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diff --git a/epan/conv_id.h b/epan/conv_id.h
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+/** @file
+ *
+ * conv_id   2011 Robert Bullen
+ *
+ * Wireshark - Network traffic analyzer
+ * By Gerald Combs <gerald@wireshark.org>
+ * Copyright 1998 Gerald Combs
+ *
+ * SPDX-License-Identifier: GPL-2.0-or-later
+ */
+
+#ifndef __CONV_ID_H__
+#define __CONV_ID_H__
+
+/** conv_id_t is a type that can aid in conversation identification. When
+ *  included in a "conversation key", whatever that may be, in addition to the
+ *  typical { address, port, address, port } quadruple, it helps differentiate
+ *  in case the quadruple is not sufficiently unique. For example, it is not
+ *  uncommon to see a TCP quadruple reused these days, and employing a
+ *  conv_id_t field ensures that each instance of a reused TCP conversation is
+ *  tracked independently. Currently this type is used in both Wireshark's and
+ *  tshark's conversation tables implementations (they are different, hence
+ *  the need for a whole header file for this one silly type alias).
+ *
+ *  The "protocol" or "statistic" code responsible for instantiating the
+ *  "conversation key" is also responsible for assigning its conv_id_t, and
+ *  therefore its interpretation is specific to its assignor. For example, the
+ *  TCP conversations tables in Wireshark and tshark assign the value of
+ *  tcp.stream. If a conv_id_t field is not used, it should be assigned the
+ *  value CONV_ID_UNSET.
+ */
+typedef guint32 conv_id_t;
+#define CONV_ID_UNSET G_MAXUINT32
+
+#endif /* __CONV_ID_H__ */