Impact of Delayed Acknowledgments on Transport Layer Performance over Low Orbit Constellations

摘要

Satellite transmissions can suffer from high channel impairments, especially on the link between a satellite and a mobile end user. To cope with these errors, physical and link-layer reliability schemes have been introduced at the price of an increased end-to-end delay seen by the transport layer [for example, Transmission Control Protocol (TCP)]. By default, the TCP enables delayed acknowledgment (DelAck) that might increase the end-to-end delay when performing over satellite link-layer recovery schemes. As a matter of fact, even if this option enables decreasing the feedback path load and the stack processing overhead, it might be counterproductive in a satellite context. This motivates the present paper, which aims to quantify the impact of such a TCP option in the context of low Earth orbit satellite constellations. Several simulation measurements are performed with two well-deployed TCP variants, and it is shown that DelAck should be disabled when used over link-layer Hybrid Automatic Repeat Request schemes, particularly when these schemes enable reordering the buffer.