Internet DRAFT - draft-vanderstok-core-bc
draft-vanderstok-core-bc
CoRE P. van der Stok
Internet-Draft Philips Research
Intended status: Informational K. Lynn
Expires: May 2, 2012 Consultant
October 30, 2011
CoAP Utilization for Building Control
draft-vanderstok-core-bc-05
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.
This proposal supports the view that 1) service discovery is
complementary to resource discovery and facilitates control network
scaling, and 2) 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.
The authority portion of the URI is used to identify a device (group)
and the resulting DNS name is bound to a unicast (multicast) address.
Group addressing has consequence for the naming convention of the
resources of a device. Naming of URI is building or organization
dependent, must be flexible, and SHOULD conform to some local
convention. Naming of resources MUST be standardised preferrable by
a building control related organisation.
It is shown that DNS-based service discovery can be used to locate
URIs on the scale necessary in large commercial BAC deployments. The
relation of DNS-SD and a Resource Directory is discussed. Finally, a
method is proposed for mapping URIs onto legacy BAC resources, e.g.,
to discover application-layer gateways, proxies, and their dependent
services.
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/.
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This Internet-Draft will expire on May 2, 2012.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4
1.1. Terminology . . . . . . . . . . . . . . . . . . . . . . . 4
1.2. Motivation . . . . . . . . . . . . . . . . . . . . . . . . 4
2. URI structure . . . . . . . . . . . . . . . . . . . . . . . . 6
2.1. Scheme part . . . . . . . . . . . . . . . . . . . . . . . 7
2.2. Authority part . . . . . . . . . . . . . . . . . . . . . . 7
2.3. Path part . . . . . . . . . . . . . . . . . . . . . . . . 8
3. Group Naming and Addressing . . . . . . . . . . . . . . . . . 10
4. Discovery . . . . . . . . . . . . . . . . . . . . . . . . . . 12
4.1. Service discovery goals . . . . . . . . . . . . . . . . . 12
4.2. DNS-Based Service Discovery . . . . . . . . . . . . . . . 13
4.3. Browsing for Services . . . . . . . . . . . . . . . . . . 14
4.4. Resource vs Service Discovery . . . . . . . . . . . . . . 14
5. DNS record structure . . . . . . . . . . . . . . . . . . . . . 15
5.1. DNS group example . . . . . . . . . . . . . . . . . . . . 18
5.2. Operational use of DNS-SD . . . . . . . . . . . . . . . . 19
5.3. Commissioning CoAP devices . . . . . . . . . . . . . . . . 20
5.3.1. DNS-SD server present . . . . . . . . . . . . . . . . 21
5.3.2. DNS-SD server not present . . . . . . . . . . . . . . 21
5.4. Proxy discovery . . . . . . . . . . . . . . . . . . . . . 22
6. Legacy data Representations in CoAP . . . . . . . . . . . . . 23
6.1. Network architectures . . . . . . . . . . . . . . . . . . 24
6.2. Discovery of legacy gateways . . . . . . . . . . . . . . . 26
7. Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . 26
8. Security considerations . . . . . . . . . . . . . . . . . . . 27
9. IANA considerations . . . . . . . . . . . . . . . . . . . . . 28
10. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 28
11. Changelog . . . . . . . . . . . . . . . . . . . . . . . . . . 28
12. References . . . . . . . . . . . . . . . . . . . . . . . . . . 29
12.1. Normative References . . . . . . . . . . . . . . . . . . . 29
12.2. Informative References . . . . . . . . . . . . . . . . . . 30
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 32
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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:
A CoAP end-point, or server, is identified by a unique {IP address,
port} tuple and characterised by a protocol. A server is completely
specified by the authority part of a URI.
A device is the physical object that is connected to the network. A
device may host one or more CoAP servers.
A service (in the service discovery sense) is a related set of
resources on a CoAP server. A URI completely specifies the syntax of
a service interface. Metadata describe the semantics of the service
interface. The semantics may include the relation between service
and the hardware connected to the device. A CoAP server may expose
one or more services.
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 full or partial host 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 for a network of devices 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 automation 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 devices in a typical building control
application is resource constrained, making the standardization of a
lightweight application protocol like CoAP a necessary requirement
for IP to penetrate the device market. The low energy consumption
requirement of battery-less devices reinforces this approach. Low
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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 a physical medium for data objects and
function invocation. Many of these industry standards also specify
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 wanted basic syntax properties 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 defines 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
encapsulates 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
devices (e.g. from a light switch to all lights in an area). The
scope of a multicast command or discovery message determines the
group of devices that is targeted. A group scope may be defined as
link-local, as a tree maintained by an IP-multicast protocol, or an
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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 group properties are:
- Devices may be part of one or more groups.
- Resources addressed by a group must be uniformly and consistently
named across all targeted devices.
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
devices in several building areas by devices inside or outside the
building, and humans may intervene to change control settings. This
I-D compares commercial building solutions with solutions for the
home.
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 [RFC3986] 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 CoAP URI scheme syntax is specified in section 6 of
[I-D.ietf-core-coap] and is compatible with the "http" scheme
specification [RFC2616]. The scheme is implicit from the perspective
of the service, but it indicates the protocol used to access the
service to potential clients.
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 device or group
of devices, and a global part specifying a (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 device 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 authority resolves to a {IP-address, port} tuple. The
IP-address may be either unicast or multicast. The authority
therefore identifies an individual server or a named group of
servers.
The CoAP spec [I-D.ietf-core-coap] states "When a CoAP server is
hosted by a 6LoWPAN device, it SHOULD also support a port in the
61616-61631 compressed UDP port space defined in [RFC4944]." 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-durable) identifiers as there is no assurance
that a CoAP server will consistently acquire the same dynamic port
and different {IP-address, port} tuples conventionally represent
different servers.
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 device within the building.
Arriving at the device identified by //bldg.5533BA-125a.nl, the
receiving service can parse the path portion of the URI and perform
the requested actions on the specified resource.
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
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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 minimal 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. //device-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 label:
//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 can lead to rather verbose URI strings in
the packet, contrary to the small packet assumption. The question
arises as to whether the syntax of the authority part needs to be
standardized for building control. Given the naming flexibility
provided by DNS, authority names for building control are more the
concern of the building owner or the installer than a standardization
concern.
2.3. Path part
The path identifies the addressable attributes of the service at the
highest possible granularity. A set of paths defines the syntax of
the service invocation and constitutes the interface description of
the service. Every network service attribute is completely
identified by a URI scheme://authority/path. In analogy, the path
part of the URI specifies the resource of a given server. The naming
of the services and their associated attributes are typically
subjects for standardization. There is no widely accepted standard
for uniformly naming building control services in a URI. A vigorous
effort is undertaken by the oBIX working group of OASIS [oBIX], but
its current impact is limited. There is also an open source point
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naming effort underway called Project Haystack [HAYSTACK].
The path is constructed like a file system path name. It consists of
a sequence of one or more name fields, with each field preceded with
a slash, like /func1/subf2/final. The set of paths is structured as
a tree. The last name in a name field sequence is called a leave of
the tree, and the authority is the root of the path tree of a given
host. The semantics of a given sub-tree in the path tree is
specified by the Interface Description (if=) attribute described in
[I-D.ietf-core-link-format]. As for file systems some tree naming
with associated semantics can be standardized such as the de facto PC
standard directory "documents and settings" with the sub-directories
"My documents", "usradmin", etc. When a given body, e.g. XXX, has
defined a name structure and semantics for the path tree, we say that
"if = XXX" when the path tree conforms to the name structure defined
by XXX.
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 server with name
t-sensor1 exists, provides a service of a given standard type (with
associated semantics) (e.g. ZigBee temperature sensor), and that
this standard type has the readable attribute: temperature. When
commands are sent to a group of servers it MUST be the case that the
targeted resource has the same path on all targeted servers.
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).
The organization responsible for defining a given industry standard
XXX (e.g. BACnet, ZigBee, etc.) can register the /.well-known/XXX
prefix and specify the allowable path-names for a server of a given
type. The same body also defines the "if=XXX" attribute. This
allows the standards development organization responsibile for XXX to
define the name space and resources associated with the prefix
together with the associated semantics. The registered /.well-known/
XXX URI effectively defines a standard object model, or schema, for
services of the XXX application protocol. Manufacturers may
optionally define proprietary resources that can be discovered
dynamically using methods described below.
Although the authority part names need not always be transported, the
path names MUST be transported in the CoAP packets. Therefore, path
names SHOULD be as short as possible, even at the detriment of the
clarity of the meaning of the path name.
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3. Group Naming and Addressing
Within building control it is necessary to send the same command to a
set of servers. Grouping allows to invoke the set of services with
one application command to be executable within a specified time
interval. Given a network configuration, 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 device groups become:
URI authority Targeted group
//all.bldg6... "all devices in building 6"
//all.west.bldg6... "all devices in west wing, building
6"
//all.floor1.west.bldg6... "all devices on floor 1, west wing,
..."
//all.bu036.floor1.west.bldg6... "all devices 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 devices 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 practical using
IPv6. The multicast address allocation strategy is beyond the scope
of this I-D, but various alternatives have been proposed
[RFC3306][RFC3307][RFC3956].
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 a multicast 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 binding of a group FQDN to a multicast address (i.e., creation of
the AAAA record in the DNS zone server) happens during the
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commissioning process. Resolution of the group name to a multicast
address happens at restart of a device. 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 is its name. Group membership may be managed by a protocol
such as Multicast Listener Discovery [RFC5790].
Similarly, a group can identify a set of resources of one server.
For examples a device contains four I/O channels. The device hosts
one server with four resources to access each of the four individual
channels separately. Commonly, it is also required to access all
four channels as one group. An additional path identifies the group
of services. An example set of services and service-group is:
URI path Targeted group
/IOchannel/1... "channel 1 of the IO channel device "
/IOchannel/2... "channel 2 of the IO channel device "
/IOchannel/3... "channel 3 of the IO channel device "
/IOchannel/4... "channel 4 of the IO channel device "
/IOchannel/... "channel 1 to 4 of the IO channel device "
A group defines a set of servers possibly containing a set of
resources. Grouping of the resources is provided by the device
manufacturer. Grouping of the servers is supported by DNS and
multicast protocols. The multicast address(es) identify the servers
belonging to the group. A given server might belong to a number of
groups. For example the server 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". From the perspective of a server, the main
consequence of joining a group is 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 infrastructure but not
necessarily on the low-resource destinations or sources. Assuming
that resolution of addresses only happens at device start-up, the
complexity of the DNS server need not affect the responsiveness of
the devices.
In summary, the authority portion of the URI resolves to an IP-
address and port number, and identifies a server or group of servers.
Authority naming is building or organization dependent, must be
flexible, and does not require standardization efforts but SHOULD
conform to some uniform convention. Path naming SHOULD conform to
the naming convention of a standardization body.
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4. Discovery
4.1. Service discovery goals
Service discovery in building control should rely on a minimal need
for intervention by humans (or complete absence of humans) during
system setup, bootstrapping, restart, configuration and daily
operation. The goals for service discovery area:
Goal Goal description
Return_instance Return all instances of a given service type
within a given domain
Group_instance Group a set of instances within a group
associated with a domain
Instance_resolution Resolve the instance name to usable invocation
information (e.g. IP address and port)
Group_resolution resolve the group name to usable invocation
information (e.g. IP address and port)
These goals are necessary to support the operation of commercial
building control. Returning the instances results in a list of
names. For building control these names can be any sequence of
characters as long as for each service instance these names are
unique within the domain. In [I-D.cheshire-dnsext-dns-sd] the office
equipment in the IT domain is recommended to use understandable and
human-readable names. The Home domain may have a need for human
understandable names. This is not the case for the commercial
building automation domain. However, uniqueness of the name is
necessary for the application that needs to address the service in a
consistent manner. Given the large number of devices in a building
(several hundreds to thousands) scaling is an important aspect of the
service discovery. A set of central DNS servers will provide the
scalability. The expectation is that names need to be managed
consistently by a central authority which can be supported by the DNS
server. Tools will assist the installer and operator of the network
to do the installation, configuration and maintenance of the network
structure. Small devices will use the DNS server to learn the
communication partners providing a given service within their domain
and to resolve the IP addresses of the communication partners.
Within the home it is more important that the names convey the
purpose of the service to the user reading the names and selecting
his favored service instance. Non-unique names, although confusing,
can probably be handled by the user of these names. Scalability is
less of an issue because a smaller number of devices is implicated.
The network in the home is probably more dynamic than its commercial
counter-part, with many movements of devices and arrival or removal
of devices.
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Section 5 presents some examples of DNS structures to show how the
choice of names influences the granularity of the discovery. In
sections 5.1 and 5.3 a grouping example and a commissioning example,
filling the DNS, are presented.
4.2. 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 within a subdomain, re-using the existing DNS
infrastructure. This section gives a cursory overview of DNS-SD; see
[I-D.cheshire-dnsext-dns-sd] for a complete description.
A DNS-SD service instance name is of the form
<Instance>.<ServiceType>.<Location>.
The Location part of the service name is identical to the DNS
subdomain part of the authority in URIs that identify the resources
of this server or group and may identify a building zone as in the
examples above.
The ServiceType SHOULD have the form [_subtype._sub.]_type._proto
(e.g. _temp._sub._bc._udp). The _proto identifier provides a
transport protocol hint as required by the SRV record definition
[RFC2782] and, in the case of CoAP, it is always "_udp". The _type
identifier is determined by standards development organization (SDO)
and MUST be registered with dns-sd.org [dns-sd] (e.g. _bc for
building control). The SDO is then free to specifiy one or more
_subtype identifiers, which must be unique for a given _type (e.g.
_temp). The _subtype and _type labels are separated by the literal
"._sub" label.The maximum length of the type and subtype fields is 14
octets, but shorter names are encouraged to reduce packet sizes.
A PTR record with the label "_type._proto" is defined for each server
in a selected domain, and this record's value is set to the service
instance name (which in turn identifies the SRV and TXT records for
the CoAP server).
The Instance part of the service name may be changed during the
commissioning process. It must be unique for a given ServiceType
within the subdomain. The complete service name uniquely identifies
an SRV and a TXT record in the DNS zone. The granularity of a
service name MAY be at the group or server level, or it could
represent a particular resource within a CoAP server. The SRV record
contains the host (AAAA record) name and port of the service. The
path part of the URI MUST be placed in the TXT record (path=) when
multiple resources belong to the same service.
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4.3. Browsing for Services
Devices in a given Location with given ServiceType, _type._proto, may
be enumerated by sending a DNS query for PTR records named
_type._proto to the authoritative server for that zone associated
with the Location. A list of instance names for SRV records matching
that <ServiceType>.<Location> is returned. Each SRV record contains
the host name and port of a CoAP server. The IP address of the
device 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. Apart from defining standardized
resources identified by if=XXX, the XXX organization may also define
the standard "key=value" pairs present in the TXT record, e.g.
type=switch. By convention, the first pair is txtver=<number> so
that different versions of the XXX schema may interoperate. For
example: A query is sent to DNS-SD to return all DALI lamps within
the domain office5/mybuilding and with ServiceType:
_lamp._sub._dali._udp. DNS-SD returns the list of all SRV records
and AAAA records of the devices within the domain providing the
wanted service.
4.4. Resource vs Service Discovery
Service discovery is concerned with finding the IP address, port,
protocol, and possibly path of a named service. Resource discovery
is a fine-grained enumeration of resources (path-names) of a server.
[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 available from the server. These
links describe resources hosted on that server.
CoAP link format can be used to enumerate attributes and populate the
DNS-SD database in a semi-automated fashion. CoAP resource
descriptions can be imported into DNS-SD for exposure to service
discovery as described in [I-D.lynn-core-discovery-mapping]. The
values stored in the DNS-SD directory are extracted from the
information stored in the resource directory associated with a set of
CoAP hosts [I-D.shelby-core-resource-directory]. The resources
describe how the services can be manipulated in detail and in
concreto.
It is assumed that a resource directory exists per 6LoWPAN [RFC4944],
possibly running on the edge router. The DNS-SD provides a larger
scope by storing the info of all services over a set of
interconnected 6LoWPANs. Where the resource directory is possibly
completely adequate for home networks, handling of multiple resource
directories can be quite cumbersome for the many 6LoWPANs envisaged
for offices. However, during network configuration, the resource
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directory can be used as long as the DNS is not yet accessible.
The DNS-SD approach is complementary to the more fine-grained
resource discovery, fits better the concept of service by discovering
servers with given properties. DNS-SD supports a hierarchical
approach to the naming of the services as discussed in section 3.
DNS-SD provides a directory structure that scales well with the
network size as shown by its present-day operation.
5. DNS record structure
An example is presented which explains the Resource Record (RR)
structure on the DNS server. This section follows the mapping
specified in [I-D.lynn-core-discovery-mapping], which defines how to
fill the DNS-SD records from the link extension values. Suppose the
services are delivered by XXX building control devices. The example
subtype- and context- names are assumed to be standardized by the XXX
alliance. All devices are situated in one office with location
office4.bldg8.example.com. The names in the examples are more
verbose than recommended to make the examples more readable. The
table presents the services provided in the office control network:
service ServiceType Number
illumination _OnOff_light._sub._bc._udp 4
presence _occup_sensor._sub._bc._udp 1
temperature _temp_sensor._sub._bc._udp 1
shading _shade_control._sub._bc._udp 1
In DNS PTR records with as label the ServiceType have as value
service instance names. The unique Instance names identify the
service instances. In the example, the names contain id-x, with x in
natural numbers. The names are usually created at the factory floor
and somehow attached to the product. The ServiceTypes have been
suffixed with .04.b8 to represent office4 in building8. The same
suffix is used as PTR label to enemerate all instance of a given
service, or within a given domain.
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_OnOff_light._sub._bc._udp.04.b8 PTR id-1._OnOff_light
bc._udp.04.b8 PTR id-1._OnOff_light
04.b8 PTR id-1._OnOff_light
_OnOff_light._sub._bc._udp.04.b8 PTR id-2._OnOff_light
bc._udp.04.b8 PTR id-2._OnOff_light
04.b8 PTR id-2._OnOff_light
_OnOff_light._sub._bc._udp.04.b8 PTR id-3._OnOff_light
bc._udp.04.b8 PTR id-3._OnOff_light
04.b8 PTR id-3._OnOff_light
_OnOff_light._sub._bc._udp.04.b8 PTR id-4._OnOff_light
bc._udp.04.b8 PTR id-4._OnOff_light
04.b8 PTR id-4._OnOff_light
_occup_sensor._sub._bc._udp.04.b8 PTR id-5._occup_sensor
bc._udp.04.b8 PTR id-5._occup_sensor
04.b8 PTR id-5._occup_sensor
_temp_sensor._sub._bc._udp.04.b8 PTR id-6._temp_sensor
bc._udp.04.b8 PTR id-6._temp_sensor
04.b8 PTR id-6._temp_sensor
_shade_control._sub._bc._udp.04.b8 PTR id-7._temp_sensor
bc._udp.04.b8 PTR id-7._temp_sensor
04.b8 PTR id-7._temp_sensor
In the above example the id-x identifiers without the subtype suffix
would be discriminating enough.
Discovery can be done with the following results. A query with the
following argument returns
query argument result list
.04.8 id-1._OnOff_light
.......
id-7._temp_sensor
_bc._udp.04.b8 id-1._OnOff_light
.......
id-7._temp_sensor
_OnOff_light._sub._bc._udp.04.b8 id-1._OnOff_light
.......
id-4._OnOff_light
_occup_sensor._sub._bc._udp.04.b8 id-5._occup_sensor
When other offices are included in the database, the query argument
04.b8 selects those entries which are associated with office4 in
building8 and rejects any others. The example shows clearly the
query granularity that can be obtained and the care that must be
exercised when defining the names of the ServiceTypes.
The service instances (value of PTR records) are the labels of the
SRV, AAAA and TXT records describing the service instance. The SRV
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record specifies the location (authority) and the port number. In
the authority o4.b8 refers to office4 in building8. The AAAA record
specifies the IP-address, while the TXT record specifies the subtype
and the data representation of the legacy parser (if = ZigBee).
id-1._OnOff_light SRV light1.o4.b8.example.com Port-x
AAAA fdfd::1234
TXT if=ZigBee
id-2._OnOff_light SRV light2.o4.b8.example.com Port-x
AAAA fdfd::1235
TXT if=ZigBee
id-3._OnOff_light SRV light3.o4.b8.example.com Port-x
AAAA fdfd::1236
TXT if=ZigBee
id-4._OnOff_light SRV light4.o4.b8.example.com Port-x
AAAA fdfd::1237
TXT if=ZigBee
id-5._occup_sensor SRV occup.o4.b8.example.com Port-x
AAAA fdfd::1238
TXT if=ZigBee
id-6._temp_sensor SRV temp.o4.b8.example.com Port-x
AAAA fdfd::1239
TXT if=ZigBee
id-7._shade_control SRV shade.o4.b8.example.com Port-x
AAAA fdfd::1240
TXT if=ZigBee
It is possible that the temperature sensor and occupancy sensor are
delivered on one device. The consequence is that one device hosts
two services. In the DNS table the four lights and the shade
controller are unaffected. However, the PTR records with the
occupancy and temperature sensor point to the same unique identifier
id-8 that is suffixed with the name of the subtype. This example
shows that the subtype suffix is needed to discriminate between the
two service instances.
_occup_sensor._sub._bc._udp PTR id-8._occup_sensor
_temp_sensor._sub._bc._udp PTR id-8._temp_sensor
Two SRV records with accompanying AAAA and TXT records describe the
two servers, each providing one service, in more detail. The servers
share the same IP address but are connected to different ports, and
do have a different paths names. The TXT record is used to specify
the path part with "path=".
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id-8._occup_sensor SRV occup.o4.b8.example.com Port-x
AAAA fdfd::1241
TXT path=/os if=ZigBee
id-8._temp_sensor SRV temp.o4.b8.example.com Port-y
AAAA fdfd::1241
TXT path=/ts if=ZigBee
The path names /ts and /os are short names for temperature_sensor and
occupancy_sensor respectively. Not all multi-function devices will
use different ports for the individual functions. It is also quite
common to use different IP interfaces with different IP addresses,
reflected by the value of the AAAA records.
5.1. DNS group example
Another aspect is the grouping of servers. Where in the former
section the names of the services are standardized names, this is
less probable for the group names. Usually the group names are
application specific or are standardized at the manufacturer. For
example, assume that a group all-light.o4.b8.example.com is created
which contains all four lights inside office4. The accompanying
ServiceType can be defined as _all_light._sub._bc._udp. The
ServiceType suffixed with 04.b8 points to a unique identifier defined
as _all_light.04.b8, assuming that this is the only _all_light group
within office 4 of building 8. The PTR record looks like:
_all_light._sub._bc._udp.04.b8 PTR _all_light.04.b8
It is assumed that the group all_light.o4.b8.example.com has received
a multicast address: ff1e::148. The accompanying SRV, AAAA, and TXT
RR become:
_all_light.04.b8 SRV all_light.o4.b8.example.com Port-z
AAAA ff1e::148
TXT if=ZigBee
When a multicast message is sent to a group, the path of the accessed
resource must be strictly the same for all servers. The naming of
the path is typically a responsibility for the standardisation
organisations describing the command set for a given application
area. However a constraint exits in the case of mult-function
devices which host multiple resource of the same type. For example a
device with three lamps with corresponding onoff attributes can be
accessed via the three different paths:
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/light/1/onoff
/light/2/onoff
/light/3/onoff
A unique path to the onoff resource of all instances of light on this
device can be provided by /light/onoff. As this is logically the
path to a single instance on a mono-function device. The
corresponding unique paths for onoff to be used in the multicast
message becomes /light/onoff. The corresponding resource records for
a luminaire, named lm1, in DNS become:
_light._sub._bc._udp.04.b8 PTR _all_light.04.b8
_light._sub._bc._udp.04.b8 PTR _light_1.04.b8
_light._sub._bc._udp.04.b8 PTR _light_2.04.b8
_light._sub._bc._udp.04.b8 PTR _light_3.04.b8
_all_light.04.b8 SRV all_light.o4.b8.example.com Port-x
AAAA ff1e::148
TXT if=ZigBee path=/light
_light_1.04.b8 SRV lm1.o4.b8.example.com Port-z
AAAA fdfd::1234
TXT if=ZigBee path=/light/1
_light_2.04.b8 SRV lm1.o4.b8.example.com Port-z
AAAA fdfd::1234
TXT if=ZigBee path=/light/2
_light_3.04.b8 SRV lm1.o4.b8.example.com Port-z
AAAA fdfd::1234
TXT if=ZigBee path=/light/3
The entries in DNS can be used to form groups with the light weight
group management protocol and multicast listener discovery [RFC5790].
5.2. Operational use of DNS-SD
The populated DNS-SD server provides the necessary support for the
applications to execute their control loops with minimum operator
support. The operation of the office network can be split up in
phases. In a first phase the network is commissioned, such that a
relation is established between the IP address, the servicetype and
the domain. The servicetype can be extracted from the link-format as
described in [I-D.shelby-core-resource-directory]. After
commissioning this information is stored in the DNS-SD files. In a
second phase groups are formed and group names with their IP address
are stored in the DNS-SD files. The IP multicast addresses are
communicated to the members of the groups. In the third and final
phase, applications query DNS-SD to find the IP addresses of the
services within a given domain, and of the groups within a given
domain.
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In the home, a commissioning phase requiring the intervention of an
installer (a "truck roll") is to be avoided if possible. Here the
first phase consists of the booting up devices which insert their
services resources to a link-format directory. The information from
the resource directory can be inserted into DNS-SD or into xmDNS
[I-D.lynn-dnsext-site-mdns] when appropriate. In the second phase
remote controllers or other hand-held devices can be used to discover
the services of a given type, to group the services, and to store the
group names into DNS-SD or xmDNS as appropriate. Pointing out the
members of a group can be in any kind of manner from typing members
in, selecting them from a browser list, etc.
5.3. Commissioning CoAP devices
For clarity it is assumed in this section that a device hosts one
server. A device has received a unique device identifier at the
production plant. Given the authority naming presented in section
2.2 the authority name represents the location of the host within the
building.
Commissioning means the following three actions:
- Defining the URI (location)
- Assigning an IP address to the URI
- mapping the unique device identifier to the URI
Two cases of the office network are considered for commissioning: (1)
no 6LBR and no DNS server connected, and (2) a 6LBR connects the
office network to a DNS server.
When an architect has designed the building and described all light
points, ventilators, heating- and cooling units, and sensors, it is
necessary to identify all these devices spatially and functionally.
Storing the triple <Instance>.<ServiceType>.<Location> into DNS-SD
represents the commissioning process. The Instance is the unique
identifier given to the device in the factory but which has no
relation to its later location. The ServiceType together with the
Location represent the spatial and functional aspects of the device
as specified by the architect.
Design decision: A commissioning tool with access to the network is
used for the commissioning phase.
For example, dependent on used technology and production process, the
following situation (state) may exist in a host after physical
installation of the devices and before commissioning:
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- A given host is unaware of its Location.
- A given host knows its ServiceType and Instance. The Instance is
also readable by bar code reader.
- The commissioning tool knows all Locations to which hosts need to
be assigned.
- Each host has a (site-local) IP address.
Consider the commissioning process (1) with a central DNS-SD server
and (2) without a central server using xmDNS. The commissioning
processes described below are just examples and should not be taken
as working procedures for commissioning devices in a building.
5.3.1. DNS-SD server present
The installer reads with a bar code reader, attached to the
commissioning tool, the identifier of the device to commission. It
is assumed that the tool can learn the IP address of the device with
the given identifier. The tool displays on a screen the physical
lay-out of the devices within the building. The installer selects,
on the screen of the tool, the physical location of the chosen
device. From the designated physical location the tool creates the
URI of the selected device. The tool inserts the URI and the IP
address into the DNS server. For example the light with URI
light1.o4.b8.example.com is represented with an AAAA record:
light1.o4.b8.example.com AAAA fdfd::1234
The tool reads the service name and type from the device using
resource information stored according to the link-format
[I-D.ietf-core-link-format]. With this information the tool
constructs the PTR, SRV and TXT records according to the example
presented in section 5.
This is done for all devices within a given part of the building.
After the commissioning process, all resources of each device have an
URI and IP address which are stored in the central DNS-SD server.
When devices are restarted, the DHCP server may allocate new IP
addresses to the device and update the DNS server.
5.3.2. DNS-SD server not present
It is assumed that the building network is composed of independent
network segments (possibly a single site) such that each device on a
given segment can communicate directly with any other device on this
segment. The segments are not connected to a 6LBR and have no access
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to DNS or other servers. The installer knows these segments and has
a list of devices for a given segment. In the tool the installer
selects the names which belong to the given building segment. The
selected names are converted to site-local authorities and stored in
the tool. All devices are assumed to have selected a site-local IP
address. Assume that every device has a unique barcode within the
building and that the corresponding device knows the bar code number.
The installer reads with a bar code reader, attached to the tool, the
Instance name of the device to commission. The installer selects, on
the screen of the tool, the physical location of the chosen device.
The tool knows the authority of the selected device. The tool
broadcasts the bar code number and authority to all connected
devices. The device with the given barcode number, extends the
authority with the path name of the resources. For each resource,
the device multicasts the site-local IP-address and the site-local
URI to the xmDNS servers in the connected devices. This concludes
the commissioning of a network segment. All resources of each device
have a site-local URI and a site-local IP address which are stored in
the xmDNS servers.
5.4. Proxy discovery
Proxies will be used in CoAP networks for at least two major reasons:
(1) http/coap proxy, and (2) proxy of service on battery-less device.
The first proxy is probably implemented as forward proxy, while the
latter is probably implemented as backward proxy. The battery-less
device will at rare occasions (when it is not sleeping) and during
installation answer the GET /.well-known/core request. The return
data are used by the installation tool to make the proxy device
return the same resource names on /.well-known/core as is returned by
the sleeping device. An installation tool installs on the proxy all
the resources of the sleeping device for which the proxy is assumed
to answer. Consequently, the proxy is discovered as a multi-server
host with as many path names as it proxies sleeping servers. The
servers on sleeping devices should not be discoverable via DNS-SD.
However, AAAA records are generated for the sleeping device host
name. This host name is used by the proxy to subscribe to the
"sporadic" services of the sleeping device. For example assume two
sleeping devices, an occupancy sensor and a temperature sensor, and
one proxy. Two service types are defined with PTR records in DNS-SD.
The identifier id-1 of the proxy is used by the installation tool to
define the Instances.
_occup_sensor._sub._bc._udp.04.b8 PTR id-1._occup_sensor
_temp_sensor._sub._bc._udp.04.b8 PTR id-1._temp_sensor
Two SRV records with accompanying AAAA and TXT records describe the
two services in more detail. The services share the same IP address,
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are connected to the same port, but do have different paths names.
The TXT record is used to specify the path part with "path=".
id-1._occup_sensor SRV proxy.o4.b8.example.com Port-x
AAAA fdfd:: 1241
TXT path=/os if=ZigBee
id-1._temp_sensor SRV proxy.o4.b8.example.com Port-x
AAAA fdfd:: 1241
TXT path=/ts if=ZigBee
sl-ts.o4.b8.example.com AAAA fdfd::1242
sl-os.o4.b8.example.com AAAA fdfd::1243
The path names /ts and /os are short names for temperature_sensor and
occupancy_sensor respectively and were taken over from link-format
information contained in the sleeping devices. Two AAAA records are
provided for the two sleeping devices. The proxy has used the domain
names of the sleeping devices to subscribe to the publications of the
two sleeping devices.
It is important to remark that there are now two services with the
same resources present on two different devices: the sleeping device
and its proxy. When a host invokes the /.well-known/core resource,
it should be possible to distinguish between the proxy (to be
invoked) and the sleeping device (not to be invoked). The
distinction is necessary once the sleeping device is discoverable and
the sleeping device is awake from time to time. It is suggested that
the link-format syntax allows to make this distinction.
6. Legacy data Representations in CoAP
Before CoAP devices can come to market, manufacturers must agree that
the type and resources of the device can be interpreted according to
some generally recognized syntax. At this moment no such generally
recognized syntax exists for CoAP devices. We do not expect an IETF
working group to standardize such a syntax, and we are convinced that
syntax standardization is the responsibility of industry standards
organizations. Given the long history of building control, many
groups have defined a data representation for building control
devices for example BACnet, ZigBee, oBIX, LON, KNX, and many others.
It is our belief that new representations will be defined and must
coexist with the named legacy ones.
The CoAP protocol should transport any data representation, and
certainly the legacy ones.It is expected that a CoAP client can
handle one or more legacy representation. Given that a CoAP client
can handle representation of standard XXX, this I-D proposes that
such a CoAP device can communicate with legacy devices via a CoAP/
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legacy gateway (router).
6.1. Network architectures
+------+ +------+ +------+
| yyy | | zzz | | zzz |
| link | | CoAP | | CoAP |
+------+ +------+ +------+
| +---------+
|---------| CoAP |-->
| | gateway |
+------+ +---------+ +-----------+
| yyy | | zzz ; yyy |
| link | | CoAP |
+------+ +-----------+
Figure 1: network with multiple representation standards
Figure 1 represents the network architecture which is expected for
the purpose of this I-D. The CoAP gateway connects one link with two
legacy devices -containing legacy data representation "yyy"- with the
wireless CoAP network composed of three CoAP hosts. Two CoAP hosts
contain the CoAP stack with a zzz representation and one host
contains the CoAP stack with a zzz and an yyy representation. The
yyy hosts can freely communicate according to the yyy link protocol
over the yyy link. The zzz CoAP hosts, including the zzz;yyy host
can freely exchange zzz data representations according to the CoAP
protocol over the wireless 6LoWPAN network. The zzz;yyy host can
send yyy data representations to the CoAP gateway which passes them
on to the specified yyy legacy host. The yyy legacy device returns
data to the requesting zzz;yyy CoAP host via the same gateway.
The CoAP hosts can address the legacy devices behind the gateway in
at least 4 ways.
- All devices of legacy network YYY share the URI with the CoAP
gateway. Every legacy device is a resource for the gateway as
seen from the CoAP host. Consequently, the CoAP host sends the
message to the IP address of the gateway and the gateway parses
the URI-Path to determine the specified legacy device.
- All devices of legacy network YYY have IP addresses different from
the IP address of the gateway. Consequently, a CoAP host sends
the message to the IP address of the specified device. The
routing protocol on the CoAP network makes the message arrive at
the CoAP gateway. The gateway determines the specified legacy
device from the destination IP address.
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- All devices of legacy network YYY have different authorities. The
authorities of the legacy device resolve to an IP address of the
gateway. This means that the possibly lengthy authority names
need to be transmitted. The gateway recognizes the authorities
and maps authority to legacy device.
- All devices of legacy network YYY have different ports. This can
be expressed in two ways (1) as :port in the URI, or (2) in the
DNS-SD records. In the latter case the port is defined in the UDP
header and is efficient in packet header size.
The major advantage of all four approaches is that the gateway only
handles the URI or IP address and port number to select the
destination legacy device independent of the type of legacy device
and the contents of the legacy payload of the message. In Figure 1
the gateway connects to a single link. For example, this would be
the case for DALI standard. Other legacy standards, like BACnet,
LON, allow networks composed of multiple links.
An example of an invocation of a ZZZ service (See figure 2). The
resource path /ZZZ identifies the parser of the ZZZ syntax. A 12
octet string completely describes the ZZZ command. The host is
completely identified by the authority in the URI. The ZZZ parser on
the host is identified by the port number in the UDP header (not
shown).
Client CoAP/ZZZ
| device
| REQUEST |
|-------- CON [0x5577] PUT /ZZZ -------->|
| binary 12 octet string |
| |
| RESPONSE |
|<---------- ACK [0x5577] 2.00 OK ----------------- |
| |
Figure 2: Sending a ZZZ command with CoAP to CoAP/ZZZ device
An example of an invocation of a DALI legacy device behind a gateway
is given in figure 3. The resource path /DALI identifies the DALI
parser. The application sets a value of 200 in the DALI device in
the resource 256 defined by the DALI spec.
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Client DALI/CoAP
| gateway
| REQUEST |
|------- CON [0x5577] PUT /DALI -------->|
| binary 16 bit payload dt*256 + 200 |
| |
| RESPONSE |
|<---------- ACK [0x5577] 2.00 OK ----------------- |
| |
Figure 3: Sending a DALI setting with CoAP to CoAP/DALI gateway
6.2. Discovery of legacy gateways
Discovery of legacy gateways is not very different from discovery of
proxies in section 5.4. the consequences for discovery are listed for
the four modes of addressing legacy devices via a gateway of section
6.1.
- The gateway presents a list of resources representing the legacy
devices. Discovery is done as for other CoAP devices.
- Each legacy device has a different IP address. The gateway must
create entries in the DNS for as many legacy devices. The
authority of the legacy device is the authority of the gateway
with a ServiceType to be specified by the gateway.
- All devices of legacy network YYY have different authorities. In
this case each legacy device has the same IP address as the
gateway. The gateway must create entries in the DNS for as many
legacy devices.
- All devices of legacy network YYY have different ports. The
gateway must create entries in the DNS for as many legacy devices.
Each entry has the authority of the gateway with a different
ServiceType and a different port number.
7. 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
naming can be used to express this hierarchy in the authority portion
of the URI, down to the group or device 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).
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The authority portion of the URI is resolved by the client, using
conventional DNS, into the unicast or multicast IP address of the
targeted device(s). Taking advantage of the CoAP design
[I-D.ietf-core-coap], the URI-Host 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 URI to distinguish between resources on a given device,
resulting in very compact identifiers.
DNS-SD [I-D.cheshire-dnsext-dns-sd] can be used to scale up service
discovery beyond the 6LoWPAN. 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 device, locate CoAP devices by
subtype, or bind service names for particular CoAP URIs.
This I-D discusses the addressing, discovery and naming of legacy
devices behind gateways. The discovery of backward proxies of
sleeping devices is handled in a similar fashion.
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.
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. Entering ServiceTypes particular to a given standard
necessitates that the standardization body declares the ServiceType
to dns.org.
8. 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 devices. The CoRE security
analysis must be broadened to include multicast scenarios.
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9. IANA considerations
This I-D proposes that associations which standardize device
representations (like BACnet, ZigBee, DALI,...) contact IANA to
reserve the prefix /.well-known/XXX for the standard XXX.
10. 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, Anders
Brandt, Matthieu Vial, Jerome Hamel, George Yianni, and Nicolas Riou.
11. Changelog
From bc-01 to bc-02
- 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.
From bc-02 to bc-03
- Elaboration on gateways, commissioning and legacy networks.
- Recommendation to extend DNS-SD naming with sn, st, and ss
attributes.
From bc-03 to bc-04
- moved core link extension sub-section to discovery mapping draft
- extended use of service type
- gave DNS record examples and worked out multifunction device
- added proxy discovery and legacy gateway discovery
- defined path tree and corresponding schema
- reviewed definition of group, device, server, service (interface),
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resopurce, and attribute.
From bc-04 to bc-05
- extended and corrected examples for multi-function devicesw
- syntax more compatible with other resource discovery I-Ds
- abstract adapted
- more stringent use of the words server, end point, service and
devices
12. References
12.1. Normative References
[RFC1034] Mockapetris, P., "Domain names - concepts and facilities",
STD 13, RFC 1034, November 1987.
[RFC1123] Braden, R., "Requirements for Internet Hosts - Application
and Support", STD 3, RFC 1123, October 1989.
[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.
[RFC3629] Yergeau, F., "UTF-8, a transformation format of ISO
10646", STD 63, RFC 3629, November 2003.
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[RFC3956] Savola, P. and B. Haberman, "Embedding the Rendezvous
Point (RP) Address in an IPv6 Multicast Address",
RFC 3956, November 2004.
[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.
[RFC5198] Klensin, J. and M. Padlipsky, "Unicode Format for Network
Interchange", RFC 5198, March 2008.
[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.
12.2. Informative References
[I-D.cheshire-dnsext-dns-sd]
Cheshire, S. and M. Krochmal, "DNS-Based Service
Discovery", draft-cheshire-dnsext-dns-sd-10 (work in
progress), February 2011.
[I-D.cheshire-dnsext-multicastdns]
Cheshire, S. and M. Krochmal, "Multicast DNS",
draft-cheshire-dnsext-multicastdns-14 (work in progress),
February 2011.
[I-D.ietf-core-coap]
Shelby, Z., Hartke, K., Bormann, C., and B. Frank,
"Constrained Application Protocol (CoAP)",
draft-ietf-core-coap-07 (work in progress), July 2011.
[I-D.ietf-core-link-format]
Shelby, Z., "CoRE Link Format",
draft-ietf-core-link-format-07 (work in progress),
July 2011.
[I-D.martocci-6lowapp-building-applications]
Martocci, J., Schoofs, A., and P. Stok, "Commercial
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Building Applications Requirements",
draft-martocci-6lowapp-building-applications-01 (work in
progress), July 2010.
[I-D.rahman-core-groupcomm]
Rahman, A. and E. Dijk, "Group Communication for CoAP",
draft-rahman-core-groupcomm-07 (work in progress),
October 2011.
[I-D.shelby-core-resource-directory]
Shelby, Z. and S. Krco, "CoRE Resource Directory",
draft-shelby-core-resource-directory-01 (work in
progress), September 2011.
[I-D.lynn-core-discovery-mapping]
Lynn, K. and Z. Shelby, "CoRE Link-Format to DNS-Based
Service Discovery Mapping",
draft-lynn-core-discovery-mapping-01 (work in progress),
July 2011.
[I-D.lynn-dnsext-site-mdns]
Lynn, K. and D. Sturek, "Extended Multicast DNS",
draft-lynn-dnsext-site-mdns-01 (work in progress),
March 2011.
[BACnet] Bender, J. and M. Newman, "BACnet/IP",
Web http://www.bacnet.org/Tutorial/BACnetIP/index.html,
2000.
[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
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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>.
[HAYSTACK]
"Project Haystack", Web http://project-haystack.org/,
2011.
[oBIX] Frank, B., Ed., "oBIX working group",
Web http://www.obix.org, 2006.
[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.
[ZigBee-IP]
"ZigBee Smart Energy Profile 2.0 Application Protocol
Specification", Draft ZigBee-11167, March 2011.
[dns-sd] "dns-sd servicetype registration",
Web http://www.dns-sd.org/ServiceTypes.html, 2011.
Authors' Addresses
Peter van der Stok
Philips Research
High Tech Campus 34-1
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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