1. Network Discovery Mechanism
March 2006
doc.: IEEE /xxxxx
May 2006
Network Discovery Mechanism
Date:
Authors:
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Dave Cavalcanti and Amjad Soomro, Philips
Dave Cavalcanti and Amjad Soomro, Philips

2. March 2006
doc.: IEEE /xxxxx
May 2006
Abstract
This submission proposes a mechanism to enable STA to discover multiple SSPNs supported by an AN, and to identify the services provided.
Addresses requirements N1, N3 and N4 of the Network Selection Cluster.
Dave Cavalcanti and Amjad Soomro, Philips
Dave Cavalcanti and Amjad Soomro, Philips

3. Outline Requirements overview Analysis of possible solutions
March 2006
doc.: IEEE /xxxxx
May 2006
Outline
Requirements overview
Analysis of possible solutions
Proposed network discovery mechanism
Conclusions
Dave Cavalcanti and Amjad Soomro, Philips
Dave Cavalcanti and Amjad Soomro, Philips

4. Requirements Overview
March 2006
doc.: IEEE /xxxxx
May 2006
Requirements Overview
N1: Define functionality by which a STA can determine whether its subscription to an SSPN would allow it to access a particular AN before actually joining a BSS within that AN. Proposals must describe their consideration of scalability.
It’s not acceptable for a STA to be required to attempt IEEE 802.1X authentication with all available networks until it finds one that works. Equally a solution is not practical if it requires every possible credential supplier to be listed in a beacon (due to scalability problems).
Dave Cavalcanti and Amjad Soomro, Philips
Dave Cavalcanti and Amjad Soomro, Philips

5. Requirements Overview (cont.)
March 2006
doc.: IEEE /xxxxx
May 2006
Requirements Overview (cont.)
N3: Define functionality to support authentication with multiple SSPNs through a single AP.
N4: Define functionality by which a STA can determine which interworking services are available before joining a BSS.
Dave Cavalcanti and Amjad Soomro, Philips
Dave Cavalcanti and Amjad Soomro, Philips

6. Foreign SSPNs with roaming agreements
March 2006
doc.: IEEE /xxxxx
May 2006
Key Issues
Access Network (AN):
How AP advertises SSPNs and supported internetworking service types?
Wireless Station (STA):
How STA gets information to enable efficient selection of one or more SSPN to authenticate to?
Supported SSPNs
Services available
SSPN 1 A
SSPN 2 B
SSPN 3 C AP
How to advertise the supported SSPNs and services?
Home SSPN
Foreign SSPNs with roaming agreements
SSPN 1
SSPN 2
STA
Which SSPNs are supported?
Which services are available?
Which SSPN or SSPNs to select for authentication?
Dave Cavalcanti and Amjad Soomro, Philips
Dave Cavalcanti and Amjad Soomro, Philips

7. Summary of Existing Solutions
March 2006
doc.: IEEE /xxxxx
May 2006
Summary of Existing Solutions
Information Elements (IE) have been proposed to carry network discovery related information
The IEs would be transmitted in
Beacons (passive discovery)
Probe responses (active discovery)
Combine beacons and probe response to advertise the whole information
Network discovery related information may include:
SSPN Id
Service types …
Different proposals define distinct information fields, but in general, the IE carries information relevant to network selection and authentication
Dave Cavalcanti and Amjad Soomro, Philips
Dave Cavalcanti and Amjad Soomro, Philips

8. Analysis of Existing Solutions
March 2006
doc.: IEEE /xxxxx
May 2006
Analysis of Existing Solutions
Passive discovery
AP broadcasts all network discovery information in a single IE added in every beacon
STA listens to beacons and discovers supported SSPNs and services
Not practical, too much overhead
Active discovery
To check availability of each SSPN, a STA probes AP and AP sends info related to that SSPN
Less overhead, but STA has to contend for channel to transmit probe and wait for response, which consumes more power
Efficient if STA is searching for a specific SSPN,
but what happens if STA can use several SSPNs and/or wants to discover all options available (SSPNS and services)?
STA has to probe the AP several times, resulting in higher power consumption and overhead
Use Case: Search for best option (on-the-spot best SSPN selection/pay per use scenario)
Dave Cavalcanti and Amjad Soomro, Philips
Dave Cavalcanti and Amjad Soomro, Philips

9. Analysis of Existing Solutions (Cont.)
March 2006
doc.: IEEE /xxxxx
May 2006
Analysis of Existing Solutions (Cont.)
Combined passive and active discovery
AP transmits a small (partial) list of SSPNs supported in beacons
To get a complete list, a STA has to probe AP
Less fixed overhead, but STA is forced to use active probes if it wants to discover all possibilities
Dave Cavalcanti and Amjad Soomro, Philips
Dave Cavalcanti and Amjad Soomro, Philips

10. Proposed Network Discovery Mechanism
March 2006
doc.: IEEE /xxxxx
May 2006
Proposed Network Discovery Mechanism
Objectives:
Provide a solution that is applicable to different scenarios:
Users trying to discover if a specific SSPN or service type is supported by a AN
Users trying to discover all connectivity options (SSPNs and inter-working services) available
Allow the AN to control the overhead that can be introduced by network discovery related information
Allow the STA to decide how to collect network discovery information
Dave Cavalcanti and Amjad Soomro, Philips
Dave Cavalcanti and Amjad Soomro, Philips

11. Overview of the proposal
March 2006
doc.: IEEE /xxxxx
May 2006
Overview of the proposal
The AN fully supports both passive and active discovery
All network discovery related information can be obtained using
Passive discovery (only),
Active discovery (only), or
Combined Passive/Active discovery
A new passive discovery mechanism is proposed in which the network discovery related information is advertised over a period of time, called Network Discovery (ND) interval
The ND interval is controlled by the AN, and may span across multiple beacon frames
Dave Cavalcanti and Amjad Soomro, Philips
Dave Cavalcanti and Amjad Soomro, Philips

12. Overview of the proposal
March 2006
doc.: IEEE /xxxxx
May 2006
Overview of the proposal
A STA decides which method to use, for example,
If a STA wants to discover all SSPNs supported by the AN, it may choose to use only passive discovery, and it is able to get all information by just listening to beacon frames
If a STA is searching for a particular SSPN it may choose to directly use active discovery and probe the AN
If a STA is searching for a particular SSPN it may try to use passive discovery, but if the desired information is not received within a certain period of time, it may use active discovery
Decision algorithm is out of the scope of the standard
Dave Cavalcanti and Amjad Soomro, Philips
Dave Cavalcanti and Amjad Soomro, Philips

13. New Passive Discovery Mechanism
March 2006
doc.: IEEE /xxxxx
May 2006
New Passive Discovery Mechanism
The overall ND information is advertised using one or more ND Information Elements (ND IE)
Each beacon carries one ND IE
The time needed to advertise the whole ND information is called ND interval
AN controls the ND interval and the amount of information per ND IE
Dave Cavalcanti and Amjad Soomro, Philips
Dave Cavalcanti and Amjad Soomro, Philips

14. Network Discovery IE (ND IE)
March 2006
doc.: IEEE /xxxxx
May 2006
Network Discovery IE (ND IE)
Element ID
Length
ND Counter
SSPN Counter
SSPN Information (Variable)
SSPN Record 1 …
SSPN Record n 1 ?
Octets:
ND Counter : Number of ND IEs (beacons) expected until the beginning of the next ND interval
SSPN Counter : Number of different SSPNs advertised in this ND IE
SSPN Record: Includes the SSPN information to be advertised
Dave Cavalcanti and Amjad Soomro, Philips
Dave Cavalcanti and Amjad Soomro, Philips

15. SSPN Record Information in this record may be used to address
March 2006
doc.: IEEE /xxxxx
May 2006
SSPN Record
Information in this record may be used to address
Network selection cluster requirements: N1, N2, and N4
Online enrolment cluster requirements: E1 and E4
SSPN ID
SSPN_Info 2
Octets: B0 B3 B4 B5 B6 B7 B8 B9
B15
Service Type
Charge Method
Enrollment Method
Emergency service
Reserved
SSPN_Info
Bits: 4 2 2 1 7
Dave Cavalcanti and Amjad Soomro, Philips
Dave Cavalcanti and Amjad Soomro, Philips

16. SSPN Info Service type field could combine information about: May 2006
March 2006
doc.: IEEE /xxxxx
May 2006
SSPN Info
Service type field could combine information about:
Type of high level connectivity available,
Internet or local access
Type of MAC service supported,
Distributed access (DCF or EDCA)
Controlled access (HCCA)
Distributed and controlled access (EDCA and HCCA)
Code
Description
0000
Open Internet access with distributed MAC access
0001
Internet access with enrollment required and controlled MAC access
0010
Internet and Private access with enrolment required and distributed and controlled MAC access
0011
Private local access with enrollment required with distributed MAC access
Dave Cavalcanti and Amjad Soomro, Philips
Dave Cavalcanti and Amjad Soomro, Philips

17. Charge /Enrolment/Emergence services
March 2006
doc.: IEEE /xxxxx
May 2006
Charge /Enrolment/Emergence services
Charge Method
Enrolment Method
Code
Description 00
Free 01
Charged per time 10
Charged per transferred bytes 11
Reserved
Code
Description 00
Method 1 01
Method 2 10 … 11
Emergency Service field
0 : No support to emergence services from this AN
1 : Emergence service supported by SSPN from this AN
Dave Cavalcanti and Amjad Soomro, Philips
Dave Cavalcanti and Amjad Soomro, Philips

18. New attributes for the 802.11 MAC MIB
March 2006
doc.: IEEE /xxxxx
May 2006
New attributes for the MAC MIB
Attribute
Description
dot11NDThreshold
Indicates the maximum number of octets that can be used to advertise ND Information within a beacon period
dot11SSPNTable
A table of attributes for all supported SSPN that needs to be advertised in the SSPN Records
dot11SSPNNumber
The number entries in the dot11SSPNTable
dot11NDInterval
This is the number of beacon periods (or ND IEs) used to advertise all SSPN Records at least once
Dave Cavalcanti and Amjad Soomro, Philips
Dave Cavalcanti and Amjad Soomro, Philips

19. ND Interval The dot11NDInterval can be computed as:
March 2006
doc.: IEEE /xxxxx
May 2006
ND Interval
The dot11NDInterval can be computed as:
Assuming 4 bytes per SSPN Record and 4 bytes of fixed overhead per ND IE
By adjusting the dot11NDThreshold the AP can control how the ND information is advertised
Under low traffic loads, AP can use a higher dot11NDThreshold and add more information per beacon
Under higher loads, AP can reduce dot11NDThreshold, send less information added in each beacon and increases the ND interval
Dave Cavalcanti and Amjad Soomro, Philips
Dave Cavalcanti and Amjad Soomro, Philips

20. dot11SSPNTable May 2006 dot11SSPNTableEntry Type dot11SSPNTableIndex
March 2006
doc.: IEEE /xxxxx
May 2006
dot11SSPNTable
dot11SSPNTableEntry
Type
dot11SSPNTableIndex
Integer
dot11SSPNTableSSPNId
Octet String
dot11SSPNTableServiceType
dot11SSPNTableChargeMode
dot11SSPNTableEnrolment
TruthValue
dot11SSPNTableEmergenceServ
Dave Cavalcanti and Amjad Soomro, Philips
Dave Cavalcanti and Amjad Soomro, Philips

21. Processing a ND IE (Scenario 1) STA is searching for a specific SSPN:
March 2006
doc.: IEEE /xxxxx
May 2006
Processing a ND IE
(Scenario 1) STA is searching for a specific SSPN:
Checks whether the desired SSPN is advertised in the ND IE (STA uses SSPN Id field in SSPN Records)
If found desired SSPN, STA reads SSPN Info field from the corresponding SSPN Record
If SSPN was not found, STA can decide to wait for the next ND IE or it can use Active probe
In the first case, STA could enter the power save mode until next beacon
In the second case, STA contends for the channel to transmit a probe request
Decision algorithm can use the ND Counter field in the ND IE,
but algorithm is out of the scope of the standard
Dave Cavalcanti and Amjad Soomro, Philips
Dave Cavalcanti and Amjad Soomro, Philips

22. Processing a ND IE (Scenario 2) STA can use several SSPNs
March 2006
doc.: IEEE /xxxxx
May 2006
Processing a ND IE
(Scenario 2) STA can use several SSPNs
STA reads the first ND IE and based on the ND Counter and on the received SSPN Records, it decides whether to select one of the SSPNs in the ND IE
If STA selects a SSPN from the first ND IE, it tries to authenticate with it
Otherwise, STA decides whether it can wait for the next ND IE or it should use active probe
If ND Counter is small and delay is not a main concern, the STA could wait for the next ND IE
If delay is a major requirement, depending on the ND counter, the STA may choose to probe the AN.
If STA decides to wait for the next ND IE, it can enter Power Save mode until next TBT
Dave Cavalcanti and Amjad Soomro, Philips
Dave Cavalcanti and Amjad Soomro, Philips

23. Advantages of the proposed solution
March 2006
doc.: IEEE /xxxxx
May 2006
Advantages of the proposed solution
Provides flexibility to AP and STAs
AP can control advertisement of ND information
STA can choose which method to use (active or passive)
Active scanning can still be used, if STAs doesn’t want to wait for several beacons to discover all possibilities
Provides a compromise between discovery delay and channel utilization
Small dot11NDThreshold  large discovery delay, but less overhead (higher channel utilization)
Large dot11NDThreshold  smaller discovery delay, but higher overhead (less channel utilization)
dot11NDThreshold and dot11NDInterval can be configured at the network set up or they can be dynamically adjusted
How to configure and/or adjust these attributes is out of the scope of the standard
Dave Cavalcanti and Amjad Soomro, Philips
Dave Cavalcanti and Amjad Soomro, Philips

24. Analysis of power requirement (G1)
March 2006
doc.: IEEE /xxxxx
May 2006
Analysis of power requirement (G1)
Operation can be adjusted to different scenarios and power saving requirements
If STA chooses to obtain all information from ND IEs sent in beacons (passive scanning only)
Usually, STAs are required to wakeup to receive beacons, therefore the passive discovery does not significantly affect power consumption
Passive discovery consumes less power than if STA has to probe the AN for every connectivity option available
If STA chooses to use active scanning, power consumption will depend on the channel conditions and number of probe requests generated
Dave Cavalcanti and Amjad Soomro, Philips
Dave Cavalcanti and Amjad Soomro, Philips

25. Analysis of security requirements (G2)
March 2006
doc.: IEEE /xxxxx
May 2006
Analysis of security requirements (G2)
As in other proposed solutions, advertised information (SSPN IDs and supported services) could be protected
For example, using Hash functions to define SSPN ID and service type code
STAs would hash the names of the SSPNs in their supported list and compare the result with the SSPN ID in the ND IE
Only STAs that know the service types would be able to detect the supported service types
Still vulnerable to attacks, but it is not worse than current solutions
Dave Cavalcanti and Amjad Soomro, Philips
Dave Cavalcanti and Amjad Soomro, Philips

26. March 2006
doc.: IEEE /xxxxx
May 2006
Conclusions
Proposed network discovery mechanism addresses requirements N1, N2 and N4
Information provided in the ND IE can also be used to address requirement N3
Proposed mechanism can also be used to advertise
Charge method (N5)
Support to online enrolment (E1, E2 and E4)
Support to emergency services (I1)
This is a flexible solution that can be adjusted to achieve a compromise between overhead in beacons, discovery time and channel utilization
Specific algorithms for STA and AN are not provided (out of the scope)
Dave Cavalcanti and Amjad Soomro, Philips
Dave Cavalcanti and Amjad Soomro, Philips