1.1.3 Protocol encapsulation

The sat-nms device driver concept encapsulates the protocol frame used for the communication with a device in a separate layer. This protocol layer describes which kind protocol frame has to be wrapped around the commands sent to a device. There are a number of important advantages with this concept:

• The protocol frame is automatically added to each command or request sent to the device. The other way round, the driver automatically strips of this 'envelope' from the data received from the device.
• A certain type of protocol frame needs to be programmed only once and may be used for several device drivers, if for example different devices from the same vendor use one and the same protocol definition.
• Some devices may be operated either by one or the other communication protocol. The protocol encapsulation allows easily to switch between the variants.

With the sat-nms software, new protocol definitions may be added to the software, simply by editing a text file for the new type of protocol frame which is needed.

If you are going to write a new device driver, you first should investigate if there is an existing protocol definition in the sat-nms library which can be used to serve the new device. If no protocol definition matches, the chapter Device communication protocolsdescribes to write a new protocol definition.