Jquery DataTable服务端获取draw,start和length参数的值为null

前端代码:

$(document).ready(function(){
$("#dtable").dataTable({
"serverSide":true,
"ajax":{
"url":"/Approval/GetApprovalFormList",
type":post
},
"columns":[
{"data":"Name"},
{"data":"ID"}
]
})
})

服务端代码:

public JsonResult GetApprovalFormList()
{
string start=this.Request["start"];
string length=this.Request["end"];
}