P2PSIP J. Jimenez
Internet-Draft Ericsson
Intended status: Standards Track J. Lopez-Vega
Expires: August 27, 2012 University of Granada
J. Maenpaa
G. Camarillo
Ericsson
February 24, 2012
A Constrained Application Protocol (CoAP) Usage for REsource LOcation
And Discovery (RELOAD)
draft-jimenez-p2psip-coap-reload-00
Abstract
This document defines a Constrained Application Protocol (CoAP) Usage
for REsource LOcation And Discovery (RELOAD). The CoAP Usage
provides the functionality to federate Wireless Sensor Networks (WSN)
in a peer-to-peer fashion. The CoAP Usage also provides a rendezvous
service for CoAP Nodes and caching of sensor information. The RELOAD
AppAttach method is used to establish a direct connection between
nodes through which CoAP messages are exchanged.
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
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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 August 27, 2012.
Copyright Notice
Copyright (c) 2012 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
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4
3. Architecture . . . . . . . . . . . . . . . . . . . . . . . . . 4
4. Registering CoAP URIs . . . . . . . . . . . . . . . . . . . . 6
5. Rendezvous . . . . . . . . . . . . . . . . . . . . . . . . . . 6
6. Forming a direct connection and reading data . . . . . . . . . 7
7. Caching Mechanisms . . . . . . . . . . . . . . . . . . . . . . 10
7.1. ProxyCache . . . . . . . . . . . . . . . . . . . . . . . . 10
7.2. SensorCache . . . . . . . . . . . . . . . . . . . . . . . 11
8. CoAP Usage Kinds Definition . . . . . . . . . . . . . . . . . 12
8.1. CoAP-REGISTRATION Kind . . . . . . . . . . . . . . . . . . 12
8.2. CoAP-CACHING Kind . . . . . . . . . . . . . . . . . . . . 13
9. Security Considerations . . . . . . . . . . . . . . . . . . . 13
10. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 13
10.1. RELOAD Sensor Type Registry . . . . . . . . . . . . . . . 13
10.2. CoAP-REGISTRATION Kind-ID . . . . . . . . . . . . . . . . 14
10.3. CoAP-CACHING Kind-ID . . . . . . . . . . . . . . . . . . . 14
11. References . . . . . . . . . . . . . . . . . . . . . . . . . . 15
11.1. Normative References . . . . . . . . . . . . . . . . . . . 15
11.2. Informative References . . . . . . . . . . . . . . . . . . 15
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 15
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1. Introduction
The Constrained Application Protocol (CoAP) is a specialized web
transfer protocol. It realizes the Representational State Transfer
(REST) architecture for the most constrained nodes, such as sensors
and actuators. CoAP can be used not only between nodes on the same
constrained network but also between constrained nodes and nodes on
the Internet. The latter is possible since CoAP can be translated to
Hypertext Transfer Protocol (HTTP) for integration with the web.
Application areas of CoAP include different forms of M2M
communication, such as home automation, construction, health care or
transportation. Areas with heavy use of sensor and actuator devices
that monitor and interact with the surrounding environment.
The CoAP Usage for RELOAD allows CoAP nodes to store resources in a
RELOAD peer-to-peer overlay, provides a rendezvous service, and
enables the use of RELOAD overlay as a cache for sensor data. This
functionality is implemented in the RELOAD overlay itself, without
the use of centralized servers. The CoAP Usage involves three basic
functions:
1. Registration: CoAP nodes can use the RELOAD data storage
functionality to store a mapping from their CoAP URI to their
Node-ID in the overlay, and to retrieve the Node-IDs of other
nodes.
2. Rendezvous: Once a CoAP node has identified the Node-ID for an
URI it wishes to retrieve, it can use the RELOAD message routing
system to set up a direct connection which can be used to
exchange CoAP messages.
3. Caching: Nodes can use the RELOAD overlay as a caching mechanism
for their sensor information. This is specially useful for
battery constrained nodes that can make their data available in
the cache provided by the overlay while in sleep mode.
For instance, a CoAP proxy (See Section 3) could register its Node-ID
(e.g. "9996172") and a list of sensors (e.g. "/temperature-1;
./temperature-2; ./temperature-3") under its URI (e.g.
"coap://overlay-1.com/proxy-1/").
When a node wants to discover the values associated with that URI, it
queries the overlay for "coap://overlay-1.com/proxy-1/" and gets back
the Node-ID of the proxy and the list of its associated sensors. The
requesting node can then use the RELOAD overlay to establish a direct
connection with the proxy and to read sensor values.
Moreover, the CoAP proxy can store the sensor information in the
overlay. In this way information can be retrieved directly from the
overlay without performing a direct connection to the storing proxy.
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2. Terminology
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].
We use the terminology and definitions from Concepts and Terminology
for Peer to Peer SIP [I-D.ietf-p2psip-concepts] and the RELOAD Base
Protocol [I-D.ietf-p2psip-base] extensively in this document.
3. Architecture
In our architecture we extend the different nodes present in RELOAD
(Peer, Client) and add support for sensor devices or other
constrained devices. Figure 1 illustrates our architecture. The
different nodes, according to their functionality are :
Client
Devices that are capable of participating in a RELOAD overlay as
client nodes, that is they do not route messages in the overlay.
Router
Devices that are members of (i.e., peers in) a RELOAD overlay and
capable of forwarding RELOAD messages following a path through the
overlay to the destination.
Sensor
Devices capable of measuring a physical quantity. Sensors usually
acquire quantifiable information about their surrounding
environment such as: temperature, humidity, electric current,
moisture, radiation, and so on.
Actuator
Devices capable of interacting and affecting their environment
such as: electrical motors, pneumatic actuators, electric
switches, and so on.
Proxy
Devices having sufficient resources to run RELOAD either as client
or peer. These devices are located at the edge of the sensor
network and, in case of Wireless Sensor Networks (WSN), act as
coordinators of the network.
Physical devices can have one or several of the previous functional
roles. According to the functionalities that are present in each of
the nodes, they can be:
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Constrained Node
A Constrained Node (CN) is a node with limited computational
capabilities. If it is wireless then it will be part of a Low-
Rate Wireless Personal Area Network (LR-WPAN), it might be movable
and often offer unreliable connectivity. Also, devices will
usually be in sleep mode in order to prevent battery drain, and
will not communicate during those periods. A CN is NOT part of
the RELOAD overlay, therefore it can not act as a client, router
nor proxy. A CN is always either a either a Sensor or an
Actuator. In the latter case the node is often connected to a
continuous energy power supply.
Reload Node
A Reload Node (RN) MUST implement the client functionality in the
Overlay. Additionally the node will often be a full RELOAD peer
with Proxy functionality. A RN may also be sensor or actuator
since it can have those devices connected to it.
+------+
| |
+--------+ RN +---------+
| | | |
+---+--+ +------+ +--+---+
| | | |
| RN | | RN |
| | | | +------------+
+---+--+ +--+---+ | WSN |
| RELOAD | | +----+ |
| OVERLAY | | +---+ CN | |
+---+--+ +--+---+ | | +----+ |
| | | +-----+ |
| RN | | PN | | |
| | | +-----+ |
+---+--+ +------+ +--+---+ | | +----+ |
| | | | | +---+ CN | |
+--------+ PN +---------+ | +----+ |
| | +------------+
+-+--+-+
| |
+--------|--|--------+
| +--+ +--+ |
| | | |
| +--+-+ +-+--+ |
| | CN | | CN | |
| +----+ +----+ |
| WSN |
+--------------------+
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Figure 1: Architecture
4. Registering CoAP URIs
CoAP URIs are typically resolved using a DNS. When CoAP is needed in
a RELOAD environment, URI resolution is provided by the overlay as a
whole. Instead of registering register a URI, a peer stores a
CoAPRegistration structure under a hash of its own URI. This uses
the CoAP REGISTRATION Kind-ID, which is formally defined in
Section 6, and that uses a DICTIONARY data model.
As an example, if a CoAP proxy that is located in an overlay overlay-
1.com using a Node-ID "9996172" wants to register three different
temperature sensors to the URI
"coap://overlay-1.com/proxy-1/.well-known/", it might store the
following mapping in the overlay:
RESOURCE-ID = h(coap://overlay-1.com/proxy-1/.well-known/)
KEY = 9996172,
VALUE = {./temperature-1;
./temperature-2;
./temperature-3}
Note that the RESOURCE-ID stored in the overlay is calculated as a
SHA-1 hash over the URI (i.e. h(URI)).
This would inform any other node performing a lookup for the previous
URI "coap://overlay-1.com/proxy-1/.well-known" that the Node-ID value
for proxy-1 is "9996172". In addition, this mapping provides
relevant information as to the number of sensors (CNs) and the URI
path to connect to them using CoAP.
5. Rendezvous
The RELOAD overlay supports rendezvous by fetching mapping
information between CoAP URIs and Node-IDs.
As an example, if a node RN located in the overlay overlay-1.com
wishes to read which resources are served at a RN with URI
coap://overlay-1.com/proxy-1/, it performs a fetch in the overlay.
The RESOURCE-ID used in this fetch is a SHA-1 hash over the URI
"coap://overlay-1.com/proxy-1/.well-known/".
After this fetch request, the overlay will return the following
result:
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RESOURCE-ID = h(coap://overlay-1.com/proxy-1/.well-known/)
KEY = 9996172,
VALUE = { ./temperature-1;
./temperature-2;
./temperature-3}
The obtained KEY is the Node-ID of the RN responsible of this KEY/
VALUE pair. The VALUE is the set of URIs necessary to read data from
the CNs associated with the RN.
Using the RELOAD DICTIONARY model allows for multiple nodes to
perform a store to the same RESOURCE-ID. This feature allows for
performing rendezvous with multiple RNs that host CNs of the same
class.
As an example, a fetch to the URI
"coap://overlay-1.com/temperature/.well-known/" could return the
following results:
RESOURCE-ID = h(coap://overlay-1.com/temperature/.well-known/)
KEY = 9992323,
VALUE = { ./temperature}
KEY = 9996172,
VALUE = { ./temperature-1;
./temperature-2;
./temperature-3}
KEY = 9996173,
VALUE = { ./temp-a;
./temp-b}
6. Forming a direct connection and reading data
Once a RN (e.g., node-A) has obtained the rendezvous information for
a node in the overlay (e.g., proxy-1), it can open a direct
connection to that node. This is performed by sending an AppAttach
request to the Node-ID obtained during the rendezvous process.
After the AppAttach negotiation, node-A can access to the values of
the CNs at proxy-1 using the URIs obtained during the rendezvous.
Following the example in Section 5, the URIs for accessing to the CNs
at proxy-1 would be:
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coap://overlay-1.com/proxy-1/temperature-1
coap://overlay-1.com/proxy-1/temperature-2
coap://overlay-1.com/proxy-1/temperature-3
Note that the ".well-known" string has been removed from the URIs, as
this is only used during CNs discovery. Figure 1 shows a sample of a
node reading humidity data.
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+---+ +-----+ +---------+ +-----+ +---+
|CNA| | PNA | | OVERLAY | | PNB | |CNB|
+---+ +-----+ +---------+ +-----+ +---+
| | | | |
| .COAP CON GET | | | |
| /humidity | 2.RELOAD | | |
|+------------->| Fetch | | |
| |+----------->| | |
| | | | |
| | 3.RELOAD | | |
| | 200 OK | | |
| |<-----------+| | |
| | | | |
| | 4.RELOAD | | |
| | Attach | | |
| |+----------->| | |
| | | 5.RELOAD | |
| | | Attach | |
| | |+---------->| |
| | | | |
| | | 6.RELOAD | |
| | 7.RELOAD | 200 OK | |
| | 200 OK |<----------+| |
| |<-----------+| | |
| | | | |
| | | |
| | --------------------- | |
| | / 8.ICE \| |
| | \ connectivity checks /| |
| | --------------------- | |
| | | |
| | 9.CoAP CON | |
| | GET humidity | |
| |+------------------------>| |
| | | 10.CoAP CON |
| | | GET humidity |
| | |+-------------->|
| | | 11.CoAP |
| | 12.CoAP | ACK 200 |
| 12.CoAP | ACK 200 |<--------------+|
| ACK 200 |<------------------------+| |
|<-------------+| | |
| | | |
Figure 2: An Example of a Message Sequence
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7. Caching Mechanisms
The CoAP protocol itself supports the caching of sensor information
in order to reduce the response time and network bandwidth
consumption of future, equivalent requests. This storage is done in
CoAP proxies.
This CoAP usage proposes an additional caching mechanism for storing
sensor information directly in the overlay. This caching mechanism
is primarily intended for CNs with sensor capabilities, not for RN
sensors. This is due to the battery constrains of CNs, forcing them
to stay in sleep mode for long periods of time.
Whenever a CN wakes up, it sends the most recent data from its
sensors to its proxy (RN), which stores the data in the overlay using
a RELOAD StoredData structure defined in Section 6 of the RELOAD base
draft. We use the StoredDataValue structure defined in Section 6.2
of the RELOAD base draft, in particular we use the SingleValue format
type to store the cached values in the overlay. From that structure
length, storage_time, lifetime and Signature are used in the same
way. The only difference is data_value which in our case can be
either a ProxyCache or a SensorCache:
struct {
uint16 coap_caching_type;
select(coap_caching_type) {
case proxy_cache: ProxyCache proxy_cache_entry;
case sensor_cache: SensorCache sensor_cache_entry;
/* extensions */
}
} CoAPCaching;
7.1. ProxyCache
ProxyCache is meant to store values and sensor information (e.g.
inactivity time) for all the sensors associated with a certain proxy,
as well as their CoAP URIs. On the other hand, SensorCache is used
for storing the information and cached value of only one sensor (CoAP
URI is not necessary, as is the same as the one used for generating
the Resource-ID associated to that SensorCache entry).
ProxyCache contains the fields NodeId and series of SensorEntry
types.
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struct {
NodeId Node_ID;
SensorEntry sensors[];
} ProxyCache;
NodeId
The NodeID of the Proxy Node (PN) responsible for different sensor
devices;
SensorEntry
List of sensors in the form of SensorEntry types;
SensorEntry contains the coap_uri, sensor_info and a series of
SensorValue types.
struct {
opaque coap_uri;
SensorInfo sensor_info;
SensorValue sensor_value[];
} SensorEntry;
coap_uri
CoAP name of the sensor device in question;
sensor_info
contains relevant sensor information;
sensor_value
contains a list of values stored by the sensor;
7.2. SensorCache
SensorCache: contains the information related to one sensor.
struct {
NodeId Node_ID;
SensorInfo sensor_info;
SensorValue sensor_value[];
} SensorCache;
Node_ID
identifies the NodeID of the Proxy Node responsible for the
sensor;
sensor_info
contains relevant sensor information;
sensor_value
contains a list of values stored by the sensor;
SensorInfo contains relevant sensor information, such as sensor_type,
duration_of_inactivity and last_awake fields.
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struct {
integer sensor_type;
uint32 duration_of_inactivity;
uint32 last_awake;
/* extensions */
} SensorInfo;
sensor_type
is an integer identifying the type of the sensor. See Figure 3;
duration_of_inactivity
contains the sleep pattern (if any) that the sensor device
follows, specified in seconds;
last_awake
indicates the last time that the sensor was awake in UNIX time;
SensorValue contains the measurement_time, lifetime and value.
struct {
uint32 measurement_time;
uint32 lifetime;
opaque value;
/* extensions */
} SensorValue;
measurement_time
indicates the moment in which the measure was taken;
lifetime
indicates the validity time of that measured value;
value
indicates the actual value measured. It can be of different types
(integer, long, string) therefore opaque has been used;
8. CoAP Usage Kinds Definition
This section defines the CoAP-REGISTRATION and CoAP-CACHING kinds.
8.1. CoAP-REGISTRATION Kind
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Kind IDs
The Resource Name for the CoAP-REGISTRATION Kind-ID is the CoAP
URI. The data stored is a CoAPRegistration, which contains a
Node-ID and a set of CoAP URIs.
Data Model
The data model for the CoAP-REGISTRATION Kind-ID is dictionary.
The dictionary key is the Node-ID of the storing RN. This allows
each RN to store a single mapping.
Access Control
URI-NODE-MATCH. The "coap:" prefix needs to be removed from the
COAP URI before matching.
Data stored under the COAP-REGISTRATION kind is of type
CoAPRegistration, defined below.
struct {
uint16 coap_uris_length;
opaque coap_uris (0..2^16-1);
} CoAPRegistration;
8.2. CoAP-CACHING Kind
KindIDs
The Resource Name for the CoAP-CACHING Kind-ID is the CoAP URI.
The data stored is a CoAPCaching, which contains a Node-ID and a
value.
Data Model
The data model for the CoAP-CACHING Kind-ID is single value.
Access Control
URI-MATCH. The "coap:" prefix needs to be removed from the COAP
URI before matching.
Data stored under the CoAP-CACHING kind is of type CoAPCaching,
defined in Section 7 .
9. Security Considerations
TBD.
10. IANA Considerations
10.1. RELOAD Sensor Type Registry
IANA SHALL create a "RELOAD sensor type" Registry. Entries in this
registry are 16-bit integers denoting method codes as described in
Section 7. The initial contents of this registry are:
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+-----------------+-------+
| Code Name | Value |
+-----------------+-------+
| temperature | 0 |
| humidity | 1 |
| acceleration | 2 |
| pressure | 3 |
| altitude | 4 |
| luminance | 5 |
| velocity | 6 |
| signal_strength | 7 |
| battery | 8 |
| heart_rate | 9 |
+-----------------+-------+
Figure 3
10.2. CoAP-REGISTRATION Kind-ID
This document introduces one additional data Kind-ID to the "RELOAD
Data Kind-ID" Registry:
+-------------------+------------+----------+
| Kind | Kind-ID | RFC |
+-------------------+------------+----------+
| CoAP-REGISTRATION | 105 | RFC-AAAA |
+-------------------+------------+----------+
This Kind-ID was defined in Section 4.
10.3. CoAP-CACHING Kind-ID
This document introduces one additional data Kind-ID to the "RELOAD
Data Kind-ID" Registry:
+--------------+------------+----------+
| Kind | Kind-ID | RFC |
+--------------+------------+----------+
| CoAP-CACHING | 106 | RFC-AAAA |
+--------------+------------+----------+
This Kind-ID was defined in Section 4.
11. References
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11.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[I-D.ietf-core-coap]
Shelby, Z., Hartke, K., Bormann, C., and B. Frank,
"Constrained Application Protocol (CoAP)",
draft-ietf-core-coap-08 (work in progress), October 2011.
[I-D.ietf-p2psip-base]
Jennings, C., Lowekamp, B., Rescorla, E., Baset, S., and
H. Schulzrinne, "REsource LOcation And Discovery (RELOAD)
Base Protocol", draft-ietf-p2psip-base-20 (work in
progress), January 2012.
11.2. Informative References
[RFC3261] Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston,
A., Peterson, J., Sparks, R., Handley, M., and E.
Schooler, "SIP: Session Initiation Protocol", RFC 3261,
June 2002.
Authors' Addresses
Jaime Jimenez
Ericsson
Hirsalantie 11
Jorvas 02420
Finland
Email: jaime.j.jimenez@ericsson.com
Jose M. Lopez-Vega
University of Granada
CITIC-UGR Periodista Rafael Gomez Montero 2
Granada 18071
Spain
Email: jmlvega@ugr.es
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Jouni Maenpaa
Ericsson
Hirsalantie 11
Jorvas 02420
Finland
Email: jouni.maenpaa@ericsson.com
Gonzalo Camarillo
Ericsson
Hirsalantie 11
Jorvas 02420
Finland
Email: gonzalo.camarillo@ericsson.com
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