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Versions: 00 01

CORE                                                      G. Moritz, Ed.
Internet-Draft                                     University of Rostock
Intended status: Informational                             June 17, 2011
Expires: December 19, 2011


                         SOAP-over-CoAP Binding
                  draft-moritz-core-soap-over-coap-01

Abstract

   The scope of this document is to provide the basis for a lightweight
   SOAP over CoAP binding.  By the binding described in this document,
   SOAP Web services can also be used in resource constrained networks.

Status of this Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.  This document may not be modified,
   and derivative works of it may not be created, and it may not be
   published except as an Internet-Draft.

   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 December 19, 2011.

Copyright Notice

   Copyright (c) 2011 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
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   described in the Simplified BSD License.



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Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3
     1.1.  Motivation . . . . . . . . . . . . . . . . . . . . . . . .  3
     1.2.  Requirements Language  . . . . . . . . . . . . . . . . . .  3
     1.3.  Terminology and Definitions  . . . . . . . . . . . . . . .  4
     1.4.  Requirements . . . . . . . . . . . . . . . . . . . . . . .  4
   2.  Use of CoAP  . . . . . . . . . . . . . . . . . . . . . . . . .  5
     2.1.  CoAP Media Types . . . . . . . . . . . . . . . . . . . . .  5
   3.  Binding Name . . . . . . . . . . . . . . . . . . . . . . . . .  5
   4.  Transport Layer Binding  . . . . . . . . . . . . . . . . . . .  5
     4.1.  Source Address and Port  . . . . . . . . . . . . . . . . .  6
   5.  Addressing . . . . . . . . . . . . . . . . . . . . . . . . . .  6
     5.1.  URI Scheme . . . . . . . . . . . . . . . . . . . . . . . .  6
     5.2.  Destination Addressing . . . . . . . . . . . . . . . . . .  6
   6.  Message Patterns . . . . . . . . . . . . . . . . . . . . . . .  6
     6.1.  Request response . . . . . . . . . . . . . . . . . . . . .  7
     6.2.  Retransmission . . . . . . . . . . . . . . . . . . . . . .  8
   7.  CoAP Header Options  . . . . . . . . . . . . . . . . . . . . .  8
     7.1.  Unicast one-way  . . . . . . . . . . . . . . . . . . . . .  8
     7.2.  Unicast request-response . . . . . . . . . . . . . . . . . 10
   8.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 11
   9.  Security Considerations  . . . . . . . . . . . . . . . . . . . 11
   10. References . . . . . . . . . . . . . . . . . . . . . . . . . . 11
     10.1. Normative References . . . . . . . . . . . . . . . . . . . 11
     10.2. Informative References . . . . . . . . . . . . . . . . . . 12
   Appendix A.  Changelog . . . . . . . . . . . . . . . . . . . . . . 12
   Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 13























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1.  Introduction

   The intention of this document is to provide the basic approach for a
   SOAP-over-CoAP binding.  Readers of this document should be basically
   familiar with the CoAP draft [I-D.ietf-core-coap], SOAP
   [W3C.REC-soap12-part0-20070427], the SOAP HTTP binding
   [W3C.REC-soap12-part1-20070427] and the SOAP UDP binding
   [SOAP-over-UDP].  Parts of this document are derived from these
   existing specifications.  This document will not provide a
   comprehensive specification.  It may be used as basis for further
   discussions and to identify required changes in the current CoAP
   [I-D.ietf-core-coap] protocol design, which is on the way to become
   an IETF standard.  This binding does not exploit from all features of
   CoAP, but uses CoAP as an application layer transport mechanism for
   SOAP envelopes.

1.1.  Motivation

   The motivation behind this document is based on the initial I-D
   [I-D.moritz-6lowapp-dpws-enhancements] and the resulting discussions.
   By combining SOAP with EXI, message size can be reduced significantly
   as presented in [I-D.moritz-6lowapp-dpws-enhancements].  Beside EXI,
   the herein described binding is the second major enabler towards
   usage of SOAP Web services in highly resource constrained
   environments.  By implementing this binding, SOAP Web services are
   not required to use inappropriate mechanisms like TCP handshakes and
   congestion control implied by the existing SOAP-over-HTTP binding.
   But in contrast to the existing standard SOAP-over-UDP binding,
   reliably messaging is guaranteed by the SOAP-over-CoAP binding
   through CoAP internal mechanisms.  In summary the major advantages
   are:

   o  more compact (binary) message format compared to SOAP-over-HTPP
      binding

   o  probably lower message parsing efforts compared to standard HTTP
      headers

   o  avoid inappropriate TCP usage implied by SOAP-over-HTTP binding

   o  avoid unreliable nature of the SOAP-over-UDP binding

1.2.  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].




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1.3.  Terminology and Definitions

   Defined below are the basic definitions for the terms used in this
   specification.

   SOAP/CoAP message
           A CoAP message containing a SOAP envelope in the CoAP message
           body

   Receiver
           The endpoint terminating a SOAP/CoAP message

   Sender
           The endpoint originating a SOAP/CoAP message

   This specification uses the constructs [action], [destination],
   [message id], [reply endpoint], [address] as defined in WS-Addressing
   [W3C.PR-ws-addr-core-20060321].

   The SOAP CoAP Binding is optional and SOAP nodes are not required to
   implement it.  A SOAP node that correctly and completely implements
   the SOAP CoAP Binding may to be said to 'conform to the CoAP
   Binding.'

1.4.  Requirements

   This specification intends to meet the following requirements:

   o  Support a one-way message-exchange pattern (MEP) where a SOAP
      envelope is carried in a CoAP message from Sender to Receiver
      only.

   o  Support a request-response message-exchange pattern (MEP) where
      SOAP envelopes are carried in CoAP messages from Sender to
      Receiver and back from the origin Receiver to the origin Sender.

   Even if supported by CoAP, supporting multicast transmissions of SOAP
   envelopes carried in CoAP messages are out of scope of this version
   of this document and require further research.  For such multicast
   messages, the existing SOAP-over-UDP binding may be sufficient.

   This binding supports SOAP 1.2 [W3C.REC-soap12-part0-20070427]
   envelopes.  Supporting SOAP 1.1 envelopes is out of scope but might
   be added in future versions of this document.

   This specification relies on WS-Addressing.  The SOAP envelope MUST
   use the mechanisms defined in WS-Addressing
   [W3C.PR-ws-addr-core-20060321].



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   Note: CoAP has no header option which corresponds to HTTP Accept and
   the existing SOAPAction HTTP header extension field.  Thus the web
   methods feature known from the HTTP binding is not possible.  In the
   current CoAP draft only few information are available how to define
   own header fields.


2.  Use of CoAP

   This binding of SOAP to CoAP is intended to make appropriate use of
   CoAP as an application protocol.  For example, successful and failure
   responses are indicated by the corresponding CoAP response codes
   (e.g. 2.xx, 4.xx, 5.xx).  This binding is not intended to fully
   exploit the features of CoAP, but rather to use CoAP specifically for
   the purpose of communicating with other SOAP nodes implementing the
   same binding.

2.1.  CoAP Media Types

   Conforming implementations of this binding:

   o  MAY be capable of sending and receiving SOAP/CoAP messages
      serialized using media type 'application/xml'.

   o  MAY be capable of sending and receiving SOAP/CoAP messages
      serialized using media type 'application/exi'.

   o  MUST be capable of sending and receiving SOAP/CoAP messages using
      such media types providing for at least the transfer of SOAP XML
      Infoset, including 'application/xml' and 'application/exi'.

   A SOAP/CoAP message MUST contain the CoAP Content-Type option.  This
   option MUST contain a value which satisfies the three points above.


3.  Binding Name

   This binding is identified by the URI (see SOAP 1.2 Part 1
   [W3C.REC-soap12-part1-20070427] SOAP Protocol Binding Framework):
   http://www.ws4d.org/2011/06/soap/bindings/CoAP/

   Note: The binding name is tentative but required to indicate the
   corresponding binding e.g. in the WSDL of a service.


4.  Transport Layer Binding

   The CoAP binding MUST operate over UDP transport layer.



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   Note: CoAP defines a maximum message size which refers to the IP
   layer.  The existing SOAP-over-UDP binding instead refers only to UDP
   and defines a general maximum packet size independent of the IP
   layer.  Hence, it might be required to define the CoAP Block
   mechanism as mandatory as follows: Endpoints which support only
   messages serialized using the media type 'application/xml' SHOULD
   implement CoAP Block.

4.1.  Source Address and Port

   The source address MUST be supplied at the IP packet level and MUST
   be the IPv4 address (limited to unicast addresses) or IPv6 address
   (limited to unicast addresses) of the sender; the receiver SHOULD
   reject IP packets containing a SOAP/CoAP message that have
   inappropriate values for the source address.

   Even though CoAP is intended to be used on the well-known ports as
   defined in CoAP, the use of CoAP is not limited to these ports.  As a
   result, it is possible to have a dedicated CoAP server for handling
   SOAP processing on a distinct port.


5.  Addressing

5.1.  URI Scheme

   The SOAP CoAP binding defines a base URI according to the rules in
   CoAP.  I.e., the base URI is the CoAP Request-URI options.

5.2.  Destination Addressing

   WS-Addressing defines a URI,
   'http://www.w3.org/2005/08/addressing/anonymous', that can appear in
   the [address] property of an endpoint reference.  If the [reply
   endpoint] property of a SOAP message transmitted over CoAP has an
   [address] property with this value, the UDP source address (and
   source port) is considered to be the address to which reply messages
   should be sent.

   In absence, the implied value of the [reply endpoint] property for
   SOAP messages transmitted over CoAP is an endpoint reference with an
   [address] property whose value is
   'http://www.w3.org/2005/08/addressing/anonymous'.


6.  Message Patterns

   This specification supports the following message patterns:



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   o  Unicast one-way

   o  Unicast request, unicast response

   as described in the remainder of this section.

   All SOAP/CoAP messages MUST use the POST method of CoAP.  In the
   response, success SHOULD be indicated by the response code '2.04
   Changed'.  This changes the original meaning of the response code and
   is only valid for this SOAP-over-CoAP binding.

   Note: In the current draft of CoAP-06, POST allows no payload in the
   response.  This will be changed in future versions of the CoAP draft.

   Note: The CoAP draft is very strict in how each response code must be
   interpreted.  Since there is no generic code similar to '200 OK' of
   HTTP, an existing response code must be adapted to conform to this
   binding.  The code might be changed after the adaptations of CoAP to
   allow payload in POST requests and responses.  Further details are
   required how to map the response codes at a HTTP/CoAP proxy to
   conform to this binding.

   Note: There is no CoAP Action option similar to SOAPAction in HTTP.
   Hence the web method feature of the HTTP binding cannot be made
   possible without extensions of CoAP.

   Note: CoAP defines Proxy mechanism for caching of responses.  Because
   the CoAP binding defined herein is intended for SOAP transport and
   not RESTful resource manipulation, caching should be avoided.  CoAP
   defines the Max-Age option to be default a non-zero value.  But the
   POST method is already not cachable.  Hence, it is not required by a
   SOAP/CoAP message to contain the Max-Age option with a value of zero.

6.1.  Request response

   To match a request with a response, the CoAP Token Option can be
   used.  The CoAP Token Option SHOULD be carried in all request-
   response SOAP/CoAP messages.  WS-Addressing defines the [message id]
   property to identify messages in time and space and also to match
   requests with response.  In case of using the SOAP/CoAP binding, the
   [message id] property SHOULD be empty and MUST contain a value in
   case if the CoAP Token Option is not present.

   Note: The intention of this paragraph is to reduce message size.  The
   [message id] property has a typical size of 45 Bytes and cannot by
   compressed by knowledge based encodings like EXI, because the value
   of this property is unique for each request/response.  The CoAP Token
   Option may be much more compact by providing the same functionality.



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   CoAP defines the feature of 'separeated responses' (c.f. piggy backed
   response).  The ACK message of a separated response SHOULD NOT carry
   any payload (e.g. a SOAP Envelope) in the CoAP message body.  If the
   value of the [reply endpoint] is not
   'http://www.w3.org/2005/08/addressing/anonymous', the origin Receiver
   cannot guarantee that the response is intended to be sent to the same
   entity like the origin Sender and SHOULD include the origin Token
   Option value in the ACK of the separated response to provide details
   of the request for the entity behind the [reply endpoint].

6.2.  Retransmission

   To avoid repeated packet collisions, any retransmission
   implementation SHOULD observe good practices such as using
   exponential back-off algorithms and spreading.  An implementation
   SHOULD use the Confirmable (CON) transaction message mechanism
   described in the CoAP specification to avoid unnecessary
   retransmissions.  For each transmission of such a message, the value
   of the [message id] property and the CoAP Token Option MUST be the
   same.

   Note: WS-Event Delivery should not use CON due to ACK flood at Event
   Source.  Multicast messages also should use NON messages.  Because
   this specification focuses SOAP in general, it is not sure if such
   requirements are in scope of this document.


7.  CoAP Header Options

   In this section, the CoAP header and CoAP header options usage is
   described in detail.

7.1.  Unicast one-way

   The unicast one-way message pattern consists one complete CoAP
   request/response, which again can be seperated in different CoAP
   message exchanges.  Only the request carries a SOAP envelope in the
   message body while the response message body is empty.

   The request is formulated according to the table below, but can be
   extended for application specific needs.










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   +--------------+----------------------------------------------------+
   | CoAP header  | Value                                              |
   | option       |                                                    |
   +--------------+----------------------------------------------------+
   | CoAP Method  | POST is the only supported method of this binding. |
   | Request URI  | The request URI confirming a CoAP URI and          |
   |              | identifying the WS-Addressing [address] endpoint   |
   |              | property (network address).  If the value of the   |
   |              | WS-Addressing [address] endpoint property is       |
   |              | 'http://www.w3.org/2005/08/addressing/anonymous'   |
   |              | (directly set or implied by an empty [address]     |
   |              | property), the CoAP Uri-Path Option and the CoAP   |
   |              | Uri-Query Option are empty.                        |
   | Token Option | Token in accordance to CoAP specification to match |
   |              | the request/response in time and space.            |
   | Content-type | Media type of CoAP message body.                   |
   | Option       |                                                    |
   | CoAP message | SOAP message serialized according to the rules for |
   | body         | carrying SOAP messages in the media type given by  |
   |              | the Content-type Option.                           |
   +--------------+----------------------------------------------------+

                     Table 1: Unicast one-way Request

   The response is formulated according to the table below, but can be
   extended for application specific needs.

   +---------+---------------------------------------------------------+
   | CoAP    | Value                                                   |
   | header  |                                                         |
   | option  |                                                         |
   +---------+---------------------------------------------------------+
   | CoAP    | Status Code in accordance to codes defined in CoAP and  |
   | Status  | in this binding.  Note: CoAP describes only a subset of |
   | Code    | HTTP status codes and adds own codes.  This requires    |
   |         | further alignment.                                      |
   | Token   | Token in accordance to CoAP specification to match the  |
   | Option  | request/response in time and space.                     |
   | CoAP    | MUST NOT be included in the one-way message pattern.    |
   | message |                                                         |
   | body    |                                                         |
   +---------+---------------------------------------------------------+

                     Table 2: Unicast one-way Response







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7.2.  Unicast request-response

   The unicast request-response message pattern consists one complete
   CoAP request/response, which again can be seperated in different CoAP
   message exchanges.  Both request and response cary a SOAP envelope in
   the message body.

   The request is formulated according to the table below, but can be
   extended for application specific needs.

   +--------------+----------------------------------------------------+
   | CoAP         | Value                                              |
   | field/header |                                                    |
   | option       |                                                    |
   +--------------+----------------------------------------------------+
   | CoAP Method  | POST is the only supported method of this binding. |
   | Request URI  | The request URI confirming a CoAP URI and          |
   |              | identifying the WS-Addressing [address] endpoint   |
   |              | property (network address).  If the value of the   |
   |              | WS-Addressing [address] endpoint property is       |
   |              | 'http://www.w3.org/2005/08/addressing/anonymous'   |
   |              | (directly set or implied by an empty [address]     |
   |              | property), the CoAP Uri-Path Option and the CoAP   |
   |              | Uri-Query Option are empty.                        |
   | Content-type | Media type of CoAP message body.                   |
   | Option       |                                                    |
   | Token Option | Token in accordance to CoAP specification to match |
   |              | the request/response in time and space.            |
   | CoAP message | SOAP message serialized according to the rules for |
   | body         | carrying SOAP messages in the media type given by  |
   |              | the Content-type Option.                           |
   +--------------+----------------------------------------------------+

                 Table 3: Unicast request-response Request

   If the request is a Confirmable CoAP message, the response consists
   of a CoAP ACK which may carry the response SOAP envelope as data in
   the CoAP message body.  For the response, the origin receiver may
   also initiate a new CoAP transaction after sending the CoAP ACK to
   the origin Sender, which can be either also Non-Confirmable or
   Confirmable. (see separated vs. piggy backed responses in CoAP)










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   +--------------+----------------------------------------------------+
   | CoAP         | Value                                              |
   | field/header |                                                    |
   | option       |                                                    |
   +--------------+----------------------------------------------------+
   | CoAP Status  | Status Code in accordance to codes defined in CoAP |
   | Code         | and in this binding.  Note: CoAP describes only a  |
   |              | subset of HTTP status codes and adds own codes.    |
   |              | This requires further alignment.                   |
   | Content-type | Media type of CoAP message body.                   |
   | Option       |                                                    |
   | Token Option | Token in accordance to CoAP specification to match |
   |              | the request/response in time and space.            |
   | CoAP message | SOAP message serialized according to the rules for |
   | body         | carrying SOAP messages in the media type given by  |
   |              | the Content-type Option.                           |
   +--------------+----------------------------------------------------+

                Table 4: Unicast request-response Response


8.  IANA Considerations

   No IANA issues have been identified in this draft.


9.  Security Considerations

   Will be added in future versions.


10.  References

10.1.  Normative References

   [I-D.ietf-core-coap]
              Shelby, Z., Hartke, K., Bormann, C., and B. Frank,
              "Constrained Application Protocol (CoAP)",
              draft-ietf-core-coap-06 (work in progress), May 2011.

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997.

   [W3C.PR-ws-addr-core-20060321]
              Gudgin, M., Hadley, M., and T. Rogers, "Web Services
              Addressing 1.0 - Core", W3C PR PR-ws-addr-core-20060321,
              March 2006.




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   [W3C.REC-soap12-part0-20070427]
              Mitra, N. and Y. Lafon, "SOAP Version 1.2 Part 0: Primer
              (Second Edition)", World Wide Web Consortium
              Recommendation REC-soap12-part0-20070427, April 2007,
              <http://www.w3.org/TR/2007/REC-soap12-part0-20070427>.

10.2.  Informative References

   [DPWS]     Driscoll and Mensch, "OASIS Devices Profile for Web
              Services (DPWS) Version 1.1", 2009,
              <http://docs.oasis-open.org/ws-dd/ns/dpws/2009/01>.

   [I-D.moritz-6lowapp-dpws-enhancements]
              Moritz, G., "DPWS for 6LoWPAN",
              draft-moritz-6lowapp-dpws-enhancements-01 (work in
              progress), June 2010.

   [SOAP-over-UDP]
              Jeyaraman, "OASIS SOAP-over-UDP Version 1.1", 2009, <http:
              //docs.oasis-open.org/ws-dd/soapoverudp/1.1/os/
              wsdd-soapoverudp-1.1-spec-os.html>.

   [W3C.REC-soap12-part1-20070427]
              Nielsen, H., Hadley, M., Karmarkar, A., Lafon, Y.,
              Mendelsohn, N., Moreau, J., and M. Gudgin, "SOAP Version
              1.2 Part 1: Messaging Framework (Second Edition)", World
              Wide Web Consortium Recommendation REC-soap12-part1-
              20070427, April 2007,
              <http://www.w3.org/TR/2007/REC-soap12-part1-20070427>.


Appendix A.  Changelog

   Changed from soap-over-coap-00 to soap-over-coap-01:

   o  Updated to coap-06

   o  Changed behavior of one-way MEP

   o  Added response code considerations

   o  Updated CoAP header option usage

   o  Changed caching considerations

   o  Editorial updates





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Author's Address

   Guido Moritz (editor)
   University of Rostock
   18051 Rostock,
   Germany

   Phone: +49 381 498 7269
   Email: guido.moritz@uni-rostock.de










































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