6top Protocol (6P)
Univ. of Sci. and Tech. Beijing 30 Xueyuan RoadBeijingHebei100083Chinawangqin@ies.ustb.edu.cnUniversitat Oberta de Catalunya156 Rambla PoblenouBarcelonaCatalonia08018Spainxvilajosana@uoc.eduAnalog Devices32990 Alvarado-Niles Road, Suite 910Union CityCA94587USAthomas.watteyne@analog.com
Internet Area
6TiSCHDraft
This document defines the 6top Protocol (6P), which enables distributed scheduling in 6TiSCH networks.
6P allows neighbor nodes to add/delete TSCH cells to one another.
6P is part of the 6TiSCH Operation Sublayer (6top), the next higher layer to the IEEE Std 802.15.4 TSCH medium access control layer.
The 6top Scheduling Function (SF) decides when to add/delete cells, and triggers 6P Transactions.
Several SFs can be defined, each identified by a different 6top Scheduling Function Identifier (SFID).
This document lists the requirements for an SF, but leaves the definition of the SF out of scope.
SFs are expected to be defined in future companion specifications.
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 RFC 2119.
All communication in a 6TiSCH network is orchestrated by a schedule .
This specification defines the 6top Protocol (6P), part of the 6TiSCH Operation sublayer (6top).
6P allows a node to communicate with a neighbor to add/delete TSCH cells to one another.
This results in distributed schedule management in a 6TiSCH network.
The example network depicted in is used to describe the interaction between nodes.
We consider the canonical case where node "A" issues 6P requests to node "B".
We keep this example throughout this document.
Throughout the document, node A will always represent the node that issues a 6P request; node B the node that receives this request.
We consider that node A monitors the communication cells it has in its schedule to node B:
If node A determines that the number of link-layer frames it is sending to B per unit of time is larger than the capacity offered by the TSCH cells it has scheduled to B, it triggers a 6P Transaction with node B to add one or more cells to the TSCH schedule of both nodes.
If the traffic is lower than the capacity, node A triggers a 6P Transaction with node B to delete one or more cells in the TSCH schedule of both nodes.
Node A MAY also monitor statistics to determine whether collisions are happening on a particular cell to node B.
If this feature is enabled, node A communicates with node B to "relocate" the cell which suffered from collisions to a different [slotOffset,channelOffset] location in the TSCH schedule.
This results in distributed schedule management in a 6TiSCH network.
The 6top Scheduling Function (SF) defines when to add/delete a cell to a neighbor.
Different applications require different SFs, so the SF is left out of scope of this document.
Different SFs are expected to be defined in future companion specifications.
A node MAY implement multiple SFs and run them at the same time.
At least one SF MUST be running.
The SFID field contained in all 6P messages allows a node to invoke the appropriate SF on a per-transaction basis.
describes the 6TiSCH Operation Sublayer (6top).
defines the 6top Protocol (6P).
provides guidelines on how to design an SF.
As depicted in , the 6TiSCH Operation Sublayer (6top) is the next higher layer to the IEEE Std 802.15.4 TSCH medium access control (MAC) layer .
We use "802.15.4" as a short version of "IEEE Std 802.15.4" in this document.
The roles of the 6top sublayer are to:
Implement and terminate the 6top Protocol (6P), which allows neighbor nodes to communicate to add/delete cells to one another.Run one or more 6top Scheduling Functions (SF), which define the rules that decide when to add/delete cells.
Each cell in the schedule is either "hard" or "soft":
a soft cell can be read, added, deleted or updated by 6top.a hard cell is read-only for 6top.
In the context of this specification, all the cells used by 6top are soft cells.
Hard cells can be used for example when "hard-coding" a schedule .
6P MAY be used alongside the Minimal 6TiSCH Configuration .
In this case, it is RECOMMENDED to use 2 slotframes, as depicted in :
Slotframe 0 is used for traffic defined in the Minimal 6TiSCH Configuration.
In , this slotframe is 5 slots long, but the slotframe can be shorter or longer.
6P allocates cells from Slotframe 1.
In , Slotframe 1 is 10 slots long, but the slotframe can be shorter or longer.
The Minimal 6TiSCH Configuration cell SHOULD be allocated from a slotframe of higher priority than the slotframe used by 6P for dynamic cell allocation.
This way, dynamically allocated cells cannot "mask" the cells used by the Minimal 6TiSCH Configuration.
6top MAY support additional slotframes; how to use additional slotframes is out of the scope for this document.
The 6top Protocol (6P) enables two neighbor nodes to add/delete/relocate cells in their TSCH schedule.
Conceptually, two neighbor nodes "negotiate" the location of the cells to add, delete, or relocate in their TSCH schedule.
We call "6P Transaction" a complete negotiation between two neighbor nodes.
A 6P Transaction starts when a node wishes to add/delete/relocate one or more cells to one of its neighbors.
A 6P Transaction ends when the cell(s) have been added/deleted/relocated in the schedule of both nodes, or when the 6P Transaction fails.
The 6P messages exchanged between nodes A and B during a 6P Transaction SHOULD be exchanged on dedicated cells between A and B.
If no dedicated cells are scheduled between nodes A and B, shared cells MAY be used.
Keeping consistency between the schedules of the two neighbor nodes is important.
A loss of consistency (e.g. node A has a transmit cell to node B, but node B does not have the corresponding reception cell) can cause loss of connectivity.
To verify consistency, neighbor nodes maintain Sequence Number (SeqNum) and Last Successful SeqNum.
Neighbor nodes exchange the SeqNum as part of each 6P Transaction to detect possible inconsistency.
This mechanism is explained in .
An implementation MUST include a mechanism to associate each scheduled cell with the SF that scheduled it.
This mechanism is implementation-specific and out of the scope of this document.
A 6P Transaction can consist of 2 or 3 steps.
An SF MUST specify whether to use 2-step transactions, 3-step transactions, or both.
We illustrate 2-step and 3-step transactions using the topology in .
shows an example 2-step 6P Transaction.
In a 2-step transaction, node A selects the candidate cells.
Several elements are left out to simplify understanding.
In this example, the 2-step transaction occurs as follows:
The SF running on node A determines that 2 extra cells need to be scheduled to node B.
The SF running on node A selects 3 candidate cells.
Node A sends a 6P ADD Request to node B, indicating it wishes to add 2 cells (the "NumCells" value), and specifying the list of 3 candidate cells (the "CellList" value).
Each cell in the CellList is a (slotOffset,channelOffset) tuple.
When it sends the 6P ADD Request, Node A sets a timer to abort the transaction if no response has been received before the timeout.
The SF running on node B selects 2 out of the 3 cells in the CellList of the 6P ADD Request.
Node B sends back a 6P Response to node A, indicating the cells that node B selected.
Upon completion of this 6P Transaction, 2 cells from A to B have been added to the TSCH schedule of both nodes A and B.
shows an example 3-step 6P Transaction.
In a 3-step transaction, node B selects the candidate cells.
Several elements are left out to simplify understanding.
In this example, the 3-step transaction occurs as follows:
The SF running on node A determines that 2 extra cells need to be scheduled to node B, but does not select candidate cells.
Node A sends a 6P ADD Request to node B, indicating it wishes to add 2 cells (the "NumCells" value), with an empty "CellList".
When it sends the 6P ADD Request, Node A sets a timer to abort the transaction if no response has been received before the timeout.
The SF running on node B selects 3 candidate cells.
Node B sends back a 6P Response to node A, indicating the 3 cells it selected.
When it sends the 6P Response to node A, Node B sets a timer to abort the transaction if no response has been received before the timeout.
The SF running on node A selects 2 cells.
Node A sends back a 6P Confirmation to node B, indicating the cells it selected.
Upon completion of this 6P Transaction, 2 cells from A to B have been added to the TSCH schedule of both nodes A and B.
6P messages travel over a single hop.
6P messages are carried as payload of an IEEE 802.15.4 Payload Information Element (IE) .
The messages are encapsulated with the Payload IE Header (per Section 7.4.3 of the ).
The Group ID is set to the IETF IE value defined in .
The content is encapsulated by a SubType ID as defined in .
Bits within each field in the 6top IE 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 copied to the packet in the order from the octet containing the lowest numbered bits to the octet containing the highest numbered bits (little endian).
This document defines the "6top IE", a SubType of the IETF IE defined in , with subtype ID IANA_6TOP_SUBIE_ID.
The SubType Content of the "6top IE" is defined in .
The length of the "6top IE" content is variable.
All 6P messages follow the generic format shown in .
The version of the 6P protocol.
Only version 0 is defined in this document.
Future specifications MAY define further versions of the 6P protocol.
Type of message.
The message types are defined in .
Reserved bits.
These two bits SHOULD be set to zero when sending the message and MUST be ignored upon reception.
The Code field contains a 6P Command Identifier when the 6P message is of Type REQUEST.
lists the 6P command identifiers.
The Code field contains a 6P Return Code when the 6P message is of Type RESPONSE or CONFIRMATION.
lists the 6P Return Codes.
The same return codes are used in both 6P Response and 6P Confirmation messages.
The identifier of the SF to use to handle this message.
The SFID is defined in .
Sequence number associated with the 6P Transaction, used to match the 6P Request, 6P Response and 6P Confirmation of the same 6P Transaction.
The value of SeqNum MUST be different at each new 6P request issued to the same neighbor.
The SeqNum is also used to ensure consistency between the schedules of the two neighbors.
details how the SeqNum is managed.
The list of other fields depends on the type of messages, and is detailed in .
An 8-bit 6P CellOptions bitmap is present in the following 6P requests: ADD, DELETE, COUNT, LIST, RELOCATE.
In the 6P ADD request, the 6P CellOptions bitmap is used to specify what type of cell to add.In the 6P DELETE request, the 6P CellOptions bitmap is used to specify what type of cell to delete.In the 6P COUNT and the 6P LIST requests, the 6P CellOptions bitmap is used as a selector of a particular type of cells.In the 6P RELOCATE request, the 6P CellOptions bitmap is used to specify what type of cell to relocate.
The contents of the 6P CellOptions bitmap apply to all elements in the CellList field.
contains the RECOMMENDED format of the 6P CellOptions bitmap.
contains the RECOMMENDED meaning of the 6P CellOptions bitmap for the 6P COUNT and 6P LIST requests.
The CellOptions is an opaque set of bits, sent unmodified to the SF.
The SF MAY redefine the format of the CellOptions bitmap.
The SF MAY redefine the meaning of the CellOptions bitmap.
A CellList field MAY be present in a 6P ADD Request, a 6P DELETE Request, a 6P RELOCATE Request, a 6P Response or a 6P Confirmation.
It is composed of zero, one or more 6P Cell containers.
The contents of the CellOptions field specify the options associated with all cells in the CellList.
This necessarily means that the same options are associated with all cells in the CellList.
The 6P Cell is a 4-byte field, its RECOMMENDED format is:
The slot offset of the cell.
The channel offset of the cell.
The CellList is an opaque set of bytes, sent unmodified to the SF.
The SF MAY redefine the format of the CellList field.
Cells are added by using the 6P ADD command.
The Type field (T) is set to REQUEST.
The Code field is set to ADD.
defines the format of a 6P ADD Request.
Used as extra signaling to the SF.
The contents of the Metadata field is an opaque set of bytes passed unmodified to the SF.
The meaning of this field depends on the SF, and is out of scope of this document.
For example, Metadata can specify in which slotframe to add the cells.
Indicates the options to associate with the cells to be added.
If more than one cell is added (NumCells>1), the same options are associated with all of them.
This necessarily means that, if node A needs to add multiple cells with different options, it needs to issue multiple 6P ADD Transactions.
The number of additional cells the sender wants to schedule to the receiver.
A list of 0, 1 or multiple candidate cells.
defines the format of a 6P ADD Response and Confirmation.
A list of 0, 1 or multiple 6P Cells.
Consider the topology in where the SF on node A decides to add NumCells cells to node B.
Node A's SF selects NumCandidate cells from its schedule as candidate cells to be scheduled to node B.
The CellOptions field specifies the type of these cells.
NumCandidate MUST be larger or equal to NumCells.
How many cells it selects (NumCandidate) and how that selection is done is specified in the SF and out of scope of this document.
Node A sends a 6P ADD Request to node B which contains the CellOptions, the value of NumCells and a selection of NumCandidate cells in the CellList.
In case the NumCandidate cells do not fit in a single packet, this operation MUST be split into multiple independent 6P ADD Requests, each for a subset of the number of cells that eventually need to be added.
Upon receiving the request, node B's SF verifies which of the cells in the CellList it can install in node B's schedule following the specified CellOptions field.
How that selection is done is specified in the SF and out of scope of this document.
The verification can succeed (NumCells cells from the CellList can be used), fail (none of the cells from the CellList can be used) or partially succeed (less than NumCells cells from the CellList can be used).
When the allocation succeeds or partially succeeds node B MUST send a 6P Response with return code set to SUCCESS, and which specifies the list of cells that were scheduled following the CellOptions field.
The returned list can contain NumCells elements (succeeded) or between 0 and NumCells elements (partially succeeded).
In the case that none of the cells could be allocated node B MUST send a 6P Response with return code set to NOALLOC, indicating that cells could not be allocated in the schedule as they are already used or reserved.
The returned list in this case contains 0 elements.
Upon receiving the response, node A adds the cells specified in the CellList according to the request CellOptions field.
Cells are deleted by using the 6P DELETE command.
The Type field (T) is set to REQUEST.
The Code field is set to DELETE.
defines the format of a 6P DELETE Request.
Same usage as for the 6P ADD command, see .
Its format is the same as that in 6P ADD command, but its contents could be different.
Indicates the options that need to be associated to the cells to delete.
Only the cells matching the CellOptions are deleted.
The number of cells from the specified CellList the sender wants to delete from the schedule of both sender and receiver.
A list of 0, 1 or multiple 6P Cells.
defines the format of a 6P DELETE Response and Confirmation.
A list of 0, 1 or multiple 6P Cells.
The behavior for deleting cells is equivalent to that of adding cells except that:
The nodes delete the cells they agree upon rather than adding them.
All cells in the CellList MUST already be scheduled between the two nodes and MUST match the CellOptions field.
If node A puts cells in its CellList that are not already scheduled between the two nodes and match the CellOptions field, node B MUST reply with a CELLLIST_ERR return code.
If the CellList in the 6P Request is empty, the SF on the receiving node SHOULD delete any cell from the sender, as long as it matches the CellOptions field.
The CellList in a 6P Request (2-step transaction) or 6P Response (3-step transaction) MUST either be empty, contain exactly NumCells cells, or more than NumCells cells.
The case where the CellList is not empty but contains less than NumCells cells is not supported.
Cell relocation consists in moving a cell to a different [slotOffset,channelOffset] location in the schedule.
The Type field (T) is set to REQUEST.
The Code is set to RELOCATE.
defines the format of a 6P RELOCATE Request.
Same usage as for the 6P ADD command, see .
Indicates the options that need to be associated to the relocated cells.
The number of cells to relocate, which MUST be equal or greater than 1.
The list of NumCells 6P Cells to relocate.
A list of NumCandidate candidate cells for node B to pick from.
NumCandidate MUST be 0, equal to NumCells, or greater than NumCells.
In a 2-step 6P RELOCATE Transaction, node A specifies both the cells it needs to relocate, and the list of candidate cells to relocate to.
In a 2-step 6P RELOCATE Transaction, the candidate CellList MUST therefore contain at least NumCells entries.
In a 3-step 6P RELOCATE Transaction, node A only specifies the cells it needs to relocate, but not the list of candidate cells to relocate to.
The Candidate CellList MUST therefore be empty.
defines the format of a 6P RELOCATE Response and Confirmation.
A list of 0, 1 or multiple 6P Cells.
Node A's SF wants to relocate NumCells cells.
Node A creates a 6P RELOCATE Request, and indicates the cells to relocate in the Relocation CellList.
It also selects NumCandidate cells from its schedule as candidate cells for node B, and puts those in the Candidate CellList.
The CellOptions field specifies the type of the cell(s) to relocate.
NumCandidate MUST be larger or equal to NumCells.
How many cells it selects (NumCandidate) and how that selection is done is specified in the SF and out of scope of this document.
Node A sends the 6P RELOCATE Request to node B.
Upon receiving the request, node B's SF verifies that all the cells in the Relocation CellList are indeed scheduled with node A, and are associate the options specified in the CellOptions field.
If that check fails, node B MUST send a 6P Response to node A with return code CELLLIST_ERR.
If that check passes, node B's SF verifies which of the cells in the Candidate CellList it can install in its schedule.
How that selection is done is specified in the SF and out of scope of this document.
That verification on Candidate CellList can succeed (NumCells cells from the Candidate CellList can be used), fail (none of the cells from the Candidate CellList can be used) or partially succeed (less than NumCells cells from the Candidate CellList can be used).
In all cases, node B MUST send a 6P Response with return code set to SUCCESS, and which specifies the list of cells that were scheduled following the CellOptions field.
That can contain 0 elements (when the verification failed), NumCells elements (succeeded) or between 0 and NumCells elements (partially succeeded).
If N < NumCells cells appear in the CellList, this means first N cells in the Relocation CellList have been relocated, the remainder have not.
Upon receiving the response, node A relocates the cells specified in Relocation CellList of its RELOCATE Request to the new location specified in the CellList of the 6P Response.
shows an example of a successful 2-step 6P RELOCATION Transaction.
shows an example of a partially successful 2-step 6P RELOCATION Transaction.
shows an example of a failed 2-step 6P RELOCATION Transaction.
shows an example of a successful 3-step 6P RELOCATION Transaction.
To retrieve the number of scheduled cells at B, node A issues a 6P COUNT command.
The Type field (T) is set to REQUEST.
The Code field is set to COUNT.
defines the format of a 6P COUNT Request.
Same usage as for the 6P ADD command, see .
Its format is the same as that in 6P ADD command, but its contents could be different.
Specifies which types of cells to be counted.
defines the format of a 6P COUNT Response.
The number of cells which correspond to the fields of the request.
Node A issues a COUNT command to node B, specifying a set of cell options.
Upon receiving the 6P COUNT request, node B goes through its schedule and counts the number of cells scheduled with node A in its own schedule, and which match the cell options in the CellOptions field of the request.
details the use of the CellOptions field.
Node B issues a 6P response to node A with return code set to SUCCESS, and with NumCells containing the number of cells that match the request.
To retrieve the list of scheduled cells at B, node A issues a 6P LIST command.
The Type field (T) is set to REQUEST.
The Code field is set to LIST.
defines the format of a 6P LIST Request.
Same usage as for the 6P ADD command, see .
Its format is the same as that in 6P ADD command, but its contents could be different.
Specifies which types of cells to be listed.
Set to 0.
The Offset of the first scheduled cell that is requested.
The mechanism assumes cells are ordered according to a rule defined in the SF.
The rule MUST always order the cells in the same way.
The maximum number of cells to be listed.
Node B MAY returns less than MaxNumCells cells, for example if MaxNumCells cells do not fit in the frame.
defines the format of a 6P LIST Response.
A list of 0, 1 or multiple 6P Cells.
When receiving a LIST command, node B returns the cells in its schedule that match the CellOptions field as specified in
When node B receives a LIST request, the returned CellList in the 6P Response contains between 1 and MaxNumCells cells, starting from the specified offset.
Node B SHOULD include as many cells as fit in the frame.
If the response contains the last cell, Node B MUST set the Code field in the response to EOL, indicating to Node A that there no more cells that match the request.
Node B MUST return at least one cell, unless the specified Offset is beyond the end of B's cell list in its schedule.
If node B has less than Offset cells that match the request, node B returns an empty CellList and a Code field set to EOL.
To clear the schedule between nodes A and B (for example after a schedule inconsistency is detected), node A issues a CLEAR command.
The Type field (T) is set to 6P Request.
The Code field is set to CLEAR.
defines the format of a 6P CLEAR Request.
Same usage as for the 6P ADD command, see .
Its format is the same as that in 6P ADD command, but its contents could be different.
defines the format of a 6P CLEAR Response.
When a 6P CLEAR command is issued from node A to node B, both nodes A and B MUST remove all the cells scheduled between them.
That is, node A MUST remove all the cells scheduled with B, and node B MUST remove all the cells scheduled with A.
In a 6P CLEAR command, the SeqNum MUST NOT be checked.
In particular, even if the request contains a SeqNum value that would normally cause node B to detect a schedule mismatch, the transaction MUST NOT be aborted.
Upon 6P CLEAR completion both SeqNum and Last Successful SeqNum MUST be set to 0.
The 6P SIGNAL messages allows the SF implementations on two neighbor nodes to exchange generic commands.
The payload in a received SIGNAL message is an opaque set of bytes passed unmodified to the SF.
How the generic SIGNAL command is used is specified by the SF, and outside of the scope of this document.
The Type field (T) is set to REQUEST.
The Code field is set to SIGNAL.
defines the format of a 6P SIGNAL Request.
Same usage as for the 6P ADD command, see .
Its format is the same as that in 6P ADD command, but its contents could be different.
defines the format of a 6P SIGNAL Response.
All messages contain a Version field.
If multiple Versions of the 6P protocol have been defined (in future specifications for Version values different from 0), a node MAY implement multiple protocol versions at the same time.
When receiving a 6P message with a Version number it does not implement, a node MUST reply with a 6P Response with a Return Code field set to VER_ERR.
The Version field in the 6P Response MUST be the same as the Version field in the corresponding 6P Request.
In a 3-step transaction, the Version field in the 6P Confirmation MUST match that of the 6P Request and 6P Response in the same transaction.
All messages contain a SFID field.
A node MAY support multiple SFs at the same time.
When receiving a 6P message with an unsupported SFID, a node MUST reply with a 6P Response and a return code of SFID_ERR.
The SFID field in the 6P Response MUST be the same as the SFID field in the corresponding 6P Request.
In a 3-step transaction, the SFID field in the 6P Confirmation MUST match that of the 6P Request and 6P Response in the same transaction.
Only a single 6P Transaction between two neighbors, in a given direction, can take place at the same time.
That is, a node MUST NOT issue a new 6P Request to a given neighbor before having received the 6P Response for a previous request to that neighbor, except when the previous 6P Transaction has timed out.
If a node receives a 6P Request from a given neighbor before having sent the 6P Response to the previous 6P Request from that neighbor, it MUST send back a 6P Response with a return code of RESET.
A node receiving RESET code MUST abort the transaction and consider it never happened.
Nodes A and B MAY support having two transactions going on at the same time, one in each direction.
Similarly, a node MAY support concurrent 6P Transactions from different neighbors.
In this case, the cells involved in an ongoing 6P Transaction MUST be locked until the transaction finishes.
For example, in , node C can have a different ongoing 6P Transaction with nodes B and R.
In case a node does not have enough resources to handle concurrent 6P Transactions from different neighbors it MUST reply with a 6P Response with return code BUSY.
In case the requested cells are locked, it MUST reply to that request with a 6P Response with return code NORES.
The node receiving BUSY or a NORES MAY implement a retry mechanism, defined by the SF.
A timeout occurs when the node sending the 6P Request has not received the 6P Response within a specified amount of time determined by the SF.
In a 3-step transaction, a timeout also occurs when the node sending the 6P Response has not received the 6P Confirmation.
The timeout should be longer than the longest possible time it can take for the exchange to finish.
The value of the timeout hence depends on the number of cells scheduled between the neighbor nodes, the maximum number of link-layer retransmissions, etc.
The SF MUST determine the value of the timeout.
The value of the timeout is out of scope of this document.
In case the receiver of a 6P Request fails during a 6P Transaction and it is unable to complete it, it SHOULD reply to that Request with a 6P Response with return code RESET.
Upon receiving this 6P Response, the initiator of the 6P Transaction MUST consider the 6P Transaction as failed.
Similarly, in the case of 3-step transaction, when the receiver of a 6P Response fails during the 6P Transaction and is unable to complete it, it MUST reply to that 6P Response with a 6P Confirmation with return code RESET.
Upon receiving this 6P Confirmation, the sender of the 6P Response MUST consider the 6P Transaction as failed.
The SeqNum is a field of the 6top IE header and is used to match Request, Response and Confirmation.
The SeqNum is used to detect and handle
duplicate commands () and
schedule inconsistencies ().
Each node remembers the last used SeqNum for each neighbor.
That is, a node remembers as many SeqNum values as it has neighbors.
In the remainder of this section, we describe the use of SeqNum between two neighbors; the same happens for each other neighbor, independently.
When a node resets or after a CLEAR transaction, it MUST reset SeqNum to 0.
The 6P Response and 6P Confirmation for a transaction MUST use the same SeqNum value as that in the Request.
After every transaction, the SeqNum MUST be incremented by exactly 1.
The SeqNum MUST be implemented as a lollipop counter: it rolls over from 0xFF to 0x01 (not to 0x00).
lists the possible values of the SeqNum.
All 6P commands are link-layer acknowledged.
A duplicate message means that a node receives a second 6P Request, Response or Confirmation.
This happens when the link-layer acknowledgment is not received, and a link-layer retransmission happens.
shows an example 2-step transaction in which Node A receives a duplicate 6P Response.
shows example 3-step transaction in which Node A receives a out-of-order duplicate 6P Response after having sent a 6P Confirmation.
A node detects a duplicate 6P message when it has the same SeqNum and type as the last frame received from the same neighbor.
When receiving a duplicate 6P message, a node MUST send a link-layer acknowledgment, but MUST silently ignore it at the 6top sublayer.
Inconsistency may happen in different situations.
The corresponding methods of detecting and handling the inconsistencies are described next.
Inconsistency may happen when L2 acknowledgment of the last packet in a transaction is lost, i.e. RESPONSE (in 2-step 6P transaction) or CONFIRMATION (in 3-step 6P transaction) have been received on one side while timeout happens on the other side.
Take 2-step 6P transaction as example, i.e. timeout happens when node B is waiting for L2 acknowledgment to its Response message.
Upon the timeout, the SF running on the node that timeout (e.g node B) MUST take action to validate the schedule state on both sides.
For example node B starts a COUNT transaction to node A to determine if there is inconsistency.
If inconsistency is found, it is up to the SF to decide what to do next.
For example, node B starts a CLEAR transaction to node A to reset schedule on both sides.
Other options include node B listing the cells on node A and deleting those that are inconsistent.
Inconsistency happens when a schedule clear does not happen simultaneously on two neighbor nodes. For example, a CLEAR transaction
ends at one side (node A) while the L2 acknowledgment to the Response packet is lost on the other side (node B).
In this case, the inconsistency is detected with the value of the SeqNum and LastSeqNum.
Considering this case in a 2-step transaction, when node B receives a 6P Request from node A with SeqNum == 0 and its LastSeqNum from node A is not 0 or node B receives a Request message from node A with SeqNum != 0 and its LastSeqNum for node A is 0, an inconsistency is detected.
When such inconsistency is detected, node B MUST respond with the return code INCON_ERR and the transaction MUST be discarded.
It is up to the SF to decide what to do next.
For example, upon receiving INCON_ERR, node A starts a LIST transaction to node B to obtain the scheduled cells with B.
A return code marked as Yes in the "Is Error" column in indicates an error.
When a node receives a 6P Response or 6P Confirmation with such an error, it MUST consider the 6P Transaction as failed.
In particular, if this was a response to a 6P ADD/DELETE/RELOCATE Request, the node MUST NOT add/delete/relocate any of the cells involved in this 6P Transaction.
Similarly, a node sending a 6P Response or a 6P Confirmation with an error code MUST NOT add/delete/relocate any cells as part of that 6P Transaction.
Defining what to do after an error has occurred is out of scope of this document.
The SF defines what to do after an error has occurred.
6P messages are secured through link-layer security.
When link-layer security is enabled, the 6P messages MUST be secured.
This is possible because 6P messages are carried as Payload IE.
Each SF has a 1-byte identifier.
defines the rules for applying for an SFID.
The specification for an SF
MUST specify an identifier for that SF.MUST specify the rule for a node to decide when to add/delete one or more cells to a neighbor.MUST specify the rule for a Transaction source to select cells to add to the CellList field in the 6P ADD Request.MUST specify the rule for a Transaction destination to select cells from CellList to add to its schedule.MUST specify a value for the 6P Timeout, or a rule/equation to calculate it.MUST specify the rule for ordering cells.MUST specify a meaning for the "Metadata" field in the 6P ADD Request.MUST specify the SF behavior of a node when it boots.MUST specify what to do after an error has occurred (either the node sent a 6P Response with an error code, or received one).
MUST specify the list of statistics to gather.
An example statistic is the number of transmitted frames to each neighbor.
In case the SF requires no statistics to be gathered, the specific of the SF MUST explicitly state so.
SHOULD clearly state the application domain the SF is created for.SHOULD contain examples which highlight normal and error scenarios.SHOULD contain a list of current implementations, at least during the I-D state of the document, per .SHOULD contain a performance evaluation of the scheme, possibly through references to external documents.SHOULD define the format of the SIGNAL command payload and its use.MAY redefine the format of the CellList field.MAY redefine the format of the CellOptions field.MAY redefine the meaning of the CellOptions field.
The following section structure for a SF document is RECOMMENDED:
IntroductionScheduling Function IdentifierRules for Adding/Deleting CellsRules for CellList6P Timeout ValueRule for Ordering CellsMeaning of the Metadata FieldNode Behavior at Boot6P Error HandlingExamplesImplementation StatusSecurity ConsiderationsIANA Considerations
This section records the status of known implementations of the protocol defined by this specification at the time of posting of this Internet-Draft, and is based on a proposal described in .
The description of implementations in this section is intended to assist the IETF in its decision processes in progressing drafts to RFCs.
Please note that the listing of any individual implementation here does not imply endorsement by the IETF.
Furthermore, no effort has been spent to verify the information presented here that was supplied by IETF contributors.
This is not intended as, and must not be construed to be, a catalog of available implementations or their features.
Readers are advised to note that other implementations may exist.
According to , "this will allow reviewers and working groups to assign due consideration to documents that have the benefit of running code, which may serve as evidence of valuable experimentation and feedback that have made the implemented protocols more mature.
It is up to the individual working groups to use this information as they see fit".
6P is one of the protocols addressed during the First F-Interop ETSI 6TiSCH plugtests organized on 14-15 July 2017 in Prague, Czech Republic.
TODO: update when event over; probably includes further open source implementation.
6P was one of the protocols addressed during the ETSI 6TiSCH #3 plugtests organized on 15-17 July 2016 in Berlin, Germany.
15 entities participated in this event, verifying the compliance and interoperability of their implementation of 6P.
This event happened under NDA, so neither the name of the entities nor the test results are public.
This event is, however, a clear indication of the maturity of 6P, and the interest it generates.
More information about the event at http://www.etsi.org/news-events/events/1077-6tisch-6lo-plugtests.
6P was one of two protocols addressed during the ETSI 6TiSCH #2 plugtests organized on 2-4 February 2016 in Paris, France.
14 entities participated in this event, verifying the compliance and interoperability of their implementation of 6P.
This event happened under NDA, so neither the name of the entities nor the test results are public.
This event is, however, a clear indication of the maturity of 6P, and the interest it generates.
More information about the event at http://www.etsi.org/news-events/events/1022-6TiSCH-2-plugtests.
6P is implemented in the OpenWSN project under a BSD open-source license.
The authors of this document are collaborating with the OpenWSN community to gather feedback about the status and performance of the protocols described in this document.
Results from that discussion will appear in this section in future revision of this specification.
More information about this implementation at http://www.openwsn.org/.
The F-Interop project is putting together an online tool to conduct online and remote interoperability/conformance tests.
6P is one of the supported protocols.
The 6TiSCH simulator is a Python-based high-level simulator which implements 6P and is built to evaluate the performance of differents SFs.
More information at https://bitbucket.org/6tisch/simulator/.
A Wireshark dissector for 6P is implemented under a BSD open-source license.
It is developed and maintained at https://github.com/openwsn-berkeley/dissectors/, and regularly merged into the main Wireshark repository.
Please see the Wireshark documentation to see what version of 6P it supports.
6P messages are carried inside 802.15.4 Payload Information Elements (IEs).
Those Payload IEs are encrypted and authenticated at the link layer through CCM*.
6P benefits from the same level of security as any other Payload IE.
The 6P protocol does not define its own security mechanisms.
A key management solution is out of scope for this document.
The 6P protocol will benefit for the key management solution used in the network.
This document adds the following number to the "IEEE Std 802.15.4 IETF IE subtype IDs" registry defined by :
This section defines sub-registries within the "IPv6 over the TSCH mode of IEEE 802.15.4e (6TiSCH) parameters" registry, hereafter referred to as the "6TiSCH parameters" registry.
Each sub-registry is described in a subsection.
The name of the sub-registry is "6P Version Numbers".
A Note included in this registry should say:
"In the 6top Protocol (6P) [RFCXXXX] there is a field to identify the version of the protocol.
This field is 4 bits in size."
Each entry in the sub-registry must include
the Version in the range 0-15,
and a reference to the 6P version's documentation.
The initial entry in this sub-registry is as follows:
All other Version Numbers are Unassigned.
The IANA policy for future additions to this sub-registry is "IETF Review or IESG Approval" as described in .
The name of the sub-registry is "6P Message Types".
A Note included in this registry should say:
"In the 6top Protocol (6P) version 0 [RFCXXXX], there is a field to identify the type of message.
This field is 2 bits in size."
Each entry in the sub-registry must include
the Type in the range b00-b11,
the corresponding Name,
and a reference to the 6P message type's documentation.
Initial entries in this sub-registry are as follows:
All other Message Types are Reserved.
The IANA policy for future additions to this sub-registry is "IETF Review or IESG Approval" as described in .
The name of the sub-registry is "6P Command Identifiers".
A Note included in this registry should say:
"In the 6top Protocol (6P) version 0 [RFCXXXX], there is a Code field which is 8 bits in size.
In a 6P Request, the value of this Code field is used to identify the command."
Each entry in the sub-registry must include
the Identifier in the range 0-255,
the corresponding Name,
and a reference to the 6P command identifier's documentation.
Initial entries in this sub-registry are as follows:
The IANA policy for future additions to this sub-registry is "IETF Review or IESG Approval" as described in .
The name of the sub-registry is "6P Return Codes".
A Note included in this registry should say:
"In the 6top Protocol (6P) version 0 [RFCXXXX], there is a Code field which is 8 bits in size.
In a 6P Response or 6P Confirmation, the value of this Code field is used to identify the return code."
Each entry in the sub-registry must include
the Code in the range 0-255,
the corresponding Name,
the corresponding Description,
and a reference to the 6P return code's documentation.
Initial entries in this sub-registry are as follows:
All other Message Types are Unassigned.
The IANA policy for future additions to this sub-registry is "IETF Review or IESG Approval" as described in .
6P Scheduling Function Identifiers.
A Note included in this registry should say:
"In the 6top Protocol (6P) version 0 [RFCXXXX], there is a field to identify the scheduling function to handle the message.
This field is 8 bits in size."
Each entry in the sub-registry must include
the SFID in the range 0-255,
the corresponding Name,
and a reference to the 6P Scheduling Function's documentation.
The initial entry in this sub-registry is as follows:
All other Message Types are Unassigned.
The IANA policy for future additions to this sub-registry depends on the value of the SFID, as defined in .
These specifications must follow the guidelines of .
The name of the sub-registry is "6P CellOptions bitmap".
A Note included in this registry should say:
"In the 6top Protocol (6P) version 0 [RFCXXXX], there is an optional CellOptions field which is 8 bits in size."
Each entry in the sub-registry must include
the bit position in the range 0-7,
the corresponding Name,
and a reference to the bit's documentation.
Initial entries in this sub-registry are as follows:
All other Message Types are Reserved.
The IANA policy for future additions to this sub-registry is "IETF Review or IESG Approval" as described in .
IEEE Std 802.15.4-2015 - IEEE Standard for Low-Rate Wireless Personal Area Networks (WPANs)IEEE standard for Information TechnologyOpenWSN: a Standards-Based Low-Power Wireless Development Environmentdraft-ietf-6tisch-6top-protocol-08
Replacing GEN counter by SeqNum and timeout.Adding SIGNAL command.Adding INCON_ERR return code.Clarifying IETF IE usage.Fixing typos.draft-ietf-6tisch-6top-protocol-07
Inverting NORES and BUSY error codes for concurrent transactions.Adding missing implementations.Fixing references.Fixing typos.draft-ietf-6tisch-6top-protocol-06
Changing error code from RESET to CELLLIST_ERR when deleting unscheduled cells.Fixing typos.draft-ietf-6tisch-6top-protocol-05
complete reorder of sections. Merged protocol behavior and command descriptionSTATUS to COUNTwritten-out IANA sectioncomplete proof-readdraft-ietf-6tisch-6top-protocol-04
recommendation on which cells to use for 6P trafficrelocation format: added numberofCells fieldcreated separate section about "cell suggestion"Added RC_ERR_CELLLIST and RC_ERR_EOL error codesAdded example for two step with the failureRecommended numbers in IANA sectionsingle generation numberIEEE802.15.4 -> IEEE Std 802.15.4 or 802.15.4complete proof-readdraft-ietf-6tisch-6top-protocol-03
Added a reference to .Added the Type field.Editorial changes (figs, typos, ...)draft-ietf-6tisch-6top-protocol-02
Rename COUNT to STATUSSplit LIST to LIST AB and LIST BAAdded generation counters and describing generation tracking of the scheduleEditorial changes (figs, typos, ...)draft-ietf-6tisch-6top-protocol-01
Clarifying locking of resources in concurrent transactionsClarifying return of RC_ERR_BUSY in case of concurrent transactions without enough resourcesdraft-ietf-6tisch-6top-protocol-00
Informational to Std trackdraft-wang-6tisch-6top-protocol-00
Editorial overhaul: fixing typos, increasing readability, clarifying figures.https://bitbucket.org/6tisch/draft-wang-6tisch-6top-protocol/issues/47https://bitbucket.org/6tisch/draft-wang-6tisch-6top-protocol/issues/54https://bitbucket.org/6tisch/draft-wang-6tisch-6top-protocol/issues/55https://bitbucket.org/6tisch/draft-wang-6tisch-6top-protocol/issues/49https://bitbucket.org/6tisch/draft-wang-6tisch-6top-protocol/issues/53https://bitbucket.org/6tisch/draft-wang-6tisch-6top-protocol/issues/44https://bitbucket.org/6tisch/draft-wang-6tisch-6top-protocol/issues/48https://bitbucket.org/6tisch/draft-wang-6tisch-6top-protocol/issues/43https://bitbucket.org/6tisch/draft-wang-6tisch-6top-protocol/issues/52https://bitbucket.org/6tisch/draft-wang-6tisch-6top-protocol/issues/45https://bitbucket.org/6tisch/draft-wang-6tisch-6top-protocol/issues/51https://bitbucket.org/6tisch/draft-wang-6tisch-6top-protocol/issues/50https://bitbucket.org/6tisch/draft-wang-6tisch-6top-protocol/issues/46https://bitbucket.org/6tisch/draft-wang-6tisch-6top-protocol/issues/41https://bitbucket.org/6tisch/draft-wang-6tisch-6top-protocol/issues/42https://bitbucket.org/6tisch/draft-wang-6tisch-6top-protocol/issues/39https://bitbucket.org/6tisch/draft-wang-6tisch-6top-protocol/issues/40draft-wang-6tisch-6top-sublayer-05
Specifies format of IEAdds token in messages to match request and responsedraft-wang-6tisch-6top-sublayer-04
Renames IANA_6TOP_IE_GROUP_ID to IANA_IETF_IE_GROUP_ID.Renames IANA_CMD and IANA_RC to IANA_6TOP_CMD and IANA_6TOP_RC.Proposes IANA_6TOP_SUBIE_ID with value 0x00 for the 6top sub-IE.draft-wang-6tisch-6top-sublayer-03
https://bitbucket.org/6tisch/draft-wang-6tisch-6top-protocol/issues/32/missing-command-listhttps://bitbucket.org/6tisch/draft-wang-6tisch-6top-protocol/issues/31/missing-command-counthttps://bitbucket.org/6tisch/draft-wang-6tisch-6top-protocol/issues/30/missing-command-clearhttps://bitbucket.org/6tisch/draft-wang-6tisch-6top-protocol/issues/37/6top-atomic-transaction-6p-transactionhttps://bitbucket.org/6tisch/draft-wang-6tisch-6top-protocol/issues/35/separate-opcode-from-rchttps://bitbucket.org/6tisch/draft-wang-6tisch-6top-protocol/issues/36/add-length-field-in-iehttps://bitbucket.org/6tisch/draft-wang-6tisch-6top-protocol/issues/27/differentiate-rc_err_busy-andhttps://bitbucket.org/6tisch/draft-wang-6tisch-6top-protocol/issues/29/missing-rc-rc_resethttps://bitbucket.org/6tisch/draft-wang-6tisch-6top-protocol/issues/28/the-sf-must-specify-the-behavior-of-a-motehttps://bitbucket.org/6tisch/draft-wang-6tisch-6top-protocol/issues/26/remove-including-their-numberhttps://bitbucket.org/6tisch/draft-wang-6tisch-6top-protocol/issues/34/6of-sfhttps://bitbucket.org/6tisch/draft-wang-6tisch-6top-protocol/issues/33/add-a-figure-showing-the-negociationdraft-wang-6tisch-6top-sublayer-02
introduces the 6P protocol and the notion of 6top Transaction.introduces the concept of 6OF and its 6OFID.