doc.: IEEE 802.15-08-0581- 02-004e Submiss ion September, 2008 Kris Pister et al. Slide 1 Project: IEEE P802.15 Working Group for Wireless Personal Area Networks (WPANs) Project: IEEE P802.15 Working Group for Wireless Personal Area Networks (WPANs) Submission Title: [Time Slotted, Channel Hopping MAC] Date Submitted: [1 Sep, 2008] Source: [Kris Pister, Chol Su Kang, Kuor Hsin Chang, Rick Enns, Clint Powell, José A. Gutierrez, Ludwig Winkel] Companies [Dust Networks, Freescale, Emerson, Siemens AG] Address: [30695 Huntwood Avenue, Hayward, CA 94544 USA; 890 N. McCarthy Blvd, Suite 120, Milpitas, CA 95035 USA; 8000 West Florissant Avenue St. Louis, Missouri 63136 USA; Siemensallee 74, Karlsruhe, Germany] Voice: [+1 (510) 400-2900, +1 (408) 904-2705, +1 (650) 327-9708, +1 (480) 413- 5413, +1 (314) 553-2667, +49 (721) 595-6098] E-Mail: [ [email protected] , [email protected] , [email protected] , [email protected] , [email protected] , [email protected] , [email protected] ] Re: [n/a] Abstract: [This document proposes extensions for IEEE802.15.4 MAC] Purpose: [This document is a response to the Call For Proposal, IEEE P802.15-08- 373-01-0043] 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.
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doc.: IEEE 802.15-08-0581-02-004e
Submission
September, 2008
Kris Pister et al.Slide 1
Project: IEEE P802.15 Working Group for Wireless Personal Area Networks (WPANs)Project: IEEE P802.15 Working Group for Wireless Personal Area Networks (WPANs)
Submission Title: [Time Slotted, Channel Hopping MAC]
Date Submitted: [1 Sep, 2008]
Source: [Kris Pister, Chol Su Kang, Kuor Hsin Chang, Rick Enns, Clint Powell, José A. Gutierrez, Ludwig Winkel] Companies [Dust Networks, Freescale, Emerson, Siemens AG]
Address: [30695 Huntwood Avenue, Hayward, CA 94544 USA; 890 N. McCarthy Blvd, Suite 120, Milpitas, CA 95035 USA; 8000 West Florissant Avenue St. Louis, Missouri 63136 USA; Siemensallee 74, Karlsruhe, Germany]
Voice: [+1 (510) 400-2900, +1 (408) 904-2705, +1 (650) 327-9708, +1 (480) 413-5413, +1 (314) 553-2667, +49 (721) 595-6098]
E-Mail: [ [email protected], [email protected], [email protected], [email protected], [email protected], [email protected], [email protected] ]
Re: [n/a]
Abstract: [This document proposes extensions for IEEE802.15.4 MAC]Purpose: [This document is a response to the Call For Proposal, IEEE P802.15-08-373-01-0043]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.
doc.: IEEE 802.15-08-0581-02-004e
Submission
September, 2008
Kris Pister et al.Slide 2
Time Slotted, Channel Hopping MAC(TSCH)
Kris Pister – UC Berkeley/Dust Networks Chol Su Kang - Dust Networks
Kuor Hsin Chang - FreescaleRick Enns - Consultant
Clinton Powell - FreescaleJosé A. Gutierrez – Emerson
Ludwig Winkel – Siemens
September, 2008
doc.: IEEE 802.15-08-0581-02-004e
Submission
September, 2008
Kris Pister et al.Slide 3
Target Applications
Industrial and commercial applications with a particular focus on:•Equipment and process monitoring•Non-critical control•Diagnostics/predictive maintenance•Asset management
doc.: IEEE 802.15-08-0581-02-004e
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September, 2008
Kris Pister et al.Slide 4
Requirements
• Industrial-Grade 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
doc.: IEEE 802.15-08-0581-02-004e
Submission
September, 2008
Kris Pister et al.Slide 5
TSCH- Accepted, Proven & Practical • Time Slotted, Channel Hopping (TSCH) technology is
the basis for the wireless network of two industrial standards– HART Foundation (www.hartcomm2.org - over 200
companies worldwide): WirelessHART- published 9/07– ISA (www.isa.org – over 30,000 members worldwide):
ISA100 Committee, ISA100.11a working group- in working group draft
• TSCH has been implemented by multiple companies on multiple 2.4 GHz IEEE std. 802.15.4 platforms
doc.: IEEE 802.15-08-0581-02-004e
Submission
September, 2008
Kris Pister et al.Slide 6
Timeslot AccessSlot Frame Cycle
Unallocated Slot Allocated Slot
Tx
RxRX
startup
Transmit Packet: Preamble, SFD, Headers, Payload, CRC
RX packet Verify MIC
Calculate ACK MIC
TransmitACK
RX startup or TX->RX
RX ACK
RX/TX turnaround
CCA: RX startup, listen, RX->TX
timeslot
Devices are configured with a slotframe and timeslots to communicate with each other.
TX/RX packet TX/RX ACK
doc.: IEEE 802.15-08-0581-02-004e
Submission
September, 2008
Kris Pister et al.Slide 7
Timeslot Basics
• All devices in the same network synchronize slotframes
• All timeslots are contained within a slotframe cycle• Timeslots repeat in time: the slotframe period• Device-to-device communication within a timeslot
includes packet Tx/Rx & ACK Tx/Rx• Configurable option for CCA before transmit in
timeslots
doc.: IEEE 802.15-08-0581-02-004e
Submission
September, 2008
Kris Pister et al.Slide 8
Timeslot Operation In DevicesDevices 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 ACK– Generating an ACK
• Synchronizes channel hops• Provide time to higher layers
doc.: IEEE 802.15-08-0581-02-004e
Submission
September, 2008
Kris Pister et al.Slide 9
Sample Timeslot
Processing
Found Rx link?
Wakup
Process Link
Statistics
Found Tx link to send packet
TransmitReceive Packet?
Process received packet
Rx NACK
Yes
Yes
No
Yes
No
No
Yes
Unicast
Remove packet from
MAC queue
Rx ACK
Yes
No
Yes
No
No
Unicast
Yes
No
Valid Packet?
Yes
Transmit NACK
No
TransmitACK
Yes
Go To Sleep
doc.: IEEE 802.15-08-0581-02-004e
Submission
September, 2008
Kris Pister et al.Slide 10
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
doc.: IEEE 802.15-08-0581-02-004e
Submission
September, 2008
Kris Pister et al.Slide 11
Sample Shared Link ProcessingShared link
Check if device has packet to
transmit
backoffCounter = 0 ?
Yes
Perform optional CCA
No
Channel busy?
Yes
NoTransmit packet
Decrement backoffCounter by 1
Done
Transmission successful?
Yes
No
Increment backoffExponentby 1
Set backoffExponentto 0
Set backoffCounter to random number between
1 and 2 backoffExponent
Done
Done Done
maxBackoffExpReached ?
No
Yes
Process TX failureSet backoffExponent to 0
Done
doc.: IEEE 802.15-08-0581-02-004e
Submission
September, 2008
Kris Pister et al.Slide 12
Channel Hopping
• Combined with timeslot access to enhance reliability
11121314151617181920212223242526
802.
15.4
Ch
ann
els
Slot nSlot n-1Slot n-2 Slot n+1 Slot n+2
doc.: IEEE 802.15-08-0581-02-004e
Submission
September, 2008
Kris Pister et al.Slide 13
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
doc.: IEEE 802.15-08-0581-02-004e
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September, 2008
Kris Pister et al.Slide 14
BA
BC
BA
CA
DA
BE
BF
B
C
Link = (Timeslot , Channel Offset)
A
Time
Chan.offset
One SlotD
• 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
FE
doc.: IEEE 802.15-08-0581-02-004e
Submission
September, 2008
Kris Pister et al.Slide 15
BA(ch 15)
BEBF
BC
BA
CADA
BA(ch25)
BC
BA
BEBF
CADA
BA(ch18)
BC
BA
CADA
BEBF
Channel Hopping
• 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.
Time
Ch
an
ne
l Off
set
N*4
Cycle N Cycle N+1 Cycle N+2N*4+1 (N+1)*4N*4+2 N*4+3ASN=
doc.: IEEE 802.15-08-0581-02-004e
Submission
September, 2008
Kris Pister et al.Slide 16
Timeslot Timing Offsets
Endof
timeslot
Startof
timeslot
TsCCAOffset
CCA
TsTxOffset
RX Packet
TX Packet
TX ACK
TsRxOffset PWT
prepare to receive
TsTxAckDelay
TsRxAckDelay AWT
RX ACKprepare to receive
process packet,prepare to ack
Timeslot with Acknowledged Transmission
T1 T2 T4T3
R1 R2 R3
Transmitter
Receiver
= transmitting packet= receiver on
PWT = TsPacketWaitTimeAWT = TsAckWaitTime
= receiving packet
doc.: IEEE 802.15-08-0581-02-004e
Submission
September, 2008
Kris Pister et al.Slide 17
Timeslot Timing Offsets (Cont’d)
Endof
timeslot
Startof
timeslot
TsCCAOffset
CCA
TsTxOffset
RX Packet
TX Packet
TsRxOffset PWT
prepare to receive
TsRxAckDelay AWT
Idle receiveprepare to receive
process packet, decide not to ack
Timeslot with Unacknowledged Transmission
T1 T2 T4T3
R1 R2
Transmitter
Receiver
= transmitting packet= receiver on
PWT = TsPacketWaitTimeAWT = TsAckWaitTime
= receiving packet
doc.: IEEE 802.15-08-0581-02-004e
Submission
September, 2008
Kris Pister et al.Slide 18
Timeslot Timing Offsets (Cont’d)
Endof
timeslot
Startof
timeslot
TsCCAOffset
CCA
TsTxOffset
RX Packet
TX Packet
TsRxOffset PWT
prepare to receive
no ack expected
process packet, decide not to ack
Timeslot with Unacknowledged Broadcast
T1 T2
R1 R2
Transmitter
Receiver
= transmitting packet= receiver on
PWT = TsPacketWaitTimeAWT = TsAckWaitTime
= receiving packet
doc.: IEEE 802.15-08-0581-02-004e
Submission
September, 2008
Kris Pister et al.Slide 19
Timeslot Timing Offsets (Cont’d)
Endof
timeslot
Startof
timeslot
TsRxOffset PWT
prepare to receive
idle
Idle rx
Timeslot with Idle Receive
R1 R2
Transmitter
Receiver idle
= receiver on
PWT = TsPacketWaitTime
doc.: IEEE 802.15-08-0581-02-004e
Submission
September, 2008
Kris Pister et al.Slide 20
Time SynchronizationTgTg
Transmit Packet: Preamble, SFD, Headers, Payload, FCS
TACKTC
CA
TProcessingEarly
Late
Perfect
TgTg
Timeslot Period
Tcomm = TTXPacket+TProcessing+TACK
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.
Transmit Packet: Preamble, SFD, Headers, Payload, FCS
TACKTProcessingTC
CA
Transmit Packet: Preamble, SFD, Headers, Payload, FCS
TACKTProcessingTC
CA
Transmit Packet: Preamble, SFD,
Headers, Payload, FCSTC
CA
doc.: IEEE 802.15-08-0581-02-004e
Submission
September, 2008
Kris Pister et al.Slide 21
Time Synchronization (Cont’d)
Receiver Timeslot
Startof
Slot
Endof
Slot
TsTxOffset
Time Adjustment (send as part of ACK/NACK or adjust own time)
Packet Expected
Here
Packet Received
Here
TsRxActual
doc.: IEEE 802.15-08-0581-02-004e
Submission
September, 2008
Kris Pister et al.Slide 22
Time Synchronization
• Acknowledgement-based Synchronization1. Transmitter node sends a packet, timing at the
start symbol.
2. Receiver timestamps the actual timing of the reception of start symbol
3. Receiver calculates TimeAdj = Expected Timing – Actual measured Timing
4. Receiver informs the sender TimeAdj
5. Transmitter adjusts its clock by TimeAdj
doc.: IEEE 802.15-08-0581-02-004e
Submission
September, 2008
Kris Pister et al.Slide 23
Time Synchronization (Cont’d)
Received Packet-based Synchronization1. Receiver timestamps the actual timing of the reception of
start symbol
2. Receiver calculates TimeAdj = TimeExpected (expected arrival time) – Actual timing
3. Receiver adjusts its own clock by TimeAdj
A node can be synchronized to more than one parent (i.e. timing reference nodes)
doc.: IEEE 802.15-08-0581-02-004e
Submission
September, 2008
Kris Pister et al.Slide 24
Non-conflicting Timeslot assignment• Devices with multiple radios can be given one or more offsets.
• Devices can be given one or more slots in a particular slotframe.
• Devices with management ability can be given a block of (slot,offset)s
Ch
an
. off
set
slot
doc.: IEEE 802.15-08-0581-02-004e
Submission
September, 2008
Kris Pister et al.Slide 25
Non-conflicting timeslot assignment• Multiple slotframes with different lengths can operate at the
same time.• 4 cycles of the 250ms slotframe 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
1,000ms
250ms 250ms 250ms
doc.: IEEE 802.15-08-0581-02-004e
Submission
September, 2008
Kris Pister et al.Slide 26
Added MAC PAN Service Primitives
Primitive Description Re-quest
Con-firm
Res-ponse
Indica-tion
SET-SLOTFRAME Add, delete, or modify a superframe X X
SET-LINK Add, delete, or modify a link X X
TSCH-MODE Operate in Time Slot Channel Hopping mode
X X
LISTEN Start listening for an advertisement X X X
doc.: IEEE 802.15-08-0581-02-004e
Submission
September, 2008
Kris Pister et al.Slide 27
SET-SLOTFRAME
• Request (Device Management TSCH MAC)– Add, delete, or change a slotframe– Parameters: slotframe Id, operation, slotframe size,
channel page, channel map, active flag
• Confirm (TSCH MAC Device Management)– Reports the results of SET-SLOTFRAME request
command– Parameters: slotframe Id, status
doc.: IEEE 802.15-08-0581-02-004e
Submission
September, 2008
Kris Pister et al.Slide 28
SET-LINK
• Request (Device Management TSCH MAC)– Add, change, or delete a link– Parameters1: operation type=ADD or CHANGE, link
handle, frame Id, timeslot, channel offset, link options, link type, node addresses
– Parameters2: operation type=DELETE, link handle
• Confirm (TSCH MAC Device Management)– Indicates the result of add, change or delete link
command– Parameters: status, link handle
doc.: IEEE 802.15-08-0581-02-004e
Submission
September, 2008
Kris Pister et al.Slide 29
TSCH-MODE
• Request (Device Management TSCH MAC)– Puts the MAC to TSCH mode of operation– Parameters: none
• Confirm (TSCH MAC Device Management)– Reports the result of the TSCH-MODE
request– Parameters: status
doc.: IEEE 802.15-08-0581-02-004e
Submission
September, 2008
Kris Pister et al.Slide 30
LISTEN
• Request (Device Management TSCH MAC)– Request the MAC to search for a network– Parameters: channel page, 802.15.4 channel, duration
• Confirm (TSCH MAC Device Management)– Reports when the MAC completes the listen operation– Parameters: status
• Indication (TSCH MAC Device Management)– Indicates that the MAC received an ADVERTISEMENT packet
while listening– Parameters: link quality, PAN ID, channel map, join priority,
slotframes, links in each slotframe (these parameters, except link quality, are received in ADVERTISEMENT packet)
doc.: IEEE 802.15-08-0581-02-004e
Submission
September, 2008
Kris Pister et al.Slide 31
New TX Option in Existing Primitive
MCPS.DATA.request Primitive• In TSCH Mode, the Next Higher Layer (NHL) may
provide TSCH MAC a list of links. The NHL may choose the links the MSPDU may be transmitted on. The TSCH MAC selects the next available link from the list.
doc.: IEEE 802.15-08-0581-02-004e
Submission
September, 2008
Kris Pister et al.Slide 32
Examples 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• Radio duty cycle (power consumption)
– Near theoretical limit for networks with moderate to high traffic
– ~0.02% for very low traffic networks• 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
doc.: IEEE 802.15-08-0581-02-004e
Submission
September, 2008
Kris Pister et al.Slide 33
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
doc.: IEEE 802.15-08-0581-02-004e
Submission
September, 2008
Kris Pister et al.Slide 34
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 802.15.4-2006 MAC
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