code: def attachRequest(PTmsiSignature_presence=0, GprsTimer_presence=0,
                    TmsiStatus_presence=0):
      
      a = TpPd(pd=0x3)
      b = MessageType(mesType=0x1)  # 0000001
      c = MsNetworkCapability()
      d = AttachTypeAndCiphKeySeqNr()
      f = DrxParameter()
      g = MobileId()
      h = RoutingAreaIdentification()
      i = MsRadioAccessCapability()
      packet = a / b / c / d / f / g / h / i
      if PTmsiSignature_presence is 1:
          j = PTmsiSignature(ieiPTS=0x19)
          packet = packet / j
      if GprsTimer_presence is 1:
          k = GprsTimer(ieiGT=0x17)
          packet = packet / k
      if TmsiStatus_presence is 1:
          l = TmsiStatus(ieiTS=0x9)
          packet = packet / l
      return packet
docs: ATTACH REQUEST Section 9.4.1