Robust system call and system return instructions are executed by a processor to transfer control between a requester and an operating system kernel. The capacitor structures include a bottom electrode, a top electrode and a dielectric layer interposed between the bottom electrode and the top electrode. The batting tee forms part of a batter training system which allows multiple batting tees and adapters to be used together to teach proper batting skills to a batter while providing immediate tactile feedback to ensure proper technique. According to the embodiments of the present invention, the PTT service with wide signal coverage and small call delay is implemented. In the case of a remote network device establishing a virtual channel with a local network device, a virtual channel request message is received from a local network device by a remote network device.