Transports

5 min read

In Ice terminology, a transport is a conduit for exchanging Ice protocol messages. Ice supports a number of transports; some of them are built into the Ice core, while others are available as plug-ins. Your transport selection will be driven by application requirements. For example, the TCP transport might be acceptable for deployment on a trusted intranet, while an Internet-facing application will generally use SSL or WSS (WebSocket Secure).

Most transports have a configuration component, which is often done statically via the application's external configuration file. Some transports also provide an API for accessing special features programmatically. Finally, certain Ice features might not be available with all transports. For example, you can send oneway invocations with any transport, whereas twoway invocations require a stream-oriented transport and datagram invocations require the UDP transport.

You'll need to choose a transport as soon as you're ready to test your first client-server prototype, if not sooner. The server's object adapter and the client's proxy must have at least one matching endpoint, where an endpoint is simply a transport name together with any necessary options. Ice uses a simple text-based syntax for configuring endpoints.

All of Ice's IP-based transports support both IPv4 and IPv6, as long as the underlying platform also supports both. Both are enabled by default; you can disable one of them with the Ice.IPv4 or Ice.IPv6 property, and make Ice try the IPv6 addresses of a host name first with Ice.PreferIPv6Address. These properties are not available in JavaScript.

The following table summarizes the transports that Ice provides and indicates whether they are built into the Ice core in C++, C#, Java, and indirectly in the C++-based implementations:

Transport	Core?	Connection Oriented?	IP-based?	Description
tcp, ssl	Yes	Yes	Yes	tcp is the default transport in Ice; ssl is tcp with TLS, using your platform's native SSL implementation.
udp	Yes	No	Yes	Supports unicast and multicast datagram invocations.
ws, wss	Yes	Yes	Yes	WebSocket and secure WebSocket, especially useful when a client needs to communicate with a back-end service from a web browser application.
bt, bts	No	Yes	No	Bluetooth, available on Linux and Android.
iap, iaps	Yes, on iOS.	Yes	No	Communicates with accessories over Bluetooth or the Lightning connector; C++ applications install it explicitly.

Ice for JavaScript supports a different set of transports:

Transport	Supported in Browser?	Supported with Node.js?	Notes
tcp	No	Yes	Ice for JavaScript can only create outgoing connections.
udp	No	No
ssl	No	No
ws	Yes	Yes (Node.js >= 24)
wss	Yes	Yes (Node.js >= 24)

Endpoint and Connection Information

The Ice runtime describes an endpoint or a connection with an information object. An endpoint's getInfo method returns an EndpointInfoEndpointInfoEndpointInfoEndpointInfoEndpointInfoEndpointInfoEndpointInfo, and a connection's getInfo method returns a ConnectionInfoConnectionInfoConnectionInfoConnectionInfoConnectionInfoConnectionInfoConnectionInfo.

Each transport provides its own subclass of these two classes, with fields specific to that transport, such as the host and port of a TCP endpoint or the local and remote addresses of a TCP connection.

A transport that runs over another transport wraps the information of that transport: the underlying field holds the information of the transport below, and is null for the transport at the bottom of the chain. For example, the information of a ws connection is a WSConnectionInfo whose underlying field holds a TCPConnectionInfo; for a wss connection, the SSL connection information sits between these two. To read the information of one transport, walk the chain and downcast each object to the class you need.