IETF 6TiSCH, a New Standardization

Effort to Combine IPv6 Connectivity

with Industrial Performancewith Industrial Performance

Xavier Vilajosana

UC Berkeley

Universitat Oberta de Catalunya

CoAP

UDP

6LoWPAN

The Internet of Things Stack

web-like interaction

Internet Integration

6LoWPAN

IEEE802.15.4e

IEEE802.15.4

Low-power reliability

simple hardware

“gap”scheduling

Outline

1. Wireless Challenges

2. IEEE802.15.4e

3. 6TiSCH

Wireless Challenges

First Challenge: External Interference

IEEE802.11

(Wi-Fi)(Wi-Fi)

IEEE802.15.1

(Bluetooth)

IEEE802.15.4

Second Challenge: Multipath Fading

Second Challenge: Multipath Fading

• Separate sender and

receiver by 100cm

• Have sender send bursts of

1000 packets

• Have receiver count the • Have receiver count the

number of received packets

• Move transmitter around in

a 20cmx35cm area and start

over

Second Challenge: Multipath Fading

ch.11

Second Challenge: Multipath Fading

ch.11

ch.13

ch.12

ch.14

ch.19

ch.21

ch.20

ch.22ch.13

ch.15

ch.17

ch.14

ch.16

ch.18

ch.21

ch.23

ch.25

ch.22

ch.24

ch.26

IEEE802.15.4e

CoAP

UDP

6LoWPAN

The Internet of Things Stackweb-like interaction

Internet Integration

6LoWPAN

IEEE802.15.4e

IEEE802.15.4

Low-power reliability

simple hardware

“gap”scheduling

Status

• Published 16 April 2012

• Only amends MAC layer of

IEEE802.15.4-2011:

– Does not modify PHY layer

• “Timeslotted Channel • “Timeslotted Channel

Hopping” (TSCH) mode:

– Ultra low-power operation by

synchronizing nodes

– Ultra high reliability through

channel hopping

A

BC

E

• A super-frame repeats over time

– Number of slots in a superframe is tunable

– Each cell can be assigned to a pair of motes, in a

given direction

Communication Schedule16

cha

nnel

offs

ets

e.g. 31 time slots (310ms)

DE

FG

H

I

J

2.120ms ≤ 4.256ms 0.800ms 0.400ms

9.976ms

A Slot

2.000ms 2.400ms

16 c

hann

el o

ffset

sChannel Hopping

2263 2268 2273 2278 2283 2288 2293

channelOffset=11

slotO

ffset=

14

AS

N*

=2

27

7

16 c

hann

el o

ffset

s

e.g. 31 time slots (310ms)

=1

4

*Absolute Slot Number

frequencyChannel=(channelOffset+ASN)%16+11

Now:

Ch. 11 (2.405GHz)

Next slotframe:

Ch. 26 (2.480GHz)

A

BC

E

• Cells are assigned according to application

requirements

• Tunable trade-off between

– packets/second

– latency

– robustness …and energy consumption

Slotted Structure: Trade-Off16

cha

nnel

offs

ets

e.g. 31 time slots (310ms)

DE

FG

H

I

J

Timeslotted Channel Hopping

D

B

C

A DATA ACK

• Trade-off bandwidth, 10s to 1000s

C->A A->C

D->B

D->C

B->A

C->A

cha

nn

elO

ffse

t

slotOffset

• Trade-off bandwidth,

redundancy, latency for power

consumption.

• 50% PDR: schedule more links

• Average power consumption:

function of number of scheduled

cells.

• How Mechanisms to monitor

and maintain schedule is out of

scope.

Typ

ica

lly

16

10s to 1000s

IEEE802.15.4e: Heritage• 2006: Dust Networks’s Time Sync. Mesh Protocol (TSMP)

– Break-through technology [1]

• 26 days

• 3.6 million packets generated

• only 17 packets lost

• 99.9995% end-to-end reliability

– Applicable to industrial application

• 2008: WirelessHART

Wireless extension of HART, the de-facto standard for – Wireless extension of HART, the de-facto standard for industrial monitoring

• 2012: IEEE 802.15.4e

– Amends MAC protocol of IEEE 802.15.4-2011

• Proven Technology. Commercial solutions are available.

[1] Channel-Specific Wireless Sensor Network Path Data,

Doherty, Linday, Simon, ICCCN 2007

6TiSCH

CoAP

UDP

6LoWPAN

The Internet of Things Stackweb-like interaction

Internet Integration

6LoWPAN

IEEE802.15.4e

IEEE802.15.4

Low-power reliability

simple hardware

“gap”scheduling

6TiSCH: Status

• Discussions started in December 2012

• Very traditional IETF procedure

– IETF mailing list created 01/24/2013

– 160+ members (mix between academic and non-

academics)academics)

– First face-to-face meetings at IETF 86 in Orlando

(March 2013)

– BOF at IETF 87 in Berlin

– IETF 88 draft adoption in Vancouver

6TiSCH: In Practice

• Mailing list

– 6tisch@ietf.org

– https://www.ietf.org/mailman/listinfo/6tisch

• Weekly Webex calls

• Homepage

– https://bitbucket.org/6tisch/

• Internet drafts:• Internet drafts:– An Architecture for IPv6 over Time Synchronized Channel Hopping

– Terminology in IPv6 over Time Slotted Channel Hopping

– Using IEEE802.15.4e TSCH in an LLN context: Overview, Problem Statement and Goals

– 6TiSCH Operation Sublayer (6top)

– Minimal 6TiSCH Configuration

– 6TiSCH Data Model for CoAP

– Security Framework and Key Management Protocol Requirements for 6TiSCH

– A standard compliant security framework for Low-power and Lossy Networks

Charter

• Define an architecture to describe the design of 6TiSCH networks.

• Define an Information Model containing the management requirements of a 6TiSCH node.

Define a Minimal mode of operation outlining • Define a Minimal mode of operation outlining how to build a 6TiSCH network using the Routing Protocol for LLNs (RPL) and a static TSCH

schedule.

SCOPE: Charter limit the scope to distributed routing over a static schedule

Architecture

6top Operational Layer

• Logical positioning of layers

Higher Layers

802.15.4e TSCH

6top

Information and Data Model for

interacting with 6top

Commands

LLN

Using 6top with a PCE• PCE has full knowledge of

topology and traffic

requirements

• PCE computes schedule

• Communicates with nodes

to configure their schedule

PCE

BBR

backbone

LLNto configure their schedule

• PCE-node protocol

– e.g. CoAPCoAP

• PCE typically schedules hard

cells

• Charter Scope: define

operational API an 6top

mechanismsnode

TSCH

6top

CoAP

6top with distributed scheduling• Distributed scheduling can

use RPL routes

• Neighbor schedule

bandwidth with each other,

rather than explicit cells

– Soft cellsB

A

– Soft cells

• 6top monitoring process

monitors performance of

cells and reschedules the

ones that perform bad.

• Charter Scope: define

operational API an 6top

mechanisms

D

C

B

E

6TiSCH Resources

• Management Resources using CoAP

Name Accessibility 6top Commands URI path

6top management resources and the related URI paths

Neighbor Table CREATE/READ/DELETE/UPDATE 6t/Neighbor

Slotframe Table CREATE/READ/DELETE/UPDATE 6t/slotframe

Cell Table CREATE/READ/DELETE/UPDATE 6t/Cell

Time Source CREATE/READ/DELETE/UPDATE 6t/TimeSource

Bundle Table CREATE/READ/DELETE/UPDATE 6t/Bundle

Track Table CREATE/READ/DELETE/UPDATE 6t/Track

EB Table CREATE/READ/DELETE/UPDATE 6t/EB

Minimal Static Schedule

RPL on Minimal

• RFC6552 “Objective Function Zero for the

Routing Protocol for Low-Power and Lossy

Networks (RPL)”

• Definitions• Definitions

– Rf: rank_factor

– Sp: step_of_rank

– Sr: stretch_of_rank

P

N

R(P)

R(N)=R(N)+rank_increase

rank_increase = (Rf*Sp + Sr) * MinHopRankIncrease

Thank you!

32

xvilajosana@eecs.berkeley.edu

Example

• Given:– Rf = 1

– Sp = 2* ETX

– Sr = 0

– minHopRankIncrease = 256 (default in RPL)

– ETX=(xmit/ack)

– r(n) = r(p) + rank_increase

0

1

2

R(0)=0

DAGRank(R(0)) = 0

R(1)=R(0)+683=683

DAGRank(R(1)) = 2

R(2)=R(1)+683=1366

DAGRank(R(1)) = 5

– r(n) = r(p) + rank_increase

– rank_increase= (Rf*Sp + Sr) * minHopRankIncrease

– rank_increase=(512*xmit/ack)

• Example:– 5-hop network

– r(0)=0

– xmit=100 ack=75 for all links

3

4

5

R(3)=R(2)+683=2049

DAGRank(R(1)) = 8

R(4)=R(3)+683=2732

DAGRank(R(1)) = 10

R(5)=R(4)+683=3415

DAGRank(R(1)) = 13