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doc.: IEEE 802.15-<doc#>
<11 January, 2008r> doc.: IEEE <doc#> July, 2008 Project: IEEE P Working Group for Wireless Personal Area Networks (WPANs) Submission Title: [Time Slotted, Channel Hopping MAC] Date Submitted: [7 July, 2008] Source: [Chol Su Kang, Kuor Hsin Chang, Rick Enns, Clint Powell] Companies [Dust Networks, Freescale] Address [30695 Huntwood Avenue, Hayward, CA 94544; 890 N. McCarthy Blvd, Suite 120, Milpitas, CA 95035] – Chol Su Kang Voice:[ , , ] –Chol Su Kang Re: [n/a] Abstract: [This document proposes extensions for IEEE MAC] Purpose: [This document is a response to the Call For Proposal, IEEE P ] Notice: This document has been prepared to assist the IEEE P 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 P Chol Su Kang et al. <author>, <company>
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doc.: IEEE 802.15-<doc#>
<11 January, 2008r> doc.: IEEE <doc#> July, 2008 Time Slotted, Channel Hopping MAC (TSCH) Chol Su Kang Dust Networks Kuor Hsin Chang - Freescale Clinton Powell - Freescale Rick Enns - Consultant José A. Gutierrez – Emerson Kris Pister – UC Berkeley/Dust Networks Ludwig Winkel – Siemens July, 2008 Chol Su Kang et al. <author>, <company>
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doc.: IEEE 802.15-<doc#>
<11 January, 2008r> doc.: IEEE <doc#> July, 2008 Target Applications Industrial and commercial applications with a particular focus on: Equipment and process monitoring Non-critical control Diagnostics/predictive maintenance Asset management Chol Su Kang et al. <author>, <company>
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doc.: IEEE 802.15-<doc#>
<11 January, 2008r> doc.: IEEE <doc#> July, 2008 Requirements Reliability and robustness in the presence of multipath, path obstructions and interference Industrial and commercial environments Sustained operation in the presence of non-standards based communications systems Long operational life for battery powered devices (> 5 years) Co-existence Flexible and scale-able Easy wireless network deployment and maintenance Chol Su Kang et al. <author>, <company>
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TSCH- Accepted, Proven & Practical
<11 January, 2008r> doc.: IEEE <doc#> July, 2008 TSCH- Accepted, Proven & Practical TSCH technology is the basis for the wireless network of two industrial standards HART Foundation ( WirelessHART- published 9/07 ISA ( ISA100 Committee, ISA100.11a working group- in working group draft TSCH has been implemented by multiple companies on multiple 2.4 GHz IEEE std platforms Chol Su Kang et al. <author>, <company>
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doc.: IEEE 802.15-<doc#>
<11 January, 2008r> doc.: IEEE <doc#> July, 2008 Timeslot Access Slot Frame Cycle Unallocated Slot Allocated Slot Tx CCA: RX startup, listen, RX->TX Transmit Packet: Preamble, SFD, Headers, Payload, CRC RX startup or TX->RX RX ACK Rx RX startup RX packet Verify MIC Calculate ACK MIC Transmit ACK RX/TX turnaround timeslot TX/RX packet TX/RX ACK Devices are configured with a slot frame and timeslots to communicate with each other. Chol Su Kang et al. <author>, <company>
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doc.: IEEE 802.15-<doc#>
<11 January, 2008r> doc.: IEEE <doc#> July, 2008 Timeslot Basics All devices in the same network synchronize slot frames All timeslots are contained within a slot frame cycle Timeslots repeat in time: the slot frame period Device-to-device communication within a timeslot includes packet Tx/Rx & ACK Tx/Rx Configurable option for CCA before transmit in timeslots Chol Su Kang et al. <author>, <company>
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Timeslot Operation In Devices
<11 January, 2008r> doc.: IEEE <doc#> July, 2008 Timeslot Operation In Devices Devices use timeslots to: Schedule when they wakeup to transmit or listen Keep time synchronized Specification on time difference tolerances Time synchronization mechanisms Time the sequence of operations Allow the source and destination to set their frequency channel Listening for a packet Sending a packet Listening for an AKC Generating an ACK Chol Su Kang et al. <author>, <company>
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doc.: IEEE 802.15-<doc#>
<11 January, 2008r> doc.: IEEE <doc#> July, 2008 Link Types Dedicated Link – assigned to one device for transmission and to one or more devices for reception A dedicated broadcast link is assigned to all devices for reception Shared Link – assigned to more than one device for transmission ACK failures detect collisions A slot based back-off algorithm resolves collisions Chol Su Kang et al. <author>, <company>
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doc.: IEEE 802.15-<doc#>
<11 January, 2008r> doc.: IEEE <doc#> July, 2008 Channel Hopping Slot n-2 Slot n-1 Slot n Slot n+1 Slot n+2 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 Channels Combined with timeslot access to enhance reliability Chol Su Kang et al. <author>, <company>
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doc.: IEEE 802.15-<doc#>
<11 January, 2008r> doc.: IEEE <doc#> July, 2008 Channel Hopping Mitigate Channel Impairments Channel hopping adds frequency diversity to mitigate the effects of interference and multipath fading Increase Network Capacity One timeslot can be used by multiple links at the same time Chol Su Kang et al. <author>, <company>
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Link = (Timeslot , Channel Offset)
<11 January, 2008r> doc.: IEEE <doc#> July, 2008 Link = (Timeslot , Channel Offset) One Slot Time D Chan. offset A BA C CA DA B BA BC E F BE BF The two links from B to A are dedicated D and C share a link for transmitting to A The shared link does not collide with the dedicated links Chol Su Kang et al. <author>, <company>
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doc.: IEEE 802.15-<doc#>
<11 January, 2008r> doc.: IEEE <doc#> July, 2008 Channel Hopping Time BA (ch 15) BA (ch25) BA (ch18) CA DA CA DA CA DA Channel Offset BA BA BA BC BC BC BE BF BE BF BE BF ASN= N*4 N*4+1 N*4+2 N*4+3 (N+1)*4 Cycle N+1 Cycle N+2 Cycle N Each link rotates through k available channels over k cycles. Ch # = Chan Hopping Seq. Table ( ( ASN + Channel Offset) % Number_of_Channels ) Blacklisting can be defined globally and locally. Chol Su Kang et al. <author>, <company>
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Timeslot Timing Offsets
<11 January, 2008r> doc.: IEEE <doc#> July, 2008 Timeslot Timing Offsets T1 T2 T3 T4 Transmitter CCA TX Packet prepare to receive RX ACK TsCCAOffset TsRxAckDelay AWT TsTxOffset Receiver RX Packet process packet, prepare to ack prepare to receive TX ACK TsRxOffset PWT TsTxAckDelay R1 R2 R3 End of timeslot Start of timeslot = transmitting packet = receiver on Timeslot with Acknowledged Transmission = receiving packet PWT = TsPacketWaitTime AWT = TsAckWaitTime Chol Su Kang et al. <author>, <company>
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Timeslot Timing Offsets (Cont’d)
<11 January, 2008r> doc.: IEEE <doc#> July, 2008 Timeslot Timing Offsets (Cont’d) T1 T2 T3 T4 Transmitter CCA TX Packet prepare to receive Idle receive TsCCAOffset TsRxAckDelay AWT TsTxOffset Receiver RX Packet prepare to receive process packet, decide not to ack TsRxOffset PWT R1 R2 End of timeslot Start of timeslot = transmitting packet = receiver on Timeslot with Unacknowledged Transmission = receiving packet PWT = TsPacketWaitTime AWT = TsAckWaitTime Chol Su Kang et al. <author>, <company>
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Timeslot Timing Offsets (Cont’d)
<11 January, 2008r> doc.: IEEE <doc#> July, 2008 Timeslot Timing Offsets (Cont’d) T1 T2 Transmitter CCA TX Packet no ack expected TsCCAOffset TsTxOffset Receiver RX Packet prepare to receive process packet, decide not to ack TsRxOffset PWT R1 R2 End of timeslot Start of timeslot = transmitting packet = receiver on Timeslot with Unacknowledged Broadcast = receiving packet PWT = TsPacketWaitTime AWT = TsAckWaitTime Chol Su Kang et al. <author>, <company>
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Timeslot Timing Offsets (Cont’d)
<11 January, 2008r> doc.: IEEE <doc#> July, 2008 Timeslot Timing Offsets (Cont’d) Transmitter idle Receiver prepare to receive Idle rx idle TsRxOffset PWT Receiver idles only for a brief time and decides to turn off receiver quickly. The short Idle listen and the a low duty cycle of a device’s assigned timeslots to the slot frame period produces low energy consumption and long battery life. R1 R2 End of timeslot Start of timeslot Timeslot with Idle Receive = receiver on PWT = TsPacketWaitTime Chol Su Kang et al. <author>, <company>
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doc.: IEEE 802.15-<doc#>
<11 January, 2008r> doc.: IEEE <doc#> Time Synchronization July, 2008 Tg Tg Tg Tg Transmit Packet: Preamble, SFD, Headers, Payload, FCS TACK TCCA TProcessing Early Transmit Packet: Preamble, SFD, Headers, Payload, FCS TACK TProcessing TCCA TCCA Transmit Packet: Preamble, SFD, Headers, Payload, FCS Perfect Late Transmit Packet: Preamble, SFD, Headers, Payload, FCS TACK TProcessing TCCA Tcomm = TTXPacket+TProcessing+TACK Timeslot Period TProcessing includes the processing of FCS and MIC validation as well as FCS and MIC generation for ACK. It’s the time from the last bit of the packet to the first bit of the preamble of the ACK. Chol Su Kang et al. <author>, <company>
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Time Synchronization (Cont’d)
<11 January, 2008r> doc.: IEEE <doc#> July, 2008 Time Synchronization (Cont’d) Chol Su Kang et al. <author>, <company>
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doc.: IEEE 802.15-<doc#>
<11 January, 2008r> doc.: IEEE <doc#> July, 2008 Time Synchronization Acknowledgement-based Synchronization Transmitter node sends a packet, timing at the start symbol. Receiver timestamps the actual timing of the reception of start symbol Receiver calculates TimeAdj = Expected Timing – Actual measured Timing Receiver informs the sender TimeAdj Transmitter adjusts its clock by TimeAdj Chol Su Kang et al. <author>, <company>
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Time Synchronization (Cont’d)
<11 January, 2008r> doc.: IEEE <doc#> July, 2008 Time Synchronization (Cont’d) Received Packet-based Synchronization Receiver timestamps the actual timing of the reception of start symbol Receiver calculates TimeAdj = TimeExpected (expected arrival time) – Actual timing Receiver adjusts its own clock by TimeAdj A node can be synchronized to more than one parent (i.e. timing reference nodes) Chol Su Kang et al. <author>, <company>
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Network Build Up Sequence Example
<11 January, 2008r> doc.: IEEE <doc#> July, 2008 Network Build Up Sequence Example A B D C A In this example, A is PAN Coordinator. B and D are FFD. C is RFD. Initializes slot-frame as configured in DB Initializes Search for Network Initializes Search for Network ASN B D This example uses six Channels 8 slots in slot-frame. Advertise Advertise Join Req 1 C Slot Frame Time Slots AALL A RX PAN Coordinator A initializes itself with Network ID, Superframe structure, etc. Channel Offset ASN= Chol Su Kang et al. <author>, <company>
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Network Build Up Seq. Example Cont’d
<11 January, 2008r> doc.: IEEE <doc#> July, 2008 Network Build Up Seq. Example Cont’d A B D C A Initializes slot-frames as configured in DB Initializes Search for Network Initializes Search for Network ASN B Advertise Advertise D Join Req 1 Join Rsp 8 Set-Link(ts=4,chO=2, BA) C 16 Set-Link(ts=2,chO=0, Adv; Rx=3,1) 24 Slot Frame Time Slots Click to Continue AALL BALL A RX B RX Channel Offset BA ASN= ASN= ASN= Chol Su Kang et al. <author>, <company>
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Network Build Up Seq. Example Cont’d
<11 January, 2008r> doc.: IEEE <doc#> July, 2008 Network Build Up Seq. Example Cont’d A B D C Initializes slot-frames as configured in DB A Initializes Search for Network Initializes Search for Network ASN B Advertise Advertise D Join Req 1 Join Rsp 8 Set-Link(ts=4,chO=2, BA) 16 C Set-Link(ts=2,chO=0, Adv; Rx=3,1) Initializes Search for Network 24 Slot Frame Advertise Advertise 32 Time Slots Join Req 33 AALL BALL DALL Join Rsp 40 Set-Link(ts=1,chO=1, DA) A RX B RX DA D RX 48 56 Set-Link(ts=6,chO=0, Adv; Rx=7,1) Channel Offset BA Click to Continue ASN= ASN= ASN= ASN= Chol Su Kang et al. <author>, <company>
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Network Build Up Seq. Example Cont’d
<11 January, 2008r> doc.: IEEE <doc#> July, 2008 Network Build Up Seq. Example Cont’d A B D C Initializes slot-frames as configured in DB A Initializes Search for Network Initializes Search for Network ASN Advertise Advertise B D Join Req 1 Join Rsp 8 Set-Link(ts=4,chO=2, BA) 16 Set-Link(ts=2,chO=0, Adv; Rx=3,1) Initializes Search for Network C 24 Slot Frame Advertise Advertise 32 Time Slots Join Req 33 Join Rsp AALL BALL BC BALL 40 DALL Set-Link(ts=5,chO=1, DA) DA D RX 48 A RX B RX 56 Set-Link(ts=6,chO=0, Adv; Rx=7,1) BA CB Advertise Advertise Channel Offset 66 Advertise Join Req 67 Join Req 68 Join Rsp 72 Set-Link(ts=5,chO=2, CB) Join Rsp 74 80 Set-Link(ts=5,chO=2, CB) 82 ASN= ASN= Click to Continue ASN= Chol Su Kang et al. <author>, <company>
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Network Build Up Seq. Example Cont’d
<11 January, 2008r> doc.: IEEE <doc#> Network Build Up Seq. Example Cont’d July, 2008 A B D C A Initializes slot-frames as configured in DB Initializes Search for Network Initializes Search for Network ASN Advertise Advertise B D Join Req 1 Join Rsp 8 Set-Link(ts=4,chO=2, BA) 16 Set-Link(ts=2,chO=0, Adv; Rx=3,1) Initializes Search for Network 24 C C Advertise Advertise 32 Join Req Slot Frame 33 40 Join Rsp Time Slots Set-Link(ts=5,chO=1, DA) 48 AALL BALL BC BALL CD DALL 56 Set-Link(ts=6,chO=0, Adv; Rx=7,1) DA D RX Advertise Advertise A RX B RX 66 Advertise Notice that C is RFD (leaf Node). Therefore, it does not have Advertising Broad-cast channel, nor does it have a dedicated RX Channel for it. Join Req BA Channel Offset CB 67 Join Req 68 Join Rsp 72 Set-Link(ts=5,chO=2, CB) Join Rsp 74 80 Set-Link(ts=5,chO=2, CB) 82 Advertise Advertise Advertise 86 Join Req 87 Join Req ASN= 93 Join Rsp 96 Join Rsp 102 Set-Link(ts=4,chO=0, CD) Set-Link(ts=4,chO=0, CD) 104 110 Click to Continue Chol Su Kang et al. <author>, <company>
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Network Build Up Seq. Example Cont’d
<11 January, 2008r> doc.: IEEE <doc#> Network Build Up Seq. Example Cont’d July, 2008 A B D C . ASN A . Advertise Advertise B 32 D Join Req 33 Join Rsp 40 Set-Link(ts=5,chO=1, DA) 48 56 Set-Link(ts=6,chO=0, Adv; Rx=7,1) Advertise Advertise C 66 Advertise Join Req 67 Join Req 68 Join Rsp Slot Frame 72 Set-Link(ts=5,chO=2, CB) Join Rsp 74 Time Slot 80 Set-Link(ts=5,chO=2, CB) AALL BALL BALL BC CD DALL 82 86 Advertise Advertise Advertise A RX B RX DA D RX Join Req 87 Notice that C is RFD (leaf Node). Therefore, it does not have Advertising Broad-cast channel, nor does it have a dedicated RX Channel for it. Join Req BA CB 93 Channel Offset Join Rsp 96 Join Rsp DB 102 Set-Link(ts=4,chO=0, CD) Set-Link(ts=4,chO=0, CD) 104 110 Advertise 114 Advertise Advertise 115 Join Req Join Req ASN= 116 Join Rsp 120 Join Rsp 122 Set-Link(ts=1,chO=3, DB) Set-Link(ts=1,chO=3, DB) 130 132 Chol Su Kang et al. <author>, <company>
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Non-conflicting Timeslot assignment
<11 January, 2008r> doc.: IEEE <doc#> Non-conflicting Timeslot assignment July, 2008 Devices with multiple radios can be given one or more offsets. Devices can be given one or more slots in a particular slot-frame. Devices with multiple radios can be given a block of (slot,offset)s slot Chan. offset Chol Su Kang et al. <author>, <company>
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Non-conflicting timeslot assignment
<11 January, 2008r> doc.: IEEE <doc#> July, 2008 Non-conflicting timeslot assignment Multiple slot-frames with different lengths can operate at the same time. 4 cycles of the 250ms slot-frame are shown, along with a 1000ms slot frame There are never collisions if the 1000ms slot frame uses only the empty slots of the 250 ms slot frame 250ms 250ms 250ms 250ms 1,000ms Chol Su Kang et al. <author>, <company>
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Example of TSCH Capability
<11 January, 2008r> doc.: IEEE <doc#> July, 2008 Example of TSCH Capability Data collection 100 pkt/s per access point channel using 10 ms slots* 1600 pkt/s (16*100) network capacity with no spatial reuse of frequency 105 MPDU bytes per packet assuming 22 bytes of MAC header, MIC-32, FCS (worst case header size) Throughput 84kbps MPDU per access point 16 * 84k = Mbps combined payload throughput w/ no spatial reuse of frequency Latency 10ms / PDR (Packet Delivery Rate) per hop: best case Statistical, but well modeled * 10 ms slots are an example – the standard can define a range of slot sizes that can be selected for use Other examples can be constructed that use a different timeslot period. The focus is on the 2.4 GHz band and the OQPSK radio. One reason to not fix the timeslot size is to accomodate other radios. Channel blacklisting reduces the number of channels available the the network throughput. Spacial reuse allows link assignments to be reused when devices are sufficiently separated so as not to interfer when the transmit on the same channel at the same time. The combined payload throughput calculated here does not take into accound any spacial reuse. Channel availablity can be modeled to determin the latency distribution over various RF environments. Chol Su Kang et al. <author>, <company>
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doc.: IEEE 802.15-<doc#>
<11 January, 2008r> doc.: IEEE <doc#> July, 2008 Built-In Flexibility Trade performance and power Sample & reporting rate Latency Reliability Throughput High bandwidth connections Tradeoffs can vary with Time Location Events Use power intelligently if you’ve got it Highest performance with powered infrastructure -Sample and reporting rate: Pick a slot frame that best meets the needs of the applications. The reporting rate can be adjusted by assigning more then one slot per slot frame for transmission. -Low latency can be accomodated in several ways: Low slot frame periods More transmission slots per slot frame Cascaded timeslot assignments: for each hop the transmit timeslot closely follows the receive timeslot -Reliability is enhanced by providing additional retransmission timeslots beyond those needed to meet the application‘s bandwidth requirements. Additional transmission timeslots can also be used to provide path redundancy when a neighbor has failed or is blocked. -The number of transmission timeslots per sedond assigned to a device determins the maximum throughput. The practical throughput depends on the retransmission rate of the device accross the channels used by the network. -Highbandwidth devices can use sort period slot frames or multiple timeslot assignments per slot frame to achieve high bandwidth. Multiple radios can also be used to transmit on more than one channel at a time. -Dynamic allocation of resources is achieved by configuring new slot frames and timeslot assignments on an scheduled basis or an event driven basis. Example the periodic uploading of a large vibration monitoring file can be scheduled by turning on a highbandwidth slot frame. -When a line powered device is available, it can be assigned a large number of timeslots for reception and transmission.reducing the packet latencies. Chol Su Kang et al. <author>, <company>
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Added MAC PAN Service Primitives
<11 January, 2008r> doc.: IEEE <doc#> July, 2008 Added MAC PAN Service Primitives Primitive Description Re-quest Con-firm Res-ponse Indica-tion SET-SUPERFRAME Add, delete, or modify a superframe X SET-LINK Add, delete, or modify a link TSCH-MODE Operate in Time Slot Channel Hopping mode ADVERTISEMENT Start the advertisement This is a list of some of the service primites needed to support the TSCH MAC extentions. Chol Su Kang et al. <author>, <company>
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doc.: IEEE 802.15-<doc#>
<11 January, 2008r> doc.: IEEE <doc#> July, 2008 TSCH Summary Proven technology- aligns with several industrial wireless standards Meets the requirement for commercial and industrial monitor and process control applications Extends the capabilities of the existing IEEE MAC Chol Su Kang et al. <author>, <company>
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