6TiSCH Q. Wang, Ed. Internet-Draft Univ. of Sci. and Tech. Beijing Intended status: Informational X. Vilajosana Expires: January 5, 2015 Universitat Oberta de Catalunya T. Watteyne Linear Technology R. Sudhaakar Cisco Systems P. Zand University of Twente July 4, 2014 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 This Internet-Draft is submitted in full conformance with the provisions of BCP 78 and BCP 79. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF). Note that other groups may also distribute working documents as Internet-Drafts. The list of current Internet- Drafts is at http://datatracker.ietf.org/drafts/current/. 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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 . . . . . . . . . . . . . . . . . . . . . . . . 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. Wang, et al. Expires January 5, 2015 [Page 2] Internet-Draft 6tisch-6top-coapie July 2014 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 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. Wang, et al. Expires January 5, 2015 [Page 3] Internet-Draft 6tisch-6top-coapie July 2014 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 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. 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. Wang, et al. Expires January 5, 2015 [Page 4] Internet-Draft 6tisch-6top-coapie July 2014 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. Wang, et al. Expires January 5, 2015 [Page 5] Internet-Draft 6tisch-6top-coapie July 2014 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; } } } } Wang, et al. Expires January 5, 2015 [Page 6] Internet-Draft 6tisch-6top-coapie July 2014 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. Wang, et al. Expires January 5, 2015 [Page 7] Internet-Draft 6tisch-6top-coapie July 2014 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". Wang, et al. Expires January 5, 2015 [Page 8] Internet-Draft 6tisch-6top-coapie July 2014 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 | | 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. Wang, et al. Expires January 5, 2015 [Page 9] Internet-Draft 6tisch-6top-coapie July 2014 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. Wang, et al. Expires January 5, 2015 [Page 10] Internet-Draft 6tisch-6top-coapie July 2014 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, "Blockwise transfers in CoAP", draft-ietf-core-block-14 (work in progress), October 2013. [I-D.ietf-6tisch-tsch] Watteyne, T., Palattella, M., and L. Grieco, "Using IEEE802.15.4e TSCH in an LLN context: Overview, Problem Statement and Goals", draft-ietf-6tisch-tsch-00 (work in progress), November 2013. [I-D.ietf-6tisch-architecture] Thubert, P., Watteyne, T., and R. Assimiti, "An Architecture for IPv6 over the TSCH mode of IEEE 802.15.4e", draft-ietf-6tisch-architecture-02 (work in progress), June 2014. [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-01 (work in progress), February 2014. [I-D.ietf-6tisch-minimal] Vilajosana, X. and K. Pister, "Minimal 6TiSCH Configuration", draft-ietf-6tisch-minimal-01 (work in progress), June 2014. [I-D.ietf-6tisch-6top-interface] Wang, Q., Vilajosana, X., and T. Watteyne, "6TiSCH Operation Sublayer (6top) Interface", draft-ietf-6tisch- 6top-interface-00 (work in progress), March 2014. [I-D.ietf-6tisch-coap] Sudhaakar, R. and P. Zand, "6TiSCH Resource Management and Interaction using CoAP", draft-ietf-6tisch-coap-00 (work in progress), May 2014. Wang, et al. Expires January 5, 2015 [Page 11] Internet-Draft 6tisch-6top-coapie July 2014 [I-D.wang-6tisch-6top-sublayer] Wang, Q., Vilajosana, X., and T. Watteyne, "6TiSCH Operation Sublayer (6top)", draft-wang-6tisch-6top- sublayer-00 (work in progress), February 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 Wang, et al. Expires January 5, 2015 [Page 12] Internet-Draft 6tisch-6top-coapie July 2014 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 Wang, et al. Expires January 5, 2015 [Page 13]