Transcript Nov. 14, 2001 IEEE 802.15-01/328r4 Project: IEEE P802.15 Working Group for Wireless Personal Area Networks (WPANs) Submission Title: MAC CTRB Parameters Issues Date Submitted:

Nov. 14, 2001
IEEE 802.15-01/328r4
Project: IEEE P802.15 Working Group for Wireless Personal Area Networks (WPANs)
Submission Title: MAC CTRB Parameters Issues
Date Submitted: [9 July 2001]
Source: [Mark E. Schrader] Company [Eastman Kodak Co.]
Address [4545 E. River Rd., Rochester, NY 14650-0898]
Voice:[+1.716.781.9561], FAX: [+1.716.781.9733], E-Mail:[[email protected]]
Re: [IEEE 802.15.3 MAC]
Abstract: QoS based Channel Time Request Block parameters are defined mathematically. Some
issues and limits of the timing are defined and briefly discussed. QoS is shown to to simple from the
PNC perspective when only allocated bandwidth is important..
Purpose: Channel Time Request Block parameters toward building a QoS algorithm.
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.
Submission
Slide 1
Mark E. Schrader, Eastman Kodak Co.
Nov. 14, 2001
IEEE 802.15-01/328r4
Document Overview
• Propose the smallest set (3) of Channel Time
Request Block (CTRB) parameters usable for
QoS-based requests.
• Define the parameters mathematically with
variables that are usable by the channel time
requestor.
• Identify issues and solutions.
Submission
Slide 2
Mark E. Schrader, Eastman Kodak Co.
Nov. 14, 2001
IEEE 802.15-01/328r4
Variable Definitions
1)fd = bits per second of delivered data.
2)NB = bits of source buffer available to store
the data to be communicated.
3)NMPDU = bits of the data portion of one packet
of data.
4)NOH = Equivalent bits of overhead of one
packet of data including: actual MAC header
bits, slot guard times, PHY or PLCP
overhead, etc., everything-but-data, etc. It
simplifies the explanation to express this as
an equivalent number of bits.
Submission
Slide 3
Mark E. Schrader, Eastman Kodak Co.
Nov. 14, 2001
IEEE 802.15-01/328r4
Definitions Continued
• NE = Channel (PHY) encoding, bits per
symbol
• fs = Channel symbol rate, symbols per
second.
• Tbcn = Beacon Period
Submission
Slide 4
Mark E. Schrader, Eastman Kodak Co.
Nov. 14, 2001
IEEE 802.15-01/328r4
CTRB Parameter 1:
Allocation Period
3) TAP = NB / fd
4) This is how often the NB buffer must be sent
to get the desired delivered data rate fd.
5) This is the size of the source buffer divided
by the desired data rate.
Submission
Slide 5
Mark E. Schrader, Eastman Kodak Co.
Nov. 14, 2001
IEEE 802.15-01/328r4
Relationships I
• We need to send NP packets over the
network in order to transmit one buffer:
• NP = NB / NMPDU Assume an integer for
simplicity.
• NT = NMPDU + NOH, the total number of bits
that would have to be sent over the network
to cover both the data and the overhead.
Submission
Slide 6
Mark E. Schrader, Eastman Kodak Co.
Nov. 14, 2001
IEEE 802.15-01/328r4
CTRB Parameter 2:
GTS Time Per Allocation Period
• TGTS is the total time requested for GTS
allocated in order to send one buffer of data.
• TGTS = ( NP NT / NE fS ).
• For the sending NP packets,
• of equivalent size, NT = ( NMPDU + NOH )
• with a PHY encoding of NE bits per symbol
• and a PHY symbol rate of fS.
Submission
Slide 7
Mark E. Schrader, Eastman Kodak Co.
Nov. 14, 2001
IEEE 802.15-01/328r4
Relationships 2
•
•
•
1 / ( NE fS ) is a constant as long as the
symbol rate and encoding method is
unchanged.
From before: NP = NB / NMPDU
Stating the obvious: NT and NP will also be
constants if the transmit packet size and the
transmit buffer size both remain constant.
Submission
Slide 8
Mark E. Schrader, Eastman Kodak Co.
Nov. 14, 2001
IEEE 802.15-01/328r4
CTRB Parameter 3: Desired (Maximum)
GTS Time per Allocation Period
• TDMG defines the maximum amount of GTS
time per allocation period that a DEV is
capable of using. TDMG > TGTS
– If there is unused bandwidth, the extra
channel bandwidth can be divided up
among DEVs based on what they can
actually use.
– Allows channel utilization to be maximized.
Submission
Slide 9
Mark E. Schrader, Eastman Kodak Co.
Nov. 14, 2001
IEEE 802.15-01/328r4
CTRB Parameter 4:
Maximum Allocation Delay
• TMAD defines an allowable time jitter to the
allocation of time slots by the piconet
coordinator, PNC.
• The maximum allocation delay starts before
the end of the allocation period, but does not
affect the PNC’s reference timing of the TAP
period. It allows some variability in position of
the GTS slot(s)..
Submission
Slide 10
Mark E. Schrader, Eastman Kodak Co.
Nov. 14, 2001
IEEE 802.15-01/328r4
The TGTS (blue) time is the total amount of slot time
that must be allocated by the PNC within the TMAD
(green) time centered around the start of the TAP
interval (vertical arrows).
TAP
½TMAD
½TMAD
TMAD
TMAD
TGTS
Submission
Slide 11
Mark E. Schrader, Eastman Kodak Co.
Nov. 14, 2001
IEEE 802.15-01/328r4
Possible PNC Slot Allocations
TMAD
TAP
Submission
Slide 12
Mark E. Schrader, Eastman Kodak Co.
Nov. 14, 2001
IEEE 802.15-01/328r4
Proposed Fragmentation Policy
• The PNC shall provide the GTS time in as
few time slots as possible. The PNC may
provide more GTS time than the amount
requested.
• The PNC shall create at least one slot for
each distinct channel time request.
Submission
Slide 13
Mark E. Schrader, Eastman Kodak Co.
Nov. 14, 2001
IEEE 802.15-01/328r4
Proposed CTRB Structure
Submission
Slide 14
Mark E. Schrader, Eastman Kodak Co.
Nov. 14, 2001
IEEE 802.15-01/328r4
Proposed CTRB Structure
Octets: 1
1
1
1
2
2
Target
Address
EPS
status
EPS
Set
Stream
index
Allocation
Period
Minimum
GTS Time
2
Desired
GTS
Time
2
Maximum
Allocation
Delay
CTRB field that exists in draft D0.8
CTRB field proposed in this proposal
CTRB field proposed in document 01/485
Submission
Slide 15
Mark E. Schrader, Eastman Kodak Co.
Nov. 14, 2001
IEEE 802.15-01/328r4
Appendix 1
Comments and Issues
Submission
Slide 16
Mark E. Schrader, Eastman Kodak Co.
Nov. 14, 2001
IEEE 802.15-01/328r4
Issue 1: QoS Restrictions to Allocation
• This is ISOC slot specification.
• A request for a fixed offset from the beacon
for low power devices, etc., will require
different additional parameters to indicate that
the time slot position is guaranteed with
respect to the beacon.
• If a QoS request defined both the a fixed
delay from the beacon and a fixed rate, it
would set the beacon period. Should this
“super QoS” mode be allowed?
Submission
Slide 17
Mark E. Schrader, Eastman Kodak Co.
Nov. 14, 2001
IEEE 802.15-01/328r4
TMAD and the Beacon
• If TMAD > TBCN + TGTS then the beacon will
never interfere with the allocation of time slots
• If TMAD is smaller than this interval, then the
following slides apply.
Submission
Slide 18
Mark E. Schrader, Eastman Kodak Co.
Nov. 14, 2001
IEEE 802.15-01/328r4
Issue 2: Beacon & CAP Delays
• Any PNC QoS strategy must take into
account accommodating the beacon/CAP.
The occurrence of the beacon plus the CAP
could delay some or all of a member’s ISOC
time slots beyond the requested interval, TAP.
• The PNC must be able guarantee a limit to
the size of the beacon and the CAP or QoS
policies will breakdown.
Submission
Slide 19
Mark E. Schrader, Eastman Kodak Co.
Nov. 14, 2001
IEEE 802.15-01/328r4
The Beacon May Upset the timing of ISOC Slots
TAP
TMAD
Delayed Interval
Alternative 1 Start of TAP
Beacon
Alternative 2 Start of TAP
Submission
Slide 20
Mark E. Schrader, Eastman Kodak Co.
Nov. 14, 2001
IEEE 802.15-01/328r4
TAP Adjustment to Beacon Delay
• How should the TAP be adjusted if the
beacon forces the slot allocation to be late.
Should the next allocation be early according
to the current TAP interval (Alternative 1), or
should it be late and sync off the most recent
slot allocation (blue) (Alternative 2)?
• The user could specify which alternative to
use if we defined the QoS parameter switch.
Submission
Slide 21
Mark E. Schrader, Eastman Kodak Co.
Nov. 14, 2001
IEEE 802.15-01/328r4
Appendix 2
Data Rate Driven QoS
Submission
Slide 22
Mark E. Schrader, Eastman Kodak Co.
Nov. 14, 2001
IEEE 802.15-01/328r4
Requirements for Data Rate Only QoS
• The transmit buffer is large enough to accept
GTS slots anywhere in the superframe.
• The amount of bandwidth only depends on
the data rate required fd, the data rate
available, and the amount of overhead.
• TAP / TGTS = ( fd / fs ) / ( NT / NENMPDU )
• Define TMAD = 0xFFFF, which will be a special
value indicating “anywhere in CFP”.
Submission
Slide 23
Mark E. Schrader, Eastman Kodak Co.