulated and sent back to the mobile device through the Access Point.
Joe Kwak, InterDigital
Joe Kwak, InterDigital

7. Service Transaction Protocol Review
July 2013
doc.: IEEE /0158r0
March 2014
Service Transaction Protocol Review
STP operates between the ULP applications in the pre-associated STA and the Service Transaction Proxy (STPxy).
As this ANDSF example shows, the encapsulation mechanism must be transparent to enable this service for ANDSF and perhaps other popular discovery services.
Joe Kwak, InterDigital
Joe Kwak, InterDigital

8. March 2014 July 2013 doc.: IEEE 802.11-14/0158r0
Joe Kwak, InterDigital
Joe Kwak, InterDigital

9. Service Transaction Protocol Review
July 2013
doc.: IEEE /0158r0
March 2014
Service Transaction Protocol Review
ULP does not need to be standardised within Tgaq
deliberately hide the details of the ULP so that we can focus on MAC design
When the higher layer ULP responds with another message B, the TXP uses another STP Encapsulation message to transmit message B back to the mobile device including the STP token. If an error occurs in the TXP transaction a Return Code may be alternatively returned to the mobile.
When the STP Encapsulation message is received by the mobile terminal the contents are passed back to the service discovery ULP.
Joe Kwak, InterDigital
Joe Kwak, InterDigital

10. Service Transaction Protocol Review
July 2013
doc.: IEEE /0158r0
March 2014
Service Transaction Protocol Review
The message sequence is bi-directional and can be initiated by the ULP co-located with the STPxy. The service information is constructed based on the ULP – it does not necessarily execute the ULP protocol over frames transmitted in the pre-associated state
IDs of ULP protocols for the STA and the AP infrastructure are required for encapsulation/decapsulation.
Possibly need to fragment large ULP frames.
GAS already has the capability for fragmentation/reassembly
To conserve the medium, using a hash of the service information in the encapsulated STP exchange may be feasible for some applications of STP. (see r0)
Messages could be signed to provide some level of data integrity.
Need to do some additional work on defining the ULP ID space and its management
Joe Kwak, InterDigital
Joe Kwak, InterDigital

11. ANDSF Example Using 11aq Transaction Protocol
July 2013
doc.: IEEE /0158r0
March 2014
ANDSF Example Using 11aq Transaction Protocol
Joe Kwak, InterDigital
Joe Kwak, InterDigital

12. 3GPP WLAN Network Architecture
March 2014
3GPP WLAN Network Architecture
Both trusted (integrated) and untrusted (over-the-top) interfaces exist
The trusted interface involves operator deployed WLAN and is being evolved in 3GPP Release 12
TWAG
Joe Kwak, InterDigital

13. July 2013
doc.: IEEE /0158r0
March 2014
Normal discovery for 3GPP UE(STA) after association and using IP transport
(Figure from 3GPP TS )
Joe Kwak, InterDigital
Joe Kwak, InterDigital

14. March 2014 Pre-association discovery for 3GPP UE(STA)
July 2013
doc.: IEEE /0158r0
March 2014
Pre-association discovery for 3GPP UE(STA)
using STPxy with limited IP transport
Joe Kwak, InterDigital
Joe Kwak, InterDigital

15. July 2013
doc.: IEEE /0158r0
March 2014
A: STPxy decapsulates message and substitutes its own IP add in header to replace dummy IP add from STA
B: STPxy substitutes dummy IP add from STA to replace its own IP add in header, then encapsulates and sends to AP
Joe Kwak, InterDigital
Joe Kwak, InterDigital

16. July 2013
doc.: IEEE /0158r0
March 2014
A: STPxy decapsulates message and substitutes its own IP add in header to replace dummy IP add from STA
B: STPxy substitutes dummy IP add from STA to replace its own IP add in header, then encapsulates and sends to AP
Joe Kwak, InterDigital
Joe Kwak, InterDigital

17. Discussion and Questions
July 2013
doc.: IEEE /0158r0
March 2014
Discussion and Questions
Questions on presentation?
Should we develop this example into draft text for the informative Annex of the 11aq amendment?
Other comments or issues?
Joe Kwak will provide draft text for this informative annex at May meeting.
THANK YOU
Joe Kwak, InterDigital
Joe Kwak, InterDigital

18. REFERENCES (listed in order of relevance to this example)
March 2014
REFERENCES (listed in order of relevance to this example)
3GPP Network Elements: Numbering, Addressing, and Identification –Explains ANDSF discovery mechanism using DNS
Generic Authentication Architecture and Access to 3GPP Network Using https: --Explains authentication and TLS security for ANDSF connection based on preconfigured or bootstrapped shared key.
HTTP over TLS—General reference for setting up https:
Specification of 3GPP-WLAN Interworking—Broad reference that provides detail on WLAN-ANDSF interface
Specification for non-3GPP Access to 3GPP Network—Includes architecture and interworking descriptions for WLAN discovery and connection to ANDSF
Study of WLAN Selection and Policy Application using ANDSF Information—provides set of illustrative examples showing how STAs use ANDSF Management Object (MO) data to select WLAN.
Specification of ANDSF MO—Complete MO details and structure of WLAN selection policy MO tree.
Joe Kwak, InterDigital