$filter with 'and' / 'or' options for select query

Dear Experts,

I have following query to handle filter options in entityset, and in the entityset, filter parameters are filled in the importing parameter - IT_FILTER_SELECT_OPTIONS and I have logic based on this internal table. And it works fine.

/sap/opu/odata/sap/ZBW_CUSTSEL_SRV/CUSTOMERSet?$filter=( Customer eq '32' and Name eq 'AT' )&$orderby=Name&$format=json

But When I use 'OR' instead of 'AND' then the system does not fill the filter parameters in IT_FILTER_SELECT_OPTIONS. What is the reason for this behavior.

I know that in both cases IV_FILTER_STRING filled, but then I have to slit this string and make sure of operators so on.

Thank you,

Murali