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Improved Contact Graph Routing in Delay Tolerant Networks with Capacity and Buffer Constraints

Tania Alhajj, Vincent Corlay

TL;DR

The paper tackles the challenge of efficient routing in delay-tolerant satellite networks where link capacity and node buffers are scarce. It introduces a global, proactive CGR framework that enforces capacity and buffer constraints during route search through contact splitting and edge pruning, aided by forecast buffer tables and optional safety margins. The method preserves optimality by operating within the subset of valid routes and demonstrates substantial improvements in delivery time and intermediate-node complexity compared with a source-routing CGR benchmark. These results suggest significant practical impact for resource-constrained space networks, with future work aimed at distributed implementations and velocity-focused routing in cislunar and large-constellation scenarios.

Abstract

Satellite communications present challenging characteristics. Continuous end-to-end connectivity may not be available due to the large distances between satellites. Moreover, resources such as link capacity and buffer memory may be limited. Routing in satellite networks is therefore both complex and crucial to avoid packet losses and long delays. The Delay Tolerant Network (DTN) paradigm has emerged as an efficient solution for managing these challenging networks. Contact Graph Routing (CGR), a deterministic routing algorithm, is one of the most popular DTN algorithms. CGR is compatible with the ``store, carry, and forward" principle, whereby a node receives a message and stores it in its buffer until a transmission opportunity becomes available. However, CGR relies on simplified models to incorporate potential constraints in the route search. For instance, the linear volume assumption is often used to consider capacity constraints. Moreover, capacity management and buffer management are mostly performed during the forwarding phase, once an issue has occurred. In this paper, we propose taking measures before or during the route search in order to find routes that respect both contact-capacity and node-buffer limits. We introduce the contact splitting and edge pruning operations to effectively account for the routing constraints. This ensures that CGR outputs the optimal solution among the subset of valid solutions. The proposed approach can also be used to book resources to be used in case of issues during the forwarding phase.

Improved Contact Graph Routing in Delay Tolerant Networks with Capacity and Buffer Constraints

TL;DR

The paper tackles the challenge of efficient routing in delay-tolerant satellite networks where link capacity and node buffers are scarce. It introduces a global, proactive CGR framework that enforces capacity and buffer constraints during route search through contact splitting and edge pruning, aided by forecast buffer tables and optional safety margins. The method preserves optimality by operating within the subset of valid routes and demonstrates substantial improvements in delivery time and intermediate-node complexity compared with a source-routing CGR benchmark. These results suggest significant practical impact for resource-constrained space networks, with future work aimed at distributed implementations and velocity-focused routing in cislunar and large-constellation scenarios.

Abstract

Satellite communications present challenging characteristics. Continuous end-to-end connectivity may not be available due to the large distances between satellites. Moreover, resources such as link capacity and buffer memory may be limited. Routing in satellite networks is therefore both complex and crucial to avoid packet losses and long delays. The Delay Tolerant Network (DTN) paradigm has emerged as an efficient solution for managing these challenging networks. Contact Graph Routing (CGR), a deterministic routing algorithm, is one of the most popular DTN algorithms. CGR is compatible with the ``store, carry, and forward" principle, whereby a node receives a message and stores it in its buffer until a transmission opportunity becomes available. However, CGR relies on simplified models to incorporate potential constraints in the route search. For instance, the linear volume assumption is often used to consider capacity constraints. Moreover, capacity management and buffer management are mostly performed during the forwarding phase, once an issue has occurred. In this paper, we propose taking measures before or during the route search in order to find routes that respect both contact-capacity and node-buffer limits. We introduce the contact splitting and edge pruning operations to effectively account for the routing constraints. This ensures that CGR outputs the optimal solution among the subset of valid solutions. The proposed approach can also be used to book resources to be used in case of issues during the forwarding phase.

Paper Structure

This paper contains 36 sections, 4 equations, 15 figures, 3 tables, 1 algorithm.

Table of Contents

  1. Introduction
  2. Background and motivations
  3. Key notions
  4. Contact graph routing (history)
  5. Contact graph routing (implementation)
  6. construction
  7. Route search
  8. Validation and forwarding
  9. Additional comments on
  10. Source-routing CGR
  11. Bundle-independent
  12. Bundle-dependent
  13. Contact-capacity and node-buffer challenges in DTNs
  14. Contact-capacity management
  15. Buffer management
  16. ...and 21 more sections

Figures (15)

  • Figure 1: Snapshot of a satellite communication scenario at time $t$ (e.g., $t_{1,1}\leq t \leq t_{2,1}$ and $t_{1,4}\leq t \leq t_{2,4}$, see Table \ref{['tb: CP']}).
  • Figure 2: Linear vs real volume consumption.
  • Figure 3: Contact splitting.
  • Figure 4: Potential overflows at node $Z_1$.
  • Figure 5: Forecast buffer table of node $Z_1$ before routing bundle b.
  • ...and 10 more figures