[CMC] MIT Technology Review article on DTN

[Adrian J. Hooke]

http://www.technologyreview.com/communications/21601/page1/
MIT Technology Review

<http://www.technologyreview.com/communications/21601/>A Better 
Network for Outer Space
By 
<http://my.technologyreview.com/mytr/social/profile.aspx?wuid=8348>Brittany 
Sauser
Monday, October 27, 2008

Why Vint Cerf wants to put Internet-style networking in space.

Having designed the networking protocols that launched the Internet, 
Vint Cerf now wants to put the same kind of robust communications 
network in outer space. Currently, astronauts and robotic spacecraft 
communicate with Earth using point-to-point radio links and 
communications schemes that are tailored to nearly every new mission. 
This inhibits interoperability and the repurposing of communications 
equipment, and as the number and complexity of missions increases, it 
will only become more problematic.

Cerf, who is Google's vice president and chief Internet evangelist, 
is working with a team at NASA's Jet Propulsion Laboratory (JPL), 
where he is also a visiting scientist, and at the MITRE Corporation, 
based in Washington, DC, to design and implement a revolutionary new 
scheme for space communication. The project, dubbed the 
Interplanetary Internet, will be tested aboard the International 
Space Station (ISS) in 2009, and Cerf hopes that by 2010, new space 
missions will be designed to use the protocols.

Ultimately, the network could interconnect manned and robotic 
spacecraft, forming the backbone of a communications system that 
reaches across the solar system.

Technology Review's Brittany Sauser caught up with Cerf to discuss 
the details of the project.

Technology Review: What's the purpose of the Interplanetary Internet?

Vint Cerf:The project started 10 years ago as an attempt to figure 
out what kind of technical networking standards would be useful to 
support interplanetary communication. Bear in mind, we have been 
flying robotic equipment to the inner and outer planets, asteroids, 
comets, and such since the 1960s. We have been able to communicate 
with those robotic devices and with manned missions using 
point-to-point radio communications. In fact, for many of these 
missions, we used a dedicated communications system called the Deep 
Space Network (DSN), built by JPL in 1964.

But one problem with space communication has been the limited use of 
standards. When we launch a spacecraft with a unique set of sensors 
onboard, we often end up writing special communication and 
application software that is adapted to that spacecraft's sensor 
systems and manipulators. In the Internet world, we use standards 
called the TCP/IP protocol suite--packet switching and 
store-and-forward methods--to allow a lot of different devices, 
billions of things, to interact compatibly with each other. The team 
set out to develop a suite of protocols that would allow us to have 
the kind of network flexibility in space that we have on Earth. The 
Interplanetary Internet project is primarily about developing a set 
of communication standards and technical specifications to support 
rich networking in space environments.

TR:What are the challenges of building such a network in space?

VC:We started by working on a set of protocols that could deal with 
two very important properties of space communication. The first is 
delay. The distances between the planets are very large. For example, 
when Earth and Mars are closest together, it still takes 3.5 minutes 
for a radio signal moving at the speed of light to propagate. If I 
were on Mars and you were on Earth, it would take seven minutes at 
best before you heard a response. When Earth and Mars are farthest 
apart, the round trip takes 40 minutes! The reason we can talk back 
and forth on Earth so easily is that propagation times are very short 
by comparison.

The other problem is that the planets and their satellites are in 
motion, and most are rotating. The rotation of the planets means that 
if you are talking to something that is on the surface of the planet, 
it may rotate out of the line of sight so you cannot talk to it 
anymore, until the device on the surface rotates into view again. The 
same could be said for some orbiting satellites. You have to develop 
protocols that will deal with the fact that you cannot always 
communicate with the other party: the communication is both delayed 
and potentially disrupted. So that is what we designed: a delay- and 
disruption-tolerant networking system [DTN]. It will allow us to 
maintain communications more effectively, getting much more data 
because we don't have to be in direct line of sight with the ultimate 
recipient in order to transfer data. The new protocols will be 
proposed to serve as a potential international standard for space networking.

TR:How does this new protocol, the delay- and disruption-tolerant 
networking system, work?

VC: We are using store-and-forward methods [routing information 
through hosts that hold on to it until a communications link can be 
established] similar to the TCP/IP design in order to service 
space-communication requirements. But our new bundle protocol is 
based on DTN principles. We have to cope with the fact that there is 
a really high potential for delay and disruption in the system. For 
example, Pluto is a long ways away, on the order of three to five 
billion miles and about 12 hours round-trip time. Using the DTN 
bundle protocol allows us to design more-complex mission 
configurations involving many devices on the surface of planets and 
in orbit around them. At Mars, for example, there are four orbiters 
and three landed and operational spacecraft. We expect to be able to 
use the standard TCP/IP protocols on the surface of planets and 
inside spacecraft, but we will use the DTN protocols for 
interplanetary distance communications.

TR: Is this going to require putting new infrastructure in space?

VC: The answer is yes and no. For example, the Deep Impact spacecraft 
[now called EPOXI] is already in orbit around the sun. It was used to 
launch a probe into a comet to examine its interior. EPOXI is being 
temporarily repurposed to test the new DTN protocols. The spacecraft 
has processing, memory, radio equipment, and solar panels for power 
so we don't have to put new hardware up. We just have to upload new 
software. We are lucky to not have to field any new equipment yet, 
but the DTN protocols eventually have to show up in a fairly 
significant number of devices in the system to create the kind of 
network that can serve space-communication needs. Some specialized 
spacecraft could become store-and-forward routers. Each time a new 
mission is launched, using the standard bundle protocol, previous 
mission assets that are still in operation could be used to support 
the communication requirements of the new mission. In this way, we 
hope to accrete a kind of interplanetary backbone network.

TR: How are you handling security issues?

VC: There are security concerns, and we have been very careful to 
build defenses into the basic design. Each bundle-aware node will 
verify the identity of any other nodes that it is communicating with, 
and it will refuse to forward data from any nodes that it does not 
recognize. We will be using strong authentication methods, 
cryptographic communication methods, to ensure that the parties that 
are using the resources are authorized to do so.

TR: What is the biggest advantage of building new protocols for space 
communication?

VC: The important part here is that we have standardized protocols 
that will allow internetworking of various spacecraft launched by all 
the spacefaring nations. Over time, as new missions are launched, you 
start to build up a backbone capability. Every time you put up a new 
mission, you basically are putting up another potential node in the 
network. Our hope in the near term is to start putting 
DTN/bundle-protocol applications up on the Internet terrestrially, 
and also put them up on the International Space Station for testing. 
Eventually, we hope to have this capability running all the time, and 
then, when new deep-space missions are launched using these standard 
protocols, they will become part of the interplanetary communications system.

-------------- next part --------------
An HTML attachment was scrubbed...
URL: http://mailman.ccsds.org/pipermail/cmc/attachments/20081027/3ef710ee/attachment.htm