diff --git a/pcapkit/foundation/extraction.py b/pcapkit/foundation/extraction.py
index 9460a1fe8..ed0f9d669 100644
--- a/pcapkit/foundation/extraction.py
+++ b/pcapkit/foundation/extraction.py
@@ -59,7 +59,7 @@
     from pcapkit.foundation.traceflow.tcp import TCP as TCP_TraceFlow
     from pcapkit.protocols.misc.pcap.frame import Frame
     from pcapkit.protocols.misc.pcapng import PCAPNG
-    from pcapkit.protocols.protocol import ProtocolBase as Protocol
+    from pcapkit.protocols.protocol import ProtocolBase
 
     #: Every key registered in :attr:`Extractor.__output__` and in
     #: :attr:`TraceFlowBase.__output__
@@ -82,7 +82,7 @@
     Packet = Union[Frame, PCAPNG, ScapyPacket, DPKTPacket, PySharkPacket,
                    PCAPFilePacket, tuple[float, bytes]]
 
-    Protocols = Union[str, Protocol, Type[Protocol]]
+    Protocols = Union[str, ProtocolBase, Type[ProtocolBase]]
     VerboseHandler = Callable[['Extractor', Packet], Any]
 
 __all__ = ['Extractor']
diff --git a/pcapkit/foundation/registry/protocols.py b/pcapkit/foundation/registry/protocols.py
index 775fc9a89..33f6cf728 100644
--- a/pcapkit/foundation/registry/protocols.py
+++ b/pcapkit/foundation/registry/protocols.py
@@ -33,7 +33,7 @@
 from pcapkit.protocols.link.link import Link
 from pcapkit.protocols.misc.pcap.frame import Frame
 from pcapkit.protocols.misc.pcapng import PCAPNG
-from pcapkit.protocols.protocol import ProtocolBase as Protocol
+from pcapkit.protocols.protocol import ProtocolBase
 from pcapkit.protocols.schema.application.httpv2 import FrameType as Schema_HTTP_FrameType
 from pcapkit.protocols.schema.internet.hip import Parameter as Schema_HIP_Parameter
 from pcapkit.protocols.schema.internet.hopopt import Option as Schema_HOPOPT_Option
@@ -144,7 +144,7 @@
 
 
 # NOTE: pcapkit.protocols.__proto__
-def register_protocol(protocol: 'Type[Protocol]') -> 'None':
+def register_protocol(protocol: 'Type[ProtocolBase]') -> 'None':
     """Registered protocol class.
 
     The protocol class must be a subclass of
@@ -213,7 +213,7 @@ class under two codes, a supported and documented thing to do, reaches
             same class under the same name is silent.
 
     """
-    if not issubclass(protocol, Protocol):
+    if not issubclass(protocol, ProtocolBase):
         raise RegistryError(f'protocol must be a Protocol subclass, not {protocol!r}')
 
     name = protocol.__name__.upper()
@@ -249,7 +249,7 @@ class under two codes, a supported and documented thing to do, reaches
 #: hand, moved into one table so :func:`register_protocol_code` can consult
 #: it. ``LinkType`` naming two classes is deliberate, not ambiguous --
 #: :func:`register_linktype` already fans out to both.
-_CODE_DESTINATIONS: 'dict[type, tuple[Type[Protocol], ...]]' = {
+_CODE_DESTINATIONS: 'dict[type, tuple[Type[ProtocolBase], ...]]' = {
     Enum_EtherType: (Link,),
     Enum_TransType: (Internet,),
     Enum_PayloadProtocolIdentifier: (SCTP,),
@@ -257,7 +257,7 @@ class under two codes, a supported and documented thing to do, reaches
 }
 
 
-def _iter_code_targets(code: 'Any') -> 'Iterator[tuple[Type[Protocol], Any]]':
+def _iter_code_targets(code: 'Any') -> 'Iterator[tuple[Type[ProtocolBase], Any]]':
     """Flatten a ``code=`` argument into ``(destination, key)`` pairs.
 
     Args:
@@ -300,7 +300,7 @@ def _iter_code_targets(code: 'Any') -> 'Iterator[tuple[Type[Protocol], Any]]':
                         f'explicit destination, e.g. code={{TCP: {code!r}}}')
 
 
-def register_protocol_code(protocol: 'Type[Protocol]', code: 'Any') -> 'None':
+def register_protocol_code(protocol: 'Type[ProtocolBase]', code: 'Any') -> 'None':
     r"""Register ``protocol`` into the next-layer dispatch registry (or
     registries) named by ``code``.
 
@@ -377,12 +377,12 @@ def register_protocol_code(protocol: 'Type[Protocol]', code: 'Any') -> 'None':
 
 
 @overload
-def register_linktype(code: 'LinkType', module: 'ModuleDescriptor[Protocol] | Type[Protocol]') -> 'None': ...
+def register_linktype(code: 'LinkType', module: 'ModuleDescriptor[ProtocolBase] | Type[ProtocolBase]') -> 'None': ...
 @overload
 def register_linktype(code: 'LinkType', module: 'str', class_: 'str') -> 'None': ...
 
 
-def register_linktype(code: 'LinkType', module: 'str | ModuleDescriptor[Protocol] | Type[Protocol]',
+def register_linktype(code: 'LinkType', module: 'str | ModuleDescriptor[ProtocolBase] | Type[ProtocolBase]',
                       class_: 'str' = NULL) -> 'None':
     r"""Register a new protocol class.
 
@@ -408,7 +408,7 @@ def register_linktype(code: 'LinkType', module: 'str | ModuleDescriptor[Protocol
 
     """
     if isinstance(module, str):
-        module = cast('ModuleDescriptor[Protocol]', ModuleDescriptor(module, class_))
+        module = cast('ModuleDescriptor[ProtocolBase]', ModuleDescriptor(module, class_))
 
     Frame.register(code, module)
     PCAPNG.register(code, module)
@@ -421,13 +421,13 @@ def register_linktype(code: 'LinkType', module: 'str | ModuleDescriptor[Protocol
 
 
 @overload
-def register_pcap(code: 'LinkType', module: 'ModuleDescriptor[Protocol] | Type[Protocol]') -> 'None': ...
+def register_pcap(code: 'LinkType', module: 'ModuleDescriptor[ProtocolBase] | Type[ProtocolBase]') -> 'None': ...
 @overload
 def register_pcap(code: 'LinkType', module: 'str', class_: 'str') -> 'None': ...
 
 
 # NOTE: pcapkit.protocols.misc.pcap.frame.Frame.__proto__
-def register_pcap(code: 'LinkType', module: 'str | ModuleDescriptor[Protocol] | Type[Protocol]',
+def register_pcap(code: 'LinkType', module: 'str | ModuleDescriptor[ProtocolBase] | Type[ProtocolBase]',
                   class_: 'str' = NULL) -> 'None':
     r"""Register a new protocol class.
 
@@ -446,7 +446,7 @@ def register_pcap(code: 'LinkType', module: 'str | ModuleDescriptor[Protocol] |
 
     """
     if isinstance(module, str):
-        module = cast('ModuleDescriptor[Protocol]', ModuleDescriptor(module, class_))
+        module = cast('ModuleDescriptor[ProtocolBase]', ModuleDescriptor(module, class_))
 
     Frame.register(code, module)
     logger.debug('registered PCAP linktype protocol: %s', code.name)
@@ -458,13 +458,13 @@ def register_pcap(code: 'LinkType', module: 'str | ModuleDescriptor[Protocol] |
 
 
 @overload
-def register_pcapng(code: 'LinkType', module: 'ModuleDescriptor[Protocol] | Type[Protocol]') -> 'None': ...
+def register_pcapng(code: 'LinkType', module: 'ModuleDescriptor[ProtocolBase] | Type[ProtocolBase]') -> 'None': ...
 @overload
 def register_pcapng(code: 'LinkType', module: 'str', class_: 'str') -> 'None': ...
 
 
 # NOTE: pcapkit.protocols.misc.pcapng.PCAPNG.__proto__
-def register_pcapng(code: 'LinkType', module: 'str | ModuleDescriptor[Protocol] | Type[Protocol]',
+def register_pcapng(code: 'LinkType', module: 'str | ModuleDescriptor[ProtocolBase] | Type[ProtocolBase]',
                     class_: 'str' = NULL) -> 'None':
     r"""Register a new protocol class.
 
@@ -483,7 +483,7 @@ def register_pcapng(code: 'LinkType', module: 'str | ModuleDescriptor[Protocol]
 
     """
     if isinstance(module, str):
-        module = cast('ModuleDescriptor[Protocol]', ModuleDescriptor(module, class_))
+        module = cast('ModuleDescriptor[ProtocolBase]', ModuleDescriptor(module, class_))
 
     PCAPNG.register(code, module)
     logger.debug('registered PCAP-NG linktype protocol: %s', code.name)
@@ -500,13 +500,13 @@ def register_pcapng(code: 'LinkType', module: 'str | ModuleDescriptor[Protocol]
 
 
 @overload
-def register_ethertype(code: 'EtherType', module: 'ModuleDescriptor[Protocol] | Type[Protocol]') -> 'None': ...
+def register_ethertype(code: 'EtherType', module: 'ModuleDescriptor[ProtocolBase] | Type[ProtocolBase]') -> 'None': ...
 @overload
 def register_ethertype(code: 'EtherType', module: 'str', class_: 'str') -> 'None': ...
 
 
 # NOTE: pcapkit.protocols.link.link.Link.__proto__
-def register_ethertype(code: 'EtherType', module: 'str | ModuleDescriptor[Protocol] | Type[Protocol]',
+def register_ethertype(code: 'EtherType', module: 'str | ModuleDescriptor[ProtocolBase] | Type[ProtocolBase]',
                        class_: 'str' = NULL) -> 'None':
     r"""Register a new protocol class.
 
@@ -525,7 +525,7 @@ def register_ethertype(code: 'EtherType', module: 'str | ModuleDescriptor[Protoc
 
     """
     if isinstance(module, str):
-        module = cast('ModuleDescriptor[Protocol]', ModuleDescriptor(module, class_))
+        module = cast('ModuleDescriptor[ProtocolBase]', ModuleDescriptor(module, class_))
 
     Link.register(code, module)
     logger.debug('registered ethertype protocol: %s', code.name)
@@ -542,13 +542,13 @@ def register_ethertype(code: 'EtherType', module: 'str | ModuleDescriptor[Protoc
 
 
 @overload
-def register_transtype(code: 'TransType', module: 'ModuleDescriptor[Protocol] | Type[Protocol]') -> 'None': ...
+def register_transtype(code: 'TransType', module: 'ModuleDescriptor[ProtocolBase] | Type[ProtocolBase]') -> 'None': ...
 @overload
 def register_transtype(code: 'TransType', module: 'str', class_: 'str') -> 'None': ...
 
 
 # NOTE: pcapkit.protocols.internet.internet.Internet.__proto__
-def register_transtype(code: 'TransType', module: 'str | ModuleDescriptor[Protocol] | Type[Protocol]',
+def register_transtype(code: 'TransType', module: 'str | ModuleDescriptor[ProtocolBase] | Type[ProtocolBase]',
                        class_: 'str' = NULL) -> 'None':
     r"""Register a new protocol class.
 
@@ -567,7 +567,7 @@ def register_transtype(code: 'TransType', module: 'str | ModuleDescriptor[Protoc
 
     """
     if isinstance(module, str):
-        module = cast('ModuleDescriptor[Protocol]', ModuleDescriptor(module, class_))
+        module = cast('ModuleDescriptor[ProtocolBase]', ModuleDescriptor(module, class_))
 
     Internet.register(code, module)
     logger.debug('registered transtype protocol: %s', code.name)
@@ -784,16 +784,16 @@ def register_mh_extension(code: 'MH_CGAExtension', meth: 'str | tuple[MH_Extensi
 
 
 @overload
-def register_apptype(code: 'int', module: 'ModuleDescriptor[Protocol] | Type[Protocol]', *, proto: 'TransportProtocol | str') -> 'None': ...
+def register_apptype(code: 'int', module: 'ModuleDescriptor[ProtocolBase] | Type[ProtocolBase]', *, proto: 'TransportProtocol | str') -> 'None': ...
 @overload
-def register_apptype(code: 'Enum_AppType', module: 'ModuleDescriptor[Protocol] | Type[Protocol]', *, proto: 'TransportProtocol | str' = ...) -> 'None': ...
+def register_apptype(code: 'Enum_AppType', module: 'ModuleDescriptor[ProtocolBase] | Type[ProtocolBase]', *, proto: 'TransportProtocol | str' = ...) -> 'None': ...
 @overload
 def register_apptype(code: 'int', module: 'str', class_: 'str', *, proto: 'TransportProtocol | str') -> 'None': ...
 @overload
 def register_apptype(code: 'Enum_AppType', module: 'str', class_: 'str', *, proto: 'TransportProtocol | str' = ...) -> 'None': ...
 
 
-def register_apptype(code: 'int | Enum_AppType', module: 'str | ModuleDescriptor[Protocol] | Type[Protocol]',
+def register_apptype(code: 'int | Enum_AppType', module: 'str | ModuleDescriptor[ProtocolBase] | Type[ProtocolBase]',
                      class_: 'str' = NULL, *, proto: 'TransportProtocol | str' = NULL) -> 'None':
     r"""Register a new protocol class.
 
@@ -833,13 +833,13 @@ def register_apptype(code: 'int | Enum_AppType', module: 'str | ModuleDescriptor
             proto = code.proto
         code = code.port
     if isinstance(module, str):
-        module = cast('ModuleDescriptor[Protocol]', ModuleDescriptor(module, class_))
+        module = cast('ModuleDescriptor[ProtocolBase]', ModuleDescriptor(module, class_))
 
     _reg = False
     if isinstance(proto, str):
         proto = TransportProtocol.get(proto.lower())
 
-    for test, cls in cast('dict[TransportProtocol, Type[Protocol]]', {
+    for test, cls in cast('dict[TransportProtocol, Type[ProtocolBase]]', {
         TransportProtocol.tcp: TCP,
         TransportProtocol.udp: UDP,
     }).items():
@@ -860,13 +860,13 @@ def register_apptype(code: 'int | Enum_AppType', module: 'str | ModuleDescriptor
 
 
 @overload
-def register_tcp(code: 'int | Enum_AppType', module: 'ModuleDescriptor[Protocol] | Type[Protocol]') -> 'None': ...
+def register_tcp(code: 'int | Enum_AppType', module: 'ModuleDescriptor[ProtocolBase] | Type[ProtocolBase]') -> 'None': ...
 @overload
 def register_tcp(code: 'int | Enum_AppType', module: 'str', class_: 'str') -> 'None': ...
 
 
 # NOTE: pcapkit.protocols.transport.tcp.TCP.__proto__
-def register_tcp(code: 'int | Enum_AppType', module: 'str | ModuleDescriptor[Protocol] | Type[Protocol]',
+def register_tcp(code: 'int | Enum_AppType', module: 'str | ModuleDescriptor[ProtocolBase] | Type[ProtocolBase]',
                  class_: 'str' = NULL) -> 'None':
     r"""Register a new protocol class.
 
@@ -887,7 +887,7 @@ def register_tcp(code: 'int | Enum_AppType', module: 'str | ModuleDescriptor[Pro
     if isinstance(code, Enum_AppType):
         code = code.port
     if isinstance(module, str):
-        module = cast('ModuleDescriptor[Protocol]', ModuleDescriptor(module, class_))
+        module = cast('ModuleDescriptor[ProtocolBase]', ModuleDescriptor(module, class_))
 
     TCP.register(code, module)
     logger.debug('registered TCP port: %s', code)
@@ -949,13 +949,13 @@ def register_tcp_mp_option(code: 'TCP_MPTCPOption', meth: 'str | tuple[TCP_MPOpt
 
 
 @overload
-def register_udp(code: 'int | Enum_AppType', module: 'ModuleDescriptor[Protocol] | Type[Protocol]') -> 'None': ...
+def register_udp(code: 'int | Enum_AppType', module: 'ModuleDescriptor[ProtocolBase] | Type[ProtocolBase]') -> 'None': ...
 @overload
 def register_udp(code: 'int | Enum_AppType', module: 'str', class_: 'str') -> 'None': ...
 
 
 # NOTE: pcapkit.protocols.transport.udp.UDP.__proto__
-def register_udp(code: 'int | Enum_AppType', module: 'str | ModuleDescriptor[Protocol] | Type[Protocol]',
+def register_udp(code: 'int | Enum_AppType', module: 'str | ModuleDescriptor[ProtocolBase] | Type[ProtocolBase]',
                  class_: 'str' = NULL) -> 'None':
     r"""Register a new protocol class.
 
@@ -976,7 +976,7 @@ def register_udp(code: 'int | Enum_AppType', module: 'str | ModuleDescriptor[Pro
     if isinstance(code, Enum_AppType):
         code = code.port
     if isinstance(module, str):
-        module = cast('ModuleDescriptor[Protocol]', ModuleDescriptor(module, class_))
+        module = cast('ModuleDescriptor[ProtocolBase]', ModuleDescriptor(module, class_))
 
     UDP.register(code, module)
     logger.debug('registered UDP port: %s', code)
@@ -988,13 +988,13 @@ def register_udp(code: 'int | Enum_AppType', module: 'str | ModuleDescriptor[Pro
 
 
 @overload
-def register_sctp(code: 'int | SCTP_PayloadProtocolIdentifier', module: 'ModuleDescriptor[Protocol] | Type[Protocol]') -> 'None': ...
+def register_sctp(code: 'int | SCTP_PayloadProtocolIdentifier', module: 'ModuleDescriptor[ProtocolBase] | Type[ProtocolBase]') -> 'None': ...
 @overload
 def register_sctp(code: 'int | SCTP_PayloadProtocolIdentifier', module: 'str', class_: 'str') -> 'None': ...
 
 
 # NOTE: pcapkit.protocols.transport.sctp.SCTP.__proto__
-def register_sctp(code: 'int | SCTP_PayloadProtocolIdentifier', module: 'str | ModuleDescriptor[Protocol] | Type[Protocol]',
+def register_sctp(code: 'int | SCTP_PayloadProtocolIdentifier', module: 'str | ModuleDescriptor[ProtocolBase] | Type[ProtocolBase]',
                   class_: 'str' = NULL) -> 'None':
     r"""Register a new protocol class.
 
@@ -1020,7 +1020,7 @@ def register_sctp(code: 'int | SCTP_PayloadProtocolIdentifier', module: 'str | M
 
     """
     if isinstance(module, str):
-        module = cast('ModuleDescriptor[Protocol]', ModuleDescriptor(module, class_))
+        module = cast('ModuleDescriptor[ProtocolBase]', ModuleDescriptor(module, class_))
 
     SCTP.register(code, module)
     logger.debug('registered SCTP payload protocol identifier: %s', code)
diff --git a/pcapkit/foundation/traceflow/traceflow.py b/pcapkit/foundation/traceflow/traceflow.py
index 82a37966a..b45bf42ba 100644
--- a/pcapkit/foundation/traceflow/traceflow.py
+++ b/pcapkit/foundation/traceflow/traceflow.py
@@ -48,7 +48,7 @@
     from typing_extensions import Literal, Self
 
     from pcapkit.corekit.infoclass import Info
-    from pcapkit.protocols.protocol import ProtocolBase as Protocol
+    from pcapkit.protocols.protocol import ProtocolBase
 
     CallbackFn = Callable[[_IT], None]
 
@@ -65,7 +65,7 @@ class TraceFlowMeta(abc.ABCMeta):
         #: Protocol name of current object.
         __protocol_name__: 'str'
         #: Protocol of current object.
-        __protocol_type__: 'Type[Protocol]'
+        __protocol_type__: 'Type[ProtocolBase]'
 
     @property
     def name(cls) -> 'str':
@@ -75,7 +75,7 @@ def name(cls) -> 'str':
         return cls.__name__
 
     @property
-    def protocol(cls) -> 'Type[Protocol]':
+    def protocol(cls) -> 'Type[ProtocolBase]':
         """Protocol of current object."""
         if hasattr(cls, '__protocol_type__'):
             return cls.__protocol_type__
@@ -131,7 +131,7 @@ class TraceFlowBase(Generic[_DT, _BT, _IT, _PT], metaclass=TraceFlowMeta):
         #: Protocol name of current reassembly object.
         __protocol_name__: 'str'
         #: Protocol of current reassembly object.
-        __protocol_type__: 'Type[Protocol]'
+        __protocol_type__: 'Type[ProtocolBase]'
 
         #: List of callback functions upon reassembled datagram.
         __callback_fn__: 'list[CallbackFn]'
@@ -179,7 +179,7 @@ def name(self) -> 'str':
         return type(self).name  # type: ignore[return-value]
 
     @property
-    def protocol(self) -> 'Type[Protocol]':
+    def protocol(self) -> 'Type[ProtocolBase]':
         """Protocol of current flow tracing object.
 
         Note:
diff --git a/pcapkit/protocols/application/application.py b/pcapkit/protocols/application/application.py
index b00fe99ac..ac55744a0 100644
--- a/pcapkit/protocols/application/application.py
+++ b/pcapkit/protocols/application/application.py
@@ -16,8 +16,7 @@
 
 from pcapkit.corekit.protochain import ProtoChain
 from pcapkit.protocols.misc.null import NoPayload
-from pcapkit.protocols.protocol import _PT, _ST
-from pcapkit.protocols.protocol import ProtocolBase as Protocol
+from pcapkit.protocols.protocol import _PT, _ST, ProtocolBase
 from pcapkit.utilities.exceptions import IntError, UnsupportedCall
 
 if TYPE_CHECKING:
@@ -28,7 +27,7 @@
 __all__ = ['Application']
 
 
-class Application(Protocol[_PT, _ST], Generic[_PT, _ST]):  # pylint: disable=abstract-method
+class Application(ProtocolBase[_PT, _ST], Generic[_PT, _ST]):  # pylint: disable=abstract-method
     """Abstract base class for transport layer protocol family."""
 
     ##########################################################################
diff --git a/pcapkit/protocols/data/data.py b/pcapkit/protocols/data/data.py
index eb1a35e1d..7f142dc8c 100644
--- a/pcapkit/protocols/data/data.py
+++ b/pcapkit/protocols/data/data.py
@@ -10,7 +10,7 @@
 if TYPE_CHECKING:
     from typing import Type
 
-    from pcapkit.protocols.protocol import ProtocolBase as Protocol
+    from pcapkit.protocols.protocol import ProtocolBase
 
 
 class Data(Info):
@@ -22,4 +22,4 @@ class Data(Info):
         #: Next field name, i.e., the name of the payload field.
         __next_name__: 'str'
         #: Next field type, i.e., the type of the payload field.
-        __next_type__: 'Type[Protocol]'
+        __next_type__: 'Type[ProtocolBase]'
diff --git a/pcapkit/protocols/internet/ah.py b/pcapkit/protocols/internet/ah.py
index 49157561d..8dcad7e9d 100644
--- a/pcapkit/protocols/internet/ah.py
+++ b/pcapkit/protocols/internet/ah.py
@@ -40,7 +40,7 @@
     from typing_extensions import Literal
 
     from pcapkit.corekit.protochain import ProtoChain
-    from pcapkit.protocols.protocol import ProtocolBase as Protocol
+    from pcapkit.protocols.protocol import ProtocolBase
     from pcapkit.protocols.schema.schema import Schema
 
 __all__ = ['AH']
@@ -65,7 +65,7 @@ def length(self) -> 'int':
         return self._info.length
 
     @property
-    def payload(self) -> 'Protocol | NoReturn':
+    def payload(self) -> 'ProtocolBase | NoReturn':
         """Payload of current instance.
 
         Raises:
@@ -160,7 +160,7 @@ def make(self,
              spi: 'int' = 0,
              seq: 'int' = 0,
              icv: 'bytes' = b'',
-             payload: 'bytes | Protocol | Schema' = b'',
+             payload: 'bytes | ProtocolBase | Schema' = b'',
              **kwargs: 'Any') -> 'Schema_AH':
         """Make (construct) packet data.
 
diff --git a/pcapkit/protocols/internet/esp.py b/pcapkit/protocols/internet/esp.py
index 73753d28e..d997dd869 100644
--- a/pcapkit/protocols/internet/esp.py
+++ b/pcapkit/protocols/internet/esp.py
@@ -192,7 +192,7 @@
     from aenum import IntEnum as AenumEnum
     from typing_extensions import Literal
 
-    from pcapkit.protocols.protocol import ProtocolBase as Protocol
+    from pcapkit.protocols.protocol import ProtocolBase
 
 #: Cached :mod:`cryptography` primitives, c.f. :func:`load_cryptography`.
 #: :data:`NotImplemented` means the import has not been attempted yet, and
@@ -1149,7 +1149,7 @@ def make(self,
              iv: 'Optional[bytes]' = None,
              pad_len: 'Optional[int]' = None,
              icv: 'bytes' = b'',
-             payload: 'bytes | Protocol | Schema' = b'',
+             payload: 'bytes | ProtocolBase | Schema' = b'',
              **kwargs: 'Any') -> 'Schema_ESP':
         """Make (construct) packet data.
 
@@ -1319,7 +1319,7 @@ def _make_data(cls, data: 'Data_ESP') -> 'dict[str, Any]':  # type: ignore[overr
         }
 
     @staticmethod
-    def _payload_bytes(payload: 'bytes | Protocol | Schema') -> 'bytes':
+    def _payload_bytes(payload: 'bytes | ProtocolBase | Schema') -> 'bytes':
         """Render ``payload`` as :obj:`bytes`.
 
         Args:
diff --git a/pcapkit/protocols/internet/hip.py b/pcapkit/protocols/internet/hip.py
index 77738eda7..e929057b1 100644
--- a/pcapkit/protocols/internet/hip.py
+++ b/pcapkit/protocols/internet/hip.py
@@ -222,7 +222,7 @@
     from pcapkit.const.hip.transport import Transport as Enum_Transport
     from pcapkit.corekit.protochain import ProtoChain
     from pcapkit.protocols.data.internet.hip import Parameter as Data_Parameter
-    from pcapkit.protocols.protocol import ProtocolBase as Protocol
+    from pcapkit.protocols.protocol import ProtocolBase
     from pcapkit.protocols.schema.internet.hip import Parameter as Schema_Parameter
 
     Parameter = OrderedMultiDict[Enum_Parameter, Data_Parameter]
@@ -451,7 +451,7 @@ def length(self) -> 'int':
         return self._info.length
 
     @property
-    def payload(self) -> 'Protocol | NoReturn':
+    def payload(self) -> 'ProtocolBase | NoReturn':
         """Payload of current instance.
 
         Raises:
@@ -580,7 +580,7 @@ def make(self,
              shit: 'int' = 0,
              rhit: 'int' = 0,
              parameters: 'Optional[list[Schema_Parameter | tuple[Enum_Parameter, dict[str, Any]] | bytes] | Parameter]' = None,  # pylint: disable=line-too-long
-             payload: 'bytes | Protocol | Schema' = b'',
+             payload: 'bytes | ProtocolBase | Schema' = b'',
              **kwargs: 'Any') -> 'Schema_HIP':
         """Make (construct) packet data.
 
diff --git a/pcapkit/protocols/internet/hopopt.py b/pcapkit/protocols/internet/hopopt.py
index b10118173..751063142 100644
--- a/pcapkit/protocols/internet/hopopt.py
+++ b/pcapkit/protocols/internet/hopopt.py
@@ -107,7 +107,7 @@
     from pcapkit.protocols.data.internet.hopopt import Option as Data_Option
     from pcapkit.protocols.data.internet.hopopt import QuickStartOption as Data_QuickStartOption
     from pcapkit.protocols.data.internet.hopopt import SMFDPDOption as Data_SMFDPDOption
-    from pcapkit.protocols.protocol import ProtocolBase as Protocol
+    from pcapkit.protocols.protocol import ProtocolBase
     from pcapkit.protocols.schema.internet.hopopt import Option as Schema_Option
     from pcapkit.protocols.schema.internet.hopopt import QuickStartOption as Schema_QuickStartOption
     from pcapkit.protocols.schema.internet.hopopt import SMFDPDOption as Schema_SMFDPDOption
@@ -228,7 +228,7 @@ def length(self) -> 'int':
         return self._info.length
 
     @property
-    def payload(self) -> 'Protocol | NoReturn':
+    def payload(self) -> 'ProtocolBase | NoReturn':
         """Payload of current instance.
 
         Raises:
@@ -314,7 +314,7 @@ def make(self,
              next_namespace: 'Optional[dict[str, int] | dict[int, str] | Type[StdlibEnum] | Type[AenumEnum]]' = None,  # pylint: disable=line-too-long
              next_reversed: 'bool' = False,
              options: 'Optional[list[Schema_Option | tuple[Enum_Option, dict[str, Any]] | bytes] | Option]' = None,  # pylint: disable=line-too-long
-             payload: 'bytes | Protocol | Schema' = b'',
+             payload: 'bytes | ProtocolBase | Schema' = b'',
              **kwargs: 'Any') -> 'Schema_HOPOPT':
         """Make (construct) packet data.
 
diff --git a/pcapkit/protocols/internet/internet.py b/pcapkit/protocols/internet/internet.py
index a98d91093..514afca93 100644
--- a/pcapkit/protocols/internet/internet.py
+++ b/pcapkit/protocols/internet/internet.py
@@ -17,8 +17,7 @@
 from pcapkit.const.reg.transtype import TransType as Enum_TransType
 from pcapkit.corekit.module import ModuleDescriptor
 from pcapkit.corekit.protochain import ProtoChain
-from pcapkit.protocols.protocol import _PT, _ST
-from pcapkit.protocols.protocol import ProtocolBase as Protocol
+from pcapkit.protocols.protocol import _PT, _ST, ProtocolBase
 from pcapkit.utilities.decorators import beholder
 from pcapkit.utilities.exceptions import RegistryError
 from pcapkit.utilities.warnings import RegistryWarning, warn
@@ -31,7 +30,7 @@
 __all__ = ['Internet']
 
 
-class Internet(Protocol[_PT, _ST], Generic[_PT, _ST]):  # pylint: disable=abstract-method
+class Internet(ProtocolBase[_PT, _ST], Generic[_PT, _ST]):  # pylint: disable=abstract-method
     """Abstract base class for internet layer protocol family.
 
     This class currently supports parsing of the following protocols, which are
@@ -85,7 +84,7 @@ class Internet(Protocol[_PT, _ST], Generic[_PT, _ST]):  # pylint: disable=abstra
     #: Layer of protocol.
     __layer__ = 'Internet'  # type: Literal['Internet']
 
-    #: DefaultDict[int, ModuleDescriptor[Protocol] | ~typing.Type[Protocol]]: Protocol index mapping for decoding next layer,
+    #: DefaultDict[int, ModuleDescriptor[ProtocolBase] | ~typing.Type[ProtocolBase]]: Protocol index mapping for decoding next layer,
     #: c.f. :meth:`self._decode_next_layer <pcapkit.protocols.internet.internet.Internet._decode_next_layer>`
     #: & :meth:`self._import_next_layer <pcapkit.protocols.internet.internet.Internet._import_next_layer>`.
     __proto__ = collections.defaultdict(
@@ -133,7 +132,7 @@ def layer(self) -> 'Literal["Internet"]':
     ##########################################################################
 
     @classmethod
-    def register(cls, code: 'Enum_TransType', protocol: 'ModuleDescriptor[Protocol] | Type[Protocol]') -> 'None':  # type: ignore[override]
+    def register(cls, code: 'Enum_TransType', protocol: 'ModuleDescriptor[ProtocolBase] | Type[ProtocolBase]') -> 'None':  # type: ignore[override]
         r"""Register a new protocol class.
 
         Notes:
@@ -161,7 +160,7 @@ def register(cls, code: 'Enum_TransType', protocol: 'ModuleDescriptor[Protocol]
         """
         if isinstance(protocol, ModuleDescriptor):
             protocol = protocol.klass
-        if not issubclass(protocol, Protocol):
+        if not issubclass(protocol, ProtocolBase):
             raise RegistryError(f'protocol must be a Protocol subclass, not {protocol!r}')
         incumbent = cls.__proto__.get(code)
         if incumbent is not None and incumbent is not protocol:
@@ -213,7 +212,7 @@ def _decode_next_layer(self, dict_: '_PT', proto: 'Optional[int]' = None,  # pyl
             be included when :meth:`Info.to_dict <pcapkit.corekit.infoclass.Info.to_dict>` is called.
 
         """
-        next_ = cast('Protocol',  # type: ignore[redundant-cast]
+        next_ = cast('ProtocolBase',  # type: ignore[redundant-cast]
                      self._import_next_layer(proto, length, packet=packet, version=version,
                                              payload=payload))  # type: ignore[arg-type,misc,call-arg]
         info, chain = next_.info, next_.protochain
@@ -240,7 +239,7 @@ def _decode_next_layer(self, dict_: '_PT', proto: 'Optional[int]' = None,  # pyl
     @beholder  # type: ignore[arg-type]
     def _import_next_layer(self, proto: 'int', length: 'Optional[int]' = None, *,  # pylint: disable=arguments-differ
                            packet: 'Optional[dict[str, Any]]' = None, version: 'Literal[4, 6]' = 4,
-                           extension: 'bool' = False, payload: 'Optional[bytes]' = None) -> 'Protocol':
+                           extension: 'bool' = False, payload: 'Optional[bytes]' = None) -> 'ProtocolBase':
         """Import next layer extractor.
 
         Arguments:
@@ -257,7 +256,7 @@ def _import_next_layer(self, proto: 'int', length: 'Optional[int]' = None, *,  #
 
         """
         if TYPE_CHECKING:
-            protocol: 'Type[Protocol]'
+            protocol: 'Type[ProtocolBase]'
 
         if payload is None:
             file_ = self.__header__.get_payload()
diff --git a/pcapkit/protocols/internet/ipv4.py b/pcapkit/protocols/internet/ipv4.py
index c034e9796..dc0883aee 100644
--- a/pcapkit/protocols/internet/ipv4.py
+++ b/pcapkit/protocols/internet/ipv4.py
@@ -113,7 +113,7 @@
     from typing_extensions import Literal
 
     from pcapkit.protocols.data.internet.ipv4 import Option as Data_Option
-    from pcapkit.protocols.protocol import ProtocolBase as Protocol
+    from pcapkit.protocols.protocol import ProtocolBase
     from pcapkit.protocols.schema.internet.ipv4 import Option as Schema_Option
 
     Option = OrderedMultiDict[Enum_OptionNumber, Data_Option]
@@ -363,7 +363,7 @@ def make(self,
              src: 'IPv4Address | str | int | bytes' = '127.0.0.1',
              dst: 'IPv4Address | str | int | bytes' = '0.0.0.0',  # nosec: B104
              options: 'Optional[list[Schema_Option | tuple[Enum_OptionNumber, dict[str, Any]] | bytes] | Option]' = None,  # pylint: disable=line-too-long
-             payload: 'bytes | Protocol | Schema' = b'',
+             payload: 'bytes | ProtocolBase | Schema' = b'',
              **kwargs: 'Any') -> 'Schema_IPv4':
         """Make (construct) packet data.
 
diff --git a/pcapkit/protocols/internet/ipv6.py b/pcapkit/protocols/internet/ipv6.py
index ea41e5f5c..100d90992 100644
--- a/pcapkit/protocols/internet/ipv6.py
+++ b/pcapkit/protocols/internet/ipv6.py
@@ -46,7 +46,7 @@
     from aenum import IntEnum as AenumEnum
     from typing_extensions import Literal
 
-    from pcapkit.protocols.protocol import ProtocolBase as Protocol
+    from pcapkit.protocols.protocol import ProtocolBase
     from pcapkit.protocols.schema.schema import Schema
 
 __all__ = ['IPv6']
@@ -88,7 +88,7 @@ def dst(self) -> 'IPv6Address':
         return self._info.dst
 
     @property
-    def extension_headers(self) -> 'OrderedMultiDict[Enum_ExtensionHeader, Protocol]':
+    def extension_headers(self) -> 'OrderedMultiDict[Enum_ExtensionHeader, ProtocolBase]':
         """IPv6 extension header records."""
         return self._exthdr
 
@@ -172,7 +172,7 @@ def make(self,
              hop_limit: 'int' = 64,  # reasonable default
              src: 'IPv6Address | str | bytes | int' = '::1',
              dst: 'IPv6Address | str | bytes | int' = '::',
-             payload: 'bytes | Protocol | Schema' = b'',
+             payload: 'bytes | ProtocolBase | Schema' = b'',
              **kwargs: 'Any') -> 'Schema_IPv6':
         """Make (construct) packet data.
 
@@ -304,7 +304,7 @@ def _decode_next_layer(self, ipv6: 'Data_IPv6', proto: 'Optional[int]' = None,
 
         """
         #: Extension headers.
-        self._exthdr = OrderedMultiDict()  # type: OrderedMultiDict[Enum_ExtensionHeader, Protocol] # pylint: disable=attribute-defined-outside-init
+        self._exthdr = OrderedMultiDict()  # type: OrderedMultiDict[Enum_ExtensionHeader, ProtocolBase] # pylint: disable=attribute-defined-outside-init
 
         hdr_len = self.length       # header length
         raw_len = ipv6.payload      # payload length
@@ -372,7 +372,7 @@ def _decode_next_layer(self, ipv6: 'Data_IPv6', proto: 'Optional[int]' = None,
     @beholder  # type: ignore[arg-type]
     def _import_next_layer(self, proto: 'int', length: 'Optional[int]' = None, *,  # pylint: disable=arguments-differ
                            packet: 'Optional[dict[str, Any]]' = None, version: 'Literal[4, 6]' = 4,
-                           extension: 'bool' = False, payload: 'Optional[bytes]' = None) -> 'Protocol':
+                           extension: 'bool' = False, payload: 'Optional[bytes]' = None) -> 'ProtocolBase':
         """Import next layer extractor.
 
         Arguments:
@@ -389,7 +389,7 @@ def _import_next_layer(self, proto: 'int', length: 'Optional[int]' = None, *,  #
 
         """
         if TYPE_CHECKING:
-            protocol: 'Type[Protocol]'
+            protocol: 'Type[ProtocolBase]'
 
         if payload is None:
             file_ = self.__header__.get_payload()
diff --git a/pcapkit/protocols/internet/ipv6_frag.py b/pcapkit/protocols/internet/ipv6_frag.py
index a8788e701..27c798cbd 100644
--- a/pcapkit/protocols/internet/ipv6_frag.py
+++ b/pcapkit/protocols/internet/ipv6_frag.py
@@ -40,7 +40,7 @@
     from typing_extensions import Literal
 
     from pcapkit.corekit.protochain import ProtoChain
-    from pcapkit.protocols.protocol import ProtocolBase as Protocol
+    from pcapkit.protocols.protocol import ProtocolBase
     from pcapkit.protocols.schema.schema import Schema
 
 __all__ = ['IPv6_Frag']
@@ -70,7 +70,7 @@ def length(self) -> 'Literal[8]':
         return 8
 
     @property
-    def payload(self) -> 'Protocol | NoReturn':
+    def payload(self) -> 'ProtocolBase | NoReturn':
         """Payload of current instance.
 
         Raises:
@@ -161,7 +161,7 @@ def make(self,
              offset: 'int' = 0,
              mf: 'bool' = False,
              id: 'int' = 0,
-             payload: 'bytes | Protocol | Schema' = b'',
+             payload: 'bytes | ProtocolBase | Schema' = b'',
              **kwargs: 'Any') -> 'Schema_IPv6_Frag':
         """Make (construct) packet data.
 
diff --git a/pcapkit/protocols/internet/ipv6_opts.py b/pcapkit/protocols/internet/ipv6_opts.py
index af6894648..6d3db2385 100644
--- a/pcapkit/protocols/internet/ipv6_opts.py
+++ b/pcapkit/protocols/internet/ipv6_opts.py
@@ -110,7 +110,7 @@
     from pcapkit.protocols.data.internet.ipv6_opts import Option as Data_Option
     from pcapkit.protocols.data.internet.ipv6_opts import QuickStartOption as Data_QuickStartOption
     from pcapkit.protocols.data.internet.ipv6_opts import SMFDPDOption as Data_SMFDPDOption
-    from pcapkit.protocols.protocol import ProtocolBase as Protocol
+    from pcapkit.protocols.protocol import ProtocolBase
     from pcapkit.protocols.schema.internet.ipv6_opts import Option as Schema_Option
     from pcapkit.protocols.schema.internet.ipv6_opts import \
         QuickStartOption as Schema_QuickStartOption
@@ -238,7 +238,7 @@ def length(self) -> 'int':
         return self._info.length
 
     @property
-    def payload(self) -> 'Protocol | NoReturn':
+    def payload(self) -> 'ProtocolBase | NoReturn':
         """Payload of current instance.
 
         Raises:
@@ -325,7 +325,7 @@ def make(self,
              next_namespace: 'Optional[dict[str, int] | dict[int, str] | Type[StdlibEnum] | Type[AenumEnum]]' = None,  # pylint: disable=line-too-long
              next_reversed: 'bool' = False,
              options: 'Optional[list[Schema_Option | tuple[Enum_Option, dict[str, Any]] | bytes] | Option]' = None,  # pylint: disable=line-too-long
-             payload: 'bytes | Protocol | Schema' = b'',
+             payload: 'bytes | ProtocolBase | Schema' = b'',
              **kwargs: 'Any') -> 'Schema_IPv6_Opts':
         """Make (construct) packet data.
 
diff --git a/pcapkit/protocols/internet/ipv6_route.py b/pcapkit/protocols/internet/ipv6_route.py
index 70b18e55a..7a5be1d8a 100644
--- a/pcapkit/protocols/internet/ipv6_route.py
+++ b/pcapkit/protocols/internet/ipv6_route.py
@@ -57,7 +57,7 @@
     from typing_extensions import Literal
 
     from pcapkit.corekit.protochain import ProtoChain
-    from pcapkit.protocols.protocol import ProtocolBase as Protocol
+    from pcapkit.protocols.protocol import ProtocolBase
     from pcapkit.protocols.schema.internet.ipv6_route import RoutingType as Schema_RoutingType
 
     TypeParser = Callable[[Schema_RoutingType, NamedArg(Schema_IPv6_Route, 'header')], Data_IPv6_Route]
@@ -132,7 +132,7 @@ def length(self) -> 'int':
         return self._info.length
 
     @property
-    def payload(self) -> 'Protocol | NoReturn':
+    def payload(self) -> 'ProtocolBase | NoReturn':
         """Payload of current instance.
 
         Raises:
@@ -264,7 +264,7 @@ def make(self,
              type_reversed: 'bool' = False,
              seg_left: 'int' = 0,
              data: 'bytes | Data_IPv6_Route | Schema_RoutingType | dict[str, Any]' = b'\x00\x00\x00\x00',
-             payload: 'Protocol | Schema | bytes' = b'',
+             payload: 'ProtocolBase | Schema | bytes' = b'',
              **kwargs: 'Any') -> 'Schema_IPv6_Route':
         """Make (construct) packet data.
 
diff --git a/pcapkit/protocols/internet/ipx.py b/pcapkit/protocols/internet/ipx.py
index e1ae5855b..29b2182a2 100644
--- a/pcapkit/protocols/internet/ipx.py
+++ b/pcapkit/protocols/internet/ipx.py
@@ -42,7 +42,7 @@
     from aenum import IntEnum as AenumEnum
     from typing_extensions import Literal
 
-    from pcapkit.protocols.protocol import ProtocolBase as Protocol
+    from pcapkit.protocols.protocol import ProtocolBase
     from pcapkit.protocols.schema.schema import Schema
 
 __all__ = ['IPX']
@@ -120,7 +120,7 @@ def make(self,
              type_reversed: 'bool' = False,
              dst: 'bytes' = b'\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00',
              src: 'bytes' = b'\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00',
-             payload: 'bytes | Protocol | Schema' = b'',
+             payload: 'bytes | ProtocolBase | Schema' = b'',
              **kwargs: 'Any') -> 'Schema_IPX':
         """Make (construct) packet data.
 
diff --git a/pcapkit/protocols/internet/mh.py b/pcapkit/protocols/internet/mh.py
index 5cd1918f1..713bcb7ac 100644
--- a/pcapkit/protocols/internet/mh.py
+++ b/pcapkit/protocols/internet/mh.py
@@ -504,7 +504,7 @@
     from pcapkit.corekit.multidict import OrderedMultiDict
     from pcapkit.corekit.protochain import ProtoChain
     from pcapkit.protocols.data.internet.mh import Option as Data_Option
-    from pcapkit.protocols.protocol import ProtocolBase as Protocol
+    from pcapkit.protocols.protocol import ProtocolBase
     from pcapkit.protocols.schema.internet.mh import Option as Schema_Option
     from pcapkit.protocols.schema.internet.mh import Packet as Schema_Packet
     from pcapkit.protocols.schema.schema import Schema
@@ -1283,7 +1283,7 @@ def length(self) -> 'int':
         return self._info.length
 
     @property
-    def payload(self) -> 'Protocol | NoReturn':
+    def payload(self) -> 'ProtocolBase | NoReturn':
         """Payload of current instance.
 
         Raises:
@@ -1407,7 +1407,7 @@ def make(self,
              type_reversed: 'bool' = False,
              chksum: 'bytes' = b'',
              data: 'bytes | Data_MH | Schema_Packet | dict[str, Any]' = b'\x00\x00',  # minimum length
-             payload: 'Protocol | Schema | bytes' = b'',
+             payload: 'ProtocolBase | Schema | bytes' = b'',
              **kwargs: 'Any') -> 'Schema_MH':
         """Make (construct) packet data.
 
diff --git a/pcapkit/protocols/link/arp.py b/pcapkit/protocols/link/arp.py
index a06b66c8f..50f5da67d 100644
--- a/pcapkit/protocols/link/arp.py
+++ b/pcapkit/protocols/link/arp.py
@@ -63,7 +63,7 @@
     from aenum import IntEnum as AenumEnum
     from typing_extensions import Literal
 
-    from pcapkit.protocols.protocol import ProtocolBase as Protocol
+    from pcapkit.protocols.protocol import ProtocolBase
     from pcapkit.protocols.schema.schema import Schema
 
 __all__ = ['ARP', 'InARP']
@@ -224,7 +224,7 @@ def make(self, *,
              spa: 'IPv4Address | IPv6Address | str | bytes | bytearray' = '0.0.0.0',  # nosec: B104
              tha: 'str | bytes | bytearray' = '00:00:00:00:00:00',
              tpa: 'IPv4Address | IPv6Address | str | bytes | bytearray' = '0.0.0.0',  # nosec: B104
-             payload: 'bytes | Protocol | Schema' = b'',
+             payload: 'bytes | ProtocolBase | Schema' = b'',
              **kwargs: 'Any') -> 'Schema_ARP':
         """Make (construct) packet data.
 
diff --git a/pcapkit/protocols/link/ethernet.py b/pcapkit/protocols/link/ethernet.py
index 1da115e7b..bafc94269 100644
--- a/pcapkit/protocols/link/ethernet.py
+++ b/pcapkit/protocols/link/ethernet.py
@@ -44,7 +44,7 @@
     from aenum import IntEnum as AenumEnum
     from typing_extensions import Literal
 
-    from pcapkit.protocols.protocol import ProtocolBase as Protocol
+    from pcapkit.protocols.protocol import ProtocolBase
     from pcapkit.protocols.schema.schema import Schema
 
 __all__ = ['Ethernet']
@@ -144,7 +144,7 @@ def make(self,
              type_default: 'Optional[int]' = None,
              type_namespace: 'Optional[dict[str, int] | dict[int, str] | Type[StdlibEnum] | Type[AenumEnum]]' = None,  # pylint: disable=line-too-long
              type_reversed: 'bool' = False,
-             payload: 'bytes | Protocol | Schema' = b'',
+             payload: 'bytes | ProtocolBase | Schema' = b'',
              **kwargs: 'Any') -> 'Schema_Ethernet':
         """Make (construct) packet data.
 
diff --git a/pcapkit/protocols/link/l2tpv2.py b/pcapkit/protocols/link/l2tpv2.py
index 4c58fad5c..ff05dea41 100644
--- a/pcapkit/protocols/link/l2tpv2.py
+++ b/pcapkit/protocols/link/l2tpv2.py
@@ -67,7 +67,7 @@
     from aenum import IntEnum as AenumEnum
     from typing_extensions import Literal
 
-    from pcapkit.protocols.protocol import ProtocolBase as Protocol
+    from pcapkit.protocols.protocol import ProtocolBase
     from pcapkit.protocols.schema.schema import Schema
 
 __all__ = ['L2TPv2']
@@ -254,7 +254,7 @@ def make(self,
              ns: 'Optional[int]' = None,
              nr: 'Optional[int]' = None,
              offset: 'Optional[int]' = None,
-             payload: 'bytes | Protocol | Schema' = b'',
+             payload: 'bytes | ProtocolBase | Schema' = b'',
              **kwargs: 'Any') -> 'Schema_L2TP':  # pylint: disable=unused-argument
         """Make (construct) packet data.
 
diff --git a/pcapkit/protocols/link/link.py b/pcapkit/protocols/link/link.py
index 7732e3066..2e761824d 100644
--- a/pcapkit/protocols/link/link.py
+++ b/pcapkit/protocols/link/link.py
@@ -21,8 +21,7 @@
 
 from pcapkit.const.reg.ethertype import EtherType as Enum_EtherType
 from pcapkit.corekit.module import ModuleDescriptor
-from pcapkit.protocols.protocol import _PT, _ST
-from pcapkit.protocols.protocol import ProtocolBase as Protocol
+from pcapkit.protocols.protocol import _PT, _ST, ProtocolBase
 from pcapkit.utilities.exceptions import RegistryError
 from pcapkit.utilities.warnings import RegistryWarning, warn
 
@@ -34,7 +33,7 @@
 __all__ = ['Link']
 
 
-class Link(Protocol[_PT, _ST], Generic[_PT, _ST]):  # pylint: disable=abstract-method
+class Link(ProtocolBase[_PT, _ST], Generic[_PT, _ST]):  # pylint: disable=abstract-method
     """Abstract base class for link layer protocol family.
 
     This class currently supports parsing of the following protocols, which are
@@ -70,7 +69,7 @@ class Link(Protocol[_PT, _ST], Generic[_PT, _ST]):  # pylint: disable=abstract-m
     #: Layer of protocol.
     __layer__ = 'Link'  # type: Literal['Link']
 
-    #: DefaultDict[int, ModuleDescriptor[Protocol] | ~typing.Type[Protocol]]: Protocol index mapping for decoding next layer,
+    #: DefaultDict[int, ModuleDescriptor[ProtocolBase] | ~typing.Type[ProtocolBase]]: Protocol index mapping for decoding next layer,
     #: c.f. :meth:`self._decode_next_layer <pcapkit.protocols.protocol.Protocol._decode_next_layer>`
     #: & :meth:`self._import_next_layer <pcapkit.protocols.protocol.Protocol._import_next_layer>`.
     __proto__ = collections.defaultdict(
@@ -96,7 +95,7 @@ class Link(Protocol[_PT, _ST], Generic[_PT, _ST]):  # pylint: disable=abstract-m
             # c.f., https://en.wikipedia.org/wiki/EtherType#Values
             0x8137:                                             ModuleDescriptor('pcapkit.protocols.internet.ipx',  'IPX'),
         },
-    )  # type: DefaultDict[int | Enum_EtherType, ModuleDescriptor[Protocol] | Type[Protocol]]
+    )  # type: DefaultDict[int | Enum_EtherType, ModuleDescriptor[ProtocolBase] | Type[ProtocolBase]]
 
     ##########################################################################
     # Properties.
@@ -113,7 +112,7 @@ def layer(self) -> 'Literal["Link"]':
     ##########################################################################
 
     @classmethod
-    def register(cls, code: 'Enum_EtherType', protocol: 'ModuleDescriptor[Protocol] | Type[Protocol]') -> 'None':  # type: ignore[override]
+    def register(cls, code: 'Enum_EtherType', protocol: 'ModuleDescriptor[ProtocolBase] | Type[ProtocolBase]') -> 'None':  # type: ignore[override]
         r"""Register a new protocol class.
 
         Notes:
@@ -141,7 +140,7 @@ def register(cls, code: 'Enum_EtherType', protocol: 'ModuleDescriptor[Protocol]
         """
         if isinstance(protocol, ModuleDescriptor):
             protocol = protocol.klass
-        if not issubclass(protocol, Protocol):
+        if not issubclass(protocol, ProtocolBase):
             raise RegistryError(f'protocol must be a Protocol subclass, not {protocol!r}')
         incumbent = cls.__proto__.get(code)
         if incumbent is not None and incumbent is not protocol:
diff --git a/pcapkit/protocols/link/ospf.py b/pcapkit/protocols/link/ospf.py
index 02d67a6f8..9438cad27 100644
--- a/pcapkit/protocols/link/ospf.py
+++ b/pcapkit/protocols/link/ospf.py
@@ -60,7 +60,7 @@
     from aenum import IntEnum as AenumEnum
     from typing_extensions import Literal
 
-    from pcapkit.protocols.protocol import ProtocolBase as Protocol
+    from pcapkit.protocols.protocol import ProtocolBase
     from pcapkit.protocols.schema.schema import Schema
 
 __all__ = ['OSPF']
@@ -208,7 +208,7 @@ def make(self,
              auth_type_namespace: 'Optional[dict[str, int] | dict[int, str] | Type[StdlibEnum] | Type[AenumEnum]]' = None,  # pylint: disable=line-too-long
              auth_type_reversed: 'bool' = False,
              auth_data: 'bytes | Schema_CrytographicAuthentication | Data_CrytographicAuthentication' = b'\x00\x00\x00\x00\x00\x00\x00\x00',
-             payload: 'bytes | Protocol | Schema' = b'',
+             payload: 'bytes | ProtocolBase | Schema' = b'',
              **kwargs: 'Any') -> 'Schema_OSPF':
         """Make (construct) packet data.
 
diff --git a/pcapkit/protocols/link/vlan.py b/pcapkit/protocols/link/vlan.py
index 812f5b290..a9a5db0e9 100644
--- a/pcapkit/protocols/link/vlan.py
+++ b/pcapkit/protocols/link/vlan.py
@@ -68,7 +68,7 @@
     from aenum import IntEnum as AenumEnum
     from typing_extensions import Literal
 
-    from pcapkit.protocols.protocol import ProtocolBase as Protocol
+    from pcapkit.protocols.protocol import ProtocolBase
     from pcapkit.protocols.schema.link.vlan import TCIType
     from pcapkit.protocols.schema.schema import Schema
 
@@ -177,7 +177,7 @@ def make(self,
              type_default: 'Optional[int]' = None,
              type_namespace: 'Optional[dict[str, int] | dict[int, str] | Type[StdlibEnum] | Type[AenumEnum]]' = None,  # pylint: disable=line-too-long
              type_reversed: 'bool' = False,
-             payload: 'bytes | Protocol | Schema' = b'',
+             payload: 'bytes | ProtocolBase | Schema' = b'',
              **kwargs: 'Any') -> 'Schema_VLAN':
         """Make (construct) packet data.
 
diff --git a/pcapkit/protocols/misc/null.py b/pcapkit/protocols/misc/null.py
index 6a13295aa..3c6c84769 100644
--- a/pcapkit/protocols/misc/null.py
+++ b/pcapkit/protocols/misc/null.py
@@ -15,7 +15,7 @@
 from typing import TYPE_CHECKING, overload
 
 from pcapkit.protocols.data.misc.null import NoPayload as Data_NoPayload
-from pcapkit.protocols.protocol import ProtocolBase as Protocol
+from pcapkit.protocols.protocol import ProtocolBase
 from pcapkit.protocols.schema.misc.null import NoPayload as Schema_NoPayload
 from pcapkit.utilities.exceptions import UnsupportedCall
 
@@ -27,7 +27,7 @@
 __all__ = ['NoPayload']
 
 
-class NoPayload(Protocol[Data_NoPayload, Schema_NoPayload],
+class NoPayload(ProtocolBase[Data_NoPayload, Schema_NoPayload],
                 schema=Schema_NoPayload, data=Data_NoPayload):
     """This class implements no-payload protocol."""
 
diff --git a/pcapkit/protocols/misc/pcap/frame.py b/pcapkit/protocols/misc/pcap/frame.py
index a39f234b7..e28de84ff 100644
--- a/pcapkit/protocols/misc/pcap/frame.py
+++ b/pcapkit/protocols/misc/pcap/frame.py
@@ -34,7 +34,7 @@
 from pcapkit.corekit.module import ModuleDescriptor
 from pcapkit.protocols.data.misc.pcap.frame import Frame as Data_Frame
 from pcapkit.protocols.data.misc.pcap.frame import FrameInfo as Data_FrameInfo
-from pcapkit.protocols.protocol import ProtocolBase as Protocol
+from pcapkit.protocols.protocol import ProtocolBase
 from pcapkit.protocols.schema.misc.pcap.frame import Frame as Schema_Frame
 from pcapkit.utilities.compat import localcontext
 from pcapkit.utilities.exceptions import RegistryError, UnsupportedCall, stacklevel
@@ -56,7 +56,7 @@
 py37 = ((version_info := sys.version_info).major >= 3 and version_info.minor >= 7)
 
 
-class Frame(Protocol[Data_Frame, Schema_Frame],
+class Frame(ProtocolBase[Data_Frame, Schema_Frame],
             schema=Schema_Frame, data=Data_Frame):
     """Per packet frame header extractor.
 
@@ -82,7 +82,7 @@ class Frame(Protocol[Data_Frame, Schema_Frame],
     # Defaults.
     ##########################################################################
 
-    #: DefaultDict[Enum_LinkType, ModuleDescriptor[Protocol] | ~typing.Type[Protocol]]: Protocol index mapping for
+    #: DefaultDict[Enum_LinkType, ModuleDescriptor[ProtocolBase] | ~typing.Type[ProtocolBase]]: Protocol index mapping for
     #: decoding next layer, c.f. :meth:`self._decode_next_layer <pcapkit.protocols.protocol.Protocol._decode_next_layer>`
     #: & :meth:`self._import_next_layer <pcapkit.protocols.protocol.Protocol._import_next_layer>`.
     #: The values should be a tuple representing the module name and class name, or
@@ -94,7 +94,7 @@ class Frame(Protocol[Data_Frame, Schema_Frame],
             Enum_LinkType.IPV4:     ModuleDescriptor('pcapkit.protocols.internet', 'IPv4'),
             Enum_LinkType.IPV6:     ModuleDescriptor('pcapkit.protocols.internet', 'IPv6'),
         },
-    )  # type: DefaultDict[Enum_LinkType | int, ModuleDescriptor[Protocol] | Type[Protocol]]
+    )  # type: DefaultDict[Enum_LinkType | int, ModuleDescriptor[ProtocolBase] | Type[ProtocolBase]]
 
     ##########################################################################
     # Properties.
@@ -120,7 +120,7 @@ def header(self) -> 'Data_Header':
     ##########################################################################
 
     @classmethod
-    def register(cls, code: 'Enum_LinkType', protocol: 'ModuleDescriptor[Protocol] | Type[Protocol]') -> 'None':  # type: ignore[override]
+    def register(cls, code: 'Enum_LinkType', protocol: 'ModuleDescriptor[ProtocolBase] | Type[ProtocolBase]') -> 'None':  # type: ignore[override]
         r"""Register a new protocol class.
 
         Notes:
@@ -148,7 +148,7 @@ def register(cls, code: 'Enum_LinkType', protocol: 'ModuleDescriptor[Protocol] |
         """
         if isinstance(protocol, ModuleDescriptor):
             protocol = protocol.klass
-        if not issubclass(protocol, Protocol):
+        if not issubclass(protocol, ProtocolBase):
             raise RegistryError(f'protocol must be a Protocol subclass, not {protocol!r}')
         incumbent = cls.__proto__.get(code)
         if incumbent is not None and incumbent is not protocol:
@@ -156,7 +156,7 @@ def register(cls, code: 'Enum_LinkType', protocol: 'ModuleDescriptor[Protocol] |
                  f'{incumbent!r} with {protocol!r}', RegistryWarning)
         cls.__proto__[code] = protocol
 
-    def index(self, name: 'str | Protocol | Type[Protocol]') -> 'int':
+    def index(self, name: 'str | ProtocolBase | Type[ProtocolBase]') -> 'int':
         """Call :meth:`ProtoChain.index <pcapkit.corekit.protochain.ProtoChain.index>`.
 
         Args:
@@ -355,7 +355,7 @@ def make(self,
              ts_usec: 'Optional[int]' = None,
              incl_len: 'Optional[int]' = None,
              orig_len: 'Optional[int]' = None,
-             packet: 'bytes | Protocol | Schema' = b'',
+             packet: 'bytes | ProtocolBase | Schema' = b'',
              nanosecond: 'bool' = False,
              **kwargs: 'Any') -> 'Schema_Frame':
         """Make frame packet data.
@@ -546,7 +546,7 @@ def _decode_next_layer(self, dict_: 'Data_Frame', proto: 'Optional[int]' = None,
             protocol chain of the current packet (frame).
 
         """
-        next_ = cast('Protocol', self._import_next_layer(proto, length, packet=packet))  # type: ignore[misc,call-arg,redundant-cast]
+        next_ = cast('ProtocolBase', self._import_next_layer(proto, length, packet=packet))  # type: ignore[misc,call-arg,redundant-cast]
         info, chain = next_.info, next_.protochain
 
         # make next layer protocol name
diff --git a/pcapkit/protocols/misc/pcap/header.py b/pcapkit/protocols/misc/pcap/header.py
index ca30bb9b3..714fc9526 100644
--- a/pcapkit/protocols/misc/pcap/header.py
+++ b/pcapkit/protocols/misc/pcap/header.py
@@ -33,7 +33,7 @@
 from pcapkit.corekit.version import VersionInfo
 from pcapkit.protocols.data.misc.pcap.header import Header as Data_Header
 from pcapkit.protocols.data.misc.pcap.header import MagicNumber as Data_MagicNumber
-from pcapkit.protocols.protocol import ProtocolBase as Protocol
+from pcapkit.protocols.protocol import ProtocolBase
 from pcapkit.protocols.schema.misc.pcap.header import Header as Schema_Header
 from pcapkit.utilities.exceptions import EndianError, FileError, UnsupportedCall
 
@@ -59,7 +59,7 @@
 }
 
 
-class Header(Protocol[Data_Header, Schema_Header],
+class Header(ProtocolBase[Data_Header, Schema_Header],
              schema=Schema_Header, data=Data_Header):
     """PCAP file global header extractor."""
 
diff --git a/pcapkit/protocols/misc/pcapng.py b/pcapkit/protocols/misc/pcapng.py
index 5b9fe9bb2..40789cf45 100644
--- a/pcapkit/protocols/misc/pcapng.py
+++ b/pcapkit/protocols/misc/pcapng.py
@@ -106,7 +106,7 @@
 from pcapkit.protocols.data.misc.pcapng import ZigBeeAPSKey as Data_ZigBeeAPSKey
 from pcapkit.protocols.data.misc.pcapng import ZigBeeNWKKey as Data_ZigBeeNWKKey
 from pcapkit.protocols.data.protocol import Packet as Data_Packet
-from pcapkit.protocols.protocol import ProtocolBase as Protocol
+from pcapkit.protocols.protocol import ProtocolBase
 from pcapkit.protocols.schema.misc.pcapng import PCAPNG as Schema_PCAPNG
 from pcapkit.protocols.schema.misc.pcapng import BlockType as Schema_BlockType
 from pcapkit.protocols.schema.misc.pcapng import CommentOption as Schema_CommentOption
@@ -293,7 +293,7 @@ class WireGuardKeyLabel(StrEnum):
     PRESHARED_KEY = 'PRESHARED_KEY'
 
 
-class PCAPNG(Protocol[Data_PCAPNG, Schema_PCAPNG],
+class PCAPNG(ProtocolBase[Data_PCAPNG, Schema_PCAPNG],
              schema=Schema_PCAPNG, data=Data_PCAPNG):
     """PCAP-NG file block extractor.
 
@@ -549,7 +549,7 @@ class PCAPNG(Protocol[Data_PCAPNG, Schema_PCAPNG],
     # Defaults.
     ##########################################################################
 
-    #: DefaultDict[Enum_LinkType, ModuleDescriptor[Protocol] | ~typing.Type[Protocol]]: Protocol index mapping for
+    #: DefaultDict[Enum_LinkType, ModuleDescriptor[ProtocolBase] | ~typing.Type[ProtocolBase]]: Protocol index mapping for
     #: decoding next layer, c.f. :meth:`self._decode_next_layer <pcapkit.protocols.protocol.Protocol._decode_next_layer>`
     #: & :meth:`self._import_next_layer <pcapkit.protocols.protocol.Protocol._import_next_layer>`.
     #: The values should be a tuple representing the module name and class name,
@@ -561,7 +561,7 @@ class PCAPNG(Protocol[Data_PCAPNG, Schema_PCAPNG],
             Enum_LinkType.IPV4:     ModuleDescriptor('pcapkit.protocols.internet', 'IPv4'),
             Enum_LinkType.IPV6:     ModuleDescriptor('pcapkit.protocols.internet', 'IPv6'),
         },
-    )  # type: DefaultDict[Enum_LinkType | int, ModuleDescriptor[Protocol] | Type[Protocol]]
+    )  # type: DefaultDict[Enum_LinkType | int, ModuleDescriptor[ProtocolBase] | Type[ProtocolBase]]
 
     #: DefaultDict[Enum_BlockType, str | tuple[BlockParser, BlockConstructor]]: Block
     #: type to method mapping. Method names are expected to be referred
@@ -854,7 +854,7 @@ def block(self) -> 'Enum_BlockType':
     ##########################################################################
 
     @classmethod
-    def register(cls, code: 'Enum_LinkType', protocol: 'ModuleDescriptor[Protocol] | Type[Protocol]') -> 'None':  # type: ignore[override]
+    def register(cls, code: 'Enum_LinkType', protocol: 'ModuleDescriptor[ProtocolBase] | Type[ProtocolBase]') -> 'None':  # type: ignore[override]
         r"""Register a new protocol class.
 
         Notes:
@@ -883,7 +883,7 @@ def register(cls, code: 'Enum_LinkType', protocol: 'ModuleDescriptor[Protocol] |
         """
         if isinstance(protocol, ModuleDescriptor):
             protocol = protocol.klass
-        if not issubclass(protocol, Protocol):
+        if not issubclass(protocol, ProtocolBase):
             raise RegistryError(f'protocol must be a Protocol subclass, not {protocol!r}')
         incumbent = cls.__proto__.get(code)
         if incumbent is not None and incumbent is not protocol:
@@ -944,7 +944,7 @@ def register_secrets(cls, code: 'Enum_SecretsType', meth: 'str | tuple[SecretsPa
             warn(f'PCAP-NG: [Secrets {code}] decryption secrets already registered', RegistryWarning)
         cls.__secrets__[code] = meth
 
-    def index(self, name: 'str | Protocol | Type[Protocol]') -> 'int':
+    def index(self, name: 'str | ProtocolBase | Type[ProtocolBase]') -> 'int':
         """Call :meth:`ProtoChain.index <pcapkit.corekit.protochain.ProtoChain.index>`.
 
         Args:
@@ -1680,7 +1680,7 @@ def _decode_next_layer(self, dict_: 'Data_PCAPNG', proto: 'Optional[int]' = None
             protocol chain of the current packet (frame).
 
         """
-        next_ = cast('Protocol', self._import_next_layer(proto, length, packet=packet))  # type: ignore[misc,call-arg,redundant-cast]
+        next_ = cast('ProtocolBase', self._import_next_layer(proto, length, packet=packet))  # type: ignore[misc,call-arg,redundant-cast]
         info, chain = next_.info, next_.protochain
 
         # make next layer protocol name
@@ -3710,7 +3710,7 @@ def _make_block_epb(self, block: 'Optional[Data_EnhancedPacketBlock]' = None, *,
                         timestamp: 'Optional[dt_type | int | float | Decimal]' = None,
                         captured_len: 'Optional[int]' = None,
                         original_len: 'Optional[int]' = None,
-                        packet_data: 'bytes | Protocol | Schema' = b'',
+                        packet_data: 'bytes | ProtocolBase | Schema' = b'',
                         options: 'Optional[Option | list[Schema_Option | tuple[Enum_OptionType, dict[str, Any]] | bytes]]' = None,
                         **kwargs: 'Any') -> 'Schema_EnhancedPacketBlock':
         """Make PCAP-NG enhanced packet block (EPB).
@@ -3766,7 +3766,7 @@ def _make_block_epb(self, block: 'Optional[Data_EnhancedPacketBlock]' = None, *,
 
     def _make_block_spb(self, block: 'Optional[Data_SimplePacketBlock]' = None, *,
                         original_len: 'Optional[int]' = None,
-                        packet_data: 'bytes | Protocol | Schema' = b'',
+                        packet_data: 'bytes | ProtocolBase | Schema' = b'',
                         **kwargs: 'Any') -> 'Schema_SimplePacketBlock':
         """Make PCAP-NG simple packet block (SPB).
 
@@ -4042,7 +4042,7 @@ def _make_block_packet(self, block: 'Optional[Data_PacketBlock]' = None, *,
                            timestamp: 'Optional[dt_type | int | float | Decimal]' = None,
                            captured_len: 'Optional[int]' = None,
                            original_len: 'Optional[int]' = None,
-                           packet_data: 'bytes | Protocol | Schema' = b'',
+                           packet_data: 'bytes | ProtocolBase | Schema' = b'',
                            options: 'Optional[Option | list[Schema_Option | tuple[Enum_OptionType, dict[str, Any]] | bytes]]' = None,
                            **kwargs: 'Any') -> 'Schema_PacketBlock':
         """Make PCAP-NG packet block (obsolete).
diff --git a/pcapkit/protocols/misc/raw.py b/pcapkit/protocols/misc/raw.py
index 92a2b3daf..48a1a04c9 100644
--- a/pcapkit/protocols/misc/raw.py
+++ b/pcapkit/protocols/misc/raw.py
@@ -16,7 +16,7 @@
 from pcapkit.corekit.protochain import ProtoChain
 from pcapkit.protocols.data.misc.raw import Raw as Data_Raw
 from pcapkit.protocols.misc.null import NoPayload
-from pcapkit.protocols.protocol import ProtocolBase as Protocol
+from pcapkit.protocols.protocol import ProtocolBase
 from pcapkit.protocols.schema.misc.raw import Raw as Schema_Raw
 from pcapkit.utilities.exceptions import UnsupportedCall
 
@@ -28,7 +28,7 @@
 __all__ = ['Raw']
 
 
-class Raw(Protocol[Data_Raw, Schema_Raw],
+class Raw(ProtocolBase[Data_Raw, Schema_Raw],
           schema=Schema_Raw, data=Data_Raw):
     """This class implements universal unknown protocol."""
 
diff --git a/pcapkit/protocols/schema/internet/ah.py b/pcapkit/protocols/schema/internet/ah.py
index 0c5b73d41..5bc31837d 100644
--- a/pcapkit/protocols/schema/internet/ah.py
+++ b/pcapkit/protocols/schema/internet/ah.py
@@ -13,7 +13,7 @@
 __all__ = ['AH']
 
 if TYPE_CHECKING:
-    from pcapkit.protocols.protocol import ProtocolBase as Protocol
+    from pcapkit.protocols.protocol import ProtocolBase
 
 
 @schema_final
@@ -37,4 +37,4 @@ class AH(Schema):
 
     if TYPE_CHECKING:
         def __init__(self, next: 'Enum_TransType', len: 'int', spi: 'int', seq: 'int',
-                     icv: 'bytes', payload: 'bytes | Protocol | Schema') -> 'None': ...
+                     icv: 'bytes', payload: 'bytes | ProtocolBase | Schema') -> 'None': ...
diff --git a/pcapkit/protocols/schema/internet/esp.py b/pcapkit/protocols/schema/internet/esp.py
index 00603a2fe..5f3566d91 100644
--- a/pcapkit/protocols/schema/internet/esp.py
+++ b/pcapkit/protocols/schema/internet/esp.py
@@ -11,7 +11,7 @@
 __all__ = ['ESP']
 
 if TYPE_CHECKING:
-    from pcapkit.protocols.protocol import ProtocolBase as Protocol
+    from pcapkit.protocols.protocol import ProtocolBase
 
 
 @schema_final
@@ -43,4 +43,4 @@ class ESP(Schema):
 
     if TYPE_CHECKING:
         def __init__(self, spi: 'int', seq: 'int',
-                     payload: 'bytes | Protocol | Schema') -> 'None': ...
+                     payload: 'bytes | ProtocolBase | Schema') -> 'None': ...
diff --git a/pcapkit/protocols/schema/internet/hip.py b/pcapkit/protocols/schema/internet/hip.py
index 34c5d05e8..1cbf14789 100644
--- a/pcapkit/protocols/schema/internet/hip.py
+++ b/pcapkit/protocols/schema/internet/hip.py
@@ -64,7 +64,7 @@
     from pcapkit.corekit.fields.field import FieldBase as Field
     from pcapkit.protocols.data.internet.hip import EncryptedParameter as Data_EncryptedParameter
     from pcapkit.protocols.data.internet.hip import HIPCipherParameter as Data_HIPCipherParameter
-    from pcapkit.protocols.protocol import ProtocolBase as Protocol
+    from pcapkit.protocols.protocol import ProtocolBase
 
 if SPHINX_TYPE_CHECKING:  # pragma: no cover
     from typing_extensions import Literal, TypedDict
@@ -1644,4 +1644,4 @@ class HIP(Schema):
         def __init__(self, next: 'Enum_TransType', len: 'int', pkt: 'PacketType',
                      ver: 'VersionType', checksum: 'bytes', control: 'ControlsType',
                      shit: 'int', rhit: 'int', param: 'bytes | list[bytes | Parameter]',
-                     payload: 'bytes | Protocol | Schema') -> 'None': ...
+                     payload: 'bytes | ProtocolBase | Schema') -> 'None': ...
diff --git a/pcapkit/protocols/schema/internet/hopopt.py b/pcapkit/protocols/schema/internet/hopopt.py
index 1b7553cc9..5215c46b2 100644
--- a/pcapkit/protocols/schema/internet/hopopt.py
+++ b/pcapkit/protocols/schema/internet/hopopt.py
@@ -41,7 +41,7 @@
     from typing import Any, DefaultDict, Optional, Type
 
     from pcapkit.corekit.fields.field import FieldBase as Field
-    from pcapkit.protocols.protocol import ProtocolBase as Protocol
+    from pcapkit.protocols.protocol import ProtocolBase
 
 if SPHINX_TYPE_CHECKING:  # pragma: no cover
     from typing_extensions import TypedDict
@@ -798,4 +798,4 @@ class HOPOPT(Schema):
     if TYPE_CHECKING:
         def __init__(self, next: 'Enum_TransType', len: 'int',
                      options: 'bytes | list[bytes | Option]',
-                     payload: 'bytes | Protocol | Schema') -> 'None': ...
+                     payload: 'bytes | ProtocolBase | Schema') -> 'None': ...
diff --git a/pcapkit/protocols/schema/internet/ipv4.py b/pcapkit/protocols/schema/internet/ipv4.py
index 1c6e9978d..ca9b9b176 100644
--- a/pcapkit/protocols/schema/internet/ipv4.py
+++ b/pcapkit/protocols/schema/internet/ipv4.py
@@ -42,7 +42,7 @@
     from typing import Any, DefaultDict, Optional, Type
 
     from pcapkit.corekit.fields.field import FieldBase as Field
-    from pcapkit.protocols.protocol import ProtocolBase as Protocol
+    from pcapkit.protocols.protocol import ProtocolBase
 
 if SPHINX_TYPE_CHECKING:  # pragma: no cover
     from typing_extensions import TypedDict
@@ -744,4 +744,4 @@ class IPv4(Schema):
         def __init__(self, vihl: 'VerIHLField', tos: 'ToSField', length: 'int', id: 'int',
                      flags: 'Flags', ttl: 'int', proto: 'Enum_TransType', chksum: 'bytes',
                      src: 'IPv4Address | str | bytes | int', dst: 'IPv4Address | str | bytes | int',
-                     options: 'list[Option | bytes] | bytes', payload: 'bytes | Protocol | Schema') -> 'None': ...
+                     options: 'list[Option | bytes] | bytes', payload: 'bytes | ProtocolBase | Schema') -> 'None': ...
diff --git a/pcapkit/protocols/schema/internet/ipv6.py b/pcapkit/protocols/schema/internet/ipv6.py
index 10190a271..507080319 100644
--- a/pcapkit/protocols/schema/internet/ipv6.py
+++ b/pcapkit/protocols/schema/internet/ipv6.py
@@ -17,7 +17,7 @@
 if TYPE_CHECKING:
     from ipaddress import IPv6Address
 
-    from pcapkit.protocols.protocol import ProtocolBase as Protocol
+    from pcapkit.protocols.protocol import ProtocolBase
 
 if SPHINX_TYPE_CHECKING:  # pragma: no cover
     from typing_extensions import TypedDict
@@ -68,4 +68,4 @@ class IPv6(Schema):
         def __init__(self, hextet: 'IPv6Hextet', length: 'int', next: 'Enum_TransType',
                      limit: 'int', src: 'IPv6Address | bytes | str | int',
                      dst: 'IPv6Address | bytes | str | int',
-                     payload: 'bytes | Protocol | Schema') -> None: ...
+                     payload: 'bytes | ProtocolBase | Schema') -> None: ...
diff --git a/pcapkit/protocols/schema/internet/ipv6_frag.py b/pcapkit/protocols/schema/internet/ipv6_frag.py
index c5a766bd7..a5ec8ffe8 100644
--- a/pcapkit/protocols/schema/internet/ipv6_frag.py
+++ b/pcapkit/protocols/schema/internet/ipv6_frag.py
@@ -15,7 +15,7 @@
 if TYPE_CHECKING:
     from typing_extensions import TypedDict
 
-    from pcapkit.protocols.protocol import ProtocolBase as Protocol
+    from pcapkit.protocols.protocol import ProtocolBase
 
     class Flags(TypedDict):
         """Fragment offset and flags."""
@@ -45,4 +45,4 @@ class IPv6_Frag(Schema):
     payload: 'bytes' = PayloadField()
 
     if TYPE_CHECKING:
-        def __init__(self, next:'Enum_TransType', flags: 'Flags', id: 'int', payload: 'bytes | Schema | Protocol') -> 'None': ...
+        def __init__(self, next:'Enum_TransType', flags: 'Flags', id: 'int', payload: 'bytes | Schema | ProtocolBase') -> 'None': ...
diff --git a/pcapkit/protocols/schema/internet/ipv6_opts.py b/pcapkit/protocols/schema/internet/ipv6_opts.py
index 1226f3c6f..2f01bfcd0 100644
--- a/pcapkit/protocols/schema/internet/ipv6_opts.py
+++ b/pcapkit/protocols/schema/internet/ipv6_opts.py
@@ -41,7 +41,7 @@
     from typing import Any, DefaultDict, Optional, Type
 
     from pcapkit.corekit.fields.field import FieldBase as Field
-    from pcapkit.protocols.protocol import ProtocolBase as Protocol
+    from pcapkit.protocols.protocol import ProtocolBase
 
 if SPHINX_TYPE_CHECKING:  # pragma: no cover
     from typing_extensions import TypedDict
@@ -803,4 +803,4 @@ class IPv6_Opts(Schema):
     if TYPE_CHECKING:
         def __init__(self, next: 'Enum_TransType', len: 'int',
                      options: 'bytes | list[bytes | Option]',
-                     payload: 'bytes | Protocol | Schema') -> 'None': ...
+                     payload: 'bytes | ProtocolBase | Schema') -> 'None': ...
diff --git a/pcapkit/protocols/schema/internet/ipv6_route.py b/pcapkit/protocols/schema/internet/ipv6_route.py
index d1631821f..f480cebb1 100644
--- a/pcapkit/protocols/schema/internet/ipv6_route.py
+++ b/pcapkit/protocols/schema/internet/ipv6_route.py
@@ -27,7 +27,7 @@
     from typing import Any, Optional
 
     from pcapkit.corekit.fields.field import FieldBase as Field
-    from pcapkit.protocols.protocol import ProtocolBase as Protocol
+    from pcapkit.protocols.protocol import ProtocolBase
 
 if SPHINX_TYPE_CHECKING:  # pragma: no cover
     from typing_extensions import TypedDict
@@ -134,7 +134,7 @@ class IPv6_Route(Schema):
 
     if TYPE_CHECKING:
         def __init__(self, next: 'Enum_TransType', length: 'int', type: 'Enum_Routing',
-                     seg_left: 'int', data: 'bytes | RoutingType', payload: 'Protocol | Schema | bytes') -> 'None': ...
+                     seg_left: 'int', data: 'bytes | RoutingType', payload: 'ProtocolBase | Schema | bytes') -> 'None': ...
 
 
 class RoutingType(EnumSchema[Enum_Routing]):
diff --git a/pcapkit/protocols/schema/internet/ipx.py b/pcapkit/protocols/schema/internet/ipx.py
index 17c6fd33f..79fa2017e 100644
--- a/pcapkit/protocols/schema/internet/ipx.py
+++ b/pcapkit/protocols/schema/internet/ipx.py
@@ -13,7 +13,7 @@
 __all__ = ['IPX']
 
 if TYPE_CHECKING:
-    from pcapkit.protocols.protocol import ProtocolBase as Protocol
+    from pcapkit.protocols.protocol import ProtocolBase
 
 
 @schema_final
@@ -37,4 +37,4 @@ class IPX(Schema):
 
     if TYPE_CHECKING:
         def __init__(self, chksum: 'bytes', len: 'int', count: 'int', type: 'Enum_Packet',
-                     dst: 'bytes', src: 'bytes', payload: 'bytes | Protocol | Schema') -> 'None': ...
+                     dst: 'bytes', src: 'bytes', payload: 'bytes | ProtocolBase | Schema') -> 'None': ...
diff --git a/pcapkit/protocols/schema/internet/mh.py b/pcapkit/protocols/schema/internet/mh.py
index ea66b5ce1..60ef14c64 100644
--- a/pcapkit/protocols/schema/internet/mh.py
+++ b/pcapkit/protocols/schema/internet/mh.py
@@ -134,7 +134,7 @@
     from typing import Any, Optional
 
     from pcapkit.corekit.fields.field import FieldBase as Field
-    from pcapkit.protocols.protocol import ProtocolBase as Protocol
+    from pcapkit.protocols.protocol import ProtocolBase
 
 if SPHINX_TYPE_CHECKING:  # pragma: no cover
     from typing_extensions import TypedDict
@@ -574,7 +574,7 @@ class MH(Schema):
 
     if TYPE_CHECKING:
         def __init__(self, next: 'Enum_TransType | int', length: 'int', type: 'Enum_Packet | int',
-                     chksum: 'bytes', data: 'Packet | bytes', payload: 'bytes | Protocol | Schema') -> 'None': ...
+                     chksum: 'bytes', data: 'Packet | bytes', payload: 'bytes | ProtocolBase | Schema') -> 'None': ...
 
 
 class Option(EnumSchema[Enum_Option]):
diff --git a/pcapkit/protocols/schema/link/arp.py b/pcapkit/protocols/schema/link/arp.py
index 69f3dd814..f3f1ac762 100644
--- a/pcapkit/protocols/schema/link/arp.py
+++ b/pcapkit/protocols/schema/link/arp.py
@@ -15,7 +15,7 @@
 __all__ = ['ARP']
 
 if TYPE_CHECKING:
-    from pcapkit.protocols.protocol import ProtocolBase as Protocol
+    from pcapkit.protocols.protocol import ProtocolBase
 
 
 @schema_final
@@ -36,4 +36,4 @@ class ARP(Schema):
     if TYPE_CHECKING:
         def __init__(self, htype: 'int', ptype: 'int', hlen: 'int', plen: 'int',
                      oper: 'int', sha: 'bytes', spa: 'bytes', tha: 'bytes',
-                     tpa: 'bytes', payload: 'bytes | Protocol | Schema') -> 'None': ...
+                     tpa: 'bytes', payload: 'bytes | ProtocolBase | Schema') -> 'None': ...
diff --git a/pcapkit/protocols/schema/link/ethernet.py b/pcapkit/protocols/schema/link/ethernet.py
index f36e92fbe..861907e09 100644
--- a/pcapkit/protocols/schema/link/ethernet.py
+++ b/pcapkit/protocols/schema/link/ethernet.py
@@ -15,7 +15,7 @@
 if TYPE_CHECKING:
     from typing import Any
 
-    from pcapkit.protocols.protocol import ProtocolBase as Protocol
+    from pcapkit.protocols.protocol import ProtocolBase
 
 
 def callback_payload(self: 'PayloadField', packet: 'dict[str, Any]') -> 'None':
@@ -68,4 +68,4 @@ class Ethernet(Schema):
 
     if TYPE_CHECKING:
         def __init__(self, dst: 'bytes', src: 'bytes', type: 'Enum_EtherType',
-                     payload: 'bytes | Protocol | Schema') -> 'None': ...
+                     payload: 'bytes | ProtocolBase | Schema') -> 'None': ...
diff --git a/pcapkit/protocols/schema/link/l2tp.py b/pcapkit/protocols/schema/link/l2tp.py
index 30d40f28a..e391d030e 100644
--- a/pcapkit/protocols/schema/link/l2tp.py
+++ b/pcapkit/protocols/schema/link/l2tp.py
@@ -15,7 +15,7 @@
 if TYPE_CHECKING:
     from typing import Optional
 
-    from pcapkit.protocols.protocol import ProtocolBase as Protocol
+    from pcapkit.protocols.protocol import ProtocolBase
 
 if SPHINX_TYPE_CHECKING:  # pragma: no cover
     from typing_extensions import Literal, TypedDict
@@ -85,4 +85,4 @@ class L2TP(Schema):
     if TYPE_CHECKING:
         def __init__(self, flags: 'FlagsType', length: 'Optional[int]', tunnel_id: 'int',
                      session_id: 'int', ns: 'Optional[int]', nr: 'Optional[int]',
-                     offset: 'Optional[int]', payload: 'bytes | Protocol | Schema') -> 'None': ...
+                     offset: 'Optional[int]', payload: 'bytes | ProtocolBase | Schema') -> 'None': ...
diff --git a/pcapkit/protocols/schema/link/ospf.py b/pcapkit/protocols/schema/link/ospf.py
index 01da361af..c2f6cab9f 100644
--- a/pcapkit/protocols/schema/link/ospf.py
+++ b/pcapkit/protocols/schema/link/ospf.py
@@ -19,7 +19,7 @@
     from typing import Any
 
     from pcapkit.corekit.fields.field import FieldBase as Field
-    from pcapkit.protocols.protocol import ProtocolBase as Protocol
+    from pcapkit.protocols.protocol import ProtocolBase
 
 
 def ospf_auth_data_selector(pkt: 'dict[str, Any]') -> 'Field':
@@ -87,4 +87,4 @@ def __init__(self, version: 'int', type: 'Enum_Packet', length: 'int',
                      area_id: 'IPv4Address | bytes | str | int',
                      checksum: 'bytes', auth_type: 'Enum_Authentication',
                      auth_data: 'bytes | CrytographicAuthentication',
-                     payload: 'bytes | Protocol | Schema') -> 'None': ...
+                     payload: 'bytes | ProtocolBase | Schema') -> 'None': ...
diff --git a/pcapkit/protocols/schema/link/vlan.py b/pcapkit/protocols/schema/link/vlan.py
index ea6f2bc6c..7a27e4bb1 100644
--- a/pcapkit/protocols/schema/link/vlan.py
+++ b/pcapkit/protocols/schema/link/vlan.py
@@ -23,7 +23,7 @@
 __all__ = ['VLAN', 'TCI']
 
 if TYPE_CHECKING:
-    from pcapkit.protocols.protocol import ProtocolBase as Protocol
+    from pcapkit.protocols.protocol import ProtocolBase
 
 if SPHINX_TYPE_CHECKING:  # pragma: no cover
     from typing_extensions import TypedDict
@@ -74,4 +74,4 @@ class VLAN(Schema):
 
     if TYPE_CHECKING:
         def __init__(self, tci: 'TCIType', type: 'Enum_EtherType',
-                     payload: 'bytes | Protocol | Schema') -> 'None': ...
+                     payload: 'bytes | ProtocolBase | Schema') -> 'None': ...
diff --git a/pcapkit/protocols/schema/misc/pcap/frame.py b/pcapkit/protocols/schema/misc/pcap/frame.py
index 1bff3d2c5..ffd0a8381 100644
--- a/pcapkit/protocols/schema/misc/pcap/frame.py
+++ b/pcapkit/protocols/schema/misc/pcap/frame.py
@@ -15,7 +15,7 @@
     from typing import Any
 
     from pcapkit.corekit.fields.numbers import NumberField as Field
-    from pcapkit.protocols.protocol import ProtocolBase as Protocol
+    from pcapkit.protocols.protocol import ProtocolBase
 
 
 def byteorder_callback(field: 'Field', packet: 'dict[str, Any]') -> 'None':
@@ -62,4 +62,4 @@ class Frame(Schema):
 
     if TYPE_CHECKING:
         def __init__(self, ts_sec: 'int', ts_usec: 'int', incl_len: 'int',
-                     orig_len: 'int', packet: 'bytes | Protocol | Schema') -> 'None': ...
+                     orig_len: 'int', packet: 'bytes | ProtocolBase | Schema') -> 'None': ...
diff --git a/pcapkit/protocols/schema/misc/pcapng.py b/pcapkit/protocols/schema/misc/pcapng.py
index 1b977082a..d4b644e6d 100644
--- a/pcapkit/protocols/schema/misc/pcapng.py
+++ b/pcapkit/protocols/schema/misc/pcapng.py
@@ -67,7 +67,7 @@
 
     from pcapkit.corekit.fields.field import FieldBase as Field
     from pcapkit.protocols.misc.pcapng import TLSKeyLabel, WireGuardKeyLabel
-    from pcapkit.protocols.protocol import ProtocolBase as Protocol
+    from pcapkit.protocols.protocol import ProtocolBase
 
 if SPHINX_TYPE_CHECKING:  # pragma: no cover
     from typing_extensions import TypedDict
@@ -1351,7 +1351,7 @@ class EnhancedPacketBlock(BlockType, code=Enum_BlockType.Enhanced_Packet_Block):
     if TYPE_CHECKING:
         def __init__(self, length: 'int', interface_id: 'int', timestamp_high: 'int',
                      timestamp_low: 'int', captured_len: 'int', original_len: 'int',
-                     packet_data: 'bytes | Protocol | Schema',
+                     packet_data: 'bytes | ProtocolBase | Schema',
                      options: 'list[Option | bytes] | bytes', length2: 'int') -> 'None': ...
 
 
@@ -1375,7 +1375,7 @@ class SimplePacketBlock(BlockType, code=Enum_BlockType.Simple_Packet_Block):
 
     if TYPE_CHECKING:
         def __init__(self, length: 'int', original_len: 'int',
-                     packet_data: 'bytes | Protocol | Schema',
+                     packet_data: 'bytes | ProtocolBase | Schema',
                      length2: 'int') -> 'None': ...
 
 
@@ -2196,5 +2196,5 @@ class PacketBlock(BlockType, code=Enum_BlockType.Packet_Block):
     if TYPE_CHECKING:
         def __init__(self, length: 'int', interface_id: 'int', drop_count: 'int',
                      timestamp_high: 'int', timestamp_low: 'int', captured_length: 'int',
-                     original_length: 'int', packet_data: 'bytes | Protocol | Schema',
+                     original_length: 'int', packet_data: 'bytes | ProtocolBase | Schema',
                      options: 'list[Option | bytes] | bytes', length2: 'int') -> 'None': ...
diff --git a/pcapkit/protocols/schema/misc/raw.py b/pcapkit/protocols/schema/misc/raw.py
index 560384079..3f1637bb7 100644
--- a/pcapkit/protocols/schema/misc/raw.py
+++ b/pcapkit/protocols/schema/misc/raw.py
@@ -10,7 +10,7 @@
 __all__ = ['Raw']
 
 if TYPE_CHECKING:
-    from pcapkit.protocols.protocol import ProtocolBase as Protocol
+    from pcapkit.protocols.protocol import ProtocolBase
 
 
 @schema_final
@@ -21,4 +21,4 @@ class Raw(Schema):
     packet: 'bytes' = PayloadField(length=lambda x: x['__length__'], default=b'')
 
     if TYPE_CHECKING:
-        def __init__(self, packet: 'bytes | Schema | Protocol') -> 'None': ...  # pylint: disable=unused-argument,super-init-not-called,multiple-statements
+        def __init__(self, packet: 'bytes | Schema | ProtocolBase') -> 'None': ...  # pylint: disable=unused-argument,super-init-not-called,multiple-statements
diff --git a/pcapkit/protocols/schema/transport/sctp.py b/pcapkit/protocols/schema/transport/sctp.py
index 978ce017e..b97b53dff 100644
--- a/pcapkit/protocols/schema/transport/sctp.py
+++ b/pcapkit/protocols/schema/transport/sctp.py
@@ -50,7 +50,7 @@
     from ipaddress import IPv4Address, IPv6Address
     from typing import Any, Callable
 
-    from pcapkit.protocols.protocol import ProtocolBase as Protocol
+    from pcapkit.protocols.protocol import ProtocolBase
 
 if SPHINX_TYPE_CHECKING:  # pragma: no cover
     from typing_extensions import TypedDict
diff --git a/pcapkit/protocols/schema/transport/tcp.py b/pcapkit/protocols/schema/transport/tcp.py
index 87d035e8f..1fdbb04a6 100644
--- a/pcapkit/protocols/schema/transport/tcp.py
+++ b/pcapkit/protocols/schema/transport/tcp.py
@@ -44,7 +44,7 @@
     from typing import Any, DefaultDict, Optional, Type
 
     from pcapkit.corekit.fields.field import FieldBase as Field
-    from pcapkit.protocols.protocol import ProtocolBase as Protocol
+    from pcapkit.protocols.protocol import ProtocolBase
 
 if SPHINX_TYPE_CHECKING:  # pragma: no cover
     from typing_extensions import TypedDict
@@ -1106,4 +1106,4 @@ class TCP(Schema):
     if TYPE_CHECKING:
         def __init__(self, srcport: 'Enum_AppType | int', dstport: 'Enum_AppType | int', seq: 'int', ack: 'int',
                      offset: 'OffsetFlag', flags: 'Flags', window: 'int', checksum: 'bytes',
-                     urgent: 'int', options: 'list[Option | bytes] | bytes', payload: 'bytes | Protocol | Schema') -> 'None': ...
+                     urgent: 'int', options: 'list[Option | bytes] | bytes', payload: 'bytes | ProtocolBase | Schema') -> 'None': ...
diff --git a/pcapkit/protocols/schema/transport/udp.py b/pcapkit/protocols/schema/transport/udp.py
index 50299cfa4..2f5f4c593 100644
--- a/pcapkit/protocols/schema/transport/udp.py
+++ b/pcapkit/protocols/schema/transport/udp.py
@@ -16,7 +16,7 @@
 if TYPE_CHECKING:
     from typing import Any
 
-    from pcapkit.protocols.protocol import ProtocolBase as Protocol
+    from pcapkit.protocols.protocol import ProtocolBase
 
 
 class PortEnumField(EnumField):
@@ -87,4 +87,4 @@ class UDP(Schema):
 
     if TYPE_CHECKING:
         def __init__(self, srcport: 'Enum_AppType | int', dstport: 'Enum_AppType | int', len: 'int',
-                     checksum: 'bytes', payload: 'bytes | Schema | Protocol') -> 'None': ...
+                     checksum: 'bytes', payload: 'bytes | Schema | ProtocolBase') -> 'None': ...
diff --git a/pcapkit/protocols/transport/sctp.py b/pcapkit/protocols/transport/sctp.py
index ff2a5ec33..b60ace5aa 100644
--- a/pcapkit/protocols/transport/sctp.py
+++ b/pcapkit/protocols/transport/sctp.py
@@ -170,7 +170,7 @@
     from pcapkit.protocols.data.transport.sctp import Chunk as Data_Chunk
     from pcapkit.protocols.data.transport.sctp import ErrorCause as Data_ErrorCause
     from pcapkit.protocols.data.transport.sctp import Parameter as Data_Parameter
-    from pcapkit.protocols.protocol import ProtocolBase as Protocol
+    from pcapkit.protocols.protocol import ProtocolBase
     from pcapkit.protocols.schema.transport.sctp import Chunk as Schema_Chunk
     from pcapkit.protocols.schema.transport.sctp import ErrorCause as Schema_ErrorCause
     from pcapkit.protocols.schema.transport.sctp import Parameter as Schema_Parameter
@@ -343,7 +343,7 @@ class SCTP(Transport[Data_SCTP, Schema_SCTP],
     #: Payload protocol identifier of the first DATA chunk found in the packet.
     _ppid = None  # type: Optional[Enum_PayloadProtocolIdentifier]
 
-    #: DefaultDict[int, ModuleDescriptor[Protocol] | ~typing.Type[Protocol]]: Protocol
+    #: DefaultDict[int, ModuleDescriptor[ProtocolBase] | ~typing.Type[ProtocolBase]]: Protocol
     #: index mapping for decoding next layer, c.f.
     #: :meth:`self._decode_next_layer <pcapkit.protocols.transport.sctp.SCTP._decode_next_layer>`
     #: & :meth:`self._import_next_layer <pcapkit.protocols.protocol.Protocol._import_next_layer>`.
@@ -363,7 +363,7 @@ class SCTP(Transport[Data_SCTP, Schema_SCTP],
             Enum_PayloadProtocolIdentifier.PayloadProtocolIdentifier_3GPP_NG_Application_Protocol: ModuleDescriptor('pcapkit.protocols.application.ngap', 'NGAP'),  # NGAP
             Enum_PayloadProtocolIdentifier.PayloadProtocolIdentifier_3GPP_NGAP_over_DTLS_over_SCTP: ModuleDescriptor('pcapkit.protocols.application.ngap', 'NGAP'),  # NGAP over DTLS
         },
-    )  # type: DefaultDict[int, ModuleDescriptor[Protocol] | Type[Protocol]]
+    )  # type: DefaultDict[int, ModuleDescriptor[ProtocolBase] | Type[ProtocolBase]]
 
     #: DefaultDict[Enum_Chunk, str | tuple[ChunkParser, ChunkConstructor]]: Chunk
     #: type to method mapping, c.f. :meth:`_read_sctp_chunks` and
@@ -590,7 +590,7 @@ def make(self,
         return schema
 
     @classmethod
-    def register(cls, code: 'Enum_PayloadProtocolIdentifier | int', protocol: 'ModuleDescriptor[Protocol] | Type[Protocol]') -> 'None':  # type: ignore[override] # pylint: disable=line-too-long
+    def register(cls, code: 'Enum_PayloadProtocolIdentifier | int', protocol: 'ModuleDescriptor[ProtocolBase] | Type[ProtocolBase]') -> 'None':  # type: ignore[override] # pylint: disable=line-too-long
         r"""Register a new protocol class for a payload protocol identifier.
 
         Notes:
diff --git a/pcapkit/protocols/transport/tcp.py b/pcapkit/protocols/transport/tcp.py
index 5df9b6613..fcc61de9e 100644
--- a/pcapkit/protocols/transport/tcp.py
+++ b/pcapkit/protocols/transport/tcp.py
@@ -150,7 +150,7 @@
     from pcapkit.protocols.data.transport.tcp import MPTCP as Data_MPTCP
     from pcapkit.protocols.data.transport.tcp import MPTCPJoin as Data_MPTCPJoin
     from pcapkit.protocols.data.transport.tcp import Option as Data_Option
-    from pcapkit.protocols.protocol import ProtocolBase as Protocol
+    from pcapkit.protocols.protocol import ProtocolBase
     from pcapkit.protocols.schema.transport.tcp import MPTCP as Schema_MPTCP
     from pcapkit.protocols.schema.transport.tcp import Flags as Schema_Flags
     from pcapkit.protocols.schema.transport.tcp import MPTCPJoin as Schema_MPTCPJoin
@@ -307,7 +307,7 @@ class TCP(Transport[Data_TCP, Schema_TCP],
     # Defaults.
     ##########################################################################
 
-    #: DefaultDict[int, ModuleDescriptor[Protocol] | ~typing.Type[Protocol]]: Protocol
+    #: DefaultDict[int, ModuleDescriptor[ProtocolBase] | ~typing.Type[ProtocolBase]]: Protocol
     #: index mapping for decoding next layer, c.f.
     #: :meth:`self._decode_next_layer <pcapkit.protocols.transport.transport.Transport._decode_next_layer>`
     #: & :meth:`self._import_next_layer <pcapkit.protocols.protocol.Protocol._import_next_layer>`.
@@ -526,7 +526,7 @@ def make(self,
              checksum: 'bytes' = b'\x00\x00',
              urgent: 'int' = 0,
              options: 'Optional[list[Schema_Option | tuple[Enum_Option, dict[str, Any]] | bytes] | Option]' = None,  # pylint: disable=line-too-long
-             payload: 'bytes | Protocol | Schema' = b'',
+             payload: 'bytes | ProtocolBase | Schema' = b'',
              **kwargs: 'Any') -> 'Schema_TCP':
         """Make (construct) packet data.
 
diff --git a/pcapkit/protocols/transport/transport.py b/pcapkit/protocols/transport/transport.py
index b22da886e..11353f6d0 100644
--- a/pcapkit/protocols/transport/transport.py
+++ b/pcapkit/protocols/transport/transport.py
@@ -17,8 +17,7 @@
 
 from pcapkit.const.reg.apptype import AppType as Enum_AppType
 from pcapkit.corekit.module import ModuleDescriptor
-from pcapkit.protocols.protocol import _PT, _ST
-from pcapkit.protocols.protocol import ProtocolBase as Protocol
+from pcapkit.protocols.protocol import _PT, _ST, ProtocolBase
 from pcapkit.utilities.exceptions import RegistryError, StructError, UnsupportedCall, stacklevel
 from pcapkit.utilities.logging import DEVMODE, get_logger
 from pcapkit.utilities.warnings import RegistryWarning, warn
@@ -38,14 +37,14 @@
 logger = get_logger(__name__)
 
 
-class Transport(Protocol[_PT, _ST], Generic[_PT, _ST]):  # pylint: disable=abstract-method
+class Transport(ProtocolBase[_PT, _ST], Generic[_PT, _ST]):  # pylint: disable=abstract-method
     """Abstract base class for transport layer protocol family."""
 
     if TYPE_CHECKING:
         #: Protocol index mapping for decoding next layer,
         #: c.f. :meth:`self._decode_next_layer <pcapkit.protocols.transport.transport.Transport._decode_next_layer>`
         #: & :meth:`self._import_next_layer <pcapkit.protocols.protocol.Protocol._import_next_layer>`.
-        __proto__: 'DefaultDict[int, ModuleDescriptor[Protocol] | Type[Protocol]]'
+        __proto__: 'DefaultDict[int, ModuleDescriptor[ProtocolBase] | Type[ProtocolBase]]'
 
     ##########################################################################
     # Defaults.
@@ -69,7 +68,7 @@ def layer(self) -> 'Literal["Transport"]':
     ##########################################################################
 
     @classmethod
-    def register(cls, code: 'int', protocol: 'ModuleDescriptor[Protocol] | Type[Protocol]') -> 'None':
+    def register(cls, code: 'int', protocol: 'ModuleDescriptor[ProtocolBase] | Type[ProtocolBase]') -> 'None':
         """Register a new protocol class.
 
         Notes:
@@ -112,7 +111,7 @@ def register(cls, code: 'int', protocol: 'ModuleDescriptor[Protocol] | Type[Prot
 
         if isinstance(protocol, ModuleDescriptor):
             protocol = protocol.klass
-        if not issubclass(protocol, Protocol):
+        if not issubclass(protocol, ProtocolBase):
             raise RegistryError(f'protocol must be a Protocol subclass, not {protocol!r}')
         incumbent = cls.__proto__.get(code)
         if incumbent is not None and incumbent is not protocol:
@@ -121,7 +120,7 @@ def register(cls, code: 'int', protocol: 'ModuleDescriptor[Protocol] | Type[Prot
         cls.__proto__[code] = protocol
 
     @classmethod
-    def analyze(cls, ports: 'tuple[int, int]', payload: 'bytes', **kwargs: 'Any') -> 'Protocol':  # type: ignore[override] # pylint: disable=arguments-renamed
+    def analyze(cls, ports: 'tuple[int, int]', payload: 'bytes', **kwargs: 'Any') -> 'ProtocolBase':  # type: ignore[override] # pylint: disable=arguments-renamed
         """Analyse packet payload.
 
         Args:
diff --git a/pcapkit/protocols/transport/udp.py b/pcapkit/protocols/transport/udp.py
index 9f5fec7ff..772876bb7 100644
--- a/pcapkit/protocols/transport/udp.py
+++ b/pcapkit/protocols/transport/udp.py
@@ -38,7 +38,7 @@
     from typing_extensions import Literal
 
     from pcapkit.const.reg.apptype import AppType as Enum_AppType
-    from pcapkit.protocols.protocol import ProtocolBase as Protocol
+    from pcapkit.protocols.protocol import ProtocolBase
     from pcapkit.protocols.schema.schema import Schema
 
 __all__ = ['UDP']
@@ -81,7 +81,7 @@ class UDP(Transport[Data_UDP, Schema_UDP],
     # Defaults.
     ##########################################################################
 
-    #: DefaultDict[int, ModuleDescriptor[Protocol] | ~typing.Type[Protocol]]: Protocol
+    #: DefaultDict[int, ModuleDescriptor[ProtocolBase] | ~typing.Type[ProtocolBase]]: Protocol
     #: index mapping for decoding next layer, c.f.
     #: :meth:`self._decode_next_layer <pcapkit.protocols.transport.transport.Transport._decode_next_layer>`
     #: & :meth:`self._import_next_layer <pcapkit.protocols.protocol.Protocol._import_next_layer>`.
@@ -184,7 +184,7 @@ def make(self,
              srcport: 'Enum_AppType | int' = 0,
              dstport: 'Enum_AppType | int' = 0,
              checksum: 'bytes' = b'\x00\x00',
-             payload: 'bytes | Schema | Protocol' = b'',
+             payload: 'bytes | Schema | ProtocolBase' = b'',
              **kwargs: 'Any') -> 'Schema_UDP':
         """Make (construct) packet data.
 
diff --git a/tests/test_base_class_contract.py b/tests/test_base_class_contract.py
index 7d2e55757..d59fdfea6 100644
--- a/tests/test_base_class_contract.py
+++ b/tests/test_base_class_contract.py
@@ -32,12 +32,13 @@
 built-ins for three years). These two tests replace the convention with
 something that fails.
 
-The sweep is complete but the migration is not: 28 of the 82 sites are renamed,
-and the other 54 sit in paths that open pull requests own -- see
-:data:`PENDING_ALIAS_PATHS`, which is the whole of the remaining work and
-shrinks to nothing as those land. The four non-``protocols`` families
-(``Engine`` 8 sites, ``Reassembly`` 3, ``Dumper`` 2, ``TraceFlow`` 2) are
-finished; every one of the 54 outstanding is a ``ProtocolBase`` site.
+The sweep and the migration are both complete: all 82 sites are renamed, the
+last 54 (all ``ProtocolBase``, across ``pcapkit/protocols/`` and three
+``pcapkit/foundation/`` modules) having landed in #514 part (c) once #726 and
+#742 merged. :data:`PENDING_ALIAS_PATHS` is therefore empty -- its intended end
+state -- and :func:`is_pending` is trivially ``False`` for every path; the dict
+stays as a mechanism rather than being deleted, in case a future ``*Base``
+family needs the same transitional carve-out.
 
 :class:`RegistrationGateTests` is a regression pin, not a new behaviour. Every
 assertion in it already held before part (c), because parts (a) and (b)
@@ -108,13 +109,10 @@
 #: the alias comes out and the entry goes with it. **An empty dict is the end
 #: state**, and :meth:`BaseClassAliasTests.test_no_library_module_imports_a_base_under_its_public_name`
 #: fails on an entry that has stopped matching anything, so a stale promise
-#: cannot sit here unnoticed once its pull request merges.
-PENDING_ALIAS_PATHS = {
-    'pcapkit/protocols/': 726,
-    'pcapkit/foundation/registry/protocols.py': 726,
-    'pcapkit/foundation/extraction.py': 742,
-    'pcapkit/foundation/traceflow/traceflow.py': 742,
-}
+#: cannot sit here unnoticed once its pull request merges. #514 part (c) landed
+#: the last 54 sites, so this is now empty and every alias check below runs
+#: unconditionally.
+PENDING_ALIAS_PATHS = {}  # type: dict[str, int]
 
 
 def is_pending(rel: 'str') -> 'bool':