6TiSCH Q. Wang, Ed.
Internet-Draft Univ. of Sci. and Tech. Beijing
Intended status: Informational X. Vilajosana
Expires: January 3, 2016 Universitat Oberta de Catalunya
T. Watteyne
Linear Technology
R. Sudhaakar
Cisco Systems
P. Zand
University of Twente
July 2, 2015
Transporting CoAP Messages over IEEE802.15.4e Information Elements
draft-wang-6tisch-6top-coapie-01
Abstract
This document describes the format of "CoAP IE", an IEEE802.15.4e
Information Element which allows CoAP messages to be transported as
part of the IEEE802.15.4e payload IE. This enables 6top-to-6top
communication between neighbor nodes in a 6TiSCH network.
Status of This Memo
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provisions of BCP 78 and BCP 79.
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document authors. All rights reserved.
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Provisions Relating to IETF Documents
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
1.1. Requirements Notation . . . . . . . . . . . . . . . . . . 2
1.2. Context within 6TiSCH . . . . . . . . . . . . . . . . . . 2
1.3. Motivation . . . . . . . . . . . . . . . . . . . . . . . 3
1.4. Status of this Document . . . . . . . . . . . . . . . . . 3
2. CoAP IE Format . . . . . . . . . . . . . . . . . . . . . . . 4
3. Softcell Negotiation Interface RPC Definition . . . . . . . . 5
4. CoAP support . . . . . . . . . . . . . . . . . . . . . . . . 7
4.1. URI setting . . . . . . . . . . . . . . . . . . . . . . . 7
4.2. CoAP Block option . . . . . . . . . . . . . . . . . . . . 7
4.3. Management Interface Protocol . . . . . . . . . . . . . . 8
4.4. Negotiation interface protocol . . . . . . . . . . . . . 8
4.5. Acknowledgement . . . . . . . . . . . . . . . . . . . . . 9
4.6. Observe . . . . . . . . . . . . . . . . . . . . . . . . . 9
5. Implementation Considerations . . . . . . . . . . . . . . . . 10
6. References . . . . . . . . . . . . . . . . . . . . . . . . . 10
6.1. Normative References . . . . . . . . . . . . . . . . . . 10
6.2. Informative References . . . . . . . . . . . . . . . . . 11
6.3. External Informative References . . . . . . . . . . . . . 12
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 12
1. Introduction
1.1. Requirements Notation
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 [RFC2119].
1.2. Context within 6TiSCH
This document fits in the work done at the IETF 6TiSCH WG as follows:
o [I-D.wang-6tisch-6top-sublayer] defines the operation of the 6top
sublayer, which monitors and manages the communication schedule
used in the [IEEE802154e] TSCH network.
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o [I-D.ietf-6tisch-6top-interface] defines the interface of the 6top
sublayer using the YANG data modeling language [RFC6020].
o [I-D.ietf-6tisch-coap] translates this YANG model in CoAP
resources and interactions, allowing an Internet host (possibly
but not necessarily constrained) to monitor and manage the 6top
sublayer of a 6TiSCH device.
o This document defines a method for transporting those CoAP
messages as part of the IEEE802.15.4e payload IE. It does so by
defining a new IEEE802.15.4e Information Element called "CoAP IE".
This allows a 6TiSCH node to monitor and manage the 6top sublayer
and enables pairwise communication for signaling and control
between neighbor nodes.
1.3. Motivation
The 6TiSCH architecture [I-D.ietf-6tisch-architecture] allows for
both centralized and distributed monitoring and management of a
6TiSCH schedule. [I-D.ietf-6tisch-coap] defines the mechanisms
necessary for the centralized case. The present document defines a
mechanism enabling the communication of nodes in a 1 hop
neighborhood, enabling a distributed approach.
In particular, it allows a node to monitor and manage its neighbor
node's MIB. Through the CoAP IE defined in this document, a node
sends link-layer frames to its neighbor which contain, as part of the
link-layer payload IE, the CoAP messages defined in
[I-D.ietf-6tisch-coap]. This allows a node to interact with the 6top
interface of its neighbor, in a way equivalent to an Internet host
interacting with a 6TiSCH device over CoAP.
In addition, this document describe the frame formats and interaction
between a node and its neighbor during softcell negotiation
[I-D.wang-6tisch-6top-sublayer], through the addition of an Remote
Procedure Call "RPC" element to the YANG model defined in
[I-D.ietf-6tisch-6top-interface].
We call "6top-to-6top" communication the interaction between a node
and its neighbor using the CoAP IE.
1.4. Status of this Document
The authors decided to present the CoAP IE as a separate document to
request discussion and suggestions for improvement from the Internet
community.
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If the document gets support, and after suggestions for improvement
have been integrated, the author propose to merge it in existing
6TiSCH I-Ds as follows:
o Section 3 would go into [I-D.ietf-6tisch-6top-interface];
o Section 4 would go into [I-D.ietf-6tisch-coap];
o Section 2 and Section 5 would go into
[I-D.wang-6tisch-6top-sublayer].
2. CoAP IE Format
The CoAP IE is a container for transporting CoAP messages as part of
the IEEE802.15.4e payload IE, as an Information Element. It is used
by both the management interface and the softcell negotiation
interface for 6top-to-6top communication.
This IE is not present in [IEEE802154e]; it is defined in this
document.
Format of a CoAP IE.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Length | SubID |T| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |
// //
| Fragmented CoAP message |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 1
The fields in CoAP IE header are defined as follows.
o Length = 1
o SubID = 0x44
o T = 0 (short type)
The content of CoAP IE is a CoAP message compliant to [RFC7252]. The
CoAP message MAY use the CoAP Block option (see Section 4.2) in order
to fragment large CoAP messages.
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Format of CoAP IE with CoAP message.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| CoAP IE header |Ver| T | TKL | Code |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Message ID | Token (0-8B, assume 2B) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Uri-path option |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 11111111 | |
+-+-+-+-+-+-+-+-+ |
// //
| CoAP message payload (variable) |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 2
The Token Length (TKL)is set to 2;
Per [RFC7252], the Uri-path field consists of the following sub-
fields:
o Option Delta: 4bits, set to 11
o Option Length: 4bits, set to 3
o Option value: 3 bytes
The first byte of the option value is set to "6" (for 6top), "4" (for
IEEE802.15.4), or "e" (for extension). The second and third bytes
refer to the resource name in the corresponding group.
3. Softcell Negotiation Interface RPC Definition
This document proposes to replace the "6top Communication Protocol"
defined in [I-D.wang-6tisch-6top-sublayer] by an extension to the
YANG data model defined in [I-D.ietf-6tisch-6top-interface]. This
allows neighbor nodes to negotiate the allocation of soft cells using
the CoAP IE.
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rpc softcell-negotiation {
input {
leaf Opcode {
type enumeration {
enum RESERVATION;
enum REMOVE;
}
}
leaf RequiredBW {
type uint8;
}
leaf SlotframeID {
type uint8;
}
leaf TrackID {
type uint16;
description
"TrackID points to a tuple(TrackOwnerAddr,
InstanceID)";
}
leaf NumofCandidate {
type uint8;
}
List CandidateList {
key "SlotOffset ChannelOffset";
leaf SlotOffset{
type uint16;
}
leaf ChannelOffset{
type uint16;
}
}
}
output {
leaf NumOfCells {
type uint8;
}
List ResultedCells {
key "SlotOffset ChannelOffset";
leaf SlotOffset{
type uint16;
}
leaf ChannelOffset{
type uint16;
}
}
}
}
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4. CoAP support
4.1. URI setting
Uri-Host option = target node address;
Uri-Path option = 6t/6/[6top resource name], or 6t/4/[15.4
resource name], or 6t/e/[extension resource name], where [6top
resource name] refers to the data resources or RPC defined by
6top, [15.4 resource name] refers to the data resources defined
by IEEE802.15.4, and [extension resource name] refers to the
data resources defined by an extensions of 6top, e.g. OTF.
[6top resource name] , [154 resource name] and [extension
resource name] are RECOMMENDED to be at most 2 bytes long.
4.2. CoAP Block option
In [I-D.ietf-core-block], two block options (Block1 and Block2) are
defined to support block-wise transfers. The format of a fragmented
message in a CoAP IE is defined as follows.
Format of CoAP IE content with fragmented message.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| CoAP IE header |Ver| T | TKL | Code |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Message ID | Token |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Uri-path option |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|option |option | option delta | NUM |M| SZX |
| delta |length | extended | | | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 11111111 | |
+++++++++++++++++ |
// //
| fragmented payload (64B) |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 3
Per [I-D.ietf-core-block], the option Delta is 23 for Block1 and 27
for Block2. Related sub-fields are defined as follows.
o Option delta: 4bits, set to 13, indicates an 8-bit unsigned
integer follows the initial byte and the Option Delta minus 13.
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o Option length: 4bits, set to 2.
o Option delta extended: 8bits, 23-13=10 and 27-13=14 for Block1 and
Block2, respectively.
Per [IEEE802154], assuming the IE size constraint is 81 bytes, the
related fields of the block option are defined as follows.
o The size of the block (SZX): 3 bits, representing block size
16B/32B/64B/128B/256B/512B/1024B. Considering the IE size
constrained by [IEEE802154], 16B/32B/64B block size will be used.
Invalid block size values will cause the packet to be dropped
quietly.
o Whether more blocks are following (M): 1 bit;
o The relative number of the block (NUM): 12 bits, within a sequence
of blocks with the given size. NUM is 4bits or 12bits, or 20bits
4.3. Management Interface Protocol
Management and MIB handling is handled by the protocol specification
defined in [I-D.ietf-6tisch-coap].
4.4. Negotiation interface protocol
The negotiation protocol is used by neighbor nodes to agree at what
slotOffset/channelOffset to add/remove sotfcells. It uses a Uri-Path
option to identify the target resource (i.e the negotiation interface
of the neighbor).
The example below illustrates the use of this negotiation interface.
It assumes the RPC softcell-negotiation is at Uri-Path "6t/6/ng".
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nodeA nodeB
| |
+------>| IEEE802.15.4e type: DATA
| POST | CoAP Header: POST (T=CON)
| | Uri-Path: "6t/6/ng"
| | Payload: CBOR(
| | Opcode=RESERVATION,
| | RequiredBW,
| | SlotframeID,
| | TrackID,
| | NumOfCandidate,
| | CandidateList
| | )
| |
|<------+ IEEE802.15.4e type: ACK
| |
|<------+ IEEE802.15.4e type: DATA
| 2.04 | CoAP Header: 2.04 Changed (T=ACK, Code=2.04)
| | Payload: CBOR(
| | NumOfCells,
| | ResultedCells
| | )
| |
+-------> IEEE802.15.4e type: ACK
| |
Node A send a CoAP POST request, using a confirmable message. Node B
sends back a IEEE802.15.4e ACK to confirm reception. This layer 2
ACK does not give any indication about the correct handling of the
command, or even about whether this command is well formatted and
understood. Node B parses the CoAP IE, and if correct, calls the
appropriate 6top command to allocate softcells. When the allocation
is done, node B sends back a CoAP Response with the appropriate
return code to node A as a IEEE802.15.4e data packet. The CoAP ACK
MUST be piggybacked on the Response.
4.5. Acknowledgement
For both non-fragmented CoAP message and fragmented CoAP message, an
Acknowledgement message of CoAP is used. The Acknowledgement message
of CoAP is inserted into a CoAP IE, which is carried in the Data
Frame or Enhanced Acknowledgement frame of [IEEE802154e].
4.6. Observe
The Observe mechanism is a option for 6top-to-6top communication.
The Token in the CoAP message is used to bind Observe message and its
Response messages.
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5. Implementation Considerations
Similar to the formatting and the parser modules used by CoAP (Layer
5), a CoAP formatting and parser modules are present in the 6top
sublayer.
+-----------------------------------+
| PCEP | CoAP | | 6LoWPAN | |
| PCC | DTLS | PANA | ND |RPL |
+------------------------------------------+
| TCP | UDP | ICMP | RSVP |
+------------------------------------------+
| IPv6 |
+------------------------------------------+
| 6LoWPAN HC |
+------------------------------------------+
| +--------------+ +----------------+ |
| | CoAP Parser | | CoAP Formatting| |
| +--------------+ +----------------+ |
| +--------------+ +----------------+ |
| | IE Parser | | IE Formatting | |
| +--------------+ +----------------+ |
+------------------------------------------+
| IEEE802.15.4e TSCH |
+------------------------------------------+
| IEEE802.15.4 |
+------------------------------------------+
Figure 4
When the IE parser identifies a CoAP IE in the data packet, it passes
the IE content (i.e. the fragmented CoAP message) to the CoAP Parser.
The CoAP Parser then assembles those fragmented CoAP messages, and
takes the appropriate action based on the CoAP Code, Uri-Path, and
payload.
When a CoAP message is formatted, it MAY be fragmented, then passed
to the IE Formatting module. The IE Formatting module puts those
(possibly fragmented) CoAP message(s) into a CoAP IE and pases them
to the IEEE802.15.4e TSCH layer as separate packets.
6. References
6.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
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6.2. Informative References
[RFC6020] Bjorklund, M., "YANG - A Data Modeling Language for the
Network Configuration Protocol (NETCONF)", RFC 6020,
October 2010.
[RFC7252] Shelby, Z., Hartke, K., and C. Bormann, "The Constrained
Application Protocol (CoAP)", RFC 7252, June 2014.
[I-D.ietf-core-block]
Bormann, C. and Z. Shelby, "Block-wise transfers in CoAP",
draft-ietf-core-block-17 (work in progress), March 2015.
[I-D.ietf-6tisch-tsch]
Watteyne, T., Palattella, M., and L. Grieco, "Using
IEEE802.15.4e TSCH in an IoT context: Overview, Problem
Statement and Goals", draft-ietf-6tisch-tsch-06 (work in
progress), March 2015.
[I-D.ietf-6tisch-architecture]
Thubert, P., "An Architecture for IPv6 over the TSCH mode
of IEEE 802.15.4", draft-ietf-6tisch-architecture-08 (work
in progress), May 2015.
[I-D.ietf-6tisch-terminology]
Palattella, M., Thubert, P., Watteyne, T., and Q. Wang,
"Terminology in IPv6 over the TSCH mode of IEEE
802.15.4e", draft-ietf-6tisch-terminology-04 (work in
progress), March 2015.
[I-D.ietf-6tisch-minimal]
Vilajosana, X. and K. Pister, "Minimal 6TiSCH
Configuration", draft-ietf-6tisch-minimal-10 (work in
progress), June 2015.
[I-D.ietf-6tisch-6top-interface]
Wang, Q., Vilajosana, X., and T. Watteyne, "6TiSCH
Operation Sublayer (6top) Interface", draft-ietf-6tisch-
6top-interface-03 (work in progress), March 2015.
[I-D.ietf-6tisch-coap]
Sudhaakar, R. and P. Zand, "6TiSCH Resource Management and
Interaction using CoAP", draft-ietf-6tisch-coap-03 (work
in progress), March 2015.
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[I-D.wang-6tisch-6top-sublayer]
Wang, Q., Vilajosana, X., and T. Watteyne, "6TiSCH
Operation Sublayer (6top)", draft-wang-6tisch-6top-
sublayer-01 (work in progress), July 2014.
6.3. External Informative References
[IEEE802154e]
IEEE standard for Information Technology, "IEEE std.
802.15.4e, Part. 15.4: Low-Rate Wireless Personal Area
Networks (LR-WPANs) Amendment 1: MAC sublayer", April
2012.
[IEEE802154]
IEEE standard for Information Technology, "IEEE std.
802.15.4, Part. 15.4: Wireless Medium Access Control (MAC)
and Physical Layer (PHY) Specifications for Low-Rate
Wireless Personal Area Networks", June 2011.
[OpenWSN] Watteyne, T., Vilajosana, X., Kerkez, B., Chraim, F.,
Weekly, K., Wang, Q., Glaser, S., and K. Pister, "OpenWSN:
a Standards-Based Low-Power Wireless Development
Environment", Transactions on Emerging Telecommunications
Technologies , August 2012.
[morell04label]
Morell, A., Vilajosana, X., Lopez-Vicario, J., and T.
Watteyne, "Label Switching over IEEE802.15.4e Networks.
Transactions on Emerging Telecommunications Technologies",
June 2013.
Authors' Addresses
Qin Wang (editor)
Univ. of Sci. and Tech. Beijing
30 Xueyuan Road
Beijing, Hebei 100083
China
Phone: +86 (10) 6233 4781
Email: wangqin@ies.ustb.edu.cn
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Xavier Vilajosana
Universitat Oberta de Catalunya
156 Rambla Poblenou
Barcelona, Catalonia 08018
Spain
Phone: +34 (646) 633 681
Email: xvilajosana@uoc.edu
Thomas Watteyne
Linear Technology
30695 Huntwood Avenue
Hayward, CA 94544
USA
Phone: +1 (510) 400-2978
Email: twatteyne@linear.com
Raghuram S Sudhaakar
Cisco Systems, Inc
Building 24
510 McCarthy Blvd
San Jose 95135
USA
Phone: +1 408 853 0844
Email: rsudhaak@cisco.com
Pouria Zand
University of Twente
Department of Computer Science
Zilverling Building
Enschede 7522 NB
The Netherlands
Phone: +31 619040718
Email: p.zand@utwente.nl
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