This routing function distribute the calls to groups based on the served ratio.
If the (call, group) served ratio is greater than the given parameter, then
this call cannot be routed to this group, until the served ratio returns below
the parameter.
There is a ratio parameter for each group that can serve this call type.
This routing policy is designed based on the fluid model.
For each call type, it requires 2 vector parameters.
Property numberList named groupList represents the list of group that can
serve this call type.
Property numberList named maxServeRatio represents the maximum served ratio
this group can have. If the served ratio of this group is higher than this parameter,
then the call cannot be routed to this group. To allow flexibility,
it is not necessary that the sum of the ratio parameters equals to 1.