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IETF RFC 8480
6TiSCH Operation Sublayer (6top) Protocol (6P)
Last modified on Monday, November 5th, 2018
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Internet Engineering Task Force (IETF) Q. Wang, Ed.
Request for Comments: 8480 Univ. of Sci. and Tech. Beijing
Category: Standards Track X. Vilajosana
ISSN: 2070-1721 Universitat Oberta de Catalunya
T. Watteyne
Analog Devices
November 2018
6TiSCH Operation Sublayer (6top) Protocol (6P)
 Abstract
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 Time-Slotted Channel Hopping (TSCH) cells to/on one
another. 6P is part of the 6TiSCH Operation Sublayer (6top), the
layer just above the IEEE Std 802.15.4 TSCH Medium Access Control
layer. 6top is composed of one or more Scheduling Functions (SFs)
and the 6top Protocol defined in this document. A 6top SF decides
when to add/delete cells, and it triggers 6P Transactions. The
definition of SFs is out of scope for this document; however, this
document provides the requirements for an SF.
Status of This Memo
This is an Internet Standards Track document.
This document is a product of the Internet Engineering Task Force
(IETF). It represents the consensus of the IETF community. It has
received public review and has been approved for publication by the
Internet Engineering Steering Group (IESG). Further information on
Internet Standards is available in Section 2 of RFC 7841.
Information about the current status of this document, any errata,
and how to provide feedback on it may be obtained at
https://www.rfc-editor.org/info/RFC 8480.
Wang, et al. Standards Track PAGE 1 
RFC 8480 6top Protocol (6P) November 2018
Copyright Notice
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.
Table of Contents
1. Introduction ....................................................3
1.1. Requirements Language ......................................5
2. 6TiSCH Operation Sublayer (6top) ................................5
2.1. Hard/Soft Cells ............................................6
2.2. Using 6P with the Minimal 6TiSCH Configuration .............6
3. 6top Protocol (6P) ..............................................7
3.1. 6P Transactions ............................................7
3.1.1. 2-Step 6P Transaction ...............................8
3.1.2. 3-Step 6P Transaction ..............................10
3.2. Message Format ............................................12
3.2.1. 6top Information Element (IE) ......................12
3.2.2. Generic 6P Message Format ..........................12
3.2.3. 6P CellOptions .....................................13
3.2.4. 6P CellList ........................................16
3.3. 6P Commands and Operations ................................17
3.3.1. Adding Cells .......................................17
3.3.2. Deleting Cells .....................................19
3.3.3. Relocating Cells ...................................21
3.3.4. Counting Cells .....................................27
3.3.5. Listing Cells ......................................28
3.3.6. Clearing the Schedule ..............................30
3.3.7. Generic Signaling between SFs ......................31
3.4. Protocol Functional Details ...............................31
3.4.1. Version Checking ...................................31
3.4.2. SFID Checking ......................................32
3.4.3. Concurrent 6P Transactions .........................32
3.4.4. 6P Timeout .........................................33
3.4.5. Aborting a 6P Transaction ..........................33
3.4.6. SeqNum Management ..................................33
3.4.7. Handling Error Responses ...........................40
3.5. Security ..................................................40
Wang, et al. Standards Track PAGE 2
RFC 8480 6top Protocol (6P) November 2018
4. Requirements for 6top Scheduling Function (SF) Specifications ..41
4.1. SF Identifier (SFID) ......................................41
4.2. Requirements for an SF Specification ......................41
5. Security Considerations ........................................42
6. IANA Considerations ............................................43
6.1. IETF IE Subtype 6P ........................................43
6.2. 6TiSCH Parameters Subregistries ...........................43
6.2.1. 6P Version Numbers .................................43
6.2.2. 6P Message Types ...................................44
6.2.3. 6P Command Identifiers .............................44
6.2.4. 6P Return Codes ....................................45
6.2.5. 6P Scheduling Function Identifiers .................46
6.2.6. 6P CellOptions Bitmap ..............................47
7. References .....................................................48
7.1. Normative References ......................................48
7.2. Informative References ....................................48
Appendix A. Recommended Structure of an SF Specification ..........49
Authors' Addresses ................................................50
1. Introduction
All communication in an "IPv6 over the TSCH mode of IEEE 802.15.4e"
(6TiSCH) network is orchestrated by a schedule [RFC 7554]. The
schedule is composed of cells, each identified by a
[slotOffset,channelOffset] (Section 3.2.4). This specification
defines the 6TiSCH Operation Sublayer (6top) Protocol (6P), which is
terminated by 6top. 6P allows a node to communicate with a neighbor
node to add/delete Time-Slotted Channel Hopping (TSCH) cells to/on
one another. This results in distributed schedule management in a
6TiSCH network. 6top is composed of one or more Scheduling Functions
(SFs) and the 6top Protocol defined in this document. The definition
of SFs is out of scope for this document; however, this document
provides the requirements for an SF.
Wang, et al. Standards Track PAGE 3
RFC 8480 6top Protocol (6P) November 2018
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 (also referred to as "commands" in this
document) to node "B". We use this example throughout this document:
node A always represents the node that issues a 6P Request, and
node B represents the node that receives this request.
(R)
/ \
/ \
(B)-----(C)
| |
| |
(A) (D)
Figure 1: A Simple 6TiSCH Network
We consider that node A monitors the communication cells it has in
its schedule to node B:
o If node A determines that the number of link-layer frames it is
sending to node B per unit of time exceeds the capacity offered by
the TSCH cells it has scheduled to node B, it triggers a 6P
Transaction with node B to add one or more cells to the TSCH
schedule of both nodes.
o If the traffic is lower than the capacity offered by the TSCH
cells it has scheduled to node B, node A triggers a 6P Transaction
with node B to delete one or more cells in the TSCH schedule of
both nodes.
o 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" this
particular cell to a different [slotOffset,channelOffset] location
in the TSCH schedule.
This results in distributed schedule management in a 6TiSCH network.
The 6top SF defines when to add/delete a cell to/on a neighbor.
Different applications require different SFs; this topic is out of
scope for 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.
Wang, et al. Standards Track PAGE 4
RFC 8480 6top Protocol (6P) November 2018
Section 2 describes 6top. Section 3 defines 6P. Section 4 provides
guidelines on how to define an SF.
1.1. Requirements Language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in
BCP 14 [RFC 2119] [RFC 8174] when, and only when, they appear in all
capitals, as shown here.
2. 6TiSCH Operation Sublayer (6top)
As depicted in Figure 2, 6top is the layer just above 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: 6top in the Protocol Stack
The roles of 6top are to:
o Terminate 6P, which allows neighbor nodes to communicate to
add/delete cells to/on one another.
o Run one or multiple 6top SFs, which define the rules that decide
when to add/delete cells.
Wang, et al. Standards Track PAGE 5
RFC 8480 6top Protocol (6P) November 2018
2.1. Hard/Soft Cells
Each cell in the schedule is either "hard" or "soft":
o A soft cell can be read, added, deleted, or updated by 6top.
o 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 [RFC 8180].
2.2. Using 6P with the Minimal 6TiSCH Configuration
6P MAY be used alongside the minimal 6TiSCH configuration [RFC 8180].
In this case, it is RECOMMENDED to use two slotframes, as depicted in
Figure 3:
o Slotframe 0 is used for traffic defined in the minimal 6TiSCH
configuration. In Figure 3, Slotframe 0 is five slots long, but
it can be shorter or longer.
o 6P allocates cells from Slotframe 1. In Figure 3, Slotframe 1 is
10 slots long, but it can be shorter or longer.
| 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.
Wang, et al. Standards Track PAGE 6
RFC 8480 6top Protocol (6P) November 2018
3. 6top Protocol (6P)
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.
3.1. 6P Transactions
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 (1) the cell(s) has been added/deleted/
relocated in the schedule of both nodes or (2) 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 nodes 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 is out of scope for this document.
A 6P Transaction can consist of two or three 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.
Wang, et al. Standards Track PAGE 7
RFC 8480 6top Protocol (6P) November 2018
3.1.1. 2-Step 6P Transaction
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 so that the diagram is easier to understand.
+----------+ +----------+
| 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:
1. The SF running on node A determines that two extra cells need to
be scheduled to node B.
2. The SF running on node A selects candidate cells for node B to
choose from. Node A MUST select at least as many candidate cells
as the number of cells to add. Here, node A selects three
candidate cells. Node A locks those candidate cells in its
schedule until it receives a 6P Response.
Wang, et al. Standards Track PAGE 8
RFC 8480 6top Protocol (6P) November 2018
3. Node A sends a 6P ADD Request to node B, indicating that it
wishes to add two cells (the "NumCells" value) and specifying the
list of three candidate cells (the "CellList" value). Each cell
in the CellList is a [slotOffset,channelOffset] tuple. This 6P
ADD Request is link-layer acknowledged by node B (labeled "L2
ACK" in Figure 4).
4. After having successfully sent the 6P ADD Request (i.e.,
receiving the link-layer acknowledgment), node A starts a 6P
Timeout to abort the 6P Transaction in the event that no response
is received from node B.
5. The SF running on node B selects two out of the three cells from
the CellList of the 6P ADD Request. Node B locks those cells in
its schedule until the transmission is successful (i.e., node B
receives a link-layer ACK from node A). Node B sends back a 6P
Response to node A, indicating the cells it has selected. The
response is link-layer acknowledged by node A.
6. Upon completion of this 6P Transaction, two cells from node A to
node B have been added to the TSCH schedule of both nodes A
and B.
7. An inconsistency in the schedule can happen if the 6P Timeout
expires when the 6P Response is in the air, if the last
link-layer ACK for the 6P Response is lost, or if one of the
nodes is power-cycled during the transaction. 6P provides an
inconsistency detection mechanism to cope with such situations;
see Section 3.4.6.2 for details.
Wang, et al. Standards Track PAGE 9
RFC 8480 6top Protocol (6P) November 2018
3.1.2. 3-Step 6P Transaction
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 so that the diagram is easier to understand.
+----------+ +----------+
| 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
Wang, et al. Standards Track PAGE 10
RFC 8480 6top Protocol (6P) November 2018
In this example, the 3-step transaction occurs as follows:
1. The SF running on node A determines that two extra cells need to
be scheduled to node B. The SF uses a 3-step transaction, so it
does not select candidate cells.
2. Node A sends a 6P ADD Request to node B, indicating that it
wishes to add two cells (the "NumCells" value), with an empty
"CellList". This 6P ADD Request is link-layer acknowledged by
node B.
3. After having successfully sent the 6P ADD Request, node A starts
a 6P Timeout to abort the transaction in the event that no 6P
Response is received from node B.
4. The SF running on node B selects three candidate cells and locks
them. Node B sends back a 6P Response to node A, indicating the
three cells it has selected. The response is link-layer
acknowledged by node A.
5. After having successfully sent the 6P Response, node B starts a
6P Timeout to abort the transaction in the event that no 6P
Confirmation is received from node A.
6. The SF running on node A selects two cells from the CellList
field in the 6P Response and locks them. Node A sends back a 6P
Confirmation to node B, indicating the cells it selected. The
confirmation is link-layer acknowledged by node B.
7. Upon completion of the 6P Transaction, two cells from node A to
node B have been added to the TSCH schedule of both nodes A
and B.
8. An inconsistency in the schedule can happen if the 6P Timeout
expires when the 6P Confirmation is in the air, if the last
link-layer ACK for the 6P Confirmation is lost, or if one of the
nodes is power-cycled during the transaction. 6P provides an
inconsistency detection mechanism to cope with such situations;
see Section 3.4.6.2 for details.
Wang, et al. Standards Track PAGE 11
RFC 8480 6top Protocol (6P) November 2018
3.2. Message Format
3.2.1. 6top Information Element (IE)
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 [RFC 8137]. The
content is encapsulated by a subtype ID, as defined in [RFC 8137].
Since 6P messages are carried in IEs, IEEE bit/byte ordering applies.
Bits within each field in the "6top IE" subtype 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 [RFC 8137], with subtype SUBID_6TOP. The subtype content of the
6top IE is defined in Section 3.2.2. The length of the 6top IE
content is variable.
3.2.2. Generic 6P Message Format
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 Version (Version): The version of 6P. Only version 0 is defined
in this document. Future specifications may define subsequent
versions of 6P.
Type (T): The type of message. The message types are defined in
Section 6.2.2.
Reserved (R): Reserved bits. These two bits SHOULD be set to zero
when sending the message and MUST be ignored upon reception.
Wang, et al. Standards Track PAGE 12
RFC 8480 6top Protocol (6P) November 2018
Code: The Code field contains a 6P command identifier when the 6P
message has a Type value of REQUEST. Section 6.2.3 lists the
6P command identifiers. The Code field contains a 6P return
code when the 6P message has a Type value of RESPONSE or
CONFIRMATION. Section 6.2.4 lists the 6P return codes. The
same return codes are used in both 6P Response and 6P
Confirmation messages.
6top Scheduling Function Identifier (SFID): The identifier of the SF
to use to handle this message. The SFID is defined in
Section 4.1.
SeqNum: The 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 for each new 6P Request issued to the same neighbor
and using the same SF. The SeqNum is also used to ensure
consistency between the schedules of the two neighbors.
Section 3.4.6 details how the SeqNum is managed.
Other Fields: The list of other fields and how they are used are
detailed in Section 3.3.
6P Request, 6P Response, and 6P Confirmation messages for a given
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.
3.2.3. 6P CellOptions
An 8-bit 6P CellOptions bitmap is present in the following 6P
Requests: ADD, DELETE, COUNT, LIST, and 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.
o In the 6P ADD Request, the 6P CellOptions bitmap is used to
specify what type of cell to add.
o In the 6P DELETE Request, the 6P CellOptions bitmap is used to
specify what type of cell to delete.
o In the 6P RELOCATE Request, the 6P CellOptions bitmap is used to
specify what type of cell to relocate.
o In the 6P COUNT and LIST Requests, the 6P CellOptions bitmap is
used as a selector of a particular type of cells.
Wang, et al. Standards Track PAGE 13
RFC 8480 6top Protocol (6P) November 2018
The content of the 6P CellOptions bitmap applies to all elements in
the CellList field. The possible values of the 6P CellOptions are as
follows:
o TX = 1 (resp. 0) refers to macTxType = TRUE (resp. FALSE) in the
macLinkTable of 802.15.4 [IEEE802154].
o RX = 1 (resp. 0) refers to macRxType = TRUE (resp. FALSE) in the
macLinkTable of 802.15.4.
o S = 1 (resp. 0) refers to macSharedType = TRUE (resp. FALSE) in
the macLinkTable of 802.15.4.
Section 6.2.6 provides the format of the 6P CellOptions bitmap; this
format applies unless redefined by the SF. Figure 7 shows the
meaning of the 6P CellOptions bitmap for the 6P ADD, DELETE, and
RELOCATE Requests (unless redefined by the SF). Figure 8 shows the
meaning of the 6P CellOptions bitmap for the 6P COUNT and LIST
Requests (unless redefined by the SF).
Note: Here, we assume that 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, and RELOCATE Requests
Wang, et al. Standards Track PAGE 14
RFC 8480 6top Protocol (6P) November 2018
Note: Here, we assume that 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, RX, and SHARED |
+-------------+-----------------------------------------------------+
Figure 8: Meaning of the 6P CellOptions Bitmap for the
6P COUNT and LIST Requests
The CellOptions constitute an opaque set of bits, sent unmodified to
the SF. The SF MAY redefine the format and meaning of the
CellOptions field.
Wang, et al. Standards Track PAGE 15
RFC 8480 6top Protocol (6P) November 2018
3.2.4. 6P CellList
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 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
slotOffset: The slot offset of the cell.
channelOffset: The channel offset of the cell.
The CellList is an opaque set of bytes, sent unmodified to the SF.
The length of the CellList field is implicit and is 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.
Wang, et al. Standards Track PAGE 16
RFC 8480 6top Protocol (6P) November 2018
3.3. 6P Commands and Operations
3.3.1. Adding Cells
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
Metadata: Used as extra signaling to the SF. The contents of the
Metadata field are an opaque set of bytes passed unmodified to
the SF. The meaning of this field depends on the SF and is out
of scope for this document. For example, Metadata can specify
in which slotframe to add the cells.
CellOptions: 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 each one. This necessarily means
that if node A needs to add multiple cells with different
options it needs to initiate multiple 6P ADD Transactions.
NumCells: The number of additional cells node A wants to schedule to
node B.
CellList: A list of zero or multiple candidate cells. Its length is
implicit and is determined by the Length field of the Payload
IE header.
Wang, et al. Standards Track PAGE 17
RFC 8480 6top Protocol (6P) November 2018
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 Format
CellList: A list of zero or more 6P Cells.
Consider the topology in Figure 1; in this case, 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 greater than or equal to NumCells. How many cells node A
selects (NumCandidate) and how that selection is done are specified
in the SF and are out of scope for this document. Node A sends a 6P
ADD Request to node B that contains the CellOptions, the value of
NumCells, and a selection of NumCandidate cells in the CellList. If
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
the 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 to see 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
number of cells in the received CellList in node B is smaller than
NumCells, node B MUST return a 6P Response with the 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 is out of scope for 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 that includes a return code set to
RC_SUCCESS and that specifies the list of cells that were scheduled
following the CellOptions field. That list can contain NumCells
elements (succeed), 0 elements (fail), or between 0 and NumCells
elements (partially succeed).
Wang, et al. Standards Track PAGE 18
RFC 8480 6top Protocol (6P) November 2018
Upon receiving the response, node A adds the cells specified in the
CellList according to the CellOptions field.
3.3.2. Deleting Cells
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
Metadata: Same usage as for the 6P ADD command; see Section 3.3.1.
Its format is the same as that in the 6P ADD command, but its
content could be different.
CellOptions: Indicates the options that need to be associated with
the cells to delete. Only cells matching the CellOptions can
be deleted.
NumCells: The number of cells from the specified CellList the sender
wants to delete from the schedule of both sender and receiver.
CellList: A list of zero or more 6P Cells. Its length is determined
by the Length field of the Payload IE header.
Wang, et al. Standards Track PAGE 19
RFC 8480 6top Protocol (6P) November 2018
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 Format
CellList: A list of zero or more 6P Cells.
The behavior for deleting cells is equivalent to that of adding cells
except that:
o The nodes delete the cells they agree upon rather than adding
them.
o 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 RC_ERR_CELLLIST return code.
o The CellList in a 6P Request (2-step transaction) or 6P Response
(3-step transaction) MUST be empty, contain exactly NumCells
cells, or contain more than NumCells cells. The case where the
CellList is not empty but contains fewer than NumCells cells is
not supported; the RC_ERR_CELLLIST code MUST be returned when the
CellList contains fewer than NumCells cells. If the CellList is
empty, the SF on the receiving node MUST choose NumCells cells
scheduled to the sender matching the CellOptions field and delete
them. If the CellList contains more than NumCells cells, the SF
on the receiving node chooses exactly NumCells cells from the
CellList to delete.
Wang, et al. Standards Track PAGE 20
RFC 8480 6top Protocol (6P) November 2018
3.3.3. Relocating Cells
Cell relocation consists of moving a cell to a different
[slotOffset,channelOffset] location in the schedule. The Type field
(T) is set to REQUEST. The Code field 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
Metadata: Same usage as for the 6P ADD command; see Section 3.3.1.
CellOptions: Indicates the options that need to be associated with
cells to be relocated.
NumCells: The number of cells to relocate. MUST be greater than or
equal to 1.
Relocation CellList: The list of NumCells 6P Cells to relocate.
Candidate CellList: A list of NumCandidate candidate cells for
node B to pick from. NumCandidate MUST be 0, equal to
NumCells, or greater than NumCells. Its length is determined
by the Length field of the Payload IE header.
In a 2-step 6P RELOCATE Transaction, node A specifies both (1) the
cells it needs to relocate and (2) 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 -- not the list of candidate cells to relocate
to. The Candidate CellList MUST therefore be empty.
Wang, et al. Standards Track PAGE 21
RFC 8480 6top Protocol (6P) November 2018
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 Format
CellList: A list of zero or more 6P Cells.
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 it puts
them in the Candidate CellList. The CellOptions field specifies the
type of the cell(s) to relocate. NumCandidate MUST be greater than
or equal to NumCells. How many cells it selects (NumCandidate) and
how that selection is done are specified in the SF and are out of
scope for this document. Node A sends the 6P RELOCATE Request to
node B.
Upon receiving the request, node B checks to see if the length of the
Candidate CellList is greater than or equal to NumCells. Node B's SF
verifies that all the cells in the Relocation CellList are scheduled
with node A and are associated with 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 is out of scope for this document. That
verification for the 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 that includes a return code set
to RC_SUCCESS and that specifies the list of cells that will be
rescheduled following the CellOptions field. That list can contain
NumCells elements (succeed), 0 elements (fail), or between 0 and
NumCells elements (partially succeed). If N < NumCells cells appear
in the CellList, this means that the first N cells in the Relocation
CellList have been relocated and the remainder have not.
Wang, et al. Standards Track PAGE 22
RFC 8480 6top Protocol (6P) November 2018
Upon receiving the response with code RC_SUCCESS, node A relocates
the cells specified in the Relocation CellList of its RELOCATE
Request to the new locations specified in the CellList of the 6P
Response, in the same order. If the received return code is
RC_ERR_CELLLIST, the transaction is aborted and no cell is relocated.
In the case of a 2-step transaction, node B relocates the selected
cells upon receiving the link-layer ACK for the 6P Response. In the
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, as this might result in the schedules of both nodes diverging
significantly.
Figure 16 shows an example of a successful 2-step 6P RELOCATE
Transaction.
+----------+ +----------+
| 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 RELOCATE Transaction
Wang, et al. Standards Track PAGE 23
RFC 8480 6top Protocol (6P) November 2018
Figure 17 shows an example of a partially successful 2-step 6P
RELOCATE 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
RELOCATE Transaction
Wang, et al. Standards Track PAGE 24
RFC 8480 6top Protocol (6P) November 2018
Figure 18 shows an example of a failed 2-step 6P RELOCATE
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)
| | or (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 RELOCATE Transaction Example
Wang, et al. Standards Track PAGE 25
RFC 8480 6top Protocol (6P) November 2018
Figure 19 shows an example of a successful 3-step 6P RELOCATE
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 RELOCATE Transaction
Wang, et al. Standards Track PAGE 26
RFC 8480 6top Protocol (6P) November 2018
3.3.4. Counting Cells
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 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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 20: 6P COUNT Request Format
Metadata: Same usage as for the 6P ADD command; see Section 3.3.1.
Its format is the same as that in the 6P ADD command, but its
content could be different.
CellOptions: Specifies which type of cell to be counted.
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
NumCells: The number of cells that correspond to the fields of the
request.
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 that 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 RC_SUCCESS and
with NumCells containing the number of cells that match the request.
Wang, et al. Standards Track PAGE 27
RFC 8480 6top Protocol (6P) November 2018
3.3.5. Listing Cells
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 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 | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Offset | MaxNumCells |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 22: 6P LIST Request Format
Metadata: Same usage as for the 6P ADD command; see Section 3.3.1.
Its format is the same as that in the 6P ADD command, but its
content could be different.
CellOptions: Specifies which type of cell to be listed.
Reserved: Reserved bits. These bits SHOULD be set to zero when
sending the message and MUST be ignored upon reception.
Offset: The offset of the first scheduled cell that is requested.
The mechanism assumes that cells are ordered according to a
rule defined in the SF. The rule MUST always order the cells
in the same way.
MaxNumCells: The maximum number of cells to be listed. Node B MAY
return fewer than MaxNumCells cells -- for example, if
MaxNumCells cells do not fit in the frame.
Wang, et al. Standards Track PAGE 28
RFC 8480 6top Protocol (6P) November 2018
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
CellList: A list of zero or more 6P Cells.
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 will 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 in Section 6.2.4), indicating to node A that there are 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.
Wang, et al. Standards Track PAGE 29
RFC 8480 6top Protocol (6P) November 2018
3.3.6. Clearing the Schedule
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 REQUEST. The Code field is set to
CLEAR. Figure 24 defines the format of a 6P CLEAR 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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 24: 6P CLEAR Request Format
Metadata: Same usage as for the 6P ADD command; see Section 3.3.1.
Its format is the same as that in the 6P ADD command, but its
content could be different.
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 sent in response 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.
Wang, et al. Standards Track PAGE 30
RFC 8480 6top Protocol (6P) November 2018
3.3.7. Generic Signaling between SFs
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 by the Length field of the
Payload IE header. How the generic SIGNAL command is used is
specified by the SF and is 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 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 | payload ...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 26: 6P SIGNAL Request Format
Metadata: Same usage as for the 6P ADD command; see Section 3.3.1.
Its format is the same as that in the 6P ADD command, but its
content could be different.
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
3.4. Protocol Functional Details
3.4.1. Version Checking
All messages contain a Version field. If multiple protocol versions
of 6P 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
Wang, et al. Standards Track PAGE 31
RFC 8480 6top Protocol (6P) November 2018
supported by all future versions of the protocol. This ensures that
when node B sends a 6P Response to node A indicating that 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.
3.4.2. SFID Checking
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 a 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.
3.4.3. Concurrent 6P Transactions
Only a single 6P Transaction at a time in a given direction can take
place between two neighbors. That is, a node MUST NOT issue a new 6P
Request to a given neighbor before the previous 6P Transaction it
initiated has finished (or 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 in
Section 6.2.4) and discard this ongoing second transaction. A node
receiving a RC_RESET code MUST abort the second transaction and treat
it as though 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. If 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
Section 6.2.4). If 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 RC_ERR_LOCKED MAY
implement a retry mechanism as defined by the SF.
Wang, et al. Standards Track PAGE 32
RFC 8480 6top Protocol (6P) November 2018
3.4.4. 6P Timeout
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 greater 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 for this document.
3.4.5. Aborting a 6P Transaction
If 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 having failed.
Similarly, in the case of a 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 having
failed.
3.4.6. SeqNum Management
The SeqNum is the field in the 6top IE header used to match Request,
Response, and Confirmation messages for a given transaction. The
SeqNum is used to detect and handle duplicate commands
(Section 3.4.6.1) and inconsistent schedules (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 the 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.
Wang, et al. Standards Track PAGE 33
RFC 8480 6top Protocol (6P) November 2018
Specifically, if node A receives the link-layer acknowledgment for
its 6P Request, it will increment the SeqNum by exactly 1 after the
6P Transaction ends. This ensures that, for the next 6P Transaction
where it sends a 6P Request, the 6P Request will have a different
SeqNum.
Similarly, 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 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.
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.
+-----------+------------------------------+
| Value | Meaning |
+-----------+------------------------------+
| 0x00 | Clear, or after device reset |
| 0x01-0xFF | Lollipop counter values |
+-----------+------------------------------+
Figure 28: Possible Values of the SeqNum
3.4.6.1. Detecting and Handling Duplicate 6P Messages
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.
Wang, et al. Standards Track PAGE 34
RFC 8480 6top Protocol (6P) November 2018
Figure 29 shows an example 2-step transaction in which node A
receives a duplicate 6P Response.
+----------+ +----------+
| 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
Wang, et al. Standards Track PAGE 35
RFC 8480 6top Protocol (6P) November 2018
Figure 30 shows an example 3-step transaction in which node A
receives an out-of-order duplicate 6P Response after having sent a 6P
Confirmation.
+----------+ +----------+
| 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
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 6top.
3.4.6.2. Detecting and Handling a Schedule Inconsistency
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 in each
message, as detailed in Section 3.4.6. A node computes the expected
Wang, et al. Standards Track PAGE 36
RFC 8480 6top Protocol (6P) November 2018
SeqNum field for the next 6P Transaction. If a node receives a 6P
Request with a SeqNum value that is not the expected value, it has
detected an inconsistency.
There are two 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 in the next 6P Transaction. This is
illustrated in Figures 31 and 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 Node B Resets
(Detected by Node B)
Wang, et al. Standards Track PAGE 37
RFC 8480 6top Protocol (6P) November 2018
+----------+ +----------+
| 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)
Wang, et al. Standards Track PAGE 38
RFC 8480 6top Protocol (6P) November 2018
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.
+----------+ +----------+
| 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 (where Maximum = 2)
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).
Wang, et al. Standards Track PAGE 39
RFC 8480 6top Protocol (6P) November 2018
The SF of the node that has detected the inconsistency MUST define
how to handle the inconsistency. Three possible ways to do this are
as follows:
o Issue a 6P CLEAR Request to clear the schedule, and then rebuild.
o Issue a 6P LIST Request to retrieve the schedule.
o Internally "roll back" the schedule.
How to handle an inconsistency is out of scope for this document.
The SF defines how to handle an inconsistency.
3.4.7. Handling Error Responses
A return code marked as Yes in the "Is Error?" column in Figure 38
(Section 6.2.4) indicates an error. When a node receives a 6P
Response or 6P Confirmation with an error, it MUST consider the 6P
Transaction as having 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, or relocate any cells as part of
that 6P Transaction. If a node receives an unrecognized return code,
the 6P Transaction MUST be considered as having failed. In
particular, in a 3-step 6P Transaction, when receiving a 6P Response
with a return code that it does not recognize, the requester (node A)
MUST send a 6P Confirmation to the responder (node B) with return
code RC_ERR and consider the transaction failed. Upon reception of a
6P Confirmation with return code RC_ERR, the responder MUST consider
the transaction failed as well. Defining what to do after an error
has occurred is out of scope for this document. The SF defines what
to do after an error has occurred.
3.5. Security
6P messages MUST be secured through link-layer security. This is
possible because 6P messages are carried as Payload IEs.
Wang, et al. Standards Track PAGE 40
RFC 8480 6top Protocol (6P) November 2018
4. Requirements for 6top Scheduling Function (SF) Specifications
4.1. SF Identifier (SFID)
Each SF has a 1-byte identifier. Section 6.2.5 defines the rules for
applying for an SFID.
4.2. Requirements for an SF Specification
The specification for an SF
o MUST specify an identifier for that SF.
o MUST specify the rule for a node to decide when to add/delete one
or more cells to/on a neighbor.
o MUST specify the rule for a transaction source to select cells to
add to the CellList field in the 6P ADD Request.
o MUST specify the rule for a transaction destination to select
cells from the CellList to add to its schedule.
o MUST specify a value for the 6P Timeout or a rule/equation to
calculate it.
o MUST specify the rule for ordering cells.
o MUST specify a meaning for the Metadata field in the 6P ADD
Request.
o MUST specify the SF behavior of a node when it boots.
o MUST specify how to handle a schedule inconsistency.
o MUST specify what to do after an error has occurred (the node
either sent a 6P Response with an error code or received one).
o MUST specify the list of statistics to gather. Example statistics
include the number of transmitted frames to each neighbor. If the
SF does not require that statistics be gathered, the SF
specification MUST explicitly say so.
o SHOULD clearly state the application domain the SF is created for.
o SHOULD contain examples that highlight normal and error scenarios.
o SHOULD contain a list of current implementations, at least during
the Internet-Draft (I-D) state of the document, per [RFC 7942].
Wang, et al. Standards Track PAGE 41
RFC 8480 6top Protocol (6P) November 2018
o SHOULD contain a performance evaluation of the scheme, possibly
through references to external documents.
o SHOULD define the format of the SIGNAL command payload and
its use.
o MAY redefine the format of the CellList field.
o MAY redefine the format of the CellOptions field.
o MAY redefine the meaning of the CellOptions field.
5. Security Considerations
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] ("CCM" stands for "Cipher block
Chaining -- Message authentication code"). 6P benefits from the same
level of security as any other Payload IE. 6P does not define its
own security mechanisms. In particular, although a key management
solution is out of scope for this document, 6P will benefit from 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 two participants.
6P does not provide protection against DoS attacks. Example attacks
include not sending confirmation messages in 3-step transactions and
sending incorrectly formatted requests. These cases SHOULD be
handled by an appropriate policy, such as rate-limiting or
time-limited blacklisting of the attacker after several attempts.
The effect on the overall network is mostly localized to the two
nodes in question, as communication happens in dedicated cells.
Wang, et al. Standards Track PAGE 42
RFC 8480 6top Protocol (6P) November 2018
6. IANA Considerations
6.1. IETF IE Subtype 6P
This document adds the following number to the "IEEE Std 802.15.4
IETF IE Subtype IDs" registry defined by [RFC 8137]:
+--------+------------+-----------+
| Value | Subtype ID | Reference |
+--------+------------+-----------+
| 1 | SUBID_6TOP | RFC 8480 |
+---------------------+-----------+
Figure 34: IETF IE Subtype SUBID_6TOP
6.2. 6TiSCH Parameters Subregistries
This section defines subregistries within the "IPv6 Over the TSCH
Mode of IEEE 802.15.4e (6TiSCH)" parameters registry, hereafter
referred to as the "6TiSCH parameters" registry. Each subregistry is
described in a subsection.
6.2.1. 6P Version Numbers
The name of the subregistry is "6P Version Numbers".
The following note is included in this registry: "In the 6top
Protocol (6P) [RFC 8480], there is a field to identify the version of
the protocol. This field is 4 bits in size."
Each entry in the subregistry must include the version in the
range 0-15 and a reference to the 6P version's documentation.
The initial entry in this subregistry is as follows:
+---------+-----------+
| Version | Reference |
+---------+-----------+
| 0 | RFC 8480 |
+---------+-----------+
Figure 35: 6P Version Number Entry
All other version numbers are Unassigned.
The IANA policy for future additions to this subregistry is "IETF
Review" or "IESG Approval" as described in [RFC 8126].
Wang, et al. Standards Track PAGE 43
RFC 8480 6top Protocol (6P) November 2018
6.2.2. 6P Message Types
The name of the subregistry is "6P Message Types".
The following note is included in this registry: "In version 0 of the
6top Protocol (6P) [RFC 8480], there is a field to identify the type
of message. This field is 2 bits in size."
Each entry in the subregistry must include the message type in the
range b00-b11, the corresponding name, and a reference to the 6P
message type's documentation.
Initial entries in this subregistry are as follows:
+------+--------------+-----------+
| Type | Name | Reference |
+------+--------------+-----------+
| b00 | REQUEST | RFC 8480 |
| b01 | RESPONSE | RFC 8480 |
| b10 | CONFIRMATION | RFC 8480 |
+------+--------------+-----------+
Figure 36: 6P Message Types
All other message types are Unassigned.
The IANA policy for future additions to this subregistry is "IETF
Review" or "IESG Approval" as described in [RFC 8126].
6.2.3. 6P Command Identifiers
The name of the subregistry is "6P Command Identifiers".
The following note is included in this registry: "In version 0 of the
6top Protocol (6P) [RFC 8480], there is a Code field that 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 subregistry must include an identifier in the
range 0-255, the corresponding name, and a reference to the 6P
command identifier's documentation.
Wang, et al. Standards Track PAGE 44
RFC 8480 6top Protocol (6P) November 2018
Initial entries in this subregistry are as follows:
+------------+------------+-----------+
| Identifier | Name | Reference |
+------------+------------+-----------+
| 0 | Reserved | RFC 8480 |
| 1 | ADD | RFC 8480 |
| 2 | DELETE | RFC 8480 |
| 3 | RELOCATE | RFC 8480 |
| 4 | COUNT | RFC 8480 |
| 5 | LIST | RFC 8480 |
| 6 | SIGNAL | RFC 8480 |
| 7 | CLEAR | RFC 8480 |
| 8-254 | Unassigned | |
| 255 | Reserved | RFC 8480 |
+------------+------------+-----------+
Figure 37: 6P Command Identifiers
The IANA policy for future additions to this subregistry is "IETF
Review" or "IESG Approval" as described in [RFC 8126].
6.2.4. 6P Return Codes
The name of the subregistry is "6P Return Codes".
The following note is included in this registry: "In version 0 of the
6top Protocol (6P) [RFC 8480], there is a Code field that 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 subregistry must include a return code in the
range 0-255, the corresponding name, the corresponding description,
and a reference to the 6P return code's documentation. If the return
code corresponds to a Response error, the "Is Error?" entry must
indicate "Yes". Otherwise, "No" must be used.
Wang, et al. Standards Track PAGE 45
RFC 8480 6top Protocol (6P) November 2018
Initial entries in this subregistry 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 subregistry is "IETF
Review" or "IESG Approval" as described in [RFC 8126].
6.2.5. 6P Scheduling Function Identifiers
The name of the subregistry is "6P Scheduling Function Identifiers".
The following note is included in this registry: "In version 0 of the
6top Protocol (6P) [RFC 8480], there is a field to identify the
Scheduling Function to handle the message. This field is 8 bits
in size."
Each entry in the subregistry must include an SFID in the
range 0-255, the corresponding name, and a reference to the 6P
Scheduling Function's documentation.
There are currently no entries in this subregistry.
+------+---------------------------------+--------------------------+
| SFID | Name | Reference |
+------+---------------------------------+--------------------------+
| 0-255| Unassigned | |
+------+---------------------------------+--------------------------+
Figure 39: SF Identifier (SFID) Entry
All message types are Unassigned.
Wang, et al. Standards Track PAGE 46
RFC 8480 6top Protocol (6P) November 2018
The IANA policy for future additions to this subregistry depends on
the value of the SFID, as shown 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
6.2.6. 6P CellOptions Bitmap
The name of the subregistry is "6P CellOptions Bitmap".
The following note is included in this registry: "In version 0 of the
6top Protocol (6P) [RFC 8480], there is an optional CellOptions field
that is 8 bits in size."
Each entry in the subregistry 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 subregistry are as follows:
+-----+---------------+-----------+
| bit | Name | Reference |
+-----+---------------+-----------+
| 0 | TX (Transmit) | RFC 8480 |
| 1 | RX (Receive) | RFC 8480 |
| 2 | SHARED | RFC 8480 |
| 3-7 | Reserved | |
+-----+---------------+-----------+
Figure 41: 6P CellOptions Bitmap
All other message types are Unassigned.
The IANA policy for future additions to this subregistry is "IETF
Review" or "IESG Approval" as described in [RFC 8126].
Wang, et al. Standards Track PAGE 47
RFC 8480 6top Protocol (6P) November 2018
7. References
7.1. Normative References
[IEEE802154]
IEEE, "IEEE Standard for Low-Rate Wireless Networks",
IEEE 802.15.4, DOI 10.1109/IEEESTD.2016.7460875.
[RFC 2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC 2119, March 1997,
<https://www.rfc-editor.org/info/RFC 2119>.
[RFC 8137] Kivinen, T. and P. Kinney, "IEEE 802.15.4 Information
Element for the IETF", RFC 8137, DOI 10.17487/RFC 8137,
May 2017, <https://www.rfc-editor.org/info/RFC 8137>.
[RFC 8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in
RFC 2119 Key Words", BCP 14, RFC 8174,
DOI 10.17487/RFC 8174, May 2017,
<https://www.rfc-editor.org/info/RFC 8174>.
7.2. Informative References
[CCM-Star] Struik, R., "Formal Specification of the CCM* Mode of
Operation", IEEE P802.15-4/0537r2, September 2005.
[RFC 7554] Watteyne, T., Ed., Palattella, M., and L. Grieco, "Using
IEEE 802.15.4e Time-Slotted Channel Hopping (TSCH) in the
Internet of Things (IoT): Problem Statement", RFC 7554,
DOI 10.17487/RFC 7554, May 2015,
<https://www.rfc-editor.org/info/RFC 7554>.
[RFC 7942] Sheffer, Y. and A. Farrel, "Improving Awareness of Running
Code: The Implementation Status Section", BCP 205,
RFC 7942, DOI 10.17487/RFC 7942, July 2016,
<https://www.rfc-editor.org/info/RFC 7942>.
[RFC 8126] Cotton, M., Leiba, B., and T. Narten, "Guidelines for
Writing an IANA Considerations Section in RFCs", BCP 26,
RFC 8126, DOI 10.17487/RFC 8126, June 2017,
<https://www.rfc-editor.org/info/RFC 8126>.
[RFC 8180] Vilajosana, X., Ed., Pister, K., and T. Watteyne, "Minimal
IPv6 over the TSCH Mode of IEEE 802.15.4e (6TiSCH)
Configuration", BCP 210, RFC 8180, DOI 10.17487/RFC 8180,
May 2017, <https://www.rfc-editor.org/info/RFC 8180>.
Wang, et al. Standards Track PAGE 48
RFC 8480 6top Protocol (6P) November 2018
Appendix A. Recommended Structure of an SF Specification
The following section structure for an SF document is RECOMMENDED:
o Introduction
o RFC 2119 Requirements Language (if applicable)
o Scheduling Function Identifier
o Rules for Adding/Deleting Cells
o Rules for CellList
o 6P Timeout Value
o Rule for Ordering Cells
o Meaning of the Metadata Field
o Node Behavior at Boot
o Schedule Inconsistency Handling
o 6P Error Handling
o Examples
o Implementation Status
o Security Considerations
o IANA Considerations
o Normative References (if applicable)
o Informative References (if applicable)
Wang, et al. Standards Track PAGE 49
RFC 8480 6top Protocol (6P) November 2018
Authors' Addresses
Qin Wang (editor)
Univ. of Sci. and Tech. Beijing
30 Xueyuan Road
Beijing, Hebei 100083
China
Email: wangqin@ies.ustb.edu.cn
Xavier Vilajosana
Universitat Oberta de Catalunya
156 Rambla Poblenou
Barcelona, Catalonia 08018
Spain
Email: xvilajosana@uoc.edu
Thomas Watteyne
Analog Devices
32990 Alvarado-Niles Road, Suite 910
Union City, CA 94587
United States of America
Email: thomas.watteyne@analog.com
Wang, et al. Standards Track PAGE 50
6TiSCH Operation Sublayer (6top) Protocol (6P)
RFC TOTAL SIZE: 107695 bytes
PUBLICATION DATE: Monday, November 5th, 2018
LEGAL RIGHTS: The IETF Trust (see BCP 78)
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