1. 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: [6 July, 2008] Source: [Chol Su Kang, Kuor Hsin Chang, Rick Enns] Company [Dust Networks, Freescale] Address [30695 Huntwood Avenue, Hayward, CA 94544; 890 N. McCarthy Blvd, Suite 120, Milpitas, CA 95035] Voice:[ , , ] 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.
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2. 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
Rick Enns - Consultant
July, 2008
Chol Su Kang et al.
<author>, <company>

3. doc.: IEEE 802.15-<doc#>
<11 January, 2008r>
doc.: IEEE <doc#>
July, 2008
Target Applications
Includes:
Equipment and process monitoring
Non-critical control
Diagnostics/predictive maintenance
Asset management
Chol Su Kang et al.
<author>, <company>

4. doc.: IEEE 802.15-<doc#>
<11 January, 2008r>
doc.: IEEE <doc#>
July, 2008
Requirements
Reliability and robustness
Long operational life for battery powered devices (> 5 years)
Co-existence
Flexible and scale-able
Coverage
Easy wireless network deployment and maintenance
Chol Su Kang et al.
<author>, <company>

5. doc.: IEEE 802.15-<doc#>
<11 January, 2008r>
doc.: IEEE <doc#>
July, 2008
Time Slot 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 CRC
Calculate ACK CRC
Transmit
ACK
RX/TX turnaround
timeslot
Each device-to-device communication happens within a scheduled timeslot
All timeslots are contained within a slot frame cycle
Cycle of timeslots repeats in time
CCA before transmit in timeslots
Chol Su Kang et al.
<author>, <company>

6. Time Slot Media Access Basics
<11 January, 2008r>
doc.: IEEE <doc#>
July, 2008
Time Slot Media Access Basics
Schedule link activity
Time synchronization required for devices in the network:
Specification on time difference tolerances
Time synchronization mechanisms
Transmission starts at a specified time after the beginning of a slot:
Allow the source and destination to set their frequency channel
Allow the receiver to begin listening
Chol Su Kang et al.
<author>, <company>

7. 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>

8. doc.: IEEE 802.15-<doc#>
<11 January, 2008r>
doc.: IEEE <doc#>
July, 2008
Channel Hopping
Frequency Diversity
Reduce the effect of Interference and Multipath Fading
Network Capacity
One timeslot can be used by multiple links at the same time
Within a network, each device has identical channel lists
Chol Su Kang et al.
<author>, <company>

9. Link = (Timeslot , Channel Offset)
<11 January, 2008r>
doc.: IEEE <doc#>
July, 2008
Link = (Timeslot , Channel Offset)
One Slot
Time D
Chan.
offset A
BA C
CA
DA B
BA
BC E F
BE
BF
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>

10. doc.: IEEE 802.15-<doc#>
<11 January, 2008r>
doc.: IEEE <doc#>
July, 2008
Channel Hopping
Time
BA
(ch 15)
BA
(ch25)
BA
(ch18)
CA
DA
CA
DA
CA
DA
Channel Offset
BA
BA
BA
BC
BC
BC
BE
BF
BE
BF
BE
BF
ASN=
N*4
N*4+1
N*4+2
N*4+3
(N+1)*4
Cycle N+2
Cycle N
Cycle N+1
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>

11. 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>

12. 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>

13. 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>

14. 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. Emphasize that this is where the majority of power saving comes from. R1 R2
End of
timeslot
Start of
timeslot
Timeslot with Idle Receive
= receiver on
PWT = TsPacketWaitTime
Chol Su Kang et al.
<author>, <company>

15. 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>

16. Time Synchronization (Cont’d)
<11 January, 2008r>
doc.: IEEE <doc#>
July, 2008
Time Synchronization (Cont’d)
Chol Su Kang et al.
<author>, <company>

17. 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>

18. 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>

19. 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
Advertise D
This example uses
six Channels
8 slots in slot-frame.
Advertise
Join Req 1 C
Slot Frame
AALL
A RX
PAN Coordinator A initializes itself with Network ID, Superframe structure, etc.
Channel Offset
ASN=
Chol Su Kang et al.
<author>, <company>

20. 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,
BA) C 16
Set-Link(ts=2,chO=0,
Adv; Rx=3,1) 24
Slot Frame
Click to Continue
AALL
BALL
A RX
B RX
Channel Offset
BA
ASN=
ASN=
ASN=
Chol Su Kang et al.
<author>, <company>

21. 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,
BA) 16 C
Set-Link(ts=2,chO=0,
Adv; Rx=3,1)
Initializes
Search for Network 24
Slot Frame
Advertise
Advertise 32
Join Req 33
AALL
BALL
DALL
Join Rsp 40
Set-Link(ts=1,chO=1, DA)
A RX
B RX
DA
D RX 48 56
Set-Link(ts=6,chO=2, Adv; Rx=7,1)
Channel Offset
BA
Click to Continue
ASN=
ASN=
ASN=
ASN=
Chol Su Kang et al.
<author>, <company>

22. 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,
BA) 16
Set-Link(ts=2,chO=0,
Adv; Rx=3,1)
Initializes
Search for Network C 24
Slot Frame
Advertise
Advertise 32
Join Req 33
Join Rsp
BALL 40
AALL
BALL
BC
DALL
Set-Link(ts=5,chO=1, DA)
DA
D RX 48
A RX
B RX 56
Set-Link(ts=6,chO=2, Adv; Rx=7,1)
Channel Offset
BA
CB
Advertise
Advertise 66
Advertise
Join Req 67
Join Req 68
Join Rsp 72
Set-Link(ts=5,chO=3,
CB)
Join Rsp 74 80
Set-Link(ts=5,chO=2, CB) 82
ASN=
ASN=
Click to Continue
ASN=
Chol Su Kang et al.
<author>, <company>

23. 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
Advertise
Advertise B D
Join Req 1
Join Rsp 8
Set-Link(ts=4,chO=2,
BA) 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
Set-Link(ts=5,chO=1, DA) 48
AALL
BALL
BALL
BC
CD
DALL 56
Set-Link(ts=6,chO=2, Adv; Rx=7,1)
A RX
B RX
DA
D RX
Advertise
Advertise 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
BA
CB 67
Join Req
Channel Offset 68
Join Rsp 72
Join Rsp 74
Set-Link(ts=5,chO=3, CB) 80
Set-Link(ts=5,chO=2, CB) 82
Advertise
Advertise 86
Advertise
Join Req 87
Join Req
ASN= 93
Join Rsp 96
Join Rsp
102
Set-Link(ts=4,chO=0, CD)
Set-Link(ts=4,chO=0,
CD)
104
110
Click to Continue
Chol Su Kang et al.
<author>, <company>

24. 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, DA) 48 56
Set-Link(ts=6,chO=2, 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=3,
CB)
Join Rsp 74
Time Slot 80
Set-Link(ts=5,chO=2, CB)
AALL
BALL
BALL
BC
CD
DALL 82 86
Advertise
Advertise
Advertise
A RX
B RX
DA
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
BA
CB 93
Channel Offset
Join Rsp 96
Join Rsp
DB
102
Set-Link(ts=4,chO=0,
CD)
Set-Link(ts=4,chO=0,
CD)
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,
DB)
Set-Link(ts=1,chO=3,
DB)
130
132
Chol Su Kang et al.
<author>, <company>

25. 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>

26. 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>

27. 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
Chol Su Kang et al.
<author>, <company>

28. 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
Chol Su Kang et al.
<author>, <company>

29. 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
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Chol Su Kang et al.
<author>, <company>