Add note about ASN protocol and fix references.

docs/api/index.md

@@ -4,11 +4,12 @@
 :maxdepth: 1
 
 xdas
+atoms
+io
 fft
-signal
-processing
 parallel
+processing
+signal
 synthetics
 virtual
-atoms
 ```

docs/api/io.md

@@ -0,0 +1,27 @@
+```{eval-rst}
+.. currentmodule:: xdas.io
+```
+
+# xdas.io
+
+```{eval-rst}
+.. autosummary::
+   :toctree: ../_autosummary
+
+    get_free_port
+```
+
+```{eval-rst}
+.. currentmodule:: xdas.io.asn
+```
+
+
+## ASN
+
+```{eval-rst}
+.. autosummary::
+   :toctree: ../_autosummary
+
+   ZMQPublisher
+   ZMQSubscriber
+```

docs/user-guide/streaming.md

@@ -79,8 +79,13 @@ To reduce the volume of the transmitted data, compression is often useful. Xdas
 
 import hdf5plugin
 
+address = f"tcp://localhost:{xd.io.get_free_port()}"
 encoding = {"chunks": (10, 10), **hdf5plugin.Zfp(accuracy=1e-6)}
 publisher = ZMQPublisher(address, encoding)  # Add encoding here, the rest is the same
 ```
 
+{py:class}`~xdas.io.asn.ZMQSubscriber`
 
+```{note}
+Xdas also implements the ZeroMQ protocol used by the OptoDAS interrogators by ASN. Equivalent {py:class}`~xdas.io.asn.ZMQPublisher` and {py:class}`~xdas.io.asn.ZMQSubscriber` can be found in {py:mod}`xdas.io.asn`. This can be useful get data in real-time from one instrument of that kind. Note that compression is not available with that protocol yet.
+```