diff --git a/doc/usage.rst b/doc/usage.rst
index 0368a73..9b66824 100644
--- a/doc/usage.rst
+++ b/doc/usage.rst
@@ -367,6 +367,32 @@ The validation output reads for the other fields the same way as for the example
         [0, 2717]                                 StationaryObject.base.is_valid(None) does not comply in SensorView.global_ground_truth.stationary_object.base
             [0, 2717]                                 BaseStationary.base_polygon.is_set(None) does not comply in SensorView.global_ground_truth.stationary_object.base
 
+Writing an OSI trace file
+--------------------------
+
+As already mentioned in the example, the OSI validator works with OSI trace files, which are a collection of, to byte code, serialized OSI messages. Upon start, the
+OSI validator splits the trace file into the individual messages and validates them. This splitting is done slightly different for
+the two allowed trace file formats .txt and .osi.
+
+For a .txt trace file, the osi validator splits the messages by searching ``$$__$$`` separators within the file. To generate a valid
+.txt trace file the file therefore has to start with a serialized OSI message, followed by a ``$$__$$`` separator (Note that the last message
+also has to be followed by a separator!). Schematically, a .txt trace file would look like this:
+
+.. code-block:: bash
+
+    [OSI Message]$$__$$[OSI Message]$$__$$[OSI Message]$$__$$...$$__$$
+
+The .osi trace files are quite similar, but instead of a separator at the end of each message, each message is preceded by a 4-byte 
+integer (in byte code) that contains the length (in byte) of the following serialized OSI message. So a .osi trace file would look
+like this:
+
+.. code-block:: bash
+
+    [integer 1250 in byte][1250 byte long osi message][integer 3000 in byte][3000 byte long osi message]....
+
+It has to be ensured that the validated trace files follow this convention, otherwise the OSI validator will not be able to
+validate them correctly.
+
 Custom Rules
 --------------
 
diff --git a/osivalidator/osi_trace.py b/osivalidator/osi_trace.py
index 19111fa..0cbe81c 100644
--- a/osivalidator/osi_trace.py
+++ b/osivalidator/osi_trace.py
@@ -320,7 +320,7 @@ def get_messages_in_index_range(self, begin, end):
             for rel_index, rel_message_offset in enumerate(rel_message_offsets):
                 rel_begin = rel_message_offset + self._int_length
                 rel_end = (
-                    rel_message_offsets[rel_index + 1] - self._int_length
+                    rel_message_offsets[rel_index + 1]
                     if rel_index + 1 < len(rel_message_offsets)
                     else message_sequence_len
                 )
diff --git a/setup.py b/setup.py
index 02317db..6365c15 100644
--- a/setup.py
+++ b/setup.py
@@ -45,12 +45,11 @@
             "sphinx_rtd_theme",
             "recommonmark",
             "open-simulation-interface",
-            "doxygen-interface",
             "defusedxml",
             "colorama",
             "tabulate",
             "progress",
-            "protobuf==3.9.1",
+            "protobuf",
         ],
         dependency_links=[
             "git+https://github.com/OpenSimulationInterface/"