18-12-2012, 01:40 PM
INTERPLANETARY NETWORK
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INTRODUCTION
The development in the space technologies are enabling the realization of deep space Scientific missions such as Mars exploration. The vision of future space exploration includes missions to deep space that require communication among planets, moons, sattelites, asteroids, robotics spacecrafts and crewed vehicles. The missions produce significant amount of scientific data to be delivered to the Earth. In addition, these missions require a tenuous space data delivery at high data rates, interactivity among the in-space instruments, security of operations, and seamless interoperability between in-spaceentities. for successfull transfer of scientific data and reliable navigational communications,NASA enterprises have outlined significant challenges for development of next-generation space network architecures.The next step in design and development of deep space networks is expected to be the internet of the deep space planetary net works and defined as the INTERPLANETARY INTERNET(IPN).
NEED FOR INTER-PLANETARY INTERNET
1. There are thousands of man-made satellites in space. We require a communication service for scientific data delivery from and to these satellites.
2. There should be navigation services for the explorer spacecrafts and orbiters of the future deep space missions.
3. Another problem is that, these communication systems are not in earth. They are connected to systems which are millions of kilometers away.
OBJECTIVE
The objective of the Interplanetary Internet project is to define the architecture and protocols necessary to permit interoperation of the Internet resident on Earth with other remotely located internets resident on other planets or spacecraft in transit.
While the Earth's Internet is basically a "network of connected networks", the Interplanetary Internet may therefore be thought of as a "network of disconnected Internets". Inter-working in this environment will require new techniques to be developed.
Many elements of the current terrestrial Internet suite of protocols are expected to be useful in low-delay space environments, such as local operations on and around other planets or within free flying space vehicles. However, the speed-of-light delays, intermittent and unidirectional connectivity, and error-rates characteristic of deep-space communication make their use unfeasible across deep-space distances
INTERPLANETARY INTERNET ARCHITECTURE
A common infrastructure for interplanetary networking and distributed communication technologies are needed to support the scientific research and possible commercial applications in the near future. Since Internet is truly horizontal and has a diverse set of open interoperable standards, building the space Internet on top of Internet technologies could enable any space mission to ‘‘plug in’’ with high quality of service and cost savings. Therefore, most of the network architectures proposed for the deep space exploration are based on Internet technologies.
• Planetary Satellite Network.
The satellites circling the planets can provide relay services between the Earth and the outer-space planet as well as communication and navigation services to the surface elements .
Some surface elements have the capability to communicate with satellites, reporting local topology upward and receiving data and commands from satellites. The PlaNetary Satellite Network includes the links between orbiting satellites, and links between satellites and surface elements. It is composed of satellites which lie in multiple layers as shown in Fig. 2.2 and provides the following services : intermediary caching and relay service between the Earth and the planet, relay service between the in-situ mission elements, and location management of Planetary Surface Networks
COMMUNICATION PROTOCOL SUITE
The InterPlaNetary Internet consists of three major networks, i.e., InterPlaNetary Backbone Network, InterPlaNetary External Network, and PlaNetary Network as shown in Fig.2. 1. As different types of networks are being deployed throughout the InterPlaNetary Internet, the ability to communicate with each other is vital. Each of these components may have to run different set of protocols that best fit the environment .
For example, a protocol stack for the InterPlaNetary Backbone Network requires protocols to handle extremely long and variable propagation delays, intermittent link connectively, and high error rates. In this section, we will explore the current and proposed protocol suites to realize communication in the InterPlaNetary Internet.
CCSDS CURRENT SPACE/GROUND PROTOCOL STACK
The current space/ground protocol stack is proposed by the CCSDS for space communications The protocol stack consists of eight layers: Space Applications, Space File Transfer, Space End-to-End Reliability, Space End-to-End Security, Space Networking, Space Link, Space Channel Coding, and Space Wireless Frequency and Modulation. A specific implementation of the stack is shown in Fig. 3.1. It is used for Mars Exploration mission communications .
DELAY TOLERANT NETWORKING PROTOCOL STACK
The ability to integrate highly optimized regional network protocols is the objective of the future space/ground protocol stack developed by the Delay-Tolerant Networking research Group (DTNRG) ]. The protocol stack relies on amiddleware layer called bundle layer ,that resides between the application and the lower layers. The bundle layer resolves the intermittent connectivity, long or variable delay, asymmetric data rates, and high error rates by using a storeandforward mechanism similar to e-mail.
It sends a bundle of message fragments to the next-hop node with per-hop error control, which increases the probability of data transmission. In addition, it provides six classes of service (CoS) for the bundle : (1) custody transfer, (2) return receipt, (3) custody-transfer notification, (4) bundleforwarding notification, (5) priority of delivery, and (6) authentication.
MOVEMENT AWARE ROUTING (MARVIN)
The fundamental concept of MARVIN algorithm is that movements of planets is highly predictable, hence, routes can be calculated in advance and stored in a routing table for any duration. This greatly reduces the need for expensive route establishment and maintenance procedures that potentially consume enormous time and power. MARVIN algorithm uses a shortest-path Dijkstra algorithm to determine the shortest route between any two nodes in the interplanetary backbone network. At any given time T, the network can be represented by a t-graph; an edge of the graph which is active has a cost determined by the following metric: distance, power or delay. Over a given period of time, MARVIN finds the optimal routes between all source-destination pairs based on a given metric. The shortest-path route starts at start Time and a route can be used until any link in it breaks. At the instant a link-break occurs, the route needs to be recomputed. This process is repeated for every link break during the period of concern, between startTime and endTime
SPACE BACKBONE ROUTING (SBR)
Space backbone routing (SBR) is proposed based on the hierarchical architecture of the IPN Internet and specifically addresses its challenges. SBR has two integral parts: SBR-external (SBR-e) and SBR-i. SBR-e forwards the control and data messagesthrough the IPN Internet and selects paths for interplanetary backbone network. The control and data messages are delivered in a store-and-forward manner and they may need to be buffered in intermediate nodes for a considerably long time.
PLANETARY ROUTING
Planetary surface network includes high power surface elements, such as rovers and landers which have the capability to connect with satellites and surface elements that can not communicate with satellites directly. These elements are often organized in clusters and spread out in an ad hoc manner, e.g., sensor nodes and balloons. Hence, the routing problem in planetary surface network is relevant and similar to the terrestrial mobile ad hoc networks and sensor networks, hence some of these emerging terrestrial technologies can be applied to the planetary surface network.
CONCLUSION
The vision of future space exploration includes missions to deep space that require communication among planets, moons, satellites, asteroids, robotic spacecrafts, and crewed vehicles. This vision involves in the design and development of next generation deep space networks, which is expected to be the Internet of the deep space planetary networks and defined as InterPlaNetary Internet. However, there exist significant challenges for the realization of this vision in several aspects of the communication architecture. In this paper, these challenges, the current status of the research efforts to address them are explored along with their short-comings. Many researchers and several international research organizations are currently engaged in developing the required technologies to realize the InterPlaNetary Internet.