Internet DRAFT - draft-jhjung-core-sensor-streaming
draft-jhjung-core-sensor-streaming
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
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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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