Subject: [manet] QoS control field in 802.11e standard

From: Yue Fang <[email-masked]>
Date: Fri, 25 Mar 2005 18:19:14 -0500 (EST)

Dear MANET people,

I have a question about the QoS control fields in the 802.11e protocol:
current 802.11e standard supports parameterized or prioritized QoS traffic
by defining different TIDs (traffic identifier). Hence the poll frame in
802.11e should contain this infomation as well as EOSP (end of service period).

802.11e introduced QoS control field to store those information, in the
draft IEEE P802.11e/D6.0, 7.1.3.5, Table 3.1 lists the QoS Control field
and defined whether data or poll the TID is associated.

My question is that when QoS Data+CF-Poll is transmitted, the TID is
associated with data, then how does the polled STA know which TID should
it transmit?

BTW, any idea why 802.11e doesn't allow CF-ACK piggybacked with CF-Poll
when they are not addressed to the same STA? (9.9.2.3)

Any input is appreciated.

Bests

Yue
-----------------------------------
Yue Fang
227 Egan Research Building
Dept. of Electrical & Computer Eng.
Northeastern University
Boston, MA, 02115
(tel) 617-373-3009
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From: "Lusheng Ji" <[email-masked]>
Date: Tue, 29 Mar 2005 13:18:18 -0500

Hi Yue,

Please see in-line comments.  Hope they help.

Regards,

Lusheng Ji, Ph.D.
Senior Technical Specialist
AT&T Labs, Research
180 Park Ave., 
Florham Park, NJ 07932

> -----Original Message-----
> From: [email-masked] [mailto:[email-masked]] On Behalf Of
> Yue Fang
> Sent: Friday, March 25, 2005 6:19 PM
> To: [email-masked]
> Subject: [manet] QoS control field in 802.11e standard
> 
> 
> Dear MANET people,
> 

A TXOP obtaining QSTA does not have to respond to a CF-Poll with a frame of
the same TID as in the CF-Poll.  It may send any frame, even management
frame, in the obtained TXOP.

Never the less, in the newest draft it is specified (sorry I forget where in
the draft exactly) that QoS(+)Data+CF-Poll cannot be used to poll any QSTA
that has already set up TS and no aggregate schedule is requested by this
QSTA.  In this case, only QoS CF-Poll and QoS CF-ACK+Poll can be used for
such a QSTA.

> when they are not addressed to the same STA? (9.9.2.3)

Two reason off the top of my head:
1. How can we determine which QSTA the ACK is for?
2. The polled QSTA may not be able to handle piggybacked ACKs
(implementation of piggybacked ACK handling is optional)

---

From: Yue Fang <[email-masked]>
Date: Wed, 30 Mar 2005 13:58:24 -0500 (EST)

Hello, Lusheng:

Thanks for your explaination, it helps me to get a more clear picture
of the protocol. Can you share with me your idea about the
following. Thanks a lot.

1. I think the inclusion of TID in QoS Data packet is necessary,
however, what do you think about including TID and EOSP information in
CF-Poll? since the polled STA may not send packet with same TID.

2. As for the piggybacked CF-ACK and CF-Poll from different station, I
remembered that in 802.11 standard, it is allowed, and the STA that just
transmitted data will treat the ACK it received as ACK to itself. Is there
any particular reason we can not do that in 802.11e?

Thanks in advance for your response.

Best Regards
Yue

---

From: "Lusheng Ji" <[email-masked]>
Date: Wed, 30 Mar 2005 15:36:09 -0500

Hi Yue,

Again, see in-line please.

Lusheng Ji, Ph.D.
1 (973) 360-7241

> From: Yue Fang [mailto:[email-masked]]
> Sent: Wednesday, March 30, 2005 1:58 PM
> To: Lusheng Ji
> Cc: [email-masked]
> Subject: RE: [manet] QoS control field in 802.11e standard
> 
> 
> Hello, Lusheng:
> 

A QSTA may respond with a frame belonging to any TS, but it is still using
schedule credit out of the polled TS.  Of course some may argue for client
side scheduling algorithms, but the philosophy of HCCA is that pretty much
HC has control over scheduling. 

> any particular reason we can not do that in 802.11e?

In current 11, PC only uses CF-ACK+CF-Poll during CFP.  Thus there is no
ambiguity for who the ACK is for in this situation.
In 11e, HC may gain WM control outside of CFP also by issuing
QoS(+)CF-Polls.  Thus QoS CF-ACK+CF-Poll may be used by the HC to gain WM
control and ack an EDCA or DCF transmission.  Need explicit ACK for acking
CP transmission.