TO build Soap Header for WSSOAP=1 to use siebel inbound webservice in .net

Hi Team

I have 2 question

First is: WHenever i try to hit the endpoint of siebel service locally i.e with port 2330 i just need to provide the Username and Password in Url and no need for WSSOAP=1

But when i try to use it from external system using ip addres of machine http://10.10.0.x/eai_enu/start.swe?SWEExtSource=WebService&SWEExtCmd=Execute&UserName=SADMIN&Passwo…

I have to provide Soap headers with Username and password and have to mention WSSOAP=1.

Why is this happening? WHY cant i use it without WSSOAP=1 . if i use i am getting error "Error in authenticating the user". or Session Token is missing or invalid or has expired