1. doc.: IEEE 802.11-11/0687r2 Submission May 2011 Michael Bahr, Siemens AGSlide 1 Need and proposal for necessary flexible DTIM setting in MBSSs with MCCA Date: 2011-05-11 Authors:

2. doc.: IEEE 802.11-11/0687r2 Submission May 2011 Michael Bahr, Siemens AGSlide 2 Abstract The setting of the DTIM interval in MCCA to a limited set of 19 absolute values unnecessarily restricts the flexibility for many applications that would benefit greatly from MCCA, for instance, VoIP, industrial WLAN networks, or emerging usage scenarios. The choice of the DTIM interval directly influences the possible beacon intervals and the possible times between two subsequent MCCAOPs of the same MCCAOP reservation. These are important parameters in applications requiring some determinism for the transmission as well as optimized duty cycles such as industrial communication. This presentation describes a simple mechanism that allows the flexible and application specific setting of the DTIM interval in MCCA where the DTIM interval has the same properties as with the limited number of absolute values (same DTIM interval or multiples by power of 2). This will support many existing and emerging applications such as industrial WLAN networks.

3. doc.: IEEE 802.11-11/0687r2 Submission May 2011 Michael Bahr, Siemens AGSlide 3 Problems to Be Solved ensure interoperability with the use of MCCA enable a wide range of applications (existing, emerging, and future) to use MCCA by providing a flexible configuration of MCCAOP reservations allow any time (in multiples of 32µs) between subsequent MCCAOPs of the same reservation allow any beacon interval in order to optimize the duty cycle and to maximize the lifetime of battery-powered devices enable an easy check of overlapping MCCA reservations

4. doc.: IEEE 802.11-11/0687r2 Submission May 2011 Michael Bahr, Siemens AGSlide 4 DTIM Interval for MCCA Current setting (D11.0): –“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 18.” –This allows only 19 DTIM interval values leading to a limited number of beacon intervals and a limited number of distances between subsequent MCCAOPs of an MCCA reservation. Proposed setting: –Mesh STA that establishes a new MBSS selects DTIM interval (Beacon Interval and DTIM Count) as required by application –Mesh STAs that become a member of this MBSS select a DTIM interval that is either the same or a multiple / quotient by a power of 2 of the discovered DTIM interval (that has been selected by the mesh STA that established this MBSS) –This achieves the goals of the current setting: DTIM intervals are of the form 2^n * m TU and do not shift with respect to each other and an easy check for overlapping MCCAOPs is possible

5. doc.: IEEE 802.11-11/0687r2 Submission May 2011 Michael Bahr, Siemens AGSlide 5 DTIM Interval DTIM Interval = Beacon Interval * DTIM Period  setting the DTIM Interval defines the possible Beacon Intervals  setting the Beacon Interval defines the possible DTIM Intervals time_d = DTIM Interval / MCCAOP Periodicity time_d represents the time between two subsequent MCCAOPs of the same MCCAOP reservation  setting the DTIM Interval defines the possible times between two subsequent MCCAOPs of the same MCCAOP reservation (time_d)  setting the time_d defines the possible DTIM Interval – MCCAOP Periodicity combinations

6. doc.: IEEE 802.11-11/0687r2 Submission May 2011 Michael Bahr, Siemens AGSlide 6 Industrial Wireless Communication very diverse applications and usage scenarios –production of gummi candy bears, cars, chemicals; sewage systems; process monitoring; environmental monitoring; factory automation, industrial automation; sensor networks, … main requirements for communication –reliability, determinism, energy efficiency –to different degrees according to application or usage scenario important configuration / design parameters –some reservation-based, timeslot-based superframe –beacon interval, time between periodic transmissions (time_d) values have to be derived from the real-world application and can be very diverse optimization of duty cycle for energy-efficiency MCCA would be useful here for using WLAN mesh networks –requires flexibility in setting the DTIM interval –beacon interval and time_d are configured  DTIM interval follows from this –Note: An MBSS would use the same* DTIM interval for all its member mesh STAs since this improves network capacity and makes the handling of MCCAOP reservations easier. However, it should be possible to set this (same*) DTIM interval to any value. * same means the same or a multiple so that each larger is a multiple of each smaller

7. doc.: IEEE 802.11-11/0687r2 Submission May 2011 Michael Bahr, Siemens AGSlide 7 Beacon Interval DTIM Interval = Beacon Interval * DTIM Period current setting: DTIM Interval = 2^n * 100 TU (0  n  18)  only 43 beacon intervals possible out of 65536 (0.066%)  only 29 beacon intervals > 100ms  only 19 beacon intervals > 1s 1, 2, 4, 5, 8, 10, 16, 20, 25, 32, 40, 50, 64, 80, 100, 128, 160, 200, 256, 320, 400, 512, 640, 800, 1024, 1280, 1600, 2048, 2560, 3200, 4096, 5120, 6400, 8192, 10240, 12800, 16384, 20480, 25600, 32768, 40960, 51200, 65536 proposed setting: –allows to choose any beacon interval at the mesh STA establishing the MBSS. This defines the (set of) DTIM interval(s) to be used in the MBSS. –mesh STA becoming a member of the MBSS choose a beacon interval that is derived from the discovered DTIM interval

8. doc.: IEEE 802.11-11/0687r2 Submission May 2011 Michael Bahr, Siemens AGSlide 8 time_d: time between subsequent MCCAOPs of the same MCCAOP reservation time_d = DTIM Interval / MCCAOP Periodicity current setting: DTIM Interval = 2^n * 100 TU (0  n  18)  only 2431 specific time_d s possible proposed setting: –allows to choose any suitable set of time_d s that is possible with a (set of) DTIM intervals at the mesh STA establishing the MBSS. This defines the (set of) DTIM interval(s) to be used in the MBSS. –mesh STA becoming a member of the MBSS choose a DTIM interval that is derived from the discovered DTIM interval giving them the same set of possible time_d s

9. doc.: IEEE 802.11-11/0687r2 Submission May 2011 Michael Bahr, Siemens AGSlide 9 Some reasons for more than 19 absolute DTIM values Mesh Density every mesh STA beacons in order to avoid network congestion by beacons, the beacon interval should be configured depending on the density of mesh STAs in wireless mesh networks, beacon interval is usually 1s, up to 5s in current DTIM interval setting, some of the possible beacon intervals (1024, 1280, 1600, 2048, 2560, 3200, 4096, 5120 TU) may require a large DTIM interval (the smallest DTIM interval for 1024 and 5120 is 25600 TU) this limits the possible time_d s (smallest time_d is approx. 100 TU)  limited design choices Optimization of duty cycle by Beacon Interval and time_d (for instance, in sensor networks) duty cycle has direct impact on battery lifetime  optimization beacon important part of duty cycle time_d between MCCAOPs also influences duty cycle beacon interval and time_d should be set to optimal value wrt. application and energy efficiency a difference of 10 s in the beacon interval or time_d might well mean a difference of a month in battery lifetime –maintenance cost issue in installations with many (sensor) nodes –regulations may require a guaranteed lifetime

10. doc.: IEEE 802.11-11/0687r2 Submission May 2011 Michael Bahr, Siemens AGSlide 10 Usage Scenario where current setting fails (19 absolute values) process automation scenario control commands of the application (process) as well as the necessary communication and its requirements for process data and process control information communication needs of process automation over wireless –superframe structure with n timeslots of 10 ms –timeslots get assigned to nodes –wireless mesh network important application for industrial wireless sensor networks

11. doc.: IEEE 802.11-11/0687r2 Submission May 2011 Michael Bahr, Siemens AGSlide 11 Problem that cannot be solved by current specification (19 fixed values) TS_length is the duration of a timeslot (fixed) nTS is the number of timeslots in a superframe (variable) SF_length is the superframe length, SF_length = nTS * TS_length time_d is the time between the same timeslots of consecutive superframes TS_length  MCCAOP duration time_d = DTIM Interval / MCCAOP periodicity time_d = nTS * TS_length = SF_length time_d == beacon interval / n –the beacon has to fall into a timeslot, otherwise it would slowly move through the timeslots and disrupt the data and control transmissions Let‘s configure such a process automation network with MCCA with only 19 fixed DTIM interval values!

12. doc.: IEEE 802.11-11/0687r2 Submission May 2011 Michael Bahr, Siemens AGSlide 12 Missing Support for Industrial Application by current setting with 19 fixed DTIM interval values SF_length * n has to be in complete TU, otherwise the beacon cannot be aligned with the superframe –choose TS_length in complete TU: 9 TU = 9,216 ms < 10 ms < 10 TU = 10,240 ms –for TS_length = 9 TU, non of the allowed beacon intervals can be used  9 TU cannot be used as TS_length! But it might be the better approximation since it is <10ms and will not cause timeout alarms. –for TS_length = 10 TU, only beacon intervals 100, 160, 300, 320, 400, 640, 800, 1280, 1600, 2560, 3200, 5120, 6400, 12400, 12800, 20480, 25600, 40960, 51200 –However, these allow only a limited set of nTS! 10, 16, 20, 32, 40 (in [10..50]) It is not possible to use nTS as a configuration parameter as required by the application! –e.g. cannot design a superframe with 24 timeslots –but nTS is an important design paramter (duty cycle, determinism, size of network)

13. doc.: IEEE 802.11-11/0687r2 Submission May 2011 Michael Bahr, Siemens AGSlide 13 Missing Support for Industrial Application (II) by current setting with 19 fixed DTIM interval values Only 5 nTS (= superframe configurations) are possible out of 41 with the following possible beacon intervals –only limited choice of beacon intervals –not possible to choose beacon interval with 300, 500, 700 for nTS = 10 –limits the optimization of the duty cycle There is only limited capabiltiy to optimize the beacon interval and therefore the duty cycle. However, the duty cycle is an important performance parameter in process automation networks!

14. doc.: IEEE 802.11-11/0687r2 Submission May 2011 Michael Bahr, Siemens AGSlide 14 Support for industrial process automation with flexible setting of Mesh DTIM interval set beacon interval to n * SF_length = n * nTS * TS_length –any beacon interval possible that is multiple of SF_length set DTIM Period to 1, 2, (3), 4, etc. set MCCAOP periodicity to nTS * n * DTIM period This allows a large set of design choices for industrial wireless communication –networks with any number of timeslots can be configured, e.g. nTS = 10... 50

15. doc.: IEEE 802.11-11/0687r2 Submission May 2011 Michael Bahr, Siemens AGSlide 15 Necessary: large range of DTIM interval values in mesh BSSs with MCCA necessary design choices for industrial wireless mesh networks significantly restricted with current specification applicability of IEEE 802.11s to industrial wireless communication – an important application area – dramatically reduced with only 19 fixed values for the DTIM interval in MCCA IEEE 802.11s has to have a specification that allows to set the DTIM interval in a mesh BSS with MCCA to a large variety of application specific values in order to be useful for the emerging market of industrial wireless mesh networks, flexible setting of the DTIM interval in mesh BSS with MCCA will provide support of IEEE 802.11s for emerging applications such as industrial wireless communication, sensor networks, as well as future application with currently unknown requirements will increase applicability and adoption of IEEE 802.11s

16. doc.: IEEE 802.11-11/0687r2 Submission May 2011 Michael Bahr, Siemens AGSlide 16 Proposed selection of DTIM interval for mesh BSS with MCCA during mesh discovery (I) at mesh STA 1, dot11MCCAActivated = true mesh STA 1 does not find suitable candidate peer mesh STA for its mesh profile establishes new mesh BSS DTIM interval of its choice (very likely to be configured by some external entity) mesh STA 1 DTIM = m (e.g. 10000 TU)

17. doc.: IEEE 802.11-11/0687r2 Submission May 2011 Michael Bahr, Siemens AGSlide 17 Proposed selection of DTIM interval for mesh BSS with MCCA during mesh discovery (II) at mesh STA 2, dot11MCCAActivated = true mesh STA 2 does find mesh STA 1 as suitable candidate peer mesh STA for its mesh profile mesh STA 2 will become a member of the mesh BSS DTIM interval is set to either –the same as the DTIM interval of mesh STA 1 (e.g. 10000) –a multiple of the DTIM interval of mesh STA 1 with a factor of 2^n (e.g. 20000, 40000, …) –a fraction of the DTIM interval of mesh STA 1 with a divisor of 2^n (e.g. 5000, 2500, …) mesh STA 1 DTIM = m (e.g. 10000 TU) mesh STA 2 DTIM = m / 2 (e.g. 5000 TU)

18. doc.: IEEE 802.11-11/0687r2 Submission May 2011 Michael Bahr, Siemens AGSlide 18 Proposed selection of DTIM interval for mesh BSS with MCCA during mesh discovery (III) at mesh STA 3, dot11MCCAActivated = true mesh STA 3 does find mesh STA 1 as suitable candidate peer mesh STA for its mesh profile mesh STA 3 will become a member of the mesh BSS DTIM interval is set to either –the same as the DTIM interval of mesh STA 1 (e.g. 10000) –a multiple of the DTIM interval of mesh STA 1 with a factor of 2^n (e.g. 20000, 40000, …) –a fraction of the DTIM interval of mesh STA 1 with a divisor of 2^n (e.g. 5000, 2500, …) mesh STA 1 DTIM = m (e.g. 10000 TU) mesh STA 2 DTIM = m / 2 (e.g. 5000 TU) mesh STA 3 DTIM = m (e.g. 10000 TU)

19. doc.: IEEE 802.11-11/0687r2 Submission May 2011 Michael Bahr, Siemens AGSlide 19 Proposed selection of DTIM interval for mesh BSS with MCCA during mesh discovery (IV) at mesh STA 4, dot11MCCAActivated = true mesh STA 4 does find mesh STA 2 as suitable candidate peer mesh STA for its mesh profile mesh STA 4 will become a member of the mesh BSS DTIM interval is set to either –the same as the DTIM interval of mesh STA 2 (e.g. 5000) –a multiple of the DTIM interval of mesh STA 2 with a factor of 2^n (e.g. 10000, 20000, …) –a fraction of the DTIM interval of mesh STA 2 with a divisor of 2^n (e.g. 2500, 1250, …) mesh STA 1 DTIM = m (e.g. 10000 TU) mesh STA 2 DTIM = m / 2 (e.g. 5000 TU) mesh STA 3 DTIM = m (e.g. 10000 TU) mesh STA 4 DTIM = m * 4 (e.g. 20000 TU)

20. doc.: IEEE 802.11-11/0687r2 Submission May 2011 Michael Bahr, Siemens AGSlide 20 Flexibility of usage of MCCA The property „that the starting times of the reservations do not change relative to each other between consecutive DTIM intervals“ is retained. Property is achieved by having DTIM intervals in the MBSS of the form m * 2^n with m being the smallest DTIM interval, n a non-negative number. The proposed DTIM interval setting allows a flexible setting of the DTIM interval with 65535 * DTIM Period possible values compared to 19 possible values with the current setting. IEEE 802.11 is dis- covering new application areas: –smart metering IEEE 802.11ah –low power IEEE 802.11 chipsets –sensor networks proposed specification all mesh STA with MCCA in an MBSS have arbitrary DTIM intervals that are the same or multiples by 2^n current specification fixed set of 19 DTIM values

21. doc.: IEEE 802.11-11/0687r2 Submission May 2011 Michael Bahr, Siemens AGSlide 21 Conclusion I current setting of DTIM interval value (19 absolute values only) limits the usability of IEEE 802.11s WLAN mesh networks for important usage areas –industrial communication, other emerging and future application areas –DTIM interval restricts the design choices significantly MCCA could be a good mechanism to support the requirements of many important applications and usages some applications using MCCA need to configure beacon interval and time_d and derive DTIM interval in the MBSS from this (DTIM interval in of form m*2^n)

22. doc.: IEEE 802.11-11/0687r2 Submission May 2011 Michael Bahr, Siemens AGSlide 22 Conclusion II Proposed DTIM interval setting supports the flexibility of costumized and usage specific DTIM and MCCA settings while still maintaining the property that the starting times of the reservations do not change relative to each other between consecutive DTIM intervals –provides enough flexibility to support a wide set of applications and usage scenarios as well as emerging and future applications and ensures the preferred characteristics of the DTIM interval in MCCA (same or multiple with factor 2^n) –opens up new opportunities for the use of IEEE 802.11s in many usage scenarios

23. doc.: IEEE 802.11-11/0687r2 Submission May 2011 Michael Bahr, Siemens AGSlide 23 Necessary text changes I (11-11/560r5) clause 9.9a.3.1 General

24. doc.: IEEE 802.11-11/0687r2 Submission May 2011 Michael Bahr, Siemens AGSlide 24 Necessary text changes II in Mesh Discovery (11-11/560r5)

25. doc.: IEEE 802.11-11/0687r2 Submission May 2011 Michael Bahr, Siemens AGSlide 25 Necessary text changes III in Mesh Discovery (11-11/560r5)

26. doc.: IEEE 802.11-11/0687r2 Submission May 2011 Michael Bahr, Siemens AGSlide 26 Motion Move to adopt the text changes provided in 11- 11/0560r5 as resolution to CIDs 4039, 4040, 4041, 4042, 4056, 4057, 4058, 4059, 4060, 4116, 4117, 4118, 4119 with resolution status „Principle“ and resolution detail „Text provided in submission 11-11/0560r5“

27. doc.: IEEE 802.11-11/0687r2 Submission May 2011 Michael Bahr, Siemens AGSlide 27 References IEEE 802.11s Draft Standard, D11.0 11-11/0703 Comments of 4th Recirculation Sponsor Ballot on IEEE 802.11s D11.0 11-11/554r2 „Setting of DTIM Interval for MCCA”, April 2011 11-11/0560r5 “text for changes”, May 2011