RTOS:
The manager which manages all the tasks efficiently of the system under consideration. The knowledge of RTOS is of utmost importance considering the kind of complexity which goes into wireless embedded systems. Be it a controlling of whole GSM operations of a city or managing your PDA or Cell phone, RTOS make things happen for you. One should have a better understanding of RTOS to build systems which are reliable. QNX is one of the RTOS which goes into making of successful MSC-BSC operations of a complex GSM networks and Symbian makes your PDAs and cell phones complex features. Implementing optimize protocol stacks in for better performance is only because of more reliable RTOS which is so much demand. RTOS knowledge today is very important while designing complex protocol designing and interfacing system application for wireless embedded systems. Some of the RTOS is as given below.

QNX:
QNX Neutrino is a microkernel operating system that makes fault-resilient, field-upgradeable systems much easier to design and implement. QNX Neutrino also offers unprecedented scalability: Developers can build their applications once, then distribute them on a single processor, across a massive cluster of processors, or on an SMP system - all without special coding. QNX Neutrino represents the latest generation of QNX OS technology, and is the product of more than 20 years' experience in the embedded market.
In QNX Neutrino, the OS kernel delivers only essential services, such as thread scheduling, IPC, and synchronization. All other OS services, drivers, and applications run as separate processes that communicate with the kernel via synchronous message passing. This message passing forms a virtual "software bus" that lets you dynamically plug in or plug out whatever services are required. Consequently, almost any module, even a device driver, can be replaced or restarted on the fly. In most Operating Systems, this would, at the very least, require a system reset.
QNX is used in some MSC as the controlling RTOS. Also some network devices like routers, access points uses QNX as there RTOS.
More details can be found on www.qnx.com.

VxWorks :
WindRiver's VxWorks distributed real-time operating system includes integrated networking facilities and a complete software development environment for Windows® and UNIX® hosts.
Major features of VxWorks include a fast, multitasking kernel with pre-emptive scheduling and fast interrupt response, extensive intertask communications and synchronization facilities, efficient UNIX-compatible memory management, multiprocessor facilities, a shell for user interface, symbolic and source level debugging capabilities, performance monitoring and an I/O file system.
The full range of VxWorks facilities are available to users, with Concurrent Technologies' VxWorks Board Support Packages (BSPs) for a wide range of target Multibus CPU card types. All BSPs have been fully validated by Concurrent Technologies for the greatest confidence and ease of use.
More details can be found on www.windriver.com