DTN LEO Satellite Communications through Ground Stations and GEO Relays

Contact Graph Routing enhancements for delay tolerant space communications

“…However, once the residual capacity of this contact is exhausted (after the 8 th bundle), the corresponding route is discarded and bundles are forwarded to 2, which is the best of the residual choices (the second contact to 3 starts much later). Although CGR delivers all bundles in a reasonable time, we observe, as in [14], three sub-optimal results: First, the order of delivery is scrambled; bundles 1 and 4 are delivered first, then 5-7 in parallel with 9-15, and 8 is delivered last. Although this is compliant with BP RFCs, it is not desirable.…”

“…Routing bundle traffic of the same priority: CGR-ETO improvements. Next we consider a more realistic scenario, similar to the LEO scenario in [14]. Here all contacts have the characteristics given in Table I.…”

“…An additional problem, identified in [14], is the present late handling of contact "overbooking". Because of their finite length and transmission rate, contacts have a finite volume or "capacity".…”

Analysis of contact graph routing enhancements for DTN space communications

“…However, once the capacity of the first 1–3 contact is fully exploited, CGR discards this route and forwards the remaining bundles via 2 (‘Delivered via 2’), which is the best of the residual choices, as the second contact to 3 starts much later. Although Original CGR is able to make use of both parallel contacts (1–2 and the first 1–3) and to deliver all bundles during these contacts, we observe, as in and , three sub‐optimal effects: first, the order of delivery is scrambled on a large scale; bundles 1 and 5 are delivered first, then 6–8 in parallel with 11–20, and 9–10 are delivered last. Although this is compliant with BP RFCs, it is not desirable.…”

“…Simulations showed that, by including estimates of queuing delay, significant improvements in both routing and estimating of end-to-end delivery delay could be achieved. In parallel, authors in [22] identified the 'overbooking problem' because of the a posteriori handling of contact oversubscription that originates from the need of enforcing priority in the presence of different priority traffic. Given that CGR-ETO and a better handling of contact oversubscription seemed complementary, authors of the corresponding mechanisms joined forces to combine the benefits of each mechanism within a single version of CGR, which incorporated both CGR-ETO and overbooking management in the actual ION CGR code.…”