We present a seamless handoff solution, called Universal Seamless Handoff Architecture (USHA). USHA is simple and requires minimal modification to the current Internet infrastructure. Therefore, it is instantly ready for real-world deployment. Using testbed experiments, we evaluate USHA by observing TCP (FTP downloading) behavior in various vertical handoff scenarios. The results shows that USHA can successfully maintain the application connectivity in all cases. Furthermore, the results also shows that when handoff from a low capacity link to a high capacity link, there is no service latency caused by the handoff; whereas when the handoff is from high capacity link to a lower capacity link, the non-negligible latency could not be alleviated unless early handoff notification can be provided.