Transporting CoAP Messages over IEEE802.15.4e Information Elements
draft-wang-6tisch-6top-coapie-00

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 header. This enables 6top-to-6top communication between neighbor nodes in a 6TiSCH network.

Status of This Memo

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This Internet-Draft will expire on January 5, 2015.

Copyright Notice

Copyright (c) 2014 IETF Trust and the persons identified as the document authors. All rights reserved.

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Table of Contents

• 1. Introduction
• 1.1. Requirements Notation
• 1.2. Context within 6TiSCH
• 1.3. Motivation
• 1.4. Status of this Document
• 2. CoAP IE Format
• 3. Softcell Negotiation Interface RPC Definition
• 4. CoAP support
• 4.1. URI setting
• 4.2. CoAP Block option
• 4.3. Management Interface Protocol
• 4.4. Negotiation interface protocol
• 4.5. Acknowledgement
• 4.6. Observe
• 5. Implementation Considerations
• 6. References
• 6.1. Normative References
• 6.2. Informative References
• 6.3. External Informative References
• Authors' Addresses

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:

• [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.
• [I-D.ietf-6tisch-6top-interface] defines the interface of the 6top sublayer using the YANG data modeling language [RFC6020].
• [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.
• This document defines a method for transporting those CoAP messages as part of the IEEE802.15.4e header. 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 header, 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.

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:

• Section 3 would go into [I-D.ietf-6tisch-6top-interface];
• Section 4 would go into [I-D.ietf-6tisch-coap];
• 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 header, 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.

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+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|   Length      |    SubID    |T|                               |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+                               |
//                                                              //
|                   Fragmented CoAP message                     |
|                                                               |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

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+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|      CoAP IE header           |Ver| T |  TKL  |   Code        |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|  Message ID                   |    Token (0-8B, assume 2B)    |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|  Uri-path option                                              |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|  11111111     |                                               |
+-+-+-+-+-+-+-+-+                                               |
//                                                              //
|                 CoAP message payload (variable)               |
|                                                               |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

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;
         }
      }
   }
}

 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)                      |
|                                                               |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

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=CON, Code=2.04)
  |       |            Payload: CBOR(
  |       |                        NumOfCells,
  |       |                        ResultedCells
  |       |                     )
  |       |
  +-------> IEEE802.15.4e type: ACK
  |       |

+-----------------------------------+
| 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                 |
+------------------------------------------+