The 'quality of service' is the quality of the current state from a specific object given in percentage (0-100%).
This quality value is used in backup scenario configurations, however if backup is not used, this value is still usefull for information purposes.

In a backup scenario there are two servers (a primary and a secondary) working as partners. Only one from these is running at a given time.
The other one is waiting in the background, ready to take over in cases of problems with its partner.
With a so called heartbeat channel both servers keep checking eachothers quality.
Depending on configuration a partner can take over when:
-Its partner does not give a heartbeat anymore (typically happens when a server crashes, or shuts off).
-The quality from the server falls below a certain value.

The quality from the gateway is defined by the quality of all the objects contained in it.
In the configurator every object has a 'Weight' percentage (0-100%). This value defines for how much percent this object's 'quality of service' value, is calculated in the total gateway quality. Typically only the upline objects are set to a weight of 100%, and the downline objects to 0%.

How the 'quality of service' is calculated for an individual object, is different for each object.
For an USBALC upline object with 4 IA's for instance, each IA on a line counts for 25%.
So if one IA drops out, the 'quality of service' will drop to 75%.