Current transport layer is facing challenges from both the original design drawbacks and new evolutionary technologies demands. The strict hierarchical layer architecture is restricted and inflexible, which makes the addition and deployment of new features difficult. While new evolutionary technologies, such as multihoming, mobility, ID/Locator split, need the transport layer import new functions urgently. In this paper, we analyze and summarize these challenges and resolve them in RTLA, an experimental Redesigned Transport Layer Architecture. Through splitting the transport service to three sublayers and some cross-layer function blocks, the RTLA is able to extend new features easily. Consequently, the RTLA provides a heuristic overview of a scalable transport service designing based the layered model with cross-layer collaboration.