Transcript - IEEE Mentor

May 2004
doc.: IEEE 802.11-04/0638r0
Network Selection
Bernard Aboba
Microsoft
http://www.ietf.org/internet-drafts/draft-ietf-eap-netsel-problem-00.txt
Submission
Slide 1
Bernard Aboba, Microsoft
May 2004
doc.: IEEE 802.11-04/0638r0
Outline
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•
•
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Problem Definition
Current Work Items
Virtual APs
Summary
Submission
Slide 2
Bernard Aboba, Microsoft
May 2004
doc.: IEEE 802.11-04/0638r0
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
Submission
Slide 3
Bernard Aboba, Microsoft
May 2004
doc.: IEEE 802.11-04/0638r0
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!
Submission
Slide 4
Bernard Aboba, Microsoft
May 2004
doc.: IEEE 802.11-04/0638r0
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
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–
Submission
How to route payload traffic in the right way
Filters and mandatory tunnels
Slide 5
Bernard Aboba, Microsoft
May 2004
doc.: IEEE 802.11-04/0638r0
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
Submission
Slide 6
Bernard Aboba, Microsoft
May 2004
doc.: IEEE 802.11-04/0638r0
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.
Submission
Slide 7
Bernard Aboba, Microsoft
May 2004
doc.: IEEE 802.11-04/0638r0
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?
Submission
Slide 8
Bernard Aboba, Microsoft
May 2004
doc.: IEEE 802.11-04/0638r0
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
Submission
Slide 9
Bernard Aboba, Microsoft
May 2004
doc.: IEEE 802.11-04/0638r0
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…
Submission
Slide 10
Bernard Aboba, Microsoft
May 2004
doc.: IEEE 802.11-04/0638r0
IETF Work In Network Selection
1. Access Network Discovery
–
No chartered work yet
2. 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
Submission
Slide 11
Bernard Aboba, Microsoft
May 2004
doc.: IEEE 802.11-04/0638r0
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
Submission
Slide 12
Bernard Aboba, Microsoft
May 2004
doc.: IEEE 802.11-04/0638r0
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.
Submission
Slide 13
Bernard Aboba, Microsoft
May 2004
doc.: IEEE 802.11-04/0638r0
Is It “Virtual” Or Is It Real?
Only Your Radio Knows For Sure!
Physical APs
Beacon/Probe
SSID: Bar
Response
BSSID: B
Rates: 1,2,5.5,11
Security: Open
Channel 6
AP B
Channel 6
STA
SSID: Foo
BSSID: A
Rates: 5.5,11
Security: WPA
AP A
Virtual APs
SSID: Bar
BSSID: B
Rates: 1,2,5.5,11
Security: Open
Channel 6
SSID: Foo
BSSID: A
Rates: 5.5,11
Security: WPA
AP A
Submission
Slide 14
Bernard Aboba, Microsoft
May 2004
doc.: IEEE 802.11-04/0638r0
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.
Submission
Slide 15
Bernard Aboba, Microsoft
May 2004
doc.: IEEE 802.11-04/0638r0
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
Submission
Slide 16
Bernard Aboba, Microsoft
May 2004
doc.: IEEE 802.11-04/0638r0
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%200302%20Handover%20in%20IEEE%20802.pdf
Submission
Slide 17
Bernard Aboba, Microsoft
May 2004
doc.: IEEE 802.11-04/0638r0
Problems with IEEE 802.1 Solutions
• IEEE 802.1ab only supports “announcements”,
not request/response
– Designed as an IEEE 802.1 “slow protocol”
• IEEE 802.1af Discovery not oriented towards
wireless
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–
–
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Submission
Does not address rate negotiation issue
May not support existing 802.11 Information Elements
In pre-auth, APs from other networks are not reachable
Unlikely to be implemented on 802.11 APs
Slide 18
Bernard Aboba, Microsoft
May 2004
doc.: IEEE 802.11-04/0638r0
Recommendations
• Work needed on enhanced scaling for network discovery
• Existing Beacon/Probe mechanism does not scale
– Problem with increasing dynamic range of rates
– Problem with large number of Virtual APs
– Problem with increasing Beacon/Probe Response size
• Work in progress does not address discovery issues
– Discovery of APs whose Beacons cannot be heard
• IEEE 802.11k Site Report only supports discovery of APs within the
same administrative domain
• Existing IEEE 802 work does not address the problem
– IEEE 802.1ab, IEEE 802.af oriented toward wired, not wireless
networks
Submission
Slide 19
Bernard Aboba, Microsoft
May 2004
doc.: IEEE 802.11-04/0638r0
Feedback?
Submission
Slide 20
Bernard Aboba, Microsoft