Protocol Specification
Each rover carries one edge node that runs two pieces of software side by side: the PBS edge adapter and a BPv7 bundle agent such as NASA/JPL ION. The adapter checks each envelope and tags it with its priority class. The bundle agent stores envelopes while the link is down and sends them, most urgent first, when it is up (PBS-DTN-MAP-01 Sections 6.3 and 9).
This simulation shows that scheduling on one link, beside a first-in, first-out (FIFO) queue on an identical link. It models the scheduling policy. The ION demonstration records NASA/JPL ION scheduling real bundles.
Left: Edge Node, Strict Priority
Transmits queued envelopes in priority order, P0 first. Strict priority is one scheduling policy permitted by PBS-PRIO-01 v1.4 Section 6; PBS leaves the algorithm to the implementation (PBS-CONFORMANCE-01 Section 6).
- P0 envelopes are transmitted before all queued lower-priority envelopes.
- P4 bulk traffic uses the capacity that remains.
- An envelope already on the link finishes before the next starts. Preemption is optional (MAY) in PBS-PRIO-01 Section 6.1.
- With ION as the bundle agent, the adapter's tag selects one of ION's three queues: CRITICAL and HIGH expedited, NORMAL standard, LOW and BULK bulk (PBS-DTN-MAP-01 Section 6.3). This simulation keeps all five PBS classes as separate queues to show the full ordering.
Goal: strict priority gets P0 (Emergency) messages through first, even when the link is saturated.
- Maintains minimal latency for critical data.
- Manages bulk traffic (Stream) to prevent head-of-line blocking.
Right: FIFO Queue
All data is transmitted in arrival order. A saturating stream delays every packet queued behind it.
- Queue delay grows with saturation.
- P0 packets wait behind earlier packets.
- This baseline sends in arrival order: the behaviour of a link served by one queue.
Procedure:
1. Saturate the links with High-Bandwidth Stream (P4).
2. Inject an Emergency (P0) event.
3. Compare the PBS and FIFO "Transit" values.
Priority Class Index (PBS-PRIO-01 Section 4)
Emergency Alert
P0 CRITICAL
Immediate life- or safety-critical data.
Bio-Telemetry
P1 HIGH
Critical health monitoring.
Mission-critical operational data.
System Telemetry
P2 NORMAL
Routine structural logs.
Routine mission data.
Payload Data
P3 LOW
Opportunistic or deferrable data.
High-Bandwidth Stream
P4 BULK
Non-urgent, high-volume data.
Instruction: Saturate the links with P4 traffic, then inject P0 to observe strict-priority scheduling.