The Interplanetary Internet Meets the DTN Architecture

1. The Interplanetary Internet Meets the DTN Architecture Robert C. Durst durst@mitre.org

2. Interplanetary Internet: The Genesis of DTN • Purpose: • Identify the architectural drivers in the IPN environment • Intermittent connectivity • Asymmetric capabilities/impacts of rad hardening • Power/mass/volume constraints • Identify the key elements of the DTN architecture for the IPN • New technologies coming…

3. Overview of Deep Space Communications Today • Expensive • Scheduled • Oversubscribed • Ground stations in “interesting” locations • Madrid, Spain; Canberra, Australia; Goldstone, California, USA • Sometimes, connectivity from the ground station to the spacecraft is better than connectivity among ground stations

4. This shows the entire Madrid Deep Space Network complex with the new Beam Waveguide Antenna in the foreground. One 26-meter (85-foot) antenna. One 70-meter (230-foot) antenna. One 34-meter (111-foot) diameter High Efficiency antenna. One 34-meter Beam Waveguide antenna. (Three at the Goldstone Complex)

5. 70 meter antennas are big. For scale: a big truck

6. Connectivity is scheduled.WAY in advance. • Excerpt from proposer information for Mars Scout missions (dated March 2002) • Spacecraft builders must identify their daily communication support requirements prior to spacecraft build • Current DSN costing favors infrequent, longer passes (due to repointing and recalibration times on the big antennas)

7. Multi-hop Connectivity

8. Start Time Contact Time (minutes) 12/09/2001 11:50:10 4.3 12/10/2001 00:40:10 6.7 12/10/2001 13:33:00 3.0 12/11/2001 13:16:30 5.3 12/12/2001 02:07:10 6.5 12/13/2001 14:43:10 5.7 12/14/2001 03:34:30 5.8 12/15/2001 03:20:30 3.3 12/15/2001 16:09:50 6.0 12/16/2001 05:01:50 5.0 Routing in predictably-intermittently-connected networks • Satellite visibility is predictable • Real time connectivity of two points via satellite requires an intersection of two schedules, but is doable • Example: MS’01 • Orbiter in Mars polar orbit, lander at Lat, Lon (0, 0) • Example based on Stanford Telecom simulations, using link budget for 128kbps data rate • Here’s a week’s contacts for a single satellite, single lander:

9. Spacecraft/Lander Realities • No current deep-space spacecraft/landers/ rovers support IP • Few support file systems • This is changing, but slowly • Efficiency requirements and lack of networking opportunities • No solution must depend on an IP-based network • Power – there’s never enough and it’s expensive • Mars: $200k/watt in orbit, $75M/watt on surface • Culture • Little perceived need for “protocols” on top of RF in some sectors • Retransmissions between earth and deep space done manually – there is a desire to continue this practice

10. Some DTN Architectural Benefits “Non-chatty” message-oriented communications • Essential in long delay environments Store-and-forward between nodes • Essential when no contemporaneous end-to-end path exists • Highly desirable to free resources at less-advantaged “leaf nodes” Routing algorithms cognizant of scheduled connectivity • Essential to accommodate scheduled connectivity • Highly desirable to be able to adaptively exploit alternate routes Use transport and network technologies appropriate to the environment • Essential to support combination of IP and non-IP networks • Essential to be able to support incremental deployment of new technologies Integral infrastructure protection • TBD: Authenticated forwarding and routing updates

11. Key Architectural Concepts (1/5) • Message-Switched overlay network with custody transfers • Application-layer “messages” are non-chatty atomic units carried by the network -- Essential • Even if no end-to-end path is present, messages can still move forward as much as possible and then wait for a path become available -- Essential • Point of retransmission progresses towards destination, “custody transfer” allows resource-starved nodes to recover retransmit buffers – Highly desirable • Reduces network load (Essential), end-to-end delay (Desirable)

12. Key Architectural Concepts (2/5) • Overlay network spanning transport technologies • Allows use of transport and network protocols appropriate to the environment -- Essential • Bundle gateways “impedance match” between environments -- Essential Application Application Bundle Bundle Bundle Bundle Bundle Bundle Transport Transport Transport Transport Network Network Network Network • Regions aggregate nodes • Aggregation based on technology, policy, proximity, etc. -- TBD • Gateways between regions providecontrol points (Desirable), store-and-forward resources (Essential), active transcoding –(Not needed in IPN now)

13. Src Dst App Source Authentication App Optional Src Dst Security Bundle Bundle Boundary Node Node Fwd Auth Fwd Auth Fwd Auth Key Architectural Concepts (3/5) • Routing across disconnection (Essential) • Cognizant of path entropy (TBD) • Persistent links • Scheduled connectivity • Predicted contacts • Opportunistic contacts • Selection based on path characteristics (Desirable) • Replication on multiple paths for robustness (Nocurrent recognized requirement in IPN) • Enables “fire-and-forget” networks robust against disruption (Essential) • Infrastructure protection (TBD) • Authenticated application registration • Signed exchanges among routers • S/MIME-like (no Diffie-Hellman exchange) • Public keys may or may not (more likely) accompany the bundle • Unclear whether perimeter control to ground networks and possibly link-layer command authentication on DS links is sufficient

14. Key Architectural Concepts (4/5) • Late binding of names to addresses • Name tuple carries destination region and administrative name • Alleviates need for universal name-to-address binding database • Implicitly supports role-based addressing – (Useful, but probably not a driver) • Late binding may be more flexibility than IPN perceives a need for • Class of Service similar to postal system • Types: Priority, regular, bulk (Essential) • Options: send notification, keep delivery record, inform on delivery (Highly desirable) • Helps to optimize resource use (Essential)

15. Key Architectural Concepts (5/5) • Application multiplexing/demultiplexing • Demultiplexing based on administrative name, syntax defined by application • Provides a new general-purpose network delivery service • Highly Desirable, but mux/demux may be done by mechanisms other than those in DTN/bundling File Xfer SA C2 Voice Msg WWW API Bundle Transport Network • Process persistence/reanimation • Useful in embedded systems that are resource poor (e.g. sensor nets) • Upon bundle arrival, application and relevant state are reinstantiated • Allows operation across (planned or unplanned) power cycles, software, OS upgrades • Supports process migration to alternate hosts • Process persistence/reanimation may be more flexibility than IPN perceives a need for

16. New Technologies • High rate interplanetary links • X-Band/Ka-Band – up to 100Mbps from Mars • Optical -- ~200Mbps(burst rate) (that’s a 6GB bandwidth delay product from Mars closest approach) • High rate instruments (can consume all available capacity) • Solid state storage – more work needed • Rad hardened electronics

17. Conclusions • IPN is well served by much, if not all, of the DTN functionality • Flexibility in application of the DTN capabilities to a particular network is essential (which is in tension with …) • Evolution and growth in deep space science will probably make even more of the DTN architecture relevant to the IPN