LTP Performance on Near-Earth Optical Links
Carlo Caini, Tomaso de Cola, Amita Shrestha, Antony Zappacosta · IEEE Transactions on Aerospace and Electronic Systems · 2023
The Licklider Transport Protocol (LTP) is the “convergence layer” of choice in Interplanetary networks based on Delay-/Disruption-Tolerant architecture. It was designed for long-delay scheduled-intermittent links, offering either a reliable or an unreliable service, with Red and Green “parts” respectively. The aim of the paper is to present Multicolor LTP, an LTP version consisting in a series of enhancements of which the most significant are the use of monochrome sessions, the introduction of an additional Orange color offering a “notified” service, and the definition of default link colors. After a thorough examination of basic LTP mechanisms for all color variants, the paper discusses two scenarios where Orange seems particularly appealing: video streaming and optical interplanetary links. Numerical results offer further insight into the complex LTP mechanisms and also highlight the difference between LTP retransmissions and Bundle Protocol retransmissions, the latter benefitting from routing reprocessing. Multicolor LTP has already been implemented as an ION plug-in and its enhancements have been proposed to CCSDS SIS-DTN working group for a possible inclusion in the next version of LTP specifications (LTPv2).