Organizations: Communication Networks Research Group (CNG), Dept. of Electrical and Electronics Engineering, Middle East Technical University (METU), Ankara, Türkiye
Deep-space communications operate under intermittent connectivity, long propagation delays, and relay storage constraints. In such networks, the Bundle Protocol enables store-carry-forward communication, requiring relay nodes to manage limited storage and scarce contact opportunities. Relay-side scheduling and dropping decisions are inherently goal-oriented: transmission resources should be allocated to bundles most valuable to downstream mission objectives. Conventional schedulers, such as FIFO, do not explicitly optimize task utility and may provide unfair service across heterogeneous planetary sources. This paper presents a closed-loop modeling and learning framework for relay-side bundle and flow management in a contact-driven deep-space network, where lunar and Martian updates are forwarded through a shared-buffer relay to Earth. We quantify destination-side information freshness using excess age Δie(t)=[Δi(t)−di(t)]+, where Δi(t) denotes the Age of Information of source i and di(t) is a source-dependent delay baseline. Based on this metric, we define a goal-oriented loss that supports source-dependent nonlinear penalties, allowing prioritization according to mission relevance. We formulate relay control as a constrained semi-Markov decision process (CSMDP) and solve it using masked Lagrangian Proximal Policy Optimization (PPO). Feasibility-aware action masking restricts transmissions to bundles that can complete within the remaining contact window. DTNSim simulations indicate improved age-based utility and inter-flow fairness compared with baseline schedulers. The proposed framework jointly optimizes relay-side bundle scheduling, dropping, and flow control under contact-driven dynamics with explicit fairness considerations across heterogeneous sources.
Figures & tables
Figure 1: Earth–Relay–Moon–Mars network.
Figure 2: Masked Lagrangian PPO architecture for event-driven relay control.
Parameter
Setting
Episode interval
t0=1800 s, T=16200 s; H=14400 s
Traffic generation
Independent Poisson; mean interarrival: Moon 180 s, Mars 360 s
Bundle sizes
20/100/300 Mbit with probabilities 0.5/0.3/0.2
Bundle TTL
5400 s from original generation
Relay capacity Bmax
1.2×109 bits
Contact cycle Tc
1800 s
Table 1: Frozen evaluation and PPO training configuration.
Policy
Aggregate ↓
Moon ↓
Mars ↓
Masked Lag. PPO
887.63
216.64
670.98
FIFO
1747.87
686.89
1060.97
LIFO
993.57
232.83
760.74
EDF
1692.38
806.15
886.23
Freshest-first
1009.56
232.82
776.74
Table 2: Excess-AoI performance over the 64 held-out traces. Values are means in seconds; lower is better.
Policy
Drops ↓
Exp. ↓
Delivered
Delivered Gbit
Bundle DR
Bit DR
Ucontact
Masked Lag. PPO
10.02
0.05
103.72
8.086
0.860
0.686
0.845
FIFO
16.20
0.00
96.28
8.578
0.801
0.727
0.897
LIFO
17.88
0.20
95.42
8.286
0.794
0.703
0.865
EDF
16.91
0.00
95.61
8.577
0.796
0.727
0.896
Freshest-first
16.78
0.17
96.56
8.262
0.803
0.701
0.863
Table 3: Mean operational performance over 64 traces. Expiries count relay-side events used in the constraint.
Figure 3: Relay operation under the PPO policy.
Policy
JCdrop
JCexp
JCfair,M
JCfair,S
Mean-feasible
Budget
17
1
0
0
—
Masked Lag. PPO
10.02
0.05
−2007.89
−1693.17
Yes
FIFO
16.20
0.00
−1764.52
−1138.05
Yes
LIFO
17.88
0.20
−2010.25
−1659.19
No
EDF
16.91
0.00
−1592.67
−1452.85
Yes
Freshest-first
16.78
0.17
−2010.25
−1658.08
Yes
Table 4: Mean episodic constraint returns over the 64 held-out traces. A policy is mean-feasible when all four empirical means satisfy their corresponding budgets.
Research Center for Information Technology Innovation (CITI), Academia Sinica (AS), Taipei 11529, Taiwan · Department of Electrical Engineering, National Taiwan Normal University (NTNU), Taipei 106308 Taiwan