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IE Propagation in an IBSS

IE Propagation in an IBSS. 11.1.4 says “ In an IBSS, a STA shall always adopt the information in the contents of a Beacon or Probe Response frame when that frame contains a matching SSID and the value of the time stamp is later than the STA’s TSF timer.”

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IE Propagation in an IBSS

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  1. IE Propagation in an IBSS • 11.1.4 says “In an IBSS, a STA shall always adopt the information in the contents of a Beacon or Probe Response frame when that frame contains a matching SSID and the value of the time stamp is later than the STA’s TSF timer.” • But what if the STA doesn’t understand some of the information in the Beacon? Mike Moreton, Synad Technologies

  2. Current Situation • The current standard does not specify behaviour of STAs joining an IBSS where the beacon includes IEs that it doesn’t understand. • We should define this behaviour to promote interoperability. • Some options follow. Mike Moreton, Synad Technologies

  3. (1) Don’t Join • “A STA should not join an IBSS where the received beacons include an IE which it doesn’t understand”. • Pros: • Well defined behaviour. • Cons: • Pretty much prevents interoperation between STAs supporting different versions of the standard. Mike Moreton, Synad Technologies

  4. (2) Copy Them • “When joining an IBSS a STA should copy all IEs from the received beacon that it doesn’t understand, and replicate them in its own beacons.” • Pros: • The STA that starts the IBSS has complete control over the BSS configuration. • Cons: • A STA may be sending out IEs that it doesn’t understand (including proprietary ones). Need to be careful that new beacon IEs can be copied in this way. Mike Moreton, Synad Technologies

  5. (3) Ignore Them • “When a STA joins an IBSS it should save only the IEs that it can understand, and replicate them in its own beacons.” • Pros: • STA is only sending stuff out that it understands. • Cons: • IBSS wide configuration can be lost as a result. For example, in TGi, a single legacy station joining could cause the IE indicating use of a broadcast CCM cipher suite to be lost, hence preventing interoperation. Mike Moreton, Synad Technologies

  6. (4) Mark Them • Use the high-order bit of the element ID to indicate “discardable”. IEs with this bit set may be discarded by the joining STA if it doesn’t understand them. If there are any IEs without this bit set, and the joining station does not understand them, then it may not join the IBSS. • Pros: • Allows greater control over the capabilities of stations admitted to the IBSS. • Cons: • Companies using proprietary element ids that are less than 128, or are 128 greater than a legal element need to move them. In practice, we need to define a standard method for companies to use proprietary ids. • Coalescing IBBSes can cause one IBSS to stop operation. Mike Moreton, Synad Technologies

  7. Capabilities • There is the same problem with capability bits, and the same solutions. • The “mark them” option would require a new “discardable capabilities” IE. Mike Moreton, Synad Technologies

  8. Straw Ballot • Which of the following techniques for IE propagation in an IBSS do you favour? • (1) Don’t Join • (2) Copy Them • (3) Ignore Them • (4) Mark Them • None of the above/Don’t Know/Abstain Mike Moreton, Synad Technologies

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