1. <author>, <company>
doc.: IEEE <doc#>
<month year>
Project: IEEE P Working Group for Wireless Personal Area Networks (WPANs)
Submission Title: [Adding BA base sequence number]
Date Submitted: [March 18, 2007]
Source: [Zhou Lan, Chang-woo Pyo, Fumihide Kojima, Hiroyuki Nakase, Shuzo Kato, Gal Basson(2) , Tal Azogui(2)]
Company [National Institute of Information and Communications Technology (NICT), Wilocity(2)]
Address1[3-4 Hikari-no-oka, Yokosuka-shi, Kanagawa , Japan]
Voice1:[] , FAX1: []
other contributors are listed in “Contributors” slides]
Re: [In response to TG3c comments (IEEE P c)]
Abstract: [Comment resolutions]
Purpose: [To be considered in TG3C baseline document.]
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 contributors acknowledge and accept that this contribution becomes the property of IEEE and may be made publicly available by P
<author>, <company>
Page 1

2. Comment # 63,94,95 63 GB
DF3
65-66 T
PHY
add a "Block-ACK base sequence field" (to optional MAC header adjuscent to BA field) - in order resolve ACK/NAK correlation ambiguity of corrupted MSDU number and BA-bit-offset 94
RJS
DF3
8.8.3b 28 3 T
MAC
There are no in-order delivery requirements in the described block ack mechanism other than "The destination transfers consecutive valid subframes to the FCSL." which from the context applies to a single aggregate frame only.
Clarify in-order delivery requirements. Address buffering requirements in receiver, retention of later (higher sequence number) frames until retransmission of earlier (lower sequence number) frames completes successfully, timeouts or other mechanisms to handle cases where retransmission frails. 95
8.7a.2 27 9
The in-order delivery requirements for low latency aggregation do not address retransmission failure.
Define behavior for the case where retransmission fails (maximum retransmits exceeded) for a particular MSDU.

3. Block ACK / aggregated MSDU correlation problem description (63,95)
current Draft text suggests that correlation of MSDU sequence to Block ACK bit offset, is based on its order-offset in the frame.
MSDU sequence numbers in the MAC frame body are not necessarily consecutive
(e.g. in case of selective retransmit)
there is no way to tell how many MSDU’s are corrupted (assuming MSDU headers are also corrupted)
No way to set/clear the correlated bit in the block-ACK

4. Problem description diagram
DEV1
DEV2
PHY HDR
MAC HDR BA
MSDU
#11
#12
#13
#14
PHY HDR
MAC HDR BA
{0,1,0,1,…}
MSDU
# …
PHY HDR
MAC HDR BA
MSDU
#11
#13
#15
#16
#17
PHY HDR
MAC HDR BA
{???,1,1,1,…}
MSDU
# …
Unknown number of MSDU corrupted from the beginning of the frame

5. Block ACK / aggregated MSDU correlation suggested solution (comments #63,95)
Add “MSDU Base Sequence Number” to the transmitted “MAC optional header”.
Each AMSDU Sequence number is an Offset from the MSDU Base Number
“MSDU base Sequence number” shall be managed by the source-DEV
Originator can abort retransmissions of a specific MSDU by advancing the “MSDU base number” beyond the specific MSDU sequence number

6. Solution description diagram
DEV1
DEV2
PHY HDR
MAC HDR BA
MSDU #0 #1 #2 #3
MSDU-BASE
# 11
PHY HDR
MAC HDR BA
{1,0,1,…}
MSDU
# …
PHY HDR
MAC HDR BA
MSDU #0 #2 #4 #5 #6
MSDU-BASE
# 11
PHY HDR
MAC HDR BA
{1,1,1,…}
MSDU
# …
Corrupted leading MSDU # are NOT acknowledged –
receiver of the BA required to retransmit non-ACKed MSDUs

7. Low Latency Aggregation Buffer Flow Control – definition (94)
A target DEV may require to limit the maximum number of MSDU received.
(similar to Delayed ACK – Max Frames, and Max Burst)
This text suggest a mechanism that allows the target DEV to signal the available buffer size to the source DEV.
An additional field added to the MAC optional header, set by the target DEV, transmitted to the source DEV – with the BA field.
(assuming Max MSDU size is known – limited to 64 DWORDS)
RX-
Buffer size
MSDU-
BASE Number
UEP BA
1 octet
2 octets
64 octets
<Free Blocks >
Number of free receive blocks (MSDU  FCSL)
<source-MSDU # >
Correlated to bit #0 of BA field
Unequal Protection Control
Block ACK - bitmap
Optional MAC header – for Low Latency aggregation mode

8. Low Latency Aggregation Buffer Flow control - recovery
Each of the two DEV’s of a bi-directional CTA manages a target-related “Rx Buffer size” primitive (TargetFreeBlockCount Primitive)
initialized to zero on each CTA period
Decreased with the number of MSDUs transmitted on the last frame (not allowed to go below zero)
Updated with the reception of every MSDU – “RX Buffer size” field.
In case of an invalid “RX Buffer size” count field (corrupted Optional MAC header), the current source-DEV may transmit
As long as its TargetFreeBlockCount is not zero
It may relinquish transmission immediately, to allow the target DEV to re-transmit an updated “RX Buffer size” count

9. “RX Buffer size” bi-dir flow diagram
TargetFreeBlock Count
TargetFreeBlock Count
DEV1
DEV2
Free buffer slots
MAC  FCSL
TargetFreeBlockCount = 0,
 no MSDUs are transmitted,
(Transmission is relinquished to DEV2 immediateley)
Free buffer slots
MAC  FCSL #0 #0 #1
#....
#64
PHY HDR
MAC HDR
RBS
#64 BA
NO MSDU #3 #4 #2 #1
PHY HDR
MAC HDR
RBS #4 BA
MSDU #1
MSDU #2
#1.-2
#....
#64
#(64-2)
PHY HDR
MAC HDR
RBS
#62 BA
MSDU #1
MSDU #2
MSDU #3
MSDU #4 #3 #4 #2 #1
#(4-4)
PHY HDR
MAC HDR
RBS #0 BA
MSDU #3
MSDU #4
MSDU #5
#(62-3)
PHY HDR
MAC HDR
RBS
#59 BA
NO MSDU #3 #4 #2 #1
#(0)
PHY HDR
MAC HDR
RBS #2 BA
MSDU #6
MSDU #7
MSDU #8
2 buffers released
MAC  FCSL
#(59-3)
#(2)

10. Frame Structure Add BA Base Sequence number – 12 bits field
The Base sequence number is the base sequence which all the sequence numbers in the MSDU headers relates to
First 3 nibbles (bits0-11)- are the base sequence number for the current aggregated MSDU
Last nibble (bits12-15) – reserved
Add RX Buffer size field- indicate the free buffer space in MSDU units (max size MSDU)