Converted protocols to mdbook.

Started an introductory section too.

1 files changed, 40 insertions, 0 deletions

diff --git a/docs/ref/proto/pull.md b/docs/ref/proto/pull.md
new file mode 100644
index 00000000..9946a887
--- /dev/null
+++ b/docs/ref/proto/pull.md
@@ -0,0 +1,40 @@
+# PULL protocol
+
+The {{i:*PULL* protocol}}{{hi:*PULL*}} is one half of a
+{{i:pipeline pattern}}.
+The other half is the [_PUSH_][push] protocol.
+
+In the pipeline pattern, pushers distribute messages to pullers.
+Each message sent
+by a pusher will be sent to one of its peer pullers,
+chosen in a round-robin fashion
+from the set of connected peers available for receiving.
+This property makes this pattern useful in {{i:load-balancing}} scenarios.
+
+### Socket Operations
+
+The [`nng_pull0_open`][nng_pull_open] functions create a
+_PULL_ socket.
+This socket may be used to receive messages, but is unable to send them.
+Attempts to send messages will result in `NNG_ENOTSUP`.
+
+When receiving messages, the _PULL_ protocol accepts messages as
+they arrive from peers.
+If two peers both have a message ready, the
+order in which messages are handled is undefined.
+
+### Protocol Versions
+
+Only version 0 of this protocol is supported.
+(At the time of writing, no other versions of this protocol have been defined.)
+
+### Protocol Options
+
+The _PULL_ protocol has no protocol-specific options.
+
+### Protocol Headers
+
+The _PULL_ protocol has no protocol-specific headers.
+
+[nng_pull_open]: TODO.md
+[push]: ./push.md