Internet DRAFT - draft-lindgren-icnrg-efficientiot
draft-lindgren-icnrg-efficientiot
ICN Research Group A. Lindgren
Internet-Draft F. Ben Abdesslem
Intended status: Experimental B. Ahlgren
Expires: January 7, 2016 SICS
O. Schelen
Lulea University of Technology
A. Malik
Ericsson
July 6, 2015
Applicability and Tradeoffs of Information-Centric Networking for
Efficient IoT
draft-lindgren-icnrg-efficientiot-03
Abstract
This document outlines the tradeoffs involved in utilizing
Information Centric Networking (ICN) for the Internet of Things (IoT)
scenarios. It describes the contexts and applications where the IoT
would benefit from ICN, and where a host-centric approach would be
better. The requirements imposed by the heterogeneous nature of IoT
networks are discussed (e.g., in terms of connectivity, power
availability, computational and storage capacity). Design choices
are then proposed for an IoT architecture to handle these
requirements, while providing efficiency and scalability. An
objective is to not require any IoT specific changes of the ICN
architecture per se, but we do indicate some potential modifications
of ICN that would improve efficiency and scalability for IoT and
other applications.
This document mainly serves as a problem statement and will not
present a conclusive architecture design. It can be used as a basis
for further discussion and to design architectures for the IoT.
Status of this Memo
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material or to cite them other than as "work in progress."
This Internet-Draft will expire on January 7, 2016.
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Table of Contents
1. Motivation . . . . . . . . . . . . . . . . . . . . . . . . . . 4
2. Advantages of using ICN for IoT . . . . . . . . . . . . . . . 5
2.1. Naming of Devices, Data and Services . . . . . . . . . . . 5
2.2. Distributed Caching . . . . . . . . . . . . . . . . . . . 5
2.3. Decoupling between Sender and Receiver . . . . . . . . . . 5
3. Design Challenges of IoT over ICN . . . . . . . . . . . . . . 6
3.1. Naming of Devices, Data and Services . . . . . . . . . . . 6
3.2. Efficiency of Distributed Caching . . . . . . . . . . . . 7
3.3. Decoupling between Sender and Receiver . . . . . . . . . . 8
4. Proposed Design Choices for IoT over ICN . . . . . . . . . . . 9
4.1. Relationship to existing Internet protocols . . . . . . . 9
4.2. Data naming, format and composition . . . . . . . . . . . 9
4.3. Immutable atomic data objects . . . . . . . . . . . . . . 10
4.4. Data naming in streams of immutable data objects . . . . . 11
4.5. The importance of time . . . . . . . . . . . . . . . . . . 12
4.6. Decoupling and roles of senders and receivers . . . . . . 13
4.7. Combination of PULL/PUSH model . . . . . . . . . . . . . . 14
4.8. Capability advertisements . . . . . . . . . . . . . . . . 15
4.9. Name-based routing vs name resolution + 1-step vs
2-step . . . . . . . . . . . . . . . . . . . . . . . . . . 16
4.10. What's naming and what's searching . . . . . . . . . . . . 16
4.11. Meta data, tagging/tracing of data . . . . . . . . . . . . 16
4.12. Handling actuators in the ICN model . . . . . . . . . . . 17
4.13. Role of constrained IoT devices as ICN nodes . . . . . . . 18
5. Security Considerations . . . . . . . . . . . . . . . . . . . 19
5.1. Retrieving trusted content from untrusted caches . . . . . 20
5.2. Enabling application-layer processing in untrusted
intermediaries . . . . . . . . . . . . . . . . . . . . . . 20
5.3. Energy efficiency of cryptographic mechanisms . . . . . . 20
6. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 22
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 23
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1. Motivation
Information Centric Networking (ICN) has been shown to efficiently
meet current usage demands of computer networks, where users consume
content from the network instead of communicating with specific
hosts. The applications and usage of the Internet of Things (IoT)
often imply information centric usage patterns, where users or
devices consume IoT generated content from the network instead of
communicating with specific hosts or devices.
However, while the IoT shares many characteristics with typical
information centric applications, it differs because of the high
heterogeneity of connected devices (including sensors and actuators),
the very high rate of new information being generated, and the
heterogeneity in requirements from applications regarding information
retrieval and dynamic actuation. Because of these differences, using
an Information Centric Network to design an architecture of the IoT
is often, but not always, beneficial. Depending on the context, the
IoT architecture may benefit from using an ICN or a host-centric
network (HCN). In practice, the right approach is a complex tradeoff
that depends on the applications and usage of the IoT network.
This document describes some advantages and inconveniences of using
an ICN for the IoT architecture, and helps finding the right tradeoff
between using an ICN or an HCN, depending on the context. In this,
we explore how to represent and model IoT on top of existing ICN
solutions, without requiring IoT specific functionality in the ICN.
We discuss this in terms of effectiveness, efficiency and
scalability. However, in some cases we do invite for discussion on
tentative additions of functionality to ICN in order to make the
overall IoT solution more efficient and scalable.
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2. Advantages of using ICN for IoT
A key concept of ICN is the ability to name data independently from
the current location at which it is stored, which simplifies caching
and enables decoupling of sender and receiver. Using ICN to design
an architecture for IoT data potentially provides such advantages
compared to using traditional host-centric networks. This section
highlights general benefits that ICN could provide to IoT networks.
2.1. Naming of Devices, Data and Services
The heterogeneity of both network equipment deployed and services
offered by IoT networks leads to a large variety of data, services
and devices. While using a traditional host-centric architecture,
only devices or their network interfaces are named at the network
level, leaving to the application layer the task to name data and
services. In many common applications of IoT networks, data and
services are the main goal, and specific communication between two
devices is secondary. The network distributes content and provides a
service, instead of establishing a communication link between two
devices. In this context, data content and services can be provided
by several devices, or group of devices, hence naming data and
services is often more important than naming the devices.
2.2. Distributed Caching
While caching mechanisms are already used by other types of overlay
networks, IoT networks can potentially benefit even more from caching
systems, because of their resource constraints. Wireless bandwidth
and power supply can be limited for multiple devices sharing a
communication channel, and for small mobile devices powered by
batteries. In this case, avoiding unnecessary transmissions with IoT
devices to retrieve and distribute IoT data to multiple places is
important, and storing such content in the network can save wireless
bandwidth and battery power. Moreover, as for other types of
networks, applications for IoT networks requiring shorter delays can
benefit from local caches to reduce delays between content request
and delivery.
2.3. Decoupling between Sender and Receiver
IoT devices may be mobile and face intermittent network connectivity.
When specific data is requested, such data can often be delivered by
ICN without any consistent direct connectivity between devices.
Apart from using structured caching systems as described previously,
information can also be spread by forwarding data opportunistically.
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3. Design Challenges of IoT over ICN
As outlined in Section 2, there are potential benefits from using ICN
to implement IoT communication architectures. However, in order to
obtain a scalable and efficient architecture there are some aspects
of ICN that must be specifically considered in making the right
design choices for IoT. In fact, using an ICN may not be beneficial
in all desired sub-functions and scenarios. This section outlines
some of the ICN specific challenges that must be considered and
describes some of the trade offs that will be involved. We will
address these challenges in our proposed design choices later in
Section 4.
3.1. Naming of Devices, Data and Services
The ICN approach of named data and services (i.e., device independent
naming) is typically desirable when retrieving IoT data. However,
data centric naming may also pose challenges.
o Naming of devices: Naming devices is often important in an IoT
network. The presence of actuators requires clients to act
specifically on a device, e.g. to switch it on or off. Also,
managing and monitoring the devices for administration purposes
requires devices to have a specific name allowing to identify them
uniquely. There are multiple ways to achieve device naming, even
in systems that are data centric by nature. For example, in
systems that are addressable or searchable based on metadata or
sensor content, the device identifier can be included as a special
kind of metadata or sensor reading.
o Size of data/service name: In information centric applications,
the size of the data is typically larger than its name. For the
IoT, sensors and actuators are very common, and they can generate
or use data as small as a short integer containing a temperature
value, or a one-byte instruction to switch off an actuator. The
name of the content for each of these pieces of data has to
uniquely identify the content. For this reason, many existing
naming schemes have long names that are likely to be longer than
the actual data content for many types of IoT applications.
Furthermore, naming schemes that have self certifying properties
(e.g., by creating the name based on a hash of the content),
suffer from the problem that the object can only be requested when
the object has been created and the content is already known, thus
requiring some form of indexing service. While this is an
acceptable overhead for larger data objects, it is infeasible for
use when the object size is on the order of a few bytes.
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o Hash-based content name: Hash algorithms are commonly used to name
content in order to verify that the content is the one requested.
This is only possible in contexts where the requested object is
already existing, and where there is a directory service to look
up names. This approach is suitable for systems with large data
objects where it is important to verify the content.
o Metadata-based content name: Relying on metadata allows to
generate a name for an object before it is created. However this
mechanism requires metadata matching semantics.
o Naming of services: Similarly to naming of devices or data,
services can be referred to with a unique identifier, provided by
a specific device or by someone assigned by a central authority as
the service provider. It can however also be a service provided
by anyone meeting some certain metadata conditions. Example of
services include content retrieval, that takes a content name/
description as input and returns the value of that content, and
actuation, that takes an actuation command as input and possibly
returns a status code afterwards.
3.2. Efficiency of Distributed Caching
Distributed caching is a key opportunity with ICN. However, an IoT
framework must be carefully designed to reap the maximum benefits of
ICN caching. When content popularity is heterogeneous, some content
is often requested repeatedly. In that case, the network can benefit
from caching. Another case where caching would be beneficial is when
devices with low duty cycle are present in the network and when
access to the cloud infrastructure is limited.
However, using distributed caching mechanisms in the network is not
useful when each object is only requested at most once, as a cache
hit can only occur for the second request and later. It may also be
less useful to have caches distributed throughout ICN nodes in cases
when there are overlays of distributed repositories, e.g., a cloud or
a Content Distribution Network (CDN), from which all clients can
retrieve the data. Using ICN to retrieve data from such services is
beneficial, but in case of dense occurrence of overlay CDN servers
the additional benefit of caching in ICN nodes would be lower.
Another example is when the name of the data has a different meaning
depending on the context, or if the name refers to an object with
variable content/state. For example, when the last value for a
sensor reading is requested, the returned data should change every
time the sensor reading is updated. In that case, ICN caching may
increase the risk that cache inconsistencies result in old data being
returned.
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3.3. Decoupling between Sender and Receiver
Decoupling the sender and receiver is useful mechanism offered by the
ICN approach, especially for content retrieval with duty cycling
devices or devices with intermittent connectivity. However, in order
to efficiently retrieve data it must be possible for requestors
(receivers) to easily deduce the name of the data to request, without
any direct contact with the responder (sender).
Nevertheless, de-coupling is a challenge when authentication is
needed for management and actuation, or when real-time interaction
between devices is necessary. Solutions for object security
supporting decoupled authentication (e.g., similar to signing by
proxy), and solutions for pushing data to decoupled entities must be
explored.
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4. Proposed Design Choices for IoT over ICN
This section describes some fundamental design choices and trade-offs
to allow for effective, efficient and scalable handling of IoT data
in an ICN network. An objective with these choices is to facilitate
that an ICN network can be used without requiring additions of IoT
application specific functionality in the ICN network. However, in
some cases we do invite for discussion on tentative additions of
functionality to ICN in order to make the overall IoT solution more
efficient and scalable.
4.1. Relationship to existing Internet protocols
IoT devices can have a role as content generators (e.g., sensors) in
where an ICN paradigm should be effective for data retrieval and
dissemination. However, IoT devices may also have roles as actuators
in which such devices shall be accessed for control purposes. The
use of an ICN network may be less natural when actuation and control
of specific devices is the key objective. As ICN networks are likely
to coexist with existing Internet protocols in most situation, often
being deployed as overlay networks, we will consider that there may
be situations where a host centric addressing is more suitable for
IoT. Thus, to facilitate support of IoT for both data generation and
control/actuation, we assume that ICN routing should therefore work
in concert with existing Internet protocols. However, we will also
investigate the possibility of utilizing ICN network primitives for
actuation as well to see what the tradeoffs are, as can be seen in
Section 4.12.
4.2. Data naming, format and composition
The data served by ICN may be aggregated from smaller components.
Although IoT data components in many cases are small and simple, a
general challenge in defining ICN applications is to decide how to
compose (i.e. group) the data so that it can be effectively named and
requested. Requesting partial data inside a composition may become a
challenge. Indeed, if data is composed and sub components are
requested, which are not directly namable by the requestor, finding
such a subset will resemble a database query which may require
processing to resolve. The ICN network should not have to support
such complexity.
A design choice regarding IoT data is therefore to keep the ICN
network free from supporting any advanced queries and instead only
support directly addressable (i.e., named) data objects. Any
advanced composition (hierarchical, graph-based, hyperlink, etc.) of
IoT data, and related searching for sub-components, would be handled
in servers/endpoints instead of inside the ICN network. The issue of
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IoT data structure and searching at that higher level is for further
study. For effective ICN interoperability, only the structure of the
atomically addressable data objects must be agreed and mapped to the
underlying ICN naming scheme. This is to avoid making new
requirements on the ICN and to make sure that the need for
computation is kept low in the ICN network, essentially limiting it
to deciding whether there is a cache hit or not. There are some
considerations following from this design choice. First, the size of
the directly addressable objects could be kept fairly small to avoid
that unwanted data is pulled over resource constrained networks and
cached in the ICN network (resulting in better resource utilization,
better localization of desired data, and ultimately better
scalability). There is however a tradeoff in that smaller data
objects results in a larger naming overhead. Second, this approach
means that a flat ICN address space would be sufficient, but for
practical reasons a hierarchical address space may add some benefits.
In any case, there is flexibility in using different addressing
schemes depending on what is supported by the existing ICN framework.
4.3. Immutable atomic data objects
The number of IoT devices as well as the amount of data produced by
these devices may potentially be very large, and the data may be
spread over very large ICN networks. The potential problem of cache
inconsistencies in an ICN network may therefore be large if we allow
for data to be mutable objects. To support scalability and
horizontal distribution it is essential to define data properties
that facilitate independency and consistency, while minimizing the
need for dynamic global synchronization.
A key design choice is therefore to mandate that IoT only uses
immutable atomic data objects. This supports large scale
distribution by ensuring that there is no stale data in the ICN
domain. A cache hit is always a clean hit. A trade-off from this is
that dynamic data must be modeled as a stream of immutable data
objects, potentially consuming more resources. However, this
challenge can be resolved by smart caching strategies where old data
is dropped.
There is however some practicalities to consider. Devices, including
IoT devices, are restarted now and then. They might in this process
loose their state, including what name they used for a particular
data value. So in practise it will be hard to implement a strong
assumption on immutable data. We therefore likely must be prepared
to handle the occasional exception to this rule.
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4.4. Data naming in streams of immutable data objects
Many IoT devices produce new sensor readings or other data values at
regular intervals or on demand. With the design choice on immutable
atomic data objects, there is a need to model the resulting stream of
sensor readings with a stream of immutable data objects in the ICN
domain. The need in this situation is very similar, if not
identical, to video streaming, where video frames or chunks are
immutable data objects in a video stream.
A key advantage of modelling IoT data as a stream of immutable data
objects is that ICN caches will not contain any stale data w r t a
given name. However, since new data objects (with new names)
representing different versions of a sensor reading may be emitted
frequently, there must be a way to tell the different versions apart.
To support immutable streamed data efficiently, while adhering to the
expected naming schemes of ICN, we recommend that names of data
objects include a sequence number. When data can be named with
sequence number, any request may or may not include such a sequence
number. If no number is included in the request, the nearest cache
hit will result in a response. If a sequence number is included in
the request, only an exact cache match will result in a response. A
client that wants the "latest" reading can according to our
previously mentioned design choice, in Section 4.2, not ask the ICN
network such a high level query, instead it must ask for the specific
(version of) information. To avoid complicated searching in the ICN
nodes, there is thus no way to explicitly ask the network for the
"latest" reading, or any other "range" of sequence numbers.
Should a client want the latest reading from a sensor, one method for
this is to make a subscription for the pushed stream of data, as
described in Section 4.7, provided that the particular ICN
architecture supports this interaction model. The confirmation of
that subscription can contain the latest reading, and then obviously
the normal stream will be received. The reason for including the
latest reading in the response is to immediately provide the "state"
of sensors that generate new data infrequently.
Another method to obtain the latest reading, or a particular reading
in the past, from a sensor is to perform adaptive probing, for
example by binary interval reduction. If a requested sequence number
does not (yet) exist, there will be a negative answer from the ICN.
This method is preferably combined with application knowledge, for
example, in the form of capability advertisements as described in
Section 4.8 that enable the client to better predict the sequence
number to request. The client that always wants the latest value
could also dynamically tune its requests for the next data value to
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the frequency of the publisher in order to minimise the latency. The
fact that non-existing data is asked for would however potentially
pose an overload threat to the ICN since each request of non-existing
data could result in cache misses that ripple through all the way to
the source, which has to respond that the data doesn't exist. It may
therefore be beneficial with negative caching. Serving requests for
non-existing data is however a generic challenge to ICN (not
specifically to IoT) to be resolved.
There is a third method "in between" the above two. If requests for
a not yet existing data object can be held for a short time until the
data object is actually available, instead of immediately returning
"not found", these requests act as one-time subscriptions. Provided
that request aggregation is being used, this mechanism would be
efficient and latency-minimising, and at the same time would not
require persistent subscription state.
The support for sequence numbers depends on the particular flavor of
ICN. The naming scheme of CCN/NDN may here provide an advantage. It
is for further study whether it is possible to use ICNs that do not
support sequence numbers as part of naming (e.g., by clever use of
metadata, namespace, and search functionality) and what the trade-
offs would be.
Two issues for further study are the size of the sequence number
space and gaps in the sequence numbers. Must sequence number
wraparound be handled, or is it possible to require a large enough
sequence number space? Wraparound means an exception to the
assumption on immutable objects. Gaps in the sequence number space
might result in inefficiencies in some of the above methods, or, if
the gaps are large, making them unfeasible. Yet, it might not always
be possible to guarantee that there are no gaps.
4.5. The importance of time
Time is almost always a very important property of IoT data, and
especially so for data that change over time. When modeling dynamic
IoT data with a stream of immutable data values, it is often the case
that a certain IoT data value is a sensor reading at a particular
point in time, and the next value in the stream is the next reading
in time. Thus, dynamic data is in this case dynamic over time, with
well defined (immutable) values for particular points in time.
We therefore argue that it is important to find a way to represent
these time-related streams of immutable data values in ICN. It
should be possible to request a data value from a certain time, and
to infer/find the name (sequence number) of the latest, most current,
data value. The question is whether or not the stream sequence
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numbers are sufficient to support time. If not, the ICN system needs
to be extended with explicit support for time, something we want to
avoid. In general, the methods outlined in the previous section are
applicable for finding an IoT data value from a particular point in
time, including the latest. What is missing is the mapping between
sequence number and time.
One possibility could be to use sequence numbers that directly
correspond to time, for instance, the Unix (POSIX) time in form of
seconds since January 1st, 1970. This would however both limit the
time resolution to seconds, and also result in large gaps in the
sequence numbers, something that can be problematic, as discussed in
the previous section.
There are several other methods for finding readings from a certain
time, or the latest reading, for example through a high level request
from a server/endpoint, or by using a naming scheme where the name
can be directly inferred, e.g., if an IoT device has advertised under
which conditions it produces data and how it is named.
To represent absolute time so that it can be directly inferred, one
method is that the producer of data in its capability advertisements
(Section 4.8) provide a mapping function between sequence number and
time. Thereby also readings on the time axis are immutable while it
is still possible to efficiently find the latest reading, as
described in Section 4.4. It should be noted that sequence numbers
then may have gaps in order to cater for triggered non periodic data,
etc. Another method is to include meta data with information on
absolute time. Using this mapping scheme data from the current
second can be efficiently requested (provided that clock
synchronisation is accurate enough, which is out of scope of this
document).
We also note that time is also important for other applications, in
particular for live streaming video. Live video also produces a
time-related stream of immutable objects, and would in the same way
benefit from such support in the ICN service.
4.6. Decoupling and roles of senders and receivers
Since ICN networks essentially support a request/response model of
interaction, we denote the receivers of information as requestors,
and the senders of information as responders. The ICN network in
itself provides decoupling of requestors and responders. It is an
important feature of the ICN that it will allow responders (e.g., IoT
devices) to be occasionally unreachable (e.g., due to intermittent
connectivity, low battery level, duty cycling). Another advantage is
that caching in the ICN will ensure that data objects are normally
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delivered only once from the IoT devices, independently of the number
of immediate requestors.
Note however, that the ICN does not (and should not) provide any
transformation or aggregation of data. The IoT dissemination
architecture should therefore allow for any number of intermediate
processing nodes. An intermediate node will be an endpoint in the
ICN network that can act as both requestor and responder. Such a
node may perform aggregation, filtering, selection, etc. The
instantiation of such nodes may for example form a directed (acyclic)
graph between ultimate responders (IoT devices) and ultimate
requestors (the final applications). It is for further study how to
define such an architecture.
It is a design choice to keep the IoT dissemination and aggregation
functionality outside of the ICN domain. That architecture would be
an overlay that may have intricate structure, and put the ICN usage
in a new context, where content from ultimate requestors to ultimate
responders may go through many IoT processing nodes that collect,
process and re-publish data through an ICN for various purposes.
4.7. Combination of PULL/PUSH model
A critical decision regarding IoT data is whether to use a PULL
model, a PUSH model, or both. In this document, we define a PULL
model as a system where data is only sent when explicitly requested,
while a PUSH model indicate that data transmission is initiated by
the source based on some trigger (either periodic, for each new
object, or based on some condition on the generated data). There are
some intrinsic trade offs between these models. The PULL model is
for example resource efficient when there is an abundant amount of
IoT information, potentially redundant from many devices, and the
clients only occasionally or partially are interested in the
information. The PUSH model is for example efficient when there is
real-time information and the clients are interested in all
information from specific devices all the time.
A design decision in the IoT domain is to support both PULL and PUSH.
The base model should be PULL, since this is the native mode of ICN,
meaning that requestors must always start by sending a request. If
the request is for some specific data, it can be resolved by
returning the data (if it exists). The pull model can be supported
efficiently and scalably by an ICN network.
A challenge with the pull model is that it may be inefficient for
retrieving new data that occur sporadically or based on specific
conditions. Our proposal for an IoT framework is therefore that
there must be support for efficiently retrieving such triggered
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information, without having to poll for it through the ICN. Our
proposal is that a request can also include triggers, which means
that data will be returned (pushed) when triggers are fulfilled,
which may be immediately, or in the future at one or several
occasions. This can be used to select alarm conditions, to request
continuous or periodic push, etc. The trigger conditions could be
set by the requestor, or be pre-defined by the responder. The former
would be more flexible but also have performance/scalability issues
since the number of trigger conditions and consequent data generation
would depend on a potential large number of requestors. The latter
is more scalable since there will be a predefined and finite number
of trigger conditions (as defined in capability advertisements). Our
recommended choice, at least for the initial phase, is to go for a
simple and scalable solution and therefore adopt the model where
available trigger conditions are defined and advertised by the
responder. The ICN would be apt for supporting such capability
advertisements, given that they are fairly static.
With this, there is no requirement raised on ICNs supporting data
push, but we recommend to have a discussion on whether an ICN network
can or should provide an option to effectively support a push model
of data. Such support could make real-time IoT data dissemination
more efficient and scalable as previously mentioned in Section 4.3.
However, since we assume that the ICN works with existing IP
protocols, such functionality can be provided without ICN, by using
traditional unicast or multicast communication. We finally note that
an ICN supported push service model would make the ICN network more
like a publish/subscribe system.
4.8. Capability advertisements
Capability advertisements and discovery can be used by requestors to
discover which data is available and/or to which responders to
connect to. In a deployment with large numbers of responders, the
functionality of automatic advertisement and discovery becomes a
critical factor to support scaling. Responders should advertise
their methods (inputs, outputs, parameters, triggers, etc) and
provide relevant metadata in the responses as advertised. Such
capability advertisements should be conservative with resources,
which suggests that new advertisements should be posted with
reasonably low frequency. This implies that an ICN network can be
used for providing capability advertisements. The advertisements
should be provided as a stream of immutable objects, or alternatively
the IoT system should be tolerant to stale caches. Should there be a
need real-time awareness of dynamic changes, a subscription/push
model of capability advertisements could be used as earlier described
in Section 4.7.
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4.9. Name-based routing vs name resolution + 1-step vs 2-step
As described in Section 4.2, the IoT framework should be defined so
that new functionality in the ICN is not needed. For data that is
frequently generated and regenerated, it makes sense to keep simple
structures and provide directly inferable naming/addressing of data
objects, so that requestors can directly address the data. For more
complex data, such as pre-processed, aggregated and structured data a
two-step resolution model is recommended. The IoT devices can
provide a higher level resolution based on for example queries and
searching, resulting in a number of concrete directly addressable ICN
objects. This is similar to what web servers do when they return
URLs that requestors can use, but in this case it is named content
that is returned.
Consequently, the IoT framework should have no requirement that the
ICN network itself should support 2-step addressing (although such
2-step methods may exist in some ICNs)
4.10. What's naming and what's searching
As described in Section 4.2, the IoT framework should be defined so
that no new functionality is required in the ICN for searching data
or subcomponents of data. The ICN network supports just naming of
atomic data objects, while any searching is provided by the IoT
framework, which in itself may be constituted by a highly distributed
set of nodes that provide processing, analysis and aggregation of IoT
data.
4.11. Meta data, tagging/tracing of data
IoT data may be tagged with metadata to tell where it originates
from. Tagging is made at the level above the ICN network and may for
example be a list of strings. It can be added/changed by the
originating node (or a node that assigns the originating ID), and
added/changed/deleted by any node that processes the data. The tag
can in some cases be used to trace data back to origins. In some
cases it makes no sense to request or transmit metadata. For
efficiency reasons the ICN network should have support for optional
delivery of metadata. This is to be conservative with scarce
resources, for example when a wireless node requests data which is
cached in the ICN network, it would be beneficial if the requestor
could tell that it is desirable to not receive any metadata. There
should be a discussion whether there should be just one, or more than
one, piece of optional information in ICN content to be future proof.
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4.12. Handling actuators in the ICN model
If actuators should be controlled using the ICN communication model,
we need to map the functionality of the actuator to named data and/or
the requesting of named data. We see two main models with some
variants as described in the following paragraphs.
In the first model, the state of the actuator is represented by a
stream of immutable named data objects. The actuator periodically
requests its new state using the name of its designated state object.
There then has to be a producer of that state data that responds with
the current state. When the actuator receives the response, it sets
that new state, invoking its actuation function. Authentication of
the producer of the state is important, but as this corresponds
directly to publisher and data object authenticity that are
fundamental in the ICN model, there are no additional requirements
for the IoT domain.
A variant of this first model is that a requester first requests the
state of the actuator. The requester supplies additional information
with the request including the name of the new state data it will
produce. The actuator responds with its state, and then requests its
new state using the name that was supplied with the additional
information in the first request. This variant enables low latency
without high frequency polling.
In the second model, the actuator invokes its actuation function as a
side-effect of receiving a particular request. There are several
plausible variants. The new state could be encoded in the name of
the requested data in the request, or could be supplied as additional
information with the request. Regardless, the actuator acts on the
new state information as a side effect, and responds with data,
possibly its state, to the requester. The security issues are
potentially more difficult with this model, since in the ICN model,
anyone could make the request. Access control and/or requester
authentication are therefore required.
To reap the advantages of caching, it should be possible to cache the
state of the actuator in both the aforementioned models. However, we
think that caching is not as relevant for actuation as it is for
other IoT use cases, and can furthermore even be quite problematic.
The first model less so, since the actuator can make sure that its
state is arbitrarily fresh with the polling method described in
Section 4.4. In other words, the latency until actuation happens can
be bounded. The variant of the first model and the second model have
larger issues. With caching, it is hard for a requester to make sure
that its request actually reaches the actuator, and thus, it is hard
to bound the actuation latency. Some caching directive might be
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needed in this case for reliable functionality.
4.13. Role of constrained IoT devices as ICN nodes
Typical ICN nodes such as routers and gateways are deemed to be rich
in resources like energy, processing, bandwidth and storage. IoT
devices, on the other hand, are quite constrained in such resources.
It is also worth noticing that some resources are more crucial than
others. In most cases energy, processing and bandwidth are quite
expensive for constrained IoT devices. In contrast, storage has
shown a considerably rapid decreasing trend in prices over the past
few years. There is reason to believe that the memory needed for IoT
devices to act as servers of their data will not be prohibitive and
that the data centric role of the devices may be elevated by
information-centric networks.
However, it is questionable whether IoT devices also should provide
caching for data produced by other IoT devices. In ad-hoc networks
this may be desirable, but often there is a desire for wireless nodes
to minimize communication by handling only data of their own concern.
Our design decision in this regard is that we logically separate IoT
server functionality (such as sensing and transmitting IoT data) and
ICN functionality (such as routing and caching data generated by
other devices). A resource constrained device may choose to only
implement IoT functionality and act as a server to the ICN, i.e., not
act as intermediate ICN node. However, since storage is getting
cheaper, IoT devices should be able to cache their own content and,
in essence, act as sources to ICN.
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5. Security Considerations
The ICN paradigm is information-centric as opposed to state-of-the-
art host-centric internet. Besides aspects like naming, content
retrieval and caching this also has security implications. ICN
advocates the model of trust in content rather than trust in network
hosts. This brings in the concept of Object Security which is
contrary to session-based security mechanisms such as TLS/DTLS
prevalent in the current host-centric internet.
Object Security is based on the idea of securing information objects
unlike session-based security mechanisms which secure the
communication channel between a pair of nodes. This reinforces an
inherent characteristic of ICN networks i.e. to decouple senders and
receivers. In the context of IoT, the Object Security model has
several concrete advantages. As discussed earlier in Section 2.1, in
many IoT applications data and services are the main goal and
specific communication between two devices is secondary. Therefore
it makes more sense to secure IoT objects instead of securing the
session between communicating endpoints.
It is important that while security mechanisms complement the ICN
architecture in a coherent fashion, they do so without laying down
any strict requirements or constraints. Therefore, the decision of
what security mechanisms are employed should be handled at a layer
above ICN, in this case within the IoT framework. However, the ICN
layer should not be completely oblivious of Object Security. At this
point it is important to distinguish between the different aspects of
Object Security i.e. integrity, authenticity and confidentiality.
ICN provides data integrity through Name-Data Integrity i.e. the
guarantee that the given data corresponds to the name with which it
was addressed. Typical ICN protocols provide Name-Data integrity
using various schemes such as hash-based names and signatures.
Signature-based schemes additionally provide data authenticity.
Otherwise data authenticity should be provided in layers above the
ICN layer. Data confidentiality should also be handled above the ICN
layer. This facilitates flexibility and allows IoT applications more
freedom to decide which encryption scheme suits them best (session-
based encryption, object-based encryption or a hybrid).
Though the idea of Object Security is very much in line with the ICN
concept, there can still be some use cases where Object Security does
not add much e.g. a Pub/Sub interaction where a client is expected to
interact more or less with the same server node (a session-based
security protocol should suffice here) or use cases where application
layer headers should also be secured (which can be achieved by TLS/
DTLS). We, therefore, effectively imply that there is no need to
modify typical ICN standards to accommodate Object Security in its
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entirety.
The following sub-sections discuss some security advantages of using
ICN and Object Security in IoT applications.
5.1. Retrieving trusted content from untrusted caches
When functioning in an ICN network, an IoT client is expected to rely
on the network to deliver the requested content in an optimal fashion
without concerning itself with where the content actually lies. This
could potentially mean that each individual object within a stream of
immutable objects is retrieved from a different source. Having a
trust relationship with each of these different sources is not
realistic. This gives rise to the need of retrieving trusted content
from untrusted nodes/caches in an ICN network. Through Name-Data
Integrity, ICN automatically guarantees data integrity to the
requester regardless of the source from where it is delivered.
Additionally, Object-based signatures and encryption are ideal in
such use cases because it relieves an IoT client application from the
hassle of having to establish trust with each node that can
potentially cache an IoT object. This also means that a requesting
client can make use of more caches in the network, hence resulting in
better throughput and latency.
5.2. Enabling application-layer processing in untrusted intermediaries
Securing content at the object level provides greater granularity and
hence more control. An ICN data object may comprise of several
distinct application-layer objects e.g. XML, JSON objects. An
example of this is an ICN object that corresponds to all the sensor
readings in a certain time interval where each sensor reading is a
JSON object. Using Object-based encryption to provide data
confidentiality allows for the possibility to encrypt a subset of
these application-layer objects while leaving others unencrypted and
available for processing in untrusted intermediary nodes (e.g.
proxies and caches). With this approach, the IoT application has
more control of the parts of data it wants to make public and the
parts of data it wants to keep confidential and visible only to peers
with the right cryptographic keys.
5.3. Energy efficiency of cryptographic mechanisms
Session-based security protocols rely on the exchange of several
messages before a secure session is established between a pair of
nodes. Use of such protocols in constrained IoT devices can have
serious consequences in terms of power efficiency because in most
cases transmission and reception of messages is more costly than the
cryptographic operations. This is especially true for wireless
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devices.
The problem is amplified proportionally with the number of nodes the
constrained device has to interact with because a secure session
would have to be established with every node. If the constrained
device is acting as a consumer of data this would mean setting up
secure sessions with every caching node that the device retrieves
data from. When acting as a producer of data the constrained device
would have to setup secure sessions with all the consumers. The
Object Security model eliminates this problem because the content is
readily available in a secure state in the network. IoT devices
producing data can secure it w.r.t. all the intended consumers and
start transmitting it right away.
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6. Acknowledgements
The work behind and the writing of this document are in part
supported by the activity `14010 Efficient IoT Content' within EIT
Digital (formerly EIT ICT labs).
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Authors' Addresses
Anders F. Lindgren
SICS Swedish ICT
Box 1263
Kista SE-164 29
SE
Phone: +46707177269
Email: andersl@sics.se
URI: http://www.sics.se/~andersl
Fehmi Ben Abdesslem
SICS Swedish ICT
Box 1263
Kista SE-164 29
SE
Phone: +46705470642
Email: fehmi@sics.se
URI: http://www.sics.se/~fehmi
Bengt Ahlgren
SICS Swedish ICT
Box 1263
Kista SE-164 29
SE
Phone: +46703141562
Email: bengta@sics.se
URI: http://www.sics.se/people/bengt-ahlgren
Olov Schelen
Lulea University of Technology
Lulea SE-971 87
SE
Phone:
Email: olov.schelen@ltu.se
URI:
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Adeel Mohammad Malik
Ericsson
Kista SE-164 80
SE
Phone: +46725074492
Email: adeel.mohammad.malik@ericsson.com
URI:
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