The original purpose of the delay-tolerant networking (DTN) protocols was to provide space communications scenarios with network-layer functionality similar to that provided by IP-based networks on Earth.
Since space communication scenarios cannot be supported by the terrestrial IP protocol suite, a new solution had to be developed.
The CCSDS Bundle Protocol (BP), based on Bundle Protocol version 6 as defined in RFC 5050 [SB07] and RFC 6260 [Bur11], is meant to provide 1️⃣ basic network-layer functionality, and 2️⃣ storage capability to enable networking benefits even in the presence of delays, disconnections, and rate mismatches [IEH+19].
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The latest version of the Bundle Protocol is version 7, as defined in RFC 9171 [BFB22], but this version has yet to be adopted by CCSDS.
For providing integrity and confidentiality services for BP bundles (see Table 1), Bundle Protocol Security (BPSec) is defined in RFC 9172 [BM22].
More concretely, the BP provides network-layer services to applications through these capabilities [CCS15, Secs. 1.1 and 2.1]:
custody transfer;
coping with intermittent connectivity;
taking advantage of scheduled, predicted or opportunistic connectivity (in addition to continuous connectivity);
notional data accountability with built-in status reporting;
late binding of names to addresses.
When used in conjunction with the Bundle Security Protocol, as defined in RFC 6257 [FWSL11], the BP also provides:
A protocol data unit (PDU) comprising a sequence of two or more blocks of data.
Bundle node
An entity that can send and/or receive bundles.
Bundle protocol agent (BPA)
A node component that offers the BP services and executes the procedures of the BP.
Convergence layer adapter (CLA)
An adapter that sends and receives bundles on behalf of a BPA.
This is necessary for interoperation with existing Internet protocols; see Fig. 1.
Fig. 1: A sample configuration with the BP and a CLA running over a transport protocol on the left, and over a data link layer on the right [CCS15, Figure 2-1]. The CLA B labelled “CL B” on the right could for instance be the interface to the Licklider Transmission Protocol (LTP) with the “Link B1” representing LTP running over one of the Space Data Link Protocols.
The BP is such an important protocol several open-source implementations exist:
NASA provides a C-based implementation of BPv6 called bplib.
CCSDS, CCSDS Bundle Protocol Specification, Recommended Standard CCSDS 734.2-B-1, The Consultative Committee for Space Data Systems, September 2015. Available at https://public.ccsds.org/Pubs/734x2b1.pdf.
[FWSL11]
S. Farrell, H. Weiss, S. Symington, and P. Lovell, Bundle Security Protocol Specification, RFC 6257, May 2011. https://doi.org/10.17487/RFC6257.
[IEH+19]
D. Israel, B. Edwards, J. Hayes, W. Knopf, A. Robles, and L. Braatz, The Benefits of Delay/Disruption Tolerant Networking (DTN) for Future NASA Science Missions, in 70th International Astronautical Congress (IAC), October 2019. Available at https://ntrs.nasa.gov/citations/20190032313.
