Ajax polling Method call in asp.net

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C#

Ajax

Hi Friends,

I want to ajax poll the call to method to get data.
This is the ajax call back, I need to auto poll the call for every 3 secs

$.ajax({
    type: "POST",
    url: "Default.aspx/getPak",
    data: "{}",
    contentType: "application/json; charset=utf-8",
    dataType: "json",
    success: function (msg) {
        strPak = msg.d;
    }
                });

Code works fine for first time. But I want to call at certain intervals like 3 secs or something.
Your help will be appreciated.
Thanks in advance.

Note: I tried

setInterval("location.reload();", 3000);

But I want optimized ajax call ;-)