Memory Dynamics and Transmission Performance of Bundle Protocol (BP) in Deep-Space Communications Abstract: Delay/disruption tolerant networking (DTN) was proposed as an end-toend networking architecture providing file delivery service in and/or through stressed communication environments. Bundle protocol (BP) of DTN utilizes the well-known store-and-forward mechanism together with custody transfer option for which a node agrees to hold a file in memory (disk storage in this paper) until its successful reception is acknowledged by the next node. The variation in memory occupancy constrains the volume of memory that is available for other DTN functions. Characterizing the memory dynamics of BP during file transfer is crucial. In this paper, we present a study of memory variation dynamics and transmission performance in the operation of BP for file transmissions over a typical relay-based deep-space communication system characterized by multiple data source nodes, an extremely long signal propagation delay, and lossy data links with both symmetric and asymmetric channel rates. Analytical models are built to estimate the memory variation dynamics and the total file delivery time (and goodput) characterizing BP transmission in deep space. The models are validated by running file transfer experiments using a testbed.