DTN metadata block: Delay-Tolerant Networking Metadata Extension Block

Internet Research Task Force (IRTF)                         S. Symington
Request for Comments: 6258                         The MITRE Corporation
Category: Experimental                                          May 2011
ISSN: 2070-1721


           Delay-Tolerant Networking Metadata Extension Block

Abstract

   This document defines an extension block that may be used with the
   Delay-Tolerant Networking (DTN) Bundle Protocol.  This Metadata
   Extension Block is designed to carry additional information that DTN
   nodes can use to make processing decisions regarding bundles, such as
   deciding whether to store a bundle or determining to which nodes to
   forward a bundle.  The metadata that is carried in a metadata block
   must be formatted according to the metadata type that is identified
   in the block's metadata type field.  One specific metadata type, for
   carrying URIs as metadata, is defined in this document.  Other
   metadata types may be defined in separate documents.  This document
   is a product of the Delay Tolerant Networking Research Group and has
   been reviewed by that group.  No objections to its publication as an
   RFC were raised.

Status of This Memo

   This document is not an Internet Standards Track specification; it is
   published for examination, experimental implementation, and
   evaluation.

   This document defines an Experimental Protocol for the Internet
   community.  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
   Delay-Tolerant 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 5741.

   Information about the current status of this document, any errata,
   and how to provide feedback on it may be obtained at
   http://www.rfc-editor.org/info/rfc6258.

Copyright Notice

   Copyright (c) 2011 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
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Table of Contents

   1. Introduction ....................................................2
      1.1. Requirements Language ......................................4
   2. Metadata Block Format ...........................................4
   3. Metadata Block Processing .......................................5
      3.1. Bundle Transmission ........................................6
      3.2. Bundle Forwarding ..........................................6
      3.3. Bundle Reception ...........................................6
   4. Predefined Metadata Types .......................................6
      4.1. URI Metadata Type ..........................................6
      4.2. Private Metadata Types .....................................7
   5. Security Considerations .........................................7
   6. IANA Considerations .............................................8
      6.1. Metadata Type Codes ........................................8
      6.2. Block Type Code for the Metadata Block .....................9
   7. References ......................................................9
      7.1. Normative References .......................................9
      7.2. Informative References .....................................9

1.  Introduction

   This document defines an extension block that may be used with the
   Bundle Protocol [RFC5050] within the context of a Delay-Tolerant
   Networking architecture [RFC4838].  The DTN Bundle Protocol [RFC5050]
   defines the bundle as its protocol data unit.  This document defines
   a bundle block called a "metadata block".  This block is designed to
   carry additional information that DTN nodes can use to make
   processing decisions regarding bundles.

   The metadata block has been deliberately defined to be flexible
   enough that it would be capable of supporting a variety of metadata
   types and formats.  Indeed, the only restriction imposed on the
   metadata to be used is that its type and format be predefined and
   registered (if public) so that it can be parsed and processed by DTN
   nodes that support metadata of that type.  Section 4 defines a
   specific metadata type and discusses the use of other metadata types
   that may be defined elsewhere.  As mentioned, it is the intention
   that the metadata that is carried in this block be application-
   related information.  For example, the metadata might be information
   that is associated with the payload of a bundle.  Additional
   extension blocks could be (and have been) defined for carrying
   additional network-related information.

   While the bundle payload may be processed opaquely by DTN nodes,
   metadata is intended to serve as a mechanism for providing DTN nodes
   with access to additional information that they can use to process
   the bundle.  Examples of such additional information include keywords
   found in the payload; payload provenance information; GPS coordinates
   (if the payload is a map, for instance); message IDs; and artist,
   album, and track name (if the payload is a song).  Even though the
   metadata is additional information related to the application, its
   purpose is to be used by DTN nodes to make decisions regarding how to
   process bundles within the network, such as whether or not a bundle
   should be stored or to which nodes a bundle should be forwarded.
   Metadata that is about bundle payload, for example, might serve as a
   content-based index of bundles that are stored in a DTN cache.  So,
   in response to a request for bundles related to a certain subject or
   related to specific GPS coordinates, for example, the metadata of
   stored bundles could be searched, and all bundles with metadata
   matching the search criteria could be retrieved and returned to the
   requestor.

   This document defines the general format of and the processing
   required to support the metadata block.  The actual metadata to be
   inserted into a metadata block MUST be formatted according to the
   metadata type that is identified in the block's metadata type field.
   One specific metadata type, for carrying Uniform Resource Identifiers
   (URIs) [RFC3986] as metadata, is defined in this document.  Other
   metadata types may be defined in separate documents, along with the
   steps required to process records of that type, if necessary.  If
   such other metadata types are defined, they should be registered to
   ensure global uniqueness (see the IANA Considerations section).

   The capabilities described in this document are OPTIONAL for
   deployment with the Bundle Protocol.  As defined in this document,
   Bundle Protocol implementations claiming to support the metadata
   block MUST be capable of:

      - generating a metadata block and inserting it into a bundle,
      - receiving bundles containing a metadata block and making the
      information contained in this metadata block's metadata field
      available for use, e.g., in bundle storage or forwarding
      decisions, and

      - deleting a metadata block from a received bundle before
      forwarding the bundle.

   Bundle Protocol implementations claiming to support a specific
   metadata type must both support the metadata block as defined above
   and be capable of parsing and processing the metadata itself
   according to the definition of the metadata type in which the
   metadata is expressed.  This metadata type may be the URI metadata
   type (see the URI metadata type section), or it may be another
   metadata type defined in a separate document.

1.1.  Requirements Language

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in RFC 2119 [RFC2119].

2.  Metadata Block Format

   The metadata block uses the Canonical Bundle Block Format as defined
   in the Bundle Protocol [RFC5050].  That is, it is comprised of the
   following elements, which are defined as in all bundle protocol
   blocks except the primary bundle block.  (Note that Self-Delimiting
   Numeric Value (SDNV) encoding is described in the Bundle Protocol.):

      - Block-type code (1 byte) - defined as in all bundle protocol
      blocks except the primary bundle block (as described in the Bundle
      Protocol).  The block-type code for the metadata block is 0x08.

      - Block processing control flags (SDNV) - defined as in all bundle
      protocol blocks except the primary bundle block.  SDNV encoding is
      described in the Bundle Protocol.  There are no constraints on the
      use of the block processing control flags.  If a bundle node
      receives a bundle with a metadata block and it is capable of
      supporting the metadata block but it is not able to parse and
      process the metadata itself, either because it does not support
      the metadata type being used or because the metadata is not well-
      formed according to the metadata type definition, the bundle node
      must process the bundle as if it cannot process the metadata
      block.  That is, it must operate according to the settings of the
      block processing control flags, including the "Delete bundle if
      block can't be processed" flag and the "Discard block if it can't
      be processed" flag.

      - Block EID-reference count and EID-references (optional) -
      composite field defined in the Bundle Protocol that is present if
      and only if the metadata block references EID elements in the
      primary block's dictionary.  Presence of this field is indicated
      by the setting of the "Block contains an EID-reference field" bit
      of the block processing control flags.  If EIDs are referenced in
      the metadata block, then their interpretation is defined by the
      particular metadata type that is being used in this metadata
      block, as indicated in the metadata type field.

      - Block data length (SDNV) - defined as in all bundle protocol
      blocks except the primary bundle block.  SDNV encoding is
      described in the Bundle Protocol.

      - Block-type-specific data fields as follows:

         - Metadata Type field (SDNV) - indicates which metadata type is
         to be used to interpret both the metadata in the metadata field
         and the EID-references in the optional Block EID-reference
         count and EID-references field (if present).  One metadata type
         is defined in this document.  Other metadata types may be
         defined in separate documents.

         - Metadata field - contains the metadata itself, formatted
         according to the metadata type that has been specified for this
         block.  One metadata type is defined in Section 4.1.  Other
         metadata types may be defined elsewhere, as discussed in
         Section 4.

   The structure of a metadata block is as follows:

   Metadata Block Format:
   +-----+------+--------------------+------+----------+----------|
   |Type |Flags |EID-Reference count |Len   | Metadata | Metadata |
   |     |(SDNV)|  and list (opt)    |(SDNV)|   Type   |          |
   +-----+------+--------------------+------+----------+----------+

                                 Figure 1

3.  Metadata Block Processing

   The following are the processing steps that a bundle node may take
   relative to generation, reception, and processing of metadata blocks.

3.1.  Bundle Transmission

   When an outbound bundle is created per the parameters of the bundle
   transmission request, this bundle MAY (as influenced by local policy
   and the metadata type being used) include one or more metadata blocks
   (as defined in this specification).

3.2.  Bundle Forwarding

   A node MAY insert one or more metadata blocks into a bundle before
   forwarding it; and a node MAY delete one or more metadata blocks from
   a bundle before forwarding it, as dictated by local policy and the
   metadata type being used.

3.3.  Bundle Reception

   If the bundle includes one or more metadata blocks, the metadata
   information records in these blocks SHALL be made available for use
   at this node (e.g., in bundle storage or forwarding decisions, or, if
   the receiving node is the bundle-destination, the metadata
   information records may be provided to the receiving application).

4.  Predefined Metadata Types

   As mentioned in the previous section, any number of different
   metadata types may be defined to indicate the format of both the
   metadata field and the EID-references in the optional Block EID-
   reference count and EID-references field (if present) and, if
   necessary, how metadata of this type should be processed.  One
   metadata type is defined in this document, URI metadata type (0x01).
   In addition, a range of metadata type values is reserved for private
   use.

4.1.  URI Metadata Type

   It is believed that use of URIs will, in many cases, be adequate for
   encoding metadata, although it is recognized that use of URIs may not
   be the most efficient method for such encoding.  Because of the
   expected utility of using URI encoding for metadata, the metadata
   type value of 0x01 is defined to indicate a metadata type of URI.
   Metadata type values other than 0x01 will be used to indicate
   alternative metadata types.

   The Metadata field for metadata of metadata type URI (0x01) consists
   of an array of bytes formed by concatenating one or more null-
   terminated URIs.  Unless determined by local policy, the specific
   processing steps that must be performed on bundles with metadata
   blocks containing metadata of type URI are expected to be indicated
   as part of the URI encoding of the metadata.  It is envisioned that
   users might define URI schemes for this purpose.  Metadata blocks
   containing metadata of type URI MUST NOT include a Block EID-
   reference count and EID-references field.  The absence of this field
   MUST be indicated by a value of 0 for the "Block contains an EID-
   reference field" flag in the block processing control flags.  Support
   for the URI metadata type is OPTIONAL.

4.2.  Private Metadata Types

   Metadata type values 192 through 255 are not defined in this
   specification and are available for private and/or experimental use.
   Such private metadata types are not required to be registered.  All
   other values of the metadata type are reserved for future use and,
   when defined, should be registered to ensure global uniqueness (see
   the IANA Considerations section).  Local policy will define how
   private metadata types are handled.

5.  Security Considerations

   The DTN Bundle Security Protocol [RFC6257] defines security-related
   blocks to provide hop-by-hop authentication, end-to-end
   authentication, end-to-end confidentiality of bundles or parts of
   bundles, and an extension security block to provide confidentiality
   and integrity for extension blocks, as well as a set of standard
   ciphersuites that may be used to calculate security-results carried
   in these security blocks.  All ciphersuites that use the strict
   canonicalization algorithm [RFC6257] to calculate and verify
   security-results (e.g., many hop-by-hop authentication ciphersuites)
   apply to all blocks in the bundle and so would apply to bundles that
   include an optional metadata block and would include that block in
   the calculation of their security-result.  In particular, bundles
   including the optional metadata block would be protected in their
   entirety for the duration of a single hop, from a forwarding node to
   an adjacent receiving node (but not from source to destination over
   multiple hops), using the standard BAB-HMAC (Bundle Authentication
   Block - Hashed Message Authentication Code) ciphersuite defined in
   the Bundle Security Protocol.

   Ciphersuites that use the mutable canonicalization algorithm to
   calculate and verify security-results (e.g., the mandatory PSH-RSA-
   SHA256 ciphersuite and most end-to-end authentication ciphersuites)
   will omit the metadata block from their calculation.  Therefore, the
   fact that metadata in the metadata block may be modified or that
   metadata blocks themselves may be added to or deleted from a bundle
   as it transits the network will not interfere with end-to-end
   security protection when using ciphersuites that use mutable
   canonicalization.

   The metadata block will not be encrypted by the mandatory CH-RSA-AES-
   PAYLOAD-PSH end-to-end confidentiality ciphersuite, which only allows
   for payload and PSH encryption.

   In order to provide the metadata block with end-to-end
   confidentiality and authentication independent of any confidentiality
   or authentication that is provided for the payload or other parts of
   the bundle, the extension security block may be used to encrypt and
   authenticate the metadata block.  A bundle may contain multiple
   metadata extension blocks.  In some cases, multiple metadata blocks
   may be carried in the bundle, possibly with each being encrypted
   separately from each other and from the payload.  Such separate
   encryption of metadata from payload would enable bundle nodes to
   perform content-based searching and routing on bundle metadata that
   they are able to decrypt, even if they are not able to decrypt the
   bundle payload.

   Given that metadata can be modified by forwarding nodes, it may be
   desirable to eventually support the ability to audit changes to the
   metadata at the individual record level.  No such capability has been
   provided in this specification as currently written.

6.  IANA Considerations

6.1.  Metadata Type Codes

   The metadata block carried in the Metadata Extension Block has a
   Metadata Type Code field (see Sections 2 and 3).  An IANA registry
   has been set up as follows.

                 Metadata Type Codes Registry

   The registration policy for this registry is:
     0-191: Specification Required
     192-255: Private and/or Experimental Use.  No assignment by IANA.

   The Value range is unsigned 8-bit integer.

   +---------+---------------------------------+---------------+
   |  Value  | Description                     | Reference     |
   +---------+---------------------------------+---------------+
   |       0 | Reserved                        | This document |
   |       1 | URI                             | This document |
   |   2-191 | Unassigned                      |               |
   | 192-255 | Private and/or experimental use | This document |
   +---------+---------------------------------+---------------+

6.2.  Block Type Code for the Metadata Block

   This specification allocates a codepoint from the Bundle Block Type
   Codes registry defined in [RFC6255] (see Section 2 of this document):

   Additional Entry for the Bundle Block Type Codes Registry:
     +-------+----------------------------------------+----------------+
     | Value | Description                            + Reference      |
     +-------+----------------------------------------+----------------+
     |     8 | Metadata Extension Block               + This document  |
     +-------+----------------------------------------+----------------+

7.  References

7.1.  Normative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997.

   [RFC3986]  Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform
              Resource Identifier (URI): Generic Syntax", STD 66,
              RFC 3986, January 2005.

   [RFC5050]  Scott, K. and S. Burleigh, "Bundle Protocol
              Specification", RFC 5050, November 2007.

   [RFC6255]  Blanchet, M., "Delay-Tolerant Networking (DTN) Bundle
              Protocol IANA Registries", RFC 6255, May 2010.

7.2.  Informative References

   [RFC4838]  Cerf, V., Burleigh, S., Hooke, A., Torgerson, L., Durst,
              R., Scott, K., Fall, K., and H. Weiss, "Delay-Tolerant
              Networking Architecture", RFC 4838, April 2007.

   [RFC6257]  Symington, S., Farrell, S., Weiss, H., and P. Lovell,
              "Bundle Security Protocol Specification", RFC 6257,
              May 2011.

Author's Address

   Susan Flynn Symington
   The MITRE Corporation
   7515 Colshire Drive
   McLean, VA  22102
   US

   Phone: +1 (703) 983-7209
   EMail: susan@mitre.org
   URI:   http://mitre.org/