Understanding ZMQ Blocks
This tutorial is under construction.
This tutorial presents the GNU Radio ZMQ blocks. It is a set of six Source Blocks and six Sink Blocks. The naming convention follows other source and sink blocks in that a source block provides data entering a GNU Radio flowgraph and a sink block sends data out of the flowgraph. It is a flowgraph-oriented perspective.
From the ZeroMQ website: "ZeroMQ (also known as ØMQ, 0MQ, or zmq) looks like an embeddable networking library but acts like a concurrency framework. It gives you sockets that carry atomic messages across various transports like in-process, inter-process, TCP, and multicast."
Types of ZMQ Blocks
The two basic groups of ZMQ blocks are those which transport stream data, and those which transport text strings. They are described below.
ZMQ blocks come in pairs:
- PUB - SUB
- PUSH - PULL
- REQ - REP
The PUB, PUSH, and REP blocks are always sink blocks; the others are source blocks. Choosing which pair to use depends on your system architecture.
- The PUB - SUB pair can be compared to broadcasting. The PUBlish sink sends out data which can be received by one or many SUBscribers.
- The PUSH - PULL is a point to point link of equal peers.
- REQuest - REPly pair is a point to point link which operates in lock-step: one REQ in gives one REP out. This case changes the perspective somewhat in that the flowgraph is acting as a server for a remote client.