Network Working Group                                      H. Tschofenig
Internet-Draft                                                  J. Arkko
Intended status: Informational                                 D. Thaler
Expires: July 1, 2013                                       D. McPherson
                                                       December 28, 2012

        Architectural Considerations in Smart Object Networking


   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.  How can different
   forms of embedded and constrained devices be interconnected?  How can
   they employ and interact with the currently deployed Internet?  This
   memo discusses smart objects and some of the architectural choices
   involved in designing smart object networks and protocols that they

   The document is being discussed at

Status of this Memo

   This Internet-Draft is submitted in full conformance with the
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   This Internet-Draft will expire on July 1, 2013.

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   Copyright (c) 2012 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents

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   ( in effect on the date of
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Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3
   2.  Specific and General Purpose Solutions . . . . . . . . . . . .  5
   3.  Deployment Constraints in the Internet . . . . . . . . . . . .  7
   4.  The Need for Standards . . . . . . . . . . . . . . . . . . . .  9
     4.1.  Managing Complexity  . . . . . . . . . . . . . . . . . . .  9
     4.2.  Interoperability Architecture  . . . . . . . . . . . . . . 10
     4.3.  Internet Protocols for Proprietary Protocol
           Developments . . . . . . . . . . . . . . . . . . . . . . . 13
     4.4.  Interoperability . . . . . . . . . . . . . . . . . . . . . 14
     4.5.  Design for Change  . . . . . . . . . . . . . . . . . . . . 16
   5.  Security Considerations  . . . . . . . . . . . . . . . . . . . 17
   6.  Privacy Considerations . . . . . . . . . . . . . . . . . . . . 18
   7.  Summary  . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
   8.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 23
   9.  Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 24
   10. Informative References . . . . . . . . . . . . . . . . . . . . 25
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 27

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1.  Introduction

   In RFC 6574 [1], we refer 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 be classified as smart objects and those that can't.

   Following the theme "Everything that can be connected will be
   connected", engineers and researchers designing smart object networks
   need to address a number of questions.  How can different forms of
   embedded and constrained devices be interconnected?  How can they
   employ and interact with the currently deployed Internet?

   These questions have been discussed at length.  For instance, when
   the Internet Architecture Board (IAB) scheduled a workshop on Smart
   Objects, the IETF community was asked to develop views on how
   Internet protocols can be utilized by smart objects.  A report of the
   discussions and the position papers received for this workshop have
   been published [1].

   This memo discusses smart objects and some of the architectural
   choices involved in designing smart object networks and protocols
   that they use.  The main issues that we focus on are interaction with
   the Internet, the use of Internet protocols for these applications,
   models of interoperability, and approach to standardization.  Many of
   the issues discussed in this memo are common to any communications
   system design or protocol development.  However, given the high
   interest for smart object networks, their somewhat specific
   requirements, and commonly occurring requests for very different
   communications tools prompted the IAB to discuss these issues in this
   specific context.

   In drawing conclusions from the prior IETF work and from the IAB
   workshop it is useful to look back at the criteria for success of the
   Internet.  Various publications provide insight into the history, and
   some of it is very much applicable to the discussion on smart
   objects.  RFC 1958 [2] says:

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

   It goes on to add:

      "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."

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   Internet protocols are immediately relevant for any smart object
   development and deployment.  However, building very small, often
   battery-operated devices is challenging.  It is difficult to resist
   the temptation to build specific solutions tailored to a particular
   application, or to re-design everything from scratch.  Yet, due to
   network effects, the case for using the Internet Protocol(s) and
   other generic technology is compelling.

   As technology keeps advancing, the constraints that the technology
   places on devices evolve as well.  Microelectronics become more
   capable as time goes by, sometimes making it even 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 tomorrow's.

   This writeup describes the IAB's view on these issues.  The document
   is being discussed at

   The rest of the document is organized as follows.  Section 2
   discusses the problems associated with vertically integrated
   industry-specific solutions, and suggests the use of generic
   technologies and a more flexible architecture as a way to reduce
   these problems.  Section 3 discusses the problems associated with
   attempting to use options and communication patterns other than those
   in current widespread use in the Internet.  Often middleboxes and
   assumptions built into existing devices makes such usage problematic.
   Section 4 discusses different levels of interoperability, and the
   different level of effort required to achieve them.  Finally,
   Section 5 presents some of the relevant security issues, Section 6
   discusses privacy, and Section 7 summarizes the recommendations.

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2.  Specific and General Purpose Solutions

   The Internet protocols are relevant for any smart object development
   and deployment.  In the context of one use case of smart objects, the
   smart grid and smart meters in particular, RFC 6272 "Internet
   Protocols for the Smart Grid" [3] identifies a range of IETF
   protocols that can be utilized.

   Of course, there are also many protocols that are unlikely to be
   needed or even suitable for the smart object environments.  For
   instance, it would difficult to imagine inter-domain routing being a
   necessary feature in these objects; there are other devices in the
   network that would normall be responsible for this functionality.
   But the wide range of protocols listed in RFC 6272 illustrates the
   view of the IAB about how a large fraction of the Internet technology
   can be readily used in these new applications.  Many commercial
   products employ proprietary or industry-specific protocol mechanisms
   that do not accommodate direct Internet connectivity.  Researchers
   have made several attempts to design new types of architectures for
   the entire Internet system.  But by and large the industry has
   understood the value of using Internet communications for various
   smart object deployments.

   Nevertheless, there are several architectural concerns that deserve
   to be highlighted.

   Vertically Specified Profiles

      The discussions at the IAB workshop (see Section 3.1.2 of [1])
      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).  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.  Profiles, particularly, full-
      stack profiles are common, for instance, in areas where existing
      legacy technology is being migrated to IP.

      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 other
      physical media than others, and that in such situations a simple

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      router could still provide an ability to communicate between the

   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 web
      services.  Benefits from using these kinds of tools include access
      to 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 that the devices are deployed.

   As a result, the following recommendations can be made.  First, while
   there are some cases where specific solutions are needed, the
   benefits of general-purpose technology are often compelling, be it
   about 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 onto them.  As an example, it rarely makes sense to
   limit communications on-link or to specific media.  We should also
   design our applications so that the participating devices can easily
   interact with multiple other applications.

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3.  Deployment Constraints in the Internet

   Despite the applicability of the Internet Protocols for smart
   objects, picking the specific protocols for a particular use case can
   be tricky.  As the Internet has evolved over time, 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 specifications 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, [4] 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, [5] tested 34 different home gateways regarding their
      packet dropping policy of UDP, TCP, DCCP, 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

      In 2011, [6] tested the behavior of networks with regard to
      various TCP extensions: "From our results we conclude the
      middleboxes implementing layer 4 functionality are very common --
      at least 25% of paths interfered with TCP in some way beyond basic

   Extending protocols to fulfill new uses and to add new functionality
   may range from very easy to difficult, as [7] investigates in great
   detail.  A challenge many protocol designers are facing is to ensure
   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?" [8] defines the ultimate goal to develop

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   protocols that are 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 [9] complicate the use of extensions in the
   basic IP protocols and transport layers.

   RFC 1958 [2] 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 clever intermediaries interacting with dumb
   end devices but we have to keep in mind what RFC 3724 [10] has 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."  RFC 4924 [11] 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.

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4.  The Need for Standards

   New smart object applications are developed every day; in many cases
   they are created using standardized Internet technology.  Even where
   a common underlying technology (such as IP) is used, current smart
   object networks often have challenges related to interoperability of
   the entire protocol stack, including application behavior.  One
   symptom of such challenges is that various components cannot easily
   be replaced by third party components.  It is of strategic importance
   to make a conscious decision about the desired level of
   interoperability and where the points of interconnection are.

4.1.  Managing Complexity

   These decisions also relate to the required effort to complete the
   application, and overall complexity of the system.  A system may
   appear complex for variety of reasons.  First, there is legitimate
   heterogeneity in the used networking technology and applications.
   This variation is necessary and useful, as for instance different
   applications and environments benefit from varying networking
   technology.  The range and other characteristics of cellular,
   wireless local area networking, and RFID are very different from each
   other, for instance.  There are literally thousands of different
   applications, and it is natural that they have differing requirements
   on what parties need to communicate with each other, what kind of
   security solutions are appropriate, and other aspects.

   The answer to managing complexity in the face of this lies in layers
   of communication mechanisms and keeping the layers independent, e.g.,
   in the form of the hourglass model.  If there is a common waist of
   the hourglass, then all applications can work over all physical
   networking technology, ensuring widest possible coverage of
   networking applications.  "Everything over IP and IP over
   everything."  This model provides some guidance for thinking about
   the Internet of Things architecture.  First of all, it shows how we
   need common internetworking infrastructure (IP) to allow
   heterogeneous link media to work seamlessly with each other, and with
   the rest of the system.  Secondly, there are various transport and
   middleware communications mechanisms that will likely become useful
   in the different applications.  For instance, today embedded web
   services (HTTP, COAP, XML, and JSON) appear to be popular, regardless
   of what specific link technology they are run over.

   But there can also be undesirable complexity and variation.  Creation
   of alternative standards where one would have sufficed may be
   harmful.  Creating systems and communications mechanisms with
   unnecessary dependencies between different layers and system
   components limits our ability to migrate systems to the most economic

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   and efficient platforms, and limits our ability to connect as many
   objects as possible.

   To summarize, complexity and alternative technologies can be very
   useful as a part of architecture, or can be problematic when it
   creates unnecessary competition and deployment barriers in the market
   place.  In an optimal situation, complexity will be addressed by
   regular technological evolution in the industry through underlying
   layering and modular architecture.

4.2.  Interoperability Architecture

   It is also valuable to look back at earlier IETF publications, for
   example, RFC 1263 [12] considers different protocol design strategies
   and makes an interesting observation about the decision to design new
   protocols from scratch or to design them in a non-backwards
   compatible way based on existing protocols:

      "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 [12] was written in 1991 when the standardization process in
   the Internet community was far more lightweight than today (among
   other reasons, because fewer stakeholders were interested in
   participating in the standards process) it is remarkable to read
   these thoughts since they are even more relevant today [13] [14].
   This is particularly true for the smart object environment.

   Regardless of how hard we work on optimizing the standard process,
   designing systems in an open and transparent consensus process where
   many parties participate takes longer than letting individual
   stakeholders develop their own proprietary solutions.  Therefore, it
   is important to make architectural decisions that keep a good balance
   between proprietary developments vs. standardized components.

   While RFC 1263 [12] certainly provides good food for thought, it also
   gives recommendations that may not always be appropriate for the

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   smart object space, such as the preference for a so-called
   evolutionary protocol design where new versions of the protocols are
   allowed to be non-backwards compatible and all run independently on
   the same device.  RFC 1263 adds:

      "... the only real disadvantage of protocol evolution is the
      amount of memory required to run several versions of the same
      protocol.  Fortunately, memory is not the scarcest resource in
      modern workstations (it may, however, be at a premium in the BSD
      kernel and its derivatives).  Since old versions may rarely if
      ever be executed, the old versions can be swapped out to disk with
      little performance loss.  Finally, since this cost is explicit,
      there is a huge incentive to eliminate old protocol versions from
      the network."

   Even though it is common practice today to run many different
   software applications that have similar functionality (for example,
   multiple Instant Messaging clients) in parallel it may indeed not be
   the most preferred approach for smart objects, which may have severe
   limitations regarding RAM, flash memory, and also power constraints.

   To deal with exactly this problem, profiles have been suggested in
   many cases.  Saying "no" to a new protocol stack that only differs in
   minor ways may be appropriate but could be interpreted as blocking
   innovation and, as RFC 1263 [12] describes it nicely "In the long
   term, we envision protocols being designed on an application by
   application basis, without the need for central approval.".  "Central
   approval" here refers to the approval process that happens in a
   respective standards developing organization.

   So, how can we embrace rapid innovation with distributed developments
   and at the same time accomplish a high level of interoperability?

   Clearly, standardization of every domain-specific profile will not be
   the solution.  Many domain-specific profiles are optimizations that
   will be already obsoleted by technological developments (e.g., new
   protocol developments), new security threats, new stakeholders
   entering the system or changing needs of existing stakeholders, new
   business models, changed usage patterns, etc.  RFC 1263 [12] states
   the problem succinctly: "The most important conclusion of this RFC is
   that protocol change happens and is currently happening at a very
   respectable clip.  We simply propose to explicitly deal with the
   changes rather keep trying to hold back the flood."

   Even worse, different stakeholders that are part of the Internet
   milieu have interests that may be adverse to each other, and these
   parties each vie to favor their particular interests.  In [15],
   Clark, et al. call this process 'the tussle' and ask the important

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   question "How can we, as designers, build systems with desired
   characteristics and improve the chances that they come out the way we
   want?".  In an attempt to answer that question, the authors of [15]
   develop a high-level principle, which is not tailored to smart object
   designs but to Internet protocol develop in general:

      "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 designs will be broken; designs
      that permit variation will flex under pressure and survive."

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

   1.  Break complex systems into modular parts.

   2.  Design for choice.

   These are valid guidelines, and many protocols standardized in the
   IETF have taken exactly this approach, namely to identify building
   blocks that can be used in a wide variety of deployments.  Others
   then put the building blocks together in a way that suits their
   needs.  There are, however, limits to this approach.  Certain
   building blocks are only useful in a limited set of architectural
   variants and producing generic building blocks requires a good
   understanding of the different architectural variants and often
   limits the ability to optimize.  Sometimes the value of an individual
   building block is hard for others to understand without providing the
   larger context, which requires at least to illustrate one deployment
   variant that comes with a specific architectural setup.  That said,
   it is also critical to consider systemic interdependencies between
   the set of elements that constitute a system, lest they impose
   constraints that weren't envisioned at the outset.

   Since many Internet protocols are used as building blocks by other
   organizations or in deployments that may have never been envisioned
   by the original designs, one can argue that this approach has been
   fairly successful.  It may, however, not lead to the level of
   interoperability many desire: they want interoperability of the
   entire system rather than interoperability at a specific protocol
   level.  Consequently, an important architectural question arises,
   namely "What level of interoperability should Internet protocol
   engineers aim for?"

   In the diagrams below, we illustrate a few interoperability scenarios
   with different interoperability needs.  Note that these are highly
   simplified versions of what protocol architects are facing, since
   there are often more parties involved in a sequence of required

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   protocol exchanges, and the entire protocol stack has to be
   considered - not just a single protocol layer.  As such, the required
   coordination and agreement between the different stakeholders is
   likely to be far more challenging than illustrated.  We do, however,
   believe that these figures illustrate that the desired level of
   interoperability needs to be carefully chosen.

4.3.  Internet Protocols for Proprietary Protocol Developments

   Figure 1 shows a typical deployment of many Internet applications.
   Here an application service provider ( in our
   illustration) wants to make an HTTP-based protocol interface
   available to its customers. allows their customers to
   upload sensor measurements using a RESTful HTTP design.  Customers
   need to write code for their embedded systems to make use of the
   HTTP-based protocol interface (and keying material for authentication
   and authorization of the uploaded data).  These applications work
   with the servers operated by and with nobody else.  There
   is no interoperability with third parties (at the application layer
   at least).  For instance, Alice, a customer of, cannot
   use their embedded system which was programmed to use the protocol
   interface for with another service provider without re-
   writing at least parts of her embedded software.  Nevertheless, use standardized protocol components to allow for
   communication across the Internet and for speeding-up the process of
   software development.  This is certainly useful from a time-to-market
   and cost efficiency point of view.  For example, could
   rely on HTTP, offer JSON to encode sensor data, and use IP to allow
   various nodes to communicate with each other.

            |  Application  |
            |  Service      |
            |  Provider     |
            |  |
                _,   .
              ,'      `.      Proprietary
           _,'          `.    Protocol offered
         ,'               `._ by
       -'                    -
    ,'''''''''''''|       ,''''''''| Sensors
    | Temperature |       | Light  | operated by
    | Sensor      |       | Sensor | customers of
    |.............'       |........'

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                     Figure 1: Proprietary Deployment

   Clearly, the above scenario does not provide a lot of
   interoperability even though standardized Internet protocols are

   Figure 2 shows another scenario.  Here is focused on
   storage of sensor data and not on the actually processing it offers
   an HTTP-based protocol interface to others to get access to the
   uploaded sensor data.  In our example, and are two of such companies that make use of this
   functionality in order to provide data visualization and data mining
   computations. again uses standardized protocols (such as
   RESTful HTTP design combined with OAuth) for offering access but
   overall the entire protocol stack is not standardized.

                                              |  Application  |
                                             .|  Service      |
                                          ,-` |  Provider     |
                                        .`    | |
                                     ,-`      |_______________|
             .................  ,-`
             |  Application  |-` Proprietary
             |  Service      |   Protocol
             |  Provider     |
             |  |-,
             |_______________|  '.
                  _,              `',
    Proprietary ,'                   '.             ...
    Protocol _,'                       `',    .................
           ,'                             '.  |  Application  |
         -'                                 `'|  Service      |
      ,''''''''|                              |  Provider     |
      | Light  |                              | |
      | Sensor |                              |_______________|

                      Figure 2: Backend Interworking

4.4.  Interoperability

   In contrast to the scenario described in Section 4.3, Figure 3
   illustrates a sensor where two devices developed by independent
   manufacturers are desired to interwork.  This is shown in Figure 3.

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   To pick an example from [1], consider a light bulb that talks to a
   light switch with the requirement that each may be manufactured by a
   different company, represented as company A and B.

                        _,,,,    ,,,,
                       /     -'``    \
                      |               |
                      \               |
                      /               \
    ,''''''''|       /   Standardized  .       ,''''''''|
    | Light  | ------|---Protocol-------\------| Light  |
    | Bulb   |        .                 |      | Switch |
    |........'         `'-              /      |........'
                          \      _-...-`
    Manufacturer           `. ,.'              Manufacturer
        A                    `                      B

        Figure 3: Interoperability between two independent devices

   In order for this scenario to work manufacturer A, B, and probably
   many other manufacturers f lightbulbs and light switches need to get
   together and agree on the protocol stack they would like to use.  Let
   us assume that they do not want any manual configuration by the user
   to happen and that these devices should work in a typical home
   network this consortium needs to make a decision about the following
   protocol design aspects:

   o  Which physical layer should be supported?

   o  Which IP version should be used?

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

   o  Which communication architecture shall be supported? (see [16];
      Arkko, et al. explain how the complexity of an application heavily
      depends on the chosen communication architecture and discusses an
      application with limited communication capabilities, which also
      translates into low energy consumption. )

   o  Whether there is 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 is used for conveying the sensor
      readings/sensor commands? (e.g., UDP)

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   o  Which application layer protocol is used? (for example, CoAP)

   o  How are requests encoded? (e.g., as URIs) How is the return data
      encoded? (e.g., JSON)

   o  What data model is used for expressing the different light levels?
      (e.g., [17])

   o  Finally, some thoughts will have to be spent about the security
      architecture.  This includes questions like: what are the
      ssecurity 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 reside?

   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
   to accomplish a full level of interoperability between two devices
   manufactured by different vendors will take time.

4.5.  Design for Change

   With the description in Section 4.3 and in Section 4.4 we present two
   extreme cases of interoperability.  To "design for varation in
   outcome", as postulated by [15], the design of the system does not
   need to be cast in stone during the standardization process but may
   be changed during run-time using software updates.

   For many reasons, not only for adding new functionality, it can be
   said that many smart objects will need a solid software update
   mechanism.  Note that adding new functionality to smart objects may
   not be possible for certain classes of constrained devices, namely
   those with severe memory limitations.  As such, a certain level of
   sophistication from the embedded device is assumed in this section.

   Software updates are common in operating systems and application
   programs today.  Arguably, the Web today employs a very successful
   software update mechanism with code being provided by many different
   parties (i.e., by websites loaded into the browser or by the Web
   application).  While JavaScript (or the proposed successor, Dart) may
   not be the right choice of software distribution for smart objects,
   and other languages such as embedded eLua [18] may be more
   appropriate, the basic idea of offering software distribution
   mechanisms may present a middleground between the two extreme
   interoperability scenario presented in this section.

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5.  Security Considerations

   Section 3.3 of [1] reminds us about the IETF workstyle regarding

      In the development of smart object applications, as with any other
      protocol application solution, security must be considered early
      in the design process.  As such, the recommendations currently
      provided to IETF protocol architects, such as RFC 3552 [19], and
      RFC 4101 [20], 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, [3] offers a survey of IETF security mechanisms instead
   of suggesting a preferred one.

   A more detailed security discussion can be found in the report from
   the 'Smart Object Security' workshop. that was held prior to the IETF
   meeting in Paris, March 2012.  [[Comment.1: The workshop report has
   not been published yet.  It will happen soon.]]

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6.  Privacy Considerations

   In 1980, the Organization for Economic Co-operation and Development
   (OECD) published eight Guidelines on the Protection of Privacy and
   Trans-Border Flows of Personal Data [21], which are often referred to
   as Fair Information Practices (FIPs).  The FIPs, like other privacy
   principles, are abstract in their nature and have to be applied to a
   specific context.

   From a technical point of view, many smart object designs are not
   radically different from other application design.  Often, however,
   the lack of a classical user interface, such as is used on a PC or a
   phone, that allows users to interact with the devices in a convenient
   and familiar way creates problems to provide users with information
   about the data collection, and to offer them the ability to express
   consent.  Furthermore, in some verticals (e.g., smart meter
   deployments) users are not presented with the choice of voluntarily
   signing up for the service but deployments are instead mandated
   through regulation.  Therefore, these users have no right to consent;
   a right that is core to many privacy principles including the FIPs.
   In other cases, the design is more focused on dealing with privacy at
   the level of a privacy notice rather than by building privacy into
   the design of the system, which [22] asks engineers to do.

   Similarly, in many applications smart objects technology is deployed
   by someone other than the potentially impacted parties.  For
   instance, manufacturers and shops deploy RFID tags in products or
   governments deploy roadside sensors.  In these applications the
   impacted parties, such as a shopper or car-owner may not even be
   aware that such technology is used, and information about about the
   impacted party may be collected.

   The interoperability models described in this document highlight that
   standardized interfaces are not needed in all cases, nor that this is
   even desirable.  Depending on the choice of certain underlying
   technologies, various privacy problems may be inherited by the upper-
   layer protocols and therefore difficult to resolve as an
   afterthought.  Many smart objects leave users little ability for
   enabling privacy-improving configuration changes.  Technologies exist
   that can be applied also to smart objects to involve users in
   authorization decisions before data sharing takes place.

   As a summary, for an Internet protocol architect, the guidelines
   described in [22] are applicable.  For those looking at privacy from
   a deployment point of view, the following additional guidelines are

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   Transparency:  The data processing should be completely transparent
      to the smart object owner, users, and possibly impacted parties.
      Users and impacted parties must, except in rare exceptional cases,
      be put in a position to easily understand what items of personal
      information concerning them are collected and stored, as well for
      what purposes they are sought.

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

   Data Access:  Before deployment starts, it is necessary to consider
      who can access the personal data recorded in smart objects and
      under which conditions, particularly with regard to data subjects,
      to whom (in principle) full and free access to his/her own data
      should be recognised.  Appropriate and clear procedures should be
      established in order to allow data subjects to properly exercise
      their rights.  A privacy and data protection impact assessment is
      considered a useful tool for this analysis.

   Data Security:   Standardized data security measures to prevent
      unlawful access, alteration or loss of smart object data need to
      be defined and universally adopted.  Robust cryptographic
      techniques and proper authentication frameworks should be used to
      limit the risk of unintended data transfers or harmful attacks.
      The end-user and impacted parties should be able to verify, in a
      straight-forward manner, that smart objects are in full compliance
      with these standards.

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7.  Summary

   Interconnecting smart objects with the Internet creates exciting new
   use cases and engineers are eager to play with small and constrained
   devices.  With various standardization efforts ongoing and the
   impression that smart objects require a new Internet Protocol and
   many new extensions, we would like to provide a cautious warning.  We
   believe that protocol architects are best served by the following
   high level guidance:

   Use Internet protocols

      Most, if not all, smart object deployments should employ the
      Internet protocol suite.  The Internet protocols can be applied to
      almost any environment, and the rest of the suite can be tailored
      for the specific needs.

   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 deployments is, in many cases, far
      too opimistic since already available deployed infrastructure is

   Decide about the level of interoperability

      Offering interoperability between every entity in an architecture
      may be an ideal situation for a standards person but comes with a
      certain cost.  As such, starting with a less ambigious
      standardization goal may be appropriate, particularly for early

   Don't optimize too early

      The constrained nature of smart objects invites engineers to
      invent each and every technique to optimize protocols for special
      use cases.  While some of these optimizations may be necessary,
      many of them make the overal design complex and the outcome less
      usable for the generic use case.  Examples of current, useful
      optimizations include tailoring web services transport mechanisms
      for smart objects while keeping the overall web services model
      intact ([23]) or education about good ways to implement IP-based
      protocol stacks ([24]).

   This memo provides also some additional, more detailed suggestions
   for different audiences.  The following recommendations are for the
   designers of smart object systems:

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   o  Even in the smart object space, try to aim for a generic design
      instead of optimizing too early.  Note that some optimizations
      will only be possible in an architectural context, rather than at
      the level of an individual protocol.

   o  We encourage engineers to take existing deployment constraints
      into consideration to allow for a smooth transition path.  This
      requires a clear understanding of the deployment status and also
      an analysis of the incentives of the different stakeholders.

         Over time, a wide range of middleboxes have been introduced to
         the Internet protocol suite.  Introducing middleboxes in smart
         object deployments has been proposed many times but their usage
         may turn out to be dangerous.  We recommend carefully
         investigaing whether new features introduced can be supported
         without any change to middleboxes.  This investigation will
         likely have to go beyond pure specification work, and may
         require extensive interoperability testing and a clearly
         articulated extensiblity story.  The guidance in [7] is
         relevant to this discussion.  The added architectural
         complexity, including security and privacy challenges, has to
         be a subject of design considerations.  Middleboxes are often
         operated by parties other than the communication endpoints.  As
         such, they introduce additional stakeholders into the
         architecture that often want to be involved when new features
         are introduced and as such may slow down the ability to
         innovate at a high speed.

   o  The application space has historically seen faster innovation
      cycles, and separating network-layer from application-layer
      functionality is therefore recommended.  In general, we suggest
      avoiding standardizing complete protocol stacks.  The likelihood
      that those will be outdated by the time standardization is
      finished is far too high, particularly with application-layer

   o  Consider what type of interoperability model is appropriate for
      the task at hand.  An architecture that requires fewer
      interoperability components often has a faster time to market.
      Selecting what interfaces are open for interworking between
      components from different operators and vendors is very important.

   These recommendations are for the designers of new protocols or
   protocol extensions in IETF or elsewhere:

   o  The Internet Protocol stack has a number of building blocks that
      have proven useful for many applications.  We encourage continuing
      the development of building blocks that are usable in a number of

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      deployment scenarios.

      For the development of new components, the recommendations in [1]
      provide a good starting point.  We do, however, encourage protocol
      engineers to document the interworking of various protocols in at
      least one architectural variant to ensure that the individual
      parts indeed fit together without creating gaps or conflicts.

   For researchers we offer the following suggestions:

   o  We believe that the area of mobile code distribution provides a
      promising way to solve a range of security problems and the
      ability to deliver new functionality.  The rich experience from
      the Web environment can be taken into consideration as a starting

   o  We encourage funding of software projects that produce libraries
      and open source code for operating systems, basic IP protocol
      stacks, and web tools suitable for small, autonomously operating
      devices.  The success of many IETF protocols can be attributed to
      the availability of running code.

   o  We also propose to conduct ongoing research of the deployment
      status of various Internet protocols.  These investigations
      provide a snapshot for further interactions with the operator
      community to ensure that IETF protocols can indeed be deployed in
      today's Internet and may stimulate discussions on how to deal with
      unpleasant deployment artifacts.

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8.  IANA Considerations

   This document does not require actions by IANA.

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9.  Acknowledgements

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

   Furthermore, we would like to thank Jan Holler, Patrick Wetterwald,
   Atte Lansisalmi, Hannu Flinck, Joel Halpern, Markku Tuohino, and the
   IAB for their review comments.

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10.  Informative References

   [1]   Tschofenig, H. and J. Arkko, "Report from the Smart Object
         Workshop", RFC 6574, April 2012.

   [2]   Carpenter, B., "Architectural Principles of the Internet",
         RFC 1958, June 1996.

   [3]   Baker, F. and D. Meyer, "Internet Protocols for the Smart
         Grid", RFC 6272, June 2011.

   [4]   Fonseca, R., Porter, G., Katz, R., Shenker, S., and I. Stoica,
         "IP options are not an option, Technical Report UCB/EECS",

   [5]   Eggert, L., "An experimental study of home gateway
         characteristics, In Proceedings of the '10th annual conference
         on Internet measurement'", 2010.

   [6]   Honda, M., Nishida, Y., Greenhalgh, A., Handley, M., and H.
         Tokuda, "Is it Still Possible to Extend TCP? In Proc. ACM
         Internet Measurement Conference (IMC), Berlin, Germany",
         Nov 2011.

   [7]   Carpenter, B., Aboba, B., and S. Cheshire, "Design
         Considerations for Protocol Extensions", RFC 6709,
         September 2012.

   [8]   Thaler, D. and B. Aboba, "What Makes For a Successful
         Protocol?", RFC 5218, July 2008.

   [9]   Carpenter, B. and S. Brim, "Middleboxes: Taxonomy and Issues",
         RFC 3234, February 2002.

   [10]  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.

   [11]  Aboba, B. and E. Davies, "Reflections on Internet
         Transparency", RFC 4924, July 2007.

   [12]  O'Malley, S. and L. Peterson, "TCP Extensions Considered
         Harmful", RFC 1263, October 1991.

   [13]  Tschofenig, H., Aboba, B., Peterson, J., and D. McPherson,
         "Trends in Web Applications and the Implications on
         Standardization", draft-tschofenig-post-standardization-02
         (work in progress), May 2012.

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   [14]  Rosenberg, J., "UDP and TCP as the New Waist of the Internet
         Hourglass", draft-rosenberg-internet-waist-hourglass-00 (work
         in progress), February 2008.

   [15]  Clark, D., Wroslawski, J., Sollins, K., and R. Braden, "Tussle
         in Cyberspace: Defining Tomorrow's Internet, In Proc. ACM
         SIGCOMM", 2002.

   [16]  Arkko, J., Rissanen, H., Loreto, S., Turanyi, Z., and O. Novo,
         "Implementing Tiny COAP Sensors",
         draft-arkko-core-sleepy-sensors-01 (work in progress),
         July 2011.

   [17]  Jennings, C., Shelby, Z., and J. Arkko, "Media Types for Sensor
         Markup Language (SENML)", draft-jennings-senml-10 (work in
         progress), October 2012.

   [18]  "Embedded Lua Project", 2012.

   [19]  Rescorla, E. and B. Korver, "Guidelines for Writing RFC Text on
         Security Considerations", BCP 72, RFC 3552, July 2003.

   [20]  Rescorla, E. and IAB, "Writing Protocol Models", RFC 4101,
         June 2005.

   [21]  Organization for Economic Co-operation and Development, "OECD
         Guidelines on the Protection of Privacy and Transborder Flows
         of Personal Data", available at (September 2010) , http://
         0,,EN-document-0-nodirectorate-no-24-10255-0,00.html, 1980.

   [22]  Cooper, A., Tschofenig, H., Aboba, B., Peterson, J., Morris,
         J., Hansen, M., and R. Smith, "Privacy Considerations for
         Internet Protocols", draft-iab-privacy-considerations-03 (work
         in progress), July 2012.

   [23]  Shelby, Z., Hartke, K., Bormann, C., and B. Frank, "Constrained
         Application Protocol (CoAP)", draft-ietf-core-coap-13 (work in
         progress), December 2012.

   [24]  Bormann, C., "Guidance for Light-Weight Implementations of the
         Internet Protocol Suite", draft-bormann-lwig-guidance-01 (work
         in progress), January 2012.

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Authors' Addresses

   Hannes Tschofenig
   Linnoitustie 6
   Espoo  02600

   Phone: +358 (50) 4871445

   Jari Arkko
   Jorvas  02420


   Dave Thaler


   Danny McPherson


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