1. Coexistence of Legacy & RSN STAs in Public WLAN
Month 2003
Coexistence of Legacy & RSN STAs in Public WLAN
Byoung-Jo “J” Kim
AT&T Labs-Research
March ‘03, Dallas

2. Purpose A Twist in Public Access Scenario:
Month 2003
Purpose
A Twist in Public Access Scenario:
Must Support “Simultaneously”
Legacy STAs with WEP off
For various reasons, at least for a while
RSN (or WPA) STAs
For privacy protection if STAs capable
Not a requirement for PWLAN in general: You should assume you’re on your own.
But Use it if available: Must do more for customers for their protection.

3. Month 2003
Possible Solutions
Shares many issues with doc by Bernard Aboba, and Also maybe a special case of TSN
Use Two SSIDs with Two Radios
Use Two SSIDs with a Single Radio
Common implementation has Primary SSID in Beacon, others Revealed with Probe
Problems: Refer to
Most importantly: Two SSID may confuse people
Trying to build a “consumer” service.
Preference toward single SSID
Risk to Network is accepted factor of any ISP

4. Possible Solutions: continued
Month 2003
Possible Solutions: continued
Single SSID: Beacon with Privacy off and RSN IE included
No problem with Legacy STAs
Not Sure How RSN STAs will behave
Not a valid option in Draft 3.1
Capability Information field
Add the following paragraphs to Clause :
STAs (including APs) that include the RSN IE in beacons and probe responses shall set the Privacy subfield to 1 in any frame that includes it.
Attempt to associate, auth via 1x and run RSN? Good!
Don’t even try to associate since Privacy bit is OFF?

5. TSN Policy does not cover this case
Month 2003
TSN Policy does not cover this case
TSN policy selection
<<snip snip>>
If an AP operating within a TSN receives a (Re)association request without an RSN IE, it shall allow communications only if a WEP key has been configured to secure communication. If a WEP key is not installed, the AP shall reject the association request; if a WEP key is configured, the AP may accept the request.

6. Observations with “one” current HW
Month 2003
Observations with “one” current HW
Setup:
Beacon WEP off, Some STAs configured to use 1x authentication/key exchange and Some configured no WEP. All Pre-RSN/WPA
Broadcast unencrypted by AP if non-1x STA present
No-WEP STAs associate and work fine
Some 1x STA models won’t even try to send assoc-req
Most do and associate/authenticate successfully
Some do accept unencrypted broadcast like DHCP
Some do not
Some 1x STA broadcast unencrypted but refuse reception

7. Month 2003
Broadcast/Multicast
ARP for gateway, DHCP, etc are necessary for service
STA to AP is no problem, whether encrypted or not
AP can be smart about whether to encrypt or not by keeping track of the interactions.
May need to look at the IP payload, since many sloppy implementations use Broadcast addresses even when unicast address can be known, just based on the IP protocol type.
Peer-to-peer in BSS cannot be charged: APs may be configured to drop direct communication between STAs

8. Month 2003
Suggestions
Make “Beacon/Probe Privacy OFF” with RSN IE” a legitimate mode, a particular mode of TSN?
Specify STA behaviors for this Case
“Attempt RSN operation based on RNS IE only, regardless of WEP bit”?
Specify what to do with broadcast/multicast traffic