TCP Tactical™—A Control Plane
Tactical networks operate under conditions of high loss rates, path asymmetry, and link intermittency not normally encountered in the commercial Internet. Additionally, security assurances that must be provided in a military setting preclude many TCP performance improvements that rely on modification of the TCP header by intermediate routers as packets traverse the network.
These conditions and constraints can cripple the performance of “legacy TCP, ” which assumes that a very small percentage of transmitted packets are lost due to packet corruption—in effect, that all packet losses are the result of network congestion—and responds by reducing an end-host's transmission rate. Corruptive loss in a tactical network is, however, commonplace and can be caused by, for example, inherently lossy RF transmission links and antenna misalignment.
TCP Tactical addresses legacy TCP's poor performance in challenging tactical environments. It is a TCP stack replacement that provides order-of-magnitude throughput improvements to TCP applications deployed in tactical environments. It optimizes tactical-network throughput on the fly by considering bandwidth, loss, and latency metrics. TCP Tactical is a software-only solution that can be implemented as an end-host transport-protocol replacement or as an edge-network proxy. It therefore preserves existing investment in application-level software and routing infrastructure. Legacy applications require no modification to benefit from TCP Tactical's throughput improvements, and no routing-infrastructure changes are required.
Figures 1 and 2 illustrate TCP Tactical's operation.
Figure 1. Figure 2.
TCP Tactical is deployed at the network edges, where the network challenge occurs. The network core (i.e., the global information grid, or GIG) is high-quality, high-speed fiber. The assumptions upon which legacy TCP was developed apply to this GIG core. A Path Characterization Service (PCS) informs the TCP Tactical stack of network challenges in terms of bandwidth (max. send rate), corruptive loss rate, and latency. The stack optimizes transmission to take fully advantage of available bandwidth. The TCP Tactical stack reverts to legacy TCP operation if opposing endpoint is not TCP Tactical enabled.
Testing performed by DARPA's red team contractor has shown that when run over tactically challenged links, TCP-Tactical can achieve 4x-100x improvements over legacy TCP, as depicted in Figures 3 and 4.