Minimal IPv6 over the TSCH Mode of IEEE 802.15.4e (6TiSCH) Configuration
RFC 8180 also known as BCP 210

Internet Engineering Task Force (IETF) X. Vilajosana, Ed.
Request for Comments: 8180 Universitat Oberta de Catalunya
BCP: 210 K. Pister
Category: Best Current Practice University of California Berkeley
ISSN: 2070-1721 T. Watteyne
 Analog Devices
 May 2017
Minimal IPv6 over the TSCH Mode of IEEE 802.15.4e (6TiSCH) Configuration
Abstract
 This document describes a minimal mode of operation for an IPv6 over
 the TSCH mode of IEEE 802.15.4e (6TiSCH) network. This minimal mode
 of operation specifies the baseline set of protocols that need to be
 supported and the recommended configurations and modes of operation
 sufficient to enable a 6TiSCH functional network. 6TiSCH provides
 IPv6 connectivity over a Time-Slotted Channel Hopping (TSCH) mesh
 composed of IEEE Std 802.15.4 TSCH links. This minimal mode uses a
 collection of protocols with the respective configurations, including
 the IPv6 Low-Power Wireless Personal Area Network (6LoWPAN)
 framework, enabling interoperable IPv6 connectivity over IEEE Std
 802.15.4 TSCH. This minimal configuration provides the necessary
 bandwidth for network and security bootstrapping and defines the
 proper link between the IETF protocols that interface to IEEE Std
 802.15.4 TSCH. This minimal mode of operation should be implemented
 by all 6TiSCH-compliant devices.
Status of This Memo
 This memo documents an Internet Best Current Practice.
 This document is a product of the Internet Engineering Task Force
 (IETF). It represents the consensus of the IETF community. It has
 received public review and has been approved for publication by the
 Internet Engineering Steering Group (IESG). Further information on
 BCPs is available in Section 2 of RFC 7841.
 Information about the current status of this document, any errata,
 and how to provide feedback on it may be obtained at
 http://www.rfc-editor.org/info/rfc8180.
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Copyright Notice
 Copyright (c) 2017 IETF Trust and the persons identified as the
 document authors. All rights reserved.
 This document is subject to BCP 78 and the IETF Trust's Legal
 Provisions Relating to IETF Documents
 (http://trustee.ietf.org/license-info) in effect on the date of
 publication of this document. Please review these documents
 carefully, as they describe your rights and restrictions with respect
 to this document. Code Components extracted from this document must
 include Simplified BSD License text as described in Section 4.e of
 the Trust Legal Provisions and are provided without warranty as
 described in the Simplified BSD License.
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Table of Contents
 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 4
 2. Requirements Language . . . . . . . . . . . . . . . . . . . . 4
 3. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 5
 4. IEEE Std 802.15.4 Settings . . . . . . . . . . . . . . . . . 5
 4.1. TSCH Schedule . . . . . . . . . . . . . . . . . . . . . . 6
 4.2. Cell Options . . . . . . . . . . . . . . . . . . . . . . 8
 4.3. Retransmissions . . . . . . . . . . . . . . . . . . . . . 8
 4.4. Timeslot Timing . . . . . . . . . . . . . . . . . . . . . 8
 4.5. Frame Contents . . . . . . . . . . . . . . . . . . . . . 8
 4.5.1. IEEE Std 802.15.4 Header . . . . . . . . . . . . . . 8
 4.5.2. Enhanced Beacon Frame . . . . . . . . . . . . . . . . 9
 4.5.3. Acknowledgment Frame . . . . . . . . . . . . . . . . 10
 4.6. Link-Layer Security . . . . . . . . . . . . . . . . . . . 10
 5. RPL Settings . . . . . . . . . . . . . . . . . . . . . . . . 11
 5.1. Objective Function . . . . . . . . . . . . . . . . . . . 11
 5.1.1. Rank Computation . . . . . . . . . . . . . . . . . . 11
 5.1.2. Rank Computation Example . . . . . . . . . . . . . . 13
 5.2. Mode of Operation . . . . . . . . . . . . . . . . . . . . 14
 5.3. Trickle Timer . . . . . . . . . . . . . . . . . . . . . . 14
 5.4. Packet Contents . . . . . . . . . . . . . . . . . . . . . 14
 6. Network Formation and Lifetime . . . . . . . . . . . . . . . 14
 6.1. Value of the Join Metric Field . . . . . . . . . . . . . 14
 6.2. Time-Source Neighbor Selection . . . . . . . . . . . . . 15
 6.3. When to Start Sending EBs . . . . . . . . . . . . . . . . 15
 6.4. Hysteresis . . . . . . . . . . . . . . . . . . . . . . . 15
 7. Implementation Recommendations . . . . . . . . . . . . . . . 16
 7.1. Neighbor Table . . . . . . . . . . . . . . . . . . . . . 16
 7.2. Queues and Priorities . . . . . . . . . . . . . . . . . . 16
 7.3. Recommended Settings . . . . . . . . . . . . . . . . . . 17
 8. Security Considerations . . . . . . . . . . . . . . . . . . . 17
 9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 19
 10. References . . . . . . . . . . . . . . . . . . . . . . . . . 19
 10.1. Normative References . . . . . . . . . . . . . . . . . . 19
 10.2. Informative References . . . . . . . . . . . . . . . . . 21
 Appendix A. Examples . . . . . . . . . . . . . . . . . . . . . . 23
 A.1. Example: EB with Default Timeslot Template . . . . . . . 23
 A.2. Example: EB with Custom Timeslot Template . . . . . . . . 25
 A.3. Example: Link-layer Acknowledgment . . . . . . . . . . . 27
 A.4. Example: Auxiliary Security Header . . . . . . . . . . . 27
 Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . 28
 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 28
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1. Introduction
 A 6TiSCH network provides IPv6 connectivity [RFC2460] over a Time-
 Slotted Channel Hopping (TSCH) mesh [RFC7554] composed of IEEE Std
 802.15.4 TSCH links [IEEE.802.15.4]. IPv6 connectivity is obtained
 by the use of the 6LoWPAN framework ([RFC4944], [RFC6282],
 [RFC8025],[RFC8138], and [RFC6775]), RPL [RFC6550], and the RPL
 Objective Function 0 (OF0) [RFC6552].
 This specification defines operational parameters and procedures for
 a minimal mode of operation to build a 6TiSCH network. Any 6TiSCH-
 compliant device should implement this mode of operation. This
 operational parameter configuration provides the necessary bandwidth
 for nodes to bootstrap the network. The bootstrap process includes
 initial network configuration and security bootstrapping. In this
 specification, the 802.15.4 TSCH mode, the 6LoWPAN framework, RPL
 [RFC6550], and the RPL Objective Function 0 (OF0) [RFC6552] are used
 unmodified. Parameters and particular operations of TSCH are
 specified to guarantee interoperability between nodes in a 6TiSCH
 network.
 In a 6TiSCH network, nodes follow a communication schedule as per
 802.15.4 TSCH. Nodes learn the communication schedule upon joining
 the network. When following this specification, the learned schedule
 is the same for all nodes and does not change over time. Future
 specifications may define mechanisms for dynamically managing the
 communication schedule. Dynamic scheduling solutions are out of
 scope of this document.
 IPv6 addressing and compression are achieved by the 6LoWPAN
 framework. The framework includes [RFC4944], [RFC6282], [RFC8025],
 the 6LoWPAN Routing Header dispatch [RFC8138] for addressing and
 header compression, and [RFC6775] for Duplicate Address Detection
 (DAD) and address resolution.
 More advanced work is expected in the future to complement the
 minimal configuration with dynamic operations that can adapt the
 schedule to the needs of the traffic at run time.
2. Requirements Language
 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
 "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
 "OPTIONAL" in this document are to be interpreted as described in BCP
 14 [RFC2119] [RFC8174] when, and only when, they appear in all
 capitals, as shown here.
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3. Terminology
 This document uses terminology from [TERMS-6TiSCH]. The following
 concepts are used in this document:
 802.15.4: We use "802.15.4" as a short version of "IEEE Std
 802.15.4" in this document.
 SFD: Start of Frame Delimiter
 RX: Reception
 TX: Transmission
 IE: Information Element
 EB: Enhanced Beacon
 ASN: Absolute Slot Number
 Join Metric: Field in the TSCH Synchronization IE representing the
 topological distance between the node sending the EB and the PAN
 coordinator.
 PAN: Personal Area Network
 MLME: MAC Layer Management Entity
4. IEEE Std 802.15.4 Settings
 An implementation compliant with this specification MUST implement
 IEEE Std 802.15.4 [IEEE.802.15.4] in Time-Slotted Channel Hopping
 (TSCH) mode.
 The remainder of this section details the RECOMMENDED TSCH settings,
 which are summarized in Figure 1. Any of the properties marked in
 the EB column are announced in the EBs the nodes send [IEEE.802.15.4]
 and learned by those joining the network. Changing their value means
 changing the contents of the EB.
 In case of discrepancy between the values in this specification and
 IEEE Std 802.15.4 [IEEE.802.15.4], the IEEE standard has precedence.
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 +--------------------------------+------------------------------+---+
 | Property | Recommended Setting |EB*|
 +--------------------------------+------------------------------+---+
 | Slotframe Size | Tunable. Trades off | X |
 | | bandwidth against energy. | |
 +--------------------------------+------------------------------+---+
 | Number of scheduled cells** | 1 | X |
 | (active) | Timeslot 0x0000 | |
 | | Channel Offset 0x0000 | |
 | | Link Options = (TX Link = 1, | |
 | | RX Link = 1, Shared Link = 1,| |
 | | Timekeeping = 1) | |
 +--------------------------------+------------------------------+---+
 | Number of unscheduled cells | All remaining cells in the | X |
 | (off) | slotframe. | |
 +--------------------------------+------------------------------+---+
 | Max Number MAC retransmissions | 3 (4 transmission attempts) | |
 +--------------------------------+------------------------------+---+
 | Timeslot template | IEEE Std 802.15.4 default | X |
 | | (macTimeslotTemplateId=0) | |
 +--------------------------------+------------------------------+---+
 | Enhanced Beacon Period | Tunable. Trades off join | |
 | (EB_PERIOD) | time against energy. | |
 +--------------------------------+------------------------------+---+
 | Number used frequencies | IEEE Std 802.15.4 default | X |
 | (2.4 GHz O-QPSK PHY) | (16) | |
 +--------------------------------+------------------------------+---+
 | Channel Hopping sequence | IEEE Std 802.15.4 default | X |
 | (2.4 GHz O-QPSK PHY) | (macHoppingSequenceID = 0) | |
 +--------------------------------+------------------------------+---+
 * An "X" in this column means this property's value is announced
 in the EB; hence, a new node learns it when joining.
 ** This cell LinkType is set to ADVERTISING.
 Figure 1: Recommended IEEE Std 802.15.4 TSCH Settings
4.1. TSCH Schedule
 This minimal mode of operation uses a single slotframe. The TSCH
 slotframe is composed of a tunable number of timeslots. The
 slotframe size (i.e., the number of timeslots it contains) trades off
 bandwidth for energy consumption. The slotframe size needs to be
 tuned; the way of tuning it is out of scope of this specification.
 The slotframe size is announced in the EB. The RECOMMENDED value for
 the slotframe handle (macSlotframeHandle) is 0x00. An implementation
 MAY choose to use a different slotframe handle, for example, to add
 other slotframes with higher priority. The use of other slotframes
 is out of the scope of this document.
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 There is only a single scheduled cell in the slotframe. This cell
 MAY be scheduled at any slotOffset/channelOffset within the
 slotframe. The location of that cell in the schedule is announced in
 the EB. The LinkType of the scheduled cell is ADVERTISING to allow
 EBs to be sent on it.
 Figure 2 shows an example of a slotframe of length 101 timeslots,
 resulting in a radio duty cycle below 0.99%.
 Chan. +----------+----------+ +----------+
 Off.0 | TxRxS/EB | OFF | | OFF |
 Chan. +----------+----------+ +----------+
 Off.1 | OFF | OFF | ... | OFF |
 +----------+----------+ +----------+
 .
 .
 .
 Chan. +----------+----------+ +----------+
 Off.15 | OFF | OFF | | OFF |
 +----------+----------+ +----------+
 slotOffset 0 1 100
 EB: Enhanced Beacon
 Tx: Transmit
 Rx: Receive
 S: Shared
 OFF: Unscheduled by this specification
 Figure 2: Example Slotframe of Length 101 Timeslots
 A node MAY use the scheduled cell to transmit/receive all types of
 link-layer frames. EBs are sent to the link-layer broadcast address
 and are not acknowledged. Data frames are sent unicast and are
 acknowledged by the receiving neighbor.
 All remaining cells in the slotframe are unscheduled. Dynamic
 scheduling solutions may be defined in the future that schedule those
 cells. One example is the 6top Protocol (6P) [PROTO-6P]. Dynamic
 scheduling solutions are out of scope of this document.
 The default values of the TSCH timeslot template (defined in
 Section 8.4.2.2.3 of [IEEE.802.15.4]) and channel hopping sequence
 (defined in Section 6.2.10 of [IEEE.802.15.4]) SHOULD be used. A
 node MAY use different values by properly announcing them in its EB.
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4.2. Cell Options
 In the scheduled cell, a node transmits if there is a packet to
 transmit and listens otherwise (both "TX" and "RX" bits are set).
 When a node transmits, requesting a link-layer acknowledgment per
 [IEEE.802.15.4], and does not receive the requested acknowledgement,
 it uses a back-off mechanism to resolve possible collisions ("Shared"
 bit is set). A node joining the network maintains time
 synchronization to its initial time-source neighbor using that cell
 ("Timekeeping" bit is set).
 This translates into a Link Option for this cell:
 b0 = TX Link = 1 (set)
 b1 = RX Link = 1 (set)
 b2 = Shared Link = 1 (set)
 b3 = Timekeeping = 1 (set)
 b4 = Priority = 0 (clear)
 b5-b7 = Reserved = 0 (clear)
4.3. Retransmissions
 Per Figure 1, the RECOMMENDED maximum number of link-layer
 retransmissions is 3. This means that, for packets requiring an
 acknowledgment, if none are received after a total of 4 attempts, the
 transmission is considered failed and the link layer MUST notify the
 upper layer. Packets not requiring an acknowledgment (including EBs)
 are not retransmitted.
4.4. Timeslot Timing
 Per Figure 1, the RECOMMENDED timeslot template is the default one
 (macTimeslotTemplateId=0) defined in [IEEE.802.15.4].
4.5. Frame Contents
 [IEEE.802.15.4] defines the format of frames. Through a set of
 flags, [IEEE.802.15.4] allows for several fields to be present (or
 not), to have different lengths, and to have different values. This
 specification details the RECOMMENDED contents of 802.15.4 frames,
 while strictly complying with [IEEE.802.15.4].
4.5.1. IEEE Std 802.15.4 Header
 The Frame Version field MUST be set to 0b10 (Frame Version 2). The
 Sequence Number field MAY be elided.
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 The EB Destination Address field MUST be set to 0xFFFF (short
 broadcast address). The EB Source Address field SHOULD be set as the
 node's short address if this is supported. Otherwise, the long
 address MUST be used.
 The PAN ID Compression bit SHOULD indicate that the Source PAN ID is
 "Not Present" and the Destination PAN ID is "Present". The value of
 the PAN ID Compression bit is specified in Table 7-2 of the IEEE Std
 802.15.4-2015 specification and depends on the type of the
 destination and source link-layer addresses (e.g., short, extended,
 not present).
 Nodes follow the reception and rejection rules as per Section 6.7.2
 of [IEEE.802.15.4].
 The nonce is formatted according to [IEEE.802.15.4]. In the IEEE Std
 802.15.4 specification [IEEE.802.15.4], nonce generation is described
 in Section 9.3.2.2, and byte ordering is described in Section 9.3.1,
 Annex B.2, and Annex B.2.2.
4.5.2. Enhanced Beacon Frame
 After booting, a TSCH node starts in an unsynchronized, unjoined
 state. Initial synchronization is achieved by listening for EBs.
 EBs from multiple networks may be heard. Many mechanisms exist for
 discrimination between networks, the details of which are out of
 scope.
 The IEEE Std 802.15.4 specification does not define how often EBs are
 sent, nor their contents [IEEE.802.15.4]. In a minimal TSCH
 configuration, a node SHOULD send an EB every EB_PERIOD. Tuning
 EB_PERIOD allows a trade-off between joining time and energy
 consumption.
 EBs should be used to obtain information about local networks and to
 synchronize ASN and time offset of the specific network that the node
 decides to join. Once joined to a particular network, a node MAY
 choose to continue to listen for EBs, to gather more information
 about other networks, for example. During the joining process,
 before secure connections to time parents have been created, a node
 MAY maintain synchronization using EBs. [RFC7554] discusses
 different time synchronization approaches.
 The IEEE Std 802.15.4 specification requires EBs to be sent in order
 to enable nodes to join the network. The EBs SHOULD carry the
 Information Elements (IEs) listed below [IEEE.802.15.4].
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 TSCH Synchronization IE: Contains synchronization information such
 as ASN and Join Metric. The value of the Join Metric field is
 discussed in Section 6.1.
 TSCH Timeslot IE: Contains the timeslot template identifier. This
 template is used to specify the internal timing of the timeslot.
 This specification RECOMMENDS the default timeslot template.
 Channel Hopping IE: Contains the channel hopping sequence
 identifier. This specification RECOMMENDS the default channel
 hopping sequence.
 TSCH Slotframe and Link IE: Enables joining nodes to learn the
 initial schedule to be used as they join the network. This
 document RECOMMENDS the use of a single cell.
 If a node strictly follows the recommended setting from Figure 1, the
 EB it sends has the exact same contents as an EB it received when
 joining, except for the Join Metric field in the TSCH Synchronization
 IE.
 When a node has already joined a network (i.e., it has received an
 EB) synchronized to the EB sender and configured its schedule
 following this specification, the node SHOULD ignore subsequent EBs
 that try to change the configured parameters. This does not preclude
 listening to EBs from other networks.
4.5.3. Acknowledgment Frame
 Per [IEEE.802.15.4], each acknowledgment contains an ACK/NACK Time
 Correction IE.
4.6. Link-Layer Security
 When securing link-layer frames, link-layer frames MUST be secured by
 the link-layer security mechanisms defined in IEEE Std 802.15.4
 [IEEE.802.15.4]. Link-layer authentication MUST be applied to the
 entire frame, including the 802.15.4 header. Link-layer encryption
 MAY be applied to 802.15.4 Payload IEs and the 802.15.4 payload.
 This specification assumes the existence of two cryptographic keys:
 Key K1 is used to authenticate EBs. EBs MUST be authenticated
 only (no encryption); their contents are defined in Section 4.5.2.
 Key K2 is used to authenticate and encrypt DATA and ACKNOWLEDGMENT
 frames.
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 These keys can be pre-configured or learned during a key distribution
 phase. Key distribution mechanisms are defined, for example, in
 [SEC-6TISCH] and [SEC-JOIN-6TISCH]. Key distribution is out of scope
 of this document.
 The behavior of a Joining Node (JN) is different depending on which
 key(s) are pre-configured:
 If both keys K1 and K2 are pre-configured, the JN does not rely on
 a key distribution phase to learn K1 or K2.
 If key K1 is pre-configured but not key K2, the JN authenticates
 EBs using K1 and relies on the key distribution phase to learn K2.
 If neither key K1 nor key K2 is pre-configured, the JN accepts EBs
 as defined in Section 6.3.1.2 of IEEE Std 802.15.4
 [IEEE.802.15.4], i.e., they are passed forward even "if the status
 of the unsecuring process indicated an error". The JN then runs
 the key distribution phase to learn K1 and K2. During that
 process, the node that JN is talking to uses the secExempt
 mechanism (see Section 9.2.4 of [IEEE.802.15.4]) to process frames
 from JN. Once the key distribution phase is done, the node that
 has installed secExempts for the JN MUST clear the installed
 exception rules.
 In the event of a network reset, the new network MUST either use new
 cryptographic keys or ensure that the ASN remains monotonically
 increasing.
5. RPL Settings
 In a multi-hop topology, the RPL routing protocol [RFC6550] MAY be
 used.
5.1. Objective Function
 If RPL is used, nodes MUST implement the RPL Objective Function Zero
 (OF0) [RFC6552].
5.1.1. Rank Computation
 The Rank computation is described in Section 4.1 of [RFC6552]. A
 node's Rank (see Figure 4 for an example) is computed by the
 following equations:
 R(N) = R(P) + rank_increment
 rank_increment = (Rf*Sp + Sr) * MinHopRankIncrease
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 Figure 3 lists the OF0 parameter values that MUST be used if RPL is
 used.
 +----------------------+-------------------------------------+
 | OF0 Parameters | Value |
 +----------------------+-------------------------------------+
 | Rf | 1 |
 +----------------------+-------------------------------------+
 | Sp | (3*ETX)-2 |
 +----------------------+-------------------------------------+
 | Sr | 0 |
 +----------------------+-------------------------------------+
 | MinHopRankIncrease | DEFAULT_MIN_HOP_RANK_INCREASE (256) |
 +----------------------+-------------------------------------+
 | MINIMUM_STEP_OF_RANK | 1 |
 +----------------------+-------------------------------------+
 | MAXIMUM_STEP_OF_RANK | 9 |
 +----------------------+-------------------------------------+
 | ETX limit to select | 3 |
 | a parent | |
 +----------------------+-------------------------------------+
 Figure 3: OF0 Parameters
 The step_of_rank (Sp) uses the Expected Transmission Count (ETX)
 [RFC6551].
 An implementation MUST follow OF0's normalization guidance as
 discussed in Sections 1 and 4.1 of [RFC6552]. Sp SHOULD be
 calculated as (3*ETX)-2. The minimum value of Sp
 (MINIMUM_STEP_OF_RANK) indicates a good quality link. The maximum
 value of Sp (MAXIMUM_STEP_OF_RANK) indicates a poor quality link.
 The default value of Sp (DEFAULT_STEP_OF_RANK) indicates an average
 quality link. Candidate parents with ETX greater than 3 SHOULD NOT
 be selected. This avoids having ETX values on used links that are
 larger that the maximum allowed transmission attempts.
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5.1.2. Rank Computation Example
 This section illustrates the use of OF0 (see Figure 4). We have:
 rank_increment = ((3*numTx/numTxAck)-2)*minHopRankIncrease = 512
 +-------+
 | 0 | R(minHopRankIncrease) = 256
 | | DAGRank(R(0)) = 1
 +-------+
 |
 |
 +-------+
 | 1 | R(1)=R(0) + 512 = 768
 | | DAGRank(R(1)) = 3
 +-------+
 |
 |
 +-------+
 | 2 | R(2)=R(1) + 512 = 1280
 | | DAGRank(R(2)) = 5
 +-------+
 |
 |
 +-------+
 | 3 | R(3)=R(2) + 512 = 1792
 | | DAGRank(R(3)) = 7
 +-------+
 |
 |
 +-------+
 | 4 | R(4)=R(3) + 512 = 2304
 | | DAGRank(R(4)) = 9
 +-------+
 |
 |
 +-------+
 | 5 | R(5)=R(4) + 512 = 2816
 | | DAGRank(R(5)) = 11
 +-------+
 Figure 4: Rank computation example for a 5-hop network where
 numTx=100 and numTxAck=75 for all links.
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5.2. Mode of Operation
 When RPL is used, nodes MUST implement the non-storing mode of
 operation (see Section 9.7 of [RFC6550]). The storing mode of
 operation (see Section 9.8 of [RFC6550]) SHOULD be implemented by
 nodes with enough capabilities. Nodes not implementing RPL MUST join
 as leaf nodes.
5.3. Trickle Timer
 RPL signaling messages such as DODAG Information Objects (DIOs) are
 sent using the Trickle algorithm (see Section 8.3.1 of [RFC6550] and
 Section 4.2 of [RFC6206]). For this specification, the Trickle timer
 MUST be used with the RPL-defined default values (see Section 8.3.1
 of [RFC6550]).
5.4. Packet Contents
 RPL information and hop-by-hop extension headers MUST follow
 [RFC6553] and [RFC6554]. For cases in which the packets formed at
 the Low-Power and Lossy Network (LLN) need to cross through
 intermediate routers, these MUST follow the IP-in-IP encapsulation
 requirement specified by [RFC6282] and [RFC2460]. Routing extension
 headers such as RPL Packet Information (RPI) [RFC6550] and Source
 Routing Header (SRH) [RFC6554], and outer IP headers in case of
 encapsulation, MUST be compressed according to [RFC8138] and
 [RFC8025].
6. Network Formation and Lifetime
6.1. Value of the Join Metric Field
 The Join Metric of the TSCH Synchronization IE in the EB MUST be
 calculated based on the routing metric of the node, normalized to a
 value between 0 and 255. A lower value of the Join Metric indicates
 the node sending the EB is topologically "closer" to the root of the
 network. A lower value of the Join Metric hence indicates higher
 preference for a joining node to synchronize to that neighbor.
 In case the network uses RPL, the Join Metric of any node (including
 the Directed Acyclic Graph (DAG) root) MUST be set to
 DAGRank(rank)-1. According to Section 5.1.1, DAGRank(rank(0)) = 1.
 DAGRank(rank(0))-1 = 0 is compliant with 802.15.4's requirement of
 having the root use Join Metric = 0.
 In case the network does not use RPL, the Join Metric value MUST
 follow the rules specified by [IEEE.802.15.4].
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6.2. Time-Source Neighbor Selection
 When a node joins a network, it may hear EBs sent by different nodes
 already in the network. The decision of which neighbor to
 synchronize to (e.g., which neighbor becomes the node's initial time-
 source neighbor) is implementation specific. For example, after
 having received the first EB, a node MAY listen for at most
 MAX_EB_DELAY seconds until it has received EBs from
 NUM_NEIGHBOURS_TO_WAIT distinct neighbors. Recommended values for
 MAX_EB_DELAY and NUM_NEIGHBOURS_TO_WAIT are defined in Figure 5.
 When receiving EBs from distinct neighbors, the node MAY use the Join
 Metric field in each EB to select the initial time-source neighbor,
 as described in Section 6.3.6 of IEEE Std 802.15.4 [IEEE.802.15.4].
 At any time, a node MUST maintain synchronization to at least one
 time-source neighbor. A node's time-source neighbor MUST be chosen
 among the neighbors in its RPL routing parent set when RPL is used.
 In the case a node cannot maintain connectivity to at least one time-
 source neighbor, the node looses synchronization and needs to join
 the network again.
6.3. When to Start Sending EBs
 When a RPL node joins the network, it MUST NOT send EBs before having
 acquired a RPL Rank to avoid inconsistencies in the time
 synchronization structure. This applies to other routing protocols
 with their corresponding routing metrics. As soon as a node acquires
 routing information (e.g., a RPL Rank, see Section 5.1.1), it SHOULD
 start sending EBs.
6.4. Hysteresis
 Per [RFC6552] and [RFC6719], the specification RECOMMENDS the use of
 a boundary value (PARENT_SWITCH_THRESHOLD) to avoid constant changes
 of the parent when ranks are compared. When evaluating a parent that
 belongs to a smaller path cost than the current minimum path, the
 candidate node is selected as the new parent only if the difference
 between the new path and the current path is greater than the defined
 PARENT_SWITCH_THRESHOLD. Otherwise, the node MAY continue to use the
 current preferred parent. Per [RFC6719], the PARENT_SWITCH_THRESHOLD
 SHOULD be set to 192 when the ETX metric is used (in the form
 128*ETX); the recommendation for this document is to use
 PARENT_SWITCH_THRESHOLD equal to 640 if the metric being used is
 ((3*ETX)-2)*minHopRankIncrease or a proportional value. This deals
 with hysteresis both for routing parent and time-source neighbor
 selection.
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7. Implementation Recommendations
7.1. Neighbor Table
 The exact format of the neighbor table is implementation specific.
 The RECOMMENDED per-neighbor information is (taken from the [openwsn]
 implementation):
 identifier: Identifier(s) of the neighbor (e.g., EUI-64).
 numTx: Number of link-layer transmission attempts to that
 neighbor.
 numTxAck: Number of transmitted link-layer frames that have been
 link-layer acknowledged by that neighbor.
 numRx: Number of link-layer frames received from that neighbor.
 timestamp: When the last frame was received from that neighbor.
 This can be based on the ASN counter or any other time
 base. It can be used to trigger a keep-alive message.
 routing metric: The RPL Rank of that neighbor, for example.
 time-source neighbor: A flag indicating whether this neighbor is a
 time-source neighbor.
7.2. Queues and Priorities
 The IEEE Std 802.15.4 specification [IEEE.802.15.4] does not define
 the use of queues to handle upper-layer data (either application or
 control data from upper layers). The following rules are
 RECOMMENDED:
 A node is configured to keep in the queues a configurable number
 of upper-layer packets per link (default NUM_UPPERLAYER_PACKETS)
 for a configurable time that should cover the join process
 (default MAX_JOIN_TIME).
 Frames generated by the 802.15.4 layer (including EBs) are queued
 with a priority higher than frames coming from higher layers.
 A frame type BEACON is queued with higher priority than frame
 types DATA.
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7.3. Recommended Settings
 Figure 5 lists RECOMMENDED values for the settings discussed in this
 specification.
 +-------------------------+-------------------+
 | Parameter | RECOMMENDED Value |
 +-------------------------+-------------------+
 | MAX_EB_DELAY | 180 |
 +-------------------------+-------------------+
 | NUM_NEIGHBOURS_TO_WAIT | 2 |
 +-------------------------+-------------------+
 | PARENT_SWITCH_THRESHOLD | 640 |
 +-------------------------+-------------------+
 | NUM_UPPERLAYER_PACKETS | 1 |
 +-------------------------+-------------------+
 | MAX_JOIN_TIME | 300 |
 +-------------------------+-------------------+
 Figure 5: Recommended Settings
8. Security Considerations
 This document is concerned only with link-layer security.
 By their nature, many Internet of Things (IoT) networks have nodes in
 physically vulnerable locations. We should assume that nodes will be
 physically compromised, their memories examined, and their keys
 extracted. Fixed secrets will not remain secret. This impacts the
 node-joining process. Provisioning a network with a fixed link key
 K2 is not secure. For most applications, this implies that there
 will be a joining phase during which some level of authorization will
 be allowed for nodes that have not been authenticated. Details are
 out of scope, but the link layer must provide some flexibility here.
 If an attacker has obtained K1, it can generate fake EBs to attack a
 whole network by sending authenticated EBs. The attacker can cause
 the joining node to initiate the joining process to the attacker. In
 the case that the joining process includes authentication and
 distribution of a K2, then the joining process will fail and the JN
 will notice the attack. If K2 is also compromised, the JN will not
 notice the attack and the network will be compromised.
 Even if an attacker does not know the value of K1 and K2
 (Section 4.6), it can still generate fake EB frames authenticated
 with an arbitrary key. Here we discuss the impact these fake EBs can
 have, depending on what key(s) are pre-provisioned.
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 If both K1 and K2 are pre-provisioned; a joining node can
 distinguish legitimate from fake EBs and join the legitimate
 network. The fake EBs have no impact.
 The same holds if K1 is pre-provisioned but not K2.
 If neither K1 nor K2 is pre-provisioned, a joining node may
 mistake a fake EB for a legitimate one and initiate a joining
 process to the attacker. That joining process will fail, as the
 joining node will not be able to authenticate the attacker during
 the security handshake. This will force the joining node to start
 over listening for an EB. So while the joining node never joins
 the attacker, this costs the joining node time and energy and is a
 vector of attack.
 Choosing what key(s) to pre-provision needs to balance the different
 discussions above.
 Once the joining process is over, the node that has joined can
 authenticate EBs (it knows K1). This means it can process their
 contents and use EBs for synchronization.
 ASN provides a nonce for security operations in a slot. Any re-use
 of ASN with a given key exposes information about encrypted packet
 contents and risks replay attacks. Replay attacks are prevented
 because, when the network resets, either the new network uses new
 cryptographic key(s) or ensures that the ASN increases monotonically
 (Section 4.6).
 Maintaining accurate time synchronization is critical for network
 operation. Accepting timing information from unsecured sources MUST
 be avoided during normal network operation, as described in
 Section 4.5.2. During joining, a node may be susceptible to timing
 attacks before key K1 and K2 are learned. During network operation,
 a node MAY maintain statistics on time updates from neighbors and
 monitor for anomalies.
 Denial-of-Service (DoS) attacks at the Media Access Control (MAC)
 layer in an LLN are easy to achieve simply by Radio Frequency (RF)
 jamming. This is the base case against which more sophisticated DoS
 attacks should be judged. For example, sending fake EBs announcing a
 very low Join Metric may cause a node to waste time and energy trying
 to join a fake network even when legitimate EBs are being heard.
 Proper join security will prevent the node from joining the false
 flag, but by then the time and energy will have been wasted.
 However, the energy cost to the attacker would be lower and the
Vilajosana, et al. Best Current Practice [Page 18]
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 energy cost to the joining node would be higher if the attacker
 simply sent loud short packets in the middle of any valid EB that it
 hears.
 ACK reception probability is less than 100% due to changing channel
 conditions and unintentional or intentional jamming. This will cause
 the sending node to retransmit the same packet until it is
 acknowledged or a retransmission limit is reached. Upper-layer
 protocols should take this into account, possibly using a sequence
 number to match retransmissions.
 The 6TiSCH layer SHOULD keep track of anomalous events and report
 them to a higher authority. For example, EBs reporting low Join
 Metrics for networks that cannot be joined, as described above, may
 be a sign of attack. Additionally, in normal network operation,
 message integrity check failures on packets with a valid Cyclic
 Redundancy Check (CRC) will occur at a rate on the order of once per
 million packets. Any significant deviation from this rate may be a
 sign of a network attack. Along the same lines, time updates in ACKs
 or EBs that are inconsistent with the MAC-layer's sense of time and
 its own plausible time-error drift rate may also be a result of
 network attack.
9. IANA Considerations
 This document does not require any IANA actions.
10. References
10.1. Normative References
 [IEEE.802.15.4]
 IEEE, "IEEE Standard for Low-Rate Wireless Networks",
 IEEE 802.15.4,
 <http://ieeexplore.ieee.org/document/7460875/>.
 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
 Requirement Levels", BCP 14, RFC 2119,
 DOI 10.17487/RFC2119, March 1997,
 <http://www.rfc-editor.org/info/rfc2119>.
 [RFC2460] Deering, S. and R. Hinden, "Internet Protocol, Version 6
 (IPv6) Specification", RFC 2460, DOI 10.17487/RFC2460,
 December 1998, <http://www.rfc-editor.org/info/rfc2460>.
Vilajosana, et al. Best Current Practice [Page 19]
RFC 8180 6TiSCH Minimal May 2017
 [RFC4944] Montenegro, G., Kushalnagar, N., Hui, J., and D. Culler,
 "Transmission of IPv6 Packets over IEEE 802.15.4
 Networks", RFC 4944, DOI 10.17487/RFC4944, September 2007,
 <http://www.rfc-editor.org/info/rfc4944>.
 [RFC6206] Levis, P., Clausen, T., Hui, J., Gnawali, O., and J. Ko,
 "The Trickle Algorithm", RFC 6206, DOI 10.17487/RFC6206,
 March 2011, <http://www.rfc-editor.org/info/rfc6206>.
 [RFC6282] Hui, J., Ed. and P. Thubert, "Compression Format for IPv6
 Datagrams over IEEE 802.15.4-Based Networks", RFC 6282,
 DOI 10.17487/RFC6282, September 2011,
 <http://www.rfc-editor.org/info/rfc6282>.
 [RFC6550] Winter, T., Ed., Thubert, P., Ed., Brandt, A., Hui, J.,
 Kelsey, R., Levis, P., Pister, K., Struik, R., Vasseur,
 JP., and R. Alexander, "RPL: IPv6 Routing Protocol for
 Low-Power and Lossy Networks", RFC 6550,
 DOI 10.17487/RFC6550, March 2012,
 <http://www.rfc-editor.org/info/rfc6550>.
 [RFC6551] Vasseur, JP., Ed., Kim, M., Ed., Pister, K., Dejean, N.,
 and D. Barthel, "Routing Metrics Used for Path Calculation
 in Low-Power and Lossy Networks", RFC 6551,
 DOI 10.17487/RFC6551, March 2012,
 <http://www.rfc-editor.org/info/rfc6551>.
 [RFC6552] Thubert, P., Ed., "Objective Function Zero for the Routing
 Protocol for Low-Power and Lossy Networks (RPL)",
 RFC 6552, DOI 10.17487/RFC6552, March 2012,
 <http://www.rfc-editor.org/info/rfc6552>.
 [RFC6553] Hui, J. and JP. Vasseur, "The Routing Protocol for Low-
 Power and Lossy Networks (RPL) Option for Carrying RPL
 Information in Data-Plane Datagrams", RFC 6553,
 DOI 10.17487/RFC6553, March 2012,
 <http://www.rfc-editor.org/info/rfc6553>.
 [RFC6554] Hui, J., Vasseur, JP., Culler, D., and V. Manral, "An IPv6
 Routing Header for Source Routes with the Routing Protocol
 for Low-Power and Lossy Networks (RPL)", RFC 6554,
 DOI 10.17487/RFC6554, March 2012,
 <http://www.rfc-editor.org/info/rfc6554>.
 [RFC6719] Gnawali, O. and P. Levis, "The Minimum Rank with
 Hysteresis Objective Function", RFC 6719,
 DOI 10.17487/RFC6719, September 2012,
 <http://www.rfc-editor.org/info/rfc6719>.
Vilajosana, et al. Best Current Practice [Page 20]
RFC 8180 6TiSCH Minimal May 2017
 [RFC6775] Shelby, Z., Ed., Chakrabarti, S., Nordmark, E., and C.
 Bormann, "Neighbor Discovery Optimization for IPv6 over
 Low-Power Wireless Personal Area Networks (6LoWPANs)",
 RFC 6775, DOI 10.17487/RFC6775, November 2012,
 <http://www.rfc-editor.org/info/rfc6775>.
 [RFC8025] Thubert, P., Ed. and R. Cragie, "IPv6 over Low-Power
 Wireless Personal Area Network (6LoWPAN) Paging Dispatch",
 RFC 8025, DOI 10.17487/RFC8025, November 2016,
 <http://www.rfc-editor.org/info/rfc8025>.
 [RFC8138] Thubert, P., Ed., Bormann, C., Toutain, L., and R. Cragie,
 "IPv6 over Low-Power Wireless Personal Area Network
 (6LoWPAN) Routing Header", RFC 8138, DOI 10.17487/RFC8138,
 April 2017, <http://www.rfc-editor.org/info/rfc8138>.
 [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
 May 2017, <http://www.rfc-editor.org/info/rfc8174>.
10.2. Informative References
 [openwsn] Watteyne, T., Vilajosana, X., Kerkez, B., Chraim, F.,
 Weekly, K., Wang, Q., Glaser, S., and K. Pister, "OpenWSN:
 a standards-based low-power wireless development
 environment", Transactions on Emerging Telecommunications
 Technologies, Volume 23 Issue 5, pages 480-493, DOI
 10.1002/ett.2558, August 2012.
 [PROTO-6P]
 Wang, Q., Vilajosana, X., and T. Watteyne, "6top Protocol
 (6P)", Work in Progress, draft-ietf-6tisch-6top-protocol-
 05, May 2017.
 [RFC7554] Watteyne, T., Ed., Palattella, M., and L. Grieco, "Using
 IEEE 802.15.4e Time-Slotted Channel Hopping (TSCH) in the
 Internet of Things (IoT): Problem Statement", RFC 7554,
 DOI 10.17487/RFC7554, May 2015,
 <http://www.rfc-editor.org/info/rfc7554>.
 [SEC-6TISCH]
 Vucinic, M., Simon, J., Pister, K., and M. Richardson,
 "Minimal Security Framework for 6TiSCH", Work in
 Progress, draft-ietf-6tisch-minimal-security-02, March
 2017.
Vilajosana, et al. Best Current Practice [Page 21]
RFC 8180 6TiSCH Minimal May 2017
 [SEC-JOIN-6TISCH]
 Richardson, M., "6tisch Secure Join protocol", Work in
 Progress, draft-ietf-6tisch-dtsecurity-secure-join-01,
 February 2017.
 [TERMS-6TiSCH]
 Palattella, M., Thubert, P., Watteyne, T., and Q. Wang,
 "Terminology in IPv6 over the TSCH mode of IEEE
 802.15.4e", Work in Progress, draft-ietf-6tisch-
 terminology-08, December 2016.
Vilajosana, et al. Best Current Practice [Page 22]
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Appendix A. Examples
 This section contains several example packets. Each example contains
 (1) a schematic header diagram, (2) the corresponding bytestream, and
 (3) a description of each of the IEs that form the packet. Packet
 formats are specific for the [IEEE.802.15.4] revision and may vary in
 future releases of the IEEE standard. In case of differences between
 the packet content presented in this section and [IEEE.802.15.4], the
 latter has precedence.
 The MAC header fields are described in a specific order. All field
 formats in this example are depicted in the order in which they are
 transmitted, from left to right, where the leftmost bit is
 transmitted first. Bits within each field are numbered from 0
 (leftmost and least significant) to k - 1 (rightmost and most
 significant), where the length of the field is k bits. Fields that
 are longer than a single octet are sent to the PHY in the order from
 the octet containing the lowest numbered bits to the octet containing
 the highest numbered bits (little endian).
A.1. Example: EB with Default Timeslot Template
 1 2 3
 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 | Len1 = 0 |Element ID=0x7e|0| Len2 = 26 |GrpId=1|1|
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 | Len3 = 6 |Sub ID = 0x1a|0| ASN
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 ASN | Join Metric |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 | Len4 = 0x01 |Sub ID = 0x1c|0| TT ID = 0x00 | Len5 = 0x01
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |ID=0x9 |1| CH ID = 0x00 | Len6 = 0x0A |Sub ID = 0x1b|0|
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 | #SF = 0x01 | SF ID = 0x00 | SF LEN = 0x65 (101 slots) |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 | #Links = 0x01 | SLOT OFFSET = 0x0000 | CHANNEL
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 OFF = 0x0000 |Link OPT = 0x0F| NO MAC PAYLOAD
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 Bytestream:
 00 3F 1A 88 06 1A ASN#0 ASN#1 ASN#2 ASN#3 ASN#4 JP 01 1C 00
 01 C8 00 0A 1B 01 00 65 00 01 00 00 00 00 0F
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 Description of the IEs:
 #Header IE Header
 Len1 = Header IE Length (0)
 Element ID = 0x7e - termination IE indicating Payload IE
 coming next
 Type 0
 #Payload IE Header (MLME)
 Len2 = Payload IE Len (26 bytes)
 Group ID = 1 MLME (Nested)
 Type = 1
 #MLME-SubIE TSCH Synchronization
 Len3 = Length in bytes of the sub-IE payload (6 bytes)
 Sub-ID = 0x1a (MLME-SubIE TSCH Synchronization)
 Type = Short (0)
 ASN = Absolute Sequence Number (5 bytes)
 Join Metric = 1 byte
 #MLME-SubIE TSCH Timeslot
 Len4 = Length in bytes of the sub-IE payload (1 byte)
 Sub-ID = 0x1c (MLME-SubIE Timeslot)
 Type = Short (0)
 Timeslot template ID = 0x00 (default)
 #MLME-SubIE Channel Hopping
 Len5 = Length in bytes of the sub-IE payload (1 byte)
 Sub-ID = 0x09 (MLME-SubIE Channel Hopping)
 Type = Long (1)
 Hopping Sequence ID = 0x00 (default)
 #MLME-SubIE TSCH Slotframe and Link
 Len6 = Length in bytes of the sub-IE payload (10 bytes)
 Sub-ID = 0x1b (MLME-SubIE TSCH Slotframe and Link)
 Type = Short (0)
 Number of slotframes = 0x01
 Slotframe handle = 0x00
 Slotframe size = 101 slots (0x65)
 Number of Links (Cells) = 0x01
 Timeslot = 0x0000 (2B)
 Channel Offset = 0x0000 (2B)
 Link Options = 0x0F
 (TX Link = 1, RX Link = 1, Shared Link = 1,
 Timekeeping = 1 )
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A.2. Example: EB with Custom Timeslot Template
 Using a custom timeslot template in EBs: setting timeslot length to
 15 ms.
 1 2 3
 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 | Len1 = 0 |Element ID=0x7e|0| Len2 = 53 |GrpId=1|1|
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 | Len3 = 6 |Sub ID = 0x1a|0| ASN
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 ASN | Join Metric |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 | Len4 = 25 |Sub ID = 0x1c|0| TT ID = 0x01 | macTsCCAOffset
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 = 2700 | macTsCCA = 128 | macTsTxOffset
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 = 3180 | macTsRxOffset = 1680 | macTsRxAckDelay
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 = 1200 | macTsTxAckDelay = 1500 | macTsRxWait
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 = 3300 | macTsAckWait = 600 | macTsRxTx
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 = 192 | macTsMaxAck = 2400 | macTsMaxTx
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 = 4256 | macTsTimeslotLength = 15000 | Len5 = 0x01
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |ID=0x9 |1| CH ID = 0x00 | Len6 = 0x0A | ...
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 Bytestream:
 00 3F 1A 88 06 1A ASN#0 ASN#1 ASN#2 ASN#3 ASN#4 JP 19 1C 01 8C 0A 80
 00 6C 0C 90 06 B0 04 DC 05 E4 0C 58 02 C0 00 60 09 A0 10 98 3A 01 C8
 00 0A ...
 Description of the IEs:
 #Header IE Header
 Len1 = Header IE Length (none)
 Element ID = 0x7e - termination IE indicating Payload IE
 coming next
 Type 0
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 #Payload IE Header (MLME)
 Len2 = Payload IE Len (53 bytes)
 Group ID = 1 MLME (Nested)
 Type = 1
 #MLME-SubIE TSCH Synchronization
 Len3 = Length in bytes of the sub-IE payload (6 bytes)
 Sub-ID = 0x1a (MLME-SubIE TSCH Synchronization)
 Type = Short (0)
 ASN = Absolute Sequence Number (5 bytes)
 Join Metric = 1 byte
 #MLME-SubIE TSCH Timeslot
 Len4 = Length in bytes of the sub-IE payload (25 bytes)
 Sub-ID = 0x1c (MLME-SubIE Timeslot)
 Type = Short (0)
 Timeslot template ID = 0x01 (non-default)
 The 15 ms timeslot announced:
 +--------------------------------+------------+
 | IEEE 802.15.4 TSCH parameter | Value (us) |
 +--------------------------------+------------+
 | macTsCCAOffset | 2700 |
 +--------------------------------+------------+
 | macTsCCA | 128 |
 +--------------------------------+------------+
 | macTsTxOffset | 3180 |
 +--------------------------------+------------+
 | macTsRxOffset | 1680 |
 +--------------------------------+------------+
 | macTsRxAckDelay | 1200 |
 +--------------------------------+------------+
 | macTsTxAckDelay | 1500 |
 +--------------------------------+------------+
 | macTsRxWait | 3300 |
 +--------------------------------+------------+
 | macTsAckWait | 600 |
 +--------------------------------+------------+
 | macTsRxTx | 192 |
 +--------------------------------+------------+
 | macTsMaxAck | 2400 |
 +--------------------------------+------------+
 | macTsMaxTx | 4256 |
 +--------------------------------+------------+
 | macTsTimeslotLength | 15000 |
 +--------------------------------+------------+
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 #MLME-SubIE Channel Hopping
 Len5 = Length in bytes of the sub-IE payload. (1 byte)
 Sub-ID = 0x09 (MLME-SubIE Channel Hopping)
 Type = Long (1)
 Hopping Sequence ID = 0x00 (default)
A.3. Example: Link-layer Acknowledgment
 Enhanced Acknowledgment packets carry the Time Correction IE (Header
 IE).
 1 2 3
 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 | Len1 = 2 |Element ID=0x1e|0| Time Sync Info |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 Bytestream:
 02 0F TS#0 TS#1
 Description of the IEs:
 #Header IE Header
 Len1 = Header IE Length (2 bytes)
 Element ID = 0x1e - ACK/NACK Time Correction IE
 Type 0
A.4. Example: Auxiliary Security Header
 802.15.4 Auxiliary Security Header with the Security Level set to
 ENC-MIC-32.
 1
 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |L = 5|M=1|1|1|0|Key Index = IDX|
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 Bytestream:
 6D IDX#0
 Security Auxiliary Header fields in the example:
 #Security Control (1 byte)
 L = Security Level ENC-MIC-32 (5)
 M = Key Identifier Mode (0x01)
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 Frame Counter Suppression = 1 (omitting Frame Counter field)
 ASN in Nonce = 1 (construct Nonce from 5 byte ASN)
 Reserved = 0
 #Key Identifier (1 byte)
 Key Index = IDX (deployment-specific KeyIndex parameter that
 identifies the cryptographic key)
Acknowledgments
 The authors acknowledge the guidance and input from Rene Struik, Pat
 Kinney, Michael Richardson, Tero Kivinen, Nicola Accettura, Malisa
 Vucinic, and Jonathan Simon. Thanks to Charles Perkins, Brian E.
 Carpenter, Ralph Droms, Warren Kumari, Mirja Kuehlewind, Ben
 Campbell, Benoit Claise, and Suresh Krishnan for the exhaustive and
 detailed reviews. Thanks to Simon Duquennoy, Guillaume Gaillard,
 Tengfei Chang, and Jonathan Munoz for the detailed review of the
 examples section. Thanks to 6TiSCH co-chair Pascal Thubert for his
 guidance and advice.
Authors' Addresses
 Xavier Vilajosana (editor)
 Universitat Oberta de Catalunya
 156 Rambla Poblenou
 Barcelona, Catalonia 08018
 Spain
 Email: xvilajosana@uoc.edu
 Kris Pister
 University of California Berkeley
 512 Cory Hall
 Berkeley, California 94720
 United States of America
 Email: pister@eecs.berkeley.edu
 Thomas Watteyne
 Analog Devices
 32990 Alvarado-Niles Road, Suite 910
 Union City, CA 94587
 United States of America
 Email: twatteyne@linear.com
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