Hi Thomas,
OData model is a server-side model. In order to sort items on client-side, you have to use JSON Model. Since, it is a client-side model.
And also, is your field1 parameter is of 'integer' type. If so, they you may have to convert from string to integer type.
Will this sample help? Plunker (I have used Northwind OData service)
Regards,
Sai Vellanki.