## Publisher Protocol (_PUB_)

The ((_PUB_ protocol))(((protocol, _PUB_))) is one half of a ((publisher))/subscriber pattern.
In this pattern, a publisher sends data, which is broadcast to all subscribers.
The subscribing applications only see the data to which they have subscribed.

The _PUB_ protocol is the publisher side, and the xref:sub.adoc[_SUB_] protocol is the subscriber side.

The publisher delivers all messages to all subscribers.
The subscribers maintain their own subscriptions, and filter them locally.footnote:[Thus, this pattern should not be used in an attempt to reduce bandwidth consumption.]

The topics that subscribers subscribe to is just the first part of the message body.
Applications should construct their messages accordingly.

### Socket Operations

The xref:../sock/nng_pub_open.adoc[`nng_pub_open`] functions create a publisher socket.
This socket may be used to send messages, but is unable to receive them.
Attempts to receive messages will result in `NNG_ENOTSUP`.

### Protocol Versions

Only version 0 of this protocol is supported.footnote:[At the time of writing, no other versions of this protocol have been defined.]

### Protocol Options

The _PUB_ protocol has no protocol-specific options.

### Protocol Headers

The _PUB_ protocol has no protocol-specific headers.