php从服务器端收到信息，需要判断后回复，如何实现？

收到服务器信息如下
https://www.aaasite.com/TransferTestPage.aspx?SVSTransactionID=1000000000000049209&SVSBatchNumber=625932&Amount=10&Currency=EUR&ProcessingTime=17-08-2006 14:00:49&MerchantFreeText=FreeText&TxID=TransactionID&TxBatchNumber=1234&ClientAccountNumberAtMerchant=AccountNumber&ClientAccountNumber=1000000001&MerchantAccountNumber=100002&EventID=1
需要判断一些条件再以OK 或者 ERROR 来回复给服务器
有一个asp的范例程序 但是我要是用php的，谁能指导一下。
关键是 用什么Php的方法把 OK ERROR 回复给服务器。
ASP范例用的是 Response.Write, 我查了，这个是向浏览器输出啊。不象回复给客户端啊。
请哪个老手帮帮忙吧。

using System;
using System.Data;
using System.Configuration;
using System.Collections;
using System.Web;
using System.Web.Security;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.Web.UI.WebControls.WebParts;
using System.Web.UI.HtmlControls;
public partial class TransferPage : System.Web.UI.Page
{
protected void Page_Load(object sender, EventArgs e)
{
long SvsTransactionID = 0;
int SVSBatchNumber = 0;
string TxID = "";
string ClientAccountNumberAtMerchant = "";
int EventID = 0;
try
{
SvsTransactionID = Convert.ToInt64( Request.Params[ "SvsTransactionID" ] );
SVSBatchNumber = Convert.ToInt32( Request.Params[ "SVSBatchNumber" ] );
TxID = Request.Params[ "TxID" ];
ClientAccountNumberAtMerchant = Request.Params[ "ClientAccountNumberAtMerchant" ];
EventID = Convert.ToInt32( Request.Params[ "EventID" ] );
}
catch
{
Response.Write( "Error" );
return;
}
//Do some actions: save to db, credi user account, etc.;
if ( DoSomeActions() )
Response.Write("OK");
else
Response.Write( "Error" );
}
private bool DoSomeActions()
{
return true;
}
}