Enhancements Enabling Standby Coordinator

1. Project: IEEE P802.15 Working Group for Wireless Personal Area Networks (WPANs) Submission Title:[Enhancements enabling Standby Coordinator] Date Submitted: [1 Sept 2008] Source: [Ryoji Ono] Company [Mitsubishi Electric Corp.] [Hirohito Nishiyama] Company [Mitsubishi Electric Corp.] [Tatsuji Munaka] Company [Mitsubishi Electric Corp.] Address [5-1-1 Ofuna, Kamakura, Kanagawa, Japan] Voice:[+81-467-41-2122] E-Mail: [{Ono.Ryoji@aj,Nishiyama.Hirohito@ah,Munaka.Tatsuji@ct }.MitsubishiElectric.co.jp] Re: [IEEE 802.15.4e group] Abstract: Failure of coordinator is critical in IEEE802.15.4 network systems. Redundant system design should be available for manufacturing systems. We propose MAC enhancements enabling the failover to the standby coordinator in case of the failure of the coordinator. Purpose: To propose enhancements for IEEE802.15.4 MAC protocol. 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. Ryoji Ono, Hirohito Nishiyama, Tatsuji Munaka

2. Enhancements enabling Standby Coordinator Ryoji Ono, Hirohito Nishiyama, Tatsuji Munaka Mitsubishi Electric Corp. 1 Sep. 2008 Ryoji Ono, Hirohito Nishiyama, Tatsuji Munaka

3. Contents • Motivation and Goals • Overview of Proposed System • Issues • Proposed Super Frame Structure • Dual Beacon Scheme • Proposed Beacon Frame Structure Ryoji Ono, Hirohito Nishiyama, Tatsuji Munaka

4. Motivation and Goals • Scalability, reliability, and latency are challenging issues in wireless deployment in manufacturing systems. • Failure of coordinator is critical in IEEE802.15.4 network systems. Redundant system design should be available for manufacturing systems. • There are two ways to achieve redundancy of coordinator;(a) Wired connected standby coordinator -> out-of-scope(b) Wireless standby coordinator • IEEE802.15.4-2006 beacon mode fails to satisfy requirements for (b). • Beacons from two coordinators may collide. • No mean to resolve collision. • We propose a MAC that: • Enables failover to the standby coordinator within 1-2 superframe(s). • Avoids collision of the current and the standby coordinators. • Supplies way to negotiate to select coordinator. Ryoji Ono, Hirohito Nishiyama, Tatsuji Munaka

5. Proposed System – Overview (1) • Network topology is star-topology. • There is one (current) coordinator, one standby coordinator and zero or more other devices (RFD, FFD). • coordinator and standby coordinator have different addresses. • Standby coordinator may take over the role of coordinator in case of failure of the current coordinator. • Standby coordinator sends a sub-beacon, an additional beacon frame to enable standby function, just after the (main) beacon. • When the standby coordinator detects a failure on the current coordinator, it utilizes the sub-beacon to trigger negotiation to select the coordinator for the next superframe. • Failure detection will be performed in the upper layers and is out-of-scope of this standard. • Selection can be carried out in ECFP (Extended CFP). • Negotiation (selection) will be performed in the upper layers and is out-of-scope of this standard. Ryoji Ono, Hirohito Nishiyama, Tatsuji Munaka

6. Proposed System – Overview (2) Coordinator-A Coordinator-B Coordinator-A Coordinator-B A B A B Coordinator Beacon Sub-beacon Standby Coordinator Devices (FFD or RFD) Ryoji Ono, Hirohito Nishiyama, Tatsuji Munaka

7. Issues • When the standby coordinator tries to detect a failure of the coordinator by monitoring transmissions, it may incorrectly recognize a failure on the following conditions. 1) Transmission failure between the coordinator and the standby coordinator. 2) Failure of the standby coordinator, especially on its Rx. • If we assume the standby coordinator simply takes over the coordinator function, both the coordinators may send the beacon frames in the same time on the above conditions. • Our proposal; • adds timeslots to be used for negotiation to select a coordinator. • It ensures that the standby coordinator takes over the coordinator function only in case of actual failure. • adds sub-beacon sent by the standby coordinator. • It avoids collision of beacon from the current/standby coordinators. • It supplies GTS information for the negotiation timeslots. Ryoji Ono, Hirohito Nishiyama, Tatsuji Munaka

8. Proposed Super Frame Structure (1) • Dual beacons for current and standby coordinators. • ECFP to enable negotiation by upper layer protocol. Super Frame Super Frame CAP CFP ECFP CAP CFP ECFP Ba Bb Ba Bb time Beacons from Coordinator-A Beacons from Coordinator-B Ryoji Ono, Hirohito Nishiyama, Tatsuji Munaka

9. Proposed Super Frame Structure (2) • Superframe consists of fixed-size time slots and has several parts • Ba : Beacon frame for Coordinator-A • Bb : Beacon frame for Coordinator-B • (Current) coordinator sends main beacon frame. • Standby coordinator sends sub-beacon frame. • CAP： • CFP : • ECFP : Extended CFP used for negotiation to select coordinator. Don't care on this proposal. (can be compatible with IEEE Std.802.15.4-2006) CAP CFP ECFP Ba Bb Ryoji Ono, Hirohito Nishiyama, Tatsuji Munaka

10. Dual Beacon Scheme • Two coordinators are statically allocated to one of two beacons (Ba, Bb). • Two types of beacon frames are defined – main beacon and sub-beacon. • Main beacon: Sent by (current) coordinator. Supplies GTS information for CFP and ECFP. • Sub-beacon: Sent by standby coordinator. Only supplies GTS information for ECFP. • Any other devices in the network use GTS information in sub-beacon in case that they fail to receive main beacon. • This enables the network to negotiate for coordinator switching on the failure of the coordinator. Ryoji Ono, Hirohito Nishiyama, Tatsuji Munaka

11. Usage Scenario – Normal Case Coordinator-A continues to be the coordinator in the next superframe. superframe ECFP ECFP ECFP Ba Bb Ba Bb Ba Bb Coordinator-A no failure detected Ba Bb Ba Bb Ba Bb Coordinator-B Coordinator-B doesn’t indicate coordinator’s failure. No negotiation No negotiation No negotiation Ba Bb Ba Bb Ba Bb Device Ba Bb Ba Bb Ba Bb Device Devices receive main beacon. : main beacon : sub beacon Ryoji Ono, Hirohito Nishiyama, Tatsuji Munaka

12. Usage Scenario – Coordinator Failure superframe Main beacon is not sent. ECFP ECFP ECFP Ba Bb Coordinator-B becomes the coordinator in the next superframe. Coordinator-A Coordinator-B detects that Coordinator-A is failed. Ba Bb Bb Bb Coordinator-B Coordinator-B indicates coordinator’s failure. No negotiation Negotiation No negotiation Ba Bb Bb Bb Device Ba Bb Bb Bb Device Devices DON’T receive main beacon. : main beacon : sub beacon Ryoji Ono, Hirohito Nishiyama, Tatsuji Munaka

13. Usage Scenario – Incorrect Failure Detection Coordinator-A continues to be the coordinator in the next superframe. superframe ECFP ECFP ECFP Ba Bb Ba Bb Ba Bb Coordinator-A Coordinator-B BELIEVES that Coordinator-A is failed. Ba Bb Bb Bb Coordinator-B Coordinator-B indicates coordinator’s failure. Negotiation No negotiation Negotiation Ba Bb Ba Bb Ba Bb Device Ba Bb Bb Bb Device Devices MAY or MAY NOT receive main beacon. : main beacon : sub beacon Ryoji Ono, Hirohito Nishiyama, Tatsuji Munaka

14. Without negotiation ... superframe Ba Bb Ba Bb Coordinator-A Coordinator-B BELIEVES that Coordinator-A is failed. Ba Bb Bb Coordinator-B Coordinator-B sends main beacon. Conflicts may happen in GTS. Ba Bb Ba Bb Device GTS information can be different. Ba Bb Bb Device Devices MAY or MAY NOT receive beacons. : main beacon : sub beacon Ryoji Ono, Hirohito Nishiyama, Tatsuji Munaka

15. Proposed Beacon Frame Format • Coordinator Failure Detection: only applied for Sub-beacon. • GTS fields, Beacon Payload: • (main) contains information for both CFPand ECFP. • (sub) contains information only for ECFP. MAC Frame Format 4 or 10 0,5,6,10 or 14 2 k m n 0 or 1 2 1 Octets: 2 Frame Control Sequence Number Addressing fields Auxiliary Security Header Super frame Specification GTS fields Pending address fields Beacon Payload Coordinator Failure Detection FCS Coordinator Failure Detection Field Frame Control Field 1-7 Bits: 0 3 4 5 6 7-9 10-11 12-13 14-15 Bits: 0-2 Failure Detection Reserved Frame Type Security Enabled Frame Pending Ack Request PAN ID Compression Reserved Dest. Addressing Mode Frame Version Source Addressing Mode 000:(Main)Beacon 001:Data 010:Acknowledgment 011:MAC command 100:Sub Beacon 101-111:Reserved 0:Normal Status 1:Coordinator Failure Detection Ryoji Ono, Hirohito Nishiyama, Tatsuji Munaka

16. Thanks! Ryoji Ono, Hirohito Nishiyama, Tatsuji Munaka