def congestionControl(Cause_presence=0):
    """CONGESTION CONTROL Section 9.3.4"""
    a = TpPd(pd=0x3)
    b = MessageType(mesType=0x39)  # 00111001
    c = CongestionLevelAndSpareHalfOctets()
    packet = a / b / c
    if Cause_presence is 1:
        e = CauseHdr(ieiC=0x08, eightBitC=0x0)
        packet = packet / e
    return packet
CONGESTION CONTROL Section 9.3.4