diff --git a/libp2p/__init__.py b/libp2p/__init__.py
index b4d2a9a2..08caf256 100644
--- a/libp2p/__init__.py
+++ b/libp2p/__init__.py
@@ -1,5 +1,5 @@
 import asyncio
-from typing import Mapping, Sequence
+from typing import Sequence
 
 from libp2p.crypto.keys import KeyPair
 from libp2p.crypto.rsa import create_new_key_pair
@@ -15,10 +15,9 @@ from libp2p.routing.interfaces import IPeerRouting
 from libp2p.routing.kademlia.kademlia_peer_router import KadmeliaPeerRouter
 from libp2p.security.insecure.transport import PLAINTEXT_PROTOCOL_ID, InsecureTransport
 import libp2p.security.secio.transport as secio
-from libp2p.security.secure_transport_interface import ISecureTransport
 from libp2p.stream_muxer.mplex.mplex import MPLEX_PROTOCOL_ID, Mplex
-from libp2p.stream_muxer.muxer_multistream import MuxerClassType
 from libp2p.transport.tcp.tcp import TCP
+from libp2p.transport.typing import TMuxerOptions, TSecurityOptions
 from libp2p.transport.upgrader import TransportUpgrader
 from libp2p.typing import TProtocol
 
@@ -74,8 +73,8 @@ def initialize_default_swarm(
     key_pair: KeyPair,
     id_opt: ID = None,
     transport_opt: Sequence[str] = None,
-    muxer_opt: Mapping[TProtocol, MuxerClassType] = None,
-    sec_opt: Mapping[TProtocol, ISecureTransport] = None,
+    muxer_opt: TMuxerOptions = None,
+    sec_opt: TSecurityOptions = None,
     peerstore_opt: IPeerStore = None,
     disc_opt: IPeerRouting = None,
 ) -> Swarm:
@@ -114,8 +113,8 @@ async def new_node(
     key_pair: KeyPair = None,
     swarm_opt: INetwork = None,
     transport_opt: Sequence[str] = None,
-    muxer_opt: Mapping[TProtocol, MuxerClassType] = None,
-    sec_opt: Mapping[TProtocol, ISecureTransport] = None,
+    muxer_opt: TMuxerOptions = None,
+    sec_opt: TSecurityOptions = None,
     peerstore_opt: IPeerStore = None,
     disc_opt: IPeerRouting = None,
 ) -> BasicHost:
diff --git a/libp2p/host/basic_host.py b/libp2p/host/basic_host.py
index af4225f4..7c783d93 100644
--- a/libp2p/host/basic_host.py
+++ b/libp2p/host/basic_host.py
@@ -1,4 +1,3 @@
-import asyncio
 import logging
 from typing import List, Sequence
 
@@ -107,7 +106,7 @@ class BasicHost(IHost):
         :return: stream: new stream created
         """
 
-        net_stream = await self._network.new_stream(peer_id, protocol_ids)
+        net_stream = await self._network.new_stream(peer_id)
 
         # Perform protocol muxing to determine protocol to use
         try:
@@ -157,4 +156,4 @@ class BasicHost(IHost):
             await net_stream.reset()
             return
         net_stream.set_protocol(protocol)
-        asyncio.ensure_future(handler(net_stream))
+        await handler(net_stream)
diff --git a/libp2p/network/connection/net_connection_interface.py b/libp2p/network/connection/net_connection_interface.py
index c2c62855..e308ad65 100644
--- a/libp2p/network/connection/net_connection_interface.py
+++ b/libp2p/network/connection/net_connection_interface.py
@@ -7,7 +7,7 @@ from libp2p.stream_muxer.abc import IMuxedConn
 
 
 class INetConn(Closer):
-    conn: IMuxedConn
+    muxed_conn: IMuxedConn
 
     @abstractmethod
     async def new_stream(self) -> INetStream:
diff --git a/libp2p/network/connection/swarm_connection.py b/libp2p/network/connection/swarm_connection.py
index 15816fcb..e25d75f0 100644
--- a/libp2p/network/connection/swarm_connection.py
+++ b/libp2p/network/connection/swarm_connection.py
@@ -16,15 +16,15 @@ Reference: https://github.com/libp2p/go-libp2p-swarm/blob/04c86bbdafd390651cb2ee
 
 
 class SwarmConn(INetConn):
-    conn: IMuxedConn
+    muxed_conn: IMuxedConn
     swarm: "Swarm"
     streams: Set[NetStream]
     event_closed: asyncio.Event
 
     _tasks: List["asyncio.Future[Any]"]
 
-    def __init__(self, conn: IMuxedConn, swarm: "Swarm") -> None:
-        self.conn = conn
+    def __init__(self, muxed_conn: IMuxedConn, swarm: "Swarm") -> None:
+        self.muxed_conn = muxed_conn
         self.swarm = swarm
         self.streams = set()
         self.event_closed = asyncio.Event()
@@ -37,22 +37,26 @@ class SwarmConn(INetConn):
         self.event_closed.set()
         self.swarm.remove_conn(self)
 
-        await self.conn.close()
+        await self.muxed_conn.close()
 
         # This is just for cleaning up state. The connection has already been closed.
         # We *could* optimize this but it really isn't worth it.
         for stream in self.streams:
             await stream.reset()
-        # Schedule `self._notify_disconnected` to make it execute after `close` is finished.
-        asyncio.ensure_future(self._notify_disconnected())
 
         for task in self._tasks:
             task.cancel()
+            try:
+                await task
+            except asyncio.CancelledError:
+                pass
+        # Schedule `self._notify_disconnected` to make it execute after `close` is finished.
+        self._notify_disconnected()
 
     async def _handle_new_streams(self) -> None:
         while True:
             try:
-                stream = await self.conn.accept_stream()
+                stream = await self.muxed_conn.accept_stream()
             except MuxedConnUnavailable:
                 # If there is anything wrong in the MuxedConn,
                 # we should break the loop and close the connection.
@@ -62,22 +66,28 @@ class SwarmConn(INetConn):
 
         await self.close()
 
-    async def _handle_muxed_stream(self, muxed_stream: IMuxedStream) -> None:
-        net_stream = await self._add_stream(muxed_stream)
-        if self.swarm.common_stream_handler is not None:
-            await self.run_task(self.swarm.common_stream_handler(net_stream))
+    async def _call_stream_handler(self, net_stream: NetStream) -> None:
+        try:
+            await self.swarm.common_stream_handler(net_stream)
+        # TODO: More exact exceptions
+        except Exception:
+            # TODO: Emit logs.
+            # TODO: Clean up and remove the stream from SwarmConn if there is anything wrong.
+            self.remove_stream(net_stream)
 
-    async def _add_stream(self, muxed_stream: IMuxedStream) -> NetStream:
+    async def _handle_muxed_stream(self, muxed_stream: IMuxedStream) -> None:
+        net_stream = self._add_stream(muxed_stream)
+        if self.swarm.common_stream_handler is not None:
+            await self.run_task(self._call_stream_handler(net_stream))
+
+    def _add_stream(self, muxed_stream: IMuxedStream) -> NetStream:
         net_stream = NetStream(muxed_stream)
         self.streams.add(net_stream)
-        # Call notifiers since event occurred
-        for notifee in self.swarm.notifees:
-            await notifee.opened_stream(self.swarm, net_stream)
+        self.swarm.notify_opened_stream(net_stream)
         return net_stream
 
-    async def _notify_disconnected(self) -> None:
-        for notifee in self.swarm.notifees:
-            await notifee.disconnected(self.swarm, self.conn)
+    def _notify_disconnected(self) -> None:
+        self.swarm.notify_disconnected(self)
 
     async def start(self) -> None:
         await self.run_task(self._handle_new_streams())
@@ -86,8 +96,13 @@ class SwarmConn(INetConn):
         self._tasks.append(asyncio.ensure_future(coro))
 
     async def new_stream(self) -> NetStream:
-        muxed_stream = await self.conn.open_stream()
-        return await self._add_stream(muxed_stream)
+        muxed_stream = await self.muxed_conn.open_stream()
+        return self._add_stream(muxed_stream)
 
     async def get_streams(self) -> Tuple[NetStream, ...]:
         return tuple(self.streams)
+
+    def remove_stream(self, stream: NetStream) -> None:
+        if stream not in self.streams:
+            return
+        self.streams.remove(stream)
diff --git a/libp2p/network/network_interface.py b/libp2p/network/network_interface.py
index 470da1a9..94ddba2c 100644
--- a/libp2p/network/network_interface.py
+++ b/libp2p/network/network_interface.py
@@ -7,7 +7,7 @@ from libp2p.network.connection.net_connection_interface import INetConn
 from libp2p.peer.id import ID
 from libp2p.peer.peerstore_interface import IPeerStore
 from libp2p.transport.listener_interface import IListener
-from libp2p.typing import StreamHandlerFn, TProtocol
+from libp2p.typing import StreamHandlerFn
 
 from .stream.net_stream_interface import INetStream
 
@@ -38,9 +38,7 @@ class INetwork(ABC):
         """
 
     @abstractmethod
-    async def new_stream(
-        self, peer_id: ID, protocol_ids: Sequence[TProtocol]
-    ) -> INetStream:
+    async def new_stream(self, peer_id: ID) -> INetStream:
         """
         :param peer_id: peer_id of destination
         :param protocol_ids: available protocol ids to use for stream
@@ -61,7 +59,7 @@ class INetwork(ABC):
         """
 
     @abstractmethod
-    def notify(self, notifee: "INotifee") -> bool:
+    def register_notifee(self, notifee: "INotifee") -> None:
         """
         :param notifee: object implementing Notifee interface
         :return: true if notifee registered successfully, false otherwise
diff --git a/libp2p/network/notifee_interface.py b/libp2p/network/notifee_interface.py
index ef996bfb..c31f4732 100644
--- a/libp2p/network/notifee_interface.py
+++ b/libp2p/network/notifee_interface.py
@@ -3,8 +3,8 @@ from typing import TYPE_CHECKING
 
 from multiaddr import Multiaddr
 
+from libp2p.network.connection.net_connection_interface import INetConn
 from libp2p.network.stream.net_stream_interface import INetStream
-from libp2p.stream_muxer.abc import IMuxedConn
 
 if TYPE_CHECKING:
     from .network_interface import INetwork  # noqa: F401
@@ -26,14 +26,14 @@ class INotifee(ABC):
         """
 
     @abstractmethod
-    async def connected(self, network: "INetwork", conn: IMuxedConn) -> None:
+    async def connected(self, network: "INetwork", conn: INetConn) -> None:
         """
         :param network: network the connection was opened on
         :param conn: connection that was opened
         """
 
     @abstractmethod
-    async def disconnected(self, network: "INetwork", conn: IMuxedConn) -> None:
+    async def disconnected(self, network: "INetwork", conn: INetConn) -> None:
         """
         :param network: network the connection was closed on
         :param conn: connection that was closed
diff --git a/libp2p/network/stream/net_stream.py b/libp2p/network/stream/net_stream.py
index d500c088..0142721c 100644
--- a/libp2p/network/stream/net_stream.py
+++ b/libp2p/network/stream/net_stream.py
@@ -1,4 +1,6 @@
-from libp2p.stream_muxer.abc import IMuxedConn, IMuxedStream
+from typing import Optional
+
+from libp2p.stream_muxer.abc import IMuxedStream
 from libp2p.stream_muxer.exceptions import (
     MuxedStreamClosed,
     MuxedStreamEOF,
@@ -16,13 +18,11 @@ from .net_stream_interface import INetStream
 class NetStream(INetStream):
 
     muxed_stream: IMuxedStream
-    # TODO: Why we expose `mplex_conn` here?
-    mplex_conn: IMuxedConn
-    protocol_id: TProtocol
+    protocol_id: Optional[TProtocol]
 
     def __init__(self, muxed_stream: IMuxedStream) -> None:
         self.muxed_stream = muxed_stream
-        self.mplex_conn = muxed_stream.mplex_conn
+        self.muxed_conn = muxed_stream.muxed_conn
         self.protocol_id = None
 
     def get_protocol(self) -> TProtocol:
@@ -68,3 +68,7 @@ class NetStream(INetStream):
 
     async def reset(self) -> None:
         await self.muxed_stream.reset()
+
+    # TODO: `remove`: Called by close and write when the stream is in specific states.
+    #   It notifies `ClosedStream` after `SwarmConn.remove_stream` is called.
+    # Reference: https://github.com/libp2p/go-libp2p-swarm/blob/99831444e78c8f23c9335c17d8f7c700ba25ca14/swarm_stream.go  # noqa: E501
diff --git a/libp2p/network/stream/net_stream_interface.py b/libp2p/network/stream/net_stream_interface.py
index d0547890..41bf4239 100644
--- a/libp2p/network/stream/net_stream_interface.py
+++ b/libp2p/network/stream/net_stream_interface.py
@@ -7,7 +7,7 @@ from libp2p.typing import TProtocol
 
 class INetStream(ReadWriteCloser):
 
-    mplex_conn: IMuxedConn
+    muxed_conn: IMuxedConn
 
     @abstractmethod
     def get_protocol(self) -> TProtocol:
diff --git a/libp2p/network/swarm.py b/libp2p/network/swarm.py
index 32997203..9d507fb6 100644
--- a/libp2p/network/swarm.py
+++ b/libp2p/network/swarm.py
@@ -1,6 +1,6 @@
 import asyncio
 import logging
-from typing import Dict, List, Optional, Sequence
+from typing import Dict, List, Optional
 
 from multiaddr import Multiaddr
 
@@ -18,7 +18,7 @@ from libp2p.transport.exceptions import (
 from libp2p.transport.listener_interface import IListener
 from libp2p.transport.transport_interface import ITransport
 from libp2p.transport.upgrader import TransportUpgrader
-from libp2p.typing import StreamHandlerFn, TProtocol
+from libp2p.typing import StreamHandlerFn
 
 from .connection.raw_connection import RawConnection
 from .connection.swarm_connection import SwarmConn
@@ -141,20 +141,14 @@ class Swarm(INetwork):
 
         return swarm_conn
 
-    async def new_stream(
-        self, peer_id: ID, protocol_ids: Sequence[TProtocol]
-    ) -> INetStream:
+    async def new_stream(self, peer_id: ID) -> INetStream:
         """
         :param peer_id: peer_id of destination
         :param protocol_id: protocol id
         :raises SwarmException: raised when an error occurs
         :return: net stream instance
         """
-        logger.debug(
-            "attempting to open a stream to peer %s, over one of the protocols %s",
-            peer_id,
-            protocol_ids,
-        )
+        logger.debug("attempting to open a stream to peer %s", peer_id)
 
         swarm_conn = await self.dial_peer(peer_id)
 
@@ -229,8 +223,7 @@ class Swarm(INetwork):
                 await listener.listen(maddr)
 
                 # Call notifiers since event occurred
-                for notifee in self.notifees:
-                    await notifee.listen(self, maddr)
+                self.notify_listen(maddr)
 
                 return True
             except IOError:
@@ -240,16 +233,6 @@ class Swarm(INetwork):
         # No maddr succeeded
         return False
 
-    def notify(self, notifee: INotifee) -> bool:
-        """
-        :param notifee: object implementing Notifee interface
-        :return: true if notifee registered successfully, false otherwise
-        """
-        if isinstance(notifee, INotifee):
-            self.notifees.append(notifee)
-            return True
-        return False
-
     def add_router(self, router: IPeerRouting) -> None:
         self.router = router
 
@@ -288,9 +271,7 @@ class Swarm(INetwork):
         # Store muxed_conn with peer id
         self.connections[muxed_conn.peer_id] = swarm_conn
         # Call notifiers since event occurred
-        for notifee in self.notifees:
-            # TODO: Call with other type of conn?
-            await notifee.connected(self, muxed_conn)
+        self.notify_connected(swarm_conn)
         await swarm_conn.start()
         return swarm_conn
 
@@ -298,9 +279,38 @@ class Swarm(INetwork):
         """
         Simply remove the connection from Swarm's records, without closing the connection.
         """
-        peer_id = swarm_conn.conn.peer_id
+        peer_id = swarm_conn.muxed_conn.peer_id
         if peer_id not in self.connections:
             return
         # TODO: Should be changed to remove the exact connection,
         #   if we have several connections per peer in the future.
         del self.connections[peer_id]
+
+    # Notifee
+
+    # TODO: Remeber the spawn notifying tasks and clean them up when closing.
+
+    def register_notifee(self, notifee: INotifee) -> None:
+        """
+        :param notifee: object implementing Notifee interface
+        :return: true if notifee registered successfully, false otherwise
+        """
+        self.notifees.append(notifee)
+
+    def notify_opened_stream(self, stream: INetStream) -> None:
+        asyncio.gather(
+            *[notifee.opened_stream(self, stream) for notifee in self.notifees]
+        )
+
+    # TODO: `notify_closed_stream`
+
+    def notify_connected(self, conn: INetConn) -> None:
+        asyncio.gather(*[notifee.connected(self, conn) for notifee in self.notifees])
+
+    def notify_disconnected(self, conn: INetConn) -> None:
+        asyncio.gather(*[notifee.disconnected(self, conn) for notifee in self.notifees])
+
+    def notify_listen(self, multiaddr: Multiaddr) -> None:
+        asyncio.gather(*[notifee.listen(self, multiaddr) for notifee in self.notifees])
+
+    # TODO: `notify_listen_close`
diff --git a/libp2p/protocol_muxer/multiselect_communicator.py b/libp2p/protocol_muxer/multiselect_communicator.py
index a66a5642..6f7b715d 100644
--- a/libp2p/protocol_muxer/multiselect_communicator.py
+++ b/libp2p/protocol_muxer/multiselect_communicator.py
@@ -20,10 +20,10 @@ class MultiselectCommunicator(IMultiselectCommunicator):
         msg_bytes = encode_delim(msg_str.encode())
         try:
             await self.read_writer.write(msg_bytes)
-        except IOException:
+        except IOException as error:
             raise MultiselectCommunicatorError(
                 "fail to write to multiselect communicator"
-            )
+            ) from error
 
     async def read(self) -> str:
         """
@@ -32,8 +32,8 @@ class MultiselectCommunicator(IMultiselectCommunicator):
         try:
             data = await read_delim(self.read_writer)
         # `IOException` includes `IncompleteReadError` and `StreamError`
-        except (ParseError, IOException, ValueError):
+        except (ParseError, IOException) as error:
             raise MultiselectCommunicatorError(
                 "fail to read from multiselect communicator"
-            )
+            ) from error
         return data.decode()
diff --git a/libp2p/pubsub/pubsub.py b/libp2p/pubsub/pubsub.py
index ffc210be..cceba08a 100644
--- a/libp2p/pubsub/pubsub.py
+++ b/libp2p/pubsub/pubsub.py
@@ -98,7 +98,7 @@ class Pubsub:
 
         # Register a notifee
         self.peer_queue = asyncio.Queue()
-        self.host.get_network().notify(PubsubNotifee(self.peer_queue))
+        self.host.get_network().register_notifee(PubsubNotifee(self.peer_queue))
 
         # Register stream handlers for each pubsub router protocol to handle
         # the pubsub streams opened on those protocols
@@ -154,7 +154,7 @@ class Pubsub:
         messages from other nodes
         :param stream: stream to continously read from
         """
-        peer_id = stream.mplex_conn.peer_id
+        peer_id = stream.muxed_conn.peer_id
 
         while True:
             try:
diff --git a/libp2p/pubsub/pubsub_notifee.py b/libp2p/pubsub/pubsub_notifee.py
index 6ecab1ab..85c0bd8d 100644
--- a/libp2p/pubsub/pubsub_notifee.py
+++ b/libp2p/pubsub/pubsub_notifee.py
@@ -2,10 +2,10 @@ from typing import TYPE_CHECKING
 
 from multiaddr import Multiaddr
 
+from libp2p.network.connection.net_connection_interface import INetConn
 from libp2p.network.network_interface import INetwork
 from libp2p.network.notifee_interface import INotifee
 from libp2p.network.stream.net_stream_interface import INetStream
-from libp2p.stream_muxer.abc import IMuxedConn
 
 if TYPE_CHECKING:
     import asyncio  # noqa: F401
@@ -29,16 +29,16 @@ class PubsubNotifee(INotifee):
     async def closed_stream(self, network: INetwork, stream: INetStream) -> None:
         pass
 
-    async def connected(self, network: INetwork, conn: IMuxedConn) -> None:
+    async def connected(self, network: INetwork, conn: INetConn) -> None:
         """
         Add peer_id to initiator_peers_queue, so that this peer_id can be used to
         create a stream and we only want to have one pubsub stream with each peer.
         :param network: network the connection was opened on
         :param conn: connection that was opened
         """
-        await self.initiator_peers_queue.put(conn.peer_id)
+        await self.initiator_peers_queue.put(conn.muxed_conn.peer_id)
 
-    async def disconnected(self, network: INetwork, conn: IMuxedConn) -> None:
+    async def disconnected(self, network: INetwork, conn: INetConn) -> None:
         pass
 
     async def listen(self, network: INetwork, multiaddr: Multiaddr) -> None:
diff --git a/libp2p/security/security_multistream.py b/libp2p/security/security_multistream.py
index 466d60a8..cff55af3 100644
--- a/libp2p/security/security_multistream.py
+++ b/libp2p/security/security_multistream.py
@@ -1,6 +1,5 @@
 from abc import ABC
 from collections import OrderedDict
-from typing import Mapping
 
 from libp2p.network.connection.raw_connection_interface import IRawConnection
 from libp2p.peer.id import ID
@@ -9,6 +8,7 @@ from libp2p.protocol_muxer.multiselect_client import MultiselectClient
 from libp2p.protocol_muxer.multiselect_communicator import MultiselectCommunicator
 from libp2p.security.secure_conn_interface import ISecureConn
 from libp2p.security.secure_transport_interface import ISecureTransport
+from libp2p.transport.typing import TSecurityOptions
 from libp2p.typing import TProtocol
 
 
@@ -31,9 +31,7 @@ class SecurityMultistream(ABC):
     multiselect: Multiselect
     multiselect_client: MultiselectClient
 
-    def __init__(
-        self, secure_transports_by_protocol: Mapping[TProtocol, ISecureTransport]
-    ) -> None:
+    def __init__(self, secure_transports_by_protocol: TSecurityOptions) -> None:
         self.transports = OrderedDict()
         self.multiselect = Multiselect()
         self.multiselect_client = MultiselectClient()
diff --git a/libp2p/stream_muxer/abc.py b/libp2p/stream_muxer/abc.py
index 78438f22..4af110b6 100644
--- a/libp2p/stream_muxer/abc.py
+++ b/libp2p/stream_muxer/abc.py
@@ -55,7 +55,7 @@ class IMuxedConn(ABC):
 
 class IMuxedStream(ReadWriteCloser):
 
-    mplex_conn: IMuxedConn
+    muxed_conn: IMuxedConn
 
     @abstractmethod
     async def reset(self) -> None:
diff --git a/libp2p/stream_muxer/mplex/mplex.py b/libp2p/stream_muxer/mplex/mplex.py
index ea7e47ac..768e66c1 100644
--- a/libp2p/stream_muxer/mplex/mplex.py
+++ b/libp2p/stream_muxer/mplex/mplex.py
@@ -31,9 +31,6 @@ class Mplex(IMuxedConn):
 
     secured_conn: ISecureConn
     peer_id: ID
-    # TODO: `dataIn` in go implementation. Should be size of 8.
-    # TODO: Also, `dataIn` is closed indicating EOF in Go. We don't have similar strategies
-    #   to let the `MplexStream`s know that EOF arrived (#235).
     next_channel_id: int
     streams: Dict[StreamID, MplexStream]
     streams_lock: asyncio.Lock
@@ -43,7 +40,6 @@ class Mplex(IMuxedConn):
 
     _tasks: List["asyncio.Future[Any]"]
 
-    # TODO: `generic_protocol_handler` should be refactored out of mplex conn.
     def __init__(self, secured_conn: ISecureConn, peer_id: ID) -> None:
         """
         create a new muxed connection
diff --git a/libp2p/stream_muxer/mplex/mplex_stream.py b/libp2p/stream_muxer/mplex/mplex_stream.py
index 8cabccc4..221e238e 100644
--- a/libp2p/stream_muxer/mplex/mplex_stream.py
+++ b/libp2p/stream_muxer/mplex/mplex_stream.py
@@ -18,12 +18,13 @@ class MplexStream(IMuxedStream):
 
     name: str
     stream_id: StreamID
-    mplex_conn: "Mplex"
+    muxed_conn: "Mplex"
     read_deadline: int
     write_deadline: int
 
     close_lock: asyncio.Lock
 
+    # NOTE: `dataIn` is size of 8 in Go implementation.
     incoming_data: "asyncio.Queue[bytes]"
 
     event_local_closed: asyncio.Event
@@ -32,15 +33,15 @@ class MplexStream(IMuxedStream):
 
     _buf: bytearray
 
-    def __init__(self, name: str, stream_id: StreamID, mplex_conn: "Mplex") -> None:
+    def __init__(self, name: str, stream_id: StreamID, muxed_conn: "Mplex") -> None:
         """
         create new MuxedStream in muxer
         :param stream_id: stream id of this stream
-        :param mplex_conn: muxed connection of this muxed_stream
+        :param muxed_conn: muxed connection of this muxed_stream
         """
         self.name = name
         self.stream_id = stream_id
-        self.mplex_conn = mplex_conn
+        self.muxed_conn = muxed_conn
         self.read_deadline = None
         self.write_deadline = None
         self.event_local_closed = asyncio.Event()
@@ -147,7 +148,7 @@ class MplexStream(IMuxedStream):
             if self.is_initiator
             else HeaderTags.MessageReceiver
         )
-        return await self.mplex_conn.send_message(flag, data, self.stream_id)
+        return await self.muxed_conn.send_message(flag, data, self.stream_id)
 
     async def close(self) -> None:
         """
@@ -163,8 +164,8 @@ class MplexStream(IMuxedStream):
         flag = (
             HeaderTags.CloseInitiator if self.is_initiator else HeaderTags.CloseReceiver
         )
-        # TODO: Raise when `mplex_conn.send_message` fails and `Mplex` isn't shutdown.
-        await self.mplex_conn.send_message(flag, None, self.stream_id)
+        # TODO: Raise when `muxed_conn.send_message` fails and `Mplex` isn't shutdown.
+        await self.muxed_conn.send_message(flag, None, self.stream_id)
 
         _is_remote_closed: bool
         async with self.close_lock:
@@ -173,8 +174,8 @@ class MplexStream(IMuxedStream):
 
         if _is_remote_closed:
             # Both sides are closed, we can safely remove the buffer from the dict.
-            async with self.mplex_conn.streams_lock:
-                del self.mplex_conn.streams[self.stream_id]
+            async with self.muxed_conn.streams_lock:
+                del self.muxed_conn.streams[self.stream_id]
 
     async def reset(self) -> None:
         """
@@ -196,19 +197,19 @@ class MplexStream(IMuxedStream):
                     else HeaderTags.ResetReceiver
                 )
                 asyncio.ensure_future(
-                    self.mplex_conn.send_message(flag, None, self.stream_id)
+                    self.muxed_conn.send_message(flag, None, self.stream_id)
                 )
                 await asyncio.sleep(0)
 
             self.event_local_closed.set()
             self.event_remote_closed.set()
 
-        async with self.mplex_conn.streams_lock:
+        async with self.muxed_conn.streams_lock:
             if (
-                self.mplex_conn.streams is not None
-                and self.stream_id in self.mplex_conn.streams
+                self.muxed_conn.streams is not None
+                and self.stream_id in self.muxed_conn.streams
             ):
-                del self.mplex_conn.streams[self.stream_id]
+                del self.muxed_conn.streams[self.stream_id]
 
     # TODO deadline not in use
     def set_deadline(self, ttl: int) -> bool:
diff --git a/libp2p/stream_muxer/muxer_multistream.py b/libp2p/stream_muxer/muxer_multistream.py
index 806c90d6..7f6ee077 100644
--- a/libp2p/stream_muxer/muxer_multistream.py
+++ b/libp2p/stream_muxer/muxer_multistream.py
@@ -1,5 +1,4 @@
 from collections import OrderedDict
-from typing import Mapping, Type
 
 from libp2p.network.connection.raw_connection_interface import IRawConnection
 from libp2p.peer.id import ID
@@ -7,12 +6,11 @@ from libp2p.protocol_muxer.multiselect import Multiselect
 from libp2p.protocol_muxer.multiselect_client import MultiselectClient
 from libp2p.protocol_muxer.multiselect_communicator import MultiselectCommunicator
 from libp2p.security.secure_conn_interface import ISecureConn
+from libp2p.transport.typing import TMuxerClass, TMuxerOptions
 from libp2p.typing import TProtocol
 
 from .abc import IMuxedConn
 
-MuxerClassType = Type[IMuxedConn]
-
 # FIXME: add negotiate timeout to `MuxerMultistream`
 DEFAULT_NEGOTIATE_TIMEOUT = 60
 
@@ -24,20 +22,18 @@ class MuxerMultistream:
     """
 
     # NOTE: Can be changed to `typing.OrderedDict` since Python 3.7.2.
-    transports: "OrderedDict[TProtocol, MuxerClassType]"
+    transports: "OrderedDict[TProtocol, TMuxerClass]"
     multiselect: Multiselect
     multiselect_client: MultiselectClient
 
-    def __init__(
-        self, muxer_transports_by_protocol: Mapping[TProtocol, MuxerClassType]
-    ) -> None:
+    def __init__(self, muxer_transports_by_protocol: TMuxerOptions) -> None:
         self.transports = OrderedDict()
         self.multiselect = Multiselect()
         self.multiselect_client = MultiselectClient()
         for protocol, transport in muxer_transports_by_protocol.items():
             self.add_transport(protocol, transport)
 
-    def add_transport(self, protocol: TProtocol, transport: MuxerClassType) -> None:
+    def add_transport(self, protocol: TProtocol, transport: TMuxerClass) -> None:
         """
         Add a protocol and its corresponding transport to multistream-select(multiselect).
         The order that a protocol is added is exactly the precedence it is negotiated in
@@ -51,7 +47,7 @@ class MuxerMultistream:
         self.transports[protocol] = transport
         self.multiselect.add_handler(protocol, None)
 
-    async def select_transport(self, conn: IRawConnection) -> MuxerClassType:
+    async def select_transport(self, conn: IRawConnection) -> TMuxerClass:
         """
         Select a transport that both us and the node on the
         other end of conn support and agree on
diff --git a/libp2p/transport/typing.py b/libp2p/transport/typing.py
index 6d0047c5..f9b31dcb 100644
--- a/libp2p/transport/typing.py
+++ b/libp2p/transport/typing.py
@@ -1,4 +1,11 @@
 from asyncio import StreamReader, StreamWriter
-from typing import Awaitable, Callable
+from typing import Awaitable, Callable, Mapping, Type
+
+from libp2p.security.secure_transport_interface import ISecureTransport
+from libp2p.stream_muxer.abc import IMuxedConn
+from libp2p.typing import TProtocol
 
 THandler = Callable[[StreamReader, StreamWriter], Awaitable[None]]
+TSecurityOptions = Mapping[TProtocol, ISecureTransport]
+TMuxerClass = Type[IMuxedConn]
+TMuxerOptions = Mapping[TProtocol, TMuxerClass]
diff --git a/libp2p/transport/upgrader.py b/libp2p/transport/upgrader.py
index 9f8be990..8dda95e7 100644
--- a/libp2p/transport/upgrader.py
+++ b/libp2p/transport/upgrader.py
@@ -1,16 +1,13 @@
-from typing import Mapping
-
 from libp2p.network.connection.raw_connection_interface import IRawConnection
 from libp2p.peer.id import ID
 from libp2p.protocol_muxer.exceptions import MultiselectClientError, MultiselectError
 from libp2p.security.exceptions import HandshakeFailure
 from libp2p.security.secure_conn_interface import ISecureConn
-from libp2p.security.secure_transport_interface import ISecureTransport
 from libp2p.security.security_multistream import SecurityMultistream
 from libp2p.stream_muxer.abc import IMuxedConn
-from libp2p.stream_muxer.muxer_multistream import MuxerClassType, MuxerMultistream
+from libp2p.stream_muxer.muxer_multistream import MuxerMultistream
 from libp2p.transport.exceptions import MuxerUpgradeFailure, SecurityUpgradeFailure
-from libp2p.typing import TProtocol
+from libp2p.transport.typing import TMuxerOptions, TSecurityOptions
 
 from .listener_interface import IListener
 from .transport_interface import ITransport
@@ -22,8 +19,8 @@ class TransportUpgrader:
 
     def __init__(
         self,
-        secure_transports_by_protocol: Mapping[TProtocol, ISecureTransport],
-        muxer_transports_by_protocol: Mapping[TProtocol, MuxerClassType],
+        secure_transports_by_protocol: TSecurityOptions,
+        muxer_transports_by_protocol: TMuxerOptions,
     ):
         self.security_multistream = SecurityMultistream(secure_transports_by_protocol)
         self.muxer_multistream = MuxerMultistream(muxer_transports_by_protocol)
diff --git a/libp2p/utils.py b/libp2p/utils.py
index 0e15b567..39c79e58 100644
--- a/libp2p/utils.py
+++ b/libp2p/utils.py
@@ -73,9 +73,12 @@ def encode_delim(msg: bytes) -> bytes:
 
 async def read_delim(reader: Reader) -> bytes:
     msg_bytes = await read_varint_prefixed_bytes(reader)
-    # TODO: Investigate if it is possible to have empty `msg_bytes`
-    if len(msg_bytes) != 0 and msg_bytes[-1:] != b"\n":
-        raise ValueError(f'msg_bytes is not delimited by b"\\n": msg_bytes={msg_bytes}')
+    if len(msg_bytes) == 0:
+        raise ParseError(f"`len(msg_bytes)` should not be 0")
+    if msg_bytes[-1:] != b"\n":
+        raise ParseError(
+            f'`msg_bytes` is not delimited by b"\\n": `msg_bytes`={msg_bytes}'
+        )
     return msg_bytes[:-1]
 
 
diff --git a/tests/factories.py b/tests/factories.py
index e39b12d3..b4e8be23 100644
--- a/tests/factories.py
+++ b/tests/factories.py
@@ -6,6 +6,7 @@ import factory
 from libp2p import generate_new_rsa_identity, initialize_default_swarm
 from libp2p.crypto.keys import KeyPair
 from libp2p.host.basic_host import BasicHost
+from libp2p.network.connection.swarm_connection import SwarmConn
 from libp2p.network.stream.net_stream_interface import INetStream
 from libp2p.network.swarm import Swarm
 from libp2p.pubsub.floodsub import FloodSub
@@ -14,6 +15,9 @@ from libp2p.pubsub.pubsub import Pubsub
 from libp2p.security.base_transport import BaseSecureTransport
 from libp2p.security.insecure.transport import PLAINTEXT_PROTOCOL_ID, InsecureTransport
 import libp2p.security.secio.transport as secio
+from libp2p.stream_muxer.mplex.mplex import MPLEX_PROTOCOL_ID, Mplex
+from libp2p.stream_muxer.mplex.mplex_stream import MplexStream
+from libp2p.transport.typing import TMuxerOptions
 from libp2p.typing import TProtocol
 from tests.configs import LISTEN_MADDR
 from tests.pubsub.configs import (
@@ -33,10 +37,10 @@ def security_transport_factory(
         return {secio.ID: secio.Transport(key_pair)}
 
 
-def SwarmFactory(is_secure: bool) -> Swarm:
+def SwarmFactory(is_secure: bool, muxer_opt: TMuxerOptions = None) -> Swarm:
     key_pair = generate_new_rsa_identity()
-    sec_opt = security_transport_factory(False, key_pair)
-    return initialize_default_swarm(key_pair, sec_opt=sec_opt)
+    sec_opt = security_transport_factory(is_secure, key_pair)
+    return initialize_default_swarm(key_pair, sec_opt=sec_opt, muxer_opt=muxer_opt)
 
 
 class ListeningSwarmFactory(factory.Factory):
@@ -44,17 +48,22 @@ class ListeningSwarmFactory(factory.Factory):
         model = Swarm
 
     @classmethod
-    async def create_and_listen(cls, is_secure: bool) -> Swarm:
-        swarm = SwarmFactory(is_secure)
+    async def create_and_listen(
+        cls, is_secure: bool, muxer_opt: TMuxerOptions = None
+    ) -> Swarm:
+        swarm = SwarmFactory(is_secure, muxer_opt=muxer_opt)
         await swarm.listen(LISTEN_MADDR)
         return swarm
 
     @classmethod
     async def create_batch_and_listen(
-        cls, is_secure: bool, number: int
+        cls, is_secure: bool, number: int, muxer_opt: TMuxerOptions = None
     ) -> Tuple[Swarm, ...]:
         return await asyncio.gather(
-            *[cls.create_and_listen(is_secure) for _ in range(number)]
+            *[
+                cls.create_and_listen(is_secure, muxer_opt=muxer_opt)
+                for _ in range(number)
+            ]
         )
 
 
@@ -111,8 +120,12 @@ class PubsubFactory(factory.Factory):
     cache_size = None
 
 
-async def swarm_pair_factory(is_secure: bool) -> Tuple[Swarm, Swarm]:
-    swarms = await ListeningSwarmFactory.create_batch_and_listen(is_secure, 2)
+async def swarm_pair_factory(
+    is_secure: bool, muxer_opt: TMuxerOptions = None
+) -> Tuple[Swarm, Swarm]:
+    swarms = await ListeningSwarmFactory.create_batch_and_listen(
+        is_secure, 2, muxer_opt=muxer_opt
+    )
     await connect_swarm(swarms[0], swarms[1])
     return swarms[0], swarms[1]
 
@@ -128,11 +141,37 @@ async def host_pair_factory(is_secure) -> Tuple[BasicHost, BasicHost]:
     return hosts[0], hosts[1]
 
 
-# async def connection_pair_factory() -> Tuple[Mplex, BasicHost, Mplex, BasicHost]:
-#     host_0, host_1 = await host_pair_factory()
-#     mplex_conn_0 = host_0.get_network().connections[host_1.get_id()]
-#     mplex_conn_1 = host_1.get_network().connections[host_0.get_id()]
-#     return mplex_conn_0, host_0, mplex_conn_1, host_1
+async def swarm_conn_pair_factory(
+    is_secure: bool, muxer_opt: TMuxerOptions = None
+) -> Tuple[SwarmConn, Swarm, SwarmConn, Swarm]:
+    swarms = await swarm_pair_factory(is_secure)
+    conn_0 = swarms[0].connections[swarms[1].get_peer_id()]
+    conn_1 = swarms[1].connections[swarms[0].get_peer_id()]
+    return conn_0, swarms[0], conn_1, swarms[1]
+
+
+async def mplex_conn_pair_factory(is_secure: bool) -> Tuple[Mplex, Swarm, Mplex, Swarm]:
+    muxer_opt = {MPLEX_PROTOCOL_ID: Mplex}
+    conn_0, swarm_0, conn_1, swarm_1 = await swarm_conn_pair_factory(
+        is_secure, muxer_opt=muxer_opt
+    )
+    return conn_0.muxed_conn, swarm_0, conn_1.muxed_conn, swarm_1
+
+
+async def mplex_stream_pair_factory(
+    is_secure: bool
+) -> Tuple[MplexStream, Swarm, MplexStream, Swarm]:
+    mplex_conn_0, swarm_0, mplex_conn_1, swarm_1 = await mplex_conn_pair_factory(
+        is_secure
+    )
+    stream_0 = await mplex_conn_0.open_stream()
+    await asyncio.sleep(0.01)
+    stream_1: MplexStream
+    async with mplex_conn_1.streams_lock:
+        if len(mplex_conn_1.streams) != 1:
+            raise Exception("Mplex should not have any stream upon connection")
+        stream_1 = tuple(mplex_conn_1.streams.values())[0]
+    return stream_0, swarm_0, stream_1, swarm_1
 
 
 async def net_stream_pair_factory(
diff --git a/tests/libp2p/test_notify.py b/tests/libp2p/test_notify.py
deleted file mode 100644
index b9a8707e..00000000
--- a/tests/libp2p/test_notify.py
+++ /dev/null
@@ -1,351 +0,0 @@
-"""
-Test Notify and Notifee by ensuring that the proper events get
-called, and that the stream passed into opened_stream is correct
-
-Note: Listen event does not get hit because MyNotifee is passed
-into network after network has already started listening
-
-TODO: Add tests for closed_stream disconnected, listen_close when those
-features are implemented in swarm
-"""
-
-import multiaddr
-import pytest
-
-from libp2p import initialize_default_swarm, new_node
-from libp2p.crypto.rsa import create_new_key_pair
-from libp2p.host.basic_host import BasicHost
-from libp2p.network.notifee_interface import INotifee
-from tests.constants import MAX_READ_LEN
-from tests.utils import perform_two_host_set_up
-
-ACK = "ack:"
-
-
-class MyNotifee(INotifee):
-    def __init__(self, events, val_to_append_to_event):
-        self.events = events
-        self.val_to_append_to_event = val_to_append_to_event
-
-    async def opened_stream(self, network, stream):
-        self.events.append(["opened_stream" + self.val_to_append_to_event, stream])
-
-    async def closed_stream(self, network, stream):
-        pass
-
-    async def connected(self, network, conn):
-        self.events.append(["connected" + self.val_to_append_to_event, conn])
-
-    async def disconnected(self, network, conn):
-        pass
-
-    async def listen(self, network, _multiaddr):
-        self.events.append(["listened" + self.val_to_append_to_event, _multiaddr])
-
-    async def listen_close(self, network, _multiaddr):
-        pass
-
-
-class InvalidNotifee:
-    def __init__(self):
-        pass
-
-    async def opened_stream(self):
-        assert False
-
-    async def closed_stream(self):
-        assert False
-
-    async def connected(self):
-        assert False
-
-    async def disconnected(self):
-        assert False
-
-    async def listen(self):
-        assert False
-
-
-@pytest.mark.asyncio
-async def test_one_notifier():
-    node_a, node_b = await perform_two_host_set_up()
-
-    # Add notifee for node_a
-    events = []
-    assert node_a.get_network().notify(MyNotifee(events, "0"))
-
-    stream = await node_a.new_stream(node_b.get_id(), ["/echo/1.0.0"])
-
-    # Ensure the connected and opened_stream events were hit in MyNotifee obj
-    # and that stream passed into opened_stream matches the stream created on
-    # node_a
-    assert events == [["connected0", stream.mplex_conn], ["opened_stream0", stream]]
-
-    messages = ["hello", "hello"]
-    for message in messages:
-        expected_resp = ACK + message
-        await stream.write(message.encode())
-
-        response = (await stream.read(len(expected_resp))).decode()
-
-        assert response == expected_resp
-
-    # Success, terminate pending tasks.
-
-
-@pytest.mark.asyncio
-async def test_one_notifier_on_two_nodes():
-    events_b = []
-    messages = ["hello", "hello"]
-
-    async def my_stream_handler(stream):
-        # Ensure the connected and opened_stream events were hit in Notifee obj
-        # and that the stream passed into opened_stream matches the stream created on
-        # node_b
-        assert events_b == [
-            ["connectedb", stream.mplex_conn],
-            ["opened_streamb", stream],
-        ]
-        for message in messages:
-            read_string = (await stream.read(len(message))).decode()
-
-            resp = ACK + read_string
-            await stream.write(resp.encode())
-
-    node_a, node_b = await perform_two_host_set_up(my_stream_handler)
-
-    # Add notifee for node_a
-    events_a = []
-    assert node_a.get_network().notify(MyNotifee(events_a, "a"))
-
-    # Add notifee for node_b
-    assert node_b.get_network().notify(MyNotifee(events_b, "b"))
-
-    stream = await node_a.new_stream(node_b.get_id(), ["/echo/1.0.0"])
-
-    # Ensure the connected and opened_stream events were hit in MyNotifee obj
-    # and that stream passed into opened_stream matches the stream created on
-    # node_a
-    assert events_a == [["connecteda", stream.mplex_conn], ["opened_streama", stream]]
-
-    for message in messages:
-        expected_resp = ACK + message
-        await stream.write(message.encode())
-
-        response = (await stream.read(len(expected_resp))).decode()
-
-        assert response == expected_resp
-
-    # Success, terminate pending tasks.
-
-
-@pytest.mark.asyncio
-async def test_one_notifier_on_two_nodes_with_listen():
-    events_b = []
-    messages = ["hello", "hello"]
-
-    node_a_key_pair = create_new_key_pair()
-    node_a_transport_opt = ["/ip4/127.0.0.1/tcp/0"]
-    node_a = await new_node(node_a_key_pair, transport_opt=node_a_transport_opt)
-    await node_a.get_network().listen(multiaddr.Multiaddr(node_a_transport_opt[0]))
-
-    # Set up node_b swarm to pass into host
-    node_b_key_pair = create_new_key_pair()
-    node_b_transport_opt = ["/ip4/127.0.0.1/tcp/0"]
-    node_b_multiaddr = multiaddr.Multiaddr(node_b_transport_opt[0])
-    node_b_swarm = initialize_default_swarm(
-        node_b_key_pair, transport_opt=node_b_transport_opt
-    )
-    node_b = BasicHost(node_b_swarm)
-
-    async def my_stream_handler(stream):
-        # Ensure the listened, connected and opened_stream events were hit in Notifee obj
-        # and that the stream passed into opened_stream matches the stream created on
-        # node_b
-        assert events_b == [
-            ["listenedb", node_b_multiaddr],
-            ["connectedb", stream.mplex_conn],
-            ["opened_streamb", stream],
-        ]
-        for message in messages:
-            read_string = (await stream.read(len(message))).decode()
-            resp = ACK + read_string
-            await stream.write(resp.encode())
-
-    # Add notifee for node_a
-    events_a = []
-    assert node_a.get_network().notify(MyNotifee(events_a, "a"))
-
-    # Add notifee for node_b
-    assert node_b.get_network().notify(MyNotifee(events_b, "b"))
-
-    # start listen on node_b_swarm
-    await node_b.get_network().listen(node_b_multiaddr)
-
-    node_b.set_stream_handler("/echo/1.0.0", my_stream_handler)
-    # Associate the peer with local ip address (see default parameters of Libp2p())
-    node_a.get_peerstore().add_addrs(node_b.get_id(), node_b.get_addrs(), 10)
-    stream = await node_a.new_stream(node_b.get_id(), ["/echo/1.0.0"])
-
-    # Ensure the connected and opened_stream events were hit in MyNotifee obj
-    # and that stream passed into opened_stream matches the stream created on
-    # node_a
-    assert events_a == [["connecteda", stream.mplex_conn], ["opened_streama", stream]]
-
-    for message in messages:
-        expected_resp = ACK + message
-        await stream.write(message.encode())
-
-        response = (await stream.read(len(expected_resp))).decode()
-
-        assert response == expected_resp
-
-    # Success, terminate pending tasks.
-
-
-@pytest.mark.asyncio
-async def test_two_notifiers():
-    node_a, node_b = await perform_two_host_set_up()
-
-    # Add notifee for node_a
-    events0 = []
-    assert node_a.get_network().notify(MyNotifee(events0, "0"))
-
-    events1 = []
-    assert node_a.get_network().notify(MyNotifee(events1, "1"))
-
-    stream = await node_a.new_stream(node_b.get_id(), ["/echo/1.0.0"])
-
-    # Ensure the connected and opened_stream events were hit in both Notifee objs
-    # and that the stream passed into opened_stream matches the stream created on
-    # node_a
-    assert events0 == [["connected0", stream.mplex_conn], ["opened_stream0", stream]]
-    assert events1 == [["connected1", stream.mplex_conn], ["opened_stream1", stream]]
-
-    messages = ["hello", "hello"]
-    for message in messages:
-        expected_resp = ACK + message
-        await stream.write(message.encode())
-
-        response = (await stream.read(len(expected_resp))).decode()
-
-        assert response == expected_resp
-
-    # Success, terminate pending tasks.
-
-
-@pytest.mark.asyncio
-async def test_ten_notifiers():
-    num_notifiers = 10
-
-    node_a, node_b = await perform_two_host_set_up()
-
-    # Add notifee for node_a
-    events_lst = []
-    for i in range(num_notifiers):
-        events_lst.append([])
-        assert node_a.get_network().notify(MyNotifee(events_lst[i], str(i)))
-
-    stream = await node_a.new_stream(node_b.get_id(), ["/echo/1.0.0"])
-
-    # Ensure the connected and opened_stream events were hit in both Notifee objs
-    # and that the stream passed into opened_stream matches the stream created on
-    # node_a
-    for i in range(num_notifiers):
-        assert events_lst[i] == [
-            ["connected" + str(i), stream.mplex_conn],
-            ["opened_stream" + str(i), stream],
-        ]
-
-    messages = ["hello", "hello"]
-    for message in messages:
-        expected_resp = ACK + message
-        await stream.write(message.encode())
-
-        response = (await stream.read(len(expected_resp))).decode()
-
-        assert response == expected_resp
-
-    # Success, terminate pending tasks.
-
-
-@pytest.mark.asyncio
-async def test_ten_notifiers_on_two_nodes():
-    num_notifiers = 10
-    events_lst_b = []
-
-    async def my_stream_handler(stream):
-        # Ensure the connected and opened_stream events were hit in all Notifee objs
-        # and that the stream passed into opened_stream matches the stream created on
-        # node_b
-        for i in range(num_notifiers):
-            assert events_lst_b[i] == [
-                ["connectedb" + str(i), stream.mplex_conn],
-                ["opened_streamb" + str(i), stream],
-            ]
-        while True:
-            read_string = (await stream.read(MAX_READ_LEN)).decode()
-
-            resp = ACK + read_string
-            await stream.write(resp.encode())
-
-    node_a, node_b = await perform_two_host_set_up(my_stream_handler)
-
-    # Add notifee for node_a and node_b
-    events_lst_a = []
-    for i in range(num_notifiers):
-        events_lst_a.append([])
-        events_lst_b.append([])
-        assert node_a.get_network().notify(MyNotifee(events_lst_a[i], "a" + str(i)))
-        assert node_b.get_network().notify(MyNotifee(events_lst_b[i], "b" + str(i)))
-
-    stream = await node_a.new_stream(node_b.get_id(), ["/echo/1.0.0"])
-
-    # Ensure the connected and opened_stream events were hit in all Notifee objs
-    # and that the stream passed into opened_stream matches the stream created on
-    # node_a
-    for i in range(num_notifiers):
-        assert events_lst_a[i] == [
-            ["connecteda" + str(i), stream.mplex_conn],
-            ["opened_streama" + str(i), stream],
-        ]
-
-    messages = ["hello", "hello"]
-    for message in messages:
-        expected_resp = ACK + message
-        await stream.write(message.encode())
-
-        response = (await stream.read(len(expected_resp))).decode()
-
-        assert response == expected_resp
-
-    # Success, terminate pending tasks.
-
-
-@pytest.mark.asyncio
-async def test_invalid_notifee():
-    num_notifiers = 10
-
-    node_a, node_b = await perform_two_host_set_up()
-
-    # Add notifee for node_a
-    events_lst = []
-    for _ in range(num_notifiers):
-        events_lst.append([])
-        assert not node_a.get_network().notify(InvalidNotifee())
-
-    stream = await node_a.new_stream(node_b.get_id(), ["/echo/1.0.0"])
-
-    # If this point is reached, this implies that the InvalidNotifee instance
-    # did not assert false, i.e. no functions of InvalidNotifee were called (which is correct
-    # given that InvalidNotifee should not have been added as a notifee)
-    messages = ["hello", "hello"]
-    for message in messages:
-        expected_resp = ACK + message
-        await stream.write(message.encode())
-
-        response = (await stream.read(len(expected_resp))).decode()
-
-        assert response == expected_resp
-
-    # Success, terminate pending tasks.
diff --git a/tests/network/conftest.py b/tests/network/conftest.py
index 47d5c5f0..018e822d 100644
--- a/tests/network/conftest.py
+++ b/tests/network/conftest.py
@@ -2,7 +2,11 @@ import asyncio
 
 import pytest
 
-from tests.factories import net_stream_pair_factory, swarm_pair_factory
+from tests.factories import (
+    net_stream_pair_factory,
+    swarm_conn_pair_factory,
+    swarm_pair_factory,
+)
 
 
 @pytest.fixture
@@ -21,3 +25,12 @@ async def swarm_pair(is_host_secure):
         yield swarm_0, swarm_1
     finally:
         await asyncio.gather(*[swarm_0.close(), swarm_1.close()])
+
+
+@pytest.fixture
+async def swarm_conn_pair(is_host_secure):
+    conn_0, swarm_0, conn_1, swarm_1 = await swarm_conn_pair_factory(is_host_secure)
+    try:
+        yield conn_0, conn_1
+    finally:
+        await asyncio.gather(*[swarm_0.close(), swarm_1.close()])
diff --git a/tests/network/test_net_stream.py b/tests/network/test_net_stream.py
index 80bed6ce..9229069f 100644
--- a/tests/network/test_net_stream.py
+++ b/tests/network/test_net_stream.py
@@ -7,9 +7,6 @@ from tests.constants import MAX_READ_LEN
 
 DATA = b"data_123"
 
-# TODO: Move `muxed_stream` specific(currently we are using `MplexStream`) tests to its
-#   own file, after `generic_protocol_handler` is refactored out of `Mplex`.
-
 
 @pytest.mark.asyncio
 async def test_net_stream_read_write(net_stream_pair):
@@ -56,11 +53,9 @@ async def test_net_stream_read_until_eof(net_stream_pair):
 @pytest.mark.asyncio
 async def test_net_stream_read_after_remote_closed(net_stream_pair):
     stream_0, stream_1 = net_stream_pair
-    assert not stream_1.muxed_stream.event_remote_closed.is_set()
     await stream_0.write(DATA)
     await stream_0.close()
     await asyncio.sleep(0.01)
-    assert stream_1.muxed_stream.event_remote_closed.is_set()
     assert (await stream_1.read(MAX_READ_LEN)) == DATA
     with pytest.raises(StreamEOF):
         await stream_1.read(MAX_READ_LEN)
diff --git a/tests/network/test_notify.py b/tests/network/test_notify.py
new file mode 100644
index 00000000..aaf0ed55
--- /dev/null
+++ b/tests/network/test_notify.py
@@ -0,0 +1,112 @@
+"""
+Test Notify and Notifee by ensuring that the proper events get
+called, and that the stream passed into opened_stream is correct
+
+Note: Listen event does not get hit because MyNotifee is passed
+into network after network has already started listening
+
+TODO: Add tests for closed_stream, listen_close when those
+features are implemented in swarm
+"""
+
+import asyncio
+import enum
+
+import pytest
+
+from libp2p.network.notifee_interface import INotifee
+from tests.configs import LISTEN_MADDR
+from tests.factories import SwarmFactory
+from tests.utils import connect_swarm
+
+
+class Event(enum.Enum):
+    OpenedStream = 0
+    ClosedStream = 1  # Not implemented
+    Connected = 2
+    Disconnected = 3
+    Listen = 4
+    ListenClose = 5  # Not implemented
+
+
+class MyNotifee(INotifee):
+    def __init__(self, events):
+        self.events = events
+
+    async def opened_stream(self, network, stream):
+        self.events.append(Event.OpenedStream)
+
+    async def closed_stream(self, network, stream):
+        # TODO: It is not implemented yet.
+        pass
+
+    async def connected(self, network, conn):
+        self.events.append(Event.Connected)
+
+    async def disconnected(self, network, conn):
+        self.events.append(Event.Disconnected)
+
+    async def listen(self, network, _multiaddr):
+        self.events.append(Event.Listen)
+
+    async def listen_close(self, network, _multiaddr):
+        # TODO: It is not implemented yet.
+        pass
+
+
+@pytest.mark.asyncio
+async def test_notify(is_host_secure):
+    swarms = [SwarmFactory(is_host_secure) for _ in range(2)]
+
+    events_0_0 = []
+    events_1_0 = []
+    events_0_without_listen = []
+    swarms[0].register_notifee(MyNotifee(events_0_0))
+    swarms[1].register_notifee(MyNotifee(events_1_0))
+    # Listen
+    await asyncio.gather(*[swarm.listen(LISTEN_MADDR) for swarm in swarms])
+
+    swarms[0].register_notifee(MyNotifee(events_0_without_listen))
+
+    # Connected
+    await connect_swarm(swarms[0], swarms[1])
+    # OpenedStream: first
+    await swarms[0].new_stream(swarms[1].get_peer_id())
+    # OpenedStream: second
+    await swarms[0].new_stream(swarms[1].get_peer_id())
+    # OpenedStream: third, but different direction.
+    await swarms[1].new_stream(swarms[0].get_peer_id())
+
+    await asyncio.sleep(0.01)
+
+    # TODO: Check `ClosedStream` and `ListenClose` events after they are ready.
+
+    # Disconnected
+    await swarms[0].close_peer(swarms[1].get_peer_id())
+    await asyncio.sleep(0.01)
+
+    # Connected again, but different direction.
+    await connect_swarm(swarms[1], swarms[0])
+    await asyncio.sleep(0.01)
+
+    # Disconnected again, but different direction.
+    await swarms[1].close_peer(swarms[0].get_peer_id())
+    await asyncio.sleep(0.01)
+
+    expected_events_without_listen = [
+        Event.Connected,
+        Event.OpenedStream,
+        Event.OpenedStream,
+        Event.OpenedStream,
+        Event.Disconnected,
+        Event.Connected,
+        Event.Disconnected,
+    ]
+    expected_events = [Event.Listen] + expected_events_without_listen
+
+    assert events_0_0 == expected_events
+    assert events_1_0 == expected_events
+    assert events_0_without_listen == expected_events_without_listen
+
+    # Clean up
+    await asyncio.gather(*[swarm.close() for swarm in swarms])
diff --git a/tests/network/test_swarm_conn.py b/tests/network/test_swarm_conn.py
new file mode 100644
index 00000000..2abc7d0f
--- /dev/null
+++ b/tests/network/test_swarm_conn.py
@@ -0,0 +1,45 @@
+import asyncio
+
+import pytest
+
+
+@pytest.mark.asyncio
+async def test_swarm_conn_close(swarm_conn_pair):
+    conn_0, conn_1 = swarm_conn_pair
+
+    assert not conn_0.event_closed.is_set()
+    assert not conn_1.event_closed.is_set()
+
+    await conn_0.close()
+
+    await asyncio.sleep(0.01)
+
+    assert conn_0.event_closed.is_set()
+    assert conn_1.event_closed.is_set()
+    assert conn_0 not in conn_0.swarm.connections.values()
+    assert conn_1 not in conn_1.swarm.connections.values()
+
+
+@pytest.mark.asyncio
+async def test_swarm_conn_streams(swarm_conn_pair):
+    conn_0, conn_1 = swarm_conn_pair
+
+    assert len(await conn_0.get_streams()) == 0
+    assert len(await conn_1.get_streams()) == 0
+
+    stream_0_0 = await conn_0.new_stream()
+    await asyncio.sleep(0.01)
+    assert len(await conn_0.get_streams()) == 1
+    assert len(await conn_1.get_streams()) == 1
+
+    stream_0_1 = await conn_0.new_stream()
+    await asyncio.sleep(0.01)
+    assert len(await conn_0.get_streams()) == 2
+    assert len(await conn_1.get_streams()) == 2
+
+    conn_0.remove_stream(stream_0_0)
+    assert len(await conn_0.get_streams()) == 1
+    conn_0.remove_stream(stream_0_1)
+    assert len(await conn_0.get_streams()) == 0
+    # Nothing happen if `stream_0_1` is not present or already removed.
+    conn_0.remove_stream(stream_0_1)
diff --git a/tests/pubsub/test_pubsub.py b/tests/pubsub/test_pubsub.py
index 34139494..29fdf363 100644
--- a/tests/pubsub/test_pubsub.py
+++ b/tests/pubsub/test_pubsub.py
@@ -233,7 +233,7 @@ class FakeNetStream:
     class FakeMplexConn(NamedTuple):
         peer_id: ID = ID(b"\x12\x20" + b"\x00" * 32)
 
-    mplex_conn = FakeMplexConn()
+    muxed_conn = FakeMplexConn()
 
     def __init__(self) -> None:
         self._queue = asyncio.Queue()
diff --git a/tests/security/test_security_multistream.py b/tests/security/test_security_multistream.py
index 26d31401..a9fe031f 100644
--- a/tests/security/test_security_multistream.py
+++ b/tests/security/test_security_multistream.py
@@ -53,8 +53,8 @@ async def perform_simple_test(
     node2_conn = node2.get_network().connections[peer_id_for_node(node1)]
 
     # Perform assertion
-    assertion_func(node1_conn.conn.secured_conn)
-    assertion_func(node2_conn.conn.secured_conn)
+    assertion_func(node1_conn.muxed_conn.secured_conn)
+    assertion_func(node2_conn.muxed_conn.secured_conn)
 
     # Success, terminate pending tasks.
 
diff --git a/tests/stream_muxer/__init__.py b/tests/stream_muxer/__init__.py
new file mode 100644
index 00000000..e69de29b
diff --git a/tests/stream_muxer/conftest.py b/tests/stream_muxer/conftest.py
new file mode 100644
index 00000000..b1d6c114
--- /dev/null
+++ b/tests/stream_muxer/conftest.py
@@ -0,0 +1,29 @@
+import asyncio
+
+import pytest
+
+from tests.factories import mplex_conn_pair_factory, mplex_stream_pair_factory
+
+
+@pytest.fixture
+async def mplex_conn_pair(is_host_secure):
+    mplex_conn_0, swarm_0, mplex_conn_1, swarm_1 = await mplex_conn_pair_factory(
+        is_host_secure
+    )
+    assert mplex_conn_0.initiator
+    assert not mplex_conn_1.initiator
+    try:
+        yield mplex_conn_0, mplex_conn_1
+    finally:
+        await asyncio.gather(*[swarm_0.close(), swarm_1.close()])
+
+
+@pytest.fixture
+async def mplex_stream_pair(is_host_secure):
+    mplex_stream_0, swarm_0, mplex_stream_1, swarm_1 = await mplex_stream_pair_factory(
+        is_host_secure
+    )
+    try:
+        yield mplex_stream_0, mplex_stream_1
+    finally:
+        await asyncio.gather(*[swarm_0.close(), swarm_1.close()])
diff --git a/tests/stream_muxer/test_mplex_conn.py b/tests/stream_muxer/test_mplex_conn.py
new file mode 100644
index 00000000..6dc98ad6
--- /dev/null
+++ b/tests/stream_muxer/test_mplex_conn.py
@@ -0,0 +1,50 @@
+import asyncio
+
+import pytest
+
+
+@pytest.mark.asyncio
+async def test_mplex_conn(mplex_conn_pair):
+    conn_0, conn_1 = mplex_conn_pair
+
+    assert len(conn_0.streams) == 0
+    assert len(conn_1.streams) == 0
+    assert not conn_0.event_shutting_down.is_set()
+    assert not conn_1.event_shutting_down.is_set()
+    assert not conn_0.event_closed.is_set()
+    assert not conn_1.event_closed.is_set()
+
+    # Test: Open a stream, and both side get 1 more stream.
+    stream_0 = await conn_0.open_stream()
+    await asyncio.sleep(0.01)
+    assert len(conn_0.streams) == 1
+    assert len(conn_1.streams) == 1
+    # Test: From another side.
+    stream_1 = await conn_1.open_stream()
+    await asyncio.sleep(0.01)
+    assert len(conn_0.streams) == 2
+    assert len(conn_1.streams) == 2
+
+    # Close from one side.
+    await conn_0.close()
+    # Sleep for a while for both side to handle `close`.
+    await asyncio.sleep(0.01)
+    # Test: Both side is closed.
+    assert conn_0.event_shutting_down.is_set()
+    assert conn_0.event_closed.is_set()
+    assert conn_1.event_shutting_down.is_set()
+    assert conn_1.event_closed.is_set()
+    # Test: All streams should have been closed.
+    assert stream_0.event_remote_closed.is_set()
+    assert stream_0.event_reset.is_set()
+    assert stream_0.event_local_closed.is_set()
+    assert conn_0.streams is None
+    # Test: All streams on the other side are also closed.
+    assert stream_1.event_remote_closed.is_set()
+    assert stream_1.event_reset.is_set()
+    assert stream_1.event_local_closed.is_set()
+    assert conn_1.streams is None
+
+    # Test: No effect to close more than once between two side.
+    await conn_0.close()
+    await conn_1.close()
diff --git a/tests/stream_muxer/test_mplex_stream.py b/tests/stream_muxer/test_mplex_stream.py
new file mode 100644
index 00000000..e2bcb244
--- /dev/null
+++ b/tests/stream_muxer/test_mplex_stream.py
@@ -0,0 +1,182 @@
+import asyncio
+
+import pytest
+
+from libp2p.stream_muxer.mplex.exceptions import (
+    MplexStreamClosed,
+    MplexStreamEOF,
+    MplexStreamReset,
+)
+from tests.constants import MAX_READ_LEN
+
+DATA = b"data_123"
+
+
+@pytest.mark.asyncio
+async def test_mplex_stream_read_write(mplex_stream_pair):
+    stream_0, stream_1 = mplex_stream_pair
+    await stream_0.write(DATA)
+    assert (await stream_1.read(MAX_READ_LEN)) == DATA
+
+
+@pytest.mark.asyncio
+async def test_mplex_stream_pair_read_until_eof(mplex_stream_pair):
+    read_bytes = bytearray()
+    stream_0, stream_1 = mplex_stream_pair
+
+    async def read_until_eof():
+        read_bytes.extend(await stream_1.read())
+
+    task = asyncio.ensure_future(read_until_eof())
+
+    expected_data = bytearray()
+
+    # Test: `read` doesn't return before `close` is called.
+    await stream_0.write(DATA)
+    expected_data.extend(DATA)
+    await asyncio.sleep(0.01)
+    assert len(read_bytes) == 0
+    # Test: `read` doesn't return before `close` is called.
+    await stream_0.write(DATA)
+    expected_data.extend(DATA)
+    await asyncio.sleep(0.01)
+    assert len(read_bytes) == 0
+
+    # Test: Close the stream, `read` returns, and receive previous sent data.
+    await stream_0.close()
+    await asyncio.sleep(0.01)
+    assert read_bytes == expected_data
+
+    task.cancel()
+
+
+@pytest.mark.asyncio
+async def test_mplex_stream_read_after_remote_closed(mplex_stream_pair):
+    stream_0, stream_1 = mplex_stream_pair
+    assert not stream_1.event_remote_closed.is_set()
+    await stream_0.write(DATA)
+    await stream_0.close()
+    await asyncio.sleep(0.01)
+    assert stream_1.event_remote_closed.is_set()
+    assert (await stream_1.read(MAX_READ_LEN)) == DATA
+    with pytest.raises(MplexStreamEOF):
+        await stream_1.read(MAX_READ_LEN)
+
+
+@pytest.mark.asyncio
+async def test_mplex_stream_read_after_local_reset(mplex_stream_pair):
+    stream_0, stream_1 = mplex_stream_pair
+    await stream_0.reset()
+    with pytest.raises(MplexStreamReset):
+        await stream_0.read(MAX_READ_LEN)
+
+
+@pytest.mark.asyncio
+async def test_mplex_stream_read_after_remote_reset(mplex_stream_pair):
+    stream_0, stream_1 = mplex_stream_pair
+    await stream_0.write(DATA)
+    await stream_0.reset()
+    # Sleep to let `stream_1` receive the message.
+    await asyncio.sleep(0.01)
+    with pytest.raises(MplexStreamReset):
+        await stream_1.read(MAX_READ_LEN)
+
+
+@pytest.mark.asyncio
+async def test_mplex_stream_read_after_remote_closed_and_reset(mplex_stream_pair):
+    stream_0, stream_1 = mplex_stream_pair
+    await stream_0.write(DATA)
+    await stream_0.close()
+    await stream_0.reset()
+    # Sleep to let `stream_1` receive the message.
+    await asyncio.sleep(0.01)
+    assert (await stream_1.read(MAX_READ_LEN)) == DATA
+
+
+@pytest.mark.asyncio
+async def test_mplex_stream_write_after_local_closed(mplex_stream_pair):
+    stream_0, stream_1 = mplex_stream_pair
+    await stream_0.write(DATA)
+    await stream_0.close()
+    with pytest.raises(MplexStreamClosed):
+        await stream_0.write(DATA)
+
+
+@pytest.mark.asyncio
+async def test_mplex_stream_write_after_local_reset(mplex_stream_pair):
+    stream_0, stream_1 = mplex_stream_pair
+    await stream_0.reset()
+    with pytest.raises(MplexStreamClosed):
+        await stream_0.write(DATA)
+
+
+@pytest.mark.asyncio
+async def test_mplex_stream_write_after_remote_reset(mplex_stream_pair):
+    stream_0, stream_1 = mplex_stream_pair
+    await stream_1.reset()
+    await asyncio.sleep(0.01)
+    with pytest.raises(MplexStreamClosed):
+        await stream_0.write(DATA)
+
+
+@pytest.mark.asyncio
+async def test_mplex_stream_both_close(mplex_stream_pair):
+    stream_0, stream_1 = mplex_stream_pair
+    # Flags are not set initially.
+    assert not stream_0.event_local_closed.is_set()
+    assert not stream_1.event_local_closed.is_set()
+    assert not stream_0.event_remote_closed.is_set()
+    assert not stream_1.event_remote_closed.is_set()
+    # Streams are present in their `mplex_conn`.
+    assert stream_0 in stream_0.muxed_conn.streams.values()
+    assert stream_1 in stream_1.muxed_conn.streams.values()
+
+    # Test: Close one side.
+    await stream_0.close()
+    await asyncio.sleep(0.01)
+
+    assert stream_0.event_local_closed.is_set()
+    assert not stream_1.event_local_closed.is_set()
+    assert not stream_0.event_remote_closed.is_set()
+    assert stream_1.event_remote_closed.is_set()
+    # Streams are still present in their `mplex_conn`.
+    assert stream_0 in stream_0.muxed_conn.streams.values()
+    assert stream_1 in stream_1.muxed_conn.streams.values()
+
+    # Test: Close the other side.
+    await stream_1.close()
+    await asyncio.sleep(0.01)
+    # Both sides are closed.
+    assert stream_0.event_local_closed.is_set()
+    assert stream_1.event_local_closed.is_set()
+    assert stream_0.event_remote_closed.is_set()
+    assert stream_1.event_remote_closed.is_set()
+    # Streams are removed from their `mplex_conn`.
+    assert stream_0 not in stream_0.muxed_conn.streams.values()
+    assert stream_1 not in stream_1.muxed_conn.streams.values()
+
+    # Test: Reset after both close.
+    await stream_0.reset()
+
+
+@pytest.mark.asyncio
+async def test_mplex_stream_reset(mplex_stream_pair):
+    stream_0, stream_1 = mplex_stream_pair
+    await stream_0.reset()
+    await asyncio.sleep(0.01)
+
+    # Both sides are closed.
+    assert stream_0.event_local_closed.is_set()
+    assert stream_1.event_local_closed.is_set()
+    assert stream_0.event_remote_closed.is_set()
+    assert stream_1.event_remote_closed.is_set()
+    # Streams are removed from their `mplex_conn`.
+    assert stream_0 not in stream_0.muxed_conn.streams.values()
+    assert stream_1 not in stream_1.muxed_conn.streams.values()
+
+    # `close` should do nothing.
+    await stream_0.close()
+    await stream_1.close()
+    # `reset` should do nothing as well.
+    await stream_0.reset()
+    await stream_1.reset()
diff --git a/tests_interop/test_bindings.py b/tests_interop/test_bindings.py
index 1e78ff43..dc0a2707 100644
--- a/tests_interop/test_bindings.py
+++ b/tests_interop/test_bindings.py
@@ -22,6 +22,5 @@ async def test_connect(hosts, p2pds):
     assert len(host.get_network().connections) == 1
     # Test: `disconnect` from Go
     await p2pd.control.disconnect(host.get_id())
-    # FIXME: Failed to handle disconnect
     await asyncio.sleep(0.01)
     assert len(host.get_network().connections) == 0