1. IEEE 802.21 MEDIA INDEPENDENT HANDOVER
DCN:
Title: Initial Network Selection in WLAN
Date Submitted: June, 2007
Presented at IEEE session in ETRI
Authors or Source(s):
Vivek Gupta, Stephen McCann, Dave Stephenson
Abstract: This provides an update on initial Network Selection procedures/flow in network using services.

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3. Add this in Annex H8 in Draft D5.1:
Comment 5583 in LB-1d
Add this in Annex H8 in Draft D5.1:
Network Selection in (WLAN) using MIH Protocol:

4. Network Selection in WLAN with 802.11u & 802.21: Fig-1

5. Use Case: Query SSPN List: Fig-2
STA
(802.11u-capable) AP
(802.11u-capable) IS
(local Access Network) IS
(“home” SSPN)
Pre-configuration
Advertising protocol ID (APID) = IS
Maximum acceptable length (LEN) for query responses
Pre-configuration
Beacon (Interworking IE, GAS:APID)
Probe Request
Probe Response (Interworking IE,
GAS:APID)
Relay MIH frame (with query content)
Transport method: (1) 802.3, (2) IP
GAS initial request (request IE, APID)
Query content (“list of SSPNs?”)
GAS Initial Response (Query ID, Dialog
Token, comeback delay)
COLOR KEY
(optional – STA to PS mode)
Comeback delay
MIH Response (transaction ID,
answer information); may be delayed
until answer is ready
Out of scope
802.11
GAS Comeback Request (Query ID)
802.21
GAS Comeback Response (Query ID,
answer information)

6. Steps in Network Selection
Fig-1 shows the general topology of an (WLAN) network operating with an IS.
The steps in Network selection as shown in Fig-2 are as follows:
1) Pre-configuration: The AP is preconfigured with advertising protocol identifier (APID) of choice and is pre-configured to use MIIS. The AP may discover the MIIS through a variety of different mechanisms that are outside the scope of specification. The maximum length of response messages from MIIS is also set. The AP may communicate with MIIS at L2 or at L3 using a protocol defined elsewhere.
2) Discover AP/Access Network Capabilities: The AP sends out a beacon with Inter-working IE set and APID set to GAS (Generic Access Protocol). The STA may discover access network capabilities by listening to beacons or it could also send a probe request and discover access network capabilities through the probe response.
3) Query list of SSPNs: The STA sends out a query asking for list of available SSPNs? The query is defined using an specific MIH frame. The MIH frame is then relayed by the AP to the MIIS. Meanwhile the AP sends out the initial GAS response to the STA with initial delay (comeback delay)
4) GAS response: The MIIS interprets the query and retrieves the response either from local or remote repository. It then packs the response in an appropriate MIH frame and sends it to the AP. Subsequently when the STA sends the GAS comeback request to the AP, the AP responds with the available information in the MIH frame. The STA then retrieves the information out of the MIH frame and obtains the answer to the query.

7. Backup

8. Questions and notes What is the AP-to-IS communication?
What is the protocol used? Is it direct L2 connection, MIPSHOP, RADIUS/DIAMETER, or something else entirely?
Potential resolution: needs to create an IP-based transport protocol.
Is a query ID necessary to match STA query to IS responses?
Potential resolution: AP assures that Transaction ID is unique on a per-STA basis for a reasonable time interval, and rewrites Transaction ID if necessary for uniqueness
This works as a long as transactions are not integrity protected. There is no security in state 1, so this may not be a big drawback. Does the STA need to refrain from using integrity protection in state 1?
How much interpretation does AP do of MIH requests?
If none, then will any claimed frame from STA be relayed to IS?
How much of the MIH packet does the AP need to understand? Query and response should be opaque. How much of the header is necessary?