构建PHP soap查询

Maybe anybody can help to build PHP soap request. Server is C++ API to accept query. I have request XML code that is correct, but little bit confused on how-to-do-it.

Here it is:

<s:Envelope xmlns:s="http://schemas.xmlsoap.org/soap/envelope/">
  <s:Body>
    <GetSessionKey xmlns="http://tempuri.org/">
      <request xmlns:a="http://schemas.datacontract.org/2004/07/Core.WcfExtenssions" xmlns:i="http://www.w3.org/2001/XMLSchema-instance">
        <a:MethodName i:nil="true"/>
        <a:Password i:nil="true"/>
        <a:RequestData xmlns:b="http://schemas.datacontract.org/2004/07/MotorServices.MotorDataTransferObjects.Args">
          <b:Password>PASSWORD</b:Password>
          <b:UserName>USERNAME</b:UserName>
        </a:RequestData>
        <a:RequestID>eb8b6fe8-2ef3-4b97-bf11-26a733e13158</a:RequestID>
        <a:Timestamp>2013-04-19T12:35:50.395084+02:00</a:Timestamp>
        <a:UserName i:nil="true"/>
      </request>
    </GetSessionKey>
  </s:Body>
</s:Envelope>

This is my example how I did it. Simple code, but server retur fault "Object reference not set to an instance of an object".

try {
            $ServiceClient = new SoapClient(URL,
                    array(
                            'trace' => 1,
                            'connection_timeout' => 20,
                            'timeout' => 20
                    ));
            $arguments = array(
                    'request' => array(
                            'RequestData' => array(
                                    'Password' => PASS,
                                    'UserName' => USER
                            )
                    )
            );
            $session = $ServiceClient->__soapCall("GetSessionKey", $arguments);
        } catch (SoapFault $soapFault) {
             var_dump($soapFault);
        }

In C/C++ Login method look like code below. This method is used to login to service and acquire session key. I expected to create similar method, but I don't understand structure of request in PHP. So my question is.. How looks right request structure in PHP for XML code from above?

public static Guid Login()
{
   Response<GetSessionKeyResult> getSessionKeyResult = FamilyInsuranceServiceProxy.FamilyInsuranceServiceWithoutClose.GetSessionKey(new FamilyRequest<GetSessionKeyArgs>()
       { RequestData = new GetSessionKeyArgs() { AgentId = Username, Password = Password } });
   CurrentSessionKey = getSessionKeyResult.ResponseData.SessionKey;
   return getSessionKeyResult.ResponseData.SessionKey;
}