just use only

$response=array();
$response["0"]=array("ip"     => "192.168.0.1",
                     "port"   => "2016");
$json=json_encode($response,JSON_FORCE_OBJECT);

If these classes cannot implement JsonSerializable you may access the protected properties using Reflection.

Example:

class Publisher {
    protected $name;
    protected $id;
    public function __construct($id, $name) {
        $this->id = $id;
        $this->name = $name;
    }
}

function getPublisherExportData($publishers) {
    $out = [];
    foreach($publishers as $publisher) {
        $currentPData = [];
        $refl = new ReflectionClass($publisher);
        $props = $refl->getProperties(ReflectionProperty::IS_PROTECTED);
        foreach($props as $prop) {
            $prop->setAccessible(true);
            $currentPData[$prop->getName()] = $prop->getValue($publisher);
        }
        $out[] = $currentPData;
    }

    return $out;
}

var_dump(json_encode(getPublisherExportData([new Publisher(12, 'My Name'), new Publisher(15, 'NameProperty')]), JSON_PRETTY_PRINT));

Will result in:

string(121) "[ { "name": "My Name", "id": 12 }, { "name": "NameProperty", "id": 15 } ]"

However, you will need to handle object graphs and conditional exports yourself. Depending on the required json output you might think about replacing $out with an instance of stdClass and write using the $out->{$prop->getName()} = $val syntax to it.

If you are able to use your custom implementations you could add a method using get_object_vars($this) to avoid most of the code above, however if you could do that you should consider implementing JsonSerializable which is meant for that task.