Beaconing in Mesh

1. Beaconing in Mesh Authors: Date: 2007-09-12 Kneckt

2. Abstract The presentation analyses beaconing mechanisms on the MESH. The stand-by power consumption and robustness of the mechanisms are analyzed. The presentation is questioning should there be so many beaconing mechanisms available and what will be the default beaconing mechanism. Kneckt

3. Targets of the beaconing • Beaconing is used: • To advertise Mesh network, to enable the discovery of the network. • To reduce stand-by power consumption. In stand-by the operation only the beaconing is used to maintain the connectivity and availability of the MPs. • To create synchronization of the MPs. Beacon frame carries the time reference for the network. Kneckt

4. Current options for beaconing • Current 802.11s contains 3 different beacon transmission mechanisms: • Infrastructure beaconing • IBSS beaconing • IBSS beaconing with Designated Beacon Broadcaster. • The infrastructure and IBSS beaconing are defined in the base 802.11 standard. Designated Beacon Broadcaster mechanism is new and introduced in 802.11s standard. Kneckt

5. Advantages Simple Robust: Each MP has own beacon. Easy to monitor the existence of the MPs. Information on the Mesh is distributed widely. Mesh DTIM interval enables infrequent beaconing. Suitable with multiple synchronization modes. Scaleable. The amount of devices in MESH does not affect on the beaconing performance Disadvantages Requires relatively large amount of beacon frame transmissions, one beacon per Mp. Reduces efficiency of the power save: The MP in power save may need to wake up multiple times to receive peer MPs beacons. If peer MPs use multiple Mesh DTIM periods, the amount of waking ups to receive the beacons from peer MPs may be very high. Infrastructure beaconing Kneckt

6. Advantages Reduces the amount of transmitted beacons, i.e. reduces the usage of air time available. Ideally the stand-by power consumption may be smaller than in infrastructure beaconing. (less amount of beacons) MPs discovery is performed through the same beacon and ATIM transmission. (may not find all MPs in the area). Disadvantages Scales poorly. 2nd hop neighbors using the same beacon may have difficulties on receiving the beacons. no Mesh DTIM period. The same beacon transmission interval used all the time. It is likely that IBSS beacons will be transmitted more often than infrastructure beacons. The TSF in Beacon frame defines the TSF for all MP participating to the beaconing. IBSS beaconing Kneckt

7. Advantages Fits well to ‘IBSS operation mode’, where WLAN terminals share only the joint beaconing. In some conditions the power consumption of the devices is reduced, due to reduced number of beacons. Disadvantages Creates extra complexity to IBSS beacon operation. Reduces the random selection of the beacon transmission. Some devices may not beacon at all and other data frame transmission from these MPs is required. Connectivity reports generate complexity to beaconing rules. IBSS beaconing with DBB Kneckt

8. Design targets of the DBB • DBB was created to improve the controllability of the WLAN IBSS (ad hoc) network. • DBB operation is build on top of IBSS beaconing, the DBB just has better channel access parameters to compete on the beacon transmission. • DBB reduces possibility of other MPs using the same IBSS beacon to transmit their beacon. Thus, the MPs should use some other frames to indicate their existence and to maintain their peer links. • The DBB operation mode is suitable for the situations, when no peer link setup between MPs is used. • DBB uses the IBSS logic, which defines that participating to beaconing equals to being able to exchange frames with all MPs in beaconing group. • The DBB coordinates the amount of the MPs participating to beaconing and collects information of the power management mode for the MPs, which use the beacon of the DBB. • The coordination of the MPs using the same beacon is not very relevant in 802.11s, because peer link establishment is required in order to associate and start to exchange data. Kneckt

9. DBB design targets continue • Rotation of the DBB role is designed to enable all devices to transmit a beacon. • Connectivity Reports are targeted to reduce problems caused by lack of beacon frames. • The DBB rotation requires knowledge of the MPs, which are using the IBSS beacon. • If DBB is the only beaconing device in the IBSS synchronization profile, there may not be good knowledge which devices are present in IBSS synch. Profile. • Selection logic for new DBB • The New DBB should be available for all MPs, which use the IBSS beacon. • Possible security risk. If new DBB does not have link to MP, which used the DBB’s beacon, the beacon should not contain MAC addresses of the MPs using the same IBSS beacon and their power management status. Kneckt

10. Conclusions on DBB operation • DBB operation is complicated and operational details how DBB should be used are not clear. • Benefits of the DBB are not clear in 802.11s MESH network. DBB does not offer any new information, which is not present in other beaconing modes. • Beaconing mechanisms define profound operation of the network. Fewer beaconing modes makes the implementation simpler. • For 802.11s progress it seems to make sense to delete the DBB operation. Kneckt

11. Motion • Delete Designated Beacon Broadcaster and Connectivity Report mechanisms from the 802.11s standard • Delete sections 11A.12.3.2.1 , 11A.12.3.2.2 and 11A.12.3.2.3. • Delete the lines 10 -18 from page 219, section 11A.13.4.2 • Delete the lines 61 -65 from page 211 and lines 1-4 from page 212, section 11A.12.3.2 Beaconing by synchronizing MPs • Delete section 7.3.2.68 Connectivity Report element • Remove Table s25—Mesh Resource Coordination Action field values action field 9 • Delete section 7.4.13.10 Connectivity Report frame format To resolve comments: - Beacon broadcast (complete list will be added later) Moved: Seconded: YES: No: Abstain: Kneckt