6TiSCH X. Vilajosana, Ed.
Internet-Draft Universitat Oberta de Catalunya
Intended status: Best Current Practice K. Pister
Expires: June 1, 2017 University of California Berkeley
November 28, 2016
Minimal 6TiSCH Configuration
draft-ietf-6tisch-minimal-17
Abstract
This document describes a minimal mode of operation for a 6TiSCH
Network. It provides IPv6 connectivity over a Non-Broadcast Multi-
Access (NBMA) mesh composed of IEEE802.15.4 Timeslotted Channel
Hopping (TSCH) links. This minimal mode uses a collection of
protocols including the 6LoWPAN framework to enable interoperable
IPv6 connectivity over IEEE802.15.4 TSCH with minimal network
configuration and infrastructure.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
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This Internet-Draft will expire on June 1, 2017.
Copyright Notice
Copyright (c) 2016 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
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publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect
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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.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Requirements Language . . . . . . . . . . . . . . . . . . . . 3
3. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3
4. IEEE802.15.4 Settings . . . . . . . . . . . . . . . . . . . . 4
4.1. TSCH Schedule . . . . . . . . . . . . . . . . . . . . . . 5
4.2. Cell Options . . . . . . . . . . . . . . . . . . . . . . 7
4.3. Retransmissions . . . . . . . . . . . . . . . . . . . . . 7
4.4. Timeslot Timing . . . . . . . . . . . . . . . . . . . . . 7
4.5. Frame Formats . . . . . . . . . . . . . . . . . . . . . . 8
4.5.1. IEEE802.15.4 Header . . . . . . . . . . . . . . . . . 8
4.5.2. Enhanced Beacon Frame . . . . . . . . . . . . . . . . 9
4.5.3. Acknowledgment Frame . . . . . . . . . . . . . . . . 10
4.6. Link-Layer Security . . . . . . . . . . . . . . . . . . . 10
5. RPL Settings . . . . . . . . . . . . . . . . . . . . . . . . 10
5.1. Objective Function . . . . . . . . . . . . . . . . . . . 10
5.1.1. Rank Computation . . . . . . . . . . . . . . . . . . 11
5.1.2. Rank Computation Example . . . . . . . . . . . . . . 12
5.2. Mode of Operation . . . . . . . . . . . . . . . . . . . . 13
5.3. Trickle Timer . . . . . . . . . . . . . . . . . . . . . . 13
5.4. Packet Formats . . . . . . . . . . . . . . . . . . . . . 13
6. Network Formation and Lifetime . . . . . . . . . . . . . . . 13
6.1. Value of the Join Metric Field . . . . . . . . . . . . . 13
6.2. Initial Time Source Neighbor Selection . . . . . . . . . 13
6.3. When to Start Sending EBs . . . . . . . . . . . . . . . . 14
6.4. Time Source Neighbor Selection . . . . . . . . . . . . . 14
6.5. Hysteresis . . . . . . . . . . . . . . . . . . . . . . . 14
7. Implementation Recommendations . . . . . . . . . . . . . . . 14
7.1. Neighbor Table . . . . . . . . . . . . . . . . . . . . . 15
7.2. Queues and Priorities . . . . . . . . . . . . . . . . . . 15
7.3. Recommended Settings . . . . . . . . . . . . . . . . . . 16
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 16
9. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 16
10. References . . . . . . . . . . . . . . . . . . . . . . . . . 16
10.1. Normative References . . . . . . . . . . . . . . . . . . 16
10.2. Informative References . . . . . . . . . . . . . . . . . 18
10.3. External Informative References . . . . . . . . . . . . 18
Appendix A. Examples . . . . . . . . . . . . . . . . . . . . . . 18
A.1. Example: EB with Default Timeslot Template . . . . . . . 19
A.2. Example: EB with Custom Timeslot Template . . . . . . . 20
A.3. Example: Link-layer Acknowledgment . . . . . . . . . . . 22
A.4. Example: Auxiliary Security Header . . . . . . . . . . . 23
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 24
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1. Introduction
A 6TiSCH Network provides IPv6 connectivity over a Non-Broadcast
Multi-Access (NBMA) network that is composed of IEEE802.15.4
Timeslotted Channel Hopping (TSCH) links.
Nodes in an IEEE802.15.4 TSCH network follow a communication
schedule. When following this specification, a node learns the
schedule of the network when joining, the schedule is static and the
same for all nodes.
This specification defines operational parameters and procedures for
a minimal mode of operation to build a 6TiSCH Network. The 802.15.4
TSCH mode, the 6LoWPAN framework, RPL [RFC6550], and its 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. RPL is a natural
choice for routing on top of IEEE802.15.4 TSCH, and the specifics for
interoperable interaction between RPL and TSCH are described.
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", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC 2119 [RFC2119].
3. Terminology
This document uses terminology from [I-D.ietf-6tisch-terminology].
The following concepts are used in this document:
SFD: Start of Frame Delimiter.
RX: Reception.
TX: Transmission.
Join Metric: Field in the TSCH Synchronization IE. Number of hops
separating the node sending the EB, and the PAN coordinator.
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4. IEEE802.15.4 Settings
An implementation compliant to this specification MUST implement the
IEEE802.15.4 [IEEE802154-2015] in "timeslotted channel hopping"
(TSCH) mode.
The remainder of this section details the RECOMMENDED TSCH settings,
which are summarized in Figure 1. A node MAY use different values.
Any of the properties marked in the EB column are announced in the
Enhanced Beacons (EB) the nodes send [IEEE802154-2015]. Changing
their value hence means changing the contents of the EB.
In case of discrepancy between the values in this specification and
the IEEE802.15.4 specification [IEEE802154-2015], the IEEE standard
has precedence.
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+--------------------------------+------------------------------+---+
| Property | Recommended Setting |EB*|
+--------------------------------+------------------------------+---+
| Slotframe Length | Tunable. Trades-off | X |
| | bandwidth against energy. | |
+--------------------------------+------------------------------+---+
| Number of scheduled cells | 1 (slotOffset 0x00) | X |
| (active) | (chOffset 0x00) | |
| | (link Option 0x0f) | |
| | (macLinkType ADVERTISING) | |
+--------------------------------+------------------------------+---+
| Number of unscheduled cells | All remaining cells in the | X |
| (off) | slotframe | |
+--------------------------------+------------------------------+---+
| Max Number MAC retransmissions | 3 (4 transmission attempts) | |
+--------------------------------+------------------------------+---+
| Timeslot template | IEEE802.15.4 default | X |
| | (macTimeslotTemplateId=0) | |
+--------------------------------+------------------------------+---+
| Enhanced Beacon Period | Tunable. Trades-off join | |
| (EB_PERIOD) | time against energy. | |
+--------------------------------+------------------------------+---+
| Number used frequencies | IEEE802.15.4 default | X |
| (2.4 GHz O-QPSK PHY) | (16) | |
+--------------------------------+------------------------------+---+
| Channel Hopping sequence | IEEE802.15.4 default | X |
| (2.4 GHz O-QPSK PHY) | [5, 6, 12, 7, 15, 4, 14, 11, | |
| | 8, 0, 1, 2, 13, 3, 9, 10] | |
+--------------------------------+------------------------------+---+
* an "X" in this column means this property's value is announced in
the EB; a new node hence learns it when joining.
Figure 1: Recommended IEEE802.15.4 TSCH Settings.
4.1. TSCH Schedule
The TSCH slotframe is composed of a tunable number of timeslots. The
slotframe length (i.e. the number of timeslots it contains) trades
off bandwidth for energy consumption. The slotframe length needs to
be tuned; the way of tuning it is out of scope of this specification.
The slotframe length is announced in the EB.
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 macLinkType of the scheduled cell is ADVERTISING to
allow EBs to be sent on it.
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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 not acknowledged. Data frames are sent unicast, and acknowledged
by the receiving neighbor.
All remaining cells in the slotframe are unscheduled. Dynamic
scheduling solutions MAY be defined in the future which schedule
those cells. One example is the 6top Protocol (6P)
[I-D.ietf-6tisch-6top-protocol]. Dynamic scheduling solutions are
out of scope of this document. Details about the usage of the non-
scheduled cells are out of scope of this document. In particular,
this specification does not make any restriction on the Link Option
bitmap associated with those dynamically scheduled cells (i.e. they
can be "Hard" or "Soft" cells, see [I-D.ietf-6tisch-terminology]).
The default values of the Timeslot template and Channel Hopping
sequence (defined in [IEEE802154-2015]) SHOULD be used. A node MAY
use different values by properly announcing it in its Enhanced
Beacon.
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4.2. Cell Options
In the scheduled cell, a node transmits if there is a packet to
transmit, listens otherwise (both "TX" and "RX" bits are set). When
a node transmits and does not receive a link-layer acknowledgment, 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 of value 0x0f:
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)
The scheduled cell is a "Hard cell" [I-D.ietf-6tisch-terminology],
i.e. it cannot be moved or relocated by any dynamic scheduling
mechanism.
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
Figure 3 shows an active timeslot in which a packet is sent from the
transmitter node (TX) to the receiver node (RX). A link-layer
acknowledgment is sent by the RX node to the TX node when the packet
is to be acknowledged. The tsTxOffset duration defines the instant
in the timeslot when the first bit after the Start of Frame Delimiter
(SFD) of the transmitted packet leaves the radio of the TX node. The
radio of the RX node is turned on tsRxWait/2 before that instant, and
listens for at least tsRxWait. This allows for a de-synchronization
between the two nodes of at most tsRxWait/2 in either direction
(early or late). The RX node needs to send the first bit after the
SFD of the MAC acknowledgment exactly tsTxAckDelay after the end of
the last byte of the received packet. TX's radio has to be turned on
tsAckWait/2 before that time, and keep listening for at least
tsAckWait. The TX node can perform a Clear Channel Assessment (CCA)
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if required; this does not interfere with the scope of this document.
The use of CCA is OPTIONAL.
/---------------------- Timeslot Duration -----------------------/
| / (5) / |
| | / tsRxAckDelay /| | | |
|-------------------+--------------+------------------+------+---|
TX |/(1)/ (2) / (3) /| TX frame | |RX ACK| |
|----+-------+------+--------------+------------------+------+---|
|/ tsTxOffset /| | | | |
| | | | | |
|-------------------+--------------+------------------+------+---|
RX | | | | RX frame | |TX ACK| |
|----------------+--+--+-----------+------------------+------+---|
| | | | | | | |
| / (4) / / tsTxAckDelay / | |
Start End
of of
Slot Slot
/(1)/ tsCCAOffset
/(2)/ tsCCA
/(3)/ tsRxTx
/(4)/ tsRxWait
/(5)/ tsAckWait
Figure 3: Timeslot internal timing diagram (refer to Figure 6-43 in
IEEE802.15.4-2015.)
Per Figure 1, the RECOMMENDED timeslot template is the default one
defined in [IEEE802154-2015].
4.5. Frame Formats
The following sections detail the RECOMMENDED format of link-layer
frames of different types. A node MAY use a different formats (bit
settings, etc), but MUST implement IEEE802.15.4 TSCH correctly. As
long as an implementation follows IEEE802.15.4 TSCH correctly, it is
compliant to this specification.
4.5.1. IEEE802.15.4 Header
The IEEE802.15.4 header of BEACON, DATA and ACKNOWLEDGMENT frames
SHOULD include the Source Address field and the Destination Address
field. The Frame Version field SHOULD be set to 0b10 (Frame Version
2). The IEEE802.15.4 header SHOULD include Source Address field and
the Destination Address field. The Sequence Number field MAY be
elided.
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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 7-6 of the
IEEE802.15.4 2015 specification, and depends on the type of the
destination and source link-layer addresses (short, extended, not
present).
While listening for EBs, a joining node set its own PAN ID to 0xffff
in order to meet the filtering rules in the IEEE802.15.4
specification [IEEE802154-2015].
The Nonce is formatted according to [IEEE802154-2015]. In the
IEEE802.15.4 specification [IEEE802154-2015], nonce generation is
described in Section 9.3.2.2, and byte ordering in Section 9.3.1,
Annex B.2 and Annex B.2.2.
4.5.2. Enhanced Beacon Frame
The IEEE802.15.4 specification does not define how often EBs are
sent, nor their contents [IEEE802154-2015]. 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 NOT be used for time synchronization. Time
synchronization SHOULD only be achieved through normal data traffic
and keep-alive frames. [RFC7554] further discusses different time
synchronization approaches.
EBs MUST be sent as per the IEEE802.15.4 specification and SHOULD
carry the Information Elements (IEs) listed below [IEEE802154-2015].
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.
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If a node strictly follows the recommended setting from Figure 1, the
EB it sends has the exact same contents as an EB it has received when
joining, except for the Join Metric field in the TSCH Synchronization
IE.
4.5.3. Acknowledgment Frame
Per [IEEE802154-2015], each acknowledgment contain an ACK/NACK Time
Correction IE.
4.6. Link-Layer Security
All link-layer frames MUST be secured by the link-layer security
mechanisms defined in IEEE802.15.4 [IEEE802154-2015]: link-layer
authentication and link-layer encryption. Link-layer authentication
applies to the entire frame, including the IEEE802.15.4 header.
Link-layer encryption applies only to IEEE802.15.4 payload IEs and
the IEEE802.15.4 payload.
This specification assumes the existence of two cryptographic keys.
These keys can be pre-configured, or learned during a key
distribution phase. Key distribution is out of scope of this
document.
Key K1 is used to authenticate EBs. As defined in Section 4.5.2, EBs
MUST be authenticated only (no encryption). This facilitates logical
segregation of distinct networks.
Key K2 is used to authenticate and encrypt DATA and ACKNOWLEDGMENT
frames. Depending on the security policy, K1 and K2 could be the
same key.
For early interoperability testing, value 36 54 69 53 43 48 20 6D 69
6E 69 6D 61 6C 31 35 ("6TiSCH minimal15") MAY be used for K1.
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].
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5.1.1. Rank Computation
The Rank computation is described at [RFC6552], Section 4.1. 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
Figure 4 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 4: OF0 parameters.
The step_of_rank (Sp) uses Expected Transmission Count (ETX)
[RFC6551]. ETX is computed using the reception/non-reception of
link-layer ACKs.
An implementation MUST follow OF0's normalization guidance as
discussed in Section 1 and Section 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 which are
larger that the maximum allowed transmission attempts.
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5.1.2. Rank Computation Example
This section illustrates the use of the Objective Function Zero (see
Figure 5). 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 5: Rank computation example for 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 support the non-storing ([RFC6550]
Section 9.7) mode of operation. The storing ([RFC6550] Section 9.8)
mode of operation SHOULD be supported by nodes with enough
capabilities. Nodes not supporting RPL MUST join as leaf nodes.
5.3. Trickle Timer
RPL signaling messages such as DIOs are sent using the Trickle
Algorithm [RFC6550] (Section 8.3.1) and [RFC6206] (Section 4.2). For
this specification, the Trickle Timer MUST be used with the RPL
defined default values [RFC6550] (Section 8.3.1).
5.4. Packet Formats
RPL information and hop-by-hop extension headers MUST follow
[RFC6553] and [RFC6554] specification. In the case the packets
formed at the LLN need to cross through intermediate routers, these
MUST follow the IP-in-IP encapsulation requirement specified by the
[RFC6282] and [RFC2460]. Routing extension headers such as RPI
[RFC6550] and SRH [RFC6554], and outer IP headers in case of
encapsulation MUST be compressed according to
[I-D.ietf-6lo-routing-dispatch] and [I-D.ietf-6lo-paging-dispatch].
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 that the network uses RPL, the Join Metric of any node
(including the 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 IEEE802.15.4's requirement of having the root use Join
Metric = 0.
6.2. Initial 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.
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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. 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
IEEE802.15.4 [IEEE802154-2015], Section 6.3.6.
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 Enhanced Beacons.
6.4. Time Source Neighbor Selection
At any time, a node MUST maintain connectivity to at least one time
source neighbor. A node's time source neighbor MUST be chosen among
the neighbors in its routing parent set.
6.5. Hysteresis
Per [RFC6552] and [RFC6719], the specification RECOMMENDS the use of
a boundary value (PARENT_SWITCH_THRESHOLD) to avoid constant changes
of 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 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 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. In case a node has a security association with its
parent, including routing parent or time source neighbor, the node
SHOULD be allowed to keep the association despite of fluctuations of
the rank.
7. Implementation Recommendations
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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: Such as the RPL Rank of that neighbor.
time source neighbor: A flag indicating whether this neighbor is a
time source neighbor.
7.2. Queues and Priorities
The IEEE802.15.4 specification [IEEE802154-2015] 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 IEEE802.15.4 layer (including EBs) are
queued with a priority higher than frames coming from higher-
layers.
Frame types BEACON and COMMAND are queued with higher priority
than frame types DATA and ACK.
One entry in the queue is reserved at all times for frames of
types BEACON and COMMAND frames.
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7.3. Recommended Settings
Figure 6 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 6: Recommended Settings.
8. IANA Considerations
This document requests no immediate action by IANA.
9. Acknowledgments
The authors acknowledge the guidance and input from Rene Struik, Pat
Kinney, Michael Richardson, Tero Kivinen, Nicola Accettura, Malisa
Vucinic, and thank Charles Perkins and Suresh Krishnan for the
exhaustive and detailed review. Thanks to Simon Duquennoy, Guillaume
Gaillard, Tengfei Chang and Jonathan Munoz for the detailed review of
the examples section. Thanks to 6TiSCH co-chairs Pascal Thubert and
Thomas Watteyne for their guidance and advice.
10. References
10.1. Normative References
[I-D.ietf-6lo-routing-dispatch]
Thubert, P., Bormann, C., Toutain, L., and R. Cragie,
"6LoWPAN Routing Header", draft-ietf-6lo-routing-
dispatch-05 (work in progress), February 2016.
[I-D.ietf-6lo-paging-dispatch]
Thubert, P. and R. Cragie, "6LoWPAN Paging Dispatch",
draft-ietf-6lo-paging-dispatch-05 (work in progress),
October 2016.
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[IEEE802154-2015]
IEEE standard for Information Technology, "IEEE Std
802.15.4-2015 Standard for Low-Rate Wireless Personal Area
Networks (WPANs)", December 2015.
[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>.
[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>.
[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>.
[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>.
[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>.
[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>.
[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>.
[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>.
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[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>.
[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>.
10.2. Informative References
[I-D.ietf-6tisch-6top-protocol]
Wang, Q. and X. Vilajosana, "6top Protocol (6P)", draft-
ietf-6tisch-6top-protocol-03 (work in progress), October
2016.
[I-D.ietf-6tisch-terminology]
Palattella, M., Thubert, P., Watteyne, T., and Q. Wang,
"Terminology in IPv6 over the TSCH mode of IEEE
802.15.4e", draft-ietf-6tisch-terminology-07 (work in
progress), March 2016.
[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>.
10.3. External 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 , August 2012.
Appendix A. Examples
This section contains several example packets. Each example contains
(1) a schematic header diagram, (2) the corresponding bytestream, (3)
a description of each of the IEs that form the packet. Packet
formats are specific for the [IEEE802154-2015] revision and may vary
in future releases of the IEEE standard. In case of differences
between the packet content presented in this section and
[IEEE802154-2015], the latter has precedence.
The MAC header fields are described in a specific order. All field
formats in this examples are depicted in the order in which they are
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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
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)
GroupID = 1 MLME (Nested)
Type = 1
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#MLME-SubIE TSCH Synchronization
Len3 = Length in bytes of the sub-IE payload (6 Bytes)
SubID = 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)
SubID = 0x1c (MLME-SubIE Timeslot)
Type = Short (0)
TimeSlot template ID = 0x00 (default)
#MLME-SubIE Ch. Hopping
Len5 = Length in bytes of the sub-IE payload (1 Byte)
SubID = 0x09 (MLME-SubIE Ch. Hopping)
Type = Long (1)
Channel Hopping Sequence ID = 0x00 (default)
#MLME-SubIE TSCH Slotframe and Link
Len6 = Length in bytes of the sub-IE payload (10 Bytes)
SubID = 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 = 0x01
Timeslot = 0x0000 (2B)
Channel Offset = 0x0000 (2B)
Link Option = 0x0F (tx,rx,shared,timekeeping)
A.2. Example: EB with Custom Timeslot Template
Using a custom timeslot template in EBs: setting timeslot length to
15ms.
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
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+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
= 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
#Payload IE Header (MLME)
Len2 = Payload IE Len (53 Bytes)
GroupID = 1 MLME (Nested)
Type = 1
#MLME-SubIE TSCH Synchronization
Len3 = Length in bytes of the sub-IE payload (6 Bytes)
SubID = 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)
SubID = 0x1c (MLME-SubIE Timeslot)
Type = Short (0)
TimeSlot template ID = 0x01 (non-default)
The 15ms timeslot announced:
+--------------------------------+------------+
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| IEEE802.15.4 TSCH parameter | Value (us) |
+--------------------------------+------------+
| tsCCAOffset | 2700 |
+--------------------------------+------------+
| tsCCA | 128 |
+--------------------------------+------------+
| tsTxOffset | 3180 |
+--------------------------------+------------+
| tsRxOffset | 1680 |
+--------------------------------+------------+
| tsRxAckDelay | 1200 |
+--------------------------------+------------+
| tsTxAckDelay | 1500 |
+--------------------------------+------------+
| tsRxWait | 3300 |
+--------------------------------+------------+
| tsAckWait | 600 |
+--------------------------------+------------+
| tsRxTx | 192 |
+--------------------------------+------------+
| tsMaxAck | 2400 |
+--------------------------------+------------+
| tsMaxTx | 4256 |
+--------------------------------+------------+
| Timeslot duration | 15000 |
+--------------------------------+------------+
#MLME-SubIE Ch. Hopping
Len5 = Length in bytes of the sub-IE payload. (1 Byte)
SubID = 0x09 (MLME-SubIE Ch. Hopping)
Type = Long (1)
Channel Hopping Sequence ID = 0x00 (default)
A.3. Example: Link-layer Acknowledgment
Enhanced Acknowledgment packets carry the Time Correction IE (Header
IE).
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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
IEEE802.15.4 Auxiliary Security Header with 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)
Frame Counter Suppression = 1 (omitting Frame Counter field)
Frame Counter Size = 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)
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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
USA
Email: pister@eecs.berkeley.edu
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