29.2 ns-3 TCP

ns-3 contains a port of the TCP model from GTNetS. This model is a full TCP, in that it is bidirectional and attempts to model the connection setup and close logic. In fact, it is a more complete implementation of the TCP state machine than ns-2’s "FullTcp" model. This TCP model was originally written by George Riley as part of GTNetS and ported to ns-3 by Raj Bhattacharjea.

The implementation of TCP is contained in the following files:

src/internet-stack/tcp-header.{cc,h}
src/internet-stack/tcp-l4-protocol.{cc,h}
src/internet-stack/tcp-socket-factory-impl.{cc,h}
src/internet-stack/tcp-socket-impl.{cc,h}
src/internet-stack/tcp-typedefs.h
src/internet-stack/rtt-estimator.{cc,h}
src/internet-stack/sequence-number.{cc,h}

29.2.1 Usage

The file examples/tcp-star-server.cc contains an example that makes use of ns3::OnOffApplication and ns3::PacketSink applications.

Using the helper functions defined in src/helper, here is how one would create a TCP receiver:

  // Create a packet sink on the star "hub" to receive these packets
  uint16_t port = 50000;
  Address sinkLocalAddress(InetSocketAddress (Ipv4Address::GetAny (), port));
  PacketSinkHelper sinkHelper ("ns3::TcpSocketFactory", sinkLocalAddress);
  ApplicationContainer sinkApp = sinkHelper.Install (serverNode);
  sinkApp.Start (Seconds (1.0));
  sinkApp.Stop (Seconds (10.0));

Similarly, the below snippet configures OnOffApplication traffic source to use TCP:

  // Create the OnOff applications to send TCP to the server
  OnOffHelper clientHelper ("ns3::TcpSocketFactory", Address ());

The careful reader will note above that we have specified the TypeId of an abstract base class TcpSocketFactory. How does the script tell ns-3 that it wants the native ns-3 TCP vs. some other one? Well, when internet stacks are added to the node, the default TCP implementation that is aggregated to the node is the ns-3 TCP. This can be overridden as we show below when using Network Simulation Cradle. So, by default, when using the ns-3 helper API, the TCP that is aggregated to nodes with an Internet stack is the native ns-3 TCP.

Once a TCP socket is created, you will want to follow conventional socket logic and either connect() and send() (for a TCP client) or bind(), listen(), and accept() (for a TCP server). See section Sockets API for a review of how sockets are used in ns-3.

To configure behavior of TCP, a number of parameters are exported through the ns-3 attribute system. These are documented in the Doxygen for class TcpSocket.

29.2.2 Current limitations

• Only Tahoe congestion control is presently supported.
• Only IPv4 is supported (IPv6 support will start to be added after ns-3.6).

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