How to get URL from where the Web method has been called

Hello Every one,
I am workingon a web service where we need to featch the URL of web page from where the web method has been called for the audit propose so can any one tell me how can I do so? Eg. http://mywebservice/service.asmx and the web method is called on the web site http://mywebsite/default.aspx 
Now I would require to get the URL of the website such as in above case it is  http://mywebsite/default.aspx.
Please help me.

 

 

 
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