Overview
--------

This document is intended as a quick guide to converting existing
OpenDDS applications to work with the OpenDDS 3.0 transport
configuration.  Because of the flexibility of the new design,
most applications can remove all transport-related source code
from the publisher and subscriber.  Many applications can remove
any existing transport configuration sections from the OpenDDS
configuration files (*.ini) as well.  Some applications may need
to manually convert the configuration files.  Applications no
longer need to use ACE Service Configurator files (*.conf) to
load transport libraries.  These still may be required for TAO
configuration.

For a full discussion of the new transport configuration
design see Section 6.3 of the OpenDDS 3.0 Developer's Guide.

There are two general scenarios for conversion.  In the first,
each process in the application only uses a single transport.
The second has multiple transports used in each process.


Single Transport Applications
-----------------------------

Remove all of the transport-related code from your C++ source
code files:
  - Any #includes under dds/DCPS/transport
  - Any code involving TransportImpl
  - Any code involving TransportFactory or TheTransportFactory
  - Any code involving TransportConfiguration
  - Any attach calls on the TransportImpl (and the AttachStatus enum type)
  - Any attach_transport calls on the PublisherImpl or SubscriberImpl

Convert (or create) an OpenDDS configuration file (*.ini) containing
your transport details.  In the simplest case:

    [common]
    DCPSGlobalTransportConfig=myconfig

    [config/myconfig]
    transports=mytcp

    [transport/mytcp]
    transport_type=tcp

If you have existing files, make the following changes to them:
  - Change any sections of the form [transport_impl*] sections
    to be of the form [transport/<transport_name>].
  - Add a [config/<config_name>] section
  - Add the property "transports=<transport_name> to your config
    section.
  - Add the DCPSGlobalTransportConfig=<config_name> property to
    the [common] section.
Configuration files are loaded as in previous OpenDDS versions,
with the "-DCPSConfigFile <file>" command line option.

For example, suppose we started with this configuration file:

    # OpenDDS 2.4 config file
    [transport_impl_1]
    transport_type=SimpleTcp
    swap_bytes=0
    optimum_packet_size=8192

This would convert to something like this:

    # OpenDDS 3.0 config file
    [common]
    DCPSGlobalTransportConfig=config1

    [config/config1]
    transports=transport1

    [transport/transport1]
    transport_type=tcp
    swap_bytes=0
    optimum_packet_size=8192

All processes loading this configuration file would use the tcp
transport configures as shown.


Multiple Transport Applications
-------------------------------

Modifying applications that use multiple transports per
application is roughly the same as the Single Transport
application approach above with a couple of important
differences.

First, when converting the configuration file, create a
separate [config/*] section for each transport in the file.
For example, when starting with this configuration file
(where some parts of an application uses tcp and some
multicast):

    # OpenDDS 2.4 config file
    [transport_impl_1]
    transport_type=SimpleTcp

    [transport_impl_2]
    transport_type=multicast

Converting this file results in something like this:

    # OpenDDS 3.0 config file
    [config/tcp_config]
    transports=mytcp

    [config/multicast_config]
    transports=mymulticast

    [transport/mytcp]
    transport_type=tcp

    [transport/mymulticast]
    transport_type=multicast

Now we just need to modify the source code to bind the
appropriate readers and writers to the appropriate configurations.
When modifying your source code, any calls to attach() on the
TransportImpl or attach_transport() should be replaced with
calls to bind() in the TransportRegistry.

For example, code such as this:

    // OpenDDS 2.4 code
    // Get the transport_impl for [transport_impl_1]
    OpenDDS::DCPS::TransportIdType transport_impl_id = 1;
    OpenDDS::DCPS::TransportImpl_rch transport_impl =
      TheTransportFactory->create_transport_impl(transport_impl_id,
                                                 OpenDDS::DCPS::AUTO_CONFIG);

    // Attach the current publisher "pub" to this transport
    OpenDDS::DCPS::AttachStatus status = transport_impl->attach(pub.in());
    if (status != OpenDDS::DCPS::ATTACH_OK) {
      std::cerr << "Failed to attach to the transport." << std::endl;
      return 1;
    }

should change to:

    // Bind [config/tcp_config] configuration to the publisher "pub"
    OpenDDS::DCPS::TheTransportRegistry->bind_config("tcp_config", pub);


Other differences
-----------------

* The name of the tcp transport has been changed from "SimpleTcp"
  to "tcp".
* The passive_connect_duration option no longer applies to
  individual transports.  You can now set this option on the
  transport configuration.
* The semantics of the multicast port_offset option have changed.
  This option is no longer an offset, but is now simply the port
  number to use when group_address is not set.
* Entities setting Reliability QoS to Reliable, can no longer use
  the UDP transport or Multicast transport in best-effort mode.
  Either remove this QoS setting or select a transport (multicast
  or tcp) that is reliable.