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Fragmenting Data for IEEE 802.11 Compatibility

Learn how to split large data into Separate Information Elements to adhere to IEEE 802.11-2012 standards and ensure compatibility. This technique involves creating a new Fragment IE to break down data in manageable sizes. Discover the importance of IE ordering and maintaining backward compatibility.

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Fragmenting Data for IEEE 802.11 Compatibility

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  1. Dan Harkins, Aruba Networks How To Fragment An IE Authors: • Date: 2013-05-14

  2. Dan Harkins, Aruba Networks Abstract • A technique to fragment data that is too large to fit in one IE is presented

  3. Dan Harkins, Aruba Networks IE Size Limitation • Section 8.4.2.1 of IEEE Std 802.11-2012 gives base format for an IE: • The Length field defines the length of the Information field • One octet Length means Information cannot be greater than 255 octets! • Some IEs have fixed components after the Length that further reduce the size of the Information field Element ID Length Information Octets: 1 1 variable

  4. Dan Harkins, Aruba Networks Public Key Definition in P802.11ai D0.5 Element ID Length Key Type FILS Public Key • With a Key Type component (indicates certificate or 2 kinds of raw public key), the public key is limited to 254 octets! • This may be acceptable for certain raw ECC public keys • Too small for acceptable FFC public keys • Too small for certificates (even those with ECC public keys) • Need some way to convey data > 255 octets using IEs that limit data to 255 octets! Octets: 1 1 1 variable

  5. Dan Harkins, Aruba Networks Fragmenting Data into Separate IEs • Use a new Fragment IE • Fragmented data is represented by the original IE into which the data would not fit (leading IE) followed by a series of 1 or more Fragment IEs that follow the IE Fragment ID Length Fragmented Data Octets: 1 1 variable

  6. Dan Harkins, Aruba Networks Fragmenting Data into Separate IEs 585 octets PK ID Len KT • For example directly following the PK IE (with length 255) are 2 FR IEs with lengths necessary to fragment the data • Reassembly stops when there are no more FR IEs KT PK ID 255 FR 255 FR FR 75

  7. Dan Harkins, Aruba Networks Backwards Compatibility • IEEE 802.11-2012 says in section 8.3.3.1 • IEs have a fixed order in a frame • IEs that are not understood are skipped over • Implications of IE ordering • Cannot rearrange order of existing IEs • New IEs can be defined to go in any order without affecting existing implementations • New IEs that can be fragmented are defined as such with a fixed order • Fragment IE is special • It uses the same order of the IE that is being fragmented • It will be skipped over by existing implementations

  8. Dan Harkins, Aruba Networks References • 11-13-0478-00-00ai-fragmenting-large-ies

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