Internet Engineering Task Force A. Pelov, Ed. Internet-Draft Acklio Intended status: Informational L. Toutain, Ed. Expires: January 5, 2016 Telecom Bretagne Y. Delibie, Ed. Kerlink July 4, 2015 Constrained Signaling Over LR-WAN draft-pelov-core-cosol-00 Abstract This document presents a new type of far-reaching, low-rate radio technologies and an extensible mechanism to operate these networks based on CoAP. The emerging Wide Area Networks based on them - Low- Rate WAN (LR-WAN) preset a particular set of constraints, which places them at the intersection of infrastructure networks, ultra- dense networks, delay-tolerant networks and low-power and lossy networks. The main objectives of LR-WAN signaling is to minimize the number of exchanged messages, minimize the size of each message in a secure and extensible manner. This document describes the use of the Constrained Application Protocol (CoAP) as the main signaling protocol for LR-WANs, over which minimal messages are exchanged allowing the full operation of the network, such as authentication, authorization, and management. The use of CoAP signaling provides a generic mechanism that can be applied to different LR-WAN technologies. 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/. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." This Internet-Draft will expire on January 5, 2016. Pelov, et al. Expires January 5, 2016 [Page 1] Internet-Draft Constrained Signaling Over LR-WAN July 2015 Copyright Notice Copyright (c) 2015 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 (http://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 . . . . . . . . . . . . . . . . . . . . . . . . 2 1.1. Requirements Language . . . . . . . . . . . . . . . . . . 5 2. LR-WAN Technologies . . . . . . . . . . . . . . . . . . . . . 5 2.1. FARE technologies . . . . . . . . . . . . . . . . . . . . 5 2.2. Physical Layer Characteristics . . . . . . . . . . . . . 5 2.2.1. Ultra Narrowband FARE radios . . . . . . . . . . . . 6 2.2.2. Spread-spectrum FARE radios . . . . . . . . . . . . . 6 2.3. MAC Layer Characteristics . . . . . . . . . . . . . . . . 6 3. CoSOL Architecture . . . . . . . . . . . . . . . . . . . . . 7 3.1. General LR-WAN architecture . . . . . . . . . . . . . . . 7 3.2. Node-F lifecycle . . . . . . . . . . . . . . . . . . . . 8 3.3. CoAP as Signaling Protocol for LR-WANs . . . . . . . . . 10 3.3.1. Semi-Association . . . . . . . . . . . . . . . . . . 10 3.3.2. Network Discovery . . . . . . . . . . . . . . . . . . 11 3.3.3. Association . . . . . . . . . . . . . . . . . . . . . 12 3.3.4. Authentication . . . . . . . . . . . . . . . . . . . 13 3.3.5. Dissociation . . . . . . . . . . . . . . . . . . . . 14 3.4. Shared resource tree . . . . . . . . . . . . . . . . . . 15 4. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 17 5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 17 6. Security Considerations . . . . . . . . . . . . . . . . . . . 17 7. References . . . . . . . . . . . . . . . . . . . . . . . . . 17 7.1. Normative References . . . . . . . . . . . . . . . . . . 17 7.2. Informative References . . . . . . . . . . . . . . . . . 17 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 18 1. Introduction The goal of this document is to provide the necessary mechanisms to operate a Low-Rate Wide-Area Network (LR-WAN) by using IETF CoAP [RFC7252] as a core signaling protocol. Pelov, et al. Expires January 5, 2016 [Page 2] Internet-Draft Constrained Signaling Over LR-WAN July 2015 Far-Reaching, low-rate communication technologies (FARE) have emerged in the past several years, and are the base for building Low-Rate Wide-Area Networks (LR-WAN). LR-WANs have the following characteristics: o Work in narrow, license-free (ISM) bands with good propagation properties (< 1GHz) o Low- to very-low throughput (1-200 kbps) o Low-power operation (25 mW in Europe) o Far-Reaching communication capabilities (up to 30 km with line-of- sight, several km in urban environment) o Strong channel access restrictions (1% to 10% duty cycling) o Infrastructure-based o Star topology LR-WANs are built on Far-Reaching Radio communication technologies (FARE), which use advanced signal processing techniques and combination of appropriate modulation and coding approaches to provide the aforementioned radio characteristics. The absence of license fees and the Far-Reaching connectivity allow for an extremely competitive pricing of LR-WANs compared to other networking technologies, e.g. cellular or mesh. LR-WANs are sometimes referred to as LPWAN (Low-Power WAN), e.g. by Semtech [LoRa]. Even though LR-WANs are extremely limited in terms of network performance, they are enough for a wide class of applications, among which [LTN001]: o Metering (water, gas, electricity) o Infrastructure networks (water, gas, electricity, roads, pipelines, drains) o Environment/Smart City (waste management, air pollution monitoring and alerting, acoustic noise monitoring, public lighting management, parking management, self service bike rental, digital board monitoring, water pipe leakage monitoring) o Environment/Country side (soil quality, livestock surveillance, cattle and pet monitoring, climate, irrigation) o Remote monitoring (house, building) Pelov, et al. Expires January 5, 2016 [Page 3] Internet-Draft Constrained Signaling Over LR-WAN July 2015 o Industrial (water tank, asset tracking) o Automotive (vehicle tracking, impact detection, pay as you drive, assistance request, ...) o Logistics (goods tracking, conservation monitoring) o Healthcare (patient monitoring, home medical equipment usage) o House appliances (pet tracking, white goods, personal asset) o Truck (tyre monitoring) o Identification (authentication) The IEEE is studying LR-WANs, but limited to the case of low-energy critical infrastructure monitoring (LECIM), under the group IEEE 802.15.4k [IEEE.802-15.4k]. The combination of the above characteristics and the envisioned applications define a new class of networks with the following unique constraints: o Potentially extremely high density (expected of up to 10k-100k+ end-devices managed by a single radio antena) o Coexistence of delay-tolerant and critical applications (metering and alarms) o Low-power, low-throughput, lossy connectivity (use of ISM bands) o Limited payload (100 bytes max, typically less than 50 bytes, 12 bytes for UNB) CoAP is a client-server protocol specialized for constrained networks and devices. CoAP is highly optimized, extensible, standard protocol, which in conjunction with the Concise Binary Object Representation (CBOR) is the ideal candidate for the signaling protocol of the control plane of an LR-WAN. It can be used during all stages of the lifecycle of the network, e.g. discovery, authentication, operation. Furthermore, this can be achieved by following RESTful management paradigm, by using a particular resource tree definition or adopting CoMI [I-D.vanderstok-core-comi]. Pelov, et al. Expires January 5, 2016 [Page 4] Internet-Draft Constrained Signaling Over LR-WAN July 2015 1.1. Requirements Language The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in RFC 2119 [RFC2119]. 2. LR-WAN Technologies 2.1. FARE technologies There are two classes of Far-Reaching radio Technologies, using different radio modulation approaches: o Ultra Narrow Band (UNB) o Spread-spectrum (SS) An example of UNB is the technology developed and promoted by SigFox [SigFox]. Semtech LoRa [LoRa] uses a direct-sequence spread-spectrum with orthogonal codes (OSSS). Both approaches have their advantages and will coexist in the future, as there are currently several operators, which deploy the two types in the same areas. 2.2. Physical Layer Characteristics At the physical layer, the important part is the possibility to reconstruct the signal at long distances. The used ISM bands are defined around the world (e.g. 868 MHz in Europe and 900 MHz in USA) and require a 1% (or 10%) duty cycling, or alternatively - advanced detection and channel reallocation techniques. In reality, all deployed networks use the duty cycling limitation, with the following distinction. There is one 100kHz band in which 10% duty cycling is allowed, with a slightly more emission power. The rest of the bands are limited at 1% duty cycling and very restricted power of emission (e.g. 25 mW in Europe). UNB LR-WANs make the distinction between Uplink and Downlink, first depending on the modulation, and second with the 10% duty-cycling channel been used for the Downlink. OSSS LR-WANs make no such distinction, although for the operation of a network, an operator can chose to use the same Uplink/Downlink channel separation. Note that the 1% or 10% duty-cycle limitation counts for all trafic originating from an electronic equipment, e.g. an antena managing 100k objects must obey the same limitation as an end-device, with all Pelov, et al. Expires January 5, 2016 [Page 5] Internet-Draft Constrained Signaling Over LR-WAN July 2015 frames emitted from the antena (data, acknowledgements) counting towards its quota. 2.2.1. Ultra Narrowband FARE radios Ultra Narrowband (UNB) technologies generally possess the following physical layer characteristics [LTN003]: o Uplink: * channelization mask 100kHz (600 kHz USA) * baud rate 100 bauds (600 bauds USA) * modulation BPSK o Downlink: * channelization mask: dynamic selection * down link baud rate: 600 baud * modulation scheme: GFSK * downlink transmission power: 500 mW, 10% duty cycle 2.2.2. Spread-spectrum FARE radios OSSS technologies possess the following physical layer characteristics [LTN003]: o channelization mask: from 8 kHz to 500 kHz (depending on spreading factor) o chip rate: 8 kcps up to 500 kcps o data rate: 30-50 000 bps o modulation scheme: equivalent to DSSS with orthogonal signaling No particular distinction is made between the Uplink and the Downlink. 2.3. MAC Layer Characteristics Several proprietary MAC frame formats exist for UNB and OSSS. However, they are designed to operate the network in a centralized, highly-vertically-integrated fashion. The only standard MAC frame Pelov, et al. Expires January 5, 2016 [Page 6] Internet-Draft Constrained Signaling Over LR-WAN July 2015 format is the IEEE 802.15.4k, which is based on the well-known IEEE 802.15.4 with the addition of a fragmentation sub-layer. The channel access method is based on ALOHA, although it is up to the network operator to chose if an appropriate Node-F polling should be implemented. 3. CoSOL Architecture 3.1. General LR-WAN architecture We can identify three types of entities in a typical LR-WAN. These are: o Node-F: far-reachable node, e.g. the end-point, object, device o Node-R: radio relay, bridging the Far-Reaching radio technology to a different medium (often a LAN or cellular WAN) o Node-G: gateway node, interconnection between the radio-relay node and the Internet +--------+ +--------+ +--------+ | Node-F | <-- FARE --> | Node-R | <-- IP --> | Node-G | +--------+ +--------+ +--------+ General architecture of an LR-WAN. FARE radio technology is used only between the Node-F and the Node-R. Figure 1 Of these, only Node-F and Node-R communicate through a FARE technology. However, due to the extreme constraints of these technologies, they are always behind a gateway (Node-G). Note, that the Node-R and Node-G can be collocated, e.g. on a single hardware equipment. The Node-G is connected to the Internet and is assumed to have sufficient computational resources to store a context for each of the Node-Fs. The strong limitation here is the radio link. In an actual deployment, a (limited) set of Node-Rs cover a large area with a potentially very-high number of Node-Fs. A single Node-G is capable of controlling all Node-Rs. Pelov, et al. Expires January 5, 2016 [Page 7] Internet-Draft Constrained Signaling Over LR-WAN July 2015 o o o o (((*)))-------\ o o | o o | o (((*)))---------------+------Node-G o o | o o | o (((*)))-------------------+ o | o o o o | o (((*)))-----------/ o o o o o = Node-F (((*))) = Node-R An example coverage of an area with several Node-Rs. Note that a single Node-F may be covered by several Node-Rs. Figure 2 3.2. Node-F lifecycle Similar to other wireless infrastructure-based technologies, a Node-F can go through several stages: o Semi-Association o Network Discovery o Authentication o Association o Dissociation The Node-F state machine is then the following: Pelov, et al. Expires January 5, 2016 [Page 8] Internet-Draft Constrained Signaling Over LR-WAN July 2015 +-----------------------------------------------------+ | | V | Semi-associated ----------+ | | ^ | | | | | | V | V | Disconnected -> Network discovery -> Associated -> Authenticated ^ | | | +-----------------------------------------------------+ Node-F connectivity state machine. Figure 3 The Node-F can be in Semi-Associated mode. Upon start, and depending on the application, a Node-F can use a state of uni-directional communication, where it is considered semi-associated to the network. In that state, the Node-F broadcasts frames, handled by the Node-G, but the network cannot join the Node-F on a regular basis. This is a degraded LR-WAN operating mode and if caution is not used, can lead to significant scalability and evolvability issues. The Network Discovery can be reactive or proactive. The former is based on detecting beacon frames sent periodically by the network (e.g. Node-G). The latter is implemented by the Node-F broadcasting probe request frames, to which all appropriate Node-Gs must respond. Once a network has been discovered, the Node-F and the Node-G can perform mutual authentication. Upon authentication, the Node-G configures the necessary network parameters of the Node-F, which is henceforth associated to the network. The association request may be explicit or implicit, in which case after successful authentication the Node-F enters automatically the associated state. In this stage there is bi- directional communication between the Node-F and the Node-G. Finally, the Node-F may decide to dissociate from the network by sending an explicit request. Upon dissociation the Node-G may release all contexts related to the Node-F and re-association requires going through the authentication stage again. Node mobility is achieved by explicitly dissociating from the old Node-G and then authenticating to the new Node-G. Implicit dissociation is also possible upon the expiration of predefined timers, or in case of mobility optimization. Pelov, et al. Expires January 5, 2016 [Page 9] Internet-Draft Constrained Signaling Over LR-WAN July 2015 3.3. CoAP as Signaling Protocol for LR-WANs Use as CoAP for signaling is implemented as follows. The MAC, network and/or transport layers MUST provide a mechanism to differentiate user data from signaling data frames (e.g. by using separate MAC addresses, IP addresses and/or UDP-ports). Both the Node-G and the Node-F are running CoAP servers for implementing the control plane. Frames exchanged over the FARE radio interface and marked as "signaling data" are handled by the corresponding control plane CoAP servers. CoAP requests are thus used to keep a shared vision of the network and the node between the two. This is realized by a virtual, shared resource-tree as described in Section 3.4. The Node-G runs a (virtual) CoAP server for each Node-F. This server is identified with a DNS name, e.g. "node123.home.node- g.example.com", which can be used explicitly in the CoAP messages via the Proxy-Uri option if needed. Note, that the Node-R acts only as a transceiver and as such is transparent from protocol point of view. As such, the following management scheme applies: +--------+ +--------+ | Node-F | <-- LR-WAN constraints --> | Node-G | +--------+ +--------+ Node-F connectivity state machine. Figure 4 3.3.1. Semi-Association When in a semi-associated state, a Node-F broadcasts its messages without performing network discovery, or association. If the Node-F is under the coverage of a Node-G, the Node-G will receive the broadcast, and forward the user data. The frames SHOULD be signed, so that they could be authenticated by the network. Layer 2 acknowledgements MUST be used, and in some cases piggybacking on them can provoke the Node-F to associate to the network. The broadcast messages MUST include the necessary information to join the user data destination, and enough information for the Node-G to authenticate the message sender. This can be achieved through a Confirmable CoAP message, where the user data are POSTed to a well- known resource defined on the Node-G. DTLS with integrity check can be used, with long-lived keys negotiated by the Node-F and the network. Pelov, et al. Expires January 5, 2016 [Page 10] Internet-Draft Constrained Signaling Over LR-WAN July 2015 Even though an application can be implemented by using only simplex association capabilities, there are huge negative consequences related to scalability and evolvability in this case. For example, a Node-F which periodically broadcasts information will occupy the spectrum, even if there is no operator willing to accept its trafic. In addition, no channel access management can be applied. Node-F Node-G | | | | +--------->| Header: POST | POST | Uri-Host: "destination.example.com" | | Uri-Path: "temp" | | | | |<---------+ Header: 2.01 Created | 2.01 | | | | | Sending a message in a semi-associated state. Figure 5 3.3.2. Network Discovery A network can be discovered by a Node-F reactively or proactively. Reactive network discovery is based on the detection of periodic beacons emitted by the Node-G. The beacons are implemented with CoAP messages with the No-Response option [I-D.tcs-coap-no-response-option]. The Node-G POSTs its information to a well-known resource, e.g. "/network/node-G/" or a resource alias "/g" or CoMI YANG hash ID "/mg/GgQ". Node-F Node-G | | | | |<---------+ Header: POST | POST /g | Uri-Path: "g" | | [No-Responce] | | | | Reactive network discovery. The Node-G sends periodically beacon messages, containing information pertinent to this network. Figure 6 Pelov, et al. Expires January 5, 2016 [Page 11] Internet-Draft Constrained Signaling Over LR-WAN July 2015 The CoAP POST request is processed at the Node-F. A resource is created locally, with the representation, which provides the appropriate network parameters, e.g. network ID, Node-G ID, and other radio-related parameters, such as channel, beacon frequency and so forth. This information allows the Node-F to begin the authentication phase. A Node-F may chose to proactively probe for the existence of network coverage. In that case, it sends a Confirmable CoAP GET request to obtain the information from a well-known resource, normally published by the beacon messages, e.g. "/network/node-G/" or a resource alias "/g" or CoMI YANG hash ID "/mg/GgQ". Node-F Node-G | | | | +--------->| Header: GET | GET /g | Uri-Path: "g" | | Accept: application/cbor | | | | |<---------+ Header: 2.05 Content | 2.05 | Payload: ... | | Proactive network discovery. The Node-F request the information of all surrounding Node-Gs. Figure 7 Once the network is discovered, the Node-F has all necessary information to start the authentication phase. 3.3.3. Association Before being able to communicate, the Node-F must associate to the network, and then eventually authenticate. The association phase signals to the Node-G that there is a new device willing to communicate with the network. This association SHOULD provide enough information to allow the Node-G to start the authentication process. For example, it may provide the AAA server, which could authenticate the Node-F, or its EAP-Identity. Note, that the Node-F may elect to mark the association message with the No-response option [I-D.tcs-coap-no-response-option], waiting for the subsequent authentication request from the Node-G. Pelov, et al. Expires January 5, 2016 [Page 12] Internet-Draft Constrained Signaling Over LR-WAN July 2015 Node-F Node-G | | | | +--------->| Header: POST | POST /n | Uri-Path: "n" | | Payload: ... | | |<---------+ Header: 2.01 Created | 2.01 | Location-Path: "/n/n705" | | Node-F associates to a network, by creating a corresponding resource element on the Node-G. Figure 8 3.3.4. Authentication The EAP-over-CoAP [I-D.garcia-core-security] specifies an approach to encapsulating EAP messages over CoAP. This allows to authenticate a Node-F, which wishes to join an LR-WAN, and negotiate the L2 encryption keys, and DTLS keying material. As the Node-F has already associated to the Node-G, it is the Node-G that initiates the authentification request, by going directly to Step 1) of the EAP-over-CoAP specification. Pelov, et al. Expires January 5, 2016 [Page 13] Internet-Draft Constrained Signaling Over LR-WAN July 2015 Node-F Node-G | | | | 1) |<-----------+ Header: POST | POST /auth | Uri-Path: "auth" | | [No-Responce] | | | | 2) +----------->| Header: 2.01 Created | ACK /auth | Location-Path: "/auth/5" | | | | | | 3) |<-----------+ Header: PUT | PUT /auth/5| Uri-Path: "auth/5" | | Payload: EAP-PSK MSG 1 | | | | 4) +----------->| Header: 2.04 Changed | ACK /auth/5| Payload: EAP-PSK MSG 2 | | ...... Node-F and Node-G perform mutual authentication following EAP-over- CoAP. Figure 9 Upon the end of the authentication phase, a Master Shared Key (MSK) is known by the Node-F and the Node-G, and is used to generate DTLS encryption or integrity keys. Further communications should be encrypted/signed with the freshly derived keys. 3.3.5. Dissociation If the Node-F wishes to deregister from the network, it could do so by deleting the context created upon association: Pelov, et al. Expires January 5, 2016 [Page 14] Internet-Draft Constrained Signaling Over LR-WAN July 2015 Node-F Node-G | | | | +--------------->| Header: POST | DELETE /n/n705 | Uri-Path: "n/n705" | | | | |<---------------+ Header: 2.02 Deleted | 2.02 | | | Node-F dissociates from the network by deleting its associated resources. Figure 10 3.4. Shared resource tree The Node-F and Node-G have to use any opportunity to save trafic. This can be handled by having a shared context on both devices, which is updated in an asynchronous fashion. In a RESTful approach, the shared context is a resource tree, synchronized with CoAP messages. Note, that this only concerns the control plane, responsible for managing the devices. The data plane is independent and can use any communication pattern, which fits the radio limitations. The shared resource tree can be structured freely, but will generally include the radio parameters of the Node-F and Node-G, their identities, authentication results, encryption/integrity preferences and parameters, compression methods, etc. It will can also include trafic shaping settings, restrictions, counters, and so forth. The resource tree can follow a structure defined with YANG. For example, for a typical OSSS installation, the following parameters should be specified: o Node-R beacon channels o Node-F response channel o Node-F response spreading factor o Node-F response coding rate o Node-F fall-back (default) channel o Node-F fall-back (default) spreading factor Pelov, et al. Expires January 5, 2016 [Page 15] Internet-Draft Constrained Signaling Over LR-WAN July 2015 o Node-F fall-back (default) coding rate o ... Upon authentication, the two nodes establish an authenticated connection. Each of the resources can then be accessed in read-only, read-write, or write-only mode. Access is performed with CoAPs GET, PUT, POST and DELETE methods. The most frequently accessed resource tree elements should have short aliases, in order to have short URIs. If the management server is independent from the application servers, using a single- or double- character abbreviation under the root tree is recommended. Alternatively, the use of CoMI [I-D.vanderstok-core-comi] is recommended if YANG representation is available. For example: /radio/interace/lora/lora1/spreading_factor -> /sf /radio/interace/lora/lora1/coding_rate -> /cr +--------+ +--------+ | Node-F | <------------------------> | Node-G | +--------+ +--------+ | shared | | shared | | context| | context| | | | | | /sf | | /sf | | /cr | | /cr | | /auth | | /auth | | /mac16 | | /mac16 | | /mac64 | | /mac64 | | | | | | /mg | | /mg | | ... | | ... | +--------+ +--------+ Node-F and Node-G have a shared context. Upon modification (e.g. the operator changes the spreading factor /sf of the Node-F at the Node- G), the Node-G will update the value on the Node-F with a CoaP PUT or a CoAP GET OBSERVE [I-D.ietf-core-observe] message. Figure 11 Pelov, et al. Expires January 5, 2016 [Page 16] Internet-Draft Constrained Signaling Over LR-WAN July 2015 4. Acknowledgements 5. IANA Considerations This memo includes no request to IANA. 6. Security Considerations All drafts are required to have a security considerations section. See RFC 3552 [RFC3552] for a guide. 7. References 7.1. Normative References [I-D.garcia-core-security] Garcia-Morchon, O., Kumar, S., Keoh, S., Hummen, R., and R. Struik, "Security Considerations in the IP-based Internet of Things", draft-garcia-core-security-06 (work in progress), September 2013. [I-D.ietf-core-observe] Hartke, K., "Observing Resources in CoAP", draft-ietf- core-observe-16 (work in progress), December 2014. [I-D.tcs-coap-no-response-option] Bhattacharyya, A., Bandyopadhyay, S., and A. Pal, "CoAP option for no server-response", draft-tcs-coap-no- response-option-11 (work in progress), June 2015. [I-D.vanderstok-core-comi] Stok, P., Greevenbosch, B., Bierman, A., Schoenwaelder, J., and A. Sehgal, "CoAP Management Interface", draft- vanderstok-core-comi-06 (work in progress), February 2015. [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. [RFC7252] Shelby, Z., Hartke, K., and C. Bormann, "The Constrained Application Protocol (CoAP)", RFC 7252, June 2014. 7.2. Informative References Pelov, et al. Expires January 5, 2016 [Page 17] Internet-Draft Constrained Signaling Over LR-WAN July 2015 [IEEE.802-15.4k] Institute of Electrical and Electronics Engineers, "Low- Rate Wireless Personal Area Networks (LR-WPANs) - Amendment 5: Physical Layer Specifications for Low Energy, Critical Infrastructure Monitoring Networks., IEEE 802.15.4k", IEEE Standard 802.15.4, 2013. [LoRa] Semtech, "https://web.archive.org/web/20150510011904/ https://www.semtech.com/wireless-rf/lora.html", May 2015. [LTN001] European Telecommunications Standards Institute, "Low Throughput Networks (LTN); Use Cases for Low Throughput Networks, ETSI GS LTN 001", IEEE ETSI GS LTN 001, 2014. [LTN003] European Telecommunications Standards Institute, "Low Throughput Networks (LTN); Protocols and Interfaces, ETSI GS LTN 003", IEEE ETSI GS LTN 003, 2014. [RFC3552] Rescorla, E. and B. Korver, "Guidelines for Writing RFC Text on Security Considerations", BCP 72, RFC 3552, July 2003. [SigFox] SigFox, "https://web.archive.org/web/20150628225901/ http://www.sigfox.com/en/#!/technology", June 2015. Authors' Addresses Alexander Pelov (editor) Acklio 2 Rue de la Chataigneraie Cesson-Sevigne, Bretagne 35510 FR Phone: +33299127004 Email: a@ackl.io Laurent Toutain (editor) Telecom Bretagne 2 Rue de la Chataigneraie Cesson-Sevigne, Bretagne 35510 FR Phone: +33299127026 Email: laurent.toutain@telecom-bretagne.eu Pelov, et al. Expires January 5, 2016 [Page 18] Internet-Draft Constrained Signaling Over LR-WAN July 2015 Yannick Delibie (editor) Kerlink 1 rue Jacqueline Auriol Thorigne-Fouillard, Bretagne 35235 FR Phone: +33299122900 Email: yannick.delibie@kerlink.fr Pelov, et al. Expires January 5, 2016 [Page 19]