1. Setting of DTIM Interval for MCCA
April 2011
doc.: IEEE /0554r0
April 2011
Setting of DTIM Interval for MCCA
Date:
Authors:
Michael Bahr, Siemens AG
Michael Bahr, Siemens AG

2. April 2011
doc.: IEEE /0554r0
April 2011
Abstract
The setting of the DTIM interval in MCCA to a limited set of 19 values is not flexible enough for many applications that would benefit greatly from MCCA, for instance, industrial WLAN networks.
This presentation lists several options that would allow a flexible and application specific setting of the DTIM interval in MCCA in order to support many applications such as industrial WLAN networks.
Normative text for these flexible settings of the DTIM interval is provided.
Michael Bahr, Siemens AG
Michael Bahr, Siemens AG

3. History of DTIM interval for MCCA in IEEE 802.11s
April 2011
History of DTIM interval for MCCA in IEEE s
D0.01-D3.03: Mesh DTIM element
D3.04-D5.0: “Mesh STAs that use MCCA share a DTIM interval of common length.”
D5.01-D10.0 (current): “Mesh STAs that use MCCA shall use a DTIM interval with a duration of 2^n * 100 TU with n a non-negative integer less than or equal to 5 (18 since D7.04).”
Michael Bahr, Siemens AG

4. Comment 3192 on DTIM interval for MCCA
April 2011
Comment 3192 on DTIM interval for MCCA
Sponsor Ballot on D10.0 – CID 3192
Michael Bahr, Siemens AG

5. Problems to Be Solved ensure interoperability with the use of MCCA
April 2011
Problems to Be Solved
ensure interoperability with the use of MCCA
enable a wide range of applications to use MCCA by providing a flexible configuration of MCCA reservations
allow any distance (in multiples of 32µs) between subsequent MCCAOPs of the same reservation
enable an easy check of overlapping MCCA reservations
Michael Bahr, Siemens AG

6. Options for setting of DTIM interval
April 2011
Options for setting of DTIM interval
remove any restriction since there is no problem with different DTIM intervals
state the requirement but leave it open to the external configuration to ensure it – we don‘t have to prevent people from doing dumb things
ensure the requirement during mesh discovery with flexible inital value
provide a limited set of possible absolute values for DTIM interval
distribute a common wrapper DTIM interval in the MBSS as common time basis / virtual DTIM interval
Michael Bahr, Siemens AG

7. Option A Different DTIM intervals are no problem
April 2011
Option A Different DTIM intervals are no problem
interoperability is ensured by the MCCA setup procedure even with different DTIM intervals
overlap of MCCAOP reservations can be verified with any DTIM interval
only capacity for reservations and performance of check of overlapping MCCA reservations might decrease
different DTIM intervals can be made DTIM intervals of same length for the sake of an easy check of overlapping MCCA reservations:
Assume 2 DTIM intervals dtimA and dtimB
Assume MCCA reservation in dtimA with offsetA, durationA, and periodicityA, the same for an MCCA reservation in dtimB
dtimA1 = dtimB1 = LCM(dtimA, dtimB) [least common multiple]
offsets and durations unchanged
periodicityA1 = periodicityA * dtimA1 / dtimA
periodicityB1 = periodicityB * dtimB1 / dtimB
Michael Bahr, Siemens AG

8. Option A – Necessary text changes (D10.2)
April 2011
Option A – Necessary text changes (D10.2)
remove „Mesh STAs that use MCCA shall use a DTIM interval with a duration of 2n x 100 TU with n being a non-negative integer less than or equal to 18.“ from clause 9.9a.3.1 General (page 115, lines 29-32)
remove „NOTE—The DTIM interval of the form 2n x 100 TU has been chosen to ensure that the starting times of the reservations do not change relative to each other between consecutive DTIM intervals. The restriction that n be less than or equal to 18 has been chosen to be compatible with the maximum DTIM interval and so that the range of the MCCAOP Offset in the reservation, see (MCCAOP Reservation field), is compatible with the maximal DTIM interval length.“ from clause 9.9a.3.1 General (page 115, lines 34-38)
remove „When dot11MCCAActivated is true, the mesh STA shall choose a DTIM interval with a duration of 2n x 100 TU with n a non-negative integer less than or equal to 18.“ from clause 11C TBTT selection (page 281, lines 21-23)
Michael Bahr, Siemens AG

9. Option B State requirement realize it by external management entity
April 2011
Option B State requirement realize it by external management entity
State requirement:
same DTIM interval or multiples where the factors are powers of the same n
requirement is realized by external management component outside the MLME
MCCA networks assumed to be used mainly in controlled (administrated) environments (e.g., industrial networks, machine-to-machine, VoIP, …)
provides high flexibility in using costumized and usage specific DTIM and MCCA settings in controlled environments
if misconfiguration happens, only MCCA capacity and MCCAOP overlap comparison performance might degrade, but wireless mesh will still be working correctly
we don‘t have to prevent people from doing dumb things
allows any DTIM value in order to be flexible for many usages
may provide a default value
Michael Bahr, Siemens AG

10. Option B – Necessary text changes (D10.2)
April 2011
Option B – Necessary text changes (D10.2)
Change „Mesh STAs that use MCCA shall use a DTIM interval with a duration of 2n x 100 TU with n being a non-negative integer less than or equal to 18.“ in clause 9.9a.3.1 General (page 115, lines 29-32) to „Mesh STAs that use MCCA shall use a common DTIM interval or DTIM intervals that are multiples where the factors are a power of the same natural number, e.g. 2^n.“
Change „NOTE—The DTIM interval of the form 2n x 100 TU has been chosen to ensure that the starting times of the reservations do not change relative to each other between consecutive DTIM intervals. The restriction that n be less than or equal to 18 has been chosen to be compatible with the maximum DTIM interval and so that the range of the MCCAOP Offset in the reservation, see (MCCAOP Reservation field), is compatible with the maximal DTIM interval length.“ in clause 9.9a.3.1 General (page 115, lines 34-38) to „ NOTE—The DTIM interval of this form has been chosen to ensure that the starting times of the reservations do not change relative to each other between consecutive DTIM intervals.“
Change „When dot11MCCAActivated is true, the mesh STA shall choose a DTIM interval with a duration of 2n x 100 TU with n a non-negative integer less than or equal to 18.“ in clause 11C TBTT selection (page 281, lines 21-23) to „When dot11MCCAActivated is true, the mesh STA shall choose a common DTIM interval or a DTIM interval that is a multiple where the factor is a power of the same natural number, e.g. 2^n.“
if „shall“ is a problem, replace with „should“ in order to give a strong indication for the prefered setting
Michael Bahr, Siemens AG

11. Option C Requirement ensured during mesh discovery
April 2011
Option C Requirement ensured during mesh discovery
State requirement:
same DTIM interval or multiples where the factors are powers of the same n
mesh station that establishes new mesh BSS sets DTIM value with no restrictions
flexible initial value allowing the use of costumized and usage specific DTIM and MCCA settings
„same n“ is specified in standard, possibly n=2
mesh stations that become a member of the mesh BSS set their DTIM value according to the requirement based on the DTIM interval of the candidate peer mesh STA
provides same flexibility as option B in controlled environments
provides larger flexiblity and same ensurance as restricted set of fixed values (option D)
Michael Bahr, Siemens AG

12. Option C – Necessary text changes (D10.1)
April 2011
Option C – Necessary text changes (D10.1)
Change „Mesh STAs that use MCCA shall use a DTIM interval with a duration of 2n x 100 TU with n being a non-negative integer less than or equal to 18.“ in clause 9.9a.3.1 General (page 115, lines 29-32) to „Mesh STAs that use MCCA shall use a common DTIM interval or DTIM intervals that are multiples where the factors are a power of 2.“
Change „NOTE—The DTIM interval of the form 2n x 100 TU has been chosen to ensure that the starting times of the reservations do not change relative to each other between consecutive DTIM intervals. The restriction that n be less than or equal to 18 has been chosen to be compatible with the maximum DTIM interval and so that the range of the MCCAOP Offset in the reservation, see (MCCAOP Reservation field), is compatible with the maximal DTIM interval length.“ in clause 9.9a.3.1 General (page 115, lines 34-38) to „ NOTE—The DTIM interval of this form has been chosen to ensure that the starting times of the reservations do not change relative to each other between consecutive DTIM intervals.“
remove „When dot11MCCAActivated is true, the mesh STA shall choose a DTIM interval with a duration of 2n x 100 TU with n a non-negative integer less than or equal to 18.“ in clause 11C TBTT selection (page 281, lines 21-23)
insert text from next slide in clause 11C C.2.8 Establishing or becoming a member of a mesh BSS (based on 11-11/521r4), complete instructions are provided in 11-11/0560r0.
Michael Bahr, Siemens AG

13. Option C – Necessary text changes in Mesh Discovery (11-11/521r4)
April 2011
Option C – Necessary text changes in Mesh Discovery (11-11/521r4)
Michael Bahr, Siemens AG

14. Option D Limited set of allowed absolute values
April 2011
Option D Limited set of allowed absolute values
limited flexibity in the choice of DTIM interval and interval between reserved MCCA timeslots
not flexible enough for certain appliation areas, especially in industrial communication or machine to machine communication, that require a high flexibility in setting the interval between subsequent transmissions. This might be a very exact value that cannot be approximated close enough by the allowed values.
approximation between required and possible intervals necessary leading to some difference
relative difference can be above 5%
The same concept of exponentially increasing superframe lengths has been one of the reasons why the IEEE beacon-enabled mode has not been adopted widely. An exponentially increasing beacon interval is simply to inflexible for many applications and usage scenarios.
An “unlucky” configuration of MCCA reservations (e.g. prime periodicities) is possible even with this scheme
Michael Bahr, Siemens AG

15. Option E Common wrapper DTIM interval
April 2011
Option E Common wrapper DTIM interval
distribute a common wrapper DTIM interval in the MBSS as common time basis / virtual common DTIM interval
virtual common DTIM interval is computed according to Option A
new Information Element in DTIM beacons distributing the information throughout the mesh BSS
Michael Bahr, Siemens AG

16. April 2011
Conclusion
Options B and C provide the required flexibility in setting the DTIM interval for MCCA by simple means
option B puts more responsibility to an external management entity, but this would be acceptable since
MCCA will be often used in controlled / managed environments
the world will not end and the wireless mesh will still work correctly if different DTIM intervals are used
option C allows flexibility for the initial setting of the DTIM interval for MCCA in an MBSS and deriving further DTIM interval settings for MCCA in the MBSS from this
Option D is too inflexible for important classes of applications and usage scenarios
Suggested resolution to CID 3192: Option C
provides the flexibility required by applications and ensures the preferred characteristics on the DTIM interval in MCCA (same or multiple with factor 2)
Michael Bahr, Siemens AG

17. April 2011
Motion
Move to adopt Option C of presentation 11-11/0554r0 and the text changes provided in 11-11/0560r0 as resolution to CID 3192 with resolution status „Principle“ and resolution detail „see option C in submission 11-11/0554r0. Text provided in submission 11-11/0560r0“
Michael Bahr, Siemens AG

18. April 2011
Backup
Michael Bahr, Siemens AG

19. Strawpolls (I) is acceptable to me is not acceptable to me don‘t know
April 2011
Strawpolls (I)
is acceptable to me
is not acceptable to me
don‘t know
Option B
Option C
Option D
Michael Bahr, Siemens AG

20. Comments on DTIM interval for MCCA (I)
April 2011
Comments on DTIM interval for MCCA (I)
LB 161 on D5.0 – CIDs 3043, 3224
Both commenters suggested to remove the restriction „Mesh STAs that use MCCA share a DTIM interval of common length.”
3043
3224
Michael Bahr, Siemens AG

21. Comments on DTIM interval for MCCA (II)
April 2011
Comments on DTIM interval for MCCA (II)
Sponsor Ballot on D7.0 – CIDs 143, 248
Michael Bahr, Siemens AG

22. Comments on DTIM interval for MCCA (III)
April 2011
Comments on DTIM interval for MCCA (III)
Sponsor Ballot on D9.0 – CID 2168
counter notes on Resolution Detail:
MCCAOP reservations can be selected even if the DTIM intervals drift with respect to each other
Such a shared DTIM interval can be arrived at by configuration. Most deployments of MCCA will be in an „administrated“ network environment so that there is some entity that ensures the correct configuration
Michael Bahr, Siemens AG

23. Comments on DTIM interval for MCCA (IV)
April 2011
Comments on DTIM interval for MCCA (IV)
Sponsor Ballot on D10.0 – CID 3192
Michael Bahr, Siemens AG

24. April 2011
References
IEEE s Draft Standard, different versions up to D10.02
11-10/0478r9 Comments of LB 161 on IEEE s D5.0 and their resolutions
11-10/1283r14 Comments of 1st Sponsor Ballot on IEEE s D7.0
11-11/0287r8 Comments of 2nd Recirculation Sponsor Ballot on IEEE s D9.0
11-11/0519r4 Comments of 3rd Recirculation Sponsor Ballot on IEEE s D10.0
Michael Bahr, Siemens AG