Internet Architecture Board (IAB) H. Tschofenig

Internet Architecture Board (IAB) H. Tschofenig
Request for Comments: 7452 ARM Ltd.
Category: Informational J. Arkko
ISSN: 2070-1721 D. Thaler
D. McPherson
March 2015

Architectural Considerations in Smart Object Networking

Abstract

The term "Internet of Things" (IoT) denotes a trend where a large
number of embedded devices employ communication services offered by
Internet protocols. Many of these devices, often called "smart
objects", are not directly operated by humans but exist as components
in buildings or vehicles, or are spread out in the environment.
Following the theme "Everything that can be connected will be
connected", engineers and researchers designing smart object networks
need to decide how to achieve this in practice.

This document offers guidance to engineers designing Internet-
connected smart objects.

Status of This Memo

This document is not an Internet Standards Track specification; it is
published for informational purposes.

This document is a product of the Internet Architecture Board (IAB)
and represents information that the IAB has deemed valuable to
provide for permanent record. It represents the consensus of the
Internet Architecture Board (IAB). Documents approved for
publication by the IAB are not a candidate for any level of Internet
Standard; see Section 2 of RFC 5741.

Information about the current status of this document, any errata,
and how to provide feedback on it may be obtained at
http://www.rfc-editor.org/info/rfc7452.

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Copyright Notice

Copyright (c) 2015 IETF Trust and the persons identified as the
document authors. All rights reserved.

This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect
to this document.

Table of Contents

1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Smart Object Communication Patterns . . . . . . . . . . . . . 4
2.1. Device-to-Device Communication Pattern . . . . . . . . . 4
2.2. Device-to-Cloud Communication Pattern . . . . . . . . . . 6
2.3. Device-to-Gateway Communication Pattern . . . . . . . . . 7
2.4. Back-End Data Sharing Pattern . . . . . . . . . . . . . . 9
3. Reuse Internet Protocols . . . . . . . . . . . . . . . . . . 10
4. The Deployed Internet Matters . . . . . . . . . . . . . . . . 13
5. Design for Change . . . . . . . . . . . . . . . . . . . . . . 14
6. Security Considerations . . . . . . . . . . . . . . . . . . . 16
7. Privacy Considerations . . . . . . . . . . . . . . . . . . . 18
8. Informative References . . . . . . . . . . . . . . . . . . . 19
Appendix A. IAB Members at the Time of Approval . . . . . . . . 23
Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . 23
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 24

1. Introduction

RFC 6574 [RFC6574] refers to smart objects as devices with
constraints on energy, bandwidth, memory, size, cost, etc. This is a
fuzzy definition, as there is clearly a continuum in device
capabilities and there is no hard line to draw between devices that
can run Internet protocols and those that can't.

Interconnecting smart objects with the Internet enables exciting new
use cases and products. An increasing number of products put the
Internet Protocol Suite on smaller and smaller devices and offer the
ability to process, visualize, and gain insight from the collected
sensor data. The network effect can be increased if the data
collected from many different devices can be combined.

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Developing embedded systems is a complex task, and designers must
make a number of design decisions such as:

o How long is the device designed to operate?

o How does it interact with the physical world? Is it a sensor or
actuator or both?

o How many "owners" does it have? One? Many? Is the owner likely
to change over the lifetime of the device?

o Is it continuously or intermittently powered? Does it sleep?

o Is it connected to a network, and if so, how?

o Will it be physically accessible for direct maintenance after
deployment? How does that affect the security model?

While developing embedded systems is itself a complex task, designing
Internet-connected smart objects is even harder since it requires
expertise with Internet protocols in addition to software programming
and hardware skills. To simplify the development task, and thereby
to lower the cost of developing new products and prototypes, we
believe that reuse of prior work is essential. Therefore, we provide
high-level guidance on the use of Internet technology for the
development of smart objects, and connected systems in general.

Utilize Existing Design Patterns

Design patterns are generally reusable solutions to a commonly
occurring design problem (see [Gamma] for more discussion).
Existing smart object deployments show communication patterns that
can be reused by engineers with the benefit of lowering the design
effort. As discussed in the sections below, individual patterns
also have an implication on the required interoperability between
the different entities. Depending on the desired functionality,
already-existing patterns can be reused and adjusted. Section 2
talks about various communication patterns.

Reuse Internet Protocols

Most smart object deployments can make use of the already-
standardized Internet Protocol Suite. Internet protocols can be
applied to almost any environment due to their generic design and
typically offer plenty of potential for reconfiguration, which
allows them to be tailored for the specific needs. Section 3
discusses this topic.

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The Deployed Internet Matters

When connecting smart objects to the Internet, take existing
deployment into consideration to avoid unpleasant surprises.
Assuming an ideal, clean-slate deployment is, in many cases, far
too optimistic since the already-deployed infrastructure is
convenient to use. In Section 4, we highlight the importance of
this topic.

Design for Change

The Internet infrastructure, applications, and preferred building
blocks evolve over time. Especially long-lived smart object
deployments need to take this change into account, and Section 5
is dedicated to that topic.

2. Smart Object Communication Patterns

This section illustrates a number of communication patterns utilized
in the smart object environment. It is possible that more than one
pattern can be applied at the same time in a product. Developers
reusing those patterns will benefit from the experience of others as
well as from documentation, source code, and available products.

2.1. Device-to-Device Communication Pattern

Figure 1 illustrates a communication pattern where two devices
developed by different manufacturers are desired to interoperate and
communicate directly. To pick an example from [RFC6574], consider a
light switch that talks to a light bulb with the requirement that
each may be manufactured by a different company, represented as
Manufacturer A and B. Other cases can be found with fitness
equipment, such as heart rate monitors and cadence sensors.

_,,,, ,,,,
/ -'`` \
| Wireless |
\ Network |
/ \
,''''''''| / . ,''''''''|
| Light | ------|------------------\------| Light |
| Bulb | . | | Switch |
|........' `'- / |........'
\ _-...-`
Manufacturer `. ,.' Manufacturer
A ` B

Figure 1: Device-to-Device Communication Pattern

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In order to fulfill the promise that devices from different
manufacturers are able to communicate out of the box, these vendors
need to agree on the protocol stack. They need to make decisions
about the following protocol-design aspects:

o Which physical layer(s) should be supported? Does it use low-
power radio technologies (e.g., Bluetooth Smart, IEEE 802.15.4)?

o Can devices be IPv6-only, or must they also support IPv4 for
backward-compatibility reasons? What IPv4-IPv6 transition
technologies are needed?

o Which IP address configuration mechanism(s) is integrated into the
device?

o Which communication architectures shall be supported? Which
devices are constrained, and what are those constraints? Is there
a classical client-server model or rather a peer-to-peer model?

o Is there a need for a service-discovery mechanism to allow users
to discover light bulbs they have in their home or office?

o Which transport-layer protocol (e.g., UDP) is used for conveying
the sensor readings/commands?

o Which application-layer protocol is used (for example, the
Constrained Application Protocol (CoAP) [RFC7252])?

o What information model is used for expressing the different light
levels?

o What data model is used to encode information? (See [RFC3444] for
a discussion about the difference between data models and
information models.)

o Finally, security and privacy require careful thought. This
includes questions like: What are the security threats? What
security services need to be provided to deal with the identified
threats? Where do the security credentials come from? At what
layer(s) in the protocol stack should the security mechanism(s)
reside? What privacy implications are caused by various design
decisions?

This list is not meant to be exhaustive but aims to illustrate that
for every usage scenario, many design decisions will have to be made
in order to accommodate the constrained nature of a specific device
in a certain usage scenario. Standardizing such a complete solution

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to accomplish a full level of interoperability between two devices
manufactured by different vendors takes time, but there are obvious
rewards for end customers and vendors.

2.2. Device-to-Cloud Communication Pattern

Figure 2 shows a communication pattern for uploading sensor data to
an application service provider. Often the application service
provider (example.com in our illustration) also sells smart objects.
In that case, the entire communication happens internal to the
provider and no need for interoperability arises. Still, it is
useful for example.com to reuse existing specifications to lower the
design, implementation, testing, and development effort.

While this pattern allows using IP-based communication end to end, it
may still lead to silos. To prevent silos, example.com may allow
third-party device vendors to connect to their server infrastructure
as well. For those cases, the protocol interface used to communicate
with the server infrastructure needs to be made available, and
various standards are available, such as CoAP, Datagram Transport
Layer Security (DTLS) [RFC6347], UDP, IP, etc., as shown in Figure 2.
A frequent concern from end users is that a change in the business
model (or bankruptcy) of the IoT device/service provide might make
the hardware become unusable. Companies might consider the
possibility of releasing their source code for the IoT device or
allowing other IoT operating systems (plus application software) to
be installed on the IoT device.

Similarly, in many situations it is desirable to change which cloud
service a device connects to, such as when an application service
provider changes its hosting provider. Again, standard Internet
protocols are needed.

Since the access networks to which various smart objects are
connected are typically not under the control of the application
service provider, commonly used radio technologies (such as WLAN,
wired Ethernet, and cellular radio) together with the network access
authentication technology have to be reused. The same applies to
standards used for IP address configuration.

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.................
| Application |
| Service |
| Provider |
| example.com |
|_______________|
_, .
HTTP ,' `. CoAP
TLS _,' `. DTLS
TCP ,' `._ UDP
IP -' - IP
,'''''''''''''| ,'''''''''''''''''|
| Device with | | Device with |
| Temperature | | Carbon Monoxide |
| Sensor | | Sensor |
|.............' |.................'

TLS = Transport Layer Security

Figure 2: Device-to-Cloud Communication Pattern

2.3. Device-to-Gateway Communication Pattern

The device-to-cloud communication pattern, described in Section 2.2,
is convenient for vendors of smart objects and works well if they
choose a radio technology that is widely deployed in the targeted
market, such as Wi-Fi based on IEEE 802.11 for smart home use cases.
Sometimes, less-widely-available radio technologies are needed (such
as IEEE 802.15.4) or special application-layer functionality (e.g.,
local authentication and authorization) has to be provided or
interoperability is needed with legacy, non-IP-based devices. In
those cases, some form of gateway has to be introduced into the
communication architecture that bridges between the different
technologies and performs other networking and security
functionality. Figure 3 shows this pattern graphically. Often,
these gateways are provided by the same vendor that offers the IoT
product, for example, because of the use of proprietary protocols, to
lower the dependency on other vendors or to avoid potential
interoperability problems. It is expected that in the future, more
generic gateways will be deployed to lower cost and infrastructure
complexity for end consumers, enterprises, and industrial
environments. Such generic gateways are more likely to exist if IoT
device designs make use of generic Internet protocols and not require
application-layer gateways that translate one application-layer
protocol to another one. The use of application-layer gateways will,
in general, lead to a more fragile deployment, as has been observed
in the past with [RFC3724] and [RFC3238].

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This communication pattern can frequently be found with smart object
deployments that require remote configuration capabilities and real-
time interactions. The gateway is thereby assumed to be always
connected to the Internet.

.................
| Application |
| Service |
| Provider |
| example.com |
|_______________|
|
|
| IPv4/IPv6
.................
| Local |
| Gateway |
| |
|_______________|
_, .
HTTP ,' `. CoAP
TLS _,' Bluetooth Smart `. DTLS
TCP ,' IEEE 802.11 `._ UDP
IPv6 -' IEEE 802.15.4 - IPv6
,'''''''''''''| ,'''''''''''''''''|
| Device with | | Device with |
| Temperature | | Carbon Monoxide |
| Sensor | | Sensor |
|.............' |.................'

Figure 3: Device-to-Gateway Communication Pattern

If the gateway is mobile, such as when the gateway is a smartphone,
connectivity between the devices and the Internet may be
intermittent. This limits the applicability of such a communication
pattern but is nevertheless very common with wearables and other IoT
devices that do not need always-on Internet or real-time Internet
connectivity. From an interoperability point of view, it is worth
noting that smartphones, with their sophisticated software update
mechanism via app stores, allow new functionality to be updated
regularly at the smartphone and sometimes even at the IoT device.
With special apps that are tailored to each specific IoT device,
interoperability is mainly a concern with regard to the lower layers
of the protocol stack, such as the radio interface, and less so at
the application layer (if users are willing to download a new app for
each IoT device).

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It is also worth pointing out that a gateway allows supporting both
IPv6 and IPv4 (for compatibility with legacy application service
providers) externally, while allowing devices to be IPv6-only to
reduce footprint requirements. If devices do not have the resources
to support both IPv4 and IPv6 themselves, being IPv6-only (rather
than IPv4-only) with a gateway enables the most flexibility, avoiding
the need to update devices to support IPv6 later, whereas IPv4
address exhaustion makes it ill-suited to scale to smart object
networks. See [RFC6540] for further discussion.

2.4. Back-End Data Sharing Pattern

The device-to-cloud pattern often leads to silos; IoT devices upload
data only to a single application service provider. However, users
often demand the ability to export and to analyze data in combination
with data from other sources. Hence, the desire for granting access
to the uploaded sensor data to third parties arises. This design is
shown in Figure 4. This pattern is known from the Web in case of
mashups and is, therefore, reapplied to the smart object context. To
offer familiarity for developers, typically a RESTful API design in
combination with a federated authentication and authorization
technology (like OAuth 2.0 [RFC6749]) is reused. While this offers
reuse at the level of building blocks, the entire protocol stack
(including the information/data model and RESTful Web APIs) is often
not standardized.

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.................
| Application |
.| Service |
,-` | Provider |
.` | b-example.com |
,-` |_______________|
.`
................. ,-`
| Application |-` HTTPS
| Service | OAuth 2.0
| Provider | JSON
| example.com |-,
|_______________| '.
_, `',
,' '.
_,' CoAP or `', .................
,' HTTP '. | Application |
-' `'| Service |
,''''''''| | Provider |
| Light | | c-example.com |
| Sensor | |_______________|
|........'

Figure 4: Back-End Data Sharing Pattern

3. Reuse Internet Protocols

When discussing the need for reuse of available standards versus
extending or redesigning protocols, it is useful to look back at the
criteria for success of the Internet.

RFC 1958 [RFC1958] provides lessons from the early days of the
Internet and says:

The Internet and its architecture have grown in evolutionary
fashion from modest beginnings, rather than from a Grand Plan.

And adds:

A good analogy for the development of the Internet is that of
constantly renewing the individual streets and buildings of a
city, rather than razing the city and rebuilding it.

Yet, because building very small, battery-powered devices is
challenging, it may be difficult to resist the temptation to build
solutions tailored to specific applications, or even to redesign
networks from scratch to suit a particular application.

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While developing consensus-based standards in an open and transparent
process takes longer than developing proprietary solutions, the
resulting solutions often remain relevant over a longer period of
time.

RFC 1263 [RFC1263] considers protocol-design strategy and the
decision to design new protocols or to use existing protocols in a
non-backward compatible way:

We hope to be able to design and distribute protocols in less time
than it takes a standards committee to agree on an acceptable
meeting time. This is inevitable because the basic problem with
networking is the standardization process. Over the last several
years, there has been a push in the research community for
lightweight protocols, when in fact what is needed are lightweight
standards. Also note that we have not proposed to implement some
entirely new set of 'superior' communications protocols, we have
simply proposed a system for making necessary changes to the
existing protocol suites fast enough to keep up with the
underlying change in the network. In fact, the first standards
organization that realizes that the primary impediment to
standardization is poor logistical support will probably win.

While [RFC1263] was written in 1991 when the standardization process
was more lightweight than today, these thoughts remain relevant in
smart object development.

Interestingly, a large number of already-standardized protocols are
relevant for smart object deployments. RFC 6272 [RFC6272], for
example, made the attempt to identify relevant IETF specifications
for use in smart grids.

Still, many commercial products contain proprietary or industry-
specific protocol mechanisms, and researchers have made several
attempts to design new architectures for the entire Internet system.
There are several architectural concerns that deserve to be
highlighted:

Vertical Profiles

The discussions at the IAB workshop (see Section 3.1.2 of
[RFC6574]) revealed the preference of many participants to develop
domain-specific profiles that select a minimum subset of protocols
needed for a specific operating environment. Various
standardization organizations and industry fora are currently
engaged in activities of defining their preferred profile(s).

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Ultimately, however, the number of domains where smart objects can
be used is essentially unbounded. There is also an ever-evolving
set of protocols and protocol extensions.

However, merely changing the networking protocol to IP does not
necessarily bring the kinds of benefits that industries are
looking for in their evolving smart object deployments. In
particular, a profile is rigid and leaves little room for
interoperability among slightly differing or competing technology
variations. As an example, Layer 1 through 7 type profiles do not
account for the possibility that some devices may use different
physical media than others, and that in such situations, a simple
router could still provide an ability to communicate between the
parties.

Industry-Specific Solutions

The Internet Protocol Suite is more extensive than merely the use
of IP. Often, significant benefits can be gained from using
additional, widely available, generic technologies, such as the
Web. Benefits from using these kinds of tools include access to a
large available workforce, software, and education already geared
towards employing the technology.

Tight Coupling

Many applications are built around a specific set of servers,
devices, and users. However, often the same data and devices
could be useful for many purposes, some of which may not be easily
identifiable at the time the devices are deployed.

In addition to the architectural concerns, developing new protocols
and mechanisms is generally more risky and expensive than reusing
existing standards, due to the additional costs involved in design,
implementation, testing, and deployment. Secondary costs, such as
the training of technical staff and, in the worst case, the training
of end users, can be substantial.

As a result, while there are some cases where specific solutions are
needed, the benefits of general-purpose technology are often
compelling, be it choosing IP over some more specific communication
mechanism, a widely deployed link layer (such as wireless LAN) over a
more specific one, web technology over application-specific
protocols, and so on.

However, when employing these technologies, it is important to
embrace them in their entirety, allowing for the architectural
flexibility that is built into them. As an example, it rarely makes

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sense to limit communications to on-link or to specific media.
Design your applications so that the participating devices can easily
interact with multiple other applications.

4. The Deployed Internet Matters

Despite the applicability of Internet protocols for smart objects,
picking the specific protocols for a particular use case can be
tricky. As the Internet has evolved, certain protocols and protocol
extensions have become the norm, and others have become difficult to
use in all circumstances.

Taking into account these constraints is particularly important for
smart objects, as there is often a desire to employ specific features
to support smart object communication. For instance, from a pure
protocol-specification perspective, some transport protocols may be
more desirable than others. These constraints apply both to the use
of existing protocols as well as designing new ones on top of the
Internet protocol stack.

The following list illustrates a few of those constraints, but every
communication protocol comes with its own challenges.

In 2005, Fonseca, et al. [IPoptions] studied the usage of IP
options-enabled packets in the Internet and found that overall,
approximately half of Internet paths drop packets with options,
making extensions using IP options "less ideal" for extending IP.

In 2010, Honda, et al. [HomeGateway] tested 34 different home
gateways regarding their packet dropping policy of UDP, TCP, the
Datagram Congestion Control Protocol (DCCP), the Stream Control
Transmission Protocol (SCTP), ICMP, and various timeout behavior.
For example, more than half of the tested devices do not conform to
the IETF-recommended timeouts for UDP, and for TCP the measured
timeouts are highly variable, ranging from less than 4 minutes to
longer than 25 hours. For NAT traversal of DCCP and SCTP, the
situation is poor. None of the tested devices, for example, allowed
establishing a DCCP connection.

In 2011, the behavior of networks with regard to various TCP
extensions was tested in [TCPextensions]: "From our results we
conclude that the middleboxes implementing layer 4 functionality are
very common -- at least 25% of paths interfered with TCP in some way
beyond basic firewalling."

Extending protocols to fulfill new uses and to add new functionality
may range from very easy to difficult, as [RFC6709] explains in great
detail. A challenge many protocol designers are facing is to ensure

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incremental deployability and interoperability with incumbent
elements in a number of areas. In various cases, the effort it takes
to design incrementally deployable protocols has not been taken
seriously enough at the outset. RFC 5218 on "What Makes For a
Successful Protocol" [RFC5218] defines wildly successful protocols as
protocols that are widely deployed beyond their envisioned use cases.

As these examples illustrate, protocol architects have to take
developments in the greater Internet into account, as not all
features can be expected to be usable in all environments. For
instance, middleboxes [RFC3234] complicate the use of extensions in
basic IP protocols and transport layers.

RFC 1958 [RFC1958] considers this aspect and says "... the community
believes that the goal is connectivity, the tool is the Internet
Protocol, and the intelligence is end to end rather than hidden in
the network." This statement is challenged more than ever with the
perceived need to develop intermediaries interacting with less
intelligent end devices. However, RFC 3724 [RFC3724] has this to say
about this crucial aspect: "One desirable consequence of the
end-to-end principle is protection of innovation. Requiring
modification in the network in order to deploy new services is still
typically more difficult than modifying end nodes." Even this
statement will become challenged, as large numbers of devices are
deployed, and it indeed might be the case that changing those devices
will be hard. But RFC 4924 [RFC4924] adds that a network that does
not filter or transform the data that it carries may be said to be
"transparent" or "oblivious" to the content of packets. Networks
that provide oblivious transport enable the deployment of new
services without requiring changes to the core. It is this
flexibility that is perhaps both the Internet's most essential
characteristic as well as one of the most important contributors to
its success.

5. Design for Change

How to embrace rapid innovation and at the same time accomplish a
high level of interoperability is one of the key aspects for
competing in the marketplace. RFC 1263 [RFC1263] points out that
"protocol change happens and is currently happening at a very
respectable clip...We simply propose [for engineers developing the
technology] to explicitly deal with the changes rather [than] keep
trying to hold back the flood."

In [Tussles], Clark, et al. suggest to "design for variation in
outcome, so that the outcome can be different in different places,
and the tussle takes place within the design, not by distorting or
violating it. Do not design so as to dictate the outcome. Rigid

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designs will be broken; designs that permit variation will flex under
pressure and survive." The term "tussle" refers to the process
whereby different parties, which are part of the Internet milieu and
have interests that may be adverse to each other, adapt their mix of
mechanisms to try to achieve their conflicting goals, and others
respond by adapting the mechanisms to push back.

In order to accomplish this, Clark, et al. suggest to:

1. Break complex systems into modular parts, so that one tussle does
not spill over and distort unrelated issues.

2. Design for choice to permit the different players to express
their preferences. Choice often requires open interfaces.

The main challenge with the suggested approach is predicting how
conflicts among the different players will evolve. Since tussles
evolve over time, there will be changes to the architecture, too. It
is certainly difficult to pick the right set of building blocks and
to develop a communication architecture that will last a long time,
and many smart object deployments are envisioned to be rather long
lived.

Luckily, the design of the system does not need to be cast in stone
during the design phase. It may adjust dynamically since many of the
protocols allow for configurability and dynamic discovery. But,
ultimately, software update mechanisms may provide the flexibility
needed to deal with more substantial changes.

A solid software update mechanism is needed not only for dealing with
the changing Internet communication environment and for
interoperability improvements but also for adding new features and
for fixing security bugs. This approach may appear to be in conflict
with classes of severely restricted devices since, in addition to a
software update mechanism, spare flash and RAM capacity is needed.
It is, however, a trade-off worth thinking about since better product
support comes with a price.

As technology keeps advancing, the constraints that technology places
on devices evolve as well. Microelectronics have become more capable
as time goes by, often making it possible for new devices to be both
less expensive and more capable than their predecessors. This trend
can, however, be in some cases offset by the desire to embed
communications technology in even smaller and cheaper objects. But
it is important to design communications technology not just for
today's constraints but also for tomorrow's. This is particularly
important since the cost of a product is not only determined by the

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cost of hardware but also by the cost of not reusing already-
available protocol stacks and software libraries by developing custom
solutions.

Software updates are common in operating systems and application
programs today. Without them, most devices would pose a latent risk
to the Internet at large. Arguably, the JavaScript-based web employs
a very rapid software update mechanism with code being provided by
many different parties (e.g., by websites loaded into the browser or
by smartphone apps).

6. Security Considerations

Security is often even more important for smart objects than for more
traditional computing systems, since interacting directly with the
physical world can present greater dangers, and smart objects often
operate autonomously without any human interaction for a long time
period. The problem is compounded by the fact that there are often
fewer resources available in constrained devices to actually
implement security (e.g., see the discussion of "Class 0 devices" in
Section 3 of [RFC7228]). As such, it is critical to design for
security, taking into account a number of key considerations:

o A key part of any smart object design is the problem of how to
establish trust for a smart object. Typically, bootstrapping
trust involves giving the device the credentials it needs to
operate within a larger network of devices or services.

o Smart objects will, in many cases, be deployed in places where
additional physical security is difficult or impossible.
Designers should take into account that any such device can and
will be compromised by an attacker with direct physical access.
Thus, trust models should distinguish between devices susceptible
to physical compromise and devices with some level of physical
security. Physical attacks, such as timing, power analysis, and
glitching, are commonly applied to extract secrets
[PhysicalAttacks].

o Smart objects will, in many cases, be deployed as collections of
identical or near identical devices. Protocols should be designed
so that a compromise of a single device does not result in
compromise of the entire collection, especially since the
compromise of a large number of devices can enable additional
attacks such as a distributed denial of service. Sharing secret
keys across an entire product family is, therefore, also
problematic since compromise of a single device might leave all
devices from that product family vulnerable.

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RFC 7452 Smart Object Architectural Considerations March 2015

o Smart objects will, in many cases, be deployed in ways that the
designer never considered. Designers should either seek to
minimize the impact of misuse of their systems and devices or
implement controls to prevent such misuse where applicable.

o It is anticipated that smart objects will be deployed with a long
(e.g., 5-40 years) life cycle. Any security mechanism chosen at
the outset may not be "good enough" for the full lifespan of the
device. Thus, long-lived devices should start with good security
and provide a path to deploy new security mechanisms over the
lifetime of the device.

o Security protocols often rely on random numbers, and offering
randomness in embedded devices is challenging. For this reason,
it is important to consider the use of hardware-based random
number generators during early states of the design process.

A more detailed security discussion can be found in the "Report from
the Smart Object Security Workshop" [RFC7397] that was held prior to
the IETF meeting in Paris, March 2012, and in the report from the
National Science Foundation's "Cybersecurity Ideas Lab" workshop
[NSF] that was held in February 2014. For example, [NSF] includes,
among other recommendations, these recommendations specific to the
Internet of Things:

Enhance the Security of the Internet of Things by Identifying
Enclaves: The security challenges posed by the emerging Internet
of Things should be addressed now, to prepare before it is fully
upon us. By identifying specific use segments, or "enclaves",
Internet of Things infrastructure stakeholders can address the
security requirements and devise event remediations for that
enclave.

Create a Framework for Managing Software Updates: The Internet of
Things will challenge our current channels for distributing
security updates. An environment must be developed for
distributing security patches that scales to a world where almost
everything is connected to the Internet and many "things" are
largely unattended.

Finally, we reiterate that use of standards that have gotten wide
review can often avoid a number of security issues that could
otherwise arise. Section 3.3 of [RFC6574] reminds us about the IETF
work style regarding security:

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RFC 7452 Smart Object Architectural Considerations March 2015

In the development of smart object applications, as with any other
protocol application solution, security has to be considered early
in the design process. As such, the recommendations currently
provided to IETF protocol architects, such as RFC 3552 [RFC3552],
and RFC 4101 [RFC4101], apply also to the smart object space.

In the IETF, security functionality is incorporated into each
protocol as appropriate, to deal with threats that are specific to
them. It is extremely unlikely that there is a one-size-fits-all
security solution given the large number of choices for the 'right'
protocol architecture (particularly at the application layer). For
this purpose, [RFC6272] offers a survey of IETF security mechanisms
instead of suggesting a preferred one.

7. Privacy Considerations

This document mainly focuses on an engineering audience, i.e., those
who are designing smart object protocols and architectures. Since
there is no value-free design, privacy-related decisions also have to
be made, even if they are just implicit in the reuse of certain
technologies. RFC 6973 [RFC6973] and the threat model in
[CONFIDENTIALITY] were written as guidance specifically for that
audience and are also applicable to the smart object context.

For those looking at privacy from a deployment point of view, the
following additional guidelines are suggested:

Transparency: Transparency of data collection and processing is key
to avoid unpleasant surprises for owners and users of smart
objects. Users and impacted parties must be put in a position to
understand what items of personal data concerning them are
collected and stored, as well for what purposes they are sought.

Data Collection / Use Limitation: Smart objects should only store
personal data that is adequate, relevant, and not excessive in
relation to the purpose(s) for which they are processed. The use
of anonymized data should be preferred wherever possible.

Data Access: Before deployment starts, it is necessary to consider
who can access personal data collected by smart objects and under
which conditions. Appropriate and clear procedures should be
established in order to allow data subjects to properly exercise
their rights.

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RFC 7452 Smart Object Architectural Considerations March 2015

Data Security: Standardized data security measures to prevent
unlawful access, alteration, or loss of smart object data need to
be defined and deployed. Robust cryptographic techniques and
proper authentication frameworks have to be used to limit the risk
of unintended data transfers or unauthorized access.

A more detailed treatment of privacy considerations that extend
beyond engineering can be found in a publication from the Article 29
Working Party [WP223].

8. Informative References

[CONFIDENTIALITY]
Barnes, R., Schneier, B., Jennings, C., Hardie, T.,
Trammell, B., Huitema, C., and D. Borkmann,
"Confidentiality in the Face of Pervasive Surveillance: A
Threat Model and Problem Statement", Work in Progress,
draft-iab-privsec-confidentiality-threat-04, March 2015.

[Gamma] Gamma, E., "Design Patterns: Elements of Reusable Object-
Oriented Software", 1995.

[HomeGateway]
Eggert, L., "An Experimental Study of Home Gateway
Characteristics", In Proceedings of the 10th annual
Internet Measurement Conference, 2010,
<http://eggert.org/papers/2010-imc-hgw-study.pdf>.

[IPoptions]
Fonseca, R., Porter, G., Katz, R., Shenker, S., and I.
Stoica, "IP options are not an option", Technical Report
UCB/EECS2005-24, 2005,
<http://citeseer.ist.psu.edu/viewdoc/
summary?doi=10.1.1.123.4251>.

[NSF] National Science Foundation, "Interdisciplinary Pathways
towards a More Secure Internet", A report on the NSF-
sponsored Cybersecurity Ideas Lab held in Arlington,
Virginia, February 2014, <http://www.nsf.gov/cise/news/
CybersecurityIdeasLab_July2014.pdf>.

[PhysicalAttacks]
Koeune, F. and F. Standaert, "A Tutorial on Physical
Security and Side-Channel Attacks", in Foundations of
Security Analysis and Design III: FOSAD 2004/2005 Tutorial
Lectures; Lecture Notes in Computer Science, Vol. 3655,
pp. 78-108, September 2005,
<http://link.springer.com/chapter/10.1007%2F11554578_3>.

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RFC 7452 Smart Object Architectural Considerations March 2015

[RFC1263] O'Malley, S. and L. Peterson, "TCP Extensions Considered
Harmful", RFC 1263, October 1991,
<http://www.rfc-editor.org/info/rfc1263>.

[RFC1958] Carpenter, B., "Architectural Principles of the Internet",
RFC 1958, June 1996,
<http://www.rfc-editor.org/info/rfc1958>.

[RFC3234] Carpenter, B. and S. Brim, "Middleboxes: Taxonomy and
Issues", RFC 3234, February 2002,
<http://www.rfc-editor.org/info/rfc3234>.

[RFC3238] Floyd, S. and L. Daigle, "IAB Architectural and Policy
Considerations for Open Pluggable Edge Services", RFC
3238, January 2002,
<http://www.rfc-editor.org/info/rfc3238>.

[RFC3444] Pras, A. and J. Schoenwaelder, "On the Difference between
Information Models and Data Models", RFC 3444, January
2003, <http://www.rfc-editor.org/info/rfc3444>.

[RFC3552] Rescorla, E. and B. Korver, "Guidelines for Writing RFC
Text on Security Considerations", BCP 72, RFC 3552, July
2003, <http://www.rfc-editor.org/info/rfc3552>.

[RFC3724] Kempf, J., Austein, R., and IAB, "The Rise of the Middle
and the Future of End-to-End: Reflections on the Evolution
of the Internet Architecture", RFC 3724, March 2004,
<http://www.rfc-editor.org/info/rfc3724>.

[RFC4101] Rescorla, E. and IAB, "Writing Protocol Models", RFC 4101,
June 2005, <http://www.rfc-editor.org/info/rfc4101>.

[RFC4924] Aboba, B. and E. Davies, "Reflections on Internet
Transparency", RFC 4924, July 2007,
<http://www.rfc-editor.org/info/rfc4924>.

[RFC5218] Thaler, D. and B. Aboba, "What Makes For a Successful
Protocol?", RFC 5218, July 2008,
<http://www.rfc-editor.org/info/rfc5218>.

[RFC6272] Baker, F. and D. Meyer, "Internet Protocols for the Smart
Grid", RFC 6272, June 2011,
<http://www.rfc-editor.org/info/rfc6272>.

[RFC6347] Rescorla, E. and N. Modadugu, "Datagram Transport Layer
Security Version 1.2", RFC 6347, January 2012,
<http://www.rfc-editor.org/info/rfc6347>.

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RFC 7452 Smart Object Architectural Considerations March 2015

[RFC6540] George, W., Donley, C., Liljenstolpe, C., and L. Howard,
"IPv6 Support Required for All IP-Capable Nodes", BCP 177,
RFC 6540, April 2012,
<http://www.rfc-editor.org/info/rfc6540>.

[RFC6574] Tschofenig, H. and J. Arkko, "Report from the Smart Object
Workshop", RFC 6574, April 2012,
<http://www.rfc-editor.org/info/rfc6574>.

[RFC6709] Carpenter, B., Aboba, B., and S. Cheshire, "Design
Considerations for Protocol Extensions", RFC 6709,
September 2012, <http://www.rfc-editor.org/info/rfc6709>.

[RFC6749] Hardt, D., "The OAuth 2.0 Authorization Framework", RFC
6749, October 2012,
<http://www.rfc-editor.org/info/rfc6749>.

[RFC6973] Cooper, A., Tschofenig, H., Aboba, B., Peterson, J.,
Morris, J., Hansen, M., and R. Smith, "Privacy
Considerations for Internet Protocols", RFC 6973, July
2013, <http://www.rfc-editor.org/info/rfc6973>.

[RFC7228] Bormann, C., Ersue, M., and A. Keranen, "Terminology for
Constrained-Node Networks", RFC 7228, May 2014,
<http://www.rfc-editor.org/info/rfc7228>.

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

[RFC7397] Gilger, J. and H. Tschofenig, "Report from the Smart
Object Security Workshop", RFC 7397, December 2014,
<http://www.rfc-editor.org/info/rfc7397>.

[TCPextensions]
Honda, M., Nishida, Y., Greenhalgh, A., Handley, M., and
H. Tokuda, "Is it Still Possible to Extend TCP?", In
Proceedings of the ACM Internet Measurement Conference
(IMC), Berlin, Germany, November 2011,
<http://conferences.sigcomm.org/imc/2011/docs/p181.pdf>.

[Tussles] Clark, D., Wroclawski, J., Sollins, K., and R. Braden,
"Tussle in Cyberspace: Defining Tomorrow's Internet", In
Proceedings of ACM SIGCOMM, 2002,
<http://conferences.sigcomm.org/sigcomm/2002/papers/
tussle.html>.

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RFC 7452 Smart Object Architectural Considerations March 2015

[WP223] Article 29 Data Protection Working Party, "Opinion 8/2014
on the Recent Developments on the Internet of Things", 14/
EN, WP 223, September 2014, <http://ec.europa.eu/justice/
data-protection/article-29/documentation/
opinion-recommendation/files/2014/wp223_en.pdf>.

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Appendix A. IAB Members at the Time of Approval

Jari Arkko
Mary Barnes
Marc Blanchet
Joel Halpern
Ted Hardie
Joe Hildebrand
Russ Housley
Eliot Lear
Xing Li
Erik Nordmark
Andrew Sullivan
Dave Thaler
Brian Trammell

Acknowledgements

We would like to thank the participants of the IAB Smart Object
workshop for their input to the overall discussion about smart
objects.

Furthermore, we would like to thank Mike St. Johns, Jan Holler,
Patrick Wetterwald, Atte Lansisalmi, Hannu Flinck, Bernard Aboba,
Markku Tuohino, Wes George, Robert Sparks, S. Moonsesamy, Dave
Crocker, and Steve Crocker in particular for their review comments.

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Authors' Addresses

Hannes Tschofenig
ARM Ltd.
6060 Hall in Tirol
Austria

EMail: [email protected]
URI: http://www.tschofenig.priv.at

Jari Arkko
Jorvas 02420
Finland

EMail: [email protected]

Dave Thaler
One Microsoft Way
Redmond, WA 98052
United States

EMail: [email protected]

Danny McPherson
12061 Bluemont Way
Reston, VA 20190
United States

EMail: [email protected]

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