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doc.: IEEE /0971r0 Submission Sept 2005 Jon Edney, Stefano Faccin, NokiaSlide 3 The SSID Original IEEE standard incorporated a trivially simple discovery mechanism based on a text string called the SSID Unformatted character field of up to 32 bytes which is usually constructed by ASCII characters
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Sept 2005
Jon Edney, Stefano Faccin, Nokia
Slide 1
doc.: IEEE 802.11-05/0971r0
Submission
Redefining the SSID
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Date: 2005-07-15
Name Company Address Phone email Jon Edney Nokia Cambridge, UK +441353648567 [email protected]
Stefano Faccin Nokia 3421 Dartmoor, Dallas, TX +1 972 894 4994 [email protected]
Authors:
Sept 2005
Jon Edney, Stefano Faccin, Nokia
Slide 2
doc.: IEEE 802.11-05/0971r0
Submission
Abstract
This submission proposes that the definition of the SSID should be expanded to a broader definition as appropriate to current practice and a new identifier “ESSID” strictly tied to the ESS should be defined.
Sept 2005
Jon Edney, Stefano Faccin, Nokia
Slide 3
doc.: IEEE 802.11-05/0971r0
Submission
The SSID
• Original IEEE802.11 standard incorporated a trivially simple discovery mechanism based on a text string called the SSID
• Unformatted character field of up to 32 bytes which is usually constructed by ASCII characters
Sept 2005
Jon Edney, Stefano Faccin, Nokia
Slide 4
doc.: IEEE 802.11-05/0971r0
Submission
“Correct use” of SSID
LAN HUB ROUTER LAN HUB
AP AP AP AP
SSID = “Net1” SSID = “Net2”
ESS
Sept 2005
Jon Edney, Stefano Faccin, Nokia
Slide 5
doc.: IEEE 802.11-05/0971r0
Submission
Problems with SSID
• SSIDs cannot be guaranteed unique• SSID value has no integrity• No specification for how to assign SSID default value• SSID does not scale to use in global networks
Sept 2005
Jon Edney, Stefano Faccin, Nokia
Slide 6
doc.: IEEE 802.11-05/0971r0
Submission
Importance of Legacy
• Cannot simply “replace” SSID• Hundreds of millions of legacy systems have behaviour
based on existing SSID• Any new system must be 100% backwards compatible
with simple SSID approach.
Sept 2005
Jon Edney, Stefano Faccin, Nokia
Slide 7
doc.: IEEE 802.11-05/0971r0
Submission
Current definition of SSID
• The standard says almost nothing about it:– 7.3.2.1 SSID element: The SSID element indicates the identity
of an ESS or IBSS.• The intent was that it should (uniquely) identify an ESS
to form a “roaming group” of APs• ESS is defined by layer 2 connectivity• But in practice most implementers use SSID as a
service identifier and reuse the same name across multiple ESSs - even without layer 2 connectivity
Sept 2005
Jon Edney, Stefano Faccin, Nokia
Slide 8
doc.: IEEE 802.11-05/0971r0
Submission
Current situation is a mess
• In the majority of cases the SSID is used incorrectly - based on it’s definition in the standard
• What to do?1. Write to everyone and tell them they are doing it wrong?
That won’t work!2. Adjust the definition of SSID to match current practice
That sounds dangerous - does it affect correct legacy implementations?
Sept 2005
Jon Edney, Stefano Faccin, Nokia
Slide 9
doc.: IEEE 802.11-05/0971r0
Submission
Modified Definition of SSID
• We propose that the definition is changed from:– “The SSID element indicates the identity of an ESS or IBSS.”
• to:– “The SSID element indicates the identity of an ESS a group of
ESSs or an IBSS.”
• This changes the definition to include current practice but does not affect legacy implementations that followed the “one SSID per ESS” rule
• But this still leaves a problem...
Sept 2005
Jon Edney, Stefano Faccin, Nokia
Slide 10
doc.: IEEE 802.11-05/0971r0
Submission
The need for an ESS identifier
• Since SSID is not used as an ESS identifier - and we are proposing to make this “official” - we need a new ESS identifier to allow intra-ESS roaming.
• Propose a new identifier to be included in beacons with the following information:– Unique ESS Address– ESS Name (text field)– Path Index(es)
Sept 2005
Jon Edney, Stefano Faccin, Nokia
Slide 11
doc.: IEEE 802.11-05/0971r0
Submission
Contents of ESS-ID (1)
• Unique ESS Address: a 48 bit value intended to uniquely define the ESS.– Default value can be AP’s BSSID. This ensures that AP will not
accidentally indicate membership of a roaming set unless configured.
– Value can be configure to match other APs when a roaming set is formed
– Possible recommended practice for “auto assignment” based on layer 2 broadcasts across the DS
Sept 2005
Jon Edney, Stefano Faccin, Nokia
Slide 12
doc.: IEEE 802.11-05/0971r0
Submission
Contents of ESS-ID (2)
• Name field– 32 octet field can be manually assigned to indicate ESS identity– default value is same as SSID
Sept 2005
Jon Edney, Stefano Faccin, Nokia
Slide 13
doc.: IEEE 802.11-05/0971r0
Submission
Contents of ESS-ID (3)
• Connectivity Index(es)– Each ESS can support multiple layer 2 connectivity paths.
• Could be VLANs• Could be multiple router ports (multiple IP subnets)• Could be service differentiation
– Same connectivity Index at two APs ensures that same layer2 connectivity is available at both APs
– Single octet index allows up to 256 paths to be advertised.– In short it tells the STA whether its IP address and/or VLAN
and/or service will become invalid when moving to a new ESS.
Sept 2005
Jon Edney, Stefano Faccin, Nokia
Slide 14
doc.: IEEE 802.11-05/0971r0
Submission
New ESS-ID Element
• New ESS-ID element to be carried in beacon and probe requests.
• ESS-ID element to be included in 802.11r to provide post-authentication verification that it was not modified or forged.
ESS Address ESS Name Path Index** Path Index
6 Octets 0 – 32 Octets 1-16 Octets
ENLn*
2
* EN Ln – length of ESS Name, 0 = ESS Name not present** First octet contains length
Sept 2005
Jon Edney, Stefano Faccin, Nokia
Slide 15
doc.: IEEE 802.11-05/0971r0
Submission
Mapping Service to ESSID
• If station knows ESSID it includes this is association request instead of SSID
• If station does not know correct ESSID to use it includes SSID in association request and AP returns ESSID in association response.– Useful for APs that support multiple SSIDs for different services
• Network assigned ESSID– Station provides service identifier at association– AP selects correct VLAN/IP subnet for service– AP sends value of ESSID in association response.
Sept 2005
Jon Edney, Stefano Faccin, Nokia
Slide 16
doc.: IEEE 802.11-05/0971r0
Submission
Summary of Proposal
1. Deprecate SSID to be service provider hint2. Provide new ESS-ID to enable reliable definition of
roaming groups3. ESS-ID provides hint about higher layer compatibility4. Provides post-verification of claimed ESS-ID can be
included to detect forged identity.5. Allows AP to support multiple service connectivies
and inform station at time of association
Sept 2005
Jon Edney, Stefano Faccin, Nokia
Slide 17
doc.: IEEE 802.11-05/0971r0
Submission
References
• 11-04-0614-00-frfh-what-ess.ppt• 11-05-0522-00-000u-ds-ess-subnet-and-vlan.ppt
