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May 2004
Bernard Aboba, Microsoft
Slide 1
doc.: IEEE 802.11-04/0638r0
Submission
Network Selection
Bernard Aboba
Microsofthttp://www.ietf.org/internet-drafts/draft-ietf-eap-netsel-problem-00.txt
May 2004
Bernard Aboba, Microsoft
Slide 2
doc.: IEEE 802.11-04/0638r0
Submission
Outline
• Problem Definition
• Open Issues
• Next Steps
May 2004
Bernard Aboba, Microsoft
Slide 3
doc.: IEEE 802.11-04/0638r0
Submission
Challenges for Public Access WLAN• Minimizing channel conflicts
– In some locations (e.g. airports) multiple networks are becoming the norm.• Airlines are installing 802.11 networks for use in baggage reconciliation and roving
ticket counters• Multiple wireless ISPs often also want to serve airport customers
– Radio interference is an issue• In the US and Europe 802.11b networks can support only 3 non-overlapping channels• In France and Japan only one channel is available• Once the channels are utilized by existing APs, additional APs will interfere and reduce
performance• Minimizing capital expenditures
– In this economic environment, raising capital is difficult– Undesirable to build out multiple networks in the same location - why not build
one network and share it? • Attaining high utilization of deployed Access Points
– Profitability enhanced by filling in periods of low usage on the “diurnal curve”– Implies a need to serve many different types of customers: business, consumers,
etc.• Minimizing support costs
– Desirable to support a wide variety of clients without having to preconfigure them
May 2004
Bernard Aboba, Microsoft
Slide 4
doc.: IEEE 802.11-04/0638r0
Submission
Wouldn’t It Be Great If…• A single network could be shared by multiple providers?• Each provider could retain the flexibility to announce their
own network, and select the services they wish to provide (rates, security mechanisms, etc.)?
• Each provider could manage their own users without interfering with other providers?
• Customers could discover any of the offered networks without needing to pre-configure their stations?
To get there, we need to solve the Network Selection Problem!
May 2004
Bernard Aboba, Microsoft
Slide 5
doc.: IEEE 802.11-04/0638r0
Submission
Aspects of Network Selection
1. Access Network Discovery– Which access point to attach to?
2. Identifier Selection– Which identity and credentials to use in this AP?
3. Selection of roaming intermediaries– How to route the AAA conversation to the home network?
4. Payload Routing– How to route payload traffic in the right way– Filters and mandatory tunnels
May 2004
Bernard Aboba, Microsoft
Slide 6
doc.: IEEE 802.11-04/0638r0
Submission
An alternative decomposition• Discovery
– Access networks and access points– Home networks available through these– Mediating networks
• Decision– Manual or automatic– Automatic is preferred
• Most likely needs some pre-provisioned preference information
• Indicating the selected network– Attach to the chosen network and access point– Provide the chosen identity and home domain– Possibly provide some hints about mediating networks
May 2004
Bernard Aboba, Microsoft
Slide 7
doc.: IEEE 802.11-04/0638r0
Submission
When is Network Selection an Issue?• More than one network is available, each with different
characteristics. • The user has multiple credentials, and needs to decide which
to use to authenticate to a particular network. • There is more than one roaming path between the access and
home network, and service parameters or pricing differs between them.
• The roaming relationships between access and home networks are so complicated that current AAA protocols cannot route the requests to the home network based solely on the Network Access Identifier (NAI).
• Payload packets get routed or tunneled differently, based on the roaming relationship path. This may have an impact on the available services or their pricing.
• Providers share the same infrastructure, such as wireless access points.
May 2004
Bernard Aboba, Microsoft
Slide 8
doc.: IEEE 802.11-04/0638r0
Submission
Some Thoughts…• All four problems are relevant.
• Potential need for new solutions, at least for the three first problems.
• The problems are very hard if you consider them with large number of networks, fast handoffs, security, and automatic decisions.
• The proliferation of multiple network selection technologies within IEEE 802, IETF, and 3GPP would be bad.
• Solving all problems with current link layers and existing network access devices may not be possible. Phasing?
May 2004
Bernard Aboba, Microsoft
Slide 9
doc.: IEEE 802.11-04/0638r0
Submission
Feedback from 3GPP SA2 WLAN group
• What parts of the problem does 3GPP want to solve?– Problem 1 (Access Network Discovery) and 3 (AAA
routing) are relevant to 3GPP. – Problem 2 (Identifier Selection) is considered at this stage
out of scope.– Problem 4 (Payload Routing) is considered a separate
problem within SA2 scope and is still under discussion.
• Observations [J. Arkko]– 3GPP uses existing L2 mechanisms for problem 1, expects
an IETF solution for problem 3– Needed for 3GPP Release 6
May 2004
Bernard Aboba, Microsoft
Slide 10
doc.: IEEE 802.11-04/0638r0
Submission
Recommendations from IETF 59• There is current interest in problem 1 (access
network selection)– Problem 1 belongs to layer 2– Long-term, discovery is most efficient at layer 2
• There is current interest in problem 3 (roaming intermediary selection)– Problem 3 needs at least partial IETF work, though
intermediary discovery could also be done at layer 2– Any IETF intermediary discovery solution would
necessarily be short-term• Other problems are lower priority…
May 2004
Bernard Aboba, Microsoft
Slide 11
doc.: IEEE 802.11-04/0638r0
Submission
IETF Work In Network Selection1. Access Network Discovery
– No chartered work yet2. Identifier Selection
– draft-ietf-pkix-wlan-extns-05.txt– Product of the PKIX WG
3. Selection of roaming intermediaries– draft-arkko-roamops-rfc2486bis-00.txt– Included in RADEXT WG Charter
4. Payload Routing– Improvements to AAA filtering and redirection capabilities, proposed in
RADEXT WG Charter
May 2004
Bernard Aboba, Microsoft
Slide 12
doc.: IEEE 802.11-04/0638r0
Submission
Thinking About the Access Netowrk Discovery Problem
• Why are existing solutions not adequate?– WFA: Public Access MRD
• Why are recently proposed standards not adequate? – IEEE 802.1ab, IEEE 802.1af– Answer: unlikely to be implemented by APs
May 2004
Bernard Aboba, Microsoft
Slide 13
doc.: IEEE 802.11-04/0638r0
Submission
What is a Virtual Access Point?• A “Virtual Access Point” is a logical entity that
exists within a physical Access Point (AP). • Each Virtual AP appears to stations (STAs) to be
an independent physical AP.– Virtual APs emulate the operation of physical APs at
the MAC layer. – Virtual APs provide partial emulation of the IP and
Application Layer behavior of physical APs.– Emulating the operation of a physical AP at the radio
frequency layer is typically not possible unless multiple radios are available.
May 2004
Bernard Aboba, Microsoft
Slide 14
doc.: IEEE 802.11-04/0638r0
Submission
Is It “Virtual” Or Is It Real?Only Your Radio Knows For Sure!
Channel 6Channel 6
AP AAP B STA
SSID: FooBSSID: ARates: 5.5,11Security: WPA
SSID: BarBSSID: BRates: 1,2,5.5,11Security: Open
Physical APs
AP A
Channel 6
Virtual APs
SSID: FooBSSID: ARates: 5.5,11Security: WPA
SSID: BarBSSID: BRates: 1,2,5.5,11Security: Open
Beacon/Probe Response
May 2004
Bernard Aboba, Microsoft
Slide 15
doc.: IEEE 802.11-04/0638r0
Submission
What Is Required for a Virtual AP?• Multiple SSIDs.
– Support for multiple SSID advertisement by APs– Support for STA discovery for advertised SSIDs.
• Multiple capability advertisements. – Each Virtual AP can advertise its own set of capabilities.
• Pre-authentication routing. – Determination of the target SSID prior to Association (for routing
of pre-authentication traffic). • Multiple VLANs.
– Allow a unique VLAN (and unique default key) to be assigned to each Virtual AP.
• Multiple RADIUS configurations. – Multiple RADIUS configurations, one for each virtual AP.
• Multiple virtual SNMP MIBs. – A virtual MIB instance per Virtual AP.
May 2004
Bernard Aboba, Microsoft
Slide 16
doc.: IEEE 802.11-04/0638r0
Submission
The State of “Virtual APs” Today
• IEEE 802.11-1999 does not provide guidance on required MAC-layer behavior of “Virtual APs”– Multiple approaches taken by AP vendors
– Different assumptions made by NIC vendors
– Interoperability, reliability problems abound
• Solution: WFA addressing the issue in the Public Access Group– MRD near completion; requires separate BSSID for each
advertised configuration
– Test plan to come
May 2004
Bernard Aboba, Microsoft
Slide 17
doc.: IEEE 802.11-04/0638r0
Submission
How Well do Virtual APs Scale?• Velayos & Karlsson “Techniques to Reduce
IEEE 802.11b Handover Time”, Swedish Royal Institute of Technology– http://www.it.kth.se/~hvelayos/papers/TRITA-IMIT-LCN%20R%2003-0
2%20Handover%20in%20IEEE%20802.pdf
May 2004
Bernard Aboba, Microsoft
Slide 18
doc.: IEEE 802.11-04/0638r0
Submission
Feedback?
