ZeroMQ

Unicast Transports

ØMQ provides a set of unicast transports (inproc, ipc, and tcp) and multicast transports (epgm, pgm). Multicast is an advanced technique that we’ll come to later. Don’t even start using it unless you know that your fan-out ratios will make 1-to-N unicast impossible.

For most common cases, use tcp, which is a disconnected TCP transport. It is elastic, portable, and fast enough for most cases. We call this “disconnected” because ØMQ’s tcp transport doesn’t require the endpoint to exist before you connect to it. Clients and servers can connect and bind at any time, can go and come back, and it remains transparent to applications.

The inter-process ipc transport is also disconnected. It has one limitation: it does not yet work on Windows. By convention we use endpoint names with an “.ipc” extension to avoid potential conflict with other filenames. On Unix systems, if you use ipc endpoints you need to create these with appropriate permissions; otherwise, they may not be shareable between processes running under different user IDs. You must also make sure all processes can access the files, e.g., by running in the same working directory.

The inter-thread transport, inproc, is a connected signaling transport. It is much faster than tcp or ipc. This transport has a specific limitation compared to tcp and ipc, however the server must issue a bind request before any client issues a connect. This is something future versions of ØMQ may fix, but at present ...