CoRE Z. Shelby Internet-Draft Sensinode Intended status: Informational B. Frank Expires: September 2, 2010 Tridium, Inc March 1, 2010 Constrained Application Protocol (CoAP) draft-shelby-core-coap-00 Abstract This document specifies the Constrained Application Protocol (CoAP), a RESTful protocol for use with constrained networks and nodes. CoAP easily translates to HTTP for integration with the web while meeting specialized requirements such as multicast support, very low overhead and simplicity for constrained environments. Status of this Memo This Internet-Draft is submitted to IETF in full conformance with the provisions of BCP 78 and BCP 79. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF), its areas, and its working groups. Note that other groups may also distribute working documents as Internet- Drafts. 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." The list of current Internet-Drafts can be accessed at http://www.ietf.org/ietf/1id-abstracts.txt. The list of Internet-Draft Shadow Directories can be accessed at http://www.ietf.org/shadow.html. This Internet-Draft will expire on September 2, 2010. Copyright Notice Copyright (c) 2010 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 Shelby & Frank Expires September 2, 2010 [Page 1] Internet-Draft Constrained Application Protocol (CoAP) March 2010 (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 BSD License. This document may contain material from IETF Documents or IETF Contributions published or made publicly available before November 10, 2008. The person(s) controlling the copyright in some of this material may not have granted the IETF Trust the right to allow modifications of such material outside the IETF Standards Process. Without obtaining an adequate license from the person(s) controlling the copyright in such materials, this document may not be modified outside the IETF Standards Process, and derivative works of it may not be created outside the IETF Standards Process, except to format it for publication as an RFC or to translate it into languages other than English. Shelby & Frank Expires September 2, 2010 [Page 2] Internet-Draft Constrained Application Protocol (CoAP) March 2010 Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 2. Message Formats . . . . . . . . . . . . . . . . . . . . . . . 3 2.1. Request header . . . . . . . . . . . . . . . . . . . . . . 4 2.2. Response header . . . . . . . . . . . . . . . . . . . . . 5 2.3. Header options . . . . . . . . . . . . . . . . . . . . . . 7 3. Constrained Application Protocol . . . . . . . . . . . . . . . 8 3.1. Methods . . . . . . . . . . . . . . . . . . . . . . . . . 8 3.1.1. CREATE . . . . . . . . . . . . . . . . . . . . . . . . 8 3.1.2. READ . . . . . . . . . . . . . . . . . . . . . . . . . 8 3.1.3. UPDATE . . . . . . . . . . . . . . . . . . . . . . . . 9 3.1.4. DELETE . . . . . . . . . . . . . . . . . . . . . . . . 9 3.1.5. NOTIFY . . . . . . . . . . . . . . . . . . . . . . . . 9 3.2. Response codes . . . . . . . . . . . . . . . . . . . . . . 9 3.3. URIs . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 3.4. Content-type encoding . . . . . . . . . . . . . . . . . . 10 3.5. Message processing . . . . . . . . . . . . . . . . . . . . 11 3.5.1. Request processing . . . . . . . . . . . . . . . . . . 11 3.5.2. Response processing . . . . . . . . . . . . . . . . . 11 3.5.3. Option processing . . . . . . . . . . . . . . . . . . 11 4. Transport Binding . . . . . . . . . . . . . . . . . . . . . . 11 4.1. UDP . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 4.2. TCP . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 4.3. Default Port . . . . . . . . . . . . . . . . . . . . . . . 12 5. Caching . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 5.1. Cache control . . . . . . . . . . . . . . . . . . . . . . 13 5.2. Intercept proxy caching . . . . . . . . . . . . . . . . . 13 5.3. Cache refreshing . . . . . . . . . . . . . . . . . . . . . 13 5.4. Sleeping nodes . . . . . . . . . . . . . . . . . . . . . . 13 6. Subscription and Notification . . . . . . . . . . . . . . . . 13 7. Resource Discovery . . . . . . . . . . . . . . . . . . . . . . 13 8. HTTP Mapping . . . . . . . . . . . . . . . . . . . . . . . . . 14 9. Examples . . . . . . . . . . . . . . . . . . . . . . . . . . . 14 10. Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . 14 11. Security Considerations . . . . . . . . . . . . . . . . . . . 14 12. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 14 13. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 14 14. References . . . . . . . . . . . . . . . . . . . . . . . . . . 15 14.1. Normative References . . . . . . . . . . . . . . . . . . . 15 14.2. Informative References . . . . . . . . . . . . . . . . . . 15 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 15 Shelby & Frank Expires September 2, 2010 [Page 3] Internet-Draft Constrained Application Protocol (CoAP) March 2010 1. Introduction The use of web services on the Internet has become ubiquitous in most applications, and depends on the fundamental Representational State Transfer (REST) architecture of the web. The proposed Constrained RESTful Environments (CoRE) working group aims at realizing the REST architecture in a suitable form for the most constrained nodes (e.g. 8-bit microcontrollers with limited RAM and ROM) and networks (e.g. 6LoWPAN). One of the main goals of CoRE is to design a generic RESTful protocol for the special requirements of this constrained environment, especially considering energy and building automation applications. This document specifies the RESTful Constrained Application Protocol (CoAP) which easily translates to HTTP for integration with the web while meeting specialized requirements such as multicast support, very low overhead and simplicity for constrained environments. CoAP has the following main features: o RESTful protocol design minimizing the complexity of mapping with HTTP. o Low header overhead and parsing complexity. o URI and content-type support. o Support for the discovery of resources provided by known CoAP services. o Simple subscription for a resource, and resulting push notifications. o Simple caching based on max-age. The mapping of CoAP with HTTP is also definied, allowing proxies to be built providing access to CoAP resources via HTTP in a uniform way. 2. Message Formats CoAP makes use of two message types, requests and responses, using a simple binary base header format. The base header may be followed by options in ICMP-style Type-Length-Value format. CoAP is by default bound to UDP and optionally to TCP as described in Section 4. Any bytes after the headers in the packet are considered the message body if any. The length of the message body is implied by the Shelby & Frank Expires September 2, 2010 [Page 4] Internet-Draft Constrained Application Protocol (CoAP) March 2010 datagram length. When bound to UDP the entire message MUST fit within in a single datagram. When used with 6LoWPAN [RFC4944], messages SHOULD fit into a single 802.15.4 frame to minimize fragmentation. 2.1. Request header The CoAP request message is used to initiate a CoAP interaction using the methods listed in Table 1. This message is not restricted to a pull model, but may also be used to push data e.g. using the NOTIFY method. 0 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |Ver|T|O|A| Met |_______________| Transaction ID | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Options (if any) ... +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Payload (if any) ... +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 1: Request header format IP Fields: Source Address: The unicast address of the source. Destination Address: The unicast address of the destination. A multicast address can be used with UDP. Header Fields: Ver: Version. 2-bit unsigned integer. Indicates the version of CoAP. Implementations of this specification MUST set this field to 0. The values 1-3 are reserved for future versions. T: 1-bit Message Type flag. Indicates if this message is a CoAP request (0) or a response (1) header. MUST be set to 0 in a request. O: 1-bit Option flag. Indicates if there are Option Headers following the base header. If set to 1 the byte following the base header is the first Option Type. If set to 0 the message body (if any) immediately follows the base header. Shelby & Frank Expires September 2, 2010 [Page 5] Internet-Draft Constrained Application Protocol (CoAP) March 2010 A: 1-bit Acknowledgement flag. When set to 1, indicates that the destination MUST respond with a response message matching this request (see Section 4.1). When set to 0, the destination MAY send a response if appropriate. Met: Method. 3-bit unsigned integer. Indicates the CoAP Method of the request according to Table 1. Methods are described in detail in Section 3.1 Transaction ID: 16-bit unsigned integer. A unique Transaction ID assigned by the source and used to match responses. The Transaction ID MUST be incremented for each new request (regardless of the end-point) and MUST NOT be incremented when retransmitting a request. _: This field is unused. It MUST be initialized to zero by the sender and MUST be ignored by the receiver. +--------+------+ | Method | Code | +--------+------+ | CREATE | 0x0 | | READ | 0x1 | | UPDATE | 0x2 | | DELETE | 0x3 | | NOTIFY | 0x4 | +--------+------+ Table 1: Method codes 2.2. Response header The CoAP response message is sent in response to a CoAP request when appropriate. Responses include a Transaction ID corresponding to that of the request. A response MUST be sent when the A flag is set in a request, and MAY be sent in the case of a response code or message body. A CoAP response is never used to initiate a message exchange. Shelby & Frank Expires September 2, 2010 [Page 6] Internet-Draft Constrained Application Protocol (CoAP) March 2010 0 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |Ver|T|O|_______| Code | Transaction ID | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Options (if any) ... +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Payload (if any) ... +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 2: Response header format IP Fields: Source Address: The unicast address of the responding interface. Destination Address: The source address of the corresponding Request. Header Fields: Ver: Version. 2-bit unsigned integer. Indicates the version of CoAP. Implementations of this specification MUST set this field to 0. The values 1-3 are reserved for future versions. T: 1-bit Message Type flag. Indicates if this message is a CoAP Request (0) or a Response (1) header. MUST be set to 1 in a response. O: 1-bit Option flag. Indicates if there are Option Headers following the base header. If set to 1 the byte following the base header is the first Option Type. If set to 0 the message body (if any) immediately follows the base header. _: This field is unused. It MUST be initialized to zero by the sender and MUST be ignored by the receiver. Transaction ID: 16-bit unsigned integer. A unique Transaction ID assigned by the source and used to match Responses. The Transaction ID MUST be incremented for each new Request and MUST NOT be incremented when retransmitting a Request. Code: 8-bit unsigned integer. CoAP response code as defined in Section 3.2. Shelby & Frank Expires September 2, 2010 [Page 7] Internet-Draft Constrained Application Protocol (CoAP) March 2010 2.3. Header options CoAP messages may also include one or more header options in TLV format. A reserved Option Type byte (0x0) is used to indicate the last option. To indicate that there are no options, a 0x0 byte immediately follows the header, which is followed by the message body (if any). Each option has the following format: TODO: Encode Option Type and Option Len into a single byte. 0 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Option Type | Option Len | Option Value ... +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 3: Header option format Opion Type: 8-bit unsigned integer. The type of the option as defined in Table 2. The value 0x0 is reserved to indicate no more options. An Option Type with 0x0 is immediately followed by the message body (if any). Option Len 8-bit unsigned integer. The length of the Option Value field in octets. Option Value The value in the format defined for that option in Table 2 with a length of Option Len octets. The following options are defined in this document. Future options may be defined in other documents. +--------+-----------------+-----------------+----------------------+ | Option | Name | Data type | Description | | Type | | | | +--------+-----------------+-----------------+----------------------+ | 0x0 | No-more-options | None | Indicates no more | | | | | options | | 0x1 | Content-type | 16-bit unsigned | The content-type of | | | | integer (Len = | the message-body | | | | 2) | | | 0x2 | Uri-string | String | The URI of the | | | | | resource | | 0x3 | Uri-code | 8-bit unsigned | The URI of the | | | | integer (Len = | resource | | | | 1) | | Shelby & Frank Expires September 2, 2010 [Page 8] Internet-Draft Constrained Application Protocol (CoAP) March 2010 | 0x4 | Max-age | 16-bit unsigned | The maximum age of | | | | integer (Len = | the resource for use | | | | 2) | in caching | +--------+-----------------+-----------------+----------------------+ Table 2: Option headers 3. Constrained Application Protocol This section defines CoAP and its processing. 3.1. Methods CoAP supports the basic RESTful methods of CREATE, READ, UPDATE, DELETE (CRUD) which are easily mapped to HTTP methods. In addition, a push method called NOTIFY is defined. HTTP naming has been knowingly avoided, as these are overloaded with specific HTTP semantics. In this section each method is defined along with its behaviour. As CoAP methods manipulate resources, they have the same properties of safe (only retrieval) and idempotent (N > 0 identical requests the same as a single request) as HTTP Section 9.1 [RFC2616]. The READ method is safe, therefore it SHOULD NOT take any other action on a resource other than retrieval. The READ, UPDATE, DELETE and NOTIFY methods can be considered idempotent. 3.1.1. CREATE The CREATE method is used to request the server to create a new resource under the requested URI. If a resource has been created on the server, the response should be 201 (Created) incuding the URI of the new resource in the header and any possible status in the message body. If the CREATE does not result in a new resource being created on the server, either a 200 (OK) or 204 (No Content) are used as appropriate response codes. Responses to this method are not cachable. 3.1.2. READ The READ method retrieves the information of the resource identified by the request URI. Upon success a 200 (OK) response SHOULD be sent if the message body includes a status or 204 (No Content) on success if there is no status included. The response to a READ is cachable if it meets the requirements in Shelby & Frank Expires September 2, 2010 [Page 9] Internet-Draft Constrained Application Protocol (CoAP) March 2010 Section 5. 3.1.3. UPDATE The UPDATE method requests that the resource identified by the request URI be updated with the enclosed message body. If a resource exists at that URI the message body SHOULD be considered a modified version of that resource. If no resource exists then the server MAY create a new resource with that URI, responding like the CREATE method (TBD if this behaviour of POST should be supported in CoAP). Responses to this method are not cachable. 3.1.4. DELETE The DELETE method requests that the resource identified by the request URI be deleted. The response 200 (OK) SHOULD be sent on success if the message body includes a status, 202 (Accepted) if the action has not yet been taken, or 204 (No Content) on success if there is no status included. Responses to this method are not cachable. 3.1.5. NOTIFY The NOTIFY method allows for a push interaction and can be initiated by a server or client. NOTIFY requests that the message body it contains (if any) be accepted by the resource identified by the request URI. Typically this resource is a collector for incoming data generated by subscriptions as defined in Section 6 but NOTIFY may be used for other push uses unrelated to subscription. Upon success a 200 (OK) response SHOULD be sent if the message body includes a status or 204 (No Content) on success if there is no status included. A NOTIFY request is cachable if it meets the requirements in Section 5. 3.2. Response codes CoAP makes use of (a subset of) the HTTP status codes defined in [RFC2616] (Exact subset TBD). The HTTP status code is encoded into a single byte where the top 3-bits represent the 100s decimal digit, and the bottom 5-bits represent the last two decimal digits. Example of the encoding: Shelby & Frank Expires September 2, 2010 [Page 10] Internet-Draft Constrained Application Protocol (CoAP) March 2010 1xx -> 0x2X, b001x_xxxx 2xx -> 0x4X, b010x_xxxx 3xx -> 0x6X, b011x_xxxx 4xx -> 0x8X, b100x_xxxx 5xx -> 0xAX, b101x_xxxx 200 -> 0x40 // OK 404 -> 0x84 // Not Found 415 -> 0x4F // Unsupported Media Type 417 -> 0x51 // Expectation Failed Figure 4: Response code examples 3.3. URIs The Universal Resource Locator (URI) [RFC3986] is an important feature of the REST architecture, the relative part of the URI indicates which resource is being manipulated. CoAP supports variable-length string URIs with the Uri-string Option Header. Although URIs can be designed for compactness, this still often results in 10s of bytes of overhead. For this reason an alternative 8-bit integer code can be used identify a string URI using the Uri- code Option Header. URI codes mappings to URI strings are provided in the response to CoAP resource discovery as defined in Section 7. The encoding of the Uri-string Option Header value also needs to be considered, as this is becoming increasingly complex. All URI strings in CoAP MUST be in the US-ASCII encoding defined in [RFC3986], as URI parsing is complex and may result in security problems on constrained devices. TBD if a stricter subset of the URI format should be defined. The CoAP protocol is identified in URIs when needed with "coap://" (TODO: IANA considerations). 3.4. Content-type encoding In order to support hetergenous uses, it is important that CoAP is transparent to the use of different application payloads. In order for the application process receiving a packet to properly parse a payload, its content-type and encoding should be explicitly known from the header (as e.g. with HTTP). The use of typical binary encodings for XML is discussed in [I-D.shelby-6lowapp-encoding], which includes recommendations for header indication. The draft recommends the indication of at least 10 Internet media types (MIME) [RFC2046] and 2 content transfer encodings. It is obvious that string names of Internet media types [RFC2046] are Shelby & Frank Expires September 2, 2010 [Page 11] Internet-Draft Constrained Application Protocol (CoAP) March 2010 not appropriate for use in the CoAP header. CoAP simply assign identifiers to a subset of common MIME and content transfer encoding types, which IANA should maintain (TODO: Discuss in IANA considerations section). A field of 16-bits is sufficient for encoding both media and content transfer encoding types. These 16- bit identifiers are included in the Content-type Option Header of messages to indicate the type and encoding of the message body. TBD: For extending some types, magic numbers could also be used in the beginning of the payload (as defined in associated Internet media type RFCs). This is indicated by a Content-type value indicating "See magic numbers". TODO: Content-type and content-encoding identifiers as an appendix. 3.5. Message processing This section defines the message processing of incoming requests and responses and possible options. 3.5.1. Request processing TODO 3.5.2. Response processing TODO 3.5.3. Option processing TODO 4. Transport Binding The CoAP protocol will operate by default over UDP. There may be optional functions in CoAP (e.g. delivery of larger chunks of data) which if implemented are implemented over TCP. This section defines the binding of CoAP over UDP and TCP. 4.1. UDP The goal of binding CoAP to UDP is to provide the bare minimum features for the protocol to operate over UDP, going nowhere near trying to re-create the full feature set of TCP. CoAP over UDP has the following features: TODO: Full definition of the UDP binding. Shelby & Frank Expires September 2, 2010 [Page 12] Internet-Draft Constrained Application Protocol (CoAP) March 2010 o Stop-and-wait reliability. The CoAP response message is used as an acknowledgement with retransmission support (details TBD). Not all requests require reliability, thus this is optional using the A flag in a request. Performance is not the key here and for more sophisticated reliability and flow control TCP could be used (when TBD). o The Transaction ID in CoAP message headers is used to match responses to open requests and is generated by the client (common counter across all requests). o Multicast support. Providing reliability with a multicast destination address would be very complex. Therefore the goal is to provide a non-reliable multicast service. In many cases there may not be a response to a multicast message. A multicast command might result in an action being taken at a device, but no response being sent. Therefore a multicast request may be answered with a unicast response, however without reliability (retransmission e.g.). 4.2. TCP The CoAP protocol also may also make use of TCP for some features. As TCP provides a reliable stream this binding does not require anything special from the CoAP protcol design. The same basic messages could be applied over TCP without stop-and-wait. A transaction ID should still be used over TCP. The question is for which features, or in which configurations would TCP be recommended? The following have been identified so far: o Delivering a large chunk of data. o Delivering a continuous stream of data, for example streaming sensor readings for a long period. o TCP may also be useful for providing congestion control if CoAP is being applied across the wider Internet. 4.3. Default Port CoAP has a default port of 61616 (TBD) which is within the compressed UDP port space defined in [RFC4944]. This default port is the same for UDP and TCP. 5. Caching The cachability of CoAP messages will be important, especially with Shelby & Frank Expires September 2, 2010 [Page 13] Internet-Draft Constrained Application Protocol (CoAP) March 2010 the sleeping node configurations and power limitations typically found in constrained networks and nodes. What features of cachability are really required and how much energy are we willing to spend on it? Roughly 50% of the HTTP specifications are dedicated to sohpisticated caching. With CoAP we should look at the bare minimum caching feature possible for caching responses with intercept proxy caching. The following two scenarios have been identified: o An intermediate CoAP proxy may cache resources and answer READ requests using a cached version. The resource may be cached from previous responses or notifications. This requires the Max-age Option Header. o An intermediate CoAP proxy may cache subscriptions to a sleeping node. This requires the Max-age Option Header. o An intermediate CoAP proxy may use notifications from a node to update a resource. This requires the Max-age Option Header. 5.1. Cache control Max-age approach is simplest based on timeouts. TBD if we also support an Etag style hash approach for detecting changes in a resource as well. See [I-D.frank-6lowapp-chopan]. 5.2. Intercept proxy caching See [I-D.frank-6lowapp-chopan]. 5.3. Cache refreshing See [I-D.frank-6lowapp-chopan]. 5.4. Sleeping nodes See [I-D.frank-6lowapp-chopan]. 6. Subscription and Notification See [I-D.shelby-core-coap-req]. 7. Resource Discovery See [I-D.shelby-core-coap-req]. Shelby & Frank Expires September 2, 2010 [Page 14] Internet-Draft Constrained Application Protocol (CoAP) March 2010 8. HTTP Mapping See [I-D.shelby-core-coap-req]. 9. Examples TODO 10. Conclusions TODO 11. Security Considerations TODO: Expand this section to a full security analysis, including how to use CoAP with various security options. Some of the features considered in this document will need further security considerations during a protocol design. For example the use of string URLs may have entail security risks due to complex processing on limited microcontroller implementations. The CoAP protocol will be designed for use with e.g. (D)TLS or object security. A protocol design should consider how integration with these security methods will be done, how to secure the CoAP header and other implications. 12. IANA Considerations TODO (See IANA comments in the document). 13. Acknowledgments Thanks to Carsten Bormann, Don Sturek, Michael Stuber, Richard Kelsey, Cullen Jennings, Guido Moritz, Peter Van Der Stok, Adriano Pezzuto, Lisa Dussealt, Gilbert Clark and Salvatore Loreto for helpful comments and discussions. 14. References Shelby & Frank Expires September 2, 2010 [Page 15] Internet-Draft Constrained Application Protocol (CoAP) March 2010 14.1. Normative References [I-D.frank-6lowapp-chopan] Frank, B., "Chopan - Compressed HTTP Over PANs", draft-frank-6lowapp-chopan-00 (work in progress), September 2009. [I-D.shelby-6lowapp-encoding] Shelby, Z., Luimula, M., and D. Peintner, "Efficient XML Encoding and 6LowApp", draft-shelby-6lowapp-encoding-00 (work in progress), October 2009. [I-D.shelby-core-coap-req] Shelby, Z., Stuber, M., Sturek, D., Frank, B., and R. Kelsey, "CoAP Requirements and Features", draft-shelby-core-coap-req-00 (work in progress), February 2010. [RFC2046] Freed, N. and N. Borenstein, "Multipurpose Internet Mail Extensions (MIME) Part Two: Media Types", RFC 2046, November 1996. [RFC2616] Fielding, R., Gettys, J., Mogul, J., Frystyk, H., Masinter, L., Leach, P., and T. Berners-Lee, "Hypertext Transfer Protocol -- HTTP/1.1", RFC 2616, June 1999. [RFC3986] Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform Resource Identifier (URI): Generic Syntax", STD 66, RFC 3986, January 2005. 14.2. Informative References [RFC4944] Montenegro, G., Kushalnagar, N., Hui, J., and D. Culler, "Transmission of IPv6 Packets over IEEE 802.15.4 Networks", RFC 4944, September 2007. Authors' Addresses Zach Shelby Sensinode Kidekuja 2 Vuokatti 88600 FINLAND Phone: +358407796297 Email: zach@sensinode.com Shelby & Frank Expires September 2, 2010 [Page 16] Internet-Draft Constrained Application Protocol (CoAP) March 2010 Brian Frank Tridium, Inc Richmond, VA USA Phone: Email: brian.tridium@gmail.com Shelby & Frank Expires September 2, 2010 [Page 17]