How to retrieve JSON via ASP.Net context.Request

var OrderInfo = {"ProductID": 
    "ProductIDValue",
    "ProductName": "ProductName",
    "Quantity": 1,
    "Amount": 9999,
    "SLQuantity": 9999,
    "SLDate": "08/03/2010"
};

var DTO = { 'OrderInfo': OrderInfo };
$.ajax({
    type: "POST",
    contentType: "application/json; charset=utf-8",
    url: "JasonHandler.ashx",
    data: JSON.stringify(DTO),
    dataType: "json"
 });

I'm trying to retrieve posted JSON data on server side in an ASHX file via this code:

string strrequest = context.Request["OrderInfo"];

but it always return null. What Am I doing wrong?