May 2011 doc.: IEEE 802.11-11/0687r1 May 2011 Need and proposal for necessary flexible DTIM setting in MBSSs with MCCA Date: 2011-05-11 Authors: Michael Bahr, Siemens AG Michael Bahr, Siemens AG

May 2011 doc.: IEEE 802.11-11/0687r1 May 2011 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. Michael Bahr, Siemens AG Michael Bahr, Siemens AG

Problems to Be Solved ensure interoperability with the use of MCCA May 2011 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 Michael Bahr, Siemens AG

DTIM Interval for MCCA Current setting (D11.0): Proposed setting: May 2011 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 Michael Bahr, Siemens AG

DTIM Interval DTIM Interval = Beacon Interval * DTIM Period May 2011 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 Michael Bahr, Siemens AG

Industrial Wireless Communication May 2011 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 Michael Bahr, Siemens AG

Beacon Interval DTIM Interval = Beacon Interval * DTIM Period May 2011 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 Michael Bahr, Siemens AG

time_d: time between subsequent MCCAOPs of the same MCCAOP reservation May 2011 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_ds possible proposed setting: allows to choose any suitable set of time_ds 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_ds Michael Bahr, Siemens AG

Some reasons for more than 19 absolute DTIM values May 2011 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 dynamics of the mesh network 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 Michael Bahr, Siemens AG

Usage Scenario where current setting fails (19 absolute values) May 2011 Usage Scenario where current setting fails (19 absolute values) wirelessHART scenario HART is the control protocol in industrial process automation describes the control commands of the application (process) as well as the necessary communication and its requirements for process data and process control information wirelessHART defines the communication needs of the HART protocol over wireless superframe structure with n timeslots of 10 ms timeslots get assigned to nodes wireless mesh network important specification for industrial wireless sensor networks Michael Bahr, Siemens AG

May 2011 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 mapping to MCCA TS_length  MCCA duration time_d = DTIM Interval / MCCA periodicity time_d = nTS * TS_length = SF_length time_d == beacon interval / n the beacon has to fall into a wH 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! Michael Bahr, Siemens AG

May 2011 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 BU 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 BU, 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 HART superframe with 24 timeslots but nTS is an important design paramter (duty cycle, determinism, size of network) Michael Bahr, Siemens AG

May 2011 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! Michael Bahr, Siemens AG

May 2011 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 Michael Bahr, Siemens AG

Necessary: large range of DTIM interval values in mesh BSSs with MCCA May 2011 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 Michael Bahr, Siemens AG

May 2011 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) DTIM = m (e.g. 10000 TU) mesh STA 1 Michael Bahr, Siemens AG

May 2011 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, …) DTIM = m (e.g. 10000 TU) mesh STA 1 DTIM = m / 2 (e.g. 5000 TU) mesh STA 2 Michael Bahr, Siemens AG

May 2011 Proposed selection of DTIM interval for mesh BSS with MCCA during mesh discovery (III) mesh STA 3 DTIM = m (e.g. 10000 TU) 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, …) DTIM = m (e.g. 10000 TU) mesh STA 1 mesh STA 2 DTIM = m / 2 (e.g. 5000 TU) Michael Bahr, Siemens AG

May 2011 Proposed selection of DTIM interval for mesh BSS with MCCA during mesh discovery (IV) mesh STA 3 DTIM = m (e.g. 10000 TU) 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, …) DTIM = m (e.g. 10000 TU) mesh STA 1 mesh STA 2 DTIM = m / 2 (e.g. 5000 TU) mesh STA 4 DTIM = m * 4 (e.g. 20000 TU) Michael Bahr, Siemens AG

Flexibility of usage of MCCA May 2011 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 Michael Bahr, Siemens AG

May 2011 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) Michael Bahr, Siemens AG

May 2011 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 Michael Bahr, Siemens AG

Necessary text changes I (11-11/560r5) May 2011 Necessary text changes I (11-11/560r5) clause 9.9a.3.1 General Michael Bahr, Siemens AG

Necessary text changes II in Mesh Discovery (11-11/560r5) May 2011 Necessary text changes II in Mesh Discovery (11-11/560r5) Michael Bahr, Siemens AG

Necessary text changes III in Mesh Discovery (11-11/560r5) May 2011 Necessary text changes III in Mesh Discovery (11-11/560r5) Michael Bahr, Siemens AG

May 2011 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“ Michael Bahr, Siemens AG

References IEEE 802.11s Draft Standard, D11.0 May 2011 References IEEE 802.11s Draft Standard, D11.0 11-11/0xxxry Comments of 4th Recirculation Sponsor Ballot on IEEE 802.11s D11.0 11-11/554r2 „Setting of DTIM Interval for MCCA”, April 2011 11-11/0xxxry “text for changes”, May 2011 Michael Bahr, Siemens AG