1. <January 2002>
doc.: IEEE <02/139r0>
March, 2008
Project: IEEE P Working Group for Wireless Personal Area Networks (WPANs)
Submission Title: [A Modified Aggregation Process]
Date Submitted: [March 16, 2008]
Source: [Kyungsup Kwak, Seokho Kim, Xizhi An]
Company: [Inha University]
Address: [6-141B, Inha University, 253 Yonghyun-dong, Nam-gu, Incheon, , Republic of Korea]
Voice: [], FAX: [],
Re: []
Abstract: [This document gives some comments on aggregation process in current draft standard. In order to make “3c” standard more compatible with “3” and “3b”, we propose a modified aggregation process that is transparent to MAC layer.]
Purpose: [To be considered in IEEE c standard]
Notice: This document has been prepared to assist the IEEE P 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 P
Inha Univ.
Chuck Brabenac, Intel Labs

2. Overview Review of Aggregation Process
March, 2008
Overview
Review of Aggregation Process
Current Draft (DF1):
P c-DF1_Draft_Ammendment.pdf
New Proposal of Aggregation Process
Modified Aggregation Process
New PHY frame formatting
Inha Univ.

3. Review of Aggregation Process in DF1
March, 2008
Review of Aggregation Process in DF1
Incompatible with & 3b
In section 8.7a, subframe is confused with MPDU.
In fact, the fragmentation is the same as section 8.7
Blk-ACK is unnecessary. In fact subframe just is MPDU and ACK is done on the MPDU basis, so Dly-ACK can do this job.
Subheader is similar to MAC header, however fragmentation control can not work.
Functions of different layers are mixed up!
Aggregation shall be realized in PHY layer,
“Number of subframes” field is in PHY header.
PHY frame is like a kind of “container”, which conveys MPDUs.
PHY only passes frames to the MAC that have passed the HCS test.
Fragmentation and ACK shall be performed in MAC layer.
When MSDU/MCDU is fragmented, the fragmentation control information for each fragment must be set correspondingly.
The MAC validates the error free reception of every frame by using FCS.
Inha Univ.

4. Current DF1 Section 8.7a Aggregation
March, 2008
Current DF1
Section 8.7a Aggregation
Upon receiving an MSDU from FCSL, the MAC may fragment the MSDU into subframes if the length of MSDU exceeds the pPreferred-FragmentSize as described in <xref >.
The PHY puts the subframes together, as described in <xref >, to form an aggregated frame that is sent as one PHY transmission over the medium.
The number of subframes accommodated in a single aggregated frame is contained in the PHY header as described in <xref >.
Inha Univ.

5. Current DF1 12.2.11.2 Supported fragment size encoding
March, 2008
Current DF1
Supported fragment size encoding
The encoding of the preferred fragment size for SC mode used in the Capability IE
Inha Univ.

6. Current DF1 12.2.4.1.10 Number of subframes
March, 2008
Current DF1
Number of subframes
The default setting of the Number of Subframes field shall be 0000 to indicate a non-aggregated frame. When not set to zero, the Number of Subframes field shall indicate the number of subframes minus one. The maximum allowed number of subframes is 16. For an aggregated frame, the frame header shall contain the base header as well as the optional header.
Inha Univ.

7. March, 2008
Current DF1
Inha Univ.

8. Current DF1 Fixed field: MPDU-specific: March, 2008 ACK policy
PNID, DestID, SrcID, Stream index
MPDU-specific:
Frame control / retry = retransmission policy
MSDU number = MSDU number
Fragment number = Subframe ID
Useless? FCS information
Inha Univ.

9. Review of Aggregation Process in DF1
March, 2008
Review of Aggregation Process in DF1
Prerequisites of Aggregation
ACK policy shall be Dly-ACK or No ACK.
All aggregated MPDUs have the same PNID, DestID, SrcID and Stream index.
MAC header in PHY frame
One fragment control field in MAC header is not enough for multiple fragments.
Fragment, MPDU and MAC frame have the same meaning.
Subheader shall contain fragment control field for corresponding fragment.
Inha Univ.

10. Review of Aggregation Process in DF1
March, 2008
Review of Aggregation Process in DF1
FCS information is useless and shall be removed
Only Imm-ACK frame has no frame body, and thus no FCS.
All other frames must have FCS.
It is the task of MAC layer to decide the existence of FCS.
Subframe ID is useless and its function shall be changed.
The “Number of subframes” field in PHY header and “Subframe length” in subheader can assure that the aggregated MPDUs can be perfectly de-aggregated.
Subframe ID has its meaning in PHY layer, however it is used to realize some functions of ACK and fragment which are in fact tasks of MAC layer.
It shall be changed to support fragmentation control that is missed in current aggregation process.
Instead, the “fragment number” shall be used and the length of this field shall be 7 bits.
Moreover, a whole “Fragmentation control” (3 octets) shall be added in subheader.
Inha Univ.

11. Modified Aggregation Process
March, 2008
Modified Aggregation Process
Aggregation is one of PHY functions.
Transparent to MAC layer
Fragmentation control field of every MPDU is maintained.
Inha Univ.

12. March, 2008
Current DF1
MAC performs fragmentation, so the fragmentation control field is necessary to every fragment, but there is only one MAC header in the flowchart.
The size of MSDU block is misleading.
Inha Univ.

13. March, 2008
Current DF1
Inha Univ.

14. New Proposal of Aggregation at source
March, 2008
New Proposal of Aggregation at source
Inha Univ.

15. New PHY frame formatting of Aggregation
March, 2008
New PHY frame formatting of Aggregation
Inha Univ.

16. MAC Header and Subheader
March, 2008
MAC Header and Subheader
Method 1: “Common” MAC header
“Common” MAC header contains PNID, DestID, SrcID and Stream index. The Fragmentation Control field is useless.
Each subheader contains fragment information.
There are 1 MAC header and n subheaders.
n: number of subframes
Method 2: MAC header of 1st MPDU
MAC header is exactly the MAC header of 1st MPDU to be aggregated in one PHY frame.
Subheaders are the simplified MAC headers of the rest MPDUs that are aggregated after the 1st one.
There are 1 MAC header and (n – 1) subheaders.
Note
It should be consistent with PHY frame without aggregation.
Inha Univ.

17. Summary of Aggregation Process
March, 2008
Summary of Aggregation Process
Aggregation shall be regarded as a PHY enhancement
Rearrange section 8.7a to section 12
PHY frame format
Frame Header
MAC header and subheader extraction
MAC header compression, a new term?
Transparent to MAC layer: make clear the concept of layered protocol stack
It is the whole MPDU (not so-called “subframe”) that passes through the PHY SAP.
Compatible with & 3b: Fragmentation control is necessary to every MPDU
More suitable to Dly-ACK procedure
MPDU ID in Dly-ACK frame just is the fragmentation control information.
ACK the aggregated MPDUs
Burst size = n x number of MPDU aggregated in one PHY frame
Inha Univ.

18. MAC header compression
March, 2008
MAC header compression
PHY gets multiple MPDUs via PHY SAP.
PHY separates MAC header from frame payload (with FCS).
PHY converts multiple MAC headers into one (common) MAC header and several subheaders.
Subheader has less number of octets than MAC header.
MAC header decompression just is the reverse process.
Inha Univ.

19. March, 2008
Appendix
Inha Univ.

20. March, 2008
c-resolutions-to-comments-discussed-at-taipei.pdf
Inha Univ.