Network Working Group S. Burleigh Internet-Draft Jet Propulsion Laboratory, Intended status: Experimental California Institute of Expires: May 16, 2010 Technology November 12, 2009 Compressed Bundle Header Encoding (CBHE) draft-irtf-dtnrg-cbhe-03 Abstract This document describes a convention by which Delay-Tolerant Networking (DTN) Bundle Protocol (BP) "convergence-layer" adapters may represent endpoint identifiers in a compressed manner within the primary blocks of bundles, provided those endpoint identifiers conform to the structure prescribed by this convention. CBHE compression is a convergence-layer adaptation. It is opaque to bundle processing. It therefore has no impact on the interoperability of different Bundle Protocol implementations, but instead affects only the interoperability of different convergence layer adaptation implementations. 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. 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]. Status of this Memo This Internet-Draft is submitted to IETF in full conformance with the provisions of BCP 78 and BCP 79. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF), its areas, and its working groups. Note that other groups may also distribute working documents as Internet- Drafts. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." 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Burleigh Expires May 16, 2010 [Page 2] Internet-Draft CBHE November 2009 Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4 2. Compression convention . . . . . . . . . . . . . . . . . . . . 4 2.1. Constraints . . . . . . . . . . . . . . . . . . . . . . . . 5 2.2. Method . . . . . . . . . . . . . . . . . . . . . . . . . . 7 3. Specification . . . . . . . . . . . . . . . . . . . . . . . . . 7 3.1. Transmission . . . . . . . . . . . . . . . . . . . . . . . 8 3.2. Reception . . . . . . . . . . . . . . . . . . . . . . . . . 8 4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 8 5. Security Considerations . . . . . . . . . . . . . . . . . . . . 8 6. Normative References . . . . . . . . . . . . . . . . . . . . . 9 Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 9 Burleigh Expires May 16, 2010 [Page 3] Internet-Draft CBHE November 2009 1. Introduction This document describes a convention by which Delay-Tolerant Networking (DTN) Bundle Protocol (BP) [RFC5050] "convergence-layer adapters may represent endpoint identifiers in a compressed manner within the primary blocks of bundles, provided those endpoint identifiers conform to the structure prescribed by this convention. Each DTN bundle's primary block contains at least the following four BP endpoint identifiers (EIDs), of which any two, any three, or even all four may be lexically identical: the endpoint identifiers of the source, the destination, the report-to endpoint, and the current custodian. Each EID is a Uniform Record Identifier (URI) as defined by [RFC3986]. A degree of block compression is provided by the design of the primary block: the scheme names and scheme-specific parts of the four endpoints' IDs - up to eight NULL-terminated strings - are concatenated at the end of the block in a variable-length character array called a "dictionary", enabling each EID to be represented by a pair of integers indicating the offsets (within the dictionary) of the EID's scheme name and scheme-specific part. Duplicate strings may be omitted from the dictionary, so the actual number of concatenated NULL-terminated strings in the dictionary may be less than eight and two or more of the scheme name or scheme-specific part offsets in the block may have the same value. Moreover, the eight offsets in the primary block are encoded as self-delimiting numeric values (SDNVs), which shrink to fit the encoded values; when the total length of the dictionary is less than 127 bytes, all eight offsets can be encoded into just eight bytes. However, these strategems do not prevent the scheme names and scheme- specific parts themselves from being lengthy strings of ASCII text. It is therefore still possible for the length of a bundle's primary header to be a very large fraction of the total length of the bundle when the bundle's payload is relatively small, as is anticipated for a number of DTN applications such as space flight operations. The Compressed Bundle Header Encoding (CBHE) convention was developed to improve DTN transmission efficiency for such applications by further reducing the number of bytes used by convergence-layer adapters to express EIDs in the primary blocks of bundles. 2. Compression convention Burleigh Expires May 16, 2010 [Page 4] Internet-Draft CBHE November 2009 2.1. Constraints Compressed Bundle Header Encoding (CBHE) is possible only when all endpoint IDs in the primary block of a given bundle are "CBHE- conformant". Two forms of endpoint ID are CBHE-conformant: (a) the null endpoint ID "dtn:none" and (b) any endpoint ID formed within the "dtn" scheme whose namespace-specific string (NSS) is of the form NODE_NUMBER.SERVICE_NUMBER. The EIDs formed within any number of different namespaces within the "dtn" scheme may be CBHE-conformant. However, CBHE compression is possible between a pair of convergence-layer adapters only when each one is configured to compress only EIDs formed within a single namespace *and* that designated namespace is the same for both adapters. The node number is a positive integer that notionally identifies a BP node. In a spacecraft flight operations context, for example, spacecraft identifiers might be used as node numbers. However, methods for assigning node numbers to BP nodes are beyond the scope of this document; in particular, no requirement or guarantee of a one-to-one mapping between node numbers and BP nodes may be inferred. Node number must be an integer in the range 1 to (2^64 - 1). Node number zero is reserved for representation of the null endpoint ID in the compressed form described later in this specification; decompressing a compressed null EID MUST always yield the standard null endpoint ID URI "dtn:none". Negative integers and integers larger than (2^64 - 1) cannot be compressed into the SDNVs that are used for representation of endpoint ID references in the primary blocks of bundles and therefore could not be compressed as described later. The service number is a non-negative integer that notionally functions as a de-multiplexing token. When the protocol encapsulated within the BP has its own de-multiplexing identifiers, the service number may function in a manner similar to that of the protocol number in an IP packet, characterizing the bundle payload; alternatively, the service number may function in a manner similar to that of the port number in a UDP datagram. Service numbers enable inbound bundles' application data units to be de-multiplexed to instances of application functionality that are designed to process them, so that effective communication relationships can be developed between bundle producers and consumers. Service number must not be negative or exceed (2^64 - 1) for the same reason that node number must not do so. Burleigh Expires May 16, 2010 [Page 5] Internet-Draft CBHE November 2009 For example, "dtn::ipn:9.37" would be a CBHE-conformant endpoint ID. Conversion of a CBHE-conformant EID to and from a tuple of two integers is therefore straightforward. This ease of conversion enables an array of integers to serve the same function as a dictionary of EID ASCII strings. Note, however, that CBHE decompression cannot faithfully recreate the dictionary of a compressed primary block from an array of integers unless the order of the endpoint ID reference strings in the dictionary of the original, uncompressed block is known. (The bundle protocol specification does not require that the strings in the dictionary appear in any particular order and does not require that redundant strings be omitted from the dictionary.) Therefore, a further precondition to CBHE compression is that the endpoint ID reference strings in the dictionary of the bundle to be compressed must be exactly as follows, in this order and without addition: 1. The scheme name of the destination endpoint ID. 2. The scheme-specific part of the destination endpoint ID. 3. The scheme name of the source endpoint ID, if and only if different from any prior string in the dictionary. 4. The scheme-specific part of the source endpoint ID, if and only if different from any prior string in the dictionary. 5. The scheme name of the report-to endpoint ID, if and only if different from any prior string in the dictionary. 6. The scheme-specific part of the report-to endpoint ID, if and only if different from any prior string in the dictionary. 7. The scheme name of the current custodian endpoint ID, if and only if different from any prior string in the dictionary. 8. The scheme-specific part of the current custodian endpoint ID, if and only if different from any prior string in the dictionary. Note: this constraint implies that a bundle which includes any extension blocks containing EID references to endpoint IDs other than the block's destination, source, report-to, and current custodian cannot be CBHE-compressed. Burleigh Expires May 16, 2010 [Page 6] Internet-Draft CBHE November 2009 2.2. Method When the constraints summarized above are met, the CBHE block compression method can be applied by the convergence layer adapter at the time the bundle is transmitted via a convergence-layer protocol. In a CBHE-compressed primary block, the eight SDNVs that normally contain EIDs' offsets within the dictionary are instead used to contain the eight integer values listed below, in the order shown: 1. The node number of the destination endpoint ID, or zero if the destination endpoint is the null endpoint. 2. The service number of the destination endpoint ID, or zero if the destination endpoint is the null endpoint. 3. The node number of the source endpoint ID, or zero if the source endpoint is the null endpoint. 4. The service number of the source endpoint ID, or zero if the source endpoint is the null endpoint. 5. The node number of the report-to endpoint ID, or zero if the report-to endpoint is the null endpoint. 6. The service number of the report-to endpoint ID, or zero if the report-to endpoint is the null endpoint. 7. The node number of the current custodian endpoint ID, or zero if the current custodian endpoint is the null endpoint. 8. The service number of the current custodian endpoint ID, or zero if the current custodian endpoint is the null endpoint. Further, the dictionary is omitted from the primary block and the primary block's dictionary length is set to zero. Upon reception the receiving convergence-layer adaptation de- compresses the block by simply reversing the process so that the bundle presented to the bundle protocol agent has the standard form (i.e., the dictionary is reconstituted). 3. Specification CBHE compression is a convergence-layer adaptation. It is opaque to bundle processing. It therefore has no impact on the interoperability of different Bundle Protocol implementations, but instead affects only the interoperability of different convergence Burleigh Expires May 16, 2010 [Page 7] Internet-Draft CBHE November 2009 layer adaptation implementations. Bundle Protocol convergence-layer adapters that conform to the CBHE specification must implement the following procedures. 3.1. Transmission When and only when required by the bundle protocol agent to transmit to some CBHE-conformant convergence-layer adapter a bundle whose primary block's endpoint IDs satisfy the constraints identified in section 2.1 above, the convergence layer adapter may encode the primary block of the bundle in accordance with the CBHE compression convention described in section 2.2 above. 3.2. Reception Upon receiving a bundle whose dictionary length is zero (and only in this circumstance), a CBHE-conformant convergence layer adapter MUST decode the primary block of the bundle in accordance with the CBHE compression convention described in section 2.2 above before delivering it to the bundle protocol agent. Note that when a non-CBHE-conformant convergence layer adapter receives a bundle whose dictionary length is zero, it has no choice but to pass it to the bundle agent without modification. In this case the bundle agent will be unable to dispatch the received bundle, because it will be unable to determine the destination endpoint. The behavior of the bundle agent in this circumstance is an implementation matter. 4. IANA Considerations This document has no IANA considerations. 5. Security Considerations The Bundle Security Protocol may under some conditions insert additional endpoint ID strings into the dictionary of a bundle and reference those strings in BSP blocks. Because a bundle which includes any extension blocks containing EID references to endpoint IDs other than the block's destination, source, report-to, and current custodian cannot be CBHE-compressed, bundles cannot be compressed under those conditions. Specifically, the specification detailed above implies that a bundle cannot be CBHE-compressed when the security source endpoint for the Burleigh Expires May 16, 2010 [Page 8] Internet-Draft CBHE November 2009 Bundle Authentication Block (BAB) is noted in the dictionary (typically because there is no other way for the receiving bundle protocol agent to determine the security source endpoint), when the security destination endpoint for the BAB is noted in the dictionary (in the rare case that the receiving endpoint is not the security destination endpoint), when the security source endpoint for the Payload Integrity Block (PIB), Payload Confidentiality Block (PCB), or Extension Security Block (ESB) is not the source endpoint, or when the security destination endpoint for the PIB, PCB, or ESB is not the destination endpoint. These caveats aside, CBHE introduces no new security considerations beyond those discussed in the DTN Bundle Protocol and Bundle Security Protocol specifications. 6. 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. Author's Address Scott Burleigh Jet Propulsion Laboratory, California Institute of Technology 4800 Oak Grove Drive, m/s 301-490 Pasadena, CA 91109 USA Phone: +1 818 393 3353 Email: Scott.C.Burleigh@jpl.nasa.gov Burleigh Expires May 16, 2010 [Page 9]