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Licklider Transmission Protocol (LTP) | ||||||||||
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CCSDS has adopted the Licklider Transmission Protocol (LTP) as specified in the IETF RFC 5326 [BFR08b] and the associated security extensions specified in IETF RFC 5327 [BFR08a] to provide reliability and authentication mechanisms on top of an underlying (usually data link) communication service [CCS15b, Sec. 1.1]. In an Interplanetary Internet setting deploying the Bundle Protocol [BFR08b], LTP is intended to serve as a reliable “convergence layer” protocol operating in pairwise fashion between adjacent in-range Interplanetary Internet nodes. LTP aggregates multiple layer-(N+1) PDUs into a single layer-N PDU for reliable delivery — this allows the system to reduce the acknowledgement-channel bandwidth in the case that the layer-(N+1) (and higher) protocols transmit many small PDUs, each of which might otherwise require independent acknowledgement; see Fig. 1. In CCSDS settings [CCS15b, Sec. 1.2], LTP is intended for use over package delivery services including packet telecommand and packet telemetry. For space links, LTP is typically deployed over a CCSDS data link that supports CCSDS Encapsulation Packets so that one LPT segment can be encapsulated in a single Encapsulation Packet. LTP can also operate over ground-network services, in which case it is usually deployed over UDP; see Fig. 2. Fig. 1: To protocols above LTP (e.g., Bundle Protocol), LTP enables reliable delivery of layer-(N+1) PDUs across a link [CCS15b, Figure 1-1]. For LTP, the interface to the data link is via either direct encapsulation in CCSDS Space Packets or the CCSDS Encapsulation Service. References
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