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Link and routing issues for Internet protocols in space

The first step in using Internet protocols in space is to establish the basic Internet datagram delivery service over satellite RF links. This paper discusses the low-level data link and data routing issues related to using Internet protocols to support spacecraft communications. It covers issues related to layer 1 (physical), layer 2 (data link), and layer 3 (network). It does not cover layer 4 (transport) and above. At the physical layer, the paper presents various applications of forward-error-correction (FEC) coding techniques, such as convolutional coding and Reed-Solomon. It describes approaches for using these techniques in ways that are independent of the protocols used at the data link layer and above. At the data link layer, common, commercially available framing schemes are discussed along with how they can be easily deployed. A rationale is provided for the selection of HDLC/frame relay framing along with IETF multi-protocol encapsulation. At the network layer, the Internet protocol end-to-end addressability and routing is discussed in the context of space-based applications. Standard solutions for dealing with the intermittent and mobile links of satellites are also discussed. These include a discussion of Mobile IP and mobile routing protocols. Finally, deployment of these protocols in both spacecraft and ground systems are discussed. Details of current implementations by the Operating Missions as Nodes on the Internet (OMNI) project at NASA/GSFC using operational space and ground systems such as UoSAT-12 and TDRSS are also provided.