CoRE P. van der Stok
Internet-Draft Philips Research
Intended status: Informational K. Lynn
Expires: April 28, 2011 Consultant
October 25, 2010
CoAP Utilization for Building Control
draft-vanderstok-core-bc-02
Abstract
This draft describes an example use of the RESTful CoAP protocol for
building automation and control (BAC) applications such as HVAC and
lighting. A few basic design assumptions are stated first, then URI
structure is utilized to define group as well as unicast scope for
RESTful operations. RFC 3986 defines the URI components as (1) a
scheme, (2) an authority, used here to locate the building, area, or
node under control, (3) a path, used here to locate the resource
under control, and (4) a query part (fragments are not supported in
CoAP.) Next, it is shown that DNS can be used to locate URIs on the
scale necessary in large commercial BAC deployments. Finally, a
method is proposed for mapping URIs onto legacy BAC resources, e.g.,
to facilitate application-layer gateways.
This proposal supports the view that (1) building control is likely
to move in steps toward all-IP control networks based on the legacy
efforts provided by DALI, LON, BACnet, ZigBee, and other standards,
and (2) service discovery is complimentary to resource discovery and
facilitates control network scaling.
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
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 April 28, 2011.
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Copyright Notice
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Terminology . . . . . . . . . . . . . . . . . . . . . . . 3
1.2. Motivation . . . . . . . . . . . . . . . . . . . . . . . . 3
2. URI structure . . . . . . . . . . . . . . . . . . . . . . . . 5
2.1. Scheme part . . . . . . . . . . . . . . . . . . . . . . . 6
2.2. Authority part . . . . . . . . . . . . . . . . . . . . . . 6
2.3. Path part . . . . . . . . . . . . . . . . . . . . . . . . 7
3. Group Naming and Addressing . . . . . . . . . . . . . . . . . 8
4. Discovery . . . . . . . . . . . . . . . . . . . . . . . . . . 10
4.1. DNS-Based Service Discovery . . . . . . . . . . . . . . . 10
4.2. Service vs Resource Discovery . . . . . . . . . . . . . . 11
4.3. Browsing for Services . . . . . . . . . . . . . . . . . . 11
5. Legacy Structure in CoAP . . . . . . . . . . . . . . . . . . . 11
6. Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . 12
7. Security considerations . . . . . . . . . . . . . . . . . . . 13
8. IANA considerations . . . . . . . . . . . . . . . . . . . . . 13
9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 14
10. Changelog . . . . . . . . . . . . . . . . . . . . . . . . . . 14
11. References . . . . . . . . . . . . . . . . . . . . . . . . . . 14
11.1. Normative References . . . . . . . . . . . . . . . . . . . 14
11.2. Informative References . . . . . . . . . . . . . . . . . . 15
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 16
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1. Introduction
1.1. 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 "Key words for use in
RFCs to Indicate Requirement Levels" [RFC2119].
In addition, the following conventions are used in this document.
The term "service" often means different things to different
communities and even different things to the same community. In
building control protocol standards, service is often used to refer
to a function in the RPC sense. In this context, we generally
substitute the term "function". In the IETF community, service may
often refer to an abstract capability such as "datagram delivery".
In this submission we use the term service, in the sense defined by
"DNS-based Service Discovery" [I-D.cheshire-dnsext-dns-sd], as
equivalent to a CoAP end-point.
A CoAP end-point is identified by the authority part of a URI. We
refer to this end-point (which is resolved to an {IP address, port}
tuple) as a "node". By "device" we generally mean the physical
object handled by the installer. While a device may host more than
one service, for simplicity we assume here that a given device may
only host a single CoAP node.
In examples below involving URIs, the authority is preceded by double
slashes "//" and path is preceded by a single slash "/". The
examples may make use of fully qualified or partial domain names and
the difference should be clear from the context.
1.2. Motivation
The CoAP protocol [I-D.ietf-core-coap] aims at providing a user
application protocol architecture that is targeted to a network of
nodes with a low resource provision such as memory, CPU capacity, and
energy. In general, IT application manufacturers strive to provide
the highest possible functionality and quality for a given price. In
contrast, the building controls market is highly price sensitive and
manufacturers tend to compete by delivering a given functionality and
quality for the lowest price. In the first market a decreasing
memory price leads to more software functionality, while in the
second market it leads to a lower Bill of Material (BOM).
The vast majority of nodes in a typical building control application
are resource constrained, making the standardization of a lightweight
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application protocol like CoAP a necessary requirement for IP to
penetrate the device market. This approach is further indicated by
the low energy consumption requirement of battery-less nodes. Low
resource budget implies low throughput and small packet size as for
[IEEE.802.15.4]. Reduction of the packet size is obtained by using
the header reduction of 6LoWPAN [RFC4944] and encouraging small
payloads.
Several legacy building control standards (e.g [BACnet], [DALI],
[KNX], [LON], [ZigBee], etc.) have been developed based on years of
accumulated knowledge and industry cooperation. These standards
generally specify a data model, functional interfaces, packet
formats, and sometimes the physical medium for data objects and
function invocation. Many of these industry standards also specify
lower-level functionality such as proprietary transport protocols,
necessitating expensive stateful gateways for these standards to
interoperate. Many more recent building control network include IP-
based standards for transport (at least to interconnect islands of
functionality) and other functions such as naming and discovery.
CoAP will be successful in the building control market to the extent
that it can represent a given standard's data objects and provide
functions, e.g. resource discovery, that these standards depend on.
From the above the basic syntax assumptions can be summarized as:
- Generate small payloads.
- Compatible with legacy standards (e.g LON, BACnet, DALI, ZigBee
Device Objects).
- Service/resource discovery in agreement with legacy standards and
naming conventions.
This submission aims at an approach in which the payload contains
messages with a syntax defined by legacy control standards.
Accordingly, the syntax of the service/resource discovery messages is
related to the chosen legacy control standard. The intention is a
progressive approach to all-IP in building control. In a first stage
standard IETF based protocols (e.g CoAP, DNS-SD) are used for
transport of control messages and discovery messages expressed in a
legacy syntax. This approach enables the reuse of controllers based
on the semantics of the chosen control standard. In a later stage a
complete redesign of the controllers can be envisaged guided by the
accumulated experience with all-IP control.
Two concepts, hierarchy and group, are of prime importance in
building control, particularly in lighting and HVAC. Many control
messages or events are multicast from one device to a group of
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devices (e.g. from a light switch to all lights in a room). The
scope of a multicast command or discovery message determines the
group of nodes that is targeted. A group scope may be defined as
link-local, or as a tree maintained by IP-multicast or an overlay
that corresponds to the logical structure of a building or campus,
and is independent of the underlying network structure. Techniques
for group communication are discussed in [I-D.rahman-core-groupcomm].
As described in "Commercial Building Applications Requirements"
[I-D.martocci-6lowapp-building-applications] it is typical practice
to aggregate building control at the room, area, and supervisory
levels. Furthermore, networks for different subsystems (lights,
HVAC, etc.) or based on different legacy standards have historically
been isolated from each other in so-called "silos". RESTful web
services [Fielding] represent one possible way to expose
functionality and normalize data representations between silos in
order to facilitate higher order applications such as campus-wide
energy management.
Consequently, additional protocol oriented assumptions are:
- Nodes may be addressed by more than one group.
- Resources addressed by a group must be uniformly named across all
targeted nodes.
For clarity, this I-D limits itself to two types of applications: (1)
M2M control applications running within a building area without any
human intervention after commissioning of a given network segment and
(2) maintenance oriented applications where data are collected from
node in several building areas by nodes inside or outside the
building, and humans may intervene to change control settings.
2. URI structure
This I-D considers three elements of the URI: scheme, authority, and
path, as defined in "Uniform Resource Identifier (URI): Generic
Syntax" [RFC3986]. The authority is defined within the context of
standard DNS host naming, while the path is valid in relation to a
fully qualified domain name (FQDN) plus optional port (and protocol
is implicit, based on scheme). An example based on RFC 3986 is:
foo://host.example.com:8042/over/there?name=ferret#nose, where "foo"
is the scheme, "host.example.com:8042" is the authority, "/over/
there" is the path, "name=ferret" is the query, and "nose" is the
fragment. Fragments are not supported in CoAP.
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2.1. Scheme part
The default scheme specified in this submission is "coap". We assume
syntactic compatibility with the "http" scheme specification
[RFC2616], namely that the host part of the authority may be
represented either as a literal IP address or as a fully qualified
domain name. While scheme is irrelevant from the perspective of the
service, it is used in service discovery to identify the protocol
used to access the service.
TBD: we have yet to fully explore the utility of a separate scheme
(e.g., "coapm") to support group communication models as described in
[I-D.rahman-core-groupcomm].
2.2. Authority part
The authority part is either a literal IP address or a DNS name
comprised of a local part, specifying an individual node or group of
nodes, and a global part specifying the (sub)domain that may reflect
the logical hierarchical structure of the building control network.
The result is said to be a fully qualified domain name (FQDN) which
is globally unique down to the group or node level. An optional port
number may be included in the authority following a single colon ":"
if the service port is other than the default CoAP value.
The CoAP spec [I-D.ietf-core-coap] states "When a CoAP server is
hosted by a 6LoWPAN node, it SHOULD support a port in the 61616-61631
compressed UDP port space defined in [RFC4944]. The specific port
number in use will be communicated in a URI and/or by some other
discovery mechanism." As shown below, DNS-SD
[I-D.cheshire-dnsext-dns-sd] is a viable technique for discovering
dynamic host and port assignments for a given service. However, the
use of dynamic ports in URIs is likely to lead to brittle (non-
persistent) identifiers as it is conventional to treat different
ports as representing different authorities and there is no assurance
that a coap server will consistently acquire the same dynamic port.
A building can be unambiguously addressed by it GPS coordinates or
more functionally by its zip or postal code. For example the Dutch
Internet provider, KPN, assigns to each subscriber a host name based
on its postcode. Analogously, an example authority for a building
may be given by: //bldg.zipcode-localnr.Country/ or more concretely
an imaginary address in the Netherlands as: //bldg.5533BA-125a.nl/.
The "bldg" prefix can specify the target node within the building.
Arriving at the node identified by //bldg.5533BA-125a.nl, the
receiving service can parse the path portion of the URI and perform
the requested method on the specified resource.
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Buildings have a logical internal structure dependent on their size
and function. This ranges from a single hall without any structure
to a complex building with wings, floors, offices and possibly a
structure within individual rooms. The naming of the building
control equipment and the actual control strategy are intimately
linked to the building structure. It is therefore natural to name
the equipment based on their location within the building.
Consequently, the local part of the URI identifying a piece of
equipment is expressed in the building structure. An example is:
//light-27.floor-1.west-wing...
This proposal assumes a basic level of cooperation between the IT and
building management infrastructure, namely the ability of the former
to delegate DNS subdomains to the latter. This allows the building
controls installer to implement an appropriate naming scheme with the
required granularity. For institutional real estate such as a
college or corporate campus, the authority might be based on the
organization's domain, e.g. //node-or-
group.floor.wing.bldg.campus.example.com/. In cases where subdomain
delegation is not an option, structure can still be represented in a
"flat" namespace, subject to the 63 octet limit for a DNS sub-
string: //group1-floor2-west-bldg3-campus.example.com.
Most communication is device to device (M2M) within the building.
Often a device needs to communicate to all devices of a given type
within a given area of the building. For example a thermostat may
access all radiator actuators in a zone. A light switch located at
room 25b006 of floor one, expressed as:
//switch0.25b006.floor1.5533BA-125a.nl/, might specify a command to
light1 within the same room with //light1.25b006.floor1.5533BA-
125a.nl/. This approach seems to lead to rather verbose URI strings
in the packet, contrary to the small packet assumption. However, the
design of CoAP is such that the authority portion of the URI need not
be transmitted in requests sent to origin servers. The question
arises as to whether the syntax of the authority part needs to be
standardized for building control. Given the examples later in the
text, this appears more to be the concern of the building owner or
the installer.
2.3. Path part
Every network addressable resource is completely identified by a URI
scheme://authority/path. The path part of the URI specifies the
resource within a given node. The representation of object types and
their associated attributes are typically subjects for
standardization. There is no widely accepted standard for uniformly
naming building control device structure in a URI. A vigorous effort
is undertaken by the oBIX working group of OASIS [oBIX], but its
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current impact is limited.
When a GET method with an URI like
"//t-sensor1.25b006.floor1.example.com/temperature" is sent, it
represents an a priori understanding that the node with name
t-sensor1 exists, is of a given standard type (e.g BACnet temperature
sensor), and that this standard type has the readable attribute:
temperature. When commands are sent to a group of nodes it MUST be
the case that the targeted resource has the same path on all targeted
nodes. Therefore, it is necessary to establish at least a local
uniform path naming convention to achieve this. One approach is to
include the name of the standard, e.g BACnet, as the first element in
the path and then employ the standard's chosen data scheme (in the
case of BACnet, /bacnet/device/object/property). Perhaps a better
alternative is to build on the concepts presented in
[I-D.ietf-core-link-format] and identify resources of a given type in
terms of the "/.well-known/core" prefix.
3. Group Naming and Addressing
Given a network configuration and associated prefixes, the network
operator needs to define an appropriate set of groups which can be
mapped to the building areas. Knowledge about the hierarchical
structure of the building areas may assist in defining a network
architecture which encourages an efficient group communication
implementation. IP-multicasting over the group is a possible
approach for building control, although proxy-based methods may prove
to be more appropriate in some deployments
[I-D.rahman-core-groupcomm].
Example groups become:
URI authority Targeted group
//all.bldg6... "all nodes in building 6"
//all.west.bldg6... "all nodes in west wing, building 6"
//all.floor1.west.bldg6... "all nodes on floor 1, west wing,
..."
//all.bu036.floor1.west.bldg6... "all nodes in office bu036, ..."
The granularity of this example is for illustration rather than a
recommendation. Experience will dictate the appropriate hierarchy
for a given structure as well as the appropriate number of groups per
subdomain. Note that in this example, the group name "all" is used
to identify the group of all nodes in each subdomain. In practice,
"all" could name an address record in each of the DNS zones shown
above and would bind to a different multicast address [RFC3596] in
each zone. Highly granular multicast scopes are only possible using
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IPv6. The multicast address allocation strategy is beyond the scope
of this I-D, but various alternatives have been proposed
[RFC3306][RFC3307][RFC3956]. Some techniques in this proposal, e.g.
service discovery as described below, can be accomplished with a
single coap-specific multicast address as long as the desired scope
is building-wide.
To illustrate the concept of multiple group names within a building,
consider the definition, as done with [DALI], of scenes within the
context of a floor or a single office. For example, the setting of
all blue lights in office bu036 of floor 1 can be realized by
multicasting a message to the group "//blue-lights.bu036.floor1".
Each group is associated with an IP address. Consequently, when the
application specifies the sending of an "on" message to all blue
lights in the office, the message is multicast to the associated IP
address. The uri-authority option [I-D.ietf-core-coap] need not be
sent as part of the message. However to identify the resource that
is addressed, a short version of the resource path can be inserted as
an option as explained in [I-D.ietf-core-link-format].
The binding of a group FQDN to multicast address (i.e., creation of
the AAAA record in the DNS zone server) happens during the
commissioning process. (TBD: How do we associate this name with
MLD's notion of a group?) Resolution of the group name to a
multicast address happens at restart of a source or receiver node. A
multicast address and associated group name in this context are
assumed to be long-lived. It can happen that during operation the
membership of the group changes (less or more lights) but its address
is not altered and neither its name. In the limit, the group can
degrade to a single controller that represents a non-networked
subsystem replacing the original networked group of nodes. Group
membership may be managed by a protocol such as Multicast Listener
Discovery [RFC5790].
A group defines a set of nodes. All resources on a given node are
referenced by the multicast address(es) to which the node belongs. A
given node might belong to a number of groups. For example the node
belonging to the "blue-lights" group in a given corridor might also
belong to the groups: "whole building", "given wing", "given floor",
"given corridor", and "lights in given corridor". Assuming that
belonging to a group has as only consequence for the group member
that it should accept packets for an additional IP address, the
granularity of the domain names may have an impact on the complexity
of the DNS server but not necessarily on the low-resource
destinations or sources. Assuming that resolution of addresses only
happens at node start-up, the complexity of the DNS server need not
affect the responsiveness of the nodes.
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In summary, the authority portion of the URI is used to identify a
node (group) and the resulting DNS name is bound to a unicast
(multicast) address. Naming is building or organization dependent,
must be flexible, and does not require standardization efforts but
SHOULD conform to some uniform convention.
4. Discovery
4.1. DNS-Based Service Discovery
DNS-Based Service Discovery (DNS-SD) defines a conventional way to
configure DNS PTR, SRV, and TXT records to facilitate discovery of
services such as CoAP nodes within a subdomain, using the existing
DNS infrastrucure. This section gives a cursory overview of DNS-SD;
see [I-D.cheshire-dnsext-dns-sd] for a detailed description.
A DNS-SD service is specified by a name of the form
Instance.ServiceType.Domain, where the service type for CoAP nodes is
"_coap._udp". The identifier "_udp" is required by the SRV record
definition [RFC2782] and "_coap" identifies the protocol on top of
udp. For each CoAP end-point in the zone, a PTR record with the name
_coap._udp is defined and each of these refers to SRV and TXT records
having the Instance.ServiceType.Domain name.
DNS-SD also supports one level of subtype, which could be used to
locate coap services based on object model, for example:
_bacnet._sub._coap._udp, _dali._sub._coap._udp, or
_zigbee._sub._coap._udp. The maximum length of the type and subtype
fields is 14 octets, therefore this could be extended to type-
function as _dali-light, _dali-switch, etc.
The Domain part of the service name is identical to the DNS
(sub)domain part of the authority in URIs that identify the resources
on this node or group and may identify a building zone as in the
examples above.
The Instance part of the service name is defined as part of the
commissioning process. It must be unique within the (sub)domain.
The complete service name uniquely identifies both a SRV and TXT
record in the DNS zone. The granularity of a service name MAY be
that of a host or group, or it could represent a particular resource
within a coap node. The SRV record contains the host (AAAA record)
name and port of the service. In the case where a service name
identifies a particular resource, the path part of the URI must be
placed in the TXT record.
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4.2. Service vs Resource Discovery
While service discovery is concerned with finding the IP address,
port, and protocol of a named service, resource discovery is a fine-
grained discovery of resource URIs within a web service.
[I-D.ietf-core-link-format] specifies a resource discovery pattern,
such that sending a confirmable GET message for the /.well-known/core
resource returns a set of links that identify all resources present
on this node that are exposed as functions.
Assuming the ability to multicast the GET over the local link, the
coap resource discovery can be used to populate the DNS-SD database
in a semi-automated fashion. CoAP resource descriptions can be
imported into DNS-SD for exposure to service discovery by using the
n= attribute as the basis for a unique "Instance" name, defaulting to
"_coap._udp" for the ServiceType, and using some means to establish
which domain the service should be registered in (TBD). The DNS TXT
record can be populated by importing the other resource description
attributes as they share the same key=value format specified in
Section 6 of [I-D.cheshire-dnsext-dns-sd].
4.3. Browsing for Services
CoAP nodes in a given subdomain may be enumerated by sending a DNS
query to the authoritative server for that zone for PTR records named
_coap._udp. A list of names for SRV records matching that
ServiceType.Domain is returned. Each SRV record contains the port
and host name of a CoAP node. The IP address of the node is obtained
by resolving the host name. DNS-SD also specifies an optional TXT
record, having the same name as the SRV record, which can contain
"key=value" attributes. This can be used to store information about
the device, e.g., schema=DALI, type=switch. The format of the TXT
record can be standardized by the various control standards bodies as
they adopt CoAP.
TO DO: How to handle changes in building control network
configuration.
5. Legacy Structure in CoAP
In the text above it is shown how information to locate services and
devices can be stored in a DNS zone registry. An installation tool
can populate the registry with the resource information gleaned by
the coap GET query to /.well-known/core. Applications can then query
the registry to find the address, port, and path for targeted
services/resources. Given the returned information, an application
that acts on devices of a given legacy standard can invoke the legacy
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service using coap methods. Assume a short URI-reference /dl and the
setting of a value of 200 in the DALI device, dt is the number of the
dali type stored in the TXT record, and ct=52 is the proposed
Internet media type.
Client DALI server
|
| REQUEST |
|------- CON + PUT /dl [TID = 1234, ct=52] --------->|
| binary 16 bit payload dt*256 + 200 |
| |
| RESPONSE |
|<---------- ACK + 200 OK [TID = 1234] ------------- |
| |
Figure 1: Sending a DALI setting with coap to DALI device
In the example the format of the payload is determined by the legacy
standard. The short URI /dl on this IP address is obtained from the
TXT record for this service, e.g., sh="/dl". The value dt is entered
(e.g. dt="200") as the number identifying the dali type of the dali
compatible resource.
6. Conclusions
This I-D explains how naming in building control is based on a
hierarchical structure of the building areas. It is shown that DNS
subdomain delegation and naming can be used to express this hierarchy
in the authority portion of the URI, down to the group or node level.
The hierarchical naming scheme need not be standardized, but rather
can be designed to suit the application. However, it is recommended
that the scheme be employed consistently throughout the delegated
subdomain(s).
The authority portion of the URI is resolved by the client, using
conventional DNS, into the unicast or multicast IP address of the
targeted node(s). Taking advantage of the CoAP design
[I-D.ietf-core-coap], the uri-authority option need not be
transmitted in requests to origin servers and thus there is no
performance penalty for using descriptive naming schemes. The coap
design allows sending a short url to distinguish between resources on
a given node, resulting in very compact identifiers.
DNS-SD [I-D.cheshire-dnsext-dns-sd] can be used to scale up service
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discovery beyond the local link. DNS-SD can be used to enumerate
instances of a given service type within a given sub-domain. This
affords additional flexibility, such as the ability to discover
dynamic port assignments for coap node, locate coap nodes by subtype,
or bind service names for particular coap URIs.
A targeted resource is specified by the path portion of the URI.
Again, this I-D does not mandate a universal naming standard for
resources but uses examples to show how resources could be named for
various legacy standards. An obvious requirement for resources that
are accessed by multicast is that they MUST all share the same path,
including short uri if used. It is shown that it is possible to
transport legacy commands (e.g. expressed in BACnet, LON, DALI,
ZigBee, etc.) inside a CoAP message body. This necessitates the
definition of an additional IANA mime code, and the mapping of legacy
specific discovery semantics to CoAP resource discovery messages or
DNS-SD lookups.
7. Security considerations
TBD: The detailed CoAP security analysis needs to encompass scenarios
for building control applications.
Based on the programming model presented in this I-D, security
scenarios for building control need to be stated. Appropriate
methods to counteract the proposed threats may be based on the work
done elsewhere, for example in the ZigBee over IP context.
Multicast messages are, by their nature, transmitted via UDP. Any
privacy applied to such messages must be block oriented and based on
group keys shared by all targeted nodes. The CoRE security analysis
must be broadened to include multicast scenarios.
8. IANA considerations
This I-D proposes the following additions to the Media type
identifiers in conformance with the proposals done in
[I-D.ietf-core-coap].
Internet media type Code
/application/legacy 52
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9. Acknowledgements
This I-D has benefited from conversations with and comments from
Andrew Tokmakoff, Emmanuel Frimout, Jamie Mc Cormack, Oscar Garcia,
Dee Denteneer, Joop Talstra, Zach Shelby, Jerald Martocci, Matthieu
Vial, Jerome Hamel, and Nicolas Riou.
10. Changelog
- Removed all references to multicast and multicast scope, given
draft of rahman group communication.
- Adapted examples to coap-2 and core-link drafts.
- transport short URL for destination recognition.
- Elaborated legacy discovery under DNS-SD.
11. References
11.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[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.
[RFC2782] Gulbrandsen, A., Vixie, P., and L. Esibov, "A DNS RR for
specifying the location of services (DNS SRV)", RFC 2782,
February 2000.
[RFC3306] Haberman, B. and D. Thaler, "Unicast-Prefix-based IPv6
Multicast Addresses", RFC 3306, August 2002.
[RFC3307] Haberman, B., "Allocation Guidelines for IPv6 Multicast
Addresses", RFC 3307, August 2002.
[RFC3596] Thomson, S., Huitema, C., Ksinant, V., and M. Souissi,
"DNS Extensions to Support IP Version 6", RFC 3596,
October 2003.
[RFC3956] Savola, P. and B. Haberman, "Embedding the Rendezvous
Point (RP) Address in an IPv6 Multicast Address",
RFC 3956, November 2004.
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[RFC3986] Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform
Resource Identifier (URI): Generic Syntax", STD 66,
RFC 3986, January 2005.
[RFC4944] Montenegro, G., Kushalnagar, N., Hui, J., and D. Culler,
"Transmission of IPv6 Packets over IEEE 802.15.4
Networks", RFC 4944, September 2007.
[RFC5785] Nottingham, M. and E. Hammer-Lahav, "Defining Well-Known
Uniform Resource Identifiers (URIs)", RFC 5785,
April 2010.
[RFC5790] Liu, H., Cao, W., and H. Asaeda, "Lightweight Internet
Group Management Protocol Version 3 (IGMPv3) and Multicast
Listener Discovery Version 2 (MLDv2) Protocols", RFC 5790,
February 2010.
11.2. Informative References
[I-D.cheshire-dnsext-dns-sd]
Cheshire, S. and M. Krochmal, "DNS-Based Service
Discovery", draft-cheshire-dnsext-dns-sd-06 (work in
progress), March 2010.
[I-D.cheshire-dnsext-multicastdns]
Cheshire, S. and M. Krochmal, "Multicast DNS",
draft-cheshire-dnsext-multicastdns-11 (work in progress),
March 2010.
[I-D.ietf-core-coap]
Shelby, Z., Frank, B., and D. Sturek, "Constrained
Application Protocol (CoAP)", draft-ietf-core-coap-02
(work in progress), September 2010.
[I-D.ietf-core-link-format]
Shelby, Z., "CoRE Link Format",
draft-ietf-core-link-format-00 (work in progress),
October 2010.
[I-D.martocci-6lowapp-building-applications]
Martocci, J., Schoofs, A., and P. Stok, "Commercial
Building Applications Requirements",
draft-martocci-6lowapp-building-applications-01 (work in
progress), July 2010.
[I-D.rahman-core-groupcomm]
Rahman, A., "Group Communication for CoAP",
draft-rahman-core-groupcomm-00 (work in progress),
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October 2010.
[BACnet] Bender, J. and M. Newman, "BACnet/IP",
Web http://www.bacnet.org/Tutorial/BACnetIP/index.html.
[ZigBee] Tolle, G., "A UDP/IP Adaptation of the ZigBee Application
Protocol", draft-tolle-cap-00 (work in progress),
October 2008.
[LON] "LONTalk protocol specification, version 3", 1994.
[DALI] "DALI Manual", Web http://www.dali-ag.org/c/manual_gb.pdf,
2001.
[KNX] Kastner, W., Neugschwandtner, G., and M. Koegler, "AN OPEN
APPROACH TO EIB/KNX SOFTWARE DEVELOPMENT", Web http://
www.auto.tuwien.ac.at/~gneugsch/
fet05-openapproach-preprint.pdf, 2005.
[IEEE.802.15.4]
"Information technology - Telecommunications and
information exchange between systems - Local and
metropolitan area networks - Specific requirements - Part
15.4: Wireless Medium Access Control (MAC) and Physical
Layer (PHY) Specifications for Low Rate Wireless Personal
Area Networks (LR-WPANs)", IEEE Std 802.15.4-2006,
June 2006,
<http://standards.ieee.org/getieee802/802.15.html>.
[oBIX] "oBIX working group", Web http://www.obix.org, 2003.
[Fielding]
Fielding, R., "Architectural Styles and the Design of
Network-based Software Architectures, Second Edition",
Doctoral dissertation , University of California, Irvine ,
Web http://www.ics.uci.edu/~fielding/pubs/dissertation/
top.html, 2000.
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Authors' Addresses
Peter van der Stok
Philips Research
High Tech Campus
Eindhoven, 5656 AA
The Netherlands
Email: peter.van.der.stok@philips.com
Kerry Lynn
Consultant
Phone: +1 978 460 4253
Email: kerlyn@ieee.org
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