Internet Research Task Force (IRTF) B. Wissingh
Request for Comments: 8793
Category: Informational C. Wood
ISSN: 2070-1721 University of California Irvine
Florida International University
Network Systems Research & Design
University of Basel
Information-Centric Networking (ICN): Content-Centric Networking (CCNx)
and Named Data Networking (NDN) Terminology
Information-Centric Networking (ICN) is a novel paradigm where
network communications are accomplished by requesting named content
instead of sending packets to destination addresses. Named Data
Networking (NDN) and Content-Centric Networking (CCNx) are two
prominent ICN architectures. This document provides an overview of
the terminology and definitions that have been used in describing
concepts in these two implementations of ICN. While there are other
ICN architectures, they are not part of the NDN and CCNx concepts and
as such are out of scope for this document. This document is a
product of the Information-Centric Networking Research Group (ICNRG).
Status of This Memo
This document is not an Internet Standards Track specification; it is
published for informational purposes.
This document is a product of the Internet Research Task Force
(IRTF). The IRTF publishes the results of Internet-related research
and development activities. These results might not be suitable for
deployment. This RFC represents the consensus of the Information-
Centric Networking Research Group of the Internet Research Task Force
(IRTF). Documents approved for publication by the IRSG are not a
candidate for any level of Internet Standard; see Section 2 of RFC 7841
Information about the current status of this document, any errata,
and how to provide feedback on it may be obtained at https://www.rfc-editor.org/info/rfc8793
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Table of Contents 1.
A Sketch of the Big Picture of ICN 3.
Terms by Category 3.1.
Generic Terms 3.2.
Terms Related to ICN Nodes 3.3.
Terms Related to the Forwarding Plane 3.4.
Terms Related to Packet Types 3.5.
Terms Related to Name Types 3.6.
Terms Related to Name Usage 3.7.
Terms Related to Data-Centric Security 4.
Semantics and Usage 4.1.
Data Transfer 4.2.
Data Transport 4.3.
Lookup Service 4.4.
Database Access 4.5.
Remote Procedure Call 4.6.
IANA Considerations 6.
Security Considerations 7.
Normative References 7.2.
Information-centric networking (ICN) is an architecture to evolve the
Internet infrastructure from the existing host-centric design to a
data-centric architecture, where accessing data by name becomes the
essential network primitive. The goal is to let applications refer
to data independently of their location or means of transportation,
which enables native multicast delivery, ubiquitous in-network
caching, and replication of data objects.
As the work on this topic continues to evolve, many new terms are
emerging. The goal of this document is to collect the key terms with
a corresponding definition as they are used in the CCNx and NDN
projects. Among the important documents for these projects are
], and [NDNTLV]. Other ICN projects such as
[NETINF], [PSIRP], or [MOBILITY-FIRST] are not covered and may be the
subject of other documents.
In this document, to help provide context for the individual defined
terms, we first sketch the bigger picture of an ICN network by
introducing the basic concepts and identifying the major components
of the architecture in Section 2
; after which, in Section 3
related terms are listed by different categories. Readers should be
aware that in this organization, some terms may be used in other
definitions before they themselves are defined.
While this terminology document describes both confidentiality and
integrity-related terms, it should be noted that ICN architectures
like NDN and CCNx generally do not provide data confidentiality,
which is treated in these architectures as an application-layer
This document represents the consensus of the Information-Centric
Networking Research Group (ICNRG). It has been reviewed extensively
by the Research Group (RG) members active in the specific areas of
work covered by the document. It is not an IETF product and is not
intended for standardization in the IETF.
2. A Sketch of the Big Picture of ICN
In networking terms, an ICN is a delivery infrastructure for named
data. For other complementing views, see Section 4
requestor zero or more data sources or
(node) forwarding nodes replica nodes
| | ... | |...|
| Interest(n) | | Interest(n) | |
| --------------> | | ---------------> | |
| | | -------------------> |
| | | | |
| | | Data([n],c,[s]) | |
| | | <--------------- | |
| | | <------------------- |
| Data([n],c,[s]) | | | |
| <-------------- | | | |
Legend: n=name, c=content, s=signature
Figure 1: Request-Reply Protocol of ICN Networking.
The following list describes the basic ICN concepts needed to discuss
the implementation of this service abstraction.
*Request-Reply Protocol (Interest and Data Packet):*
An ICN's lookup service is implemented by defining two types of
network packet formats: Interest packets that request content by
name and Data packets that carry the requested content. The
returned Data packet must match the request's parameters (e.g.,
having a partially or fully matching name). If the request is
ambiguous and several Data packets would satisfy the request, the
ICN network returns only one matching Data packet (thus achieving
flow balance between Interest and Data packets over individual
Layer 2 interfaces).
*Packet and Content Names:*
Without a strong cryptographic binding between the name of a Data
packet and its content, Data packet names would be useless for
fetching specific content. In ICN, verification of a Data
packet's name-to-content binding is achieved through cryptographic
means either by (1) a cryptographic signature that explicitly
binds an application-chosen name to a Data packet's content or by
(2) relying on an implicit name (cryptographic hash of the Data
packet with or without application-chosen name) that the data
consumer obtained through other means.
*Data Authenticity and Encryption:*
Any data consumer or network element can (in principle) validate
the authenticity of a Data packet by verifying its cryptographic
name-to-content binding. Note that data authenticity is distinct
from data trustworthiness, though the two concepts are related. A
packet is authentic if it has a valid name-to-content binding, but
it may still be unwise to "trust" the content for any particular
Data authenticity is distinct from data trustworthiness, though
the two concepts are related. A packet is authentic if it has a
valid name-to-content binding. A packet is trustworthy, i.e., it
comes from a reputable or trusted origin, if this binding is valid
in the context of a trust model. The trust model provides
assurance that the name used for a given piece of content is
appropriate for the value of the content. Section 6
*Segmenting and Versioning:*
An ICN network will be engineered for some packet size limit. As
application-level data objects will often be considerably larger,
objects must be segmented into multiple Data packets. The names
for these Data packets can, for example, be constructed by
choosing one application-level object name to which a different
suffix is added for each segment. The same method can be used to
handle different versions of an application-level object by
including a version number in the name of the overall object.
*Packet and Frame:*
NDN and CCNx introduce Protocol Data Units (PDUs), which typically
are larger than the maximum transmission unit of the underlying
networking technology. We refer to PDUs as packets and the
(potentially fragmented) packet parts that traverse MTU-bound
Layer 2 interfaces as frames. Handling Layer 2 technologies that
lead to fragmentation of ICN packets is done inside the ICN
network and is not visible at the service interface.
A node within an ICN network can fulfill the role of a data
producer, a data consumer, and/or a forwarder for Interest and
Data packets. When a forwarder has connectivity to neighbor
nodes, it performs Interest and Data packet forwarding in real
time. It can also behave as a store and forward node carrying an
Interest or Data packet for some time before forwarding it to the
next node. An ICN node may also run routing protocols to assist
its Interest forwarding decisions.
The canonical way of implementing packet forwarding in an ICN
network relies on three data structures that capture a node's
state: a Forwarding Interest Base (FIB), a Pending Interest
Table (PIT), and a Content Store (CS). It also utilizes Interest
forwarding strategies, which take input from both FIB and
measurements to make Interest forwarding decisions. When a node
receives an Interest packet, it checks its CS and PIT to find a
matching entry; if no match is found, the node records the
Interest in its PIT and forwards the Interest to the next hop(s)
towards the requested content, based on the information in its
3. Terms by Category
3.1. Generic Terms
*Information-Centric Networking (ICN):*
A networking architecture that retrieves Data packets in response
to Interest packets. Content-Centric Networking (CCNx 1.x) and
Named Data Networking (NDN) are two realizations (designs) of an
*Data Packet Immutability:*
After a Data packet is created, the cryptographic signature
binding the name to the content ensures that if either the content
or the name changes, that change will be detected and the packet
discarded. If the content carried in a Data packet is intended to
be mutable, versioning of the name should be used so that each
version uniquely identifies an immutable instance of the content.
This allows disambiguation of various versions of content such
that coordination among the various instances in a distributed
system can be achieved.
3.2. Terms Related to ICN Nodes
A generalization of the network interface that can represent a
physical network interface (ethernet, Wi-Fi, bluetooth adapter,
etc.), an overlay inter-node channel (IP/UDP tunnel, etc.), or an
intra-node inter-process communication (IPC) channel to an
application (unix socket, shared memory, intents, etc.).
Common aliases include: face.
An ICN entity that requests Data packets by generating and sending
out Interest packets towards local (using intra-node interfaces)
or remote (using inter-node interfaces) ICN Forwarders.
Common aliases include: consumer, information consumer, data
consumer, consumer of the content.
An ICN entity that creates Data packets and makes them available
Common aliases include: producer, publisher, information
publisher, data publisher, data producer.
An ICN entity that implements stateful forwarding.
Common aliases include: ICN router.
*ICN Data Node:*
An ICN entity that temporarily stores and potentially carries an
Interest or Data packet before forwarding it to next ICN entity.
Note that such ICN data nodes do not have all the properties of
data nodes as employed in the Delay Tolerant Networking (DTN)
3.3. Terms Related to the Forwarding Plane
A forwarding process that records incoming Interest packets in the
PIT and uses the recorded information to forward the retrieved
Data packets back to the consumer(s). The recorded information
can also be used to measure data-plane performance, e.g., to
adjust interest forwarding-strategy decisions.
Common aliases include: ICN Data plane, ICN Forwarding.
A module of the ICN stateful forwarding (ICN data) plane that
implements a decision on where/how to forward the incoming
Interest packet. The forwarding strategy can take input from the
Forwarding Information Base (FIB), measured data-plane performance
parameters, and/or use other mechanisms to make the decision.
Common aliases include: Interest forwarding strategy.
Forwarding packets in the direction of Interests (i.e., Interests
are forwarded upstream): consumer, router, router, ..., producer.
Forwarding packets in the opposite direction of Interest
forwarding (i.e., Data and Interest Nacks are forwarded
downstream): producer, router, ..., consumer(s).
A process of forwarding Interest packets using the Names carried
in the Interests. In case of stateful forwarding, this also
involves creating an entry in the PIT. The forwarding decision is
made by the Forwarding Strategy.
A process of combining multiple Interest packets with the same
Name and additional restrictions for the same Data into a single
Common aliases include: Interest collapsing.
A process of forwarding the incoming Data packet to the
interface(s) recorded in the corresponding PIT entry (entries) and
removing the corresponding PIT entry (entries).
*Satisfying an Interest:*
An overall process of returning content that satisfies the
constraints imposed by the Interest, most notably a match in the
*Interest Match in FIB (longest prefix match):*
A process of finding a FIB entry with the longest Name (in terms
of Name components) that is a prefix of the specified Name. See Section 3.5
for terms related to name prefixes.
*Interest Match in PIT (exact match):*
A process of finding a PIT entry that stores the same Name as
specified in the Interest (including Interest restrictions, if
*Data Match in PIT (all match):*
A process of finding (a set of) PIT entries that can be satisfied
with the specified Data packet.
*Interest Match in CS (any match):*
A process of finding an entry in a router's Content Store that can
satisfy the specified Interest.
*Pending Interest Table (PIT):*
A database that records received and not-yet-satisfied Interests
with the interfaces from where they were received. The PIT can
also store interfaces to where Interests were forwarded, and
information to assess data-plane performance. Interests for the
same Data are aggregated into a single PIT entry.
*Forwarding Information Base (FIB):*
A database that contains a set of prefixes, each prefix associated
with one or more faces that can be used to retrieve Data packets
with Names under the corresponding prefix. The list of faces for
each prefix can be ranked, and each face may be associated with
additional information to facilitate forwarding-strategy
*Content Store (CS):*
A database in an ICN router that provides caching.
An optional process of storing a Data packet within the network
(opportunistic caches, dedicated on/off path caches, and managed
in-network storage systems), so it can satisfy an incoming
Interest for this Data packet. The in-network storages can
optionally advertise the stored Data packets in the routing plane.
A process of temporarily storing a forwarded Data packet in the
router's memory (RAM or disk), so it can be used to satisfy future
Interests for the same Data, if any.
Common aliases include: on-path in-network caching.
The process of achieving the temporary, permanent, or scheduled
storage of a selected (set of) Data packet(s).
Common aliases include: off-path in-network storage.
*Managed In-Network Storage:*
An entity acting as an ICN publisher that implements managed
Common aliases include: repository, repo.
*ICN Routing Plane:*
An ICN protocol or a set of ICN protocols to exchange information
about Name space reachability.
*ICN Routing Information Base (RIB):*
A database that contains a set of prefix-face mappings that are
produced by running one or multiple routing protocols. The RIB is
used to populate the FIB.
3.4. Terms Related to Packet Types
A network-level packet that expresses the request for a Data
packet using either an exact name or a name prefix. An Interest
packet may optionally carry a set of additional restrictions
(e.g., Interest selectors). An Interest may be associated with
additional information to facilitate forwarding and can include
Interest lifetime, hop limit, forwarding hints, labels, etc. In
different ICN designs, the set of additional associated
information may vary.
Common aliases include: Interest, Interest message, information
A packet that contains the Interest packet and optional
annotation, which is sent by the ICN router to the interface(s)
the Interest was received from. An Interest Nack is used to
inform downstream ICN nodes about the inability to forward the
included Interest packet. The annotation can describe the reason.
Common aliases include: network NACK, Interest return.
A network-level packet that carries payload, uniquely identified
by a name, that is directly secured through cryptographic
Common aliases include: data, data object, content object,
content object packet, data message, named data object, named
A type of Data packet whose body contains the Name of another Data
packet. This inner Name is often a Full Name, i.e., it specifies
the Packet ID of the corresponding Data packet, but this is not a
Common aliases include: pointer.
A type of Data packet that contains Full Name Links to one or more
Data Packets. Manifests group collections of related Data packets
under a single Name. Manifests allow both large Data objects to
be conveniently split into individual Content Objects under one
name, and to represent sets of related Content Objects as a form
of "directory". Manifests have the additional benefit of
amortizing the signature verification cost for each Data packet
referenced by the inner Links. Manifests typically contain
additional metadata, e.g., the size (in bytes) of each linked Data
packet and the cryptographic hash digest of all Data contained in
the linked Data packets.
3.5. Terms Related to Name Types
A Data packet identifier. An ICN name is hierarchical (a sequence
of name components) and usually is semantically meaningful, making
it expressive, flexible, and application-specific (akin to an HTTP
URL). A Name may encode information about application context,
semantics, locations (topological, geographical, hyperbolic,
etc.), a service name, etc.
Common aliases include: data name, interest name, content name.
A sequence of bytes and optionally a numeric type representing a
single label in the hierarchical structured name.
Common aliases include: name segment (as in CCNx).
A unique cryptographic identifier for a Data packet. Typically,
this is a cryptographic hash digest of a Data packet (such as
]), including its name, payload, meta information,
Common aliases include: implicit digest.
A mechanism (condition) to select an individual Data packet from a
collection of Data packets that match a given Interest that
requests data using a prefix or exact Name.
Common aliases include: interest selector, restrictor, interest
A field of an Interest packet that transiently names an Interest
instance (instance of Interest for a given name). Note: the
specifications defining nonces in NDN do not necessarily satisfy
all the properties of nonces as discussed in [RFC4949
A Name that is encoded inside a Data packet and that typically
uniquely identifies this Data packet.
An exact Name with the Packet ID of the corresponding Data packet.
A Name that includes a partial sequence of Name components
(starting from the first one) of a Name encoded inside a Data
Common aliases include: prefix.
3.6. Terms Related to Name Usage
A convention, agreement, or specification for the Data packet
naming. a Naming convention structures a namespace.
Common aliases include: Naming scheme, ICN naming scheme,
*Hierarchically structured naming:*
The naming scheme that assigns and interprets a Name as a sequence
of labels (Name components) with hierarchical structure without an
assumption of a single administrative root. A structure provides
useful context information for the Name.
Common aliases include: hierarchical naming, structured naming.
The naming scheme that assigns and interprets a Name as a single
label (Name component) without any internal structure. This can
be considered a special (or degenerate) case of structured names.
A process of splitting large application content into a set of
uniquely named Data packets. When using hierarchically structured
names, each created Data packet has a common prefix and an
additional component representing the segment (chunk) number.
Common aliases include: chunking.
A process of assigning a unique Name to the revision of the
content carried in the Data packet. When using a hierarchically
structured Name, the version of the Data packet can be carried in
a dedicated Name component (e.g., prefix identifies data, unique
version component identifies the revision of the data).
A process of splitting PDUs into Frames so that they can be
transmitted over a Layer 2 interface with a smaller MTU size.
3.7. Terms Related to Data-Centric Security
A security property associated with the Data packet, including
data (Data-Centric) integrity, authenticity, and optionally
confidentiality. These security properties stay with the Data
packet regardless of where it is stored and how it is retrieved.
Common aliases include: directly securing Data packet.
A cryptographic mechanism to ensure the consistency of the Data
packet bits. The Data integrity property validates that the Data
packet content has not been corrupted during transmission, e.g.,
over lossy or otherwise unreliable paths, or been subject to
A cryptographic mechanism to ensure trustworthiness of a Data
packet based on a selected (e.g., by a consumer/producer) trust
model. Typically, data authenticity is assured through the use of
asymmetric cryptographic signatures (e.g., RSA, ECDSA) but can
also be realized using symmetric signatures (e.g., Hashed Message
Authentication Code (HMAC)) within trusted domains.
A cryptographic mechanism to ensure secrecy of a Data packet.
Data confidentiality includes separate mechanisms: Content
confidentiality and Name confidentiality.
A cryptographic mechanism to prevent an unauthorized party to get
access to the plain-text payload of a Data packet. Can be
realized through encryption (symmetric, asymmetric, hybrid) and
proper distribution of the decryption keys to authorized parties.
A cryptographic mechanism to prevent an observer of Interest-Data
exchanges (e.g., intermediate router) from gaining detailed meta
information about the Data packet. This mechanism can be realized
using encryption (same as content confidentiality) or obfuscation
4. Semantics and Usage
The terminology described above is the manifestation of intended
semantics of NDN and CCNx operations (What do we expect the network
to do?). In this section, we summarize the most commonly proposed
use cases and interpretations.
4.1. Data Transfer
The networking view of NDN and CCNx is that the request/reply
protocol implements a basic, unreliable data transfer service for
single, named packets.
4.2. Data Transport
Data transfer can be turned into a data transport service for
application-level objects by additional logic. This transport logic
must understand and construct the series of names needed to
reassemble the segmented object. Various flavors of transport can be
envisaged (reliable, streaming, mailbox, etc.).
4.3. Lookup Service
In a more distributed systems view of the basic request/reply
protocol, NDN and CCNx provide a distributed lookup service: given a
key value (=name), the service will return the corresponding value.
4.4. Database Access
A lookup service can be turned into a database access protocol by
using the namespace structure to specify names as access keys into a
database. Therefore, a name prefix stands for a collection or table
of a database, while the rest of the name specifies the query
expression to be executed.
4.5. Remote Procedure Call
The names as defined in this document for Interests and Data can
refer to Remote Procedure call functions, their input arguments, and
their results. For a comprehensive view of how to construct RPC or
other remote invocation systems, see the Association for Computing
Machinery (ACM) ICN paper on [RICE]. These capabilities can be
further extended into a full distributed computing infrastructure
such as that proposed in the ACM ICN paper [CFN].
The names as defined in this document for Interests and Data can
refer to data collections to be subscribed and individual data
objects to be published in a Publish-Subscribe application
architecture. For a fully worked example of how to construct such an
ICN-based system, see the ACM ICN paper [LESSONS-LEARNED].
5. IANA Considerations
This document has no IANA actions.
6. Security Considerations
While the terms defined in this specification do not in and of
themselves present new security considerations, the architectures
that utilize the terms most certainly do. Readers should look at
those specifications (e.g., [RFC8569
] and [NDN]) where various
security considerations are addressed in detail.
Some of the terms in this document use the words "trust",
"trustworthy", or "trust model". We intend that these have their
colloquial meanings; however, much work on trust, and specifically on
trust schemas for ICN architectures, has been published in the last
few years. For example, it is useful to look at [SCHEMATIZING-TRUST]
for more information on the approaches taken to formalize notions of
trust for current NDN and CCNx systems.
7.1. Normative References
[CFN] Krol, M., Mastorakis, S., Kutscher, D., and D. Oran,
"Compute First Networking: Distributed Computing meets
ICN", ACM ICN, DOI 10.1145/3357150.3357395, September
Nichols, K., "Lessons Learned Building a Secure Network
Measurement Framework using Basic NDN", ACM ICN,
DOI 10.1145/3357150.3357397, September 2019,
Raychaudhuri, D., Nagaraja, K., and A. Venkataramani,
"MobilityFirst: a robust and trustworthy mobility-centric
architecture for the future internet", ACM SIGMOBILE,
Volume 16, Issue 3, DOI 10.1145/2412096.2412098, July
[NDNTLV] Named Data Networking, "NDN Packet Format Specification",
[NETINF] Dannewitz, C., Kutscher, D., Ohlman, B., Farrell, S.,
Ahlgren, B., and K. Holger, "Network of Information
(NetInf) - An information-centric networking
architecture", Computer Communications, Volume 36, Issue
7, DOI 10.1016/j.comcom.2013.01.009, April 2013,
[PSIRP] Trossen, D., Tuononen, J., Xylomenos, G., Sarela, M.,
Zahemszky, A., Nikander, P., and T. Rinta-aho, "From
Design for Tussle to Tussle Networking: PSIRP Vision and
Use Cases", May 2008,
[RICE] Krol, M., Habak, K., Kutscher, D., Oran, D., and I.
Psaras, "RICE: remote method invocation in ICN", ACM ICN,
DOI 10.1145/3267955.3267956, September 2018,
Yu, Y., Afanasyev, A., Clark, D., Claffy, K. C., Jacobson,
V., and L. Zhang, "Schematizing Trust in Named Data
Networking", ACM ICN, DOI 0.1145/2810156.2810170,
7.2. Informative References
[NDN] Named Data Networking, "Named Data Networking: Executive
Summary", September 2010,
] Cerf, V., Burleigh, S., Hooke, A., Torgerson, L., Durst,
R., Scott, K., Fall, K., and H. Weiss, "Delay-Tolerant
Networking Architecture", RFC 4838
, DOI 10.17487/RFC4838
April 2007, <https://www.rfc-editor.org/info/rfc4838
] Shirey, R., "Internet Security Glossary, Version 2",
FYI 36, RFC 4949
, DOI 10.17487/RFC4949
, August 2007,
] Eastlake 3rd, D. and T. Hansen, "US Secure Hash Algorithms
(SHA and SHA-based HMAC and HKDF)", RFC 6234
, May 2011,
] Mosko, M., Solis, I., and C. Wood, "Content-Centric
Networking (CCNx) Semantics", RFC 8569
, July 2019,
] Mosko, M., Solis, I., and C. Wood, "Content-Centric
Networking (CCNx) Messages in TLV Format", RFC 8609
, July 2019,
Marc Mosko provided much guidance and helpful precision in getting
these terms carefully formed and the definitions precise. Marie-Jose
Montpetit did a thorough IRSG review, which helped a lot to improve
the text. Further comments during the IRSG Poll from Stephen
Farrell, Ari Keraenen, Spencer Dawkins, Carsten Bormann, and Brian
Trammell further improved the document. Additional helpful comments
were received as part of the IESG conflict review from Mirja
Kuehlewind and Benjamin Kaduk.
Christopher A. Wood
University of California Irvine
Florida International University
Network Systems Research & Design
University of Basel