Throughput modeling and analysis for TCP over TCP satellite communications

Abstract

When applying the Disruption Tolerant Networking (DTN) technique to satellite communications (SATCOM) with significant long delays, two problems result. First, to enhance the communication efficiency, Performance Enhancing Proxies (PEPs) used in satellite communications need to be integrated with DTN around SATCOM links, and the interoperability between DTN and PEP should be developed. Second, all data moving from a red core (secure intranet) to a black core (unsecured public network) should be encrypted using High Assurance Internet Protocol Encryption (HAIPE) devices. To solve the encryption problem, a TCP over TCP solution was proposed, which encodes original TCP flow information from HAIPE, and then reconstructs new TCP streams and encapsulates HAIPE-encrypted original TCP packets in them. These new TCP streams can be natively handled by PEPs and thus the full TCP performance can be achieved. However, the TCP over TCP solution requires special mechanisms to deal with the interaction between the congestion control of the inner and outer TCP links. To achieve congestion goals, this paper develops a throughput system model, and provides an analysis of the impacts of TCP retransmission. Our analysis shows a throughput reduction when both inner and outer TCP react to packet loss. Possible solutions are also proposed using delay shaping to remove the congestion control of the TCP tunnel. An analysis is provided to explain the mechanisms behind our solutions, and experiment results are also provided to support our design.