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Internet Draft                                           Joong H. Jung
Intended status: Standards Track                          Dong K. Choi
Expires: April 2019                                        Seok J. Koh
                                         Kyungpook National University
                                                      October 22, 2018


                CoAP Sensor Streaming Using Buffer Control
                 draft-jhjung-core-sensor-streaming-00.txt


Status of this Memo

   This Internet-Draft is submitted to IETF in full conformance with the
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   This Internet-Draft will expire on April 22, 2019.

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Abstract

   As the Internet of Things (IoT) technology grows with the development
   of wireless communication and sensors, many people are interested in
   Constrained Application Protocol (CoAP), which is the representative
   protocol of the IoT. In addition, attempts have been made to apply
   CoAP to sensors that support existing real-time streaming services.
   However, the CoAP is not suitable for services to support streaming
   services such as smart band and CCTV. To overcome this drawback,
   there is an extension called CoAP Observe, but streaming services
   using CoAP Observe imposes a load on the server, which is not
   suitable for environments where low power devices act as servers,
   such as data transfer between sensors and gateways. In this
   specification, we are considering the situation in which the sensor
   acts as a server, and in this environment, we define one mechanism to
   provide efficient streaming service.

Table of Contents


   1. Introduction ................................................ 2
      1.1. Background ............................................. 2
      1.2. Terminology ............................................ 2
      1.3. Overview of the proposed scheme ........................ 2
   2. The Buffer-Control Option ................................... 7
      2.1. Buffer-Control Option meaning in request ............... 7
      2.2. Buffer-Control Option meaning in a notification ........ 8
   3. Subject Side Operation ...................................... 8
      3.1. Register ............................................... 8
      3.2. Caching ................................................ 8
      3.3. Change the buffer size ................................. 9
      3.4. Unregister ............................................. 9
   4. Observer Side Operation ..................................... 9
      4.1. Register ............................................... 9
      4.2. Buffer Control ......................................... 9
      4.3. Reordering ............................................. 9
   5. Security consideration ..................................... 10
   6. IANA Considerations ........................................ 10
   7. References ................................................. 10
      7.1. Normative References .................................. 10
   Authors' Addresses ............................................ 10








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1. Introduction

1.1. Background

   The Constrained Application Protocol (CoAP) is the most widely used
   protocol in constrained environments such as sensor networks. Along
   with the growth of the Internet of Things services (IoT), a variety
   of real-time streaming services (e.g., CCTV) are provided by using
   the CoAP.

   However, how to effectively use CoAP for real-time streaming services
   is still under study. Since the CoAP has been basically designed to
   support RESTful services, it may not be suitable to use for streaming
   services. To overcome these drawbacks, the CoAP Observe Extension
   [RFC7641] has been studied. This extension supports the well-known
   CoAP observer design pattern. But, In case that a sensor acts as a
   server, the extension needs to be enhanced, because a lot of loads
   may be given to the server.

   In this document, the CoAP Observe extension [RFC7641] will be
   extended to support real-time streaming services so as to deal with
   packet error appropriately and to reduce the load on the sensor. To
   achieve this goal, a new option "Buffer-Control" of the CoAP Observe
   extension is additionally defined. This option is used to control the
   buffer in sensor for real-time streaming service.

1.2. Terminology

   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 BCP
   14 [RFC2119] [RFC8174] when, and only when, they appear in all
   capitals, as shown here.

1.3. Overview of the proposed scheme

   The main purpose of this document is to propose a new mechanism for
   real-time streaming. This mechanism will be effective when the sensor
   device periodically transmits the sensing data to the gateway, such
   as CCTV or smart band. In this document, a sensor device acts as a
   CoAP server, and a gateway acts as a client that requests data
   transmission to the sensor. Our description will be based on the
   terms defined in RFC 7641. The entity that transmits data
   periodically is called the subject, and the entity that receives the
   data is called the observer.




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   The receiver who wants streaming service MUST go through the
   registration procedure. The receiver sends a POST message to request
   the creation of a streaming service to the subject. Various
   parameters for the streaming service (e.g., authentication
   information, the interval between messages, or the buffer size) are
   transmitted with the POST message. The subject receiving the message
   checks the parameters and returns a 4.xx error code with an error
   message if it cannot create a resource for streaming. When the
   resource is successfully created, the subject returns the URL of the
   generated resource. The observer then issues a GET request with the
   Observe Option to the received URL, and if the resource
   representative is normally received, the registration procedure for
   the streaming service is completed. Figure 1 shows an example flow of
   registration process.


































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+---------+                     +----------+
| Subject |                     | Observer |
+---------+                     +----------+
     |        POST /Streaming         |
     |          Token: 0x71           |
     |       Buffer-Control: 0        |
     |      Payload: Parameters       |
     |<-------------------------------+
     |                                |
     |          2.01 CREATED          |
     |          Token: 0x71           |
     |        Payload: Stream1        |
     +------------------------------->|
     |                                |
     |      GET /Streaming/stream1    |
     |          Token: 0x71           |
     |           Observe: 0           |
     |Payload: Resource Representative|
     |<-------------------------------+
     |                                |
     |          2.05 CONTENT          |
     |          Token: 0x72           |
     |           Observe: 0           |
     |       Buffer-Control: 7        |
     |Payload: Resource Representative|
     +------------------------------->|
     |                                |
     |          2.05 CONTENT          |
     |          Token: 0x72           |
     |           Observe: 1           |
     |       Buffer-Control: 6        |
     |Payload: Resource Representative|
     +------------------------------->|
     |                                |

                    Figure 1: Streaming Service Request



   When the registration process is completed, the subject periodically
   transmits the sensing information to the observer, until it receives
   a DELETE message or until the buffer is full. The subject transmits
   only non-confirmable messages and stores them in the buffer. If an
   observer receives the message, it performs reordering with Observe
   option value as a sequence number. Then, it transmits a PUT message
   to clear the buffer to avoid that the sensor buffer is full. A PUT
   message is transmitted for each number of messages of 'sensor buffer


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   size / 2 - 1'. For instance, if the buffer size is 8, when the
   observer receives 3 messages from the subject, it transmits a PUT
   message. Therefore, two PUT messages can be transmitted before the
   buffer is full, and even if one PUT message is lost, the transmission
   of the message continues without block time. The PUT message MUST
   include Buffer-Control option.  The last sequence number received as
   option value until now The PUT message MUST be confirmable. The
   Subject receiving the PUT message deletes messages from the buffer
   which have a smaller sequence number than the sequence number
   included in the message. In other words, the PUT message acts as a
   cumulative ACK of TCP.

   Figure 2 shows a simple example of transferring data. If a message
   sent by a subject is lost, the observer can send a GET request to
   request a message of a specific sequence number. The GET request MUST
   include Buffer-Control and the positive integer number meaning the
   specific sequence number as. The observer can also stop the streaming
   service by sending a DELETE message, and the subject deletes the URL
   when it receives a delete.





























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+---------+                     +----------+
| Subject |                     | Observer |
+---------+                     +----------+
     |          2.05 CONTENT          |
     |          Token: 0x72           |
     |           Observe: 0           |
     |       Buffer-Control: 7        |
     |Payload: Resource Representative|
     +------------------------------->|
     |                                |
     |          2.05 CONTENT          |
     |          Token: 0x72           |
     |           Observe: 1           |
     |       Buffer-Control: 6        |
     |Payload: Resource Representative|
     +------------------------------->|
     |                                |
     |          2.05 CONTENT          |
     |          Token: 0x72           |
     |           Observe: 2           |
     |       Buffer-Control: 5        |
     |Payload: Resource Representative|
     +------------------------------->|
     |                                |
     |     PUT /Streaming/stream1     |
     |          Token: 0x73           |
     |       Buffer-Control: 2        |
     |<-------------------------------+
     |          2.05 CONTENT          |
     |          Token: 0x72           |
     |           Observe: 3           |
     |       Buffer-Control: 4        |
     |Payload: Resource Representative|
     +------------------------------->|
     |          2.04 CHANGED          |
     |          Token: 0x73           |
     |       Buffer-Control: 7        |
     +------------------------------->|
     |                                |
     |          2.05 CONTENT          |
     |          Token: 0x72           |
     |           Observe: 4           |
     |       Buffer-Control: 6        |
     |Payload: Resource Representative|
     +------------------------------->|

                    Figure 2: Transferring Data Example


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2. The Buffer-Control Option

   The Buffer-Control option has different meanings, depending on the
   request's method, Option Value, whether it is included in the request
   for the message, or included in the response.

2.1. Buffer-Control Option meaning in request

   Table 1 shows the meaning of the options depending on the method.

    +-------+------------------+-------------------------------------+
    |       |   Option Value   |             Description             |
    +-------+------------------+-------------------------------------+
    |  GET  | Positive Integer |Sequence number of message to request|
    +-------+------------------+-------------------------------------+
    |  PUT  |         0        |        Buffer size to change        |
    +-------+------------------+-------------------------------------+
    |  PUT  | Positive Integer | Sequence number of the last message |
    +-------+------------------+-------------------------------------+
    | POST  |         0        |        Buffer size to change        |
    +-------+------------------+-------------------------------------+


                 TABLE 1: Meaning of Buffer-Control Option



   When included in a GET request, the Buffer-Control Option identifies
   the specific sequence number of the message. A GET request with the
   Buffer-Control option is a message that the observer transmits to the
   subject to request a message that was lost during transmission. In
   this case, the Buffer-Control option indicates the sequence number of
   the message to be re-requested, and the option value is a positive
   integer.

   When the option is included in a PUT request, the Buffer-Control
   option has a different meaning depending on the Option value as
   follows :

         If the option value is 0, the Buffer-Control option is used to
         change the buffer size. The buffer size to be changed is
         included in the payload.

         If the option value is a positive integer number, the Buffer-
         Control option is used to empty the subject's buffer. In this


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         case, the option value includes the sequence number of the
         recently received message, and the Buffer-Control option is
         used like TCP's cumulative ack. The subject that receives the
         message containing this option deletes messages whose sequence
         number is less than or equal to the sequence number contained
         in the option value of the Buffer-Control option in its buffer.

   The Buffer-Control option is included in the PUT message and has the
   same meaning as when the option value is 0. In POST messages, the
   Buffer-Control option has an option value of only 0.

2.2. Buffer-Control Option meaning in a notification

   When the Buffer-Control option is included in a notification sent
   from the subject to the observer, that option indicates the size of
   the buffer that is left over.

3. Subject Side Operation

3.1. Register

   The subject who supports streaming service MUST have the resource to
   make a resource for streaming service. In this specification, the URL
   of the resource is "/streaming". Also subject MUST be able to handle
   CoAP Observe Option.

3.2. Caching

   The Subject MUST have a buffer to support Error Control. The buffer
   size is determined according to the parameters included in the POST
   message when the POST message for creating the resource for the
   streaming service is received.

3.3. Change the buffer size

   The Subject MUST have a buffer for error control and be able to
   change its buffer size. The buffer size is very important in this
   mechanism. If the size of the buffer is large, the number of PUT
   messages issued to empty the buffer can be reduced. In addition, the
   subject maintains the message transmission until the buffer is
   exhausted without considering other factors, so the observer can
   perform congestion control by changing the buffer size of
   the subject. The buffer size is transmitted until the buffer is full
   and the transmitted message is stored in the buffer. Through the PUT
   message containing the Buffer-Control option received from the
   Observer, the messages confirmed to arrive well are deleted from the
   buffer.


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3.4. Unregister

   Since this mechanism basically applies between the sensor and the
   gateway, the resources created for the streaming service can be
   observed by only one Observer. Therefore, when a DELETE message is
   received from the Observer, the corresponding resource should be
   deleted and the buffer allocated for the streaming service should be
   released.

4. Observer Side Operation

4.1. Register

   An observer who wants streaming service MUST request the creation of
   a resource for receiving the streaming service. In the extension
   defined in this specification, a resource for streaming is generated
   and serviced. Therefore, the observer MUST generate a streaming
   resource by transmitting a POST message to the subject containing
   various parameters such as the data resource to be streamed, the
   buffer size, and the interval between messages. When the resource is
   successfully created, it receives the resource URL to be streamed
   from the subject.

4.2. Buffer Control

   For the stability of streaming services, the observer should remove
   the received message from the subject's buffer. This mechanism
   minimizes the burden on the subject as much as possible, so the
   observer MUST be able to manage both the error control and the state
   of the subject buffer. In addition, it MUST be able to change the
   subject's buffer size based on network conditions. For example, if
   the error rate is high, it is possible to control the error by
   transmitting the PUT message more frequently by reducing the buffer
   size. If the error rate is low, the buffer size can be increased to
   reduce the number of control messages issued.

4.3. Reordering

   Since the CoAP message is basically UDP-based, the transmission order
   and reception order of messages may be different. Therefore, the
   observer MUST be able to re-order the message using the sequence
   number included in the CoAP Observe Option.







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5. Security consideration

   The security consideration will apply to Section 11 of [RFC7252],
   the CoAP specification, and Section 7 of [RFC7641], Observing
   resources in the CoAP.

6. IANA Considerations

   TBD

7. References

7.1. Normative References

   [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
             Requirement Levels", BCP 14, RFC 2119,
             DOI 10.17487/RFC2119, March 1997,
             <https://www.rfc-editor.org/info/rfc2119>.

   [RFC7252] Shelby, Z., Hartke, K., and C. Bormann, "The Constrained
             Application Protocol (CoAP)", RFC 7252, DOI
             10.17487/RFC7252, June 2014,
             <https://www.rfc-editor.org/info/rfc7252>.

   [RFC7641] Hartke, K., "Observing Resources in the Constrained
             Application Protocol (CoAP)", RFC 7641, DOI
             10.17487/RFC7641, September 2015,
             <https://www.rfc- editor.org/info/rfc7641>.

   [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 2119
             Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, May
             2017, <https://www.rfc-editor.org/info/rfc8174>.

Authors' Addresses

   Joong-Hwa Jung
   Kyungpook National University
   Daehakro 80, Bukgu, Daegu, South Korea 41566

   Email: godopu16@gmail.com









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   Dong-Kyu Choi
   Kyungpook National University
   Daehakro 80, Bukgu, Daegu, South Korea 41566

   Email: supergint@gmail.com


   Seok-Joo Koh
   Kyungpook National University
   Daehakro 80, Bukgu, Daegu, South Korea 41566

   Phone: +82 53 950 7356
   Email: sjkoh@knu.ac.kr



































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