Information-Centric Networking (ICN): Terminology
draft-wissingh-icnrg-terminology-01
The information below is for an old version of the document.
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| Authors | Bastiaan Wissingh, Christopher A. Wood , Alex Afanasyev , Lixia Zhang , David R. Oran , Christian Tschudin | ||
| Last updated | 2017-03-13 (Latest revision 2016-07-08) | ||
| Replaced by | draft-irtf-icnrg-terminology, draft-irtf-icnrg-terminology, RFC 8793 | ||
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draft-wissingh-icnrg-terminology-01
icnrg B. Wissingh
Internet-Draft TNO
Intended status: Informational C. Wood
Expires: September 14, 2017 University of California Irvine
A. Afanasyev
L. Zhang
UCLA
D. Oran
Network Systems Research & Design
C. Tschudin
University of Basel
March 13, 2017
Information-Centric Networking (ICN): Terminology
draft-wissingh-icnrg-terminology-01
Abstract
Information Centric Networking (ICN) is a new 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 (CCN) 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 projects. While there are other ICN architectures, they are not
part of the NDN and CCN vision and as such are out of scope for this
document.
Status of This Memo
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This Internet-Draft will expire on September 14, 2017.
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This document is subject to BCP 78 and the IETF Trust's Legal
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. A Sketch of the Big Picture of ICN . . . . . . . . . . . . . 3
3. Terms by category . . . . . . . . . . . . . . . . . . . . . . 5
3.1. Generic terms . . . . . . . . . . . . . . . . . . . . . . 5
3.2. Terms related to Name Types . . . . . . . . . . . . . . . 6
3.3. Terms related to Name Usage . . . . . . . . . . . . . . . 7
3.4. Terms related to Data-Centric Security . . . . . . . . . 8
3.5. ICN Node related terms . . . . . . . . . . . . . . . . . 9
3.6. Stateful forwarding plane related terms . . . . . . . . . 10
3.7. Specific solution related terms . . . . . . . . . . . . . 12
3.8. Uncategorized terms . . . . . . . . . . . . . . . . . . . 12
4. Semantics and Usage . . . . . . . . . . . . . . . . . . . . . 12
4.1. Data Transfer . . . . . . . . . . . . . . . . . . . . . . 13
4.2. Data Transport . . . . . . . . . . . . . . . . . . . . . 13
4.3. Lookup Service . . . . . . . . . . . . . . . . . . . . . 13
4.4. Database Access . . . . . . . . . . . . . . . . . . . . . 13
4.5. Remote Procedure Call . . . . . . . . . . . . . . . . . . 13
5. Informational References . . . . . . . . . . . . . . . . . . 13
Appendix A. Acknowledgments . . . . . . . . . . . . . . . . . . 15
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 15
1. Introduction
Information-centric networking (ICN) is an approach 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 --for immutable data items-- enables native multicast delivery,
ubiquitous in-network caching and replication of data objects.
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As the work on this topic continues to evolve, many new terms are
emerging over time. The goal of this document is to provide a
thorough collection of these terms with a corresponding definition as
they are used in the CCNx and NDN projects. Other, historic ICN
projects like NetInf, XIA or Mobility First are not covered and will
be the subject of other documents.
To help provide context for the individual terms to be defined, in
this draft 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.
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]) | | | |
| <-------------- | | | |
Figure 1: Request-Reply Protocol of ICN networking. Legend: n=name,
c=content, s=signature.
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
ambigious and several data packets would satisfy the request, the ICN
network will typically return only one matching data packet.
Packet and Content Names:
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Without an irrefutable binding between a 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 explicitely binds an application-chosen
name to a data packet's content, or (2) relying on an implicit name
(cryptographic hash of the data packet) that the data consumer
obtained through other means.
Data Authenticity and Encryption:
Any data consumer and network element can validate the authenticity
of a data packet by verifying its cryptographic name-to-content
binding. In contrast, whether a data packet's content (payload)
itself is encrypted or not is irrelevant to the ICN network: The use
and management of content encryption keys is an application-layer
concern.
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 only valid in
the context of a trust model. For example, if a corresponding trust
infrastructure (e.g., PKI) is in place, a packet's signature even
enables to assess authenticity with relation to to real world
identities which can be trusted or not.
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
into the name of the overall object.
Packet and Frame:
NDN and CCN 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 links
as 'frames'. Handling link-layer technologies which lead to
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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
like a packet mule, that is it may carry an interest or data packet
for some time before forwarding it to next node. An ICN node may
also run routing protocols to assist its interest forwarding
decisions.
--> add ASCII art here
(of a forwarding node
and its PIT, FIB, CS)
Figure 2: Structure of an ICN forwarding node.
Forwarding Plane:
The canonical way of implementing packet forwarding in an ICN network
like NDN and CCN relies on three data structures that capture a
node's state: a Forwarding Interest Table (FIB), a Pending Interest
Table (PIT), and a Content Store (CS). It also utilizes interest
forwarding strategies which takes input from both FIB and
measurements to make interest forwarding decisions. When a node
receives an ICN interest packet, it checks its CS and PIT to find a
matching name; 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. There exist
alternative approaches which aim at reducing the amount of state that
a nodes must keep, up to fully PIT-less designs using packets for
keeping state but without changing the overall service model.
3. Terms by category
3.1. Generic terms
Information-Centric Networking (ICN): a networking architecture
that retrieves data packets as response to interest packets.
Content-Centric Networking (CCN) and Named Data Networking (NDN)
are two types of ICN architectures.
Data packet: a network-level packet that carries payload, uniquely
identified by a name, and is directly secured.
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Common aliases include: data, data object, content object,
content object packet, data message, named data object, named
data.
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
Data packet immutability: after a data packet is created, it
cannot change. If the content carried in the data packet is
mutable, versioning should be used, so that each version uniquely
identifies an immutable instance of the content. This allows
disambiguation of coordination in distributed systems.
3.2. Terms related to Name Types
Name: a data packet identifier. An ICN name is expressive,
flexible and can be application-specific (akin to a HTTP URL). A
Name may encode information about application context, semantics,
locations (topological, geographical, hyperbolic, etc.), a service
name, etc. A Name is a sequence of non-empty name components (see
below). The components of a name are said to be complete if they
uniquely identify a single data packet. A Name is exact if its
components are complete.
Common aliases include: data name, interest name, content name.
Name component: a sequence of octets and optionally a numeric type
representing a single label in the hierarchical structured name.
Common aliases include: name segment (as in CCN).
Packet ID: a unique cryptographic identifier for a data packet.
Typically, this is the cryptographic hash digest of a data packet,
including its name, payload, meta information, and signature.
Full Name: An exact Name with the Packet ID of the corresponding
data packet.
Prefix Name: A Name with incomplete components.
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Common aliases include: prefix.
Selector: Depending on the implementation, some restrictors show
up as name components or as explicit fields of an interest.
Selectors are not 'names' in a proper sense although they are able
to "name content." Examples include selectors used to reference
nameless objects, specify publisher restriction, etc. In that
sense, a single data packet will have multiple 'name-like
properties' through which it can be referenced, interest packets
are able to express them.
Common aliases include: restrictor.
Nonce: Field of an interest packet that transiently 'names' an
interest instance.
3.3. Terms related to Name Usage
Naming scheme (ICN naming scheme): a convention/agreement/
specification for the data packet naming. Structures a name
space.
Hierarchically structured naming: the naming scheme that assigns
and interprets name as a sequence of labels (name components) with
hierarchical structure. 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 name as
a single label (name component) without any internal structure.
This can be considered a special (or degenerated) case of
structured names.
Segmentation: a process of splitting large application content
into a set of uniquely named data packets. When using
hierarchically structured name, each created data packet has a
common prefix and additional component representing the segment
(chunk) number.
Common aliases include: chunking (as in CCN).
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).
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Fragmentation: a process of splitting data packets into frames so
that they can be transmitted over the link with a smaller MTU
size.
3.4. Terms related to Data-Centric Security
Directly secured data packet: a data packet with inherent security
properties (authenticity and optionally confidentiality), i.e.,
the security properties stay with the data packet regardless where
it is stored and how it is retrieved.
Data authenticator: a set of parameters carried in the data packet
that is used to verify integrity and authenticity of the data
packet. The Data authenticator can include a cryptographic
signature (RSA, ECDSA, HMAC, etc.), meta information about the
signature (e.g., validity period), and additional information to
facilitate signature verification (e.g., key locator, key ID, HMAC
tag identifier, etc.)
Common aliases include: content authenticator.
Data confidentiality credentials: a set of parameters carried in
the data packet that identify the needed algorithm and key
identifiers to decrypt the confidential data.
Key owner (same as Identity): an entity (user, device, program,
program instance, module in the program instance, etc.) that owns
private key(s) and the corresponding public key(s).
Certificate: a data packet that carries a public key as payload
with optional additional meta information regarding the key (e.g.,
validity period, signature time, etc.). Ownership of the public
key is made implicitly through the name of the packet or
explicitly through meta information.
Key locator: Parameter(s) that identify the ICN key. A key
locatore can be the ICN key's name, its prefix, the ICN key ID,
etc.
Key ID: Unique identifier (e.g., hash digest) for a public or
secret key.
Trust model: a model or framework that defines trust
relationships, i.e., which entity (represented by an ICN key) is
authorized to sign which data packets.
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Trust schema: a formal description of a trust model, e.g., in the
form of a set of name-based relationships between data and key
names and a set of the trust anchors.
Trust anchor: an ICN key that is assumed to be trusted within the
context of a specific trust model.
ICN key chain: a chain of ICN keys (certificates) wherein each key
(certificate) is signed by its predecessor and the head of the
chain is a trust anchor, i.e., its authenticity is assumed.
Common aliases include: certificate chain.
3.5. ICN Node related terms
ICN Interface: a generalization of the network interface that can
represent a physical network interface (ethernet, wifi, bluetooth
adapter, etc.), an overlay inter-node channel (IP/UDP tunnel,
etc.), or an intra-node 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.
Data Mule: an ICN entity that temporarily stores and potentially
carries an interest or data packet before forwarding it to next
ICN entity.
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3.6. Stateful forwarding plane related terms
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.
Name-based routing: a process of forwarding interest packets using
the names in interests to guide the forwarding process
ICN 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.
ICN Routing plane: an ICN protocol or a set of ICN protocols to
exchange information about name space reachability.
Reverse path forwarding: a process of forwarding the incoming data
packet to the incoming interface(s) recorded in the corresponding
PIT entry (entries) and removing the PIT entry (entries).
Interest 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 ICN Forwarding Information Base
(FIB), measured data plane performance parameters, and/or use
other mechanisms to make the decision.
Common aliases include: forwarding strategy.
Satisfying an interest: overall process of returning content that
satisfies the constraints imposed by the Interest, most notably a
match in the provided name. Four different flavors of "matching"
are used in an ICN network, as described below.
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.
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Interest match in PIT (exact match): a process of finding a PIT
entry that stores the same as specified 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
router's content store that can satisfy the specified interest.
Interest aggregation: a process of combining multiple interest
packets for the same data into a single PIT entry.
Common aliases include: interest suppression, interest
collapsing.
ICN Forwarding Information Base (FIB): a database that, for a set
of prefixes, records a list of interfaces that can be used to
retrieve data packets with names under the corresponding prefixes.
The list of interfaces for each prefix can be ranked, and prefix/
interfaces mapping , and interfaces can be associated with the
additional information to facilitate forwarding strategy
decisions.
ICN Routing Information Base (RIB): a database that records a set
of prefix-interface mappings that represent a candidate interface
through which a data packet with the specified prefix can be
retrieved. RIB can be used to populate FIB.
Interest Nack: a packet that contains the interest packet and
optional annotation, which is sent by the router to the
interface(s) the Interest was received from. Interest Nack is
used to inform downstream ICN nodes about inability to forward the
included interest packet. The annotation can describe the reason.
Common aliases include: network NACK, interest return.
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 direction
opposite of interest forwarding (i.e., data and interest nacks are
forwarded downstream): producer, router, ..., consumer(s).
In-network storage: a process of storing a data packet within the
network (in routers opportunistic on-path caches, in dedicated on/
off path caches, and managed in-network storage systems), so it
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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 (or on-path in-network caching or just
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.
Managed caching (or off-path in-network storage): a process of
temporarily, permanently, or scheduled storing of a selected (set
of) data packet(s).
Content Store (CS): a database on an ICN router that provides
opportunistic caching.
Managed in-network storage (repository, repo): an entity acting as
an ICN producer that implements managed caching.
3.7. Specific solution related terms
Route-By-Name Routing (RBNR)
Lookup-By-Name Routing (LBNR)
Bread-crumbs routing
Replication-by-name
Routing Locator Signing
3.8. Uncategorized terms
Content based
ICN API
Information Centric Delay Tolerant Network
Located-Named-Data
Sessionless
4. Semantics and Usage
The terminology described above is the manifestation of intended
semantics of NDN and CCN operations (what do we expect the network to
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do?). In this section we summarize the most commonly proposed use
cases and interpretations.
4.1. Data Transfer
The networking view of NDN and CCN 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
A more distributed systems view of the basic request/reply protocol
is that NDN and CCN provide a distributed lookup service: Given a key
value (=name), the service will return the corresponding value.
4.4. Database Access
The lookup service turns into a database access protocol by ...
namespace design ... prefix standing for a collection ... The DB
query expression must be encoded as a name.
4.5. Remote Procedure Call
More generally, ... parameters in the interest ... used e.g. as
command channel for remote control of neighbor routers.
5. Informational References
[I-D.irtf-icnrg-ccnxmessages]
marc.mosko@parc.com, m., Solis, I., and c. cwood@parc.com,
"CCNx Messages in TLV Format", draft-irtf-icnrg-
ccnxmessages-03 (work in progress), June 2016.
[I-D.irtf-icnrg-ccnxsemantics]
marc.mosko@parc.com, m., Solis, I., and c. cwood@parc.com,
"CCNx Semantics", draft-irtf-icnrg-ccnxsemantics-03 (work
in progress), June 2016.
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[I-D.irtf-icnrg-challenges]
Kutscher, D., Eum, S., Pentikousis, K., Psaras, I.,
Corujo, D., Saucez, D., Schmidt, T., and M. Waehlisch,
"ICN Research Challenges", draft-irtf-icnrg-challenges-06
(work in progress), March 2016.
[I-D.irtf-icnrg-disaster]
Seedorf, J., Arumaithurai, M., Tagami, A., Ramakrishnan,
K., and N. Blefari-Melazzi, "Using ICN in disaster
scenarios", draft-irtf-icnrg-disaster-00 (work in
progress), February 2016.
[I-D.irtf-icnrg-evaluation-methodology]
Pentikousis, K., Ohlman, B., Davies, E., Spirou, S., and
G. Boggia, "Information-centric Networking: Evaluation and
Security Considerations", draft-irtf-icnrg-evaluation-
methodology-05 (work in progress), April 2016.
[I-D.irtf-icnrg-videostreaming]
cedric.westphal@huawei.com, c., Lederer, S., Mueller, C.,
Detti, A., Corujo, D., Wang, J., Montpetit, M., Murray,
N., Timmerer, C., Posch, D., aytav.azgin, a., and S.
(Will), "Adaptive Video Streaming over ICN", draft-irtf-
icnrg-videostreaming-08 (work in progress), April 2016.
[RFC7476] Pentikousis, K., Ed., Ohlman, B., Corujo, D., Boggia, G.,
Tyson, G., Davies, E., Molinaro, A., and S. Eum,
"Information-Centric Networking: Baseline Scenarios",
RFC 7476, DOI 10.17487/RFC7476, March 2016,
<http://www.rfc-editor.org/info/rfc7476>.
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Appendix A. Acknowledgments
Mark Mosco, ...
Authors' Addresses
Bastiaan Wissingh
TNO
EMail: bastiaan.wissingh@tno.nl
Christopher A. Wood
University of California Irvine
EMail: woodc1@uci.edu
Alex Afanasyev
UCLA
EMail: aa@cs.ucla.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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