| 6TiSCH | Q. Wang, Ed. |
| Internet-Draft | Univ. of Sci. and Tech. Beijing |
| Intended status: Standards Track | X. Vilajosana |
| Expires: December 22, 2018 | Universitat Oberta de Catalunya |
| T. Watteyne | |
| Analog Devices | |
| June 20, 2018 |
6TiSCH Operation Sublayer Protocol (6P)
draft-ietf-6tisch-6top-protocol-12
This document defines the IPv6 over the TSCH mode of IEEE 802.15.4e (6TiSCH) Operation Sublayer (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 layer terminates the 6top Protocol defined in this document, and runs one or more 6top Scheduling Function(s). A 6top Scheduling Function (SF) decides when to add/delete cells, and triggers 6P Transactions. This document lists the requirements for an SF, but leaves the definition of SFs out of scope.
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.
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This Internet-Draft will expire on December 22, 2018.
Copyright (c) 2018 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 (https://trustee.ietf.org/license-info) in effect on the date of publication of this document. Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Code Components extracted from this document must include Simplified BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Simplified BSD License.
All communication in a IPv6 over the TSCH mode of IEEE 802.15.4e (6TiSCH) network is orchestrated by a schedule [RFC7554]. The schedule is composed of cells, each identified by a [slotOffset,channelOffset]. This specification defines the 6TiSCH Operation Sublayer (6top) Protocol (6P), terminated by the 6TiSCH Operation sublayer (6top). 6P allows a node to communicate with a neighbor node to add/delete TSCH cells to one another. This results in distributed schedule management in a 6TiSCH network. The 6top layer terminates the 6top Protocol, and runs one or more 6top Scheduling Functions (SFs) that decide when to add/delete cells and trigger 6P Transactions. The SF is out of scope of this document but this document defines the requirements for an SF.
(R)
/ \
/ \
(B)-----(C)
| |
| |
(A) (D)
Figure 1: A simple 6TiSCH network.
The example network depicted in Figure 1 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 always represents 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:
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-6P Transaction basis.
Section 2 describes the 6TiSCH Operation Sublayer (6top). Section 3 defines the 6top Protocol (6P). Section 4 provides guidelines on how to define an SF.
As depicted in Figure 2, the 6TiSCH Operation Sublayer (6top) is the next higher layer to the IEEE Std 802.15.4 TSCH medium access control (MAC) layer [IEEE802154]. We use "802.15.4" as a short version of "IEEE Std 802.15.4" in this document.
.
| . |
| higher layers |
+------------------------------------------+
| 6top |
+------------------------------------------+
| IEEE Std 802.15.4 TSCH |
| . |
.
Figure 2: The 6top sublayer in the protocol stack.
The roles of the 6top sublayer are to:
Each cell in the schedule is either "hard" or "soft":
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 [RFC8180].
6P MAY be used alongside the Minimal 6TiSCH Configuration [RFC8180]. In this case, it is RECOMMENDED to use 2 slotframes, as depicted in Figure 3:
| 0 1 2 3 4 | 0 1 2 3 4 |
+------------------------+------------------------+
Slotframe 0 | | | | | | | | | | |
5 slots long | EB | | | | | EB | | | | |
(Minimal 6TiSCH) | | | | | | | | | | |
+-------------------------------------------------+
| 0 1 2 3 4 5 6 7 8 9 |
+-------------------------------------------------+
Slotframe 1 | | | | | | | | | | |
10 slots long | |A->B| | | | | | |B->A| |
(6P) | | | | | | | | | | |
+-------------------------------------------------+
Figure 3: 2-slotframe structure when using 6P alongside the Minimal 6TiSCH Configuration.
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 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 particular 6P Transaction is executed between two nodes as a result of an action triggered by one SF. For a 6P Transaction to succeed, both nodes must use the same SF to handle the particular transaction. A 6P Transaction starts when a node wishes to add/delete/relocate one or more cells with 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 has failed.
6P messages exchanged between nodes A and B during a 6P Transaction SHOULD be exchanged on non-shared unicast cells ("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 can cause loss of connectivity. One example is when node A has a transmit cell to node B, but node B does not have the corresponding reception cell. To verify consistency, neighbor nodes maintain a Sequence Number (SeqNum). Neighbor nodes exchange the SeqNum as part of each 6P Transaction to detect a possible inconsistency. This mechanism is explained in Section 3.4.6.2.
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 scope of this document.
A 6P Transaction can consist of 2 or 3 steps. A 2-step transaction is used when node A selects the cells to be allocated. A 3-step transaction is used when node B selects the cells to be allocated. 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 Figure 1.
Figure 4 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.
+----------+ +----------+
| Node A | | Node B |
+----+-----+ +-----+----+
| |
| 6P ADD Request |
| Type = REQUEST |
| Code = ADD |
| SeqNum = 123 |
cells | NumCells = 2 |
locked | CellList = [(1,2),(2,2),(3,5)] |
+-- |-------------------------------------->|
| | L2 ACK |
| 6P Timeout |<- - - - - - - - - - - - - - - - - - - |
| | | |
| | | 6P Response |
| | | Type = RESPONSE |
| | | Code = RC_SUCCESS |
| | | SeqNum = 123 | cells
| | | CellList = [(2,2),(3,5)] | locked
+-> X |<--------------------------------------| --+
| L2 ACK | |
| - - - - - - - - - - - - - - - - - - ->| <-+
| |
Figure 4: An example 2-step 6P Transaction.
In this example, the 2-step transaction occurs as follows:
Figure 5 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.
+----------+ +----------+
| Node A | | Node B |
+----+-----+ +-----+----+
| |
| 6P ADD Request |
| Type = REQUEST |
| Code = ADD |
| SeqNum = 178 |
| NumCells = 2 |
| CellList = [] |
|-------------------------------------->|
| L2 ACK |
6P Timeout |<- - - - - - - - - - - - - - - - - - - |
| | |
| | 6P Response |
| | Type = RESPONSE |
| | Code = RC_SUCCESS |
| | SeqNum = 178 | cells
| | CellList = [(1,2),(2,2),(3,5)] | locked
X |<--------------------------------------| --+
| L2 ACK | |
| - - - - - - - - - - - - - - - - - - ->| 6P Timeout |
| | | |
| 6P Confirmation | | |
| Type = CONFIRMATION | | |
| Code = RC_SUCCESS | | |
cells | SeqNum = 178 | | |
locked | CellList = [(2,2),(3,5)] | | |
+-- |-------------------------------------->| X <--+
| | L2 ACK |
+-> |<- - - - - - - - - - - - - - - - - - - |
| |
Figure 5: An example 3-step 6P Transaction.
In this example, the 3-step transaction occurs as follows:
6P messages travel over a single hop. 6P messages are carried as payload of an 802.15.4 Payload Information Element (IE) [IEEE802154]. The messages are encapsulated within the Payload IE Header. The Group ID is set to the IETF IE value defined in [RFC8137]. The content is encapsulated by a SubType ID, as defined in [RFC8137].
Since 6P messages are carried in IEs, IEEE bit/byte ordering applies. 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 [RFC8137], with subtype ID IANA_6TOP_SUBIE_ID. The SubType Content of the "6top IE" is defined in Section 3.2.2. The length of the "6top IE" content is variable.
All 6P messages follow the generic format shown in Figure 6.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|Version| T | R | Code | SFID | SeqNum |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Other Fields...
+-+-+-+-+-+-+-+-+-
Figure 6: Generic 6P Message Format.
6P Requests, 6P Response and 6P Confirmation messages for a same transaction MUST share the same Version, SFID and SeqNum values.
Future versions of the 6P Message SHOULD maintain the format of the 6P Version, Type and Code fields for backward compatibility.
An 8-bit 6P CellOptions bitmap is present in the following 6P requests: ADD, DELETE, COUNT, LIST, RELOCATE. The format and meaning of this field MAY be redefined by the SF; the routine that parses this field is therefore associated with a specific SF.
The content of the 6P CellOptions bitmap applies to all elements in the CellList field. The possible values of the 6P CellOptions are: TX = 1 (resp. 0) refers to macTxType = TRUE (resp. FALSE) in the macLinkTable of 802.15.4 [IEEE802154]. RX = 1 (resp. 0) refers to macRxType = TRUE (resp. FALSE) in the macLinkTable of 802.15.4. S = 1 (resp. 0) refers to macSharedType = TRUE (resp. FALSE) in the macLinkTable of 802.15.4. Section 6.2.6 contains the format of the 6P CellOptions bitmap, unless redefined by the SF. Figure 7 contains the meaning of the 6P CellOptions bitmap for the 6P ADD, DELETE, RELOCATE requests, unless redefined by the SF. Figure 8 contains the meaning of the 6P CellOptions bitmap for the 6P COUNT, LIST requests, unless redefined by the SF.
Note: assuming node A issues the 6P command to node B. +-------------+-----------------------------------------------------+ | CellOptions | The type of cells B adds/deletes/relocates to its | | Value | schedule when receiving a 6P ADD/DELETE/RELOCATE | | | Request from A. | +-------------+-----------------------------------------------------+ |TX=0,RX=0,S=0| Invalid combination. RC_ERR is returned. | +-------------+-----------------------------------------------------+ |TX=1,RX=0,S=0| add/delete/relocate RX cells at B (TX cells at A) | +-------------+-----------------------------------------------------+ |TX=0,RX=1,S=0| add/delete/relocate TX cells at B (RX cells at A) | +-------------+-----------------------------------------------------+ |TX=1,RX=1,S=0| add/delete/relocate TX|RX cells at B (and at A) | +-------------+-----------------------------------------------------+ |TX=0,RX=0,S=1| Invalid combination. RC_ERR is returned. | +-------------+-----------------------------------------------------+ |TX=1,RX=0,S=1| add/delete/relocate RX|SHARED cells at B | | | (TX|SHARED cells at A) | +-------------+-----------------------------------------------------+ |TX=0,RX=1,S=1| add/delete/relocate TX|SHARED cells at B | | | (RX|SHARED cells at A) | +-------------+-----------------------------------------------------+ |TX=1,RX=1,S=1| add/delete/relocate TX|RX|SHARED cells at B | | | (and at A) | +-------------+-----------------------------------------------------+
Figure 7: Meaning of the 6P CellOptions bitmap for the 6P ADD, DELETE, RELOCATE requests.
Note: assuming node A issues the 6P command to node B. +-------------+-----------------------------------------------------+ | CellOptions | The type of cells B selects from its schedule when | | Value | receiving a 6P COUNT or LIST Request from A, | | | from all the cells B has scheduled with A | +-------------+-----------------------------------------------------+ |TX=0,RX=0,S=0| all cells | +-------------+-----------------------------------------------------+ |TX=1,RX=0,S=0| all cells marked as RX only | +-------------+-----------------------------------------------------+ |TX=0,RX=1,S=0| all cells marked as TX only | +-------------+-----------------------------------------------------+ |TX=1,RX=1,S=0| all cells marked as TX and RX only | +-------------+-----------------------------------------------------+ |TX=0,RX=0,S=1| all cells marked as SHARED (regardless of TX, RX) | +-------------+-----------------------------------------------------+ |TX=1,RX=0,S=1| all cells marked as RX and SHARED only | +-------------+-----------------------------------------------------+ |TX=0,RX=1,S=1| all cells marked as TX and SHARED only | +-------------+-----------------------------------------------------+ |TX=1,RX=1,S=1| all cells marked as TX and RX and SHARED | +-------------+-----------------------------------------------------+
Figure 8: Meaning of the 6P CellOptions bitmap for the 6P COUNT, LIST requests.
The CellOptions is an opaque set of bits, sent unmodified to the SF. The SF MAY redefine the format and meaning of the CellOptions field.
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 a concatenation of zero, one or more 6P Cells as defined in Figure 9. The content of the CellOptions field specifies the options associated with all cells in the CellList. This necessarily means that the same options are associated with all cells in the CellList.
A 6P Cell is a 4-byte field, its default format is:
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| slotOffset | channelOffset |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 9: 6P Cell Format.
The CellList is an opaque set of bytes, sent unmodified to the SF. The length of the CellList field is implicit, and determined by the IE Length field of the Payload IE header as defined in 802.15.4. The SF MAY redefine the format of the CellList field; the routine that parses this field is therefore associated with a specific SF.
Cells are added by using the 6P ADD command. The Type field (T) is set to REQUEST. The Code field is set to ADD. Figure 10 defines the format of a 6P ADD Request.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|Version| T | R | Code | SFID | SeqNum |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Metadata | CellOptions | NumCells |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| CellList ...
+-+-+-+-+-+-+-+-+-
Figure 10: 6P ADD Request Format.
Figure 11 defines the format of a 6P ADD Response and Confirmation.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|Version| T | R | Code | SFID | SeqNum |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| CellList ...
+-+-+-+-+-+-+-+-+-
Figure 11: 6P ADD Response and Confirmation Formats.
Consider the topology in Figure 1 where the SF on node A decides to add NumCells cells to node B.
Node A's SF selects NumCandidate cells from its schedule. These are cells that are candidates to be scheduled with node B. The CellOptions field specifies the type of these cells. NumCandidate MUST be larger or equal to NumCells. How many cells node A 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. In case of a 3-step transaction, the SF is responsible for ensuring that the returned candidate CellList fits into the 6P Response.
Upon receiving the request, node B checks whether the cellOptions are set to a valid value as noted by Figure 7. If this is not the case, a Response with code RC_ERR is returned. If the cells in the received CellList in node B is smaller than NumCells, Node B MUST return a 6P Response with RC_ERR_CELLLIST code. Otherwise, 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 (fewer than NumCells cells from the CellList can be used). In all cases, node B MUST send a 6P Response with return code set to RC_SUCCESS, and which specifies the list of cells that were scheduled following the CellOptions field. That can contain NumCells elements (succeed), 0 elements (fail), or between 0 and NumCells elements (partially succeed).
Upon receiving the response, node A adds the cells specified in the CellList according to the 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. Figure 12 defines the format of a 6P DELETE Request.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|Version| T | R | Code | SFID | SeqNum |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Metadata | CellOptions | NumCells |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| CellList ...
+-+-+-+-+-+-+-+-+-
Figure 12: 6P DELETE Request Format.
Figure 13 defines the format of a 6P DELETE Response and Confirmation.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|Version| T | R | Code | SFID | SeqNum |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| CellList ...
+-+-+-+-+-+-+-+-+-
Figure 13: 6P DELETE Response and Confirmation Formats.
The behavior for deleting cells is equivalent to that of adding cells except that:
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. Figure 14 defines the format of a 6P RELOCATE Request.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|Version| T | R | Code | SFID | SeqNum |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Metadata | CellOptions | NumCells |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Relocation CellList ...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-
| Candidate CellList ...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-
Figure 14: 6P RELOCATE Request Format.
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. The Relocation CellList MUST contain exactly NumCells entries. The Candidate CellList MUST contain at least NumCells entries (NumCandidate>=NumCells).
In a 3-step 6P RELOCATE Transaction, node A specifies only the cells it needs to relocate, but not the list of candidate cells to relocate to. The Candidate CellList MUST therefore be empty.
Figure 15 defines the format of a 6P RELOCATE Response and Confirmation.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|Version| T | R | Code | SFID | SeqNum |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| CellList ...
+-+-+-+-+-+-+-+-+-
Figure 15: 6P RELOCATE Response and Confirmation Formats.
Node A's SF wants to relocate NumCells cells. Node A creates a 6P RELOCATE Request, and indicates the cells it wants to relocate in the Relocation CellList. It also selects NumCandidate cells from its schedule as candidate cells to relocate the cells to, 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 checks if the length of the Candidate CellList is larger or equal to NumCells. Node B's SF verifies that all the cells in the Relocation CellList are scheduled with node A, and are associate the options specified in the CellOptions field. If either check fails, node B MUST send a 6P Response to node A with return code RC_ERR_CELLLIST. If both checks pass, 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 (fewer 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 RC_SUCCESS, and which specifies the list of cells that will be re-scheduled following the CellOptions field. That can contain NumCells elements (succeed), 0 elements (fail), between 0 and NumCells elements (partially succeed). If N < NumCells cells appear in the CellList, this means the first N cells in the Relocation CellList have been relocated, the remainder have not.
Upon receiving the response with Code RC_SUCCESS, node A relocates the cells specified in Relocation CellList of its RELOCATE Request to the new locations specified in the CellList of the 6P Response, in the same order. In case the received return code is RC_ERR_CELLLIST, the transaction is aborted and no cell is relocated. In case of a 2-step transaction, Node B relocates the selected cells upon receiving the link-layer ACK for the 6P Response. In case of a 3-step transaction, Node B relocates the selected cells upon receiving the 6P Confirmation.
The SF SHOULD NOT relocate all cells between two nodes at the same time, which might result in the schedules of both nodes diverging significantly.
+----------+ +----------+
| Node A | | Node B |
+----+-----+ +-----+----+
| |
| 6P RELOCATE Request |
| Type = REQUEST |
| Code = RELOCATE |
| SeqNum = 11 |
| NumCells = 2 |
| R.CellList = [(1,2),(2,2)] |
| C.CellList = [(3,3),(4,3),(5,3)] |
|-------------------------------------->| B prepares
| L2 ACK | to relocate
|<- - - - - - - - - - - - - - - - - - - | (1,2)->(5,3)
| | and
| | (2,2)->(3,3)
| 6P Response |
| Code = RC_SUCCESS |
| SeqNum = 11 |
| CellList = [(5,3),(3,3)] |
A relocates|<--------------------------------------|
(1,2)->(5,3)| L2 ACK |
and | - - - - - - - - - - - - - - - - - - ->|B relocates
(2,2)->(3,3)| |(1,2)->(5,3)
| |and
| |(2,2)->(3,3)
Figure 16: Example of a successful 2-step 6P RELOCATION Transaction.
Figure 16 shows an example of a successful 2-step 6P RELOCATION Transaction.
+----------+ +----------+
| Node A | | Node B |
+----+-----+ +-----+----+
| |
| 6P RELOCATE Request |
| Type = REQUEST |
| Code = RELOCATE |
| SeqNum = 199 |
| NumCells = 2 |
| R.CellList = [(1,2),(2,2)] |
| C.CellList = [(3,3),(4,3),(5,3)] |B prepares
|-------------------------------------->|to relocate
| L2 ACK |(1,2)->(4,3)
|<- - - - - - - - - - - - - - - - - - - |but cannot
| |relocate (2,2)
| 6P Response |
| Type = RESPONSE |
| Code = RC_SUCCESS |
| SeqNum = 199 |
| CellList = [(4,3)] |
A relocates |<--------------------------------------|
(1,2)->(4,3)| L2 ACK |
| - - - - - - - - - - - - - - - - - - ->|B relocates
| |(1,2)->(4,3)
| |
| |
Figure 17: Example of a partially successful 2-step 6P RELOCATION Transaction.
Figure 17 shows an example of a partially successful 2-step 6P RELOCATION Transaction.
+----------+ +----------+
| Node A | | Node B |
+----+-----+ +-----+----+
| |
| 6P RELOCATE Request |
| Type = REQUEST |
| Code = RELOCATE |
| SeqNum = 53 |
| NumCells = 2 |
| R.CellList = [(1,2),(2,2)] |
| C.CellList = [(3,3),(4,3),(5,3)] |
|-------------------------------------->| B cannot
| L2 ACK | relocate
|<- - - - - - - - - - - - - - - - - - - | (1,2)
| | nor (2,2)
| 6P Response |
| Type = RESPONSE |
| Code = RC_SUCCESS |
| SeqNum = 53 |
| CellList = [] |
|<--------------------------------------| B does not
| L2 ACK | relocate
A does not | - - - - - - - - - - - - - - - - - - ->|
relocate | |
| |
Figure 18: Failed 2-step 6P RELOCATION Transaction Example.
Figure 18 shows an example of a failed 2-step 6P RELOCATION Transaction.
+----------+ +----------+
| Node A | | Node B |
+----+-----+ +-----+----+
| |
| 6P RELOCATE Request |
| Type = REQUEST |
| Code = RELOCATE |
| SeqNum = 11 |
| NumCells = 2 |
| R.CellList = [(1,2),(2,2)] |
| C.CellList = [] |
|-------------------------------------->|
| L2 ACK |
|<- - - - - - - - - - - - - - - - - - - | B identifies
| | candidate
| | cells
| 6P Response | (3,3),
| Code = RC_SUCCESS | (4,3) and
| SeqNum = 11 | (5,3)
| CellList = [(3,3),(4,3),(5,3)] |
A prepares |<--------------------------------------|
to relocate | L2 ACK |
(1,2)->(5,3) | - - - - - - - - - - - - - - - - - - ->|
and | |
(2,2)->(3,3) | 6P Confirmation |
| Code = RC_SUCCESS |
| SeqNum = 11 |
| CellList = [(5,3),(3,3)] |
|-------------------------------------->| B relocates
| L2 ACK | (1,2)->(5,3)
A relocates |<- - - - - - - - - - - - - - - - - - - | and
(1,2)->(5,3)| | (2,2)->(3,3)
and | |
(2,2)->(3,3)| |
| |
Figure 19: Example of a successful 3-step 6P RELOCATION Transaction.
Figure 19 shows an example of a successful 3-step 6P RELOCATION Transaction.
To retrieve the number of scheduled cells node A has with B, node A issues a 6P COUNT command. The Type field (T) is set to REQUEST. The Code field is set to COUNT. Figure 20 defines the format of a 6P COUNT Request.
1 2
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|Version| T | R | Code | SFID | SeqNum |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Metadata | CellOptions |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 20: 6P COUNT Request Format.
Figure 21 defines the format of a 6P COUNT Response.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|Version| T | R | Code | SFID | SeqNum |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| NumCells |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 21: 6P COUNT Response Format.
Node A issues a COUNT command to node B, specifying some 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 which match the cell options in the CellOptions field of the request. Section 3.2.3 details the use of the CellOptions field.
Node B issues a 6P response to node A with return code set to RC_SUCCESS, and with NumCells containing the number of cells that match the request.
To retrieve a list of scheduled cells node A has with node B, node A issues a 6P LIST command. The Type field (T) is set to REQUEST. The Code field is set to LIST. Figure 22 defines the format of a 6P LIST Request.
1 2
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|Version| T | R | Code | SFID | SeqNum |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Metadata | CellOptions | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Offset | MaxNumCells |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 22: 6P LIST Request Format.
Figure 23 defines the format of a 6P LIST Response.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|Version| T | R | Code | SFID | SeqNum |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| CellList ...
+-+-+-+-+-+-+-+-+-
Figure 23: 6P LIST Response Format.
When receiving a LIST command, node B returns the cells scheduled with A in its schedule that match the CellOptions field as specified in Section 3.2.3.
When node B receives a LIST request, the returned CellList in the 6P Response contains between 0 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 RC_EOL ("End of List", as per Figure 38), 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 fewer than Offset cells that match the request, node B returns an empty CellList and a Code field set to RC_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. Figure 24 defines the format of a 6P CLEAR Request.
1 2
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|Version| T | R | Code | SFID | SeqNum |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Metadata |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 24: 6P CLEAR Request Format.
Figure 25 defines the format of a 6P CLEAR Response.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|Version| T | R | Code | SFID | SeqNum |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 25: 6P CLEAR Response Format.
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 node B, and node B MUST remove all the cells scheduled with node 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 inconsistency, the transaction MUST NOT be aborted. Upon 6P CLEAR completion, the value of SeqNum MUST be reset to 0.
The return code to a 6P CLEAR command SHOULD be RC_SUCCESS unless the operation cannot be executed. When the CLEAR operation cannot be executed, the return code MUST be set to RC_RESET.
The 6P SIGNAL message 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. The length of the payload is determined through the length field of the Payload IE Header. How the generic SIGNAL command is used is specified by the SF, and outside the scope of this document. The Type field (T) is set to REQUEST. The Code field is set to SIGNAL. Figure 26 defines the format of a 6P SIGNAL Request.
1 2
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|Version| T | R | Code | SFID | SeqNum |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Metadata | payload ...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 26: 6P SIGNAL Request Format.
Figure 27 defines the format of a 6P SIGNAL Response.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|Version| T | R | Code | SFID | SeqNum |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| payload ...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 27: 6P SIGNAL Response Format.
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 a node receives a 6P message with a Version number it does not implement, the node MUST reply with a 6P Response with a return code field set to RC_ERR_VERSION. The format of this 6P Response message MUST be compliant with Version 0 and MUST be supported by all future versions of the protocol. This ensures that, when node B sends a 6P Response to node A indicating it does not implement the 6P version in the 6P Request, node A can successfully parse that response.
When a node supports a version number received in a 6P Request message, the Version field in the 6P Response MUST be the same as the Version field in the corresponding 6P Request. Similarly, in a 3-step transaction, the Version field in the 6P Confirmation MUST match that of the 6P Request and 6P Response of the same transaction.
All messages contain an 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 with return code of RC_ERR_SFID. 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 the 6P Response of 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 the previous 6P Transaction it initiated has finished (possibly 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 RC_RESET (as per Figure 38) and discard this ongoing second transaction. A node receiving a RC_RESET code MUST abort the second transaction and consider it never happened (i.e. reverting changes to the schedule or SeqNum done by this transaction).
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 with different neighbors. In this case, the cells involved in an ongoing 6P Transaction MUST be "locked" until the transaction finishes. For example, in Figure 1, 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 RC_ERR_BUSY (as per Figure 38). In case the requested cells are locked, it MUST reply to that request with a 6P Response with return code RC_ERR_LOCKED (as per Figure 38). The node receiving RC_ERR_BUSY or a RC_ERR_LOCKED MAY implement a retry mechanism, defined by the SF.
A timeout occurs when the node that successfully sent a 6P Request does not receive the corresponding 6P Response within an amount of time specified by the SF. In a 3-step transaction, a timeout also occurs when a node sending the 6P Response does not receive a 6P Confirmation. When a timeout occurs, the transaction MUST be canceled at the node where the timeout occurs. The value of the 6P Timeout should be larger than the longest possible time it takes to receive the 6P Response or Confirmation. The value of the 6P 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 is unable to complete it, it SHOULD reply to that Request with a 6P Response with return code RC_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 RC_RESET. Upon receiving this 6P Confirmation, the sender of the 6P Response MUST consider the 6P Transaction as failed.
The SeqNum is the field in the 6top IE header used to match Request, Response and Confirmation. The SeqNum is used to detect and handle duplicate commands (Section 3.4.6.1) and schedule inconsistencies (Section 3.4.6.2). Each node remembers the last used SeqNum for each neighbor. That is, a node stores as many SeqNum values as it has neighbors. In case of supporting multiple SFs at a time, a SeqNum value is maintained per SF and per neighbor. 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.
Specifically, if node A receives the link-layer acknowledgment for its 6P Request, it commits to incrementing the SeqNum by exactly 1 after the 6P Transaction ends. This ensure that, at the next 6P Transaction where it sends a 6P Request, 6P Request will have a different SeqNum.
Similarly, a node B increments the SeqNum by exactly 1 after having received the link-layer acknowledgment for the 6P Response (2-step 6P Transaction), or after having sent the link-layer acknowledgment for the 6P Confirmation (3-step 6P Transaction) .
When a node B receives a 6P Request from node A with SeqNum equal to 0, it checks the stored SeqNum for A. If A is a new neighbor, the stored SeqNum in B will be 0. The transaction can continue. If the stored SeqNum for A in B is different than 0, a potential inconsistency is detected. In this case, B MUST return RC_ERR_SEQNUM with SeqNum=0. The SF of node A MAY decide what to do next, as described in Section 3.4.6.2.
+-----------+-----------------------------+
| Value | Meaning |
+-----------+-----------------------------+
| 0x00 | Clear or After device Reset |
| 0x01-0xFF | Lollipop Counter values |
+-----------+-----------------------------+
Figure 28: Possible values of the SeqNum.
The SeqNum MUST be implemented as a lollipop counter: it rolls over from 0xFF to 0x01 (not to 0x00). This is used to detect a neighbor reset. Figure 28 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. Duplicate messages are normal and unavoidable.
+----------+ +----------+
| Node A | | Node B |
+----+-----+ +-----+----+
| |
| 6P Request (SeqNum=456) |
|-------------------------------------->|
| L2 ACK |
|<- - - - - - - - - - - - - - - - - - - |
| |
| 6P Response (SeqNum=456) |
|<--------------------------------------|
| L2 ACK |
| - - - - - - - - - - -X | No ACK:
| | link-layer
| 6P Response (SeqNum=456) | retransmit
duplicate |<--------------------------------------|
6P Response | L2 ACK |
received | - - - - - - - - - - - - - - - - - - ->|
| |
Figure 29: Example duplicate 6P message.
Figure 29 shows an example 2-step transaction in which Node A receives a duplicate 6P Response.
+----------+ +----------+
| Node A | | Node B |
+----+-----+ +-----+----+
| |
| 6P Request (SeqNum=123) |
|-------------------------------------->|
| L2 ACK |
|<- - - - - - - - - - - - - - - - - - - |
| |
| 6P Response (SeqNum=123) |
|<--------------------------------------|
| L2 ACK |
| - - - - - - - - - - -X | No ACK:
| | link-layer
| 6P Confirmation (SeqNum=123) | retransmit
|-------------------------------------->| |
| L2 ACK | |
|<- - - - - - - - - - - - - - - - - - - | frame
| | queued
| 6P Response (SeqNum=123) | |
duplicate |<--------------------------------------| <--+
out-of-order | L2 ACK |
6P Response | - - - - - - - - - - - - - - - - - - ->|
received | |
Figure 30: Example out-of-order duplicate 6P message.
Figure 30 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 the 6P message at the 6top sublayer.
A schedule inconsistency happens when the schedules of nodes A and B are inconsistent. For example, when node A has a transmit cell to node B, but node B does not have the corresponding receive cell, and therefore isn't listening to node A on that cell. A schedule inconsistency results in loss of connectivity.
The SeqNum field, which is present in each 6P message, is used to detect an inconsistency. The SeqNum field increments by 1 at each message, as detailed in Section 3.4.6. A node computes the expected SeqNum field for the next 6P Transaction. If a node receives a 6P Request with a SeqNum value that is not the expected one, it has detected an inconsistency.
There are at least 2 cases in which a schedule inconsistency happens.
The first case is when a node loses state, for example when it is power cycled (turned off, then on). In that case, its SeqNum value is reset to 0. Since the SeqNum is a lollipop counter, its neighbor detects an inconsistency at the next 6P transaction. This is illustrated in Figure 31 and Figure 32.
+----------+ +----------+
| Node A | | Node B |
+----+-----+ +-----+----+
SeqNum=87 | | SeqNum=87
| |
| 6P Request (SeqNum=87) |
|-------------------------------------->|
| L2 ACK |
|<- - - - - - - - - - - - - - - - - - - |
| |
| 6P Response (SeqNum=87) |
|<--------------------------------------|
| L2 ACK |
| - - - - - - - - - - - - - - - - - - ->|
| ==== power-cycle
| |
SeqNum=88 | | SeqNum=0
| |
| 6P Request (SeqNum=88) |
|-------------------------------------->| Inconsistency
| L2 ACK | Detected
|<- - - - - - - - - - - - - - - - - - - |
| |
| 6P Response (SeqNum=0, RC_ERR_SEQNUM) |
|<--------------------------------------|
| L2 ACK |
| - - - - - - - - - - - - - - - - - - ->|
Figure 31: Example of inconsistency because of node B reset. Detected by node B
+----------+ +----------+
| Node A | | Node B |
+----+-----+ +-----+----+
SeqNum=97 | | SeqNum=97
| |
| 6P Request (SeqNum=97) |
|-------------------------------------->|
| L2 ACK |
|<- - - - - - - - - - - - - - - - - - - |
| |
| 6P Response (SeqNum=97) |
|<--------------------------------------|
| L2 ACK |
| - - - - - - - - - - - - - - - - - - ->|
| ==== power-cycle
| |
SeqNum=98 | | SeqNum=0
| |
| 6P Request (SeqNum=0) |
Inconsistency|<--------------------------------------|
Detected | L2 ACK |
|- - - - - - - - - - - - - - - - - - - >|
| |
| 6P Response (SeqNum=0, RC_ERR_SEQNUM) |
|-------------------------------------->|
| L2 ACK |
|<- - - - - - - - - - - - - - - - - - - |
Figure 32: Example of inconsistency because node B resets. Detected by node A
+----------+ +----------+
| Node A | | Node B |
+----+-----+ +-----+----+
SeqNum=87 | | SeqNum=87
| |
| 6P Request (SeqNum=87) |
|-------------------------------------->|
| L2 ACK |
|<- - - - - - - - - - - - - - - - - - - |
| |
| 6P Response (SeqNum=87) |
|<--------------------------------------|
| L2 ACK |
| - - - - - - - - X |
SeqNum=88 | | no ACK:
| 6P Response (SeqNum=87) | retrans. 1
(duplicate) |<--------------------------------------|
| L2 ACK |
| - - - - - - - - X |
| | no ACK:
| 6P Response (SeqNum=87) | retrans. 2
(duplicate) |<--------------------------------------|
| L2 ACK |
| - - - - - - - - X |
| | max retrans.:
| | Inconsistency
| | Detected
Figure 33: Example inconsistency because of maximum link-layer retransmissions (here 2).
The second case is when the maximum number of link-layer retransmissions is reached on the 6P Response of a 2-step transaction (or equivalently on a 6P Confirmation of a 3-step transaction). This is illustrated in Figure 33.
In both cases, node B detects the inconsistency.
If the inconsistency is detected during a 6P Transaction (Figure 31), the node that has detected it MUST send back a 6P Response or 6P Confirmation with an error code of RC_ERR_SEQNUM. In this 6P Response or 6P Confirmation, the SeqNum field MUST be set to the value of the sender of the message (0 in the example in Figure 31).
The SF of the node which has detected the inconsistency MUST define how to handle the inconsistency. A first possibility is to issue a 6P CLEAR request to clear the schedule, and rebuild. A second possibility is to issue a 6P LIST request to retrieve the schedule. A third possibility is to internally "roll-back" the schedule. How to handle an inconsistency is out of scope of this document. The SF defines how to handle an inconsistency.
A return code marked as Yes in the "Is Error" column in Figure 38 indicates an error. When a node receives a 6P Response or 6P Confirmation with an error, it MUST consider the 6P Transaction as failed. In particular, if this was a response to a 6P ADD, DELETE or RELOCATE Request, the node MUST NOT add, delete or 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. If a node receives an unrecognized return code the 6P Transaction MUST be considered as failed. In particular, in a 3 step 6P Transaction, a 6P Response with an unrecognized return code MUST be responded with a 6P Confirmation with return code RC_ERR and consider the transaction as failed. 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 MUST be secured through link-layer security. This is possible because 6P messages are carried as Payload IEs.
Each SF has a 1-byte identifier. Section 6.2.5 defines the rules for applying for an SFID.
The specification for an SF
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* [CCM-Star]. 6P benefits from the same level of security as any other Payload IE. The 6P protocol does not define its own security mechanisms. In particular, although a key management solution is out of scope of this document, the 6P protocol will benefit for the key management solution used in the network. This is relevant as security attacks such as forgery and misattribution attacks become more damaging when a single key is shared amongst a group of more than 2 participants.
The 6P protocol does not provide protection against DOS attacks. Example attacks include, not sending confirmation messages in 3-step transaction, and sending wrongly formatted requests. These cases SHOULD be handled by an appropriate policy, such as rate-limiting or time-limited blacklisting the attacker after several attempts. The effect on the overall network is mostly localized to those two nodes, as communication happens in dedicated cells.
This document adds the following number to the "IEEE Std 802.15.4 IETF IE subtype IDs" registry defined by [RFC8137]:
+--------+------------+-----------+
| Value | Subtype ID | Reference |
+--------+------------+-----------+
| <TBD> | SUBID_6TOP | RFCXXXX |
+---------------------+-----------+
Figure 34: IETF IE Subtype SUBID_6TOP.
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:
+---------+-----------+
| Version | Reference |
+---------+-----------+
| 0 | RFCXXXX |
+---------+-----------+
Figure 35: 6P Version Numbers.
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 [RFC8126].
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 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:
+------+--------------+-----------+
| Type | Name | Reference |
+------+--------------+-----------+
| b00 | REQUEST | RFCXXXX |
| b01 | RESPONSE | RFCXXXX |
| b10 | CONFIRMATION | RFCXXXX |
+------+--------------+-----------+
Figure 36: 6P Message Types.
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 [RFC8126].
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 an 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:
+------------+------------+-----------+
| Identifier | Name | Reference |
+------------+------------+-----------+
| 0 | Reserved | |
| 1 | ADD | RFCXXXX |
| 2 | DELETE | RFCXXXX |
| 3 | RELOCATE | RFCXXXX |
| 4 | COUNT | RFCXXXX |
| 5 | LIST | RFCXXXX |
| 6 | SIGNAL | RFCXXXX |
| 7 | CLEAR | RFCXXXX |
| 8-254 | Unassigned | |
| 255 | Reserved | |
+------------+------------+-----------+
Figure 37: 6P Command Identifiers.
The IANA policy for future additions to this sub-registry is "IETF Review or IESG Approval" as described in [RFC8126].
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 a 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:
+------+-----------------+---------------------------+-----------+ | Code | Name | Description | Is Error? | +------+-----------------+---------------------------+-----------+ | 0 | RC_SUCCESS | operation succeeded | No | | 1 | RC_EOL | end of list | No | | 2 | RC_ERR | generic error | Yes | | 3 | RC_RESET | critical error, reset | Yes | | 4 | RC_ERR_VERSION | unsupported 6P version | Yes | | 5 | RC_ERR_SFID | unsupported SFID | Yes | | 6 | RC_ERR_SEQNUM | schedule inconsistency | Yes | | 7 | RC_ERR_CELLLIST | cellList error | Yes | | 8 | RC_ERR_BUSY | busy | Yes | | 9 | RC_ERR_LOCKED | cells are locked | Yes | +------+-----------------+---------------------------+-----------+
Figure 38: 6P Return Codes.
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 [RFC8126].
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 an SFID in the range 0-255, the corresponding Name, and a reference to the 6P Scheduling Function's documentation.
Initial entries in this sub-registry are as follows:
+----+---------------------------------+----------------------------+ |SFID| Name | Reference | +----+---------------------------------+----------------------------+ | 0 | Minimal Scheduling Function | draft-chang-6tisch-msf | | | (MSF) | | +----+---------------------------------+----------------------------+
Figure 39: SF Identifiers (SFID).
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 Figure 40. These specifications must follow the guidelines of Section 4.
+-----------+------------------------------+
| Range | Registration Procedures |
+-----------+------------------------------+
| 0-127 | IETF Review or IESG Approval |
| 128-255 | Expert Review |
+-----------+------------------------------+
Figure 40: SF Identifier (SFID): Registration Procedure.
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 a 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:
+-----+---------------+-----------+
| bit | Name | Reference |
+-----+---------------+-----------+
| 0 | TX (Transmit) | RFCXXXX |
| 1 | RX (Receive) | RFCXXXX |
| 2 | SHARED | RFCXXXX |
| 3-7 | Reserved | |
+-----+---------------+-----------+
Figure 41: 6P CellOptions bitmap.
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 [RFC8126].
| [IEEE802154] | IEEE standard for Information Technology, "IEEE Std 802.15.4-2015 - IEEE Standard for Low-Rate Wireless Personal Area Networks (WPANs)", October 2015. |
| [RFC2119] | Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, March 1997. |
| [RFC8137] | Kivinen, T. and P. Kinney, "IEEE 802.15.4 Information Element for the IETF", RFC 8137, DOI 10.17487/RFC8137, May 2017. |
The following section structure for a SF document is RECOMMENDED: