Web Services: runBatchJob and global variables with PHP

Dear all,

Here is my problem :

I try to call web method runBatchJob defined by port BatchJobAdmin of the Web Service interface published by DS. from a php script with the SoapClient library.

I want to set a global variable before the execution but the job is executed with the default values.

My code :

try {

    $result = $client->Run_Batch_Job(array("jobName"=>"JOB_TEST","globalVariables"=>array("G_VAR"=>"new value")));

} catch (SoapFault $sFault) {

echo($sFault->__toString());

}

How can i set a value to the global variable ?

Thanks for your help