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TIM and Page Segmentation

TIM and Page Segmentation. Authors:. Date: 2012-09-17. Authors:. Authors:. Introduction. Based on the AID hierarchical addressing [1], a Page consists of multiple blocks (e.g., 32) A page segment may refer to an ordered range of blocks (e.g., 8) out of all blocks in one Page

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TIM and Page Segmentation

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  1. TIM and Page Segmentation Authors: Date: 2012-09-17 Chittabrata Ghosh, Nokia

  2. Authors: Chittabrata Ghosh, Nokia

  3. Authors: Chittabrata Ghosh, Nokia

  4. Introduction • Based on the AID hierarchical addressing [1], a Page consists of multiple blocks (e.g., 32) • A page segment may refer to an ordered range of blocks (e.g., 8) out of all blocks in one Page • TIM segmentation is accepted in 802.11ah specification framework supporting a subset of STAs per TIM segment • Need a mechanism for assignment of page segments among multiple TIM segments • Indication of such assignment to STAs in allocated page segments Chittabrata Ghosh, Nokia

  5. Motivation • STAs waking up in DTIM for group addressed frames are assigned in subsequent TIM segments for unicast (DL/UL) traffic • Challenge – Indication of subset of STAs assigned to each TIM segment • Within assigned page segment in a TIM segment, intermediate blocks may not have buffered data at AP • STAs with no UL data in such blocks need to still wake up at assigned TIM segment • We propose to introduce a Segment Count IE in DTIM beacon frame to indicate length of page segment assigned to TIM segments • We propose a mechanism for early indication of buffered data per block Chittabrata Ghosh, Nokia

  6. Page Segmentation • We propose to have a fixed length page segment per TIM segment within one DTIM beacon interval • Length of page segment may vary over multiple DTIM beacon intervals • Length of page segment = (Number of blocks in one page / number of TIM segments in DTIM beacon interval) • Each ordered page segment is assigned sequentially to TIM segments, first page segment being assigned to DTIM segment Ordered Blocks in Page 1 Page Segment 2 Page Segment 1 Page Segment N TIM Segment 1 (DTIM) TIM Segment 2 TIM Segment N Chittabrata Ghosh, Nokia

  7. Page Bitmap for Power Save • Block level indication of buffered traffic in DTIM beacon frame • STAs with its corresponding block bit set to 0 go back to sleep after decoding DTIM beacon frame and may not wake up at assigned TIM segment • Page Bitmap field for buffered traffic indication of blocks in assigned page segments for all TIM segments in DTIM beacon interval • This field may be indicated in Segment Count IE • The first block in Page Bitmap corresponds to Page offset in segment count IE • The terminal block in Page Bitmap corresponds to end block in last assigned page segment • Size of Page Bitmap varies between 0 – 4 octets (assuming a maximum of 32 blocks in one Page) Chittabrata Ghosh, Nokia

  8. Frame Format for Segment Count IE • The segment count IE (4-8 octets) shall consist of the following fields: • Element ID (1 octet): Identification of the segment count IE • Length (1 octet): Length of this IE • Page Index (2 bits): Indication of page currently assigned in beacon • Page Segment Count (5 bits) field indicating number of TIM segments; for instance, • A value of 4 indicates 4 TIM segments in DTIM beacon interval • A value of 8 indicates 8 TIM segments in DTIM beacon • Page Offset (5 bits) field indicating the first block in assigned page segments • Reserved (4 bits): Reserved bits for future use • Page Bitmap (0- 4 octets) field for blocks of all page segments in DTIM element Element ID Length Page Index Page Segment Count Page Offset Reserved Page Bitmap Chittabrata Ghosh, Nokia

  9. Segment Count IE in Beacon • Segment count IE is only transmitted in DTIM beacon frames and not in TIM segments • This element indicates assignment of STAs in TIM segments • Indicates wake-up interval for STAs within page segments • STAs within the assigned page segment wake up at corresponding TIM segment sequentially based on the page segment count field in the IE • Length of page segment = (Number of blocks in Page Bitmap /page segment count) • Page offset and Page segment count fields in the segment count IE indicate initial block offset and range of TIM element in each TIM segment • Block offset / start = page offset + ((length of page segment) * (TIM segment number -1)) + 1 • Block Range = page offset + length of page segment * TIM segment number • STAs with their block bit set to 0 in Page Bitmap field may not wake up at assigned TIM segment Chittabrata Ghosh, Nokia

  10. TIM IE • In Extend Spec Framework: • R.4.3.1.B: When the complete traffic indication bitmap is divided into multiple segments, each segment shall indicate the range of the AIDs (bitmap) it is covering • Proposal: include the TIM Segment Number field in TIM IE • TIM Segment Number field (5 bits): indicates the index of the TIM Segment • The TIM bitmap information covered in the TIM IE is calculated as follows: • TIM segment start = page offset + ((length of page segment) * (TIM segment number -1)) + 1 • TIM segment end = page offset + length of page segment * TIM segment number Bitmap control (1 octet) Element ID Length DTIM Count DTIM Period TIM Segment Number (n) R Page Index Partial Virtual Bitmap (TIM Segment bitmap) 1 octet 1 octet 5 bit 1 bit 2 bit 1 octet 1 octet Chittabrata Ghosh, Nokia

  11. TIM Segmentation Illustration • Segment Count IE indicates assignment of page segments in following TIM segments Page (2048 STAs) in 1 DTIM Interval Beacon Page Segment 2 (512 STAs) Page Segment 3 (512 STAs) Page Segment 4 (512 STAs) Page Segment 1 (512 STAs) Page Segment Count = 4 Length of Page Segment Page Offset Short Beacon TIM Segment Number = 4 Short Beacon TIM Segment Number = 2 Short Beacon TIM Segment Number = 3 Segment Count IE for STAs in all Page Segments Page Segment 4 Page Segment 2 Page Segment 3 Page Segment 1 Chittabrata Ghosh, Nokia

  12. Summary • We proposed to introduce a segment count IE in DTIM beacon frame in order to indicate length of page segments assigned to TIM segments • We proposed to have a Page Bitmap field in segment count IE for early indication of buffered data for blocks in assigned page segments • We proposed to add the TIM Segment Number field in TIM IE Chittabrata Ghosh, Nokia

  13. Reference [1] TGah Efficient TIM Encoding, doc. IEEE 802.11-12/388r0 Chittabrata Ghosh, Nokia

  14. Straw Poll 1 • Do you agree to have a fixed length page segment per TIM segment as described in Slide 4? Chittabrata Ghosh, Nokia

  15. Straw Poll 2 • Do you agree to introduce a Page Bitmap field for early indication of block-level buffered data? Chittabrata Ghosh, Nokia

  16. Straw Poll 3 • Do you agree to have a Segment Count IE as in Slide 7 for indication of assignment of STAs in TIM segments? Chittabrata Ghosh, Nokia

  17. Straw Poll 4 • Do you agree to have the frame format for the Segment Count IE as shown in Slide 6? Chittabrata Ghosh, Nokia

  18. Straw Poll 5 • Do you agree to include the TIM Segment Number field in the TIM IE as shown in Slide 8? Chittabrata Ghosh, Nokia

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