The paper presents an optimization approach to the problem of choosing channels and parameters in the data transmission process within a Software-Defined Wide Area Network (SD-WAN). The approach presumes designing an intelligent subsystem integrated in transport agents (such as QUIC) and aimed at satisfying the given Service Level Agreement (SLA) by choosing the appropriate congestion control algorithm and Forward Error Correction (FEC) scheme. The SLA represents the constraints on four indices related to each SD-WAN channel: bandwidth, delay, jitter, and loss rate. The optimality criterion is to minimize the total average cost of successful transmission per one payload packet subject to the SLA, taking into account the quality of service provided by each channel. A valuable part of the present paper is devoted to a survey on mathematical models of data transmission networks and transport communication channels. Fundamental results and possible shortcomings are highlighted for every specific approach based on deterministic dynamic models, network calculus, and fluid approximation. The proposed optimization problem has the form of a data-driven stochastic program. Its details are provided by evaluating parameters of FEC coding schemes and their performance indices.