packet lib: add Stream Control Transmission Protocol

Signed-off-by: Yuichi Ito <ito.yuichi0@gmail.com>
Signed-off-by: FUJITA Tomonori <fujita.tomonori@lab.ntt.co.jp>

3 files changed, 2056 insertions, 0 deletions

diff --git a/ryu/lib/packet/ipv4.py b/ryu/lib/packet/ipv4.py
index 032e4254..73ad4f3b 100644
--- a/ryu/lib/packet/ipv4.py
+++ b/ryu/lib/packet/ipv4.py
@@ -21,6 +21,7 @@ from . import icmp
 from . import igmp
 from . import udp
 from . import tcp
+from . import sctp
 from ryu.ofproto import inet
 from ryu.lib import addrconv
 
@@ -138,3 +139,4 @@ ipv4.register_packet_type(icmp.icmp, inet.IPPROTO_ICMP)
 ipv4.register_packet_type(igmp.igmp, inet.IPPROTO_IGMP)
 ipv4.register_packet_type(tcp.tcp, inet.IPPROTO_TCP)
 ipv4.register_packet_type(udp.udp, inet.IPPROTO_UDP)
+ipv4.register_packet_type(sctp.sctp, inet.IPPROTO_SCTP)
diff --git a/ryu/lib/packet/ipv6.py b/ryu/lib/packet/ipv6.py
index 6a62abaf..e798f5e0 100644
--- a/ryu/lib/packet/ipv6.py
+++ b/ryu/lib/packet/ipv6.py
@@ -19,6 +19,7 @@ from . import packet_base
 from . import icmpv6
 from . import tcp
 from . import udp
+from . import sctp
 from ryu.ofproto import inet
 from ryu.lib import addrconv
 from ryu.lib import stringify
@@ -131,6 +132,7 @@ class ipv6(packet_base.PacketBase):
 ipv6.register_packet_type(icmpv6.icmpv6, inet.IPPROTO_ICMPV6)
 ipv6.register_packet_type(tcp.tcp, inet.IPPROTO_TCP)
 ipv6.register_packet_type(udp.udp, inet.IPPROTO_UDP)
+ipv6.register_packet_type(sctp.sctp, inet.IPPROTO_SCTP)
 
 
 class header(stringify.StringifyMixin):
diff --git a/ryu/lib/packet/sctp.py b/ryu/lib/packet/sctp.py
new file mode 100644
index 00000000..243c0c65
--- /dev/null
+++ b/ryu/lib/packet/sctp.py
@@ -0,0 +1,2052 @@
+# Copyright (C) 2013 Nippon Telegraph and Telephone Corporation.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#    http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or
+# implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+import abc
+import struct
+
+from ryu.lib import addrconv
+from ryu.lib import stringify
+from ryu.lib.packet import packet_base
+
+# Chunk Types
+TYPE_DATA = 0
+TYPE_INIT = 1
+TYPE_INIT_ACK = 2
+TYPE_SACK = 3
+TYPE_HEARTBEAT = 4
+TYPE_HEARTBEAT_ACK = 5
+TYPE_ABORT = 6
+TYPE_SHUTDOWN = 7
+TYPE_SHUTDOWN_ACK = 8
+TYPE_ERROR = 9
+TYPE_COOKIE_ECHO = 10
+TYPE_COOKIE_ACK = 11
+TYPE_ECN_ECHO = 12
+TYPE_CWR = 13
+TYPE_SHUTDOWN_COMPLETE = 14
+
+# Cause Code
+CCODE_INVALID_STREAM_ID = 1
+CCODE_MISSING_PARAM = 2
+CCODE_STALE_COOKIE = 3
+CCODE_OUT_OF_RESOURCE = 4
+CCODE_UNRESOLVABLE_ADDR = 5
+CCODE_UNRECOGNIZED_CHUNK = 6
+CCODE_INVALID_PARAM = 7
+CCODE_UNRECOGNIZED_PARAM = 8
+CCODE_NO_USERDATA = 9
+CCODE_COOKIE_WHILE_SHUTDOWN = 10
+CCODE_RESTART_WITH_NEW_ADDR = 11
+CCODE_USER_INITIATED_ABORT = 12
+CCODE_PROTOCOL_VIOLATION = 13
+
+# Chunk Parameter Types
+PTYPE_HEARTBEAT = 1
+PTYPE_IPV4 = 5
+PTYPE_IPV6 = 6
+PTYPE_STATE_COOKIE = 7
+PTYPE_UNRECOGNIZED_PARAM = 8
+PTYPE_COOKIE_PRESERVE = 9
+PTYPE_HOST_ADDR = 11
+PTYPE_SUPPORTED_ADDR = 12
+PTYPE_ECN = 32768
+
+
+class sctp(packet_base.PacketBase):
+    """Stream Control Transmission Protocol (SCTP)
+    header encoder/decoder class (RFC 4960).
+
+    An instance has the following attributes at least.
+    Most of them are same to the on-wire counterparts but in host byte order.
+    __init__ takes the correspondig args in this order.
+
+    .. tabularcolumns:: |l|p{30em}|l|
+
+    ============== =====================================================
+    Attribute      Description
+    ============== =====================================================
+    src_port       Source Port
+    dst_port       Destination Port
+    vtag           Verification Tag
+    csum           Checksum
+    chunks         a list of derived classes of ryu.lib.packet.sctp.chunk.
+    ============== =====================================================
+    """
+
+    _PACK_STR = '!HHII'
+    _MIN_LEN = struct.calcsize(_PACK_STR)
+    _SCTP_CHUNK_TYPE = {}
+    _class_prefixes = ['chunk_']
+
+    @staticmethod
+    def register_chunk_type(*args):
+        def _register_chunk_type(cls):
+            sctp._SCTP_CHUNK_TYPE[cls.chunk_type()] = cls
+            return cls
+        return _register_chunk_type(args[0])
+
+    def __init__(self, src_port, dst_port, vtag, csum, chunks=None):
+        super(sctp, self).__init__()
+        self.src_port = src_port
+        self.dst_port = dst_port
+        self.vtag = vtag
+        self.csum = csum
+        chunks = chunks or []
+        assert isinstance(chunks, list)
+        for one in chunks:
+            assert isinstance(one, chunk)
+        self.chunks = chunks
+
+    @classmethod
+    def parser(cls, buf):
+        (src_port, dst_port, vtag, csum) = struct.unpack_from(
+            cls._PACK_STR, buf)
+        chunks = []
+        offset = cls._MIN_LEN
+        while offset < len(buf):
+            (type_, ) = struct.unpack_from('!B', buf, offset)
+            cls_ = cls._SCTP_CHUNK_TYPE.get(type_)
+            if not cls_:
+                break
+            ins = cls_.parser(buf[offset:])
+            chunks.append(ins)
+            offset += len(ins)
+        msg = cls(src_port, dst_port, vtag, csum, chunks)
+        return msg, None, buf[offset:]
+
+    def serialize(self, payload, prev):
+        buf = bytearray(struct.pack(
+            self._PACK_STR, self.src_port, self.dst_port, self.vtag,
+            self.csum))
+        if self.chunks:
+            for one in self.chunks:
+                buf.extend(one.serialize())
+        if self.csum == 0:
+            self.csum = self._checksum(buf)
+            struct.pack_into('!I', buf, 8, self.csum)
+        return str(buf)
+
+    def _checksum(self, data):
+        # from RFC 3309
+        crc_c = [
+            0x00000000, 0xF26B8303, 0xE13B70F7, 0x1350F3F4,
+            0xC79A971F, 0x35F1141C, 0x26A1E7E8, 0xD4CA64EB,
+            0x8AD958CF, 0x78B2DBCC, 0x6BE22838, 0x9989AB3B,
+            0x4D43CFD0, 0xBF284CD3, 0xAC78BF27, 0x5E133C24,
+            0x105EC76F, 0xE235446C, 0xF165B798, 0x030E349B,
+            0xD7C45070, 0x25AFD373, 0x36FF2087, 0xC494A384,
+            0x9A879FA0, 0x68EC1CA3, 0x7BBCEF57, 0x89D76C54,
+            0x5D1D08BF, 0xAF768BBC, 0xBC267848, 0x4E4DFB4B,
+            0x20BD8EDE, 0xD2D60DDD, 0xC186FE29, 0x33ED7D2A,
+            0xE72719C1, 0x154C9AC2, 0x061C6936, 0xF477EA35,
+            0xAA64D611, 0x580F5512, 0x4B5FA6E6, 0xB93425E5,
+            0x6DFE410E, 0x9F95C20D, 0x8CC531F9, 0x7EAEB2FA,
+            0x30E349B1, 0xC288CAB2, 0xD1D83946, 0x23B3BA45,
+            0xF779DEAE, 0x05125DAD, 0x1642AE59, 0xE4292D5A,
+            0xBA3A117E, 0x4851927D, 0x5B016189, 0xA96AE28A,
+            0x7DA08661, 0x8FCB0562, 0x9C9BF696, 0x6EF07595,
+            0x417B1DBC, 0xB3109EBF, 0xA0406D4B, 0x522BEE48,
+            0x86E18AA3, 0x748A09A0, 0x67DAFA54, 0x95B17957,
+            0xCBA24573, 0x39C9C670, 0x2A993584, 0xD8F2B687,
+            0x0C38D26C, 0xFE53516F, 0xED03A29B, 0x1F682198,
+            0x5125DAD3, 0xA34E59D0, 0xB01EAA24, 0x42752927,
+            0x96BF4DCC, 0x64D4CECF, 0x77843D3B, 0x85EFBE38,
+            0xDBFC821C, 0x2997011F, 0x3AC7F2EB, 0xC8AC71E8,
+            0x1C661503, 0xEE0D9600, 0xFD5D65F4, 0x0F36E6F7,
+            0x61C69362, 0x93AD1061, 0x80FDE395, 0x72966096,
+            0xA65C047D, 0x5437877E, 0x4767748A, 0xB50CF789,
+            0xEB1FCBAD, 0x197448AE, 0x0A24BB5A, 0xF84F3859,
+            0x2C855CB2, 0xDEEEDFB1, 0xCDBE2C45, 0x3FD5AF46,
+            0x7198540D, 0x83F3D70E, 0x90A324FA, 0x62C8A7F9,
+            0xB602C312, 0x44694011, 0x5739B3E5, 0xA55230E6,
+            0xFB410CC2, 0x092A8FC1, 0x1A7A7C35, 0xE811FF36,
+            0x3CDB9BDD, 0xCEB018DE, 0xDDE0EB2A, 0x2F8B6829,
+            0x82F63B78, 0x709DB87B, 0x63CD4B8F, 0x91A6C88C,
+            0x456CAC67, 0xB7072F64, 0xA457DC90, 0x563C5F93,
+            0x082F63B7, 0xFA44E0B4, 0xE9141340, 0x1B7F9043,
+            0xCFB5F4A8, 0x3DDE77AB, 0x2E8E845F, 0xDCE5075C,
+            0x92A8FC17, 0x60C37F14, 0x73938CE0, 0x81F80FE3,
+            0x55326B08, 0xA759E80B, 0xB4091BFF, 0x466298FC,
+            0x1871A4D8, 0xEA1A27DB, 0xF94AD42F, 0x0B21572C,
+            0xDFEB33C7, 0x2D80B0C4, 0x3ED04330, 0xCCBBC033,
+            0xA24BB5A6, 0x502036A5, 0x4370C551, 0xB11B4652,
+            0x65D122B9, 0x97BAA1BA, 0x84EA524E, 0x7681D14D,
+            0x2892ED69, 0xDAF96E6A, 0xC9A99D9E, 0x3BC21E9D,
+            0xEF087A76, 0x1D63F975, 0x0E330A81, 0xFC588982,
+            0xB21572C9, 0x407EF1CA, 0x532E023E, 0xA145813D,
+            0x758FE5D6, 0x87E466D5, 0x94B49521, 0x66DF1622,
+            0x38CC2A06, 0xCAA7A905, 0xD9F75AF1, 0x2B9CD9F2,
+            0xFF56BD19, 0x0D3D3E1A, 0x1E6DCDEE, 0xEC064EED,
+            0xC38D26C4, 0x31E6A5C7, 0x22B65633, 0xD0DDD530,
+            0x0417B1DB, 0xF67C32D8, 0xE52CC12C, 0x1747422F,
+            0x49547E0B, 0xBB3FFD08, 0xA86F0EFC, 0x5A048DFF,
+            0x8ECEE914, 0x7CA56A17, 0x6FF599E3, 0x9D9E1AE0,
+            0xD3D3E1AB, 0x21B862A8, 0x32E8915C, 0xC083125F,
+            0x144976B4, 0xE622F5B7, 0xF5720643, 0x07198540,
+            0x590AB964, 0xAB613A67, 0xB831C993, 0x4A5A4A90,
+            0x9E902E7B, 0x6CFBAD78, 0x7FAB5E8C, 0x8DC0DD8F,
+            0xE330A81A, 0x115B2B19, 0x020BD8ED, 0xF0605BEE,
+            0x24AA3F05, 0xD6C1BC06, 0xC5914FF2, 0x37FACCF1,
+            0x69E9F0D5, 0x9B8273D6, 0x88D28022, 0x7AB90321,
+            0xAE7367CA, 0x5C18E4C9, 0x4F48173D, 0xBD23943E,
+            0xF36E6F75, 0x0105EC76, 0x12551F82, 0xE03E9C81,
+            0x34F4F86A, 0xC69F7B69, 0xD5CF889D, 0x27A40B9E,
+            0x79B737BA, 0x8BDCB4B9, 0x988C474D, 0x6AE7C44E,
+            0xBE2DA0A5, 0x4C4623A6, 0x5F16D052, 0xAD7D5351,
+        ]
+
+        crc32 = 0xffffffff
+        for c in str(data):
+            crc32 = (crc32 >> 8) ^ crc_c[(crc32 ^ (ord(c))) & 0xFF]
+        crc32 = (~crc32) & 0xffffffff
+        return struct.unpack(">I", struct.pack("<I", crc32))[0]
+
+
+#=======================================================================
+#
+# Chunk Types
+#
+#=======================================================================
+class chunk(stringify.StringifyMixin):
+
+    __metaclass__ = abc.ABCMeta
+    _PACK_STR = '!BBH'
+    _MIN_LEN = struct.calcsize(_PACK_STR)
+
+    @classmethod
+    @abc.abstractproperty
+    def chunk_type(cls):
+        pass
+
+    @abc.abstractmethod
+    def __init__(self, type_, length):
+        self._type = type_
+        self.length = length
+
+    @classmethod
+    @abc.abstractmethod
+    def parser(cls, buf):
+        pass
+
+    def __len__(self):
+        return self.length
+
+
+class chunk_init_base(chunk):
+
+    __metaclass__ = abc.ABCMeta
+    _PACK_STR = '!BBHIIHHI'
+    _MIN_LEN = struct.calcsize(_PACK_STR)
+
+    def __init__(self, flags, length, init_tag, a_rwnd, os, mis, i_tsn,
+                 params=None):
+        super(chunk_init_base, self).__init__(self.chunk_type(), length)
+        self.flags = flags
+        self.init_tag = init_tag
+        self.a_rwnd = a_rwnd
+        self.os = os
+        self.mis = mis
+        self.i_tsn = i_tsn
+        params = params or []
+        assert isinstance(params, list)
+        for one in params:
+            assert isinstance(one, param)
+        self.params = params
+
+    @classmethod
+    def parser_base(cls, buf, recog):
+        (_, flags, length, init_tag, a_rwnd, os, mis, i_tsn
+         ) = struct.unpack_from(cls._PACK_STR, buf)
+        params = []
+        offset = cls._MIN_LEN
+        while offset < length:
+            (ptype, ) = struct.unpack_from('!H', buf, offset)
+            cls_ = recog.get(ptype)
+            if not cls_:
+                break
+            ins = cls_.parser(buf[offset:])
+            params.append(ins)
+            offset += len(ins)
+        msg = cls(flags, length, init_tag, a_rwnd, os, mis, i_tsn, params)
+        return msg
+
+    def serialize(self):
+        buf = bytearray(struct.pack(
+            self._PACK_STR, self.chunk_type(), self.flags,
+            self.length, self.init_tag, self.a_rwnd, self.os, self.mis,
+            self.i_tsn))
+        for one in self.params:
+            buf.extend(one.serialize())
+        return str(buf)
+
+
+class chunk_heartbeat_base(chunk):
+
+    __metaclass__ = abc.ABCMeta
+
+    def __init__(self, flags, length, info):
+        super(chunk_heartbeat_base, self).__init__(
+            self.chunk_type(), length)
+        self.flags = flags
+        assert isinstance(info, param)
+        self.info = info
+
+    @classmethod
+    def parser_base(cls, buf, recog):
+        (_, flags, length) = struct.unpack_from(cls._PACK_STR, buf)
+        (ptype, ) = struct.unpack_from('!H', buf, cls._MIN_LEN)
+        cls_ = recog.get(ptype)
+        info = cls_.parser(buf[cls._MIN_LEN:])
+        msg = cls(flags, length, info)
+        return msg
+
+    def serialize(self):
+        buf = bytearray(struct.pack(
+            self._PACK_STR, self.chunk_type(), self.flags,
+            self.length))
+        buf.extend(self.info.serialize())
+        return str(buf)
+
+
+class chunk_ack_base(chunk):
+
+    __metaclass__ = abc.ABCMeta
+
+    def __init__(self, flags, length):
+        super(chunk_ack_base, self).__init__(self.chunk_type(), length)
+        self.flags = flags
+
+    @classmethod
+    def parser(cls, buf):
+        (_, flags, length) = struct.unpack_from(cls._PACK_STR, buf)
+        return cls(flags, length)
+
+    def serialize(self):
+        buf = struct.pack(
+            self._PACK_STR, self.chunk_type(), self.flags,
+            self.length)
+        return buf
+
+
+class chunk_ecn_base(chunk):
+
+    __metaclass__ = abc.ABCMeta
+    _PACK_STR = '!BBHI'
+    _MIN_LEN = struct.calcsize(_PACK_STR)
+
+    def __init__(self, flags, length, low_tsn):
+        super(chunk_ecn_base, self).__init__(self.chunk_type(), length)
+        self.flags = flags
+        self.low_tsn = low_tsn
+
+    @classmethod
+    def parser(cls, buf):
+        (_, flags, length, low_tsn) = struct.unpack_from(cls._PACK_STR, buf)
+        return cls(flags, length, low_tsn)
+
+    def serialize(self):
+        buf = struct.pack(
+            self._PACK_STR, self.chunk_type(), self.flags, self.length,
+            self.low_tsn)
+        return buf
+
+
+@sctp.register_chunk_type
+class chunk_data(chunk):
+    """Stream Control Transmission Protocol (SCTP)
+    sub encoder/decoder class for Payload Data (DATA) chunk (RFC 4960).
+
+    This is used with ryu.lib.packet.sctp.sctp.
+
+    An instance has the following attributes at least.
+    Most of them are same to the on-wire counterparts but in host byte order.
+    __init__ takes the correspondig args in this order.
+
+    .. tabularcolumns:: |l|p{30em}|l|
+
+    ============== =====================================================
+    Attribute      Description
+    ============== =====================================================
+    unordered      if set to '1', the receiver ignores the sequence number.
+    begin          if set to '1', this chunk is the first fragment.
+    end            if set to '1', this chunk is the last fragment.
+    length         length of this chunk containing this header.
+    tsn            Transmission Sequence Number.
+    sid            stream id.
+    seq            the sequence number.
+    payload_id     application specified protocol id. '0' means that
+                   no application id is identified.
+    payload_data   user data.
+    ============== =====================================================
+    """
+
+    _PACK_STR = '!BBHIHHI'
+    _MIN_LEN = struct.calcsize(_PACK_STR)
+
+    @classmethod
+    def chunk_type(cls):
+        return TYPE_DATA
+
+    def __init__(self, unordered, begin, end, length, tsn, sid, seq,
+                 payload_id, payload_data):
+        assert (1 == unordered | 1)
+        assert (1 == begin | 1)
+        assert (1 == end | 1)
+        super(chunk_data, self).__init__(self.chunk_type(), length)
+        self.unordered = unordered
+        self.begin = begin
+        self.end = end
+        self.tsn = tsn
+        self.sid = sid
+        self.seq = seq
+        self.payload_id = payload_id
+        self.payload_data = payload_data
+
+    @classmethod
+    def parser(cls, buf):
+        (_, flags, length, tsn, sid, seq, payload_id
+         ) = struct.unpack_from(cls._PACK_STR, buf)
+        unordered = (flags >> 2) & 1
+        begin = (flags >> 1) & 1
+        end = (flags >> 0) & 1
+        fmt = '!%ds' % (length - cls._MIN_LEN)
+        (payload_data, ) = struct.unpack_from(fmt, buf, cls._MIN_LEN)
+        return cls(unordered, begin, end, length, tsn, sid, seq,
+                   payload_id, payload_data)
+
+    def serialize(self):
+        flags = (
+            (self.unordered << 2) |
+            (self.begin << 1) |
+            (self.end << 0))
+        buf = bytearray(struct.pack(
+            self._PACK_STR, self.chunk_type(), flags, self.length,
+            self.tsn, self.sid, self.seq, self.payload_id))
+        buf.extend(self.payload_data)
+        return str(buf)
+
+
+@sctp.register_chunk_type
+class chunk_init(chunk_init_base):
+    """Stream Control Transmission Protocol (SCTP)
+    sub encoder/decoder class for Initiation (INIT) chunk (RFC 4960).
+
+    This is used with ryu.lib.packet.sctp.sctp.
+
+    An instance has the following attributes at least.
+    Most of them are same to the on-wire counterparts but in host byte order.
+    __init__ takes the correspondig args in this order.
+
+    .. tabularcolumns:: |l|p{30em}|l|
+
+    ============== =====================================================
+    Attribute      Description
+    ============== =====================================================
+    flags          set to '0'. this field will be ignored.
+    length         length of this chunk containing this header.
+    init_tag       the tag that be used as Verification Tag.
+    a_rwnd         Advertised Receiver Window Credit.
+    os             number of outbound streams.
+    mis            number of inbound streams.
+    i_tsn          Transmission Sequence Number that the sender will use.
+    params         Optional/Variable-Length Parameters.
+
+                   a list of derived classes of ryu.lib.packet.sctp.param.
+    ============== =====================================================
+    """
+
+    _RECOGNIZED_PARAMS = {}
+
+    @staticmethod
+    def register_param_type(*args):
+        def _register_param_type(cls):
+            chunk_init._RECOGNIZED_PARAMS[cls.param_type()] = cls
+            return cls
+        return _register_param_type(args[0])
+
+    @classmethod
+    def chunk_type(cls):
+        return TYPE_INIT
+
+    @classmethod
+    def parser(cls, buf):
+        return super(chunk_init, cls).parser_base(
+            buf, cls._RECOGNIZED_PARAMS)
+
+
+@sctp.register_chunk_type
+class chunk_init_ack(chunk_init_base):
+    """Stream Control Transmission Protocol (SCTP)
+    sub encoder/decoder class for Initiation Acknowledgement (INIT ACK)
+    chunk (RFC 4960).
+
+    This is used with ryu.lib.packet.sctp.sctp.
+
+    An instance has the following attributes at least.
+    Most of them are same to the on-wire counterparts but in host byte order.
+    __init__ takes the correspondig args in this order.
+
+    .. tabularcolumns:: |l|p{30em}|l|
+
+    ============== =====================================================
+    Attribute      Description
+    ============== =====================================================
+    flags          set to '0'. this field will be ignored.
+    length         length of this chunk containing this header.
+    init_tag       the tag that be used as Verification Tag.
+    a_rwnd         Advertised Receiver Window Credit.
+    os             number of outbound streams.
+    mis            number of inbound streams.
+    i_tsn          Transmission Sequence Number that the sender will use.
+    params         Optional/Variable-Length Parameters.
+
+                   a list of derived classes of ryu.lib.packet.sctp.param.
+    ============== =====================================================
+    """
+
+    _RECOGNIZED_PARAMS = {}
+
+    @staticmethod
+    def register_param_type(*args):
+        def _register_param_type(cls):
+            chunk_init_ack._RECOGNIZED_PARAMS[cls.param_type()] = cls
+            return cls
+        return _register_param_type(args[0])
+
+    @classmethod
+    def chunk_type(cls):
+        return TYPE_INIT_ACK
+
+    @classmethod
+    def parser(cls, buf):
+        return super(chunk_init_ack, cls).parser_base(
+            buf, cls._RECOGNIZED_PARAMS)
+
+
+@sctp.register_chunk_type
+class chunk_sack(chunk):
+    """Stream Control Transmission Protocol (SCTP)
+    sub encoder/decoder class for Selective Acknowledgement (SACK) chunk
+    (RFC 4960).
+
+    This is used with ryu.lib.packet.sctp.sctp.
+
+    An instance has the following attributes at least.
+    Most of them are same to the on-wire counterparts but in host byte order.
+    __init__ takes the correspondig args in this order.
+
+    .. tabularcolumns:: |l|p{30em}|l|
+
+    ============== =====================================================
+    Attribute      Description
+    ============== =====================================================
+    flags          set to '0'. this field will be ignored.
+    length         length of this chunk containing this header.
+    tsn_ack        TSN of the last DATA chunk received in sequence
+                   before a gap.
+    a_rwnd         Advertised Receiver Window Credit.
+    gapack_num     number of Gap Ack blocks.
+    duptsn_num     number of duplicate TSNs.
+    gapacks        a list of Gap Ack blocks. one block is made of a list
+                   with the start offset and the end offset from tsn_ack.
+                   e.g.) gapacks = [[2, 3], [10, 12], [19, 21]]
+    duptsns        a list of duplicate TSN.
+    ============== =====================================================
+    """
+
+    _PACK_STR = '!BBHIIHH'
+    _MIN_LEN = struct.calcsize(_PACK_STR)
+    _GAPACK_STR = '!HH'
+    _GAPACK_LEN = struct.calcsize(_GAPACK_STR)
+    _DUPTSN_STR = '!I'
+    _DUPTSN_LEN = struct.calcsize(_DUPTSN_STR)
+
+    @classmethod
+    def chunk_type(cls):
+        return TYPE_SACK
+
+    def __init__(self, flags, length, tsn_ack, a_rwnd, gapack_num,
+                 duptsn_num, gapacks=None, duptsns=None):
+        super(chunk_sack, self).__init__(self.chunk_type(), length)
+        self.flags = flags
+        self.tsn_ack = tsn_ack
+        self.a_rwnd = a_rwnd
+        self.gapack_num = gapack_num
+        self.duptsn_num = duptsn_num
+        gapacks = gapacks or []
+        assert isinstance(gapacks, list)
+        for one in gapacks:
+            assert isinstance(one, list)
+            assert 2 == len(one)
+        self.gapacks = gapacks
+        duptsns = duptsns or []
+        assert isinstance(duptsns, list)
+        self.duptsns = duptsns
+
+    @classmethod
+    def parser(cls, buf):
+        (_, flags, length, tsn_ack, a_rwnd, gapack_num, duptsn_num
+         ) = struct.unpack_from(cls._PACK_STR, buf)
+        gapacks = []
+        offset = cls._MIN_LEN
+        for _ in range(gapack_num):
+            (gapack_start, gapack_end) = struct.unpack_from(
+                cls._GAPACK_STR, buf, offset)
+            gapacks.append([gapack_start, gapack_end])
+            offset += cls._GAPACK_LEN
+        duptsns = []
+        for _ in range(duptsn_num):
+            (duptsn, ) = struct.unpack_from(cls._DUPTSN_STR, buf, offset)
+            duptsns.append(duptsn)
+            offset += cls._DUPTSN_LEN
+        return cls(flags, length, tsn_ack, a_rwnd, gapack_num, duptsn_num,
+                   gapacks, duptsns)
+
+    def serialize(self):
+        buf = bytearray(struct.pack(
+            self._PACK_STR, self.chunk_type(), self.flags,
+            self.length, self.tsn_ack, self.a_rwnd, self.gapack_num,
+            self.duptsn_num))
+        for one in self.gapacks:
+            buf.extend(struct.pack(chunk_sack._GAPACK_STR, one[0], one[1]))
+        for one in self.duptsns:
+            buf.extend(struct.pack(chunk_sack._DUPTSN_STR, one))
+        return str(buf)
+
+
+@sctp.register_chunk_type
+class chunk_heartbeat(chunk_heartbeat_base):
+    """Stream Control Transmission Protocol (SCTP)
+    sub encoder/decoder class for Heartbeat Request (HEARTBEAT) chunk
+    (RFC 4960).
+
+    This is used with ryu.lib.packet.sctp.sctp.
+
+    An instance has the following attributes at least.
+    Most of them are same to the on-wire counterparts but in host byte order.
+    __init__ takes the correspondig args in this order.
+
+    .. tabularcolumns:: |l|p{30em}|l|
+
+    ============== =====================================================
+    Attribute      Description
+    ============== =====================================================
+    flags          set to '0'. this field will be ignored.
+    length         length of this chunk containing this header.
+    info           ryu.lib.packet.sctp.param_heartbeat.
+    ============== =====================================================
+    """
+
+    _RECOGNIZED_PARAMS = {}
+
+    @staticmethod
+    def register_param_type(*args):
+        def _register_param_type(cls):
+            chunk_heartbeat._RECOGNIZED_PARAMS[cls.param_type()] = cls
+            return cls
+        return _register_param_type(args[0])
+
+    @classmethod
+    def chunk_type(cls):
+        return TYPE_HEARTBEAT
+
+    @classmethod
+    def parser(cls, buf):
+        return super(chunk_heartbeat, cls).parser_base(
+            buf, cls._RECOGNIZED_PARAMS)
+
+
+@sctp.register_chunk_type
+class chunk_heartbeat_ack(chunk_heartbeat_base):
+    """Stream Control Transmission Protocol (SCTP)
+    sub encoder/decoder class for Heartbeat Acknowledgement
+    (HEARTBEAT ACK) chunk (RFC 4960).
+
+    This is used with ryu.lib.packet.sctp.sctp.
+
+    An instance has the following attributes at least.
+    Most of them are same to the on-wire counterparts but in host byte order.
+    __init__ takes the correspondig args in this order.
+
+    .. tabularcolumns:: |l|p{30em}|l|
+
+    ============== =====================================================
+    Attribute      Description
+    ============== =====================================================
+    flags          set to '0'. this field will be ignored.
+    length         length of this chunk containing this header.
+    info           ryu.lib.packet.sctp.param_heartbeat.
+    ============== =====================================================
+    """
+
+    _RECOGNIZED_PARAMS = {}
+
+    @staticmethod
+    def register_param_type(*args):
+        def _register_param_type(cls):
+            chunk_heartbeat_ack._RECOGNIZED_PARAMS[cls.param_type()] = cls
+            return cls
+        return _register_param_type(args[0])
+
+    @classmethod
+    def chunk_type(cls):
+        return TYPE_HEARTBEAT_ACK
+
+    @classmethod
+    def parser(cls, buf):
+        return super(chunk_heartbeat_ack, cls).parser_base(
+            buf, cls._RECOGNIZED_PARAMS)
+
+
+@sctp.register_chunk_type
+class chunk_abort(chunk):
+    """Stream Control Transmission Protocol (SCTP)
+    sub encoder/decoder class for Abort Association (ABORT) chunk (RFC 4960).
+
+    This is used with ryu.lib.packet.sctp.sctp.
+
+    An instance has the following attributes at least.
+    Most of them are same to the on-wire counterparts but in host byte order.
+    __init__ takes the correspondig args in this order.
+
+    .. tabularcolumns:: |l|p{30em}|l|
+
+    ============== =====================================================
+    Attribute      Description
+    ============== =====================================================
+    tflag          '0' means the Verification tag is normal. '1' means
+                   the Verification tag is copy of the sender.
+    length         length of this chunk containing this header.
+    causes         a list of derived classes of ryu.lib.packet.sctp.causes.
+    ============== =====================================================
+    """
+
+    # TODO: coding and testing
+    _class_prefixes = ['cause_']
+    _RECOGNIZED_CAUSES = {}
+
+    @staticmethod
+    def register_cause_code(*args):
+        def _register_cause_code(cls):
+            chunk_abort._RECOGNIZED_CAUSES[cls.cause_code()] = cls
+            return cls
+        return _register_cause_code(args[0])
+
+    @classmethod
+    def chunk_type(cls):
+        return TYPE_ABORT
+
+    def __init__(self, tflag, length, causes=None):
+        super(chunk_abort, self).__init__(self.chunk_type(), length)
+        assert (1 == tflag | 1)
+        self.tflag = tflag
+        causes = causes or []
+        assert isinstance(causes, list)
+        for one in causes:
+            assert isinstance(one, cause)
+        self.causes = causes
+
+    @classmethod
+    def parser(cls, buf):
+        (_, flags, length) = struct.unpack_from(cls._PACK_STR, buf)
+        tflag = (flags >> 0) & 1
+        causes = []
+        offset = cls._MIN_LEN
+        while offset < length:
+            (ccode, ) = struct.unpack_from('!H', buf, offset)
+            cls_ = cls._RECOGNIZED_CAUSES.get(ccode)
+            if not cls_:
+                break
+            ins = cls_.parser(buf[offset:])
+            causes.append(ins)
+            offset += len(ins)
+        return cls(tflag, length, causes)
+
+    def serialize(self):
+        flags = (self.tflag << 0)
+        buf = bytearray(struct.pack(
+            self._PACK_STR, self.chunk_type(), flags, self.length))
+        for one in self.causes:
+            buf.extend(one.serialize())
+        return str(buf)
+
+
+@sctp.register_chunk_type
+class chunk_shutdown(chunk):
+    """Stream Control Transmission Protocol (SCTP)
+    sub encoder/decoder class for Shutdown Association (SHUTDOWN) chunk
+    (RFC 4960).
+
+    This is used with ryu.lib.packet.sctp.sctp.
+
+    An instance has the following attributes at least.
+    Most of them are same to the on-wire counterparts but in host byte order.
+    __init__ takes the correspondig args in this order.
+
+    .. tabularcolumns:: |l|p{30em}|l|
+
+    ============== =====================================================
+    Attribute      Description
+    ============== =====================================================
+    flags          set to '0'. this field will be ignored.
+    length         length of this chunk containing this header.
+    tsn_ack        TSN of the last DATA chunk received in sequence
+                   before a gap.
+    ============== =====================================================
+    """
+
+    _PACK_STR = '!BBHI'
+    _MIN_LEN = struct.calcsize(_PACK_STR)
+
+    @classmethod
+    def chunk_type(cls):
+        return TYPE_SHUTDOWN
+
+    def __init__(self, flags, length, tsn_ack):
+        super(chunk_shutdown, self).__init__(self.chunk_type(), length)
+        self.flags = flags
+        self.tsn_ack = tsn_ack
+
+    @classmethod
+    def parser(cls, buf):
+        (_, flags, length, tsn_ack
+         ) = struct.unpack_from(cls._PACK_STR, buf)
+        msg = cls(flags, length, tsn_ack)
+        return msg
+
+    def serialize(self):
+        buf = struct.pack(
+            self._PACK_STR, self.chunk_type(), self.flags,
+            self.length, self.tsn_ack)
+        return buf
+
+
+@sctp.register_chunk_type
+class chunk_shutdown_ack(chunk_ack_base):
+    """Stream Control Transmission Protocol (SCTP)
+    sub encoder/decoder class for Shutdown Acknowledgement (SHUTDOWN ACK)
+    chunk (RFC 4960).
+
+    This is used with ryu.lib.packet.sctp.sctp.
+
+    An instance has the following attributes at least.
+    Most of them are same to the on-wire counterparts but in host byte order.
+    __init__ takes the correspondig args in this order.
+
+    .. tabularcolumns:: |l|p{30em}|l|
+
+    ============== =====================================================
+    Attribute      Description
+    ============== =====================================================
+    flags          set to '0'. this field will be ignored.
+    length         length of this chunk containing this header.
+    ============== =====================================================
+    """
+
+    @classmethod
+    def chunk_type(cls):
+        return TYPE_SHUTDOWN_ACK
+
+
+@sctp.register_chunk_type
+class chunk_error(chunk):
+    """Stream Control Transmission Protocol (SCTP)
+    sub encoder/decoder class for Operation Error (ERROR) chunk (RFC 4960).
+
+    This is used with ryu.lib.packet.sctp.sctp.
+
+    An instance has the following attributes at least.
+    Most of them are same to the on-wire counterparts but in host byte order.
+    __init__ takes the correspondig args in this order.
+
+    .. tabularcolumns:: |l|p{30em}|l|
+
+    ============== =====================================================
+    Attribute      Description
+    ============== =====================================================
+    flags          set to '0'. this field will be ignored.
+    length         length of this chunk containing this header.
+    causes         a list of derived classes of ryu.lib.packet.sctp.causes.
+    ============== =====================================================
+    """
+
+    # TODO: coding and testing
+    _class_prefixes = ['cause_']
+    _RECOGNIZED_CAUSES = {}
+
+    @staticmethod
+    def register_cause_code(*args):
+        def _register_cause_code(cls):
+            chunk_error._RECOGNIZED_CAUSES[cls.cause_code()] = cls
+            return cls
+        return _register_cause_code(args[0])
+
+    @classmethod
+    def chunk_type(cls):
+        return TYPE_ERROR
+
+    def __init__(self, flags, length, causes=None):
+        super(chunk_error, self).__init__(self.chunk_type(), length)
+        self.flags = flags
+        causes = causes or []
+        assert isinstance(causes, list)
+        for one in causes:
+            assert isinstance(one, cause)
+        self.causes = causes
+
+    @classmethod
+    def parser(cls, buf):
+        (_, flags, length) = struct.unpack_from(cls._PACK_STR, buf)
+        causes = []
+        offset = cls._MIN_LEN
+        while offset < length:
+            (ccode, ) = struct.unpack_from('!H', buf, offset)
+            cls_ = cls._RECOGNIZED_CAUSES.get(ccode)
+            if not cls_:
+                break
+            ins = cls_.parser(buf[offset:])
+            causes.append(ins)
+            offset += len(ins)
+        return cls(flags, length, causes)
+
+    def serialize(self):
+        buf = bytearray(struct.pack(
+            self._PACK_STR, self.chunk_type(), self.flags, self.length))
+        for one in self.causes:
+            buf.extend(one.serialize())
+        return str(buf)
+
+
+@sctp.register_chunk_type
+class chunk_cookie_echo(chunk):
+    """Stream Control Transmission Protocol (SCTP)
+    sub encoder/decoder class for Cookie Echo (COOKIE ECHO) chunk (RFC 4960).
+
+    This is used with ryu.lib.packet.sctp.sctp.
+
+    An instance has the following attributes at least.
+    Most of them are same to the on-wire counterparts but in host byte order.
+    __init__ takes the correspondig args in this order.
+
+    .. tabularcolumns:: |l|p{30em}|l|
+
+    ============== =====================================================
+    Attribute      Description
+    ============== =====================================================
+    flags          set to '0'. this field will be ignored.
+    length         length of this chunk containing this header.
+    cookie         cookie data.
+    ============== =====================================================
+    """
+
+    _PACK_STR = '!BBH'
+    _MIN_LEN = struct.calcsize(_PACK_STR)
+
+    @classmethod
+    def chunk_type(cls):
+        return TYPE_COOKIE_ECHO
+
+    def __init__(self, flags, length, cookie):
+        super(chunk_cookie_echo, self).__init__(self.chunk_type(), length)
+        self.flags = flags
+        self.cookie = cookie
+
+    @classmethod
+    def parser(cls, buf):
+        (_, flags, length) = struct.unpack_from(cls._PACK_STR, buf)
+        fmt = '%ds' % (length - cls._MIN_LEN)
+        (cookie, ) = struct.unpack_from(fmt, buf, cls._MIN_LEN)
+        return cls(flags, length, cookie)
+
+    def serialize(self):
+        buf = bytearray(struct.pack(
+            self._PACK_STR, self.chunk_type(), self.flags,
+            self.length))
+        buf.extend(self.cookie)
+        return str(buf)
+
+
+@sctp.register_chunk_type
+class chunk_cookie_ack(chunk_ack_base):
+    """Stream Control Transmission Protocol (SCTP)
+    sub encoder/decoder class for Cookie Acknowledgement (COOKIE ACK)
+    chunk (RFC 4960).
+
+    This is used with ryu.lib.packet.sctp.sctp.
+
+    An instance has the following attributes at least.
+    Most of them are same to the on-wire counterparts but in host byte order.
+    __init__ takes the correspondig args in this order.
+
+    .. tabularcolumns:: |l|p{30em}|l|
+
+    ============== =====================================================
+    Attribute      Description
+    ============== =====================================================
+    flags          set to '0'. this field will be ignored.
+    length         length of this chunk containing this header.
+    ============== =====================================================
+    """
+
+    @classmethod
+    def chunk_type(cls):
+        return TYPE_COOKIE_ACK
+
+
+@sctp.register_chunk_type
+class chunk_ecn_echo(chunk_ecn_base):
+    """Stream Control Transmission Protocol (SCTP)
+    sub encoder/decoder class for ECN-Echo chunk (RFC 4960 Appendix A.).
+
+    This is used with ryu.lib.packet.sctp.sctp.
+
+    An instance has the following attributes at least.
+    Most of them are same to the on-wire counterparts but in host byte order.
+    __init__ takes the correspondig args in this order.
+
+    .. tabularcolumns:: |l|p{30em}|l|
+
+    ============== =====================================================
+    Attribute      Description
+    ============== =====================================================
+    flags          set to '0'. this field will be ignored.
+    length         length of this chunk containing this header.
+    low_tsn        the lowest TSN.
+    ============== =====================================================
+    """
+
+    @classmethod
+    def chunk_type(cls):
+        return TYPE_ECN_ECHO
+
+
+@sctp.register_chunk_type
+class chunk_cwr(chunk_ecn_base):
+    """Stream Control Transmission Protocol (SCTP)
+    sub encoder/decoder class for CWR chunk (RFC 4960 Appendix A.).
+
+    This is used with ryu.lib.packet.sctp.sctp.
+
+    An instance has the following attributes at least.
+    Most of them are same to the on-wire counterparts but in host byte order.
+    __init__ takes the correspondig args in this order.
+
+    .. tabularcolumns:: |l|p{30em}|l|
+
+    ============== =====================================================
+    Attribute      Description
+    ============== =====================================================
+    flags          set to '0'. this field will be ignored.
+    length         length of this chunk containing this header.
+    low_tsn        the lowest TSN.
+    ============== =====================================================
+    """
+
+    @classmethod
+    def chunk_type(cls):
+        return TYPE_CWR
+
+
+@sctp.register_chunk_type
+class chunk_shutdown_complete(chunk):
+    """Stream Control Transmission Protocol (SCTP)
+    sub encoder/decoder class for Shutdown Complete (SHUTDOWN COMPLETE)
+    chunk (RFC 4960).
+
+    This is used with ryu.lib.packet.sctp.sctp.
+
+    An instance has the following attributes at least.
+    Most of them are same to the on-wire counterparts but in host byte order.
+    __init__ takes the correspondig args in this order.
+
+    .. tabularcolumns:: |l|p{30em}|l|
+
+    ============== =====================================================
+    Attribute      Description
+    ============== =====================================================
+    tflag          '0' means the Verification tag is normal. '1' means
+                   the Verification tag is copy of the sender.
+    length         length of this chunk containing this header.
+    ============== =====================================================
+    """
+
+    _PACK_STR = '!BBH'
+    _MIN_LEN = struct.calcsize(_PACK_STR)
+
+    @classmethod
+    def chunk_type(cls):
+        return TYPE_SHUTDOWN_COMPLETE
+
+    def __init__(self, tflag, length):
+        assert (1 == tflag | 1)
+        super(chunk_shutdown_complete, self).__init__(
+            self.chunk_type(), length)
+        self.tflag = tflag
+
+    @classmethod
+    def parser(cls, buf):
+        (_, flags, length) = struct.unpack_from(cls._PACK_STR, buf)
+        tflag = flags & 1
+        msg = cls(tflag, length)
+        return msg
+
+    def serialize(self):
+        buf = struct.pack(
+            self._PACK_STR, self.chunk_type(),
+            self.tflag, self.length)
+        return buf
+
+
+#=======================================================================
+#
+# Cause Code
+#
+#=======================================================================
+class cause(stringify.StringifyMixin):
+
+    __metaclass__ = abc.ABCMeta
+    _PACK_STR = '!HH'
+    _MIN_LEN = struct.calcsize(_PACK_STR)
+
+    @classmethod
+    @abc.abstractproperty
+    def cause_code(cls):
+        pass
+
+    def __init__(self, length):
+        self.length = length
+
+    @classmethod
+    @abc.abstractmethod
+    def parser(cls, buf):
+        pass
+
+    @abc.abstractmethod
+    def serialize(self):
+        pass
+
+    def __len__(self):
+        return self.length
+
+
+class cause_with_value(cause):
+
+    __metaclass__ = abc.ABCMeta
+
+    def __init__(self, length, value):
+        super(cause_with_value, self).__init__(length)
+        self.value = value
+
+    @classmethod
+    def parser(cls, buf):
+        (_, length) = struct.unpack_from(cls._PACK_STR, buf)
+        value = None
+        if (cls._MIN_LEN < length):
+            fmt = '%ds' % (length - cls._MIN_LEN)
+            (value, ) = struct.unpack_from(fmt, buf, cls._MIN_LEN)
+        return cls(length, value)
+
+    def serialize(self):
+        buf = bytearray(struct.pack(
+            self._PACK_STR, self.cause_code(), self.length))
+        if self.value:
+            buf.extend(self.value)
+        return str(buf)
+
+
+@chunk_abort.register_cause_code
+@chunk_error.register_cause_code
+class cause_invalid_stream_id(cause_with_value):
+    """Stream Control Transmission Protocol (SCTP)
+    sub encoder/decoder class for Invalid Stream Identifier (RFC 4960).
+
+    This is used with ryu.lib.packet.sctp.chunk_abort and
+                      ryu.lib.packet.sctp.chunk_error.
+
+    An instance has the following attributes at least.
+    Most of them are same to the on-wire counterparts but in host byte order.
+    __init__ takes the correspondig args in this order.
+
+    .. tabularcolumns:: |l|p{30em}|l|
+
+    ============== =====================================================
+    Attribute      Description
+    ============== =====================================================
+    length         length of this cause containing this header.
+    value          stream id.
+    ============== =====================================================
+    """
+
+    _PACK_STR = '!HHH2x'
+    _MIN_LEN = struct.calcsize(_PACK_STR)
+
+    @classmethod
+    def cause_code(cls):
+        return CCODE_INVALID_STREAM_ID
+
+    @classmethod
+    def parser(cls, buf):
+        (_, length, value) = struct.unpack_from(cls._PACK_STR, buf)
+        return cls(length, value)
+
+    def serialize(self):
+        buf = struct.pack(
+            self._PACK_STR, self.cause_code(), self.length, self.value)
+        return buf
+
+
+@chunk_abort.register_cause_code
+@chunk_error.register_cause_code
+class cause_missing_param(cause):
+    """Stream Control Transmission Protocol (SCTP)
+    sub encoder/decoder class for Missing Mandatory Parameter (RFC 4960).
+
+    This is used with ryu.lib.packet.sctp.chunk_abort and
+                      ryu.lib.packet.sctp.chunk_error.
+
+    An instance has the following attributes at least.
+    Most of them are same to the on-wire counterparts but in host byte order.
+    __init__ takes the correspondig args in this order.
+
+    .. tabularcolumns:: |l|p{30em}|l|
+
+    ============== =====================================================
+    Attribute      Description
+    ============== =====================================================
+    length         length of this cause containing this header.
+    num            Number of missing params.
+    types          a list of missing params.
+    ============== =====================================================
+    """
+
+    _PACK_STR = '!HHI'
+    _MIN_LEN = struct.calcsize(_PACK_STR)
+
+    @classmethod
+    def cause_code(cls):
+        return CCODE_MISSING_PARAM
+
+    def __init__(self, length, num, types=None):
+        super(cause_missing_param, self).__init__(length)
+        self.num = num
+        types = types or []
+        assert isinstance(types, list)
+        for one in types:
+            assert isinstance(one, int)
+        self.types = types
+
+    @classmethod
+    def parser(cls, buf):
+        (_, length, num) = struct.unpack_from(cls._PACK_STR, buf)
+        types = []
+        offset = cls._MIN_LEN
+        for count in range(num):
+            offset = cls._MIN_LEN + (struct.calcsize('!H') * count)
+            (one, ) = struct.unpack_from('!H', buf, offset)
+            types.append(one)
+        return cls(length, num, types)
+
+    def serialize(self):
+        buf = bytearray(struct.pack(
+            self._PACK_STR, self.cause_code(), self.length, self.num))
+        for one in self.types:
+            buf.extend(struct.pack('!H', one))
+        return str(buf)
+
+
+@chunk_abort.register_cause_code
+@chunk_error.register_cause_code
+class cause_stale_cookie(cause_with_value):
+    """Stream Control Transmission Protocol (SCTP)
+    sub encoder/decoder class for Stale Cookie Error (RFC 4960).
+
+    This is used with ryu.lib.packet.sctp.chunk_abort and
+                      ryu.lib.packet.sctp.chunk_error.
+
+    An instance has the following attributes at least.
+    Most of them are same to the on-wire counterparts but in host byte order.
+    __init__ takes the correspondig args in this order.
+
+    .. tabularcolumns:: |l|p{30em}|l|
+
+    ============== =====================================================
+    Attribute      Description
+    ============== =====================================================
+    length         length of this cause containing this header.
+    value          Measure of Staleness.
+    ============== =====================================================
+    """
+
+    @classmethod
+    def cause_code(cls):
+        return CCODE_STALE_COOKIE
+
+
+@chunk_abort.register_cause_code
+@chunk_error.register_cause_code
+class cause_out_of_resource(cause):
+    """Stream Control Transmission Protocol (SCTP)
+    sub encoder/decoder class for Out of Resource (RFC 4960).
+
+    This is used with ryu.lib.packet.sctp.chunk_abort and
+                      ryu.lib.packet.sctp.chunk_error.
+
+    An instance has the following attributes at least.
+    Most of them are same to the on-wire counterparts but in host byte order.
+    __init__ takes the correspondig args in this order.
+
+    .. tabularcolumns:: |l|p{30em}|l|
+
+    ============== =====================================================
+    Attribute      Description
+    ============== =====================================================
+    length         length of this cause containing this header.
+    ============== =====================================================
+    """
+
+    @classmethod
+    def cause_code(cls):
+        return CCODE_OUT_OF_RESOURCE
+
+    @classmethod
+    def parser(cls, buf):
+        (_, length) = struct.unpack_from(cls._PACK_STR, buf)
+        return cls(length)
+
+    def serialize(self):
+        buf = struct.pack(
+            self._PACK_STR, self.cause_code(), self.length)
+        return buf
+
+
+@chunk_abort.register_cause_code
+@chunk_error.register_cause_code
+class cause_unresolvable_addr(cause_with_value):
+    """Stream Control Transmission Protocol (SCTP)
+    sub encoder/decoder class for Unresolvable Address (RFC 4960).
+
+    This is used with ryu.lib.packet.sctp.chunk_abort and
+                      ryu.lib.packet.sctp.chunk_error.
+
+    An instance has the following attributes at least.
+    Most of them are same to the on-wire counterparts but in host byte order.
+    __init__ takes the correspondig args in this order.
+
+    .. tabularcolumns:: |l|p{30em}|l|
+
+    ============== =====================================================
+    Attribute      Description
+    ============== =====================================================
+    length         length of this cause containing this header.
+    value          Unresolvable Address. one of follows:
+
+                   ryu.lib.packet.sctp.param_host_addr,
+
+                   ryu.lib.packet.sctp.param_ipv4, or
+
+                   ryu.lib.packet.sctp.param_ipv6.
+    ============== =====================================================
+    """
+
+    _RECOGNIZED_PARAMS = {}
+
+    @staticmethod
+    def register_param_type(*args):
+        def _register_param_type(cls):
+            cause_unresolvable_addr._RECOGNIZED_PARAMS[cls.param_type()] = cls
+            return cls
+        return _register_param_type(args[0])
+
+    @classmethod
+    def cause_code(cls):
+        return CCODE_UNRESOLVABLE_ADDR
+
+    def __init__(self, length, value):
+        super(cause_unresolvable_addr, self).__init__(length, value)
+
+    @classmethod
+    def parser(cls, buf):
+        (_, length) = struct.unpack_from(cls._PACK_STR, buf)
+        (ptype, ) = struct.unpack_from('!H', buf, cls._MIN_LEN)
+        cls_ = cls._RECOGNIZED_PARAMS.get(ptype)
+        value = cls_.parser(buf[cls._MIN_LEN:])
+        return cls(length, value)
+
+    def serialize(self):
+        buf = bytearray(struct.pack(
+            self._PACK_STR, self.cause_code(), self.length))
+        if self.value:
+            buf.extend(self.value.serialize())
+        return str(buf)
+
+
+@chunk_abort.register_cause_code
+@chunk_error.register_cause_code
+class cause_unrecognized_chunk(cause_with_value):
+    """Stream Control Transmission Protocol (SCTP)
+    sub encoder/decoder class for Unrecognized Chunk Type (RFC 4960).
+
+    This is used with ryu.lib.packet.sctp.chunk_abort and
+                      ryu.lib.packet.sctp.chunk_error.
+
+    An instance has the following attributes at least.
+    Most of them are same to the on-wire counterparts but in host byte order.
+    __init__ takes the correspondig args in this order.
+
+    .. tabularcolumns:: |l|p{30em}|l|
+
+    ============== =====================================================
+    Attribute      Description
+    ============== =====================================================
+    length         length of this cause containing this header.
+    value          Unrecognized Chunk.
+    ============== =====================================================
+    """
+
+    @classmethod
+    def cause_code(cls):
+        return CCODE_UNRECOGNIZED_CHUNK
+
+
+@chunk_abort.register_cause_code
+@chunk_error.register_cause_code
+class cause_invalid_param(cause):
+    """Stream Control Transmission Protocol (SCTP)
+    sub encoder/decoder class for Invalid Mandatory Parameter (RFC 4960).
+
+    This is used with ryu.lib.packet.sctp.chunk_abort and
+                      ryu.lib.packet.sctp.chunk_error.
+
+    An instance has the following attributes at least.
+    Most of them are same to the on-wire counterparts but in host byte order.
+    __init__ takes the correspondig args in this order.
+
+    .. tabularcolumns:: |l|p{30em}|l|
+
+    ============== =====================================================
+    Attribute      Description
+    ============== =====================================================
+    length         length of this cause containing this header.
+    ============== =====================================================
+    """
+
+    @classmethod
+    def cause_code(cls):
+        return CCODE_INVALID_PARAM
+
+    def __init__(self, length):
+        super(cause_invalid_param, self).__init__(length)
+
+    @classmethod
+    def parser(cls, buf):
+        (_, length) = struct.unpack_from(cls._PACK_STR, buf)
+        return cls(length)
+
+    def serialize(self):
+        buf = struct.pack(
+            self._PACK_STR, self.cause_code(), self.length)
+        return buf
+
+
+@chunk_abort.register_cause_code
+@chunk_error.register_cause_code
+class cause_unrecognized_param(cause_with_value):
+    """Stream Control Transmission Protocol (SCTP)
+    sub encoder/decoder class for Unrecognized Parameters (RFC 4960).
+
+    This is used with ryu.lib.packet.sctp.chunk_abort and
+                      ryu.lib.packet.sctp.chunk_error.
+
+    An instance has the following attributes at least.
+    Most of them are same to the on-wire counterparts but in host byte order.
+    __init__ takes the correspondig args in this order.
+
+    .. tabularcolumns:: |l|p{30em}|l|
+
+    ============== =====================================================
+    Attribute      Description
+    ============== =====================================================
+    length         length of this cause containing this header.
+    value          Unrecognized Parameter.
+    ============== =====================================================
+    """
+
+    @classmethod
+    def cause_code(cls):
+        return CCODE_UNRECOGNIZED_PARAM
+
+
+@chunk_abort.register_cause_code
+@chunk_error.register_cause_code
+class cause_no_userdata(cause_with_value):
+    """Stream Control Transmission Protocol (SCTP)
+    sub encoder/decoder class for No User Data (RFC 4960).
+
+    This is used with ryu.lib.packet.sctp.chunk_abort and
+                      ryu.lib.packet.sctp.chunk_error.
+
+    An instance has the following attributes at least.
+    Most of them are same to the on-wire counterparts but in host byte order.
+    __init__ takes the correspondig args in this order.
+
+    .. tabularcolumns:: |l|p{30em}|l|
+
+    ============== =====================================================
+    Attribute      Description
+    ============== =====================================================
+    length         length of this cause containing this header.
+    value          the TSN of the DATA chunk received with no user data
+                   field.
+    ============== =====================================================
+    """
+
+    @classmethod
+    def cause_code(cls):
+        return CCODE_NO_USERDATA
+
+
+@chunk_abort.register_cause_code
+@chunk_error.register_cause_code
+class cause_cookie_while_shutdown(cause):
+    """Stream Control Transmission Protocol (SCTP)
+    sub encoder/decoder class for Cookie Received While Shutting Down
+    (RFC 4960).
+
+    This is used with ryu.lib.packet.sctp.chunk_abort and
+                      ryu.lib.packet.sctp.chunk_error.
+
+    An instance has the following attributes at least.
+    Most of them are same to the on-wire counterparts but in host byte order.
+    __init__ takes the correspondig args in this order.
+
+    .. tabularcolumns:: |l|p{30em}|l|
+
+    ============== =====================================================
+    Attribute      Description
+    ============== =====================================================
+    length         length of this cause containing this header.
+    ============== =====================================================
+    """
+
+    @classmethod
+    def cause_code(cls):
+        return CCODE_COOKIE_WHILE_SHUTDOWN
+
+    def __init__(self, length):
+        super(cause_cookie_while_shutdown, self).__init__(length)
+
+    @classmethod
+    def parser(cls, buf):
+        (_, length) = struct.unpack_from(cls._PACK_STR, buf)
+        return cls(length)
+
+    def serialize(self):
+        buf = struct.pack(
+            self._PACK_STR, self.cause_code(), self.length)
+        return buf
+
+
+@chunk_abort.register_cause_code
+@chunk_error.register_cause_code
+class cause_restart_with_new_addr(cause_with_value):
+    """Stream Control Transmission Protocol (SCTP)
+    sub encoder/decoder class for Restart of an Association with New
+    Addresses (RFC 4960).
+
+    This is used with ryu.lib.packet.sctp.chunk_abort and
+                      ryu.lib.packet.sctp.chunk_error.
+
+    An instance has the following attributes at least.
+    Most of them are same to the on-wire counterparts but in host byte order.
+    __init__ takes the correspondig args in this order.
+
+    .. tabularcolumns:: |l|p{30em}|l|
+
+    ============== =====================================================
+    Attribute      Description
+    ============== =====================================================
+    length         length of this cause containing this header.
+    value          New Address TLVs.
+    ============== =====================================================
+    """
+
+    _RECOGNIZED_PARAMS = {}
+
+    @staticmethod
+    def register_param_type(*args):
+        def _register_param_type(cls):
+            cause_restart_with_new_addr._RECOGNIZED_PARAMS[
+                cls.param_type()] = cls
+            return cls
+        return _register_param_type(args[0])
+
+    @classmethod
+    def cause_code(cls):
+        return CCODE_RESTART_WITH_NEW_ADDR
+
+    def __init__(self, length, value):
+        if not isinstance(value, list):
+            value = [value]
+        super(cause_restart_with_new_addr, self).__init__(length, value)
+
+    @classmethod
+    def parser(cls, buf):
+        (_, length) = struct.unpack_from(cls._PACK_STR, buf)
+        value = []
+        offset = cls._MIN_LEN
+        while offset < length:
+            (ptype, ) = struct.unpack_from('!H', buf, offset)
+            cls_ = cls._RECOGNIZED_PARAMS.get(ptype)
+            if not cls_:
+                break
+            ins = cls_.parser(buf[offset:])
+            value.append(ins)
+            offset += len(ins)
+        return cls(length, value)
+
+    def serialize(self):
+        buf = bytearray(struct.pack(
+            self._PACK_STR, self.cause_code(), self.length))
+        for one in self.value:
+            buf.extend(one.serialize())
+        return str(buf)
+
+
+@chunk_abort.register_cause_code
+@chunk_error.register_cause_code
+class cause_user_initiated_abort(cause_with_value):
+    """Stream Control Transmission Protocol (SCTP)
+    sub encoder/decoder class for User-Initiated Abort (RFC 4960).
+
+    This is used with ryu.lib.packet.sctp.chunk_abort and
+                      ryu.lib.packet.sctp.chunk_error.
+
+    An instance has the following attributes at least.
+    Most of them are same to the on-wire counterparts but in host byte order.
+    __init__ takes the correspondig args in this order.
+
+    .. tabularcolumns:: |l|p{30em}|l|
+
+    ============== =====================================================
+    Attribute      Description
+    ============== =====================================================
+    length         length of this cause containing this header.
+    value          Upper Layer Abort Reason.
+    ============== =====================================================
+    """
+
+    @classmethod
+    def cause_code(cls):
+        return CCODE_USER_INITIATED_ABORT
+
+
+@chunk_abort.register_cause_code
+@chunk_error.register_cause_code
+class cause_protocol_violation(cause_with_value):
+    """Stream Control Transmission Protocol (SCTP)
+    sub encoder/decoder class for Protocol Violation (RFC 4960).
+
+    This is used with ryu.lib.packet.sctp.chunk_abort and
+                      ryu.lib.packet.sctp.chunk_error.
+
+    An instance has the following attributes at least.
+    Most of them are same to the on-wire counterparts but in host byte order.
+    __init__ takes the correspondig args in this order.
+
+    .. tabularcolumns:: |l|p{30em}|l|
+
+    ============== =====================================================
+    Attribute      Description
+    ============== =====================================================
+    length         length of this cause containing this header.
+    value          Additional Information.
+    ============== =====================================================
+    """
+
+    @classmethod
+    def cause_code(cls):
+        return CCODE_PROTOCOL_VIOLATION
+
+
+#=======================================================================
+#
+# Chunk Parameter Types
+#
+#=======================================================================
+class param(stringify.StringifyMixin):
+
+    __metaclass__ = abc.ABCMeta
+    _PACK_STR = '!HH'
+    _MIN_LEN = struct.calcsize(_PACK_STR)
+
+    @classmethod
+    @abc.abstractproperty
+    def param_type(cls):
+        pass
+
+    def __init__(self, length, value):
+        self.length = length
+        self.value = value
+
+    @classmethod
+    def parser(cls, buf):
+        (_, length) = struct.unpack_from(cls._PACK_STR, buf)
+        value = None
+        if (cls._MIN_LEN < length):
+            fmt = '%ds' % (length - cls._MIN_LEN)
+            (value, ) = struct.unpack_from(fmt, buf, cls._MIN_LEN)
+        return cls(length, value)
+
+    def serialize(self):
+        buf = bytearray(struct.pack(
+            self._PACK_STR, self.param_type(), self.length))
+        if self.value:
+            buf.extend(self.value)
+        return str(buf)
+
+    def __len__(self):
+        return self.length
+
+
+@chunk_heartbeat.register_param_type
+@chunk_heartbeat_ack.register_param_type
+class param_heartbeat(param):
+    """Stream Control Transmission Protocol (SCTP)
+    sub encoder/decoder class for Heartbeat Info Parameter (RFC 4960).
+
+    This is used with ryu.lib.packet.sctp.chunk_heartbeat and
+                      ryu.lib.packet.sctp.chunk_heartbeat_ack.
+
+    An instance has the following attributes at least.
+    Most of them are same to the on-wire counterparts but in host byte order.
+    __init__ takes the correspondig args in this order.
+
+    .. tabularcolumns:: |l|p{30em}|l|
+
+    ============== =====================================================
+    Attribute      Description
+    ============== =====================================================
+    length         length of this param containing this header.
+    value          the sender-specific heartbeat information.
+    ============== =====================================================
+    """
+
+    @classmethod
+    def param_type(cls):
+        return PTYPE_HEARTBEAT
+
+
+@chunk_init_ack.register_param_type
+class param_state_cookie(param):
+    """Stream Control Transmission Protocol (SCTP)
+    sub encoder/decoder class for State Cookie Parameter (RFC 4960).
+
+    This is used with ryu.lib.packet.sctp.chunk_init_ack.
+
+    An instance has the following attributes at least.
+    Most of them are same to the on-wire counterparts but in host byte order.
+    __init__ takes the correspondig args in this order.
+
+    .. tabularcolumns:: |l|p{30em}|l|
+
+    ============== =====================================================
+    Attribute      Description
+    ============== =====================================================
+    length         length of this param containing this header.
+    value          the state cookie. see Section 5.1.3 in RFC 4960.
+    ============== =====================================================
+    """
+
+    @classmethod
+    def param_type(cls):
+        return PTYPE_STATE_COOKIE
+
+
+@chunk_init_ack.register_param_type
+class param_unrecognized_param(param):
+    """Stream Control Transmission Protocol (SCTP)
+    sub encoder/decoder class for Unrecognized Parameter (RFC 4960).
+
+    This is used with ryu.lib.packet.sctp.chunk_init_ack.
+
+    An instance has the following attributes at least.
+    Most of them are same to the on-wire counterparts but in host byte order.
+    __init__ takes the correspondig args in this order.
+
+    .. tabularcolumns:: |l|p{30em}|l|
+
+    ============== =====================================================
+    Attribute      Description
+    ============== =====================================================
+    length         length of this param containing this header.
+    value          the unrecognized parameter in the INIT chunk.
+    ============== =====================================================
+    """
+
+    @classmethod
+    def param_type(cls):
+        return PTYPE_UNRECOGNIZED_PARAM
+
+
+@chunk_init.register_param_type
+class param_cookie_preserve(param):
+    """Stream Control Transmission Protocol (SCTP)
+    sub encoder/decoder class for Cookie Preservative Parameter (RFC 4960).
+
+    This is used with ryu.lib.packet.sctp.chunk_init.
+
+    An instance has the following attributes at least.
+    Most of them are same to the on-wire counterparts but in host byte order.
+    __init__ takes the correspondig args in this order.
+
+    .. tabularcolumns:: |l|p{30em}|l|
+
+    ============== =====================================================
+    Attribute      Description
+    ============== =====================================================
+    length         length of this param containing this header.
+    value          Suggested Cookie Life-Span Increment (msec).
+    ============== =====================================================
+    """
+
+    _PACK_STR = '!HHI'
+    _MIN_LEN = struct.calcsize(_PACK_STR)
+
+    @classmethod
+    def param_type(cls):
+        return PTYPE_COOKIE_PRESERVE
+
+    @classmethod
+    def parser(cls, buf):
+        (_, length, value) = struct.unpack_from(cls._PACK_STR, buf)
+        return cls(length, value)
+
+    def serialize(self):
+        buf = struct.pack(
+            self._PACK_STR, self.param_type(), self.length, self.value)
+        return buf
+
+
+@chunk_init.register_param_type
+@chunk_init_ack.register_param_type
+class param_ecn(param):
+    """Stream Control Transmission Protocol (SCTP)
+    sub encoder/decoder class for ECN Parameter (RFC 4960 Appendix A.).
+
+    This is used with ryu.lib.packet.sctp.chunk_init and
+                      ryu.lib.packet.sctp.chunk_init_ack.
+
+    An instance has the following attributes at least.
+    Most of them are same to the on-wire counterparts but in host byte order.
+    __init__ takes the correspondig args in this order.
+
+    .. tabularcolumns:: |l|p{30em}|l|
+
+    ============== =====================================================
+    Attribute      Description
+    ============== =====================================================
+    length         length of this param containing this header.
+    value          set to None.
+    ============== =====================================================
+    """
+
+    @classmethod
+    def param_type(cls):
+        return PTYPE_ECN
+
+
+@chunk_init.register_param_type
+@chunk_init_ack.register_param_type
+@cause_unresolvable_addr.register_param_type
+@cause_restart_with_new_addr.register_param_type
+class param_host_addr(param):
+    """Stream Control Transmission Protocol (SCTP)
+    sub encoder/decoder class for Host Name Address Parameter (RFC 4960).
+
+    This is used with ryu.lib.packet.sctp.chunk_init and
+                      ryu.lib.packet.sctp.chunk_init_ack.
+
+    An instance has the following attributes at least.
+    Most of them are same to the on-wire counterparts but in host byte order.
+    __init__ takes the correspondig args in this order.
+
+    .. tabularcolumns:: |l|p{30em}|l|
+
+    ============== =====================================================
+    Attribute      Description
+    ============== =====================================================
+    length         length of this param containing this header.
+    value          a host name that ends with null terminator.
+    ============== =====================================================
+    """
+
+    @classmethod
+    def param_type(cls):
+        return PTYPE_HOST_ADDR
+
+
+@chunk_init.register_param_type
+class param_supported_addr(param):
+    """Stream Control Transmission Protocol (SCTP)
+    sub encoder/decoder class for Supported Address Types Parameter (RFC 4960).
+
+    This is used with ryu.lib.packet.sctp.chunk_init.
+
+    An instance has the following attributes at least.
+    Most of them are same to the on-wire counterparts but in host byte order.
+    __init__ takes the correspondig args in this order.
+
+    .. tabularcolumns:: |l|p{30em}|l|
+
+    ============== =====================================================
+    Attribute      Description
+    ============== =====================================================
+    length         length of this param containing this header.
+    value          a list of parameter types. odd cases pad with 0x0000.
+    ============== =====================================================
+    """
+
+    _VALUE_STR = '!H'
+    _VALUE_LEN = struct.calcsize(_VALUE_STR)
+
+    @classmethod
+    def param_type(cls):
+        return PTYPE_SUPPORTED_ADDR
+
+    def __init__(self, length, value):
+        super(param_supported_addr, self).__init__(length, value)
+        if not isinstance(value, list):
+            value = [value]
+        for one in value:
+            assert isinstance(one, int)
+        self.length = length
+        if len(value) % 2:
+            value.append(0)
+        self.value = value
+
+    @classmethod
+    def parser(cls, buf):
+        (_, length) = struct.unpack_from(cls._PACK_STR, buf)
+        value = []
+        offset = cls._MIN_LEN
+        while offset < length:
+            (one, ) = struct.unpack_from(cls._VALUE_STR, buf, offset)
+            value.append(one)
+            offset += cls._VALUE_LEN
+        return cls(length, value)
+
+    def serialize(self):
+        buf = bytearray(struct.pack(
+            self._PACK_STR, self.param_type(), self.length))
+        for one in self.value:
+            buf.extend(struct.pack(param_supported_addr._VALUE_STR, one))
+        return str(buf)
+
+    def __len__(self):
+        return self.length if 0 == self.length % 4 else self.length + 2
+
+
+@chunk_init.register_param_type
+@chunk_init_ack.register_param_type
+@cause_restart_with_new_addr.register_param_type
+class param_ipv4(param):
+    """Stream Control Transmission Protocol (SCTP)
+    sub encoder/decoder class for IPv4 Address Parameter (RFC 4960).
+
+    This is used with ryu.lib.packet.sctp.chunk_init and
+                      ryu.lib.packet.sctp.chunk_init_ack.
+
+    An instance has the following attributes at least.
+    Most of them are same to the on-wire counterparts but in host byte order.
+    __init__ takes the correspondig args in this order.
+
+    .. tabularcolumns:: |l|p{30em}|l|
+
+    ============== =====================================================
+    Attribute      Description
+    ============== =====================================================
+    length         length of this param containing this header.
+    value          IPv4 address of the sending endpoint.
+    ============== =====================================================
+    """
+
+    _TYPE = {'ascii': ['value']}
+
+    @classmethod
+    def param_type(cls):
+        return PTYPE_IPV4
+
+    @classmethod
+    def parser(cls, buf):
+        (_, length) = struct.unpack_from(cls._PACK_STR, buf)
+        value = None
+        if (cls._MIN_LEN < length):
+            fmt = '%ds' % (length - cls._MIN_LEN)
+            (value, ) = struct.unpack_from(fmt, buf, cls._MIN_LEN)
+        return cls(length, addrconv.ipv4.bin_to_text(value))
+
+    def serialize(self):
+        buf = bytearray(struct.pack(
+            self._PACK_STR, self.param_type(), self.length))
+        if self.value:
+            buf.extend(addrconv.ipv4.text_to_bin(self.value))
+        return str(buf)
+
+
+@chunk_init.register_param_type
+@chunk_init_ack.register_param_type
+@cause_restart_with_new_addr.register_param_type
+class param_ipv6(param):
+    """Stream Control Transmission Protocol (SCTP)
+    sub encoder/decoder class for IPv6 Address Parameter (RFC 4960).
+
+    This is used with ryu.lib.packet.sctp.chunk_init and
+                      ryu.lib.packet.sctp.chunk_init_ack.
+
+    An instance has the following attributes at least.
+    Most of them are same to the on-wire counterparts but in host byte order.
+    __init__ takes the correspondig args in this order.
+
+    .. tabularcolumns:: |l|p{30em}|l|
+
+    ============== =====================================================
+    Attribute      Description
+    ============== =====================================================
+    length         length of this param containing this header.
+    value          IPv6 address of the sending endpoint.
+    ============== =====================================================
+    """
+
+    _TYPE = {'ascii': ['value']}
+
+    @classmethod
+    def param_type(cls):
+        return PTYPE_IPV6
+
+    @classmethod
+    def parser(cls, buf):
+        (_, length) = struct.unpack_from(cls._PACK_STR, buf)
+        value = None
+        if (cls._MIN_LEN < length):
+            fmt = '%ds' % (length - cls._MIN_LEN)
+            (value, ) = struct.unpack_from(fmt, buf, cls._MIN_LEN)
+        return cls(length, addrconv.ipv6.bin_to_text(value))
+
+    def serialize(self):
+        buf = bytearray(struct.pack(
+            self._PACK_STR, self.param_type(), self.length))
+        if self.value:
+            buf.extend(addrconv.ipv6.text_to_bin(self.value))
+        return str(buf)