Interplanetary interenet : Disruption Tolerant Networking

For interplanetary missions, spacecrafts-satellites have to communicate with each-other or earth-based control centers through large distance in space. Sometimes, due to certain reasons, the communication links breaks and the transferred data is lost. NASA is working on a new innovative technology to develop internet with disruption tolerant networking system for interplanetary space missions.

How does internet work ?

The Internet works through a packet routing network in accordance with the Internet Protocol (IP), the Transport Control Protocol (TCP) and other protocols. A protocol is a set of rules that specifies how a computer should communicate with other computer. For instance, the Transport Control Protocol has a rule that if one computer sends data to another computer then the destination computer sends a signal to source computer if any data is missing or not. Similarly, the Internet Protocol (IP) specifies how computer should route (choosing a path for sending information in a network) information to other computers by attaching addresses (IP addresses) onto the data it sends. IP is a set of specifications that standardize how things work in devices connected to the internet. However, IP does not guarantee reliable packet delivery over a network (This is why TCP and IP are used together for internet).

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Command-line utility ping showing the packet receiving time for my computer from server

The Transport Control Protocol is not used for satellite communication because of its inefficiency. In an article published by some researchers from Paris about TCP for satellite communication they said, "....we outlined TCP inadequacies in the context of satellite communications. The most limiting factors inherent to geostationary satellites appear to be the long propagation delay and the asymmetric nature of the connection. The most affected mechanisms are the timeout and retransmission mechanisms on the one hand (not accurate enough), and the window increase algorithms during Slow Start and Congestion avoidance phases on the other hand (too conservative)."

IP is not a reliable protocol for sending data packets. What's a packet ? Data sent across the Internet is called a message. Before a message is sent, it is first split in many fragments called packets. These packets are sent independently of each other.

During the propagation of data packets in a network using Internet Protocol if, a link breaks down between two hops the data packets are lost. NASA is working on an innovative technology to store the data packets until the connection is re-established with the next hop. Thus, there will be no loss of data. This 'Disruption Tolerant Networking' will be very useful for internet communication on Earth as well as space missions into deep space.

Data Sources:
S. Oueslati-Boulahia, A. Serhrouchni, S. Tohmé, S. Baier, M. Berrada. TCP Over Satellite Links : Problems and Solutions. Researchgate. July 2000.

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