In this paper, licensed-Assisted access (LAA) for dual-band small cell network is investigated. A framework for LTE coexisting with incumbent unlicensed systems is firstly introduced. The analytical expressions are also derived to characterize the transmission strategies for both LTE and wireless fidelity (WiFi) systems over unlicensed spectrum. Based on the natures provided by analytical models, a discontinuous transmission (DTX)-enabled LAA (DLA) mechanism is proposed to maximize energy efficiency with quality-of-service (QoS) support. Also, a dual access-based opportunistic traffic offloading (DOTO) scheme is developed to determine whether traffic offloading or channel aggregation, i.e., WiFi or LAA, shall be adopted in unlicensed spectrum. Numerical results demonstrate that the proposed DLA mechanism can dynamically adjust DTX pattern to opportunistic share unlicensed spectrum or achieve energy conservation from the perspective of energy efficiency. The tradeoff between traffic offloading and channel aggregation over unlicensed spectrum is also provided by evaluating the performance of proposed DOTO scheme.