| 6TiSCH | X. Vilajosana, Ed. |
| Internet-Draft | Universitat Oberta de Catalunya |
| Intended status: Informational | K. Pister |
| Expires: December 14, 2015 | University of California Berkeley |
| June 12, 2015 |
Minimal 6TiSCH Configuration
draft-ietf-6tisch-minimal-07
This document describes the minimal set of rules to operate an IEEE 802.15.4 Timeslotted Channel Hopping (TSCH) network. This minimal mode of operation can be used during network bootstrap, as a fall-back mode of operation when no dynamic scheduling solution is available or functioning, or during early interoperability testing and development.
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The nodes in a IEEE 802.15.4 TSCH network follow a communication schedule. The entity (centralized or decentralized) responsible for building and maintaining that schedule has precise control over the trade-off between the network's latency, bandwidth, reliability and power consumption.During early interoperability testing and development, however, simplicity is more important than efficiency. One goal of this document is to define the simplest set of rules for building a TSCH-compliant network, at the necessary price of lesser efficiency. Yet, this minimal mode of operation MAY also be used during network bootstrap before any schedule is installed into the network so nodes can self-organize and the management and configuration information be distributed. In addition, the minimal configuration MAY be used as a fall-back mode of operation, ensuring connectivity of nodes in case that dynamic scheduling mechanisms fail or are not available. [IEEE802154] provides a mechanism whereby the details of slotframe length, timeslot timing, and channel hopping pattern are communicated when a node synchronizes to the network. This document describes specific settings for these parameters. Nodes MUST broadcast properly-formed Enhanced Beacons to announce these values.
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].
In order to form a network, a minimum schedule configuration is required so nodes can advertise the presence of the network, and allow other nodes to join.
The slotframe, as defined in [I-D.ietf-6tisch-terminology], is an abstraction of the link layer that defines a collection of time slots of equal length, and which repeats over time. In order to set up a minimal TSCH network, nodes need to be synchronized with the same slotframe configuration so they can communicate. This document recommends the following slotframe configuration.
Minimal configuration
+------------------------------------+----------------------+ | Property | Value | +------------------------------------+----------------------+ | Number of time slots per Slotframe | Variable | +------------------------------------+----------------------+ | Number of available frequencies | 16 | +------------------------------------+----------------------+ | Number of scheduled cells | 1 (slotOffset 0) | | | (macLinkType NORMAL) | +------------------------------------+----------------------+ | Number of unscheduled cells | The remainder of the | | | slotframe | +------------------------------------+----------------------+ | Number of MAC retransmissions (max)| 3 (4 transmission | | | attempts) | +------------------------------------+----------------------+
The slotframe is composed of a configurable number of time slots. Choosing the number of time slots per slotframe needs to take into account network requirements such as density, bandwidth per node, etc. In the minimal configuration, there is only a single active slot in slotframe, used to transmit/receive both EBs and data link-layer frames. The trade-off between bandwidth, latency and energy consumption can be controlled by choosing a different slotframe length. The active slot MAY be scheduled at the slotOffset 0x00 and channelOffset 0x00 and MUST be announced in the EBs. EBs are sent using this active slot to the link-layer broadcast address (and are therefore not acknowledged). Data packets, as described in Section 3.2, use the same active slot. Per [IEEE802154], data packets sent unicast on this cell are acknowledged by the receiver. The remaining cells in the slotframe are unscheduled, and MAY be used by dynamic scheduling solutions. Details about such dynamic scheduling solution are out of scope of this document.
The slotframe length (expressed in number of time slots) is configurable. The length used determines the duty cycle of the network. For example, a network with a 0.99% duty cycle is composed of a slotframe of 101 slots, which includes 1 active slot. The present document RECOMMENDS the use of a default slot duration set to 10ms and its corresponding default timeslot timings defined by the [IEEE802154] macTimeslotTemplate. The use of the default macTimeslotTemplate MUST be announced in the EB by using the Timeslot IE containing only the default macTimeslotTemplateId. Other time slot durations MAY be supported and MUST be announced in the EBs. If one uses a timeslot duration different than 10ms, EBs MUST contain the complete TimeSlot IE as described in Section 3.4. This document also recommends to clearly indicate nodes not supporting the default timeslot value.
Example schedule with 0.99% duty cycle
Chan. +----------+----------+ +----------+
Off.0 | TxRxS/EB | OFF | | OFF |
Chan. +----------+----------+ +----------+
Off.1 | | | ... | |
+----------+----------+ +----------+
.
.
.
Chan. +----------+----------+ +----------+
Off.15 | | | | |
+----------+----------+ +----------+
slotOffset 0 1 100
EB: Enhanced Beacon
Tx: Transmit
Rx: Receive
S: Shared
OFF: Unscheduled (MAY be used by a dynamic scheduling mechanism)
Per [IEEE802154] TSCH, each scheduled cell has an associated bitmap of cell options, called LinkOptions. The scheduled cell in the minimal schedule is configured as a Hard cell [RFC7554][I-D.ietf-6tisch-6top-interface]. Additional available cells MAY be scheduled by a dynamic scheduling solution. The dynamic scheduling solution is out of scope, and this specification does not make any restriction on the LinkOption associated with those dynamically scheduled cells (i.e. they can be hard cells or soft cells).
The active cell is assigned the bitmap of cell options below. Because both the "Transmit" and "Receive" bits are set, a node transmits if there is a packet in its queue, listens otherwise. Because the "shared" bit is set, the back-off mechanism defined in [IEEE802154] is used to resolve contention when transmitting. This results in "Slotted Aloha" behavior. The "Timekeeping" flag is never set, since the time source neighbor is selected using the DODAG structure of the network (detailed below).
All remaining cells are unscheduled. In unscheduled cells, the nodes SHOULD keep their radio off. In a memory-efficient implementation, scheduled cells can be represented by a circular linked list. Unscheduled cells SHOULD NOT occupy any memory.
The maximum number of link layer retransmissions is set to 3. For packets which require an acknowledgment, if none is received after a total of 4 attempts, the transmission is considered failed and the link layer MUST notify the upper layer. Packets sent to the broadcast MAC address (including EBs) are not acknowledged and therefore not retransmitted.
The figure below 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) if required, this does not interfere with the scope of this draft. As for a minimal configuration, CCA is OPTIONAL.
Time slot internal timing diagram
/---------------------- Time Slot 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
The timing parameters for the default macTimeslotTemplate (macTimeslotTemplateId = 0) MUST be used when utilizing the default time slot duration. In this case, the Timeslot IE only transports the macTimeslotTemplateId with value 0x00. If a timeslot template other than the default is used, the EB MUST contain a complete TimeSlot IE indicating the timeslot duration and the corresponding timeslot timings. Note however that in case of discrepancy between the values in this document and [IEEE802154], the IEEE standard has precedence.
[IEEE802154] does not define how often EBs are sent, nor their contents. EBs MUST NOT in general be used for synchronization. Synchronization is achieved via acknowledgements to normal packet traffic, and keepalives. For a minimal TSCH configuration, a mote SHOULD send an EB every EB_PERIOD. For additional reference see [RFC7554] where different synchronization approaches are summarized. EBs are only authenticated and neither Payload IEs nor the frame payload are encrypted. Refer to the 6TiSCH architecture document [I-D.ietf-6tisch-architecture] for further details on security aspects.
EBs MUST be sent as per [IEEE802154] and MUST carry the Information Elements (IEs) listed below. Refer to Section 10.1 for an example of the Information Elements Header Content.
Link-layer acknowledgment frames are built according to [IEEE802154]. Unicast frames sent to a unicast MAC destination address request an acknowledgment. The sender node MUST set the ACK requested bit in the MAC header. The acknowledgment frame is of type ACK (version 0x10). Each acknowledgment contains the following IE:
[IEEE802154] does not define how and when each node in the network keeps information about its neighbors. Keeping the following information in the neighbor table is RECOMMENDED:
The exact format of the neighbor table is implementation-specific, but it SHOULD contain the following information for each neighbor:
In addition to that information, each node has to be able to compute some RPL Objective Function (OF), taking into account the neighbor and connectivity statistics. An example RPL objective function is the OF Zero as described in [RFC6552] and Section 9.1.1.
Each node MUST select at least one Time Source Neighbor among the nodes in its RPL routing parent set. When a node joins a network, it has no routing information. To select its time source neighbor, it uses the Join Priority field in the EB, as described in [IEEE802154]. The Sync IE contains the ASN and 1 Byte field named Join Priority. The Join Priority of any node MUST be equivalent to the result of the function DAGRank(rank) as defined by [RFC6550] and Section 9.1.1. The Join Priority of the DAG root is zero, i.e., EBs sent from the DAG root are sent with Join Priority equal to 0. A lower value of the Join Priority indicates higher preference to connect to that device. When a node joins the network, it MUST NOT send EBs before having acquired a RPL rank. This avoids routing loops and matches RPL topology with underlying mesh topology. As soon as a node acquires a RPL rank (see [RFC6550] and Section 9.1.1), it SHOULD send Enhanced Beacons including a Sync IE with Join Priority field set to DAGRank(rank), where rank is the node's rank. If a node receives EBs from different nodes with equal Join Priority, the time source neighbor selection SHOULD be assessed by other metrics that can help determine the better connectivity link. Time source neighbor hysteresis SHOULD be used, according to the rules defined in Section 9.2.3. If connectivity to the time source neighbor is lost, a new time source neighbor MUST be chosen among the neighbors in the RPL routing parent set.
The decision for a node to select one Time Source Neighbor when multiple EBs are received is implementation-specific.
For example, a node MAY wait until one EB from NUM_NEIGHBOURS_TO_WAIT neighbors have been received to select the best Time Source Neighbor. This condition MAY apply unless a second EB is not received after MAX_EB_DELAY seconds. This avoids initial hysteresis when selecting a first Time Source Neighbor.
Optionally, some form of hysteresis SHOULD be implemented to avoid frequent changes in time source neighbors.
[IEEE802154] does not define the use of queues to handle upper layer data (either application or control data from upper layers). The use of a single queue with the following rules is RECOMMENDED:
As this document refers to the interaction between Layer 3 and Layer 2 protocols, this interaction MUST be secured by L2 security mechanisms as defined by [IEEE802154]. Two security mechanisms are considered, authentication and encryption, authentication applies to all packet content while encryption applies to header IEs and MAC payload. Key distribution is out of scope of this document, but examples include pre-configured keys at the nodes, shared keys among peers or well-known keys. Refer to the 6TiSCH architecture document [I-D.ietf-6tisch-architecture] for further details on key distribution and advanced security aspects.
The present document assumes the existence of two cryptographic keys, which can be pre-configured. One of the keys (K1) is used to authenticate EBs. As defined in Section 4, EBs MUST be authenticated, with no payload encryption. This facilitates logical segregation of distinct networks. A second key (K2) is used to authenticate DATA, ACKNOWLEDGEMENT, MAC COMMAND frame types and respective header IEs, with payload encryption. Depending on security policy, these keys could be the same (i.e., K1=K2).
For early interoperability, K1 MAY be set to 36 54 69 53 43 48 6D 69 6E 69 6D 61 6C 31 35 ("6TiSCHminimal15").
Nodes in the network MUST use the RPL routing protocol [RFC6550].
Nodes in the network MUST use the RPL routing protocol [RFC6550] and implement the RPL Objective Function Zero [RFC6552].
The rank computation is described at [RFC6552], Section 4.1. A node rank is computed by the following equation:
R(N) = R(P) + rank_increment
rank_increment = (Rf*Sp + Sr) * MinHopRankIncrease
Where:
Rank computation scenario
+-------+
| P | R(P)
| |
+-------+
|
|
+-------+
| N | R(N)=R(P) + rank_increment
| | rank_increment = (Rf*Sp + Sr) * MinHopRankIncrease
+-------+ Sp=2*ETX
This section illustrates with an example the use of the Objective Function Zero. Assume the following parameters:
Rank computation example for 5 hop network where numTx=100 and numTxAck=75 for all nodes
+-------+
| 0 | R(minHopRankIncrease) = 256
| | DAGRank(R(0)) = 1
+-------+
|
|
+-------+
| 1 | R(1)=R(0) + 683 = 939
| | DAGRank(R(1)) = 3
+-------+
|
|
+-------+
| 2 | R(2)=R(1) + 683 = 1622
| | DAGRank(R(2)) = 6
+-------+
|
|
+-------+
| 3 | R(3)=R(2)+683=2305
| | DAGRank(R(3)) = 9
+-------+
|
|
+-------+
| 4 | R(4)=R(3)+683=2988
| | DAGRank(R(4)) = 11
+-------+
|
|
+-------+
| 5 | R(5)=R(4)+683=3671
| | DAGRank(R(5)) = 14
+-------+
In addition to the Objective Function (OF), a minimal configuration for RPL SHOULD indicate the preferred mode of operation (either Storing Mode or Non-Storing Mode) so different RPL implementations can inter-operate. RPL information and hop-by-hop extension headers MUST follow [RFC6553] and [RFC6554] specification. In the case that the packets formed at the LLN need to cross through intermediate routers, these MUST obey to the IP in IP encapsulation requirement specified by the [RFC6282] and [RFC2460]. RPI and RH3 extension headers and inner IP headers MUST be compressed according to [RFC6282].
For downstream route maintenance, in a minimal configuration, RPL SHOULD be set to operate in the Non-Storing mode as described by [RFC6550] Section 9.7. Storing mode ([RFC6550] Section 9.8) MAY be supported in less constrained devices.
RPL signaling messages such as DIOs are sent using the Trickle Algorithm [RFC6550] (Section 8.3.1) and [RFC6206]. For this specification, the Trickle Timer MUST be used with the RPL defined default values [RFC6550] (Section 8.3.1). For a description of the Trickle timer operation see Section 4.2 on [RFC6206].
According to [RFC6552], [RFC6719] 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 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. As for [RFC6719] the recommended value for PARENT_SWITCH_THRESHOLD is 192 when ETX metric is used (in the form 128*ETX), the recommendation for this document is to use PARENT_SWITCH_THRESHOLD equal to 768 as the metric being used is 2*ETX*minHopRankIncrease. This is mechanism is suited to deal with parent hysteresis in both cases routing parent and time source neighbor selection.
The following table presents the RECOMMENDED values for the RPL-related variables defined in the previous section.
Recommended variable values
+-------------------------+-------+ | Variable | Value | +-------------------------+-------+ | EB_PERIOD | 10s | +-------------------------+-------+ | MAX_EB_DELAY | 180 | +-------------------------+-------+ | NUM_NEIGHBOURS_TO_WAIT | 2 | +-------------------------+-------+ | PARENT_SWITCH_THRESHOLD | 768 | +-------------------------+-------+
Several examples are provided to illustrate the content of the packets used by the minimal configuration as proposed by this document. Each example follows the same structure presenting first a schematic header diagram, then the LSB stream of bytes that conform the header and finally a description of each of the IEs the form the packet. The packet formats are specific for the [IEEE802154] revision and MAY vary in future releases of the IEEE standard. In case of differences between the packet content presented in this section and the [IEEE802154], the later has presedence.
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 transmitted by the PHY, from left to right, where the leftmost bit is transmitted first in time. 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, hence LSB format.
Mandatory content for the EB as proposed by this draft. The example uses a slotframe of 101 slots. The following figure represents schematically the Header IE and Payload IE content of an EB.
Schematic representation of the IE header in an EB:
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 Priority |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Len4 = 1 |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 = 0x01 | SF LEN = 0x65 (101 slots) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| #Links = 0x01 | SLOT OFFSET = 0x0000 | CHANNEL
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
OFF = 0x0000 |Link OPT = 0x07| Len7 = 0x00 |ID=0xf |1|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
REST OF MAC PAYLOAD ...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Stream of bytes (in LSB format) that derive from the previous
schematic header:
00 FC 1A 88 06 34 ASN#0 ASN#1 ASN#2 ASN#3 ASN#4 JP 01 38 00
00 33 00 0A 36 01 01 65 00 01 00 00 00 00 07 00 1F ...
Description of the IE fields in the example:
#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
#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 Priority = 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 = 0x07 (tx,rx,shared)
#Payload IE Header (Termination IE) (MAY be ommitted)
Len7 = Payload IE Len (0)
GroupID = 0xf Termination
Type = 0
Using a non-default timeslot template in EBs. Timeslot length set to 15ms instead of the 10ms default.
Schematic representation of the IE header in an EB:
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 Priority |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 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 | ...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Stream of bytes (in LSB format) that derive from the previous
schematic header:
00 FC 1A 88 06 34 ASN#0 ASN#1 ASN#2 ASN#3 ASN#4 JP 19 38 00 33 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 IE fields in the example:
#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 Priority = 1 Byte
#MLME-SubIE TSCH TimeSlot
Len4 = Lenght in bytes of the sub-IE payload (25 Bytes)
SubID = 0x1c (MLME-SubIE Timeslot)
Type = Short (0)
TimeSlot template ID = 0x01 (non-default)
Example timeslot timming using 15ms timeslot.
+--------------------------------+------------+
| 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 |
+--------------------------------+------------+
| Time Slot 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)
Acknowledgement packets carry the ACK/NACK Time Correction IE (Header IE). The following example illustrates the IE format as specified in [IEEE802154].
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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Stream of bytes (in LSB format) that derive from the previous schematic
header:
40 F0 TS#0 TS#1
Description of the IE fields in the example:
#Header IE Header
Len1 = Header IE Length (2 Bytes)
Element ID = 0x1e - ACK/NACK Time Correction IE
Type 0
The example illustrates content of the Auxiliary Security Header as mandated by this document, if security is enabled. Security Level in the example is set to ENC-MIC-32 (5).
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|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Stream of bytes (in LSB format) that derive from the schematic header:
6D IDX#0
Description of the 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)
The authors would like to acknowledge the guidance and input provided by Rene Struik, Pat Kinney, Michael Richardson, Tero Kivinen, Nicola Accettura, Malisa Vucinic and the 6TiSCH Chairs Pascal Thubert and Thomas Watteyne.
| [CCM] | National Institute of Standards and Technology, "Recommendation for Block Cipher Modes of Operation: The CCM Mode for Authentication and Confidentiality. SP 800-38C", May 2004. |
| [CCM-Star] | Struik, R., "Formal Specification of the CCM* Mode of Operation, IEEE P802.15 Working Group for Wireless Personal Area Networks (WPANs).", September 2005. |
| [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. |