Technology2/Resource2...] - Optional extra devices to check
If you need more than one enter them as Technology2/Resource2&Technology3/Resource3&.....
Specification of the device(s) to check. These must be in the format of
Technology/Resource, where Technology represents a particular channel driver, and Resource represents a resource available to that particular channel driver.
a- Check for all available channels, not only the first one
s- Consider the channel unavailable if the channel is in use at all
t- Simply checks if specified channels exist in the channel list
This documentation was imported from Asterisk Version GIT-master14-7d17164ba91710