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For this RFC, original HTML is available from the RFC-Editor: RFC8793



Internet Research Task Force (IRTF)                          B. Wissingh
Request for Comments: 8793                                           TNO
Category: Informational                                          C. Wood
ISSN: 2070-1721                          University of California Irvine
                                                            A. Afanasyev
                                        Florida International University
                                                                L. Zhang
                                                                    UCLA
                                                                 D. Oran
                                       Network Systems Research & Design
                                                             C. Tschudin
                                                     University of Basel
                                                               June 2020


Information-Centric Networking (ICN): Content-Centric Networking (CCNx)
              and Named Data Networking (NDN) Terminology

Abstract

   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.

Copyright Notice

   Copyright (c) 2020 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
   (https://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
   to this document.

Table of Contents

   1.  Introduction
   2.  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.  Publish/Subscribe
   5.  IANA Considerations
   6.  Security Considerations
   7.  References
     7.1.  Normative References
     7.2.  Informative References
   Acknowledgments
   Authors' Addresses

1.  Introduction

   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
   [RFC8569], [RFC8609], 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, ICN-
   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
   concern.

   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
      purpose.

   *Trust:*

      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 discusses
      this further.

   *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.

   *ICN Node:*

      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.

   *Forwarding Plane:*

      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
      FIB.

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
      ICN architecture.

   *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

   *ICN Interface:*

      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.

   *ICN Consumer:*

      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.

   *ICN Producer:*

      An ICN entity that creates Data packets and makes them available
      for retrieval.

         Common aliases include: producer, publisher, information
         publisher, data publisher, data producer.

   *ICN Forwarder:*

      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)
      [RFC4838] specifications.

3.3.  Terms Related to the Forwarding Plane

   *Stateful Forwarding:*

      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.

   *Forwarding Strategy:*

      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.

   *Upstream (forwarding):*

      Forwarding packets in the direction of Interests (i.e., Interests
      are forwarded upstream): consumer, router, router, ..., producer.

   *Downstream (forwarding):*

      Forwarding packets in the opposite direction of Interest
      forwarding (i.e., Data and Interest Nacks are forwarded
      downstream): producer, router, ..., consumer(s).

   *Interest Forwarding:*

      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.

   *Interest Aggregation:*

      A process of combining multiple Interest packets with the same
      Name and additional restrictions for the same Data into a single
      PIT entry.

         Common aliases include: Interest collapsing.

   *Data Forwarding:*

      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
      provided Name.

   *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
      any).

   *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
      decisions.

   *Content Store (CS):*

      A database in an ICN router that provides caching.

   *In-Network Storage:*

      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.

   *Opportunistic Caching:*

      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.

   *Managed 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
      caching.

         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

   *Interest Packet:*

      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
         request.

   *Interest Nack:*

      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.

   *Data Packet:*

      A network-level packet that carries payload, uniquely identified
      by a name, that is directly secured through cryptographic
      signature mechanisms.

         Common aliases include: data, data object, content object,
         content object packet, data message, named data object, named
         data.

   *Link:*

      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
      requirement.

         Common aliases include: pointer.

   *Manifest:*

      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

   *Name:*

      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.

   *Name component:*

      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).

   *Packet ID:*

      A unique cryptographic identifier for a Data packet.  Typically,
      this is a cryptographic hash digest of a Data packet (such as
      SHA256 [RFC6234]), including its name, payload, meta information,
      and signature.

         Common aliases include: implicit digest.

   *Selector:*

      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
         restrictor.

   *Nonce:*

      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].

   *Exact Name:*

      A Name that is encoded inside a Data packet and that typically
      uniquely identifies this Data packet.

   *Full Name:*

      An exact Name with the Packet ID of the corresponding Data packet.

   *Prefix Name:*

      A Name that includes a partial sequence of Name components
      (starting from the first one) of a Name encoded inside a Data
      packet.

         Common aliases include: prefix.

3.6.  Terms Related to Name Usage

   *Naming conventions:*

      A convention, agreement, or specification for the Data packet
      naming. a Naming convention structures a namespace.

         Common aliases include: Naming scheme, ICN naming scheme,
         namespace convention.

   *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.

   *Flat 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.

   *Segmentation:*

      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.

   *Versioning:*

      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).

   *Fragmentation:*

      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

   *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.

   *Data Integrity*

      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
      deliberate modification.

   *Data Authenticity*

      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.

   *Data Confidentiality*

      A cryptographic mechanism to ensure secrecy of a Data packet.
      Data confidentiality includes separate mechanisms: Content
      confidentiality and Name confidentiality.

   *Content 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.

   *Name Confidentiality*

      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
      mechanisms.

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].

4.6.  Publish/Subscribe

   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.  References

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
              2019, <https://dl.acm.org/citation.cfm?id=3357395>.

   [LESSONS-LEARNED]
              Nichols, K., "Lessons Learned Building a Secure Network
              Measurement Framework using Basic NDN", ACM ICN,
              DOI 10.1145/3357150.3357397, September 2019,
              <https://dl.acm.org/citation.cfm?id=3357397>.

   [MOBILITY-FIRST]
              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
              2012, <https://dl.acm.org/citation.cfm?id=2412098>.

   [NDNTLV]   Named Data Networking, "NDN Packet Format Specification",
              <https://named-data.net/doc/ndn-tlv/>.

   [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,
              <https://dl.acm.org/citation.cfm?id=2459643>.

   [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,
              <http://www.psirp.org/files/Deliverables/PSIRP-
              TR08-0001_Vision.pdf>.

   [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,
              <https://dx.doi.org/10.1145/3267955.3267956>.

   [SCHEMATIZING-TRUST]
              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,
              September 2015,
              <https://dx.doi.org/10.1145/2810156.2810170>.

7.2.  Informative References

   [NDN]      Named Data Networking, "Named Data Networking: Executive
              Summary", September 2010,
              <https://named-data.net/project/execsummary/>.

   [RFC4838]  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>.

   [RFC4949]  Shirey, R., "Internet Security Glossary, Version 2",
              FYI 36, RFC 4949, DOI 10.17487/RFC4949, August 2007,
              <https://www.rfc-editor.org/info/rfc4949>.

   [RFC6234]  Eastlake 3rd, D. and T. Hansen, "US Secure Hash Algorithms
              (SHA and SHA-based HMAC and HKDF)", RFC 6234,
              DOI 10.17487/RFC6234, May 2011,
              <https://www.rfc-editor.org/info/rfc6234>.

   [RFC8569]  Mosko, M., Solis, I., and C. Wood, "Content-Centric
              Networking (CCNx) Semantics", RFC 8569,
              DOI 10.17487/RFC8569, July 2019,
              <https://www.rfc-editor.org/info/rfc8569>.

   [RFC8609]  Mosko, M., Solis, I., and C. Wood, "Content-Centric
              Networking (CCNx) Messages in TLV Format", RFC 8609,
              DOI 10.17487/RFC8609, July 2019,
              <https://www.rfc-editor.org/info/rfc8609>.

Acknowledgments

   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.

Authors' Addresses

   Bastiaan Wissingh
   TNO

   Email: bastiaan.wissingh@tno.nl


   Christopher A. Wood
   University of California Irvine

   Email: caw@heapingbits.net


   Alex Afanasyev
   Florida International University

   Email: aa@cs.fiu.edu


   Lixia Zhang
   UCLA

   Email: lixia@cs.ucla.edu


   David Oran
   Network Systems Research & Design

   Email: daveoran@orandom.net


   Christian Tschudin
   University of Basel

   Email: christian.tschudin@unibas.ch


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