Transcript 21-07-0238-02-0000-Initial_NetSel_in_WLAN

 IEEE 802.21 MEDIA INDEPENDENT HANDOVER
 DCN: 21-07-0238-02-0000
 Title: Initial Network Selection in WLAN
 Date Submitted: June, 2007
 Presented at IEEE 802.21 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 802.11 network using 802.21 services.
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Comment 5583 in LB-1d
Add this in Annex H8 in Draft D5.1:
Network Selection in 802.11 (WLAN) using
802.21:
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Network Selection in WLAN with 802.11 & 802.21: Fig-1
SSPN #1
802.21 IS
NAP Core Network
AAA
MIH Protocol
AAA Proxy
802.21 local IS
Internet
MIH Protocol
MIH Protocol
MIH Protocol
802.21 IS
Hotspot-1
802.11u
802.11u
AAA
Hotspot-2
SSPN #2
Mobile Devices with WLAN
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SSPN: Subscription Service Provider Network
MIH: Media Independent Handover
802.21 IS: MIH Information Service
NAP: Network Access Provider
Use Case: Query SSPN List: Fig-2
STA
AP
802.21 IS
802.21 IS
(local Access Network)
(“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
Comeback delay
(optional – STA to PS mode)
GAS initial request (request IE, APID)
Query content (“list of SSPNs?”)
GAS Initial Response (Query ID, Dialog
Token, comeback delay)
MIH Response (transaction ID,
answer information); may be delayed
until answer is ready
GAS Comeback Request (Query ID)
GAS Comeback Response (Query ID,
answer information)
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Legend
802.11
802.21
Steps in Network Selection
Fig-1 shows the general topology of an 802.11 (WLAN) network operating with an 802.21 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 802.21 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 Advertisement Service). 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 802.21 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.
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Backup
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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: 802.21 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 802.21 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?
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