在swift中接收UDP数据包

我正在尝试从呼叫者id接口接收udp数据包，但无法这样做。我使用下面的代码来监听，但没有得到任何数据

call tester应用程序的链接位于此处

class InSocket: NSObject, GCDAsyncUdpSocketDelegate {
    let IP = "255.255.255.255"
    let PORT:UInt16 = 3520

    var socket:GCDAsyncUdpSocket!

    override init(){
        super.init()
        setupConnection()
    }

    func setupConnection(){
        let error : NSError?
        socket = GCDAsyncUdpSocket(delegate: self, delegateQueue: dispatch_get_main_queue())
        do {
            try socket.connectToHost(IP, onPort: PORT)
            try socket.beginReceiving()
        }catch let cError as NSCocoaError{
            print(cError)
        } catch {
            print(error)
        }
    }

    func udpSocket(sock: GCDAsyncUdpSocket, didReceiveData data: NSData, fromAddress address: NSData, withFilterContext filterContext: AnyObject?) {
        print("incoming message: \(data)");
    }
}