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Project: IEEE P802.15 Working Group for Wireless Personal Area Networks (WPANs)

Overview of MAC layer packet fragmentation proposal to improve IP support, efficiency, and layer independence in 802.15.4 architecture. Proposal includes goals, technical concepts, and related efforts.

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Project: IEEE P802.15 Working Group for Wireless Personal Area Networks (WPANs)

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  1. Project: IEEE P802.15 Working Group for Wireless Personal Area Networks (WPANs) Submission Title: [MAC Layer MSDU Fragmentation Proposal Overview] Date Submitted: [27 June, 2008] Source: [Benjamin A. Rolfe] Company [Blind Creek Associates] Address [] Voice:[+1.408.395.7207] E-Mail:[ben@blindcreek.com] Re: [] Abstract: Discussion of a proposal to add MAC layer packet fragmentation. Purpose: To stimulate discussion I task group 15.4e Notice: This document has been prepared to assist the IEEE P802.15. It is offered as a basis for discussion and is not binding on the contributing individual(s) or organization(s). The material in this document is subject to change in form and content after further study. The contributor(s) reserve(s) the right to add, amend or withdraw material contained herein. Release: The contributor acknowledges and accepts that this contribution becomes the property of IEEE and may be made publicly available by P802.15. Ben Rolfe

  2. MAC Layer Fragmentation Technical Overview Benjamin A. Rolfe ben@blindcreek.com Ben Rolfe

  3. Summary/Contents • Purpose • Goals • Fitting the 802.15.4 Architecture • Scope • Technical Concept (9) • Related MAC Efforts Ben Rolfe

  4. Purpose • Better support for IP • Upper layer fragmentation support • ZigBee, 6LoWPAN, ISA100-11a • Efficiency to be gained with MAC help • Better layer independence Ben Rolfe

  5. Goals • Better control of timing between fragment frames • Lower overhead when fragmentation is needed • More consistent behavior and performance. • Ability to interrupt and/or insert (interleave) other higher priority packets in the midst of a fragmented series (if the MAC has a concept of priority). • Better match between higher layer protocols such as IP (and heterogeneous networks). Ben Rolfe

  6. Frame Sizes, 15.4-2006 802.15.4-2006 PHY Frame 802.15.4-2006 MAC Frame, General Format Ben Rolfe

  7. Fitting the 802.15.4 Architecture • Simple and Low Cost • Easily realizable in silicon, firmware • MAC • Improve PHY access mechanisms • Improve efficiency of data service • Higher Layers; • Policy (intelligence) decisions Ben Rolfe

  8. Scope • MAC-SAP (NHL Interface) • Control parameters (SAP, PIB) • Max MSDU > 1 PSDU payload • New indications • MAC Frames • MAC Procedures • Related MAC features Ben Rolfe

  9. Technical Concept (1) • MSDU size independent of PHY • Fragmentation control parameters • Minimal fragmentation overhead • Sequence control • ACK, Retry Ben Rolfe

  10. Technical Concept (2) • MSDU size independent of PHY • Implementation/resource dependent • aMaxMACSafePayloadSize • Change: Make independent of PHY payload size • Remains consistent with existing 15.4 • Minimal upper layer impact • Make visible to NHL (PIB attribute?) Ben Rolfe

  11. Technical Concept (3) • Fragmentation control parameters • MCPS-SAP (per MSDU) • M-PIB (Global) • Smarts belong in upper layers Ben Rolfe

  12. Technical Concept (4) Fragmentation Control Parameters Ben Rolfe

  13. Technical Concept (5) • Reference higher layer Packet Sizes: • Min IPv6 == 1280 • Max IPv6 == 65575 • 802.3 MTU == 1518 Ben Rolfe

  14. Technical Concept (6) • Minimal fragmentation overhead • More (or Last) bit • Retry bit • Fragment number (tag) • (10 bits == Max IP, 5 bits == 802.3 MTU) • Fragment “header” could be 8 bits Ben Rolfe

  15. Technical Concept (7) • Sequence control • Higher Priority Interrupt • Abandon fragmented exchange, start over • Suspend fragmented exchange, continue • Can’t interrupt first two (need some restrictions to keep it simple and efficient) • Receive side • Suspend (requires more memory) • Maintain fragments que • Accept non-frag (different que) • Abandon on error • Number pending de-frag implementation dependent • Need minimum # Ben Rolfe

  16. Technical Concept (8) • NACK and Automatic Retry • NACK for signaling receiver giving up • Spares wasted time on air • Could have NACK TYPE subfield Ben Rolfe

  17. Related MAC Efforts • QoS • Prioritization • Robustness • Stronger link quality assessment and reporting • ACK/NACK/Retry Ben Rolfe

  18. Free the MAC Free the 802.15.4 MAC From Short PHY Frames Ben Rolfe

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