diff --git a/example/examples/echo-dialer.rs b/example/examples/echo-dialer.rs
index 8cbbd0f3..fb4e8854 100644
--- a/example/examples/echo-dialer.rs
+++ b/example/examples/echo-dialer.rs
@@ -32,7 +32,8 @@ extern crate tokio_io;
 use futures::{Future, Sink, Stream};
 use futures::sync::oneshot;
 use std::env;
-use swarm::{DeniedConnectionUpgrade, SimpleProtocol, Transport, UpgradeExt};
+use swarm::Transport;
+use swarm::upgrade::{self, DeniedConnectionUpgrade, SimpleProtocol, UpgradeExt};
 use tcp::TcpConfig;
 use tokio_core::reactor::Core;
 use tokio_io::AsyncRead;
@@ -62,7 +63,7 @@ fn main() {
         // On top of TCP/IP, we will use either the plaintext protocol or the secio protocol,
         // depending on which one the remote supports.
         .with_upgrade({
-            let plain_text = swarm::PlainTextConfig;
+            let plain_text = upgrade::PlainTextConfig;
 
             let secio = {
                 let private_key = include_bytes!("test-private-key.pk8");
diff --git a/example/examples/echo-server.rs b/example/examples/echo-server.rs
index aa0fca83..4c11f66f 100644
--- a/example/examples/echo-server.rs
+++ b/example/examples/echo-server.rs
@@ -32,7 +32,8 @@ extern crate tokio_io;
 use futures::future::{loop_fn, Future, IntoFuture, Loop};
 use futures::{Sink, Stream};
 use std::env;
-use swarm::{SimpleProtocol, Transport, UpgradeExt};
+use swarm::Transport;
+use swarm::upgrade::{self, SimpleProtocol, UpgradeExt};
 use tcp::TcpConfig;
 use tokio_core::reactor::Core;
 use tokio_io::AsyncRead;
@@ -61,7 +62,7 @@ fn main() {
         // On top of TCP/IP, we will use either the plaintext protocol or the secio protocol,
         // depending on which one the remote supports.
         .with_upgrade({
-            let plain_text = swarm::PlainTextConfig;
+            let plain_text = upgrade::PlainTextConfig;
 
             let secio = {
                 let private_key = include_bytes!("test-private-key.pk8");
diff --git a/example/examples/floodsub.rs b/example/examples/floodsub.rs
index 3da19aa2..54edd4fc 100644
--- a/example/examples/floodsub.rs
+++ b/example/examples/floodsub.rs
@@ -37,7 +37,8 @@ use futures::future::Future;
 use futures::Stream;
 use peerstore::PeerId;
 use std::{env, mem};
-use swarm::{Multiaddr, Transport, UpgradeExt};
+use swarm::{Multiaddr, Transport};
+use swarm::upgrade::{self, UpgradeExt};
 use tcp::TcpConfig;
 use tokio_core::reactor::Core;
 use websocket::WsConfig;
@@ -64,7 +65,7 @@ fn main() {
         // On top of TCP/IP, we will use either the plaintext protocol or the secio protocol,
         // depending on which one the remote supports.
         .with_upgrade({
-            let plain_text = swarm::PlainTextConfig;
+            let plain_text = upgrade::PlainTextConfig;
 
             let secio = {
                 let private_key = include_bytes!("test-private-key.pk8");
diff --git a/example/examples/kademlia.rs b/example/examples/kademlia.rs
index cfb3b763..6ed14742 100644
--- a/example/examples/kademlia.rs
+++ b/example/examples/kademlia.rs
@@ -39,7 +39,8 @@ use peerstore::PeerId;
 use std::env;
 use std::sync::Arc;
 use std::time::Duration;
-use swarm::{Transport, UpgradeExt};
+use swarm::Transport;
+use swarm::upgrade::{self, UpgradeExt};
 use tcp::TcpConfig;
 use tokio_core::reactor::Core;
 
@@ -69,7 +70,7 @@ fn main() {
         // On top of TCP/IP, we will use either the plaintext protocol or the secio protocol,
         // depending on which one the remote supports.
         .with_upgrade({
-            let plain_text = swarm::PlainTextConfig;
+            let plain_text = upgrade::PlainTextConfig;
 
             let secio = {
                 let private_key = include_bytes!("test-private-key.pk8");
diff --git a/example/examples/ping-client.rs b/example/examples/ping-client.rs
index 2a721408..5e7a5abc 100644
--- a/example/examples/ping-client.rs
+++ b/example/examples/ping-client.rs
@@ -32,7 +32,8 @@ extern crate tokio_io;
 use futures::Future;
 use futures::sync::oneshot;
 use std::env;
-use swarm::{DeniedConnectionUpgrade, Transport, UpgradeExt};
+use swarm::Transport;
+use swarm::upgrade::{self, DeniedConnectionUpgrade, UpgradeExt};
 use tcp::TcpConfig;
 use tokio_core::reactor::Core;
 
@@ -54,7 +55,7 @@ fn main() {
         // On top of TCP/IP, we will use either the plaintext protocol or the secio protocol,
         // depending on which one the remote supports.
         .with_upgrade({
-            let plain_text = swarm::PlainTextConfig;
+            let plain_text = upgrade::PlainTextConfig;
 
             let secio = {
                 let private_key = include_bytes!("test-private-key.pk8");
diff --git a/ping/src/lib.rs b/ping/src/lib.rs
index daea084e..4b6daf5b 100644
--- a/ping/src/lib.rs
+++ b/ping/src/lib.rs
@@ -92,8 +92,7 @@ use bytes::{BufMut, Bytes, BytesMut};
 use futures::{Future, Sink, Stream};
 use futures::future::{loop_fn, FutureResult, IntoFuture, Loop};
 use futures::sync::{mpsc, oneshot};
-use libp2p_swarm::Multiaddr;
-use libp2p_swarm::transport::{ConnectionUpgrade, Endpoint};
+use libp2p_swarm::{ConnectionUpgrade, Endpoint, Multiaddr};
 use log::Level;
 use parking_lot::Mutex;
 use rand::Rand;
@@ -310,7 +309,7 @@ mod tests {
     use futures::future::join_all;
     use futures::Future;
     use futures::Stream;
-    use libp2p_swarm::transport::{ConnectionUpgrade, Endpoint};
+    use libp2p_swarm::{ConnectionUpgrade, Endpoint};
 
     #[test]
     fn ping_pong() {
diff --git a/swarm/src/connection_reuse.rs b/swarm/src/connection_reuse.rs
index b3e822ee..a771257e 100644
--- a/swarm/src/connection_reuse.rs
+++ b/swarm/src/connection_reuse.rs
@@ -50,7 +50,8 @@ use muxing::StreamMuxer;
 use parking_lot::Mutex;
 use std::io::Error as IoError;
 use std::sync::Arc;
-use transport::{ConnectionUpgrade, MuxedTransport, Transport, UpgradedNode};
+use transport::{MuxedTransport, Transport, UpgradedNode};
+use upgrade::ConnectionUpgrade;
 
 /// Allows reusing the same muxed connection multiple times.
 ///
diff --git a/swarm/src/either.rs b/swarm/src/either.rs
new file mode 100644
index 00000000..e143b368
--- /dev/null
+++ b/swarm/src/either.rs
@@ -0,0 +1,216 @@
+// Copyright 2017 Parity Technologies (UK) Ltd.
+//
+// Permission is hereby granted, free of charge, to any person obtaining a
+// copy of this software and associated documentation files (the "Software"),
+// to deal in the Software without restriction, including without limitation
+// the rights to use, copy, modify, merge, publish, distribute, sublicense,
+// and/or sell copies of the Software, and to permit persons to whom the
+// Software is furnished to do so, subject to the following conditions:
+//
+// The above copyright notice and this permission notice shall be included in
+// all copies or substantial portions of the Software.
+//
+// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS
+// OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
+// FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
+// DEALINGS IN THE SOFTWARE.
+
+use futures::prelude::*;
+use multiaddr::Multiaddr;
+use muxing::StreamMuxer;
+use std::io::{Error as IoError, Read, Write};
+use tokio_io::{AsyncRead, AsyncWrite};
+
+/// Implements `AsyncRead` and `AsyncWrite` and dispatches all method calls to
+/// either `First` or `Second`.
+#[derive(Debug, Copy, Clone)]
+pub enum EitherSocket<A, B> {
+    First(A),
+    Second(B),
+}
+
+impl<A, B> AsyncRead for EitherSocket<A, B>
+where
+    A: AsyncRead,
+    B: AsyncRead,
+{
+    #[inline]
+    unsafe fn prepare_uninitialized_buffer(&self, buf: &mut [u8]) -> bool {
+        match self {
+            &EitherSocket::First(ref a) => a.prepare_uninitialized_buffer(buf),
+            &EitherSocket::Second(ref b) => b.prepare_uninitialized_buffer(buf),
+        }
+    }
+}
+
+impl<A, B> Read for EitherSocket<A, B>
+where
+    A: Read,
+    B: Read,
+{
+    #[inline]
+    fn read(&mut self, buf: &mut [u8]) -> Result<usize, IoError> {
+        match self {
+            &mut EitherSocket::First(ref mut a) => a.read(buf),
+            &mut EitherSocket::Second(ref mut b) => b.read(buf),
+        }
+    }
+}
+
+impl<A, B> AsyncWrite for EitherSocket<A, B>
+where
+    A: AsyncWrite,
+    B: AsyncWrite,
+{
+    #[inline]
+    fn shutdown(&mut self) -> Poll<(), IoError> {
+        match self {
+            &mut EitherSocket::First(ref mut a) => a.shutdown(),
+            &mut EitherSocket::Second(ref mut b) => b.shutdown(),
+        }
+    }
+}
+
+impl<A, B> Write for EitherSocket<A, B>
+where
+    A: Write,
+    B: Write,
+{
+    #[inline]
+    fn write(&mut self, buf: &[u8]) -> Result<usize, IoError> {
+        match self {
+            &mut EitherSocket::First(ref mut a) => a.write(buf),
+            &mut EitherSocket::Second(ref mut b) => b.write(buf),
+        }
+    }
+
+    #[inline]
+    fn flush(&mut self) -> Result<(), IoError> {
+        match self {
+            &mut EitherSocket::First(ref mut a) => a.flush(),
+            &mut EitherSocket::Second(ref mut b) => b.flush(),
+        }
+    }
+}
+
+impl<A, B> StreamMuxer for EitherSocket<A, B>
+where
+    A: StreamMuxer,
+    B: StreamMuxer,
+{
+    type Substream = EitherSocket<A::Substream, B::Substream>;
+    type InboundSubstream = EitherTransportFuture<A::InboundSubstream, B::InboundSubstream>;
+    type OutboundSubstream = EitherTransportFuture<A::OutboundSubstream, B::OutboundSubstream>;
+
+    #[inline]
+    fn inbound(self) -> Self::InboundSubstream {
+        match self {
+            EitherSocket::First(a) => EitherTransportFuture::First(a.inbound()),
+            EitherSocket::Second(b) => EitherTransportFuture::Second(b.inbound()),
+        }
+    }
+
+    #[inline]
+    fn outbound(self) -> Self::OutboundSubstream {
+        match self {
+            EitherSocket::First(a) => EitherTransportFuture::First(a.outbound()),
+            EitherSocket::Second(b) => EitherTransportFuture::Second(b.outbound()),
+        }
+    }
+}
+
+/// Implements `Future` and redirects calls to either `First` or `Second`.
+///
+/// Additionally, the output will be wrapped inside a `EitherSocket`.
+// TODO: This type is needed because of the lack of `impl Trait` in stable Rust.
+//         If Rust had impl Trait we could use the Either enum from the futures crate and add some
+//         modifiers to it. This custom enum is a combination of Either and these modifiers.
+#[derive(Debug, Copy, Clone)]
+pub enum EitherTransportFuture<A, B> {
+    First(A),
+    Second(B),
+}
+
+impl<A, B> Future for EitherTransportFuture<A, B>
+where
+    A: Future<Error = IoError>,
+    B: Future<Error = IoError>,
+{
+    type Item = EitherSocket<A::Item, B::Item>;
+    type Error = IoError;
+
+    #[inline]
+    fn poll(&mut self) -> Poll<Self::Item, Self::Error> {
+        match self {
+            &mut EitherTransportFuture::First(ref mut a) => {
+                let item = try_ready!(a.poll());
+                Ok(Async::Ready(EitherSocket::First(item)))
+            }
+            &mut EitherTransportFuture::Second(ref mut b) => {
+                let item = try_ready!(b.poll());
+                Ok(Async::Ready(EitherSocket::Second(item)))
+            }
+        }
+    }
+}
+
+/// Implements `Stream` and dispatches all method calls to either `First` or `Second`.
+#[derive(Debug, Copy, Clone)]
+pub enum EitherListenStream<A, B> {
+    First(A),
+    Second(B),
+}
+
+impl<AStream, BStream, AInner, BInner> Stream for EitherListenStream<AStream, BStream>
+where
+    AStream: Stream<Item = AInner, Error = IoError>,
+    BStream: Stream<Item = BInner, Error = IoError>,
+{
+    type Item = EitherListenUpgrade<AInner, BInner>;
+    type Error = IoError;
+
+    #[inline]
+    fn poll(&mut self) -> Poll<Option<Self::Item>, Self::Error> {
+        match self {
+            &mut EitherListenStream::First(ref mut a) => a.poll()
+                .map(|i| i.map(|v| v.map(EitherListenUpgrade::First))),
+            &mut EitherListenStream::Second(ref mut a) => a.poll()
+                .map(|i| i.map(|v| v.map(EitherListenUpgrade::Second))),
+        }
+    }
+}
+
+// TODO: This type is needed because of the lack of `impl Trait` in stable Rust.
+//         If Rust had impl Trait we could use the Either enum from the futures crate and add some
+//         modifiers to it. This custom enum is a combination of Either and these modifiers.
+#[derive(Debug, Copy, Clone)]
+pub enum EitherListenUpgrade<A, B> {
+    First(A),
+    Second(B),
+}
+
+impl<A, B, Ao, Bo> Future for EitherListenUpgrade<A, B>
+where
+    A: Future<Item = (Ao, Multiaddr), Error = IoError>,
+    B: Future<Item = (Bo, Multiaddr), Error = IoError>,
+{
+    type Item = (EitherSocket<Ao, Bo>, Multiaddr);
+    type Error = IoError;
+
+    #[inline]
+    fn poll(&mut self) -> Poll<Self::Item, Self::Error> {
+        match self {
+            &mut EitherListenUpgrade::First(ref mut a) => {
+                let (item, addr) = try_ready!(a.poll());
+                Ok(Async::Ready((EitherSocket::First(item), addr)))
+            }
+            &mut EitherListenUpgrade::Second(ref mut b) => {
+                let (item, addr) = try_ready!(b.poll());
+                Ok(Async::Ready((EitherSocket::Second(item), addr)))
+            }
+        }
+    }
+}
diff --git a/swarm/src/lib.rs b/swarm/src/lib.rs
index b042ddeb..730a8f79 100644
--- a/swarm/src/lib.rs
+++ b/swarm/src/lib.rs
@@ -94,7 +94,7 @@
 //! # fn main() {
 //! let tokio_core = tokio_core::reactor::Core::new().unwrap();
 //! let tcp_transport = libp2p_tcp_transport::TcpConfig::new(tokio_core.handle());
-//! let upgraded = tcp_transport.with_upgrade(libp2p_swarm::PlainTextConfig);
+//! let upgraded = tcp_transport.with_upgrade(libp2p_swarm::upgrade::PlainTextConfig);
 //!
 //! // upgraded.dial(...)   // automatically applies the plain text protocol on the socket
 //! # }
@@ -217,14 +217,16 @@ extern crate tokio_io;
 pub extern crate multiaddr;
 
 mod connection_reuse;
-pub mod swarm;
+mod either;
+
 pub mod muxing;
+pub mod swarm;
 pub mod transport;
+pub mod upgrade;
 
 pub use self::connection_reuse::ConnectionReuse;
 pub use self::multiaddr::{AddrComponent, Multiaddr};
 pub use self::muxing::StreamMuxer;
 pub use self::swarm::{swarm, SwarmController, SwarmFuture};
-pub use self::transport::{ConnectionUpgrade, OrUpgrade, PlainTextConfig, Transport, UpgradedNode};
-pub use self::transport::{Endpoint, MuxedTransport, SimpleProtocol, UpgradeExt};
-pub use self::transport::DeniedConnectionUpgrade;
+pub use self::transport::{MuxedTransport, Transport};
+pub use self::upgrade::{ConnectionUpgrade, Endpoint};
diff --git a/swarm/src/swarm.rs b/swarm/src/swarm.rs
index 34962790..3a8242d4 100644
--- a/swarm/src/swarm.rs
+++ b/swarm/src/swarm.rs
@@ -23,7 +23,8 @@ use std::io::Error as IoError;
 use futures::{future, Async, Future, IntoFuture, Poll, Stream};
 use futures::stream::{FuturesUnordered, StreamFuture};
 use futures::sync::mpsc;
-use {ConnectionUpgrade, Multiaddr, MuxedTransport, UpgradedNode};
+use transport::UpgradedNode;
+use {ConnectionUpgrade, Multiaddr, MuxedTransport};
 
 /// Creates a swarm.
 ///
diff --git a/swarm/src/transport.rs b/swarm/src/transport.rs
deleted file mode 100644
index 1a733c08..00000000
--- a/swarm/src/transport.rs
+++ /dev/null
@@ -1,1165 +0,0 @@
-// Copyright 2017 Parity Technologies (UK) Ltd.
-//
-// Permission is hereby granted, free of charge, to any person obtaining a
-// copy of this software and associated documentation files (the "Software"),
-// to deal in the Software without restriction, including without limitation
-// the rights to use, copy, modify, merge, publish, distribute, sublicense,
-// and/or sell copies of the Software, and to permit persons to whom the
-// Software is furnished to do so, subject to the following conditions:
-//
-// The above copyright notice and this permission notice shall be included in
-// all copies or substantial portions of the Software.
-//
-// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS
-// OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
-// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
-// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
-// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
-// FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
-// DEALINGS IN THE SOFTWARE.
-
-//! Handles entering a connection with a peer.
-//!
-//! The two main elements of this module are the `Transport` and `ConnectionUpgrade` traits.
-//! `Transport` is implemented on objects that allow dialing and listening. `ConnectionUpgrade` is
-//! implemented on objects that make it possible to upgrade a connection (for example by adding an
-//! encryption middleware to the connection).
-//!
-//! Thanks to the `Transport::or_transport`, `Transport::with_upgrade` and
-//! `UpgradedNode::or_upgrade` methods, you can combine multiple transports and/or upgrades
-//! together in a complex chain of protocols negotiation.
-
-use bytes::Bytes;
-use connection_reuse::ConnectionReuse;
-use futures::{stream, Async, Poll, Stream};
-use futures::future::{self, FromErr, Future, FutureResult, IntoFuture};
-use multiaddr::Multiaddr;
-use multistream_select;
-use muxing::StreamMuxer;
-use std::io::{Cursor, Error as IoError, ErrorKind as IoErrorKind, Read, Write};
-use std::iter;
-use std::sync::Arc;
-use tokio_io::{AsyncRead, AsyncWrite};
-
-/// A transport is an object that can be used to produce connections by listening or dialing a
-/// peer.
-///
-/// This trait is implemented on concrete transports (eg. TCP, UDP, etc.), but also on wrappers
-/// around them.
-///
-/// > **Note**: The methods of this trait use `self` and not `&self` or `&mut self`. In other
-/// >           words, listening or dialing consumes the transport object. This has been designed
-/// >           so that you would implement this trait on `&Foo` or `&mut Foo` instead of directly
-/// >           on `Foo`.
-pub trait Transport {
-    /// The raw connection to a peer.
-    type RawConn: AsyncRead + AsyncWrite;
-
-    /// The listener produces incoming connections.
-    ///
-    /// An item should be produced whenever a connection is received at the lowest level of the
-    /// transport stack. The item is a `Future` that is signalled once some pre-processing has
-    /// taken place, and that connection has been upgraded to the wanted protocols.
-    type Listener: Stream<Item = Self::ListenerUpgrade, Error = IoError>;
-
-    /// After a connection has been received, we may need to do some asynchronous pre-processing
-    /// on it (eg. an intermediary protocol negotiation). While this pre-processing takes place, we
-    /// want to be able to continue polling on the listener.
-    type ListenerUpgrade: Future<Item = (Self::RawConn, Multiaddr), Error = IoError>;
-
-    /// A future which indicates that we are currently dialing to a peer.
-    type Dial: IntoFuture<Item = (Self::RawConn, Multiaddr), Error = IoError>;
-
-    /// Listen on the given multiaddr. Returns a stream of incoming connections, plus a modified
-    /// version of the `Multiaddr`. This new `Multiaddr` is the one that that should be advertised
-    /// to other nodes, instead of the one passed as parameter.
-    ///
-    /// Returns the address back if it isn't supported.
-    ///
-    /// > **Note**: The reason why we need to change the `Multiaddr` on success is to handle
-    /// >             situations such as turning `/ip4/127.0.0.1/tcp/0` into
-    /// >             `/ip4/127.0.0.1/tcp/<actual port>`.
-    fn listen_on(self, addr: Multiaddr) -> Result<(Self::Listener, Multiaddr), (Self, Multiaddr)>
-    where
-        Self: Sized;
-
-    /// Dial to the given multi-addr.
-    ///
-    /// Returns either a future which may resolve to a connection, or gives back the multiaddress.
-    fn dial(self, addr: Multiaddr) -> Result<Self::Dial, (Self, Multiaddr)>
-    where
-        Self: Sized;
-
-    /// Takes a multiaddress we're listening on (`server`), and tries to convert it to an
-    /// externally-visible multiaddress. In order to do so, we pass an `observed` address which
-    /// a remote node observes for one of our dialers.
-    ///
-    /// For example, if `server` is `/ip4/0.0.0.0/tcp/3000` and `observed` is
-    /// `/ip4/80.81.82.83/tcp/29601`, then we should return `/ip4/80.81.82.83/tcp/3000`. Each
-    /// implementation of `Transport` is only responsible for handling the protocols it supports.
-    ///
-    /// Returns `None` if nothing can be determined. This happens if this trait implementation
-    /// doesn't recognize the protocols, or if `server` and `observed` are related.
-    fn nat_traversal(&self, server: &Multiaddr, observed: &Multiaddr) -> Option<Multiaddr>;
-
-    /// Builds a new struct that implements `Transport` that contains both `self` and `other`.
-    ///
-    /// The returned object will redirect its calls to `self`, except that if `listen_on` or `dial`
-    /// return an error then `other` will be tried.
-    #[inline]
-    fn or_transport<T>(self, other: T) -> OrTransport<Self, T>
-    where
-        Self: Sized,
-    {
-        OrTransport(self, other)
-    }
-
-    /// Wraps this transport inside an upgrade. Whenever a connection that uses this transport
-    /// is established, it is wrapped inside the upgrade.
-    ///
-    /// > **Note**: The concept of an *upgrade* for example includes middlewares such *secio*
-    /// >           (communication encryption), *multiplex*, but also a protocol handler.
-    #[inline]
-    fn with_upgrade<U>(self, upgrade: U) -> UpgradedNode<Self, U>
-    where
-        Self: Sized,
-        U: ConnectionUpgrade<Self::RawConn>,
-    {
-        UpgradedNode {
-            transports: self,
-            upgrade: upgrade,
-        }
-    }
-
-    /// Builds a dummy implementation of `MuxedTransport` that uses this transport.
-    ///
-    /// The resulting object will not actually use muxing. This means that dialing the same node
-    /// twice will result in two different connections instead of two substreams on the same
-    /// connection.
-    #[inline]
-    fn with_dummy_muxing(self) -> DummyMuxing<Self>
-    where
-        Self: Sized,
-    {
-        DummyMuxing { inner: self }
-    }
-}
-
-/// Extension trait for `Transport`. Implemented on structs that provide a `Transport` on which
-/// the dialed node can dial you back.
-pub trait MuxedTransport: Transport {
-    /// Future resolving to a future that will resolve to an incoming connection.
-    type Incoming: Future<Item = Self::IncomingUpgrade, Error = IoError>;
-    /// Future resolving to an incoming connection.
-    type IncomingUpgrade: Future<Item = (Self::RawConn, Multiaddr), Error = IoError>;
-
-    /// Returns the next incoming substream opened by a node that we dialed ourselves.
-    ///
-    /// > **Note**: Doesn't produce incoming substreams coming from addresses we are listening on.
-    /// >            This only concerns nodes that we dialed with `dial()`.
-    fn next_incoming(self) -> Self::Incoming
-    where
-        Self: Sized;
-
-    /// Returns a stream of incoming connections.
-    #[inline]
-    fn incoming(
-        self,
-    ) -> stream::AndThen<stream::Repeat<Self, IoError>, fn(Self) -> Self::Incoming, Self::Incoming>
-    where
-        Self: Sized + Clone,
-    {
-        stream::repeat(self).and_then(|me| me.next_incoming())
-    }
-}
-
-/// Dummy implementation of `Transport` that just denies every single attempt.
-#[derive(Debug, Copy, Clone)]
-pub struct DeniedTransport;
-
-impl Transport for DeniedTransport {
-    // TODO: could use `!` for associated types once stable
-    type RawConn = Cursor<Vec<u8>>;
-    type Listener = Box<Stream<Item = Self::ListenerUpgrade, Error = IoError>>;
-    type ListenerUpgrade = Box<Future<Item = (Self::RawConn, Multiaddr), Error = IoError>>;
-    type Dial = Box<Future<Item = (Self::RawConn, Multiaddr), Error = IoError>>;
-
-    #[inline]
-    fn listen_on(self, addr: Multiaddr) -> Result<(Self::Listener, Multiaddr), (Self, Multiaddr)> {
-        Err((DeniedTransport, addr))
-    }
-
-    #[inline]
-    fn dial(self, addr: Multiaddr) -> Result<Self::Dial, (Self, Multiaddr)> {
-        Err((DeniedTransport, addr))
-    }
-
-    #[inline]
-    fn nat_traversal(&self, _: &Multiaddr, _: &Multiaddr) -> Option<Multiaddr> {
-        None
-    }
-}
-
-impl MuxedTransport for DeniedTransport {
-    type Incoming = future::Empty<Self::IncomingUpgrade, IoError>;
-    type IncomingUpgrade = future::Empty<(Self::RawConn, Multiaddr), IoError>;
-
-    #[inline]
-    fn next_incoming(self) -> Self::Incoming {
-        future::empty()
-    }
-}
-
-/// Struct returned by `or_transport()`.
-#[derive(Debug, Copy, Clone)]
-pub struct OrTransport<A, B>(A, B);
-
-impl<A, B> Transport for OrTransport<A, B>
-where
-    A: Transport,
-    B: Transport,
-{
-    type RawConn = EitherSocket<A::RawConn, B::RawConn>;
-    type Listener = EitherListenStream<A::Listener, B::Listener>;
-    type ListenerUpgrade = EitherListenUpgrade<A::ListenerUpgrade, B::ListenerUpgrade>;
-    type Dial =
-        EitherListenUpgrade<<A::Dial as IntoFuture>::Future, <B::Dial as IntoFuture>::Future>;
-
-    fn listen_on(self, addr: Multiaddr) -> Result<(Self::Listener, Multiaddr), (Self, Multiaddr)> {
-        let (first, addr) = match self.0.listen_on(addr) {
-            Ok((connec, addr)) => return Ok((EitherListenStream::First(connec), addr)),
-            Err(err) => err,
-        };
-
-        match self.1.listen_on(addr) {
-            Ok((connec, addr)) => Ok((EitherListenStream::Second(connec), addr)),
-            Err((second, addr)) => Err((OrTransport(first, second), addr)),
-        }
-    }
-
-    fn dial(self, addr: Multiaddr) -> Result<Self::Dial, (Self, Multiaddr)> {
-        let (first, addr) = match self.0.dial(addr) {
-            Ok(connec) => return Ok(EitherListenUpgrade::First(connec.into_future())),
-            Err(err) => err,
-        };
-
-        match self.1.dial(addr) {
-            Ok(connec) => Ok(EitherListenUpgrade::Second(connec.into_future())),
-            Err((second, addr)) => Err((OrTransport(first, second), addr)),
-        }
-    }
-
-    #[inline]
-    fn nat_traversal(&self, server: &Multiaddr, observed: &Multiaddr) -> Option<Multiaddr> {
-        let first = self.0.nat_traversal(server, observed);
-        if let Some(first) = first {
-            return Some(first);
-        }
-
-        self.1.nat_traversal(server, observed)
-    }
-}
-
-/// Implementation of `ConnectionUpgrade`. Convenient to use with small protocols.
-#[derive(Debug)]
-pub struct SimpleProtocol<F> {
-    name: Bytes,
-    // Note: we put the closure `F` in an `Arc` because Rust closures aren't automatically clonable
-    // yet.
-    upgrade: Arc<F>,
-}
-
-impl<F> SimpleProtocol<F> {
-    /// Builds a `SimpleProtocol`.
-    #[inline]
-    pub fn new<N>(name: N, upgrade: F) -> SimpleProtocol<F>
-    where
-        N: Into<Bytes>,
-    {
-        SimpleProtocol {
-            name: name.into(),
-            upgrade: Arc::new(upgrade),
-        }
-    }
-}
-
-impl<F> Clone for SimpleProtocol<F> {
-    #[inline]
-    fn clone(&self) -> Self {
-        SimpleProtocol {
-            name: self.name.clone(),
-            upgrade: self.upgrade.clone(),
-        }
-    }
-}
-
-impl<A, B> MuxedTransport for OrTransport<A, B>
-where
-    A: MuxedTransport,
-    B: MuxedTransport,
-    A::Incoming: 'static,        // TODO: meh :-/
-    B::Incoming: 'static,        // TODO: meh :-/
-    A::IncomingUpgrade: 'static, // TODO: meh :-/
-    B::IncomingUpgrade: 'static, // TODO: meh :-/
-    A::RawConn: 'static,         // TODO: meh :-/
-    B::RawConn: 'static,         // TODO: meh :-/
-{
-    type Incoming = Box<Future<Item = Self::IncomingUpgrade, Error = IoError>>;
-    type IncomingUpgrade =
-        Box<Future<Item = (EitherSocket<A::RawConn, B::RawConn>, Multiaddr), Error = IoError>>;
-
-    #[inline]
-    fn next_incoming(self) -> Self::Incoming {
-        let first = self.0.next_incoming().map(|out| {
-            let fut = out.map(move |(v, addr)| (EitherSocket::First(v), addr));
-            Box::new(fut) as Box<Future<Item = _, Error = _>>
-        });
-        let second = self.1.next_incoming().map(|out| {
-            let fut = out.map(move |(v, addr)| (EitherSocket::Second(v), addr));
-            Box::new(fut) as Box<Future<Item = _, Error = _>>
-        });
-        let future = first.select(second).map(|(i, _)| i).map_err(|(e, _)| e);
-        Box::new(future) as Box<_>
-    }
-}
-
-impl<C, F, O> ConnectionUpgrade<C> for SimpleProtocol<F>
-where
-    C: AsyncRead + AsyncWrite,
-    F: Fn(C) -> O,
-    O: IntoFuture<Error = IoError>,
-{
-    type NamesIter = iter::Once<(Bytes, ())>;
-    type UpgradeIdentifier = ();
-
-    #[inline]
-    fn protocol_names(&self) -> Self::NamesIter {
-        iter::once((self.name.clone(), ()))
-    }
-
-    type Output = O::Item;
-    type Future = FromErr<O::Future, IoError>;
-
-    #[inline]
-    fn upgrade(self, socket: C, _: (), _: Endpoint, _: &Multiaddr) -> Self::Future {
-        let upgrade = &self.upgrade;
-        upgrade(socket).into_future().from_err()
-    }
-}
-
-/// Implements `Stream` and dispatches all method calls to either `First` or `Second`.
-#[derive(Debug, Copy, Clone)]
-pub enum EitherListenStream<A, B> {
-    First(A),
-    Second(B),
-}
-
-impl<AStream, BStream, AInner, BInner> Stream for EitherListenStream<AStream, BStream>
-where
-    AStream: Stream<Item = AInner, Error = IoError>,
-    BStream: Stream<Item = BInner, Error = IoError>,
-{
-    type Item = EitherListenUpgrade<AInner, BInner>;
-    type Error = IoError;
-
-    #[inline]
-    fn poll(&mut self) -> Poll<Option<Self::Item>, Self::Error> {
-        match self {
-            &mut EitherListenStream::First(ref mut a) => a.poll()
-                .map(|i| i.map(|v| v.map(EitherListenUpgrade::First))),
-            &mut EitherListenStream::Second(ref mut a) => a.poll()
-                .map(|i| i.map(|v| v.map(EitherListenUpgrade::Second))),
-        }
-    }
-}
-
-/// Implements `Stream` and dispatches all method calls to either `First` or `Second`.
-#[derive(Debug, Copy, Clone)]
-pub enum EitherIncomingStream<A, B> {
-    First(A),
-    Second(B),
-}
-
-impl<A, B, Sa, Sb> Stream for EitherIncomingStream<A, B>
-where
-    A: Stream<Item = Sa, Error = IoError>,
-    B: Stream<Item = Sb, Error = IoError>,
-{
-    type Item = EitherSocket<Sa, Sb>;
-    type Error = IoError;
-
-    #[inline]
-    fn poll(&mut self) -> Poll<Option<Self::Item>, Self::Error> {
-        match self {
-            &mut EitherIncomingStream::First(ref mut a) => {
-                a.poll().map(|i| i.map(|v| v.map(EitherSocket::First)))
-            }
-            &mut EitherIncomingStream::Second(ref mut a) => {
-                a.poll().map(|i| i.map(|v| v.map(EitherSocket::Second)))
-            }
-        }
-    }
-}
-
-// TODO: This type is needed because of the lack of `impl Trait` in stable Rust.
-//         If Rust had impl Trait we could use the Either enum from the futures crate and add some
-//         modifiers to it. This custom enum is a combination of Either and these modifiers.
-#[derive(Debug, Copy, Clone)]
-pub enum EitherListenUpgrade<A, B> {
-    First(A),
-    Second(B),
-}
-
-impl<A, B, Ao, Bo> Future for EitherListenUpgrade<A, B>
-where
-    A: Future<Item = (Ao, Multiaddr), Error = IoError>,
-    B: Future<Item = (Bo, Multiaddr), Error = IoError>,
-{
-    type Item = (EitherSocket<Ao, Bo>, Multiaddr);
-    type Error = IoError;
-
-    #[inline]
-    fn poll(&mut self) -> Poll<Self::Item, Self::Error> {
-        match self {
-            &mut EitherListenUpgrade::First(ref mut a) => {
-                let (item, addr) = try_ready!(a.poll());
-                Ok(Async::Ready((EitherSocket::First(item), addr)))
-            }
-            &mut EitherListenUpgrade::Second(ref mut b) => {
-                let (item, addr) = try_ready!(b.poll());
-                Ok(Async::Ready((EitherSocket::Second(item), addr)))
-            }
-        }
-    }
-}
-
-/// Implements `Future` and redirects calls to either `First` or `Second`.
-///
-/// Additionally, the output will be wrapped inside a `EitherSocket`.
-// TODO: This type is needed because of the lack of `impl Trait` in stable Rust.
-//         If Rust had impl Trait we could use the Either enum from the futures crate and add some
-//         modifiers to it. This custom enum is a combination of Either and these modifiers.
-#[derive(Debug, Copy, Clone)]
-pub enum EitherTransportFuture<A, B> {
-    First(A),
-    Second(B),
-}
-
-impl<A, B> Future for EitherTransportFuture<A, B>
-where
-    A: Future<Error = IoError>,
-    B: Future<Error = IoError>,
-{
-    type Item = EitherSocket<A::Item, B::Item>;
-    type Error = IoError;
-
-    #[inline]
-    fn poll(&mut self) -> Poll<Self::Item, Self::Error> {
-        match self {
-            &mut EitherTransportFuture::First(ref mut a) => {
-                let item = try_ready!(a.poll());
-                Ok(Async::Ready(EitherSocket::First(item)))
-            }
-            &mut EitherTransportFuture::Second(ref mut b) => {
-                let item = try_ready!(b.poll());
-                Ok(Async::Ready(EitherSocket::Second(item)))
-            }
-        }
-    }
-}
-
-/// Implements `AsyncRead` and `AsyncWrite` and dispatches all method calls to either `First` or
-/// `Second`.
-#[derive(Debug, Copy, Clone)]
-pub enum EitherSocket<A, B> {
-    First(A),
-    Second(B),
-}
-
-impl<A, B> AsyncRead for EitherSocket<A, B>
-where
-    A: AsyncRead,
-    B: AsyncRead,
-{
-    #[inline]
-    unsafe fn prepare_uninitialized_buffer(&self, buf: &mut [u8]) -> bool {
-        match self {
-            &EitherSocket::First(ref a) => a.prepare_uninitialized_buffer(buf),
-            &EitherSocket::Second(ref b) => b.prepare_uninitialized_buffer(buf),
-        }
-    }
-}
-
-impl<A, B> Read for EitherSocket<A, B>
-where
-    A: Read,
-    B: Read,
-{
-    #[inline]
-    fn read(&mut self, buf: &mut [u8]) -> Result<usize, IoError> {
-        match self {
-            &mut EitherSocket::First(ref mut a) => a.read(buf),
-            &mut EitherSocket::Second(ref mut b) => b.read(buf),
-        }
-    }
-}
-
-impl<A, B> AsyncWrite for EitherSocket<A, B>
-where
-    A: AsyncWrite,
-    B: AsyncWrite,
-{
-    #[inline]
-    fn shutdown(&mut self) -> Poll<(), IoError> {
-        match self {
-            &mut EitherSocket::First(ref mut a) => a.shutdown(),
-            &mut EitherSocket::Second(ref mut b) => b.shutdown(),
-        }
-    }
-}
-
-impl<A, B> Write for EitherSocket<A, B>
-where
-    A: Write,
-    B: Write,
-{
-    #[inline]
-    fn write(&mut self, buf: &[u8]) -> Result<usize, IoError> {
-        match self {
-            &mut EitherSocket::First(ref mut a) => a.write(buf),
-            &mut EitherSocket::Second(ref mut b) => b.write(buf),
-        }
-    }
-
-    #[inline]
-    fn flush(&mut self) -> Result<(), IoError> {
-        match self {
-            &mut EitherSocket::First(ref mut a) => a.flush(),
-            &mut EitherSocket::Second(ref mut b) => b.flush(),
-        }
-    }
-}
-
-impl<A, B> StreamMuxer for EitherSocket<A, B>
-where
-    A: StreamMuxer,
-    B: StreamMuxer,
-{
-    type Substream = EitherSocket<A::Substream, B::Substream>;
-    type InboundSubstream = EitherTransportFuture<A::InboundSubstream, B::InboundSubstream>;
-    type OutboundSubstream = EitherTransportFuture<A::OutboundSubstream, B::OutboundSubstream>;
-
-    #[inline]
-    fn inbound(self) -> Self::InboundSubstream {
-        match self {
-            EitherSocket::First(a) => EitherTransportFuture::First(a.inbound()),
-            EitherSocket::Second(b) => EitherTransportFuture::Second(b.inbound()),
-        }
-    }
-
-    #[inline]
-    fn outbound(self) -> Self::OutboundSubstream {
-        match self {
-            EitherSocket::First(a) => EitherTransportFuture::First(a.outbound()),
-            EitherSocket::Second(b) => EitherTransportFuture::Second(b.outbound()),
-        }
-    }
-}
-
-/// Implemented on structs that describe a possible upgrade to a connection between two peers.
-///
-/// The generic `C` is the type of the incoming connection before it is upgraded.
-///
-/// > **Note**: The `upgrade` method of this trait uses `self` and not `&self` or `&mut self`.
-/// >           This has been designed so that you would implement this trait on `&Foo` or
-/// >           `&mut Foo` instead of directly on `Foo`.
-pub trait ConnectionUpgrade<C: AsyncRead + AsyncWrite> {
-    /// Iterator returned by `protocol_names`.
-    type NamesIter: Iterator<Item = (Bytes, Self::UpgradeIdentifier)>;
-    /// Type that serves as an identifier for the protocol. This type only exists to be returned
-    /// by the `NamesIter` and then be passed to `upgrade`.
-    ///
-    /// This is only useful on implementations that dispatch between multiple possible upgrades.
-    /// Any basic implementation will probably just use the `()` type.
-    type UpgradeIdentifier;
-
-    /// Returns the name of the protocols to advertise to the remote.
-    fn protocol_names(&self) -> Self::NamesIter;
-
-    /// Type of the stream that has been upgraded. Generally wraps around `C` and `Self`.
-    ///
-    /// > **Note**: For upgrades that add an intermediary layer (such as `secio` or `multiplex`),
-    /// >           this associated type must implement `AsyncRead + AsyncWrite`.
-    type Output;
-    /// Type of the future that will resolve to `Self::Output`.
-    type Future: Future<Item = Self::Output, Error = IoError>;
-
-    /// This method is called after protocol negotiation has been performed.
-    ///
-    /// Because performing the upgrade may not be instantaneous (eg. it may require a handshake),
-    /// this function returns a future instead of the direct output.
-    fn upgrade(
-        self,
-        socket: C,
-        id: Self::UpgradeIdentifier,
-        ty: Endpoint,
-        remote_addr: &Multiaddr,
-    ) -> Self::Future;
-}
-
-/// Type of connection for the upgrade.
-#[derive(Debug, Copy, Clone, PartialEq, Eq)]
-pub enum Endpoint {
-    /// The socket comes from a dialer.
-    Dialer,
-    /// The socket comes from a listener.
-    Listener,
-}
-
-/// Implementation of `ConnectionUpgrade` that always fails to negotiate.
-#[derive(Debug, Copy, Clone)]
-pub struct DeniedConnectionUpgrade;
-
-impl<C> ConnectionUpgrade<C> for DeniedConnectionUpgrade
-where
-    C: AsyncRead + AsyncWrite,
-{
-    type NamesIter = iter::Empty<(Bytes, ())>;
-    type UpgradeIdentifier = (); // TODO: could use `!`
-    type Output = (); // TODO: could use `!`
-    type Future = Box<Future<Item = (), Error = IoError>>; // TODO: could use `!`
-
-    #[inline]
-    fn protocol_names(&self) -> Self::NamesIter {
-        iter::empty()
-    }
-
-    #[inline]
-    fn upgrade(self, _: C, _: Self::UpgradeIdentifier, _: Endpoint, _: &Multiaddr) -> Self::Future {
-        unreachable!("the denied connection upgrade always fails to negotiate")
-    }
-}
-
-/// Extension trait for `ConnectionUpgrade`. Automatically implemented on everything.
-pub trait UpgradeExt {
-    /// Builds a struct that will choose an upgrade between `self` and `other`, depending on what
-    /// the remote supports.
-    fn or_upgrade<T>(self, other: T) -> OrUpgrade<Self, T>
-    where
-        Self: Sized;
-}
-
-impl<T> UpgradeExt for T {
-    #[inline]
-    fn or_upgrade<U>(self, other: U) -> OrUpgrade<Self, U> {
-        OrUpgrade(self, other)
-    }
-}
-
-/// See `or_upgrade()`.
-#[derive(Debug, Copy, Clone)]
-pub struct OrUpgrade<A, B>(A, B);
-
-impl<C, A, B> ConnectionUpgrade<C> for OrUpgrade<A, B>
-where
-    C: AsyncRead + AsyncWrite,
-    A: ConnectionUpgrade<C>,
-    B: ConnectionUpgrade<C>,
-{
-    type NamesIter = NamesIterChain<A::NamesIter, B::NamesIter>;
-    type UpgradeIdentifier = EitherUpgradeIdentifier<A::UpgradeIdentifier, B::UpgradeIdentifier>;
-
-    #[inline]
-    fn protocol_names(&self) -> Self::NamesIter {
-        NamesIterChain {
-            first: self.0.protocol_names(),
-            second: self.1.protocol_names(),
-        }
-    }
-
-    type Output = EitherSocket<A::Output, B::Output>;
-    type Future = EitherConnUpgrFuture<A::Future, B::Future>;
-
-    #[inline]
-    fn upgrade(
-        self,
-        socket: C,
-        id: Self::UpgradeIdentifier,
-        ty: Endpoint,
-        remote_addr: &Multiaddr,
-    ) -> Self::Future {
-        match id {
-            EitherUpgradeIdentifier::First(id) => {
-                EitherConnUpgrFuture::First(self.0.upgrade(socket, id, ty, remote_addr))
-            }
-            EitherUpgradeIdentifier::Second(id) => {
-                EitherConnUpgrFuture::Second(self.1.upgrade(socket, id, ty, remote_addr))
-            }
-        }
-    }
-}
-
-/// Internal struct used by the `OrUpgrade` trait.
-#[derive(Debug, Copy, Clone)]
-pub enum EitherUpgradeIdentifier<A, B> {
-    First(A),
-    Second(B),
-}
-
-/// Implements `Future` and redirects calls to either `First` or `Second`.
-///
-/// Additionally, the output will be wrapped inside a `EitherSocket`.
-///
-// TODO: This type is needed because of the lack of `impl Trait` in stable Rust.
-//         If Rust had impl Trait we could use the Either enum from the futures crate and add some
-//         modifiers to it. This custom enum is a combination of Either and these modifiers.
-#[derive(Debug, Copy, Clone)]
-pub enum EitherConnUpgrFuture<A, B> {
-    First(A),
-    Second(B),
-}
-
-impl<A, B> Future for EitherConnUpgrFuture<A, B>
-where
-    A: Future<Error = IoError>,
-    B: Future<Error = IoError>,
-{
-    type Item = EitherSocket<A::Item, B::Item>;
-    type Error = IoError;
-
-    #[inline]
-    fn poll(&mut self) -> Poll<Self::Item, Self::Error> {
-        match self {
-            &mut EitherConnUpgrFuture::First(ref mut a) => {
-                let item = try_ready!(a.poll());
-                Ok(Async::Ready(EitherSocket::First(item)))
-            }
-            &mut EitherConnUpgrFuture::Second(ref mut b) => {
-                let item = try_ready!(b.poll());
-                Ok(Async::Ready(EitherSocket::Second(item)))
-            }
-        }
-    }
-}
-
-/// Internal type used by the `OrUpgrade` struct.
-///
-/// > **Note**: This type is needed because of the lack of `-> impl Trait` in Rust. It can be
-/// >           removed eventually.
-#[derive(Debug, Copy, Clone)]
-pub struct NamesIterChain<A, B> {
-    first: A,
-    second: B,
-}
-
-impl<A, B, AId, BId> Iterator for NamesIterChain<A, B>
-where
-    A: Iterator<Item = (Bytes, AId)>,
-    B: Iterator<Item = (Bytes, BId)>,
-{
-    type Item = (Bytes, EitherUpgradeIdentifier<AId, BId>);
-
-    #[inline]
-    fn next(&mut self) -> Option<Self::Item> {
-        if let Some((name, id)) = self.first.next() {
-            return Some((name, EitherUpgradeIdentifier::First(id)));
-        }
-        if let Some((name, id)) = self.second.next() {
-            return Some((name, EitherUpgradeIdentifier::Second(id)));
-        }
-        None
-    }
-
-    #[inline]
-    fn size_hint(&self) -> (usize, Option<usize>) {
-        let (min1, max1) = self.first.size_hint();
-        let (min2, max2) = self.second.size_hint();
-        let max = match (max1, max2) {
-            (Some(max1), Some(max2)) => max1.checked_add(max2),
-            _ => None,
-        };
-        (min1.saturating_add(min2), max)
-    }
-}
-
-/// Implementation of the `ConnectionUpgrade` that negotiates the `/plaintext/1.0.0` protocol and
-/// simply passes communications through without doing anything more.
-///
-/// > **Note**: Generally used as an alternative to `secio` if a security layer is not desirable.
-// TODO: move `PlainTextConfig` to a separate crate?
-#[derive(Debug, Copy, Clone)]
-pub struct PlainTextConfig;
-
-impl<C> ConnectionUpgrade<C> for PlainTextConfig
-where
-    C: AsyncRead + AsyncWrite,
-{
-    type Output = C;
-    type Future = FutureResult<C, IoError>;
-    type UpgradeIdentifier = ();
-    type NamesIter = iter::Once<(Bytes, ())>;
-
-    #[inline]
-    fn upgrade(self, i: C, _: (), _: Endpoint, _: &Multiaddr) -> Self::Future {
-        future::ok(i)
-    }
-
-    #[inline]
-    fn protocol_names(&self) -> Self::NamesIter {
-        iter::once((Bytes::from("/plaintext/1.0.0"), ()))
-    }
-}
-
-/// Dummy implementation of `MuxedTransport` that uses an inner `Transport`.
-#[derive(Debug, Copy, Clone)]
-pub struct DummyMuxing<T> {
-    inner: T,
-}
-
-impl<T> MuxedTransport for DummyMuxing<T>
-where
-    T: Transport,
-{
-    type Incoming = future::Empty<Self::IncomingUpgrade, IoError>;
-    type IncomingUpgrade = future::Empty<(T::RawConn, Multiaddr), IoError>;
-
-    fn next_incoming(self) -> Self::Incoming
-    where
-        Self: Sized,
-    {
-        future::empty()
-    }
-}
-
-impl<T> Transport for DummyMuxing<T>
-where
-    T: Transport,
-{
-    type RawConn = T::RawConn;
-    type Listener = T::Listener;
-    type ListenerUpgrade = T::ListenerUpgrade;
-    type Dial = T::Dial;
-
-    #[inline]
-    fn listen_on(self, addr: Multiaddr) -> Result<(Self::Listener, Multiaddr), (Self, Multiaddr)>
-    where
-        Self: Sized,
-    {
-        self.inner
-            .listen_on(addr)
-            .map_err(|(inner, addr)| (DummyMuxing { inner }, addr))
-    }
-
-    #[inline]
-    fn dial(self, addr: Multiaddr) -> Result<Self::Dial, (Self, Multiaddr)>
-    where
-        Self: Sized,
-    {
-        self.inner
-            .dial(addr)
-            .map_err(|(inner, addr)| (DummyMuxing { inner }, addr))
-    }
-
-    #[inline]
-    fn nat_traversal(&self, server: &Multiaddr, observed: &Multiaddr) -> Option<Multiaddr> {
-        self.inner.nat_traversal(server, observed)
-    }
-}
-
-/// Implements the `Transport` trait. Dials or listens, then upgrades any dialed or received
-/// connection.
-///
-/// See the `Transport::with_upgrade` method.
-#[derive(Debug, Clone)]
-pub struct UpgradedNode<T, C> {
-    transports: T,
-    upgrade: C,
-}
-
-impl<'a, T, C> UpgradedNode<T, C>
-where
-    T: Transport + 'a,
-    C: ConnectionUpgrade<T::RawConn> + 'a,
-{
-    /// Turns this upgraded node into a `ConnectionReuse`. If the `Output` implements the
-    /// `StreamMuxer` trait, the returned object will implement `Transport` and `MuxedTransport`.
-    #[inline]
-    pub fn into_connection_reuse(self) -> ConnectionReuse<T, C>
-    where
-        C::Output: StreamMuxer,
-    {
-        From::from(self)
-    }
-
-    /// Returns a reference to the inner `Transport`.
-    #[inline]
-    pub fn transport(&self) -> &T {
-        &self.transports
-    }
-
-    /// Tries to dial on the `Multiaddr` using the transport that was passed to `new`, then upgrade
-    /// the connection.
-    ///
-    /// Note that this does the same as `Transport::dial`, but with less restrictions on the trait
-    /// requirements.
-    #[inline]
-    pub fn dial(
-        self,
-        addr: Multiaddr,
-    ) -> Result<Box<Future<Item = (C::Output, Multiaddr), Error = IoError> + 'a>, (Self, Multiaddr)>
-    {
-        let upgrade = self.upgrade;
-
-        let dialed_fut = match self.transports.dial(addr.clone()) {
-            Ok(f) => f.into_future(),
-            Err((trans, addr)) => {
-                let builder = UpgradedNode {
-                    transports: trans,
-                    upgrade: upgrade,
-                };
-
-                return Err((builder, addr));
-            }
-        };
-
-        let future = dialed_fut
-            // Try to negotiate the protocol.
-            .and_then(move |(connection, client_addr)| {
-                let iter = upgrade.protocol_names()
-                    .map(|(name, id)| (name, <Bytes as PartialEq>::eq, id));
-                debug!(target: "libp2p-swarm", "Starting protocol negotiation (dialer)");
-                let negotiated = multistream_select::dialer_select_proto(connection, iter)
-                    .map_err(|err| IoError::new(IoErrorKind::Other, err));
-                negotiated.map(|(upgrade_id, conn)| (upgrade_id, conn, upgrade, client_addr))
-            })
-            .then(|negotiated| {
-                match negotiated {
-                    Ok((_, _, _, ref client_addr)) => {
-                        debug!(target: "libp2p-swarm", "Successfully negotiated protocol \
-                               upgrade with {}", client_addr)
-                    },
-                    Err(ref err) => {
-                        debug!(target: "libp2p-swarm", "Error while negotiated protocol \
-                               upgrade: {:?}", err)
-                    },
-                };
-                negotiated
-            })
-            .and_then(move |(upgrade_id, connection, upgrade, client_addr)| {
-                let f = upgrade.upgrade(connection, upgrade_id, Endpoint::Dialer, &client_addr);
-                debug!(target: "libp2p-swarm", "Trying to apply negotiated protocol with {}",
-                       client_addr);
-                f.map(|v| (v, client_addr))
-            })
-            .then(|val| {
-                match val {
-                    Ok(_) => debug!(target: "libp2p-swarm", "Successfully applied negotiated \
-                                                             protocol"),
-                    Err(_) => debug!(target: "libp2p-swarm", "Failed to apply negotiated protocol"),
-                }
-                val
-            });
-
-        Ok(Box::new(future))
-    }
-
-    /// If the underlying transport is a `MuxedTransport`, then after calling `dial` we may receive
-    /// substreams opened by the dialed nodes.
-    ///
-    /// This function returns the next incoming substream. You are strongly encouraged to call it
-    /// if you have a muxed transport.
-    pub fn next_incoming(
-        self,
-    ) -> Box<
-        Future<
-            Item = Box<Future<Item = (C::Output, Multiaddr), Error = IoError> + 'a>,
-            Error = IoError,
-        >
-            + 'a,
-    >
-    where
-        T: MuxedTransport,
-        C::NamesIter: Clone, // TODO: not elegant
-        C: Clone,
-    {
-        let upgrade = self.upgrade;
-
-        let future = self.transports.next_incoming().map(|future| {
-            // Try to negotiate the protocol.
-            let future = future
-                .and_then(move |(connection, addr)| {
-                    let iter = upgrade
-                        .protocol_names()
-                        .map::<_, fn(_) -> _>(|(name, id)| (name, <Bytes as PartialEq>::eq, id));
-                    debug!(target: "libp2p-swarm", "Starting protocol negotiation (incoming)");
-                    let negotiated = multistream_select::listener_select_proto(connection, iter)
-                        .map_err(|err| IoError::new(IoErrorKind::Other, err));
-                    negotiated.map(move |(upgrade_id, conn)| (upgrade_id, conn, upgrade, addr))
-                })
-                .then(|negotiated| {
-                    match negotiated {
-                        Ok((_, _, _, ref client_addr)) => {
-                            debug!(target: "libp2p-swarm", "Successfully negotiated protocol \
-                                upgrade with {}", client_addr)
-                        }
-                        Err(ref err) => {
-                            debug!(target: "libp2p-swarm", "Error while negotiated protocol \
-                                upgrade: {:?}", err)
-                        }
-                    };
-                    negotiated
-                })
-                .and_then(move |(upgrade_id, connection, upgrade, addr)| {
-                    let upg = upgrade.upgrade(connection, upgrade_id, Endpoint::Listener, &addr);
-                    debug!(target: "libp2p-swarm", "Trying to apply negotiated protocol with {}",
-                           addr);
-                    upg.map(|u| (u, addr))
-                })
-                .then(|val| {
-                    match val {
-                        Ok(_) => debug!(target: "libp2p-swarm", "Successfully applied negotiated \
-                                                                 protocol"),
-                        Err(_) => debug!(target: "libp2p-swarm", "Failed to apply negotiated \
-                                                                  protocol"),
-                    }
-                    val
-                });
-
-            Box::new(future) as Box<Future<Item = _, Error = _>>
-        });
-
-        Box::new(future) as Box<_>
-    }
-
-    /// Start listening on the multiaddr using the transport that was passed to `new`.
-    /// Then whenever a connection is opened, it is upgraded.
-    ///
-    /// Note that this does the same as `Transport::listen_on`, but with less restrictions on the
-    /// trait requirements.
-    #[inline]
-    pub fn listen_on(
-        self,
-        addr: Multiaddr,
-    ) -> Result<
-        (
-            Box<
-                Stream<
-                    Item = Box<Future<Item = (C::Output, Multiaddr), Error = IoError> + 'a>,
-                    Error = IoError,
-                >
-                    + 'a,
-            >,
-            Multiaddr,
-        ),
-        (Self, Multiaddr),
-    >
-    where
-        C::NamesIter: Clone, // TODO: not elegant
-        C: Clone,
-    {
-        let upgrade = self.upgrade;
-
-        let (listening_stream, new_addr) = match self.transports.listen_on(addr) {
-            Ok((l, new_addr)) => (l, new_addr),
-            Err((trans, addr)) => {
-                let builder = UpgradedNode {
-                    transports: trans,
-                    upgrade: upgrade,
-                };
-
-                return Err((builder, addr));
-            }
-        };
-
-        // Try to negotiate the protocol.
-        // Note that failing to negotiate a protocol will never produce a future with an error.
-        // Instead the `stream` will produce `Ok(Err(...))`.
-        // `stream` can only produce an `Err` if `listening_stream` produces an `Err`.
-        let stream = listening_stream.map(move |connection| {
-            let upgrade = upgrade.clone();
-            let connection = connection
-                    // Try to negotiate the protocol
-                    .and_then(move |(connection, remote_addr)| {
-                        let iter = upgrade.protocol_names()
-                            .map::<_, fn(_) -> _>(|(n, t)| (n, <Bytes as PartialEq>::eq, t));
-                        let remote_addr2 = remote_addr.clone();
-                        debug!(target: "libp2p-swarm", "Starting protocol negotiation (listener)");
-                        multistream_select::listener_select_proto(connection, iter)
-                            .map_err(|err| IoError::new(IoErrorKind::Other, err))
-                            .then(move |negotiated| {
-                                match negotiated {
-                                    Ok(_) => {
-                                        debug!(target: "libp2p-swarm", "Successfully negotiated \
-                                               protocol upgrade with {}", remote_addr2)
-                                    },
-                                    Err(ref err) => {
-                                        debug!(target: "libp2p-swarm", "Error while negotiated \
-                                               protocol upgrade: {:?}", err)
-                                    },
-                                };
-                                negotiated
-                            })
-                            .and_then(move |(upgrade_id, connection)| {
-                                let fut = upgrade.upgrade(
-                                    connection,
-                                    upgrade_id,
-                                    Endpoint::Listener,
-                                    &remote_addr,
-                                );
-                                fut.map(move |c| (c, remote_addr))
-                            })
-                            .into_future()
-                    });
-
-            Box::new(connection) as Box<_>
-        });
-
-        Ok((Box::new(stream), new_addr))
-    }
-}
-
-impl<T, C> Transport for UpgradedNode<T, C>
-where
-    T: Transport + 'static,
-    C: ConnectionUpgrade<T::RawConn> + 'static,
-    C::Output: AsyncRead + AsyncWrite,
-    C::NamesIter: Clone, // TODO: not elegant
-    C: Clone,
-{
-    type RawConn = C::Output;
-    type Listener = Box<Stream<Item = Self::ListenerUpgrade, Error = IoError>>;
-    type ListenerUpgrade = Box<Future<Item = (C::Output, Multiaddr), Error = IoError>>;
-    type Dial = Box<Future<Item = (C::Output, Multiaddr), Error = IoError>>;
-
-    #[inline]
-    fn listen_on(self, addr: Multiaddr) -> Result<(Self::Listener, Multiaddr), (Self, Multiaddr)> {
-        self.listen_on(addr)
-    }
-
-    #[inline]
-    fn dial(self, addr: Multiaddr) -> Result<Self::Dial, (Self, Multiaddr)> {
-        self.dial(addr)
-    }
-
-    #[inline]
-    fn nat_traversal(&self, server: &Multiaddr, observed: &Multiaddr) -> Option<Multiaddr> {
-        self.transports.nat_traversal(server, observed)
-    }
-}
-
-impl<T, C> MuxedTransport for UpgradedNode<T, C>
-where
-    T: MuxedTransport + 'static,
-    C: ConnectionUpgrade<T::RawConn> + 'static,
-    C::Output: AsyncRead + AsyncWrite,
-    C::NamesIter: Clone, // TODO: not elegant
-    C: Clone,
-{
-    type Incoming = Box<Future<Item = Self::IncomingUpgrade, Error = IoError>>;
-    type IncomingUpgrade = Box<Future<Item = (C::Output, Multiaddr), Error = IoError>>;
-
-    #[inline]
-    fn next_incoming(self) -> Self::Incoming {
-        self.next_incoming()
-    }
-}
diff --git a/swarm/src/transport/choice.rs b/swarm/src/transport/choice.rs
new file mode 100644
index 00000000..dd37a121
--- /dev/null
+++ b/swarm/src/transport/choice.rs
@@ -0,0 +1,111 @@
+// Copyright 2017 Parity Technologies (UK) Ltd.
+//
+// Permission is hereby granted, free of charge, to any person obtaining a
+// copy of this software and associated documentation files (the "Software"),
+// to deal in the Software without restriction, including without limitation
+// the rights to use, copy, modify, merge, publish, distribute, sublicense,
+// and/or sell copies of the Software, and to permit persons to whom the
+// Software is furnished to do so, subject to the following conditions:
+//
+// The above copyright notice and this permission notice shall be included in
+// all copies or substantial portions of the Software.
+//
+// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS
+// OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
+// FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
+// DEALINGS IN THE SOFTWARE.
+
+use either::{EitherListenStream, EitherListenUpgrade, EitherSocket};
+use futures::prelude::*;
+use multiaddr::Multiaddr;
+use std::io::Error as IoError;
+use transport::{MuxedTransport, Transport};
+
+/// Struct returned by `or_transport()`.
+#[derive(Debug, Copy, Clone)]
+pub struct OrTransport<A, B>(A, B);
+
+impl<A, B> OrTransport<A, B> {
+    pub fn new(a: A, b: B) -> OrTransport<A, B> {
+        OrTransport(a, b)
+    }
+}
+
+impl<A, B> Transport for OrTransport<A, B>
+where
+    A: Transport,
+    B: Transport,
+{
+    type RawConn = EitherSocket<A::RawConn, B::RawConn>;
+    type Listener = EitherListenStream<A::Listener, B::Listener>;
+    type ListenerUpgrade = EitherListenUpgrade<A::ListenerUpgrade, B::ListenerUpgrade>;
+    type Dial =
+        EitherListenUpgrade<<A::Dial as IntoFuture>::Future, <B::Dial as IntoFuture>::Future>;
+
+    fn listen_on(self, addr: Multiaddr) -> Result<(Self::Listener, Multiaddr), (Self, Multiaddr)> {
+        let (first, addr) = match self.0.listen_on(addr) {
+            Ok((connec, addr)) => return Ok((EitherListenStream::First(connec), addr)),
+            Err(err) => err,
+        };
+
+        match self.1.listen_on(addr) {
+            Ok((connec, addr)) => Ok((EitherListenStream::Second(connec), addr)),
+            Err((second, addr)) => Err((OrTransport(first, second), addr)),
+        }
+    }
+
+    fn dial(self, addr: Multiaddr) -> Result<Self::Dial, (Self, Multiaddr)> {
+        let (first, addr) = match self.0.dial(addr) {
+            Ok(connec) => return Ok(EitherListenUpgrade::First(connec.into_future())),
+            Err(err) => err,
+        };
+
+        match self.1.dial(addr) {
+            Ok(connec) => Ok(EitherListenUpgrade::Second(connec.into_future())),
+            Err((second, addr)) => Err((OrTransport(first, second), addr)),
+        }
+    }
+
+    #[inline]
+    fn nat_traversal(&self, server: &Multiaddr, observed: &Multiaddr) -> Option<Multiaddr> {
+        let first = self.0.nat_traversal(server, observed);
+        if let Some(first) = first {
+            return Some(first);
+        }
+
+        self.1.nat_traversal(server, observed)
+    }
+}
+
+impl<A, B> MuxedTransport for OrTransport<A, B>
+where
+    A: MuxedTransport,
+    B: MuxedTransport,
+    A::Incoming: 'static,        // TODO: meh :-/
+    B::Incoming: 'static,        // TODO: meh :-/
+    A::IncomingUpgrade: 'static, // TODO: meh :-/
+    B::IncomingUpgrade: 'static, // TODO: meh :-/
+    A::RawConn: 'static,         // TODO: meh :-/
+    B::RawConn: 'static,         // TODO: meh :-/
+{
+    type Incoming = Box<Future<Item = Self::IncomingUpgrade, Error = IoError>>;
+    type IncomingUpgrade =
+        Box<Future<Item = (EitherSocket<A::RawConn, B::RawConn>, Multiaddr), Error = IoError>>;
+
+    #[inline]
+    fn next_incoming(self) -> Self::Incoming {
+        let first = self.0.next_incoming().map(|out| {
+            let fut = out.map(move |(v, addr)| (EitherSocket::First(v), addr));
+            Box::new(fut) as Box<Future<Item = _, Error = _>>
+        });
+        let second = self.1.next_incoming().map(|out| {
+            let fut = out.map(move |(v, addr)| (EitherSocket::Second(v), addr));
+            Box::new(fut) as Box<Future<Item = _, Error = _>>
+        });
+        let future = first.select(second).map(|(i, _)| i).map_err(|(e, _)| e);
+        Box::new(future) as Box<_>
+    }
+}
diff --git a/swarm/src/transport/denied.rs b/swarm/src/transport/denied.rs
new file mode 100644
index 00000000..b59df8bd
--- /dev/null
+++ b/swarm/src/transport/denied.rs
@@ -0,0 +1,63 @@
+// Copyright 2017 Parity Technologies (UK) Ltd.
+//
+// Permission is hereby granted, free of charge, to any person obtaining a
+// copy of this software and associated documentation files (the "Software"),
+// to deal in the Software without restriction, including without limitation
+// the rights to use, copy, modify, merge, publish, distribute, sublicense,
+// and/or sell copies of the Software, and to permit persons to whom the
+// Software is furnished to do so, subject to the following conditions:
+//
+// The above copyright notice and this permission notice shall be included in
+// all copies or substantial portions of the Software.
+//
+// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS
+// OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
+// FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
+// DEALINGS IN THE SOFTWARE.
+
+use futures::future;
+use futures::prelude::*;
+use multiaddr::Multiaddr;
+use std::io::{self, Cursor};
+use transport::Transport;
+use transport::MuxedTransport;
+
+/// Dummy implementation of `Transport` that just denies every single attempt.
+#[derive(Debug, Copy, Clone)]
+pub struct DeniedTransport;
+
+impl Transport for DeniedTransport {
+    // TODO: could use `!` for associated types once stable
+    type RawConn = Cursor<Vec<u8>>;
+    type Listener = Box<Stream<Item = Self::ListenerUpgrade, Error = io::Error>>;
+    type ListenerUpgrade = Box<Future<Item = (Self::RawConn, Multiaddr), Error = io::Error>>;
+    type Dial = Box<Future<Item = (Self::RawConn, Multiaddr), Error = io::Error>>;
+
+    #[inline]
+    fn listen_on(self, addr: Multiaddr) -> Result<(Self::Listener, Multiaddr), (Self, Multiaddr)> {
+        Err((DeniedTransport, addr))
+    }
+
+    #[inline]
+    fn dial(self, addr: Multiaddr) -> Result<Self::Dial, (Self, Multiaddr)> {
+        Err((DeniedTransport, addr))
+    }
+
+    #[inline]
+    fn nat_traversal(&self, _: &Multiaddr, _: &Multiaddr) -> Option<Multiaddr> {
+        None
+    }
+}
+
+impl MuxedTransport for DeniedTransport {
+    type Incoming = future::Empty<Self::IncomingUpgrade, io::Error>;
+    type IncomingUpgrade = future::Empty<(Self::RawConn, Multiaddr), io::Error>;
+
+    #[inline]
+    fn next_incoming(self) -> Self::Incoming {
+        future::empty()
+    }
+}
diff --git a/swarm/src/transport/dummy.rs b/swarm/src/transport/dummy.rs
new file mode 100644
index 00000000..8a3940fa
--- /dev/null
+++ b/swarm/src/transport/dummy.rs
@@ -0,0 +1,86 @@
+// Copyright 2017 Parity Technologies (UK) Ltd.
+//
+// Permission is hereby granted, free of charge, to any person obtaining a
+// copy of this software and associated documentation files (the "Software"),
+// to deal in the Software without restriction, including without limitation
+// the rights to use, copy, modify, merge, publish, distribute, sublicense,
+// and/or sell copies of the Software, and to permit persons to whom the
+// Software is furnished to do so, subject to the following conditions:
+//
+// The above copyright notice and this permission notice shall be included in
+// all copies or substantial portions of the Software.
+//
+// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS
+// OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
+// FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
+// DEALINGS IN THE SOFTWARE.
+
+use futures::future;
+use multiaddr::Multiaddr;
+use std::io::Error as IoError;
+use transport::{MuxedTransport, Transport};
+
+/// Dummy implementation of `MuxedTransport` that uses an inner `Transport`.
+#[derive(Debug, Copy, Clone)]
+pub struct DummyMuxing<T> {
+    inner: T,
+}
+
+impl<T> DummyMuxing<T> {
+    pub fn new(transport: T) -> DummyMuxing<T> {
+        DummyMuxing { inner: transport }
+    }
+}
+
+impl<T> MuxedTransport for DummyMuxing<T>
+where
+    T: Transport,
+{
+    type Incoming = future::Empty<Self::IncomingUpgrade, IoError>;
+    type IncomingUpgrade = future::Empty<(T::RawConn, Multiaddr), IoError>;
+
+    fn next_incoming(self) -> Self::Incoming
+    where
+        Self: Sized,
+    {
+        future::empty()
+    }
+}
+
+impl<T> Transport for DummyMuxing<T>
+where
+    T: Transport,
+{
+    type RawConn = T::RawConn;
+    type Listener = T::Listener;
+    type ListenerUpgrade = T::ListenerUpgrade;
+    type Dial = T::Dial;
+
+    #[inline]
+    fn listen_on(self, addr: Multiaddr) -> Result<(Self::Listener, Multiaddr), (Self, Multiaddr)>
+    where
+        Self: Sized,
+    {
+        self.inner
+            .listen_on(addr)
+            .map_err(|(inner, addr)| (DummyMuxing { inner }, addr))
+    }
+
+    #[inline]
+    fn dial(self, addr: Multiaddr) -> Result<Self::Dial, (Self, Multiaddr)>
+    where
+        Self: Sized,
+    {
+        self.inner
+            .dial(addr)
+            .map_err(|(inner, addr)| (DummyMuxing { inner }, addr))
+    }
+
+    #[inline]
+    fn nat_traversal(&self, server: &Multiaddr, observed: &Multiaddr) -> Option<Multiaddr> {
+        self.inner.nat_traversal(server, observed)
+    }
+}
diff --git a/swarm/src/transport/mod.rs b/swarm/src/transport/mod.rs
new file mode 100644
index 00000000..865ea389
--- /dev/null
+++ b/swarm/src/transport/mod.rs
@@ -0,0 +1,149 @@
+// Copyright 2017 Parity Technologies (UK) Ltd.
+//
+// Permission is hereby granted, free of charge, to any person obtaining a
+// copy of this software and associated documentation files (the "Software"),
+// to deal in the Software without restriction, including without limitation
+// the rights to use, copy, modify, merge, publish, distribute, sublicense,
+// and/or sell copies of the Software, and to permit persons to whom the
+// Software is furnished to do so, subject to the following conditions:
+//
+// The above copyright notice and this permission notice shall be included in
+// all copies or substantial portions of the Software.
+//
+// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS
+// OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
+// FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
+// DEALINGS IN THE SOFTWARE.
+
+//! Handles entering a connection with a peer.
+//!
+//! The two main elements of this module are the `Transport` and `ConnectionUpgrade` traits.
+//! `Transport` is implemented on objects that allow dialing and listening. `ConnectionUpgrade` is
+//! implemented on objects that make it possible to upgrade a connection (for example by adding an
+//! encryption middleware to the connection).
+//!
+//! Thanks to the `Transport::or_transport`, `Transport::with_upgrade` and
+//! `UpgradedNode::or_upgrade` methods, you can combine multiple transports and/or upgrades
+//! together in a complex chain of protocols negotiation.
+
+use futures::prelude::*;
+use multiaddr::Multiaddr;
+use std::io::Error as IoError;
+use tokio_io::{AsyncRead, AsyncWrite};
+use upgrade::ConnectionUpgrade;
+
+pub mod choice;
+pub mod denied;
+pub mod dummy;
+pub mod muxed;
+pub mod upgrade;
+
+pub use self::choice::OrTransport;
+pub use self::denied::DeniedTransport;
+pub use self::dummy::DummyMuxing;
+pub use self::muxed::MuxedTransport;
+pub use self::upgrade::UpgradedNode;
+
+/// A transport is an object that can be used to produce connections by listening or dialing a
+/// peer.
+///
+/// This trait is implemented on concrete transports (eg. TCP, UDP, etc.), but also on wrappers
+/// around them.
+///
+/// > **Note**: The methods of this trait use `self` and not `&self` or `&mut self`. In other
+/// >           words, listening or dialing consumes the transport object. This has been designed
+/// >           so that you would implement this trait on `&Foo` or `&mut Foo` instead of directly
+/// >           on `Foo`.
+pub trait Transport {
+    /// The raw connection to a peer.
+    type RawConn: AsyncRead + AsyncWrite;
+
+    /// The listener produces incoming connections.
+    ///
+    /// An item should be produced whenever a connection is received at the lowest level of the
+    /// transport stack. The item is a `Future` that is signalled once some pre-processing has
+    /// taken place, and that connection has been upgraded to the wanted protocols.
+    type Listener: Stream<Item = Self::ListenerUpgrade, Error = IoError>;
+
+    /// After a connection has been received, we may need to do some asynchronous pre-processing
+    /// on it (eg. an intermediary protocol negotiation). While this pre-processing takes place, we
+    /// want to be able to continue polling on the listener.
+    type ListenerUpgrade: Future<Item = (Self::RawConn, Multiaddr), Error = IoError>;
+
+    /// A future which indicates that we are currently dialing to a peer.
+    type Dial: IntoFuture<Item = (Self::RawConn, Multiaddr), Error = IoError>;
+
+    /// Listen on the given multiaddr. Returns a stream of incoming connections, plus a modified
+    /// version of the `Multiaddr`. This new `Multiaddr` is the one that that should be advertised
+    /// to other nodes, instead of the one passed as parameter.
+    ///
+    /// Returns the address back if it isn't supported.
+    ///
+    /// > **Note**: The reason why we need to change the `Multiaddr` on success is to handle
+    /// >             situations such as turning `/ip4/127.0.0.1/tcp/0` into
+    /// >             `/ip4/127.0.0.1/tcp/<actual port>`.
+    fn listen_on(self, addr: Multiaddr) -> Result<(Self::Listener, Multiaddr), (Self, Multiaddr)>
+    where
+        Self: Sized;
+
+    /// Dial to the given multi-addr.
+    ///
+    /// Returns either a future which may resolve to a connection, or gives back the multiaddress.
+    fn dial(self, addr: Multiaddr) -> Result<Self::Dial, (Self, Multiaddr)>
+    where
+        Self: Sized;
+
+    /// Takes a multiaddress we're listening on (`server`), and tries to convert it to an
+    /// externally-visible multiaddress. In order to do so, we pass an `observed` address which
+    /// a remote node observes for one of our dialers.
+    ///
+    /// For example, if `server` is `/ip4/0.0.0.0/tcp/3000` and `observed` is
+    /// `/ip4/80.81.82.83/tcp/29601`, then we should return `/ip4/80.81.82.83/tcp/3000`. Each
+    /// implementation of `Transport` is only responsible for handling the protocols it supports.
+    ///
+    /// Returns `None` if nothing can be determined. This happens if this trait implementation
+    /// doesn't recognize the protocols, or if `server` and `observed` are related.
+    fn nat_traversal(&self, server: &Multiaddr, observed: &Multiaddr) -> Option<Multiaddr>;
+
+    /// Builds a new struct that implements `Transport` that contains both `self` and `other`.
+    ///
+    /// The returned object will redirect its calls to `self`, except that if `listen_on` or `dial`
+    /// return an error then `other` will be tried.
+    #[inline]
+    fn or_transport<T>(self, other: T) -> OrTransport<Self, T>
+    where
+        Self: Sized,
+    {
+        OrTransport::new(self, other)
+    }
+
+    /// Wraps this transport inside an upgrade. Whenever a connection that uses this transport
+    /// is established, it is wrapped inside the upgrade.
+    ///
+    /// > **Note**: The concept of an *upgrade* for example includes middlewares such *secio*
+    /// >           (communication encryption), *multiplex*, but also a protocol handler.
+    #[inline]
+    fn with_upgrade<U>(self, upgrade: U) -> UpgradedNode<Self, U>
+    where
+        Self: Sized,
+        U: ConnectionUpgrade<Self::RawConn>,
+    {
+        UpgradedNode::new(self, upgrade)
+    }
+
+    /// Builds a dummy implementation of `MuxedTransport` that uses this transport.
+    ///
+    /// The resulting object will not actually use muxing. This means that dialing the same node
+    /// twice will result in two different connections instead of two substreams on the same
+    /// connection.
+    #[inline]
+    fn with_dummy_muxing(self) -> DummyMuxing<Self>
+    where
+        Self: Sized,
+    {
+        DummyMuxing::new(self)
+    }
+}
diff --git a/swarm/src/transport/muxed.rs b/swarm/src/transport/muxed.rs
new file mode 100644
index 00000000..42798d92
--- /dev/null
+++ b/swarm/src/transport/muxed.rs
@@ -0,0 +1,53 @@
+// Copyright 2017 Parity Technologies (UK) Ltd.
+//
+// Permission is hereby granted, free of charge, to any person obtaining a
+// copy of this software and associated documentation files (the "Software"),
+// to deal in the Software without restriction, including without limitation
+// the rights to use, copy, modify, merge, publish, distribute, sublicense,
+// and/or sell copies of the Software, and to permit persons to whom the
+// Software is furnished to do so, subject to the following conditions:
+//
+// The above copyright notice and this permission notice shall be included in
+// all copies or substantial portions of the Software.
+//
+// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS
+// OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
+// FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
+// DEALINGS IN THE SOFTWARE.
+
+use futures::prelude::*;
+use futures::stream;
+use multiaddr::Multiaddr;
+use std::io::Error as IoError;
+use transport::Transport;
+
+/// Extension trait for `Transport`. Implemented on structs that provide a `Transport` on which
+/// the dialed node can dial you back.
+pub trait MuxedTransport: Transport {
+    /// Future resolving to a future that will resolve to an incoming connection.
+    type Incoming: Future<Item = Self::IncomingUpgrade, Error = IoError>;
+    /// Future resolving to an incoming connection.
+    type IncomingUpgrade: Future<Item = (Self::RawConn, Multiaddr), Error = IoError>;
+
+    /// Returns the next incoming substream opened by a node that we dialed ourselves.
+    ///
+    /// > **Note**: Doesn't produce incoming substreams coming from addresses we are listening on.
+    /// >            This only concerns nodes that we dialed with `dial()`.
+    fn next_incoming(self) -> Self::Incoming
+    where
+        Self: Sized;
+
+    /// Returns a stream of incoming connections.
+    #[inline]
+    fn incoming(
+        self,
+    ) -> stream::AndThen<stream::Repeat<Self, IoError>, fn(Self) -> Self::Incoming, Self::Incoming>
+    where
+        Self: Sized + Clone,
+    {
+        stream::repeat(self).and_then(|me| me.next_incoming())
+    }
+}
diff --git a/swarm/src/transport/upgrade.rs b/swarm/src/transport/upgrade.rs
new file mode 100644
index 00000000..63aade23
--- /dev/null
+++ b/swarm/src/transport/upgrade.rs
@@ -0,0 +1,337 @@
+// Copyright 2017 Parity Technologies (UK) Ltd.
+//
+// Permission is hereby granted, free of charge, to any person obtaining a
+// copy of this software and associated documentation files (the "Software"),
+// to deal in the Software without restriction, including without limitation
+// the rights to use, copy, modify, merge, publish, distribute, sublicense,
+// and/or sell copies of the Software, and to permit persons to whom the
+// Software is furnished to do so, subject to the following conditions:
+//
+// The above copyright notice and this permission notice shall be included in
+// all copies or substantial portions of the Software.
+//
+// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS
+// OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
+// FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
+// DEALINGS IN THE SOFTWARE.
+
+use bytes::Bytes;
+use connection_reuse::ConnectionReuse;
+use futures::prelude::*;
+use multiaddr::Multiaddr;
+use multistream_select;
+use muxing::StreamMuxer;
+use std::io::{Error as IoError, ErrorKind as IoErrorKind};
+use tokio_io::{AsyncRead, AsyncWrite};
+use transport::{MuxedTransport, Transport};
+use upgrade::{ConnectionUpgrade, Endpoint};
+
+/// Implements the `Transport` trait. Dials or listens, then upgrades any dialed or received
+/// connection.
+///
+/// See the `Transport::with_upgrade` method.
+#[derive(Debug, Clone)]
+pub struct UpgradedNode<T, C> {
+    transports: T,
+    upgrade: C,
+}
+
+impl<T, C> UpgradedNode<T, C> {
+    pub fn new(transports: T, upgrade: C) -> UpgradedNode<T, C> {
+        UpgradedNode {
+            transports,
+            upgrade,
+        }
+    }
+}
+
+impl<'a, T, C> UpgradedNode<T, C>
+where
+    T: Transport + 'a,
+    C: ConnectionUpgrade<T::RawConn> + 'a,
+{
+    /// Turns this upgraded node into a `ConnectionReuse`. If the `Output` implements the
+    /// `StreamMuxer` trait, the returned object will implement `Transport` and `MuxedTransport`.
+    #[inline]
+    pub fn into_connection_reuse(self) -> ConnectionReuse<T, C>
+    where
+        C::Output: StreamMuxer,
+    {
+        From::from(self)
+    }
+
+    /// Returns a reference to the inner `Transport`.
+    #[inline]
+    pub fn transport(&self) -> &T {
+        &self.transports
+    }
+
+    /// Tries to dial on the `Multiaddr` using the transport that was passed to `new`, then upgrade
+    /// the connection.
+    ///
+    /// Note that this does the same as `Transport::dial`, but with less restrictions on the trait
+    /// requirements.
+    #[inline]
+    pub fn dial(
+        self,
+        addr: Multiaddr,
+    ) -> Result<Box<Future<Item = (C::Output, Multiaddr), Error = IoError> + 'a>, (Self, Multiaddr)>
+    {
+        let upgrade = self.upgrade;
+
+        let dialed_fut = match self.transports.dial(addr.clone()) {
+            Ok(f) => f.into_future(),
+            Err((trans, addr)) => {
+                let builder = UpgradedNode {
+                    transports: trans,
+                    upgrade: upgrade,
+                };
+
+                return Err((builder, addr));
+            }
+        };
+
+        let future = dialed_fut
+            // Try to negotiate the protocol.
+            .and_then(move |(connection, client_addr)| {
+                let iter = upgrade.protocol_names()
+                    .map(|(name, id)| (name, <Bytes as PartialEq>::eq, id));
+                debug!(target: "libp2p-swarm", "Starting protocol negotiation (dialer)");
+                let negotiated = multistream_select::dialer_select_proto(connection, iter)
+                    .map_err(|err| IoError::new(IoErrorKind::Other, err));
+                negotiated.map(|(upgrade_id, conn)| (upgrade_id, conn, upgrade, client_addr))
+            })
+            .then(|negotiated| {
+                match negotiated {
+                    Ok((_, _, _, ref client_addr)) => {
+                        debug!(target: "libp2p-swarm", "Successfully negotiated protocol \
+                               upgrade with {}", client_addr)
+                    },
+                    Err(ref err) => {
+                        debug!(target: "libp2p-swarm", "Error while negotiated protocol \
+                               upgrade: {:?}", err)
+                    },
+                };
+                negotiated
+            })
+            .and_then(move |(upgrade_id, connection, upgrade, client_addr)| {
+                let f = upgrade.upgrade(connection, upgrade_id, Endpoint::Dialer, &client_addr);
+                debug!(target: "libp2p-swarm", "Trying to apply negotiated protocol with {}",
+                       client_addr);
+                f.map(|v| (v, client_addr))
+            })
+            .then(|val| {
+                match val {
+                    Ok(_) => debug!(target: "libp2p-swarm", "Successfully applied negotiated \
+                                                             protocol"),
+                    Err(_) => debug!(target: "libp2p-swarm", "Failed to apply negotiated protocol"),
+                }
+                val
+            });
+
+        Ok(Box::new(future))
+    }
+
+    /// If the underlying transport is a `MuxedTransport`, then after calling `dial` we may receive
+    /// substreams opened by the dialed nodes.
+    ///
+    /// This function returns the next incoming substream. You are strongly encouraged to call it
+    /// if you have a muxed transport.
+    pub fn next_incoming(
+        self,
+    ) -> Box<
+        Future<
+            Item = Box<Future<Item = (C::Output, Multiaddr), Error = IoError> + 'a>,
+            Error = IoError,
+        >
+            + 'a,
+    >
+    where
+        T: MuxedTransport,
+        C::NamesIter: Clone, // TODO: not elegant
+        C: Clone,
+    {
+        let upgrade = self.upgrade;
+
+        let future = self.transports.next_incoming().map(|future| {
+            // Try to negotiate the protocol.
+            let future = future
+                .and_then(move |(connection, addr)| {
+                    let iter = upgrade
+                        .protocol_names()
+                        .map::<_, fn(_) -> _>(|(name, id)| (name, <Bytes as PartialEq>::eq, id));
+                    debug!(target: "libp2p-swarm", "Starting protocol negotiation (incoming)");
+                    let negotiated = multistream_select::listener_select_proto(connection, iter)
+                        .map_err(|err| IoError::new(IoErrorKind::Other, err));
+                    negotiated.map(move |(upgrade_id, conn)| (upgrade_id, conn, upgrade, addr))
+                })
+                .then(|negotiated| {
+                    match negotiated {
+                        Ok((_, _, _, ref client_addr)) => {
+                            debug!(target: "libp2p-swarm", "Successfully negotiated protocol \
+                                upgrade with {}", client_addr)
+                        }
+                        Err(ref err) => {
+                            debug!(target: "libp2p-swarm", "Error while negotiated protocol \
+                                upgrade: {:?}", err)
+                        }
+                    };
+                    negotiated
+                })
+                .and_then(move |(upgrade_id, connection, upgrade, addr)| {
+                    let upg = upgrade.upgrade(connection, upgrade_id, Endpoint::Listener, &addr);
+                    debug!(target: "libp2p-swarm", "Trying to apply negotiated protocol with {}",
+                           addr);
+                    upg.map(|u| (u, addr))
+                })
+                .then(|val| {
+                    match val {
+                        Ok(_) => debug!(target: "libp2p-swarm", "Successfully applied negotiated \
+                                                                 protocol"),
+                        Err(_) => debug!(target: "libp2p-swarm", "Failed to apply negotiated \
+                                                                  protocol"),
+                    }
+                    val
+                });
+
+            Box::new(future) as Box<Future<Item = _, Error = _>>
+        });
+
+        Box::new(future) as Box<_>
+    }
+
+    /// Start listening on the multiaddr using the transport that was passed to `new`.
+    /// Then whenever a connection is opened, it is upgraded.
+    ///
+    /// Note that this does the same as `Transport::listen_on`, but with less restrictions on the
+    /// trait requirements.
+    #[inline]
+    pub fn listen_on(
+        self,
+        addr: Multiaddr,
+    ) -> Result<
+        (
+            Box<
+                Stream<
+                    Item = Box<Future<Item = (C::Output, Multiaddr), Error = IoError> + 'a>,
+                    Error = IoError,
+                >
+                    + 'a,
+            >,
+            Multiaddr,
+        ),
+        (Self, Multiaddr),
+    >
+    where
+        C::NamesIter: Clone, // TODO: not elegant
+        C: Clone,
+    {
+        let upgrade = self.upgrade;
+
+        let (listening_stream, new_addr) = match self.transports.listen_on(addr) {
+            Ok((l, new_addr)) => (l, new_addr),
+            Err((trans, addr)) => {
+                let builder = UpgradedNode {
+                    transports: trans,
+                    upgrade: upgrade,
+                };
+
+                return Err((builder, addr));
+            }
+        };
+
+        // Try to negotiate the protocol.
+        // Note that failing to negotiate a protocol will never produce a future with an error.
+        // Instead the `stream` will produce `Ok(Err(...))`.
+        // `stream` can only produce an `Err` if `listening_stream` produces an `Err`.
+        let stream = listening_stream.map(move |connection| {
+            let upgrade = upgrade.clone();
+            let connection = connection
+                    // Try to negotiate the protocol
+                    .and_then(move |(connection, remote_addr)| {
+                        let iter = upgrade.protocol_names()
+                            .map::<_, fn(_) -> _>(|(n, t)| (n, <Bytes as PartialEq>::eq, t));
+                        let remote_addr2 = remote_addr.clone();
+                        debug!(target: "libp2p-swarm", "Starting protocol negotiation (listener)");
+                        multistream_select::listener_select_proto(connection, iter)
+                            .map_err(|err| IoError::new(IoErrorKind::Other, err))
+                            .then(move |negotiated| {
+                                match negotiated {
+                                    Ok(_) => {
+                                        debug!(target: "libp2p-swarm", "Successfully negotiated \
+                                               protocol upgrade with {}", remote_addr2)
+                                    },
+                                    Err(ref err) => {
+                                        debug!(target: "libp2p-swarm", "Error while negotiated \
+                                               protocol upgrade: {:?}", err)
+                                    },
+                                };
+                                negotiated
+                            })
+                            .and_then(move |(upgrade_id, connection)| {
+                                let fut = upgrade.upgrade(
+                                    connection,
+                                    upgrade_id,
+                                    Endpoint::Listener,
+                                    &remote_addr,
+                                );
+                                fut.map(move |c| (c, remote_addr))
+                            })
+                            .into_future()
+                    });
+
+            Box::new(connection) as Box<_>
+        });
+
+        Ok((Box::new(stream), new_addr))
+    }
+}
+
+impl<T, C> Transport for UpgradedNode<T, C>
+where
+    T: Transport + 'static,
+    C: ConnectionUpgrade<T::RawConn> + 'static,
+    C::Output: AsyncRead + AsyncWrite,
+    C::NamesIter: Clone, // TODO: not elegant
+    C: Clone,
+{
+    type RawConn = C::Output;
+    type Listener = Box<Stream<Item = Self::ListenerUpgrade, Error = IoError>>;
+    type ListenerUpgrade = Box<Future<Item = (C::Output, Multiaddr), Error = IoError>>;
+    type Dial = Box<Future<Item = (C::Output, Multiaddr), Error = IoError>>;
+
+    #[inline]
+    fn listen_on(self, addr: Multiaddr) -> Result<(Self::Listener, Multiaddr), (Self, Multiaddr)> {
+        self.listen_on(addr)
+    }
+
+    #[inline]
+    fn dial(self, addr: Multiaddr) -> Result<Self::Dial, (Self, Multiaddr)> {
+        self.dial(addr)
+    }
+
+    #[inline]
+    fn nat_traversal(&self, server: &Multiaddr, observed: &Multiaddr) -> Option<Multiaddr> {
+        self.transports.nat_traversal(server, observed)
+    }
+}
+
+impl<T, C> MuxedTransport for UpgradedNode<T, C>
+where
+    T: MuxedTransport + 'static,
+    C: ConnectionUpgrade<T::RawConn> + 'static,
+    C::Output: AsyncRead + AsyncWrite,
+    C::NamesIter: Clone, // TODO: not elegant
+    C: Clone,
+{
+    type Incoming = Box<Future<Item = Self::IncomingUpgrade, Error = IoError>>;
+    type IncomingUpgrade = Box<Future<Item = (C::Output, Multiaddr), Error = IoError>>;
+
+    #[inline]
+    fn next_incoming(self) -> Self::Incoming {
+        self.next_incoming()
+    }
+}
diff --git a/swarm/src/upgrade/choice.rs b/swarm/src/upgrade/choice.rs
new file mode 100644
index 00000000..1fd5aaaf
--- /dev/null
+++ b/swarm/src/upgrade/choice.rs
@@ -0,0 +1,159 @@
+// Copyright 2017 Parity Technologies (UK) Ltd.
+//
+// Permission is hereby granted, free of charge, to any person obtaining a
+// copy of this software and associated documentation files (the "Software"),
+// to deal in the Software without restriction, including without limitation
+// the rights to use, copy, modify, merge, publish, distribute, sublicense,
+// and/or sell copies of the Software, and to permit persons to whom the
+// Software is furnished to do so, subject to the following conditions:
+//
+// The above copyright notice and this permission notice shall be included in
+// all copies or substantial portions of the Software.
+//
+// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS
+// OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
+// FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
+// DEALINGS IN THE SOFTWARE.
+
+use bytes::Bytes;
+use either::EitherSocket;
+use futures::prelude::*;
+use multiaddr::Multiaddr;
+use std::io::Error as IoError;
+use tokio_io::{AsyncRead, AsyncWrite};
+use upgrade::{ConnectionUpgrade, Endpoint};
+
+/// See `transport::Transport::or_upgrade()`.
+#[derive(Debug, Copy, Clone)]
+pub struct OrUpgrade<A, B>(A, B);
+
+impl<A, B> OrUpgrade<A, B> {
+    pub fn new(a: A, b: B) -> OrUpgrade<A, B> {
+        OrUpgrade(a, b)
+    }
+}
+
+impl<C, A, B> ConnectionUpgrade<C> for OrUpgrade<A, B>
+where
+    C: AsyncRead + AsyncWrite,
+    A: ConnectionUpgrade<C>,
+    B: ConnectionUpgrade<C>,
+{
+    type NamesIter = NamesIterChain<A::NamesIter, B::NamesIter>;
+    type UpgradeIdentifier = EitherUpgradeIdentifier<A::UpgradeIdentifier, B::UpgradeIdentifier>;
+
+    #[inline]
+    fn protocol_names(&self) -> Self::NamesIter {
+        NamesIterChain {
+            first: self.0.protocol_names(),
+            second: self.1.protocol_names(),
+        }
+    }
+
+    type Output = EitherSocket<A::Output, B::Output>;
+    type Future = EitherConnUpgrFuture<A::Future, B::Future>;
+
+    #[inline]
+    fn upgrade(
+        self,
+        socket: C,
+        id: Self::UpgradeIdentifier,
+        ty: Endpoint,
+        remote_addr: &Multiaddr,
+    ) -> Self::Future {
+        match id {
+            EitherUpgradeIdentifier::First(id) => {
+                EitherConnUpgrFuture::First(self.0.upgrade(socket, id, ty, remote_addr))
+            }
+            EitherUpgradeIdentifier::Second(id) => {
+                EitherConnUpgrFuture::Second(self.1.upgrade(socket, id, ty, remote_addr))
+            }
+        }
+    }
+}
+
+/// Internal struct used by the `OrUpgrade` trait.
+#[derive(Debug, Copy, Clone)]
+pub enum EitherUpgradeIdentifier<A, B> {
+    First(A),
+    Second(B),
+}
+
+/// Implements `Future` and redirects calls to either `First` or `Second`.
+///
+/// Additionally, the output will be wrapped inside a `EitherSocket`.
+///
+// TODO: This type is needed because of the lack of `impl Trait` in stable Rust.
+//         If Rust had impl Trait we could use the Either enum from the futures crate and add some
+//         modifiers to it. This custom enum is a combination of Either and these modifiers.
+#[derive(Debug, Copy, Clone)]
+pub enum EitherConnUpgrFuture<A, B> {
+    First(A),
+    Second(B),
+}
+
+impl<A, B> Future for EitherConnUpgrFuture<A, B>
+where
+    A: Future<Error = IoError>,
+    B: Future<Error = IoError>,
+{
+    type Item = EitherSocket<A::Item, B::Item>;
+    type Error = IoError;
+
+    #[inline]
+    fn poll(&mut self) -> Poll<Self::Item, Self::Error> {
+        match self {
+            &mut EitherConnUpgrFuture::First(ref mut a) => {
+                let item = try_ready!(a.poll());
+                Ok(Async::Ready(EitherSocket::First(item)))
+            }
+            &mut EitherConnUpgrFuture::Second(ref mut b) => {
+                let item = try_ready!(b.poll());
+                Ok(Async::Ready(EitherSocket::Second(item)))
+            }
+        }
+    }
+}
+
+/// Internal type used by the `OrUpgrade` struct.
+///
+/// > **Note**: This type is needed because of the lack of `-> impl Trait` in Rust. It can be
+/// >           removed eventually.
+#[derive(Debug, Copy, Clone)]
+pub struct NamesIterChain<A, B> {
+    first: A,
+    second: B,
+}
+
+impl<A, B, AId, BId> Iterator for NamesIterChain<A, B>
+where
+    A: Iterator<Item = (Bytes, AId)>,
+    B: Iterator<Item = (Bytes, BId)>,
+{
+    type Item = (Bytes, EitherUpgradeIdentifier<AId, BId>);
+
+    #[inline]
+    fn next(&mut self) -> Option<Self::Item> {
+        if let Some((name, id)) = self.first.next() {
+            return Some((name, EitherUpgradeIdentifier::First(id)));
+        }
+        if let Some((name, id)) = self.second.next() {
+            return Some((name, EitherUpgradeIdentifier::Second(id)));
+        }
+        None
+    }
+
+    #[inline]
+    fn size_hint(&self) -> (usize, Option<usize>) {
+        let (min1, max1) = self.first.size_hint();
+        let (min2, max2) = self.second.size_hint();
+        let max = match (max1, max2) {
+            (Some(max1), Some(max2)) => max1.checked_add(max2),
+            _ => None,
+        };
+        (min1.saturating_add(min2), max)
+    }
+}
diff --git a/swarm/src/upgrade/denied.rs b/swarm/src/upgrade/denied.rs
new file mode 100644
index 00000000..b5938965
--- /dev/null
+++ b/swarm/src/upgrade/denied.rs
@@ -0,0 +1,50 @@
+// Copyright 2017 Parity Technologies (UK) Ltd.
+//
+// Permission is hereby granted, free of charge, to any person obtaining a
+// copy of this software and associated documentation files (the "Software"),
+// to deal in the Software without restriction, including without limitation
+// the rights to use, copy, modify, merge, publish, distribute, sublicense,
+// and/or sell copies of the Software, and to permit persons to whom the
+// Software is furnished to do so, subject to the following conditions:
+//
+// The above copyright notice and this permission notice shall be included in
+// all copies or substantial portions of the Software.
+//
+// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS
+// OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
+// FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
+// DEALINGS IN THE SOFTWARE.
+
+use bytes::Bytes;
+use upgrade::{ConnectionUpgrade, Endpoint};
+use futures::prelude::*;
+use multiaddr::Multiaddr;
+use std::{io, iter};
+use tokio_io::{AsyncRead, AsyncWrite};
+
+/// Implementation of `ConnectionUpgrade` that always fails to negotiate.
+#[derive(Debug, Copy, Clone)]
+pub struct DeniedConnectionUpgrade;
+
+impl<C> ConnectionUpgrade<C> for DeniedConnectionUpgrade
+where
+    C: AsyncRead + AsyncWrite,
+{
+    type NamesIter = iter::Empty<(Bytes, ())>;
+    type UpgradeIdentifier = (); // TODO: could use `!`
+    type Output = (); // TODO: could use `!`
+    type Future = Box<Future<Item = (), Error = io::Error>>; // TODO: could use `!`
+
+    #[inline]
+    fn protocol_names(&self) -> Self::NamesIter {
+        iter::empty()
+    }
+
+    #[inline]
+    fn upgrade(self, _: C, _: Self::UpgradeIdentifier, _: Endpoint, _: &Multiaddr) -> Self::Future {
+        unreachable!("the denied connection upgrade always fails to negotiate")
+    }
+}
diff --git a/swarm/src/upgrade/mod.rs b/swarm/src/upgrade/mod.rs
new file mode 100644
index 00000000..2db5df18
--- /dev/null
+++ b/swarm/src/upgrade/mod.rs
@@ -0,0 +1,31 @@
+// Copyright 2017 Parity Technologies (UK) Ltd.
+//
+// Permission is hereby granted, free of charge, to any person obtaining a
+// copy of this software and associated documentation files (the "Software"),
+// to deal in the Software without restriction, including without limitation
+// the rights to use, copy, modify, merge, publish, distribute, sublicense,
+// and/or sell copies of the Software, and to permit persons to whom the
+// Software is furnished to do so, subject to the following conditions:
+//
+// The above copyright notice and this permission notice shall be included in
+// all copies or substantial portions of the Software.
+//
+// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS
+// OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
+// FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
+// DEALINGS IN THE SOFTWARE.
+
+pub mod denied;
+pub mod traits;
+pub mod choice;
+pub mod plaintext;
+pub mod simple;
+
+pub use self::choice::OrUpgrade;
+pub use self::denied::DeniedConnectionUpgrade;
+pub use self::plaintext::PlainTextConfig;
+pub use self::simple::SimpleProtocol;
+pub use self::traits::{ConnectionUpgrade, Endpoint, UpgradeExt};
diff --git a/swarm/src/upgrade/plaintext.rs b/swarm/src/upgrade/plaintext.rs
new file mode 100644
index 00000000..7250759d
--- /dev/null
+++ b/swarm/src/upgrade/plaintext.rs
@@ -0,0 +1,54 @@
+// Copyright 2017 Parity Technologies (UK) Ltd.
+//
+// Permission is hereby granted, free of charge, to any person obtaining a
+// copy of this software and associated documentation files (the "Software"),
+// to deal in the Software without restriction, including without limitation
+// the rights to use, copy, modify, merge, publish, distribute, sublicense,
+// and/or sell copies of the Software, and to permit persons to whom the
+// Software is furnished to do so, subject to the following conditions:
+//
+// The above copyright notice and this permission notice shall be included in
+// all copies or substantial portions of the Software.
+//
+// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS
+// OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
+// FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
+// DEALINGS IN THE SOFTWARE.
+
+use bytes::Bytes;
+use futures::future::{self, FutureResult};
+use multiaddr::Multiaddr;
+use std::{iter, io::Error as IoError};
+use tokio_io::{AsyncRead, AsyncWrite};
+use upgrade::{ConnectionUpgrade, Endpoint};
+
+/// Implementation of the `ConnectionUpgrade` that negotiates the `/plaintext/1.0.0` protocol and
+/// simply passes communications through without doing anything more.
+///
+/// > **Note**: Generally used as an alternative to `secio` if a security layer is not desirable.
+// TODO: move to a separate crate?
+#[derive(Debug, Copy, Clone)]
+pub struct PlainTextConfig;
+
+impl<C> ConnectionUpgrade<C> for PlainTextConfig
+where
+    C: AsyncRead + AsyncWrite,
+{
+    type Output = C;
+    type Future = FutureResult<C, IoError>;
+    type UpgradeIdentifier = ();
+    type NamesIter = iter::Once<(Bytes, ())>;
+
+    #[inline]
+    fn upgrade(self, i: C, _: (), _: Endpoint, _: &Multiaddr) -> Self::Future {
+        future::ok(i)
+    }
+
+    #[inline]
+    fn protocol_names(&self) -> Self::NamesIter {
+        iter::once((Bytes::from("/plaintext/1.0.0"), ()))
+    }
+}
diff --git a/swarm/src/upgrade/simple.rs b/swarm/src/upgrade/simple.rs
new file mode 100644
index 00000000..2d75a671
--- /dev/null
+++ b/swarm/src/upgrade/simple.rs
@@ -0,0 +1,84 @@
+// Copyright 2017 Parity Technologies (UK) Ltd.
+//
+// Permission is hereby granted, free of charge, to any person obtaining a
+// copy of this software and associated documentation files (the "Software"),
+// to deal in the Software without restriction, including without limitation
+// the rights to use, copy, modify, merge, publish, distribute, sublicense,
+// and/or sell copies of the Software, and to permit persons to whom the
+// Software is furnished to do so, subject to the following conditions:
+//
+// The above copyright notice and this permission notice shall be included in
+// all copies or substantial portions of the Software.
+//
+// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS
+// OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
+// FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
+// DEALINGS IN THE SOFTWARE.
+
+use bytes::Bytes;
+use futures::future::FromErr;
+use futures::prelude::*;
+use multiaddr::Multiaddr;
+use std::{iter, io::Error as IoError, sync::Arc};
+use tokio_io::{AsyncRead, AsyncWrite};
+use upgrade::{ConnectionUpgrade, Endpoint};
+
+/// Implementation of `ConnectionUpgrade`. Convenient to use with small protocols.
+#[derive(Debug)]
+pub struct SimpleProtocol<F> {
+    name: Bytes,
+    // Note: we put the closure `F` in an `Arc` because Rust closures aren't automatically clonable
+    // yet.
+    upgrade: Arc<F>,
+}
+
+impl<F> SimpleProtocol<F> {
+    /// Builds a `SimpleProtocol`.
+    #[inline]
+    pub fn new<N>(name: N, upgrade: F) -> SimpleProtocol<F>
+    where
+        N: Into<Bytes>,
+    {
+        SimpleProtocol {
+            name: name.into(),
+            upgrade: Arc::new(upgrade),
+        }
+    }
+}
+
+impl<F> Clone for SimpleProtocol<F> {
+    #[inline]
+    fn clone(&self) -> Self {
+        SimpleProtocol {
+            name: self.name.clone(),
+            upgrade: self.upgrade.clone(),
+        }
+    }
+}
+
+impl<C, F, O> ConnectionUpgrade<C> for SimpleProtocol<F>
+where
+    C: AsyncRead + AsyncWrite,
+    F: Fn(C) -> O,
+    O: IntoFuture<Error = IoError>,
+{
+    type NamesIter = iter::Once<(Bytes, ())>;
+    type UpgradeIdentifier = ();
+
+    #[inline]
+    fn protocol_names(&self) -> Self::NamesIter {
+        iter::once((self.name.clone(), ()))
+    }
+
+    type Output = O::Item;
+    type Future = FromErr<O::Future, IoError>;
+
+    #[inline]
+    fn upgrade(self, socket: C, _: (), _: Endpoint, _: &Multiaddr) -> Self::Future {
+        let upgrade = &self.upgrade;
+        upgrade(socket).into_future().from_err()
+    }
+}
diff --git a/swarm/src/upgrade/traits.rs b/swarm/src/upgrade/traits.rs
new file mode 100644
index 00000000..465d1964
--- /dev/null
+++ b/swarm/src/upgrade/traits.rs
@@ -0,0 +1,92 @@
+// Copyright 2017 Parity Technologies (UK) Ltd.
+//
+// Permission is hereby granted, free of charge, to any person obtaining a
+// copy of this software and associated documentation files (the "Software"),
+// to deal in the Software without restriction, including without limitation
+// the rights to use, copy, modify, merge, publish, distribute, sublicense,
+// and/or sell copies of the Software, and to permit persons to whom the
+// Software is furnished to do so, subject to the following conditions:
+//
+// The above copyright notice and this permission notice shall be included in
+// all copies or substantial portions of the Software.
+//
+// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS
+// OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
+// FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
+// DEALINGS IN THE SOFTWARE.
+
+use bytes::Bytes;
+use futures::future::Future;
+use multiaddr::Multiaddr;
+use std::io::Error as IoError;
+use tokio_io::{AsyncRead, AsyncWrite};
+use upgrade::choice::OrUpgrade;
+
+/// Type of connection for the upgrade.
+#[derive(Debug, Copy, Clone, PartialEq, Eq)]
+pub enum Endpoint {
+    /// The socket comes from a dialer.
+    Dialer,
+    /// The socket comes from a listener.
+    Listener,
+}
+
+/// Implemented on structs that describe a possible upgrade to a connection between two peers.
+///
+/// The generic `C` is the type of the incoming connection before it is upgraded.
+///
+/// > **Note**: The `upgrade` method of this trait uses `self` and not `&self` or `&mut self`.
+/// >           This has been designed so that you would implement this trait on `&Foo` or
+/// >           `&mut Foo` instead of directly on `Foo`.
+pub trait ConnectionUpgrade<C: AsyncRead + AsyncWrite> {
+    /// Iterator returned by `protocol_names`.
+    type NamesIter: Iterator<Item = (Bytes, Self::UpgradeIdentifier)>;
+    /// Type that serves as an identifier for the protocol. This type only exists to be returned
+    /// by the `NamesIter` and then be passed to `upgrade`.
+    ///
+    /// This is only useful on implementations that dispatch between multiple possible upgrades.
+    /// Any basic implementation will probably just use the `()` type.
+    type UpgradeIdentifier;
+
+    /// Returns the name of the protocols to advertise to the remote.
+    fn protocol_names(&self) -> Self::NamesIter;
+
+    /// Type of the stream that has been upgraded. Generally wraps around `C` and `Self`.
+    ///
+    /// > **Note**: For upgrades that add an intermediary layer (such as `secio` or `multiplex`),
+    /// >           this associated type must implement `AsyncRead + AsyncWrite`.
+    type Output;
+    /// Type of the future that will resolve to `Self::Output`.
+    type Future: Future<Item = Self::Output, Error = IoError>;
+
+    /// This method is called after protocol negotiation has been performed.
+    ///
+    /// Because performing the upgrade may not be instantaneous (eg. it may require a handshake),
+    /// this function returns a future instead of the direct output.
+    fn upgrade(
+        self,
+        socket: C,
+        id: Self::UpgradeIdentifier,
+        ty: Endpoint,
+        remote_addr: &Multiaddr,
+    ) -> Self::Future;
+}
+
+/// Extension trait for `ConnectionUpgrade`. Automatically implemented on everything.
+pub trait UpgradeExt {
+    /// Builds a struct that will choose an upgrade between `self` and `other`, depending on what
+    /// the remote supports.
+    fn or_upgrade<T>(self, other: T) -> OrUpgrade<Self, T>
+    where
+        Self: Sized;
+}
+
+impl<T> UpgradeExt for T {
+    #[inline]
+    fn or_upgrade<U>(self, other: U) -> OrUpgrade<Self, U> {
+        OrUpgrade::new(self, other)
+    }
+}