Add new dissector for GSM RLP protocol (3GPP TS 24.022)

This protocol is used in the user plane of non-transparent CSD (Circuit
Switched Data) calls in GSM networks. RLP frames are sent over the Um
air interface, and are sent as modified V.110 frames over 64k TDM
channels in the back-haul/core network.  For modern implementations,
this means in RFC4040  RTP CLEARMODE.

As there's no V.110 decoder in wireshark, we cannot connect the RLP
decoder to that.  However, we hook it up to the GSMTAP dissector to
enable other software to pass the decoded RLP frames into wireshark.

4 files changed, 341 insertions, 0 deletions

diff --git a/epan/dissectors/CMakeLists.txt b/epan/dissectors/CMakeLists.txt
index 489810c2d9..810563546b 100644
--- a/epan/dissectors/CMakeLists.txt
+++ b/epan/dissectors/CMakeLists.txt
@@ -1194,6 +1194,7 @@ set(DISSECTOR_SRC
 	${CMAKE_CURRENT_SOURCE_DIR}/packet-gsm_osmux.c
 	${CMAKE_CURRENT_SOURCE_DIR}/packet-gsm_r_uus1.c
 	${CMAKE_CURRENT_SOURCE_DIR}/packet-gsm_rlcmac.c
+	${CMAKE_CURRENT_SOURCE_DIR}/packet-gsm_rlp.c
 	${CMAKE_CURRENT_SOURCE_DIR}/packet-gsm_sim.c
 	${CMAKE_CURRENT_SOURCE_DIR}/packet-gsm_sms.c
 	${CMAKE_CURRENT_SOURCE_DIR}/packet-gsm_sms_ud.c
diff --git a/epan/dissectors/packet-gsm_rlp.c b/epan/dissectors/packet-gsm_rlp.c
new file mode 100644
index 0000000000..f4c9a4f3ed
--- /dev/null
+++ b/epan/dissectors/packet-gsm_rlp.c
@@ -0,0 +1,333 @@
+/* packet-gsm_rlp.c
+ * Routines for GSM RLP (3GPP TS 24.022) frame dissection
+ * (C) 2023 Harald Welte <laforge@osmocom.org>
+ *
+ * Wireshark - Network traffic analyzer
+ * By Gerald Combs <gerald@wireshark.org>
+ * Copyright 1998
+ *
+ * SPDX-License-Identifier: GPL-2.0-or-later
+ */
+
+#include "config.h"
+
+#include <epan/packet.h>
+#include <epan/prefs.h>
+#include <epan/expert.h>
+#include <epan/reassemble.h>
+#include <epan/conversation.h>
+
+void proto_register_gsmrlp(void);
+
+static int proto_gsmrlp = -1;
+
+static int hf_gsmrlp_cr = -1;
+static int hf_gsmrlp_pf = -1;
+static int hf_gsmrlp_n_r = -1;
+static int hf_gsmrlp_n_s = -1;
+static int hf_gsmrlp_ftype = -1;
+static int hf_gsmrlp_s_ftype = -1;
+static int hf_gsmrlp_u_ftype = -1;
+static int hf_gsmrlp_fcs = -1;
+static int hf_gsmrlp_fcs_status = -1;
+
+static int hf_gsmrlp_xid_p_type = -1;
+static int hf_gsmrlp_xid_p_len = -1;
+static int hf_gsmrlp_xid_p_val = -1;
+
+static int ett_gsmrlp = -1;
+static int ett_gsmrlp_xid = -1;
+
+static expert_field ei_gsmrlp_fcs_bad = EI_INIT;
+
+/* 3GPP TS 24.002 Section 5.2.1 */
+enum rlp_ftype {
+	RLP_FT_U,
+	RLP_FT_S,
+	RLP_FT_IS,
+};
+
+static const value_string rlp_ftype_vals[] = {
+	{ RLP_FT_U,	"U" },
+	{ RLP_FT_S,	"S" },
+	{ RLP_FT_IS,	"IS" },
+	{ 0, NULL }
+};
+
+/* 3GPP TS 24.002 Section 5.2.1 */
+enum rlp_u_ftype {
+	RLP_U_FT_SABM	= 0x07,
+	RLP_U_FT_UA	= 0x0c,
+	RLP_U_FT_DISC	= 0x08,
+	RLP_U_FT_DM	= 0x03,
+	RLP_U_FT_NULL	= 0x0f,
+	RLP_U_FT_UI	= 0x00,
+	RLP_U_FT_XID	= 0x17,
+	RLP_U_FT_TEST	= 0x1c,
+	RLP_U_FT_REMAP	= 0x11,
+};
+static const value_string rlp_ftype_u_vals[] = {
+	{ RLP_U_FT_SABM,	"SABM" },
+	{ RLP_U_FT_UA,		"UA" },
+	{ RLP_U_FT_DISC,	"DISC" },
+	{ RLP_U_FT_DM,		"DM" },
+	{ RLP_U_FT_NULL,	"NULL" },
+	{ RLP_U_FT_UI,		"UI" },
+	{ RLP_U_FT_XID,		"XID" },
+	{ RLP_U_FT_TEST,	"TEST" },
+	{ RLP_U_FT_REMAP,	"REMAP" },
+	{ 0, NULL }
+};
+
+/* 3GPP TS 24.002 Section 5.2.1 */
+enum rlp_s_ftype {
+	RLP_S_FT_RR	= 0,
+	RLP_S_FT_REJ	= 2,
+	RLP_S_FT_RNR	= 1,
+	RLP_S_FT_SREJ	= 3,
+};
+static const value_string rlp_ftype_s_vals[] = {
+	{ RLP_S_FT_RR,		"RR" },
+	{ RLP_S_FT_REJ,		"REJ" },
+	{ RLP_S_FT_RNR,		"RNR" },
+	{ RLP_S_FT_SREJ,	"SREJ" },
+	{ 0, NULL }
+};
+
+/* 3GPP TS 24.002 Section 5.2.2.6 */
+enum rlp_xid_param_type {
+	XID_P_DELIMITER			= 0,
+	XID_P_RLP_VERSION		= 1,
+	XID_P_IWF_TO_UE_WIN_SIZE	= 2,
+	XID_P_UE_TO_IWF_WIN_SIZE	= 3,
+	XID_P_ACK_TIMER_T1		= 4,
+	XID_P_RETRANS_ATTEMPTS_N2	= 5,
+	XID_P_REPLY_DELAY_T2		= 6,
+	XID_P_COMPRESSION_PT		= 7,
+	XID_P_RESEQUENCING_T4		= 8,
+	XID_P_OPTIONAL_FEATURES		= 9,
+};
+
+static const value_string rlp_xid_param_vals[] = {
+	{ XID_P_DELIMITER,		"Delimiter (end of parameters)" },
+	{ XID_P_RLP_VERSION, 		"RLP version number" },
+	{ XID_P_IWF_TO_UE_WIN_SIZE,	"IWF to UE window size" },
+	{ XID_P_UE_TO_IWF_WIN_SIZE,	"UE to IWF window size" },
+	{ XID_P_ACK_TIMER_T1,		"Acknowledgement Timer (T1)" },
+	{ XID_P_RETRANS_ATTEMPTS_N2,	"Retransmission attempts (N2)" },
+	{ XID_P_REPLY_DELAY_T2,		"Reply delay (T2)" },
+	{ XID_P_COMPRESSION_PT,		"Compression PT" },
+	{ XID_P_RESEQUENCING_T4,	"Re-sequencing timer (T4)" },
+	{ XID_P_OPTIONAL_FEATURES,	"Optional Features" },
+	{ 0, NULL }
+};
+
+static const guint32 rlp_fcs_table[256] = {
+	0x00B29D2D, 0x00643A5B, 0x0044D87A, 0x00927F0C, 0x00051C38, 0x00D3BB4E, 0x00F3596F, 0x0025FE19,
+	0x008694BC, 0x005033CA, 0x0070D1EB, 0x00A6769D, 0x003115A9, 0x00E7B2DF, 0x00C750FE, 0x0011F788,
+	0x00DA8E0F, 0x000C2979, 0x002CCB58, 0x00FA6C2E, 0x006D0F1A, 0x00BBA86C, 0x009B4A4D, 0x004DED3B,
+	0x00EE879E, 0x003820E8, 0x0018C2C9, 0x00CE65BF, 0x0059068B, 0x008FA1FD, 0x00AF43DC, 0x0079E4AA,
+	0x0062BB69, 0x00B41C1F, 0x0094FE3E, 0x00425948, 0x00D53A7C, 0x00039D0A, 0x00237F2B, 0x00F5D85D,
+	0x0056B2F8, 0x0080158E, 0x00A0F7AF, 0x007650D9, 0x00E133ED, 0x0037949B, 0x001776BA, 0x00C1D1CC,
+	0x000AA84B, 0x00DC0F3D, 0x00FCED1C, 0x002A4A6A, 0x00BD295E, 0x006B8E28, 0x004B6C09, 0x009DCB7F,
+	0x003EA1DA, 0x00E806AC, 0x00C8E48D, 0x001E43FB, 0x008920CF, 0x005F87B9, 0x007F6598, 0x00A9C2EE,
+	0x0049DA1E, 0x009F7D68, 0x00BF9F49, 0x0069383F, 0x00FE5B0B, 0x0028FC7D, 0x00081E5C, 0x00DEB92A,
+	0x007DD38F, 0x00AB74F9, 0x008B96D8, 0x005D31AE, 0x00CA529A, 0x001CF5EC, 0x003C17CD, 0x00EAB0BB,
+	0x0021C93C, 0x00F76E4A, 0x00D78C6B, 0x00012B1D, 0x00964829, 0x0040EF5F, 0x00600D7E, 0x00B6AA08,
+	0x0015C0AD, 0x00C367DB, 0x00E385FA, 0x0035228C, 0x00A241B8, 0x0074E6CE, 0x005404EF, 0x0082A399,
+	0x0099FC5A, 0x004F5B2C, 0x006FB90D, 0x00B91E7B, 0x002E7D4F, 0x00F8DA39, 0x00D83818, 0x000E9F6E,
+	0x00ADF5CB, 0x007B52BD, 0x005BB09C, 0x008D17EA, 0x001A74DE, 0x00CCD3A8, 0x00EC3189, 0x003A96FF,
+	0x00F1EF78, 0x0027480E, 0x0007AA2F, 0x00D10D59, 0x00466E6D, 0x0090C91B, 0x00B02B3A, 0x00668C4C,
+	0x00C5E6E9, 0x0013419F, 0x0033A3BE, 0x00E504C8, 0x007267FC, 0x00A4C08A, 0x008422AB, 0x005285DD,
+	0x001F18F0, 0x00C9BF86, 0x00E95DA7, 0x003FFAD1, 0x00A899E5, 0x007E3E93, 0x005EDCB2, 0x00887BC4,
+	0x002B1161, 0x00FDB617, 0x00DD5436, 0x000BF340, 0x009C9074, 0x004A3702, 0x006AD523, 0x00BC7255,
+	0x00770BD2, 0x00A1ACA4, 0x00814E85, 0x0057E9F3, 0x00C08AC7, 0x00162DB1, 0x0036CF90, 0x00E068E6,
+	0x00430243, 0x0095A535, 0x00B54714, 0x0063E062, 0x00F48356, 0x00222420, 0x0002C601, 0x00D46177,
+	0x00CF3EB4, 0x001999C2, 0x00397BE3, 0x00EFDC95, 0x0078BFA1, 0x00AE18D7, 0x008EFAF6, 0x00585D80,
+	0x00FB3725, 0x002D9053, 0x000D7272, 0x00DBD504, 0x004CB630, 0x009A1146, 0x00BAF367, 0x006C5411,
+	0x00A72D96, 0x00718AE0, 0x005168C1, 0x0087CFB7, 0x0010AC83, 0x00C60BF5, 0x00E6E9D4, 0x00304EA2,
+	0x00932407, 0x00458371, 0x00656150, 0x00B3C626, 0x0024A512, 0x00F20264, 0x00D2E045, 0x00044733,
+	0x00E45FC3, 0x0032F8B5, 0x00121A94, 0x00C4BDE2, 0x0053DED6, 0x008579A0, 0x00A59B81, 0x00733CF7,
+	0x00D05652, 0x0006F124, 0x00261305, 0x00F0B473, 0x0067D747, 0x00B17031, 0x00919210, 0x00473566,
+	0x008C4CE1, 0x005AEB97, 0x007A09B6, 0x00ACAEC0, 0x003BCDF4, 0x00ED6A82, 0x00CD88A3, 0x001B2FD5,
+	0x00B84570, 0x006EE206, 0x004E0027, 0x0098A751, 0x000FC465, 0x00D96313, 0x00F98132, 0x002F2644,
+	0x00347987, 0x00E2DEF1, 0x00C23CD0, 0x00149BA6, 0x0083F892, 0x00555FE4, 0x0075BDC5, 0x00A31AB3,
+	0x00007016, 0x00D6D760, 0x00F63541, 0x00209237, 0x00B7F103, 0x00615675, 0x0041B454, 0x00971322,
+	0x005C6AA5, 0x008ACDD3, 0x00AA2FF2, 0x007C8884, 0x00EBEBB0, 0x003D4CC6, 0x001DAEE7, 0x00CB0991,
+	0x00686334, 0x00BEC442, 0x009E2663, 0x00488115, 0x00DFE221, 0x00094557, 0x0029A776, 0x00FF0000
+};
+
+/*! compute RLP FCS according to 3GPP TS 24.022 Section 4.4 */
+static guint32 rlp_fcs_compute(const guchar *in, size_t in_len)
+{
+	guint32 divider = 0;
+	size_t i;
+
+	for (i = 0; i < in_len; i++) {
+		guchar input = in[i] ^ (divider & 0xff);
+		divider = (divider >> 8) ^ rlp_fcs_table[input];
+	}
+
+	return ((divider & 0xff) << 16) | (divider & 0xff00) | ((divider & 0xff0000) >> 16);
+}
+
+static int
+dissect_gsmrlp_xid(tvbuff_t *tvb, gint offset, packet_info *pinfo _U_, proto_tree *tree)
+{
+	gint cur;
+
+	for (cur = offset; cur < (gint) tvb_reported_length(tvb);) {
+		guint8 len = tvb_get_guint8(tvb, cur) & 0x0f;
+		guint8 type = tvb_get_guint8(tvb, cur) >> 4;
+		proto_tree *xid_tree;
+
+		proto_tree_add_subtree_format(tree, tvb, cur, 1 + len, ett_gsmrlp_xid, &xid_tree, "XID Parameter: %s",
+					val_to_str(type, rlp_xid_param_vals, "Unknown"));
+		proto_tree_add_item(xid_tree, hf_gsmrlp_xid_p_type, tvb, cur, 1, ENC_BIG_ENDIAN);
+		proto_tree_add_item(xid_tree, hf_gsmrlp_xid_p_len, tvb, cur, 1, ENC_BIG_ENDIAN);
+		if (len)
+			proto_tree_add_item(xid_tree, hf_gsmrlp_xid_p_val, tvb, cur + 1, len, ENC_BIG_ENDIAN);
+		cur += 1 + len;
+		if (type == XID_P_DELIMITER)
+			break;
+	}
+
+	return cur - offset;
+}
+
+
+/* Dissect a RLP v0/v1 message as described in TS 24.022 section 5.2 */
+static int
+dissect_gsmrlp(tvbuff_t *tvb, packet_info *pinfo, proto_tree *tree, void* data _U_)
+{
+	int reported_len = tvb_reported_length(tvb);
+	proto_tree *rlp_tree;
+	proto_item *ti;
+	guint8 n_s, n_r;
+
+	/* we currently support the 16bit header of RLP v0 + v1 */
+
+	col_set_str(pinfo->cinfo, COL_PROTOCOL, "GSM-RLP");
+
+	n_s = (tvb_get_guint8(tvb, 0)) >> 3 | ((tvb_get_guint8(tvb, 1) & 1) << 5);
+	n_r = (tvb_get_guint8(tvb, 1) >> 2);
+
+	ti = proto_tree_add_protocol_format(tree, proto_gsmrlp, tvb, 0, reported_len,
+					    "GSM RLP");
+	rlp_tree = proto_item_add_subtree(ti, ett_gsmrlp);
+
+	proto_tree_add_item(rlp_tree, hf_gsmrlp_cr, tvb, 0, 1, ENC_BIG_ENDIAN);
+	proto_tree_add_item(rlp_tree, hf_gsmrlp_pf, tvb, 1, 1, ENC_BIG_ENDIAN);
+	if (n_s == 0x3f) { /* U frame */
+		guint u_ftype;
+		proto_tree_add_uint(rlp_tree, hf_gsmrlp_ftype, tvb, 0, 1, RLP_FT_U);
+		proto_tree_add_item_ret_uint(rlp_tree, hf_gsmrlp_u_ftype, tvb, 1, 1, ENC_BIG_ENDIAN, &u_ftype);
+		if ((n_r & 0x1f) == RLP_U_FT_XID)
+			dissect_gsmrlp_xid(tvb, 2, pinfo, rlp_tree);
+		proto_item_append_text(ti, " U-Frame: %s", val_to_str(u_ftype, rlp_ftype_u_vals, "Unknown 0x%02x"));
+	} else if (n_s == 0x3e) { /* S Frame */
+		guint s_ftype;
+		proto_tree_add_uint(rlp_tree, hf_gsmrlp_ftype, tvb, 0, 1, RLP_FT_S);
+		proto_tree_add_item_ret_uint(rlp_tree, hf_gsmrlp_s_ftype, tvb, 0, 1, ENC_BIG_ENDIAN, &s_ftype);
+		proto_tree_add_uint(rlp_tree, hf_gsmrlp_n_r, tvb, 1, 1, n_r);
+		proto_item_append_text(ti, " S-Frame: %s, N(S): %u, N(R): %u",
+				       val_to_str(s_ftype, rlp_ftype_s_vals, "Unknown 0x%02x"), n_s, n_r);
+	} else { /* IS Frame */
+		tvbuff_t *next_tvb;
+		guint s_ftype;
+		int data_len;
+
+		proto_tree_add_uint(rlp_tree, hf_gsmrlp_ftype, tvb, 0, 1, RLP_FT_IS);
+		proto_tree_add_item_ret_uint(rlp_tree, hf_gsmrlp_s_ftype, tvb, 0, 1, ENC_BIG_ENDIAN, &s_ftype);
+		proto_tree_add_uint(rlp_tree, hf_gsmrlp_n_s, tvb, 0, 2, n_s);
+		proto_tree_add_uint(rlp_tree, hf_gsmrlp_n_r, tvb, 1, 1, n_r);
+		proto_item_append_text(ti, " IS-Frame: %s, N(S): %u, N(R): %u",
+				       val_to_str(s_ftype, rlp_ftype_s_vals, "Unknown 0x%02x"), n_s, n_r);
+
+		/* dispatch user data */
+		data_len = reported_len - 2 /* header */ - 3 /* FCS */;
+		next_tvb = tvb_new_subset_length(tvb, 2, data_len);
+		call_data_dissector(next_tvb, pinfo, rlp_tree);
+	}
+
+	/* FCS is always the last 3 bytes of the message */
+	guint32 fcs_computed = rlp_fcs_compute(tvb_get_ptr(tvb, 0, reported_len - 3), reported_len - 3);
+	proto_tree_add_checksum(rlp_tree, tvb, reported_len - 3, hf_gsmrlp_fcs, hf_gsmrlp_fcs_status,
+				&ei_gsmrlp_fcs_bad, pinfo, fcs_computed, ENC_BIG_ENDIAN, PROTO_CHECKSUM_VERIFY);
+
+	return tvb_reported_length(tvb);
+}
+
+void
+proto_register_gsmrlp(void)
+{
+	static hf_register_info hf[] = {
+	    { &hf_gsmrlp_cr,
+	      { "C/R", "gsm_rlp.cr", FT_UINT8, BASE_DEC, NULL, 0x01,
+		"Command/Response bit", HFILL }},
+	    { &hf_gsmrlp_pf,
+	      { "P/F", "gsm_rlp.pf", FT_UINT8, BASE_DEC, NULL, 0x02,
+		"Poll/Final bit", HFILL }},
+	    { &hf_gsmrlp_n_r,
+	      { "N(R)", "gsm_rlp.n_r", FT_UINT8, BASE_DEC, NULL, 0,
+		"Receive Sequence Number", HFILL }},
+	    { &hf_gsmrlp_n_s,
+	      { "N(S)", "gsm_rlp.n_s", FT_UINT8, BASE_DEC, NULL, 0,
+		"Send Sequence Number", HFILL }},
+	    { &hf_gsmrlp_ftype,
+	      { "Frame type", "gsm_rlp.ftype", FT_UINT8, BASE_HEX,
+		VALS(rlp_ftype_vals), 0, NULL, HFILL }},
+	    { &hf_gsmrlp_u_ftype,
+	      { "U Frame type", "gsm_rlp.u_ftype", FT_UINT8, BASE_HEX,
+		VALS(rlp_ftype_u_vals), 0x7c, NULL, HFILL }},
+	    { &hf_gsmrlp_s_ftype,
+	      { "S frame type", "gsm_rlp.s_ftype", FT_UINT8, BASE_HEX,
+		VALS(rlp_ftype_s_vals), 0x06, NULL, HFILL }},
+	    { &hf_gsmrlp_fcs,
+	      { "Frame Check Sequence", "gsm_rlp.fcs", FT_UINT24, BASE_HEX,
+		NULL, 0, NULL, HFILL }},
+	    { &hf_gsmrlp_fcs_status,
+	      { "FCS Status", "gsm_rlp.fcs.status", FT_UINT8, BASE_NONE,
+		VALS(proto_checksum_vals), 0, NULL, HFILL }},
+
+	    { &hf_gsmrlp_xid_p_type,
+	      { "XID Parameter Type", "gsm_rlp.xid.param_type", FT_UINT8, BASE_HEX,
+		VALS(rlp_xid_param_vals), 0xf0, NULL, HFILL }},
+	    { &hf_gsmrlp_xid_p_len,
+	      { "XID Parameter Length", "gsm_rlp.xid.param_len", FT_UINT8, BASE_DEC,
+		NULL, 0x0f, NULL, HFILL }},
+	    { &hf_gsmrlp_xid_p_val,
+	      { "XID Parameter Value", "gsm_rlp.xid.param_value", FT_UINT8, BASE_DEC,
+		NULL, 0, NULL, HFILL }},
+	};
+	static gint *ett[] = {
+		&ett_gsmrlp,
+		&ett_gsmrlp_xid,
+	};
+	static ei_register_info ei[] = {
+		{ &ei_gsmrlp_fcs_bad, { "gsm_rlp.fcs_bad", PI_CHECKSUM, PI_ERROR, "Bad checksum" , EXPFILL }},
+	};
+	module_t *rlp_module;
+	expert_module_t *expert_gsmrlp;
+
+	proto_gsmrlp = proto_register_protocol("GSM Radio Link Protocol (RLP)", "GSM-RLP", "gsm_rlp");
+	proto_register_field_array(proto_gsmrlp, hf, array_length(hf));
+	proto_register_subtree_array(ett, array_length(ett));
+	expert_gsmrlp = expert_register_protocol(proto_gsmrlp);
+	expert_register_field_array(expert_gsmrlp, ei, array_length(ei));
+
+	register_dissector("gsm_rlp", dissect_gsmrlp, proto_gsmrlp);
+}
+
+/*
+ * Editor modelines  -  https://www.wireshark.org/tools/modelines.html
+ *
+ * Local variables:
+ * c-basic-offset: 4
+ * tab-width: 8
+ * indent-tabs-mode: nil
+ * End:
+ *
+ * vi: set shiftwidth=4 tabstop=8 expandtab:
+ * :indentSize=4:tabSize=8:noTabs=true:
+ */
diff --git a/epan/dissectors/packet-gsmtap.c b/epan/dissectors/packet-gsmtap.c
index cbdec44e6e..be0d114768 100644
--- a/epan/dissectors/packet-gsmtap.c
+++ b/epan/dissectors/packet-gsmtap.c
@@ -111,6 +111,7 @@ enum {
 	GSMTAP_SUB_LAPD,
 	GSMTAP_SUB_FR,
 	GSMTAP_SUB_V5EF,
+	GSMTAP_SUB_GSM_RLP,
 
 	GSMTAP_SUB_MAX
 };
@@ -440,6 +441,7 @@ static const value_string gsmtap_types[] = {
 	{ GSMTAP_TYPE_QC_DIAG,		"Qualcomm DIAG" },
 	{ GSMTAP_TYPE_LTE_NAS,		"LTE NAS" },
 	{ GSMTAP_TYPE_E1T1,		"E1/T1" },
+	{ GSMTAP_TYPE_GSM_RLP,		"GSM RLP" },
 	{ 0,			NULL },
 };
 
@@ -1109,6 +1111,9 @@ dissect_gsmtap(tvbuff_t *tvb, packet_info *pinfo, proto_tree *tree, void* data _
 			break;
 		}
 		break;
+	case GSMTAP_TYPE_GSM_RLP:
+		sub_handle = GSMTAP_SUB_GSM_RLP;
+		break;
 	case GSMTAP_TYPE_UM_BURST:
 	default:
 		sub_handle = GSMTAP_SUB_DATA;
@@ -1244,6 +1249,7 @@ proto_reg_handoff_gsmtap(void)
 	sub_handles[GSMTAP_SUB_LAPD] = find_dissector_add_dependency("lapd-phdr", proto_gsmtap);
 	sub_handles[GSMTAP_SUB_FR] = find_dissector_add_dependency("fr", proto_gsmtap);
 	sub_handles[GSMTAP_SUB_V5EF] = find_dissector_add_dependency("v5ef", proto_gsmtap);
+	sub_handles[GSMTAP_SUB_GSM_RLP] = find_dissector_add_dependency("gsm_rlp", proto_gsmtap);
 
 	rrc_sub_handles[GSMTAP_RRC_SUB_DL_DCCH_Message] = find_dissector_add_dependency("rrc.dl.dcch", proto_gsmtap);
 	rrc_sub_handles[GSMTAP_RRC_SUB_UL_DCCH_Message] = find_dissector_add_dependency("rrc.ul.dcch", proto_gsmtap);
diff --git a/epan/dissectors/packet-gsmtap.h b/epan/dissectors/packet-gsmtap.h
index d286b19a1a..b618149644 100644
--- a/epan/dissectors/packet-gsmtap.h
+++ b/epan/dissectors/packet-gsmtap.h
@@ -41,6 +41,7 @@
 #define GSMTAP_TYPE_QC_DIAG		0x11	/* Qualcomm DIAG frame */
 #define GSMTAP_TYPE_LTE_NAS		0x12	/* LTE Non-Access Stratum */
 #define GSMTAP_TYPE_E1T1		0x13	/* E1/T1 line traces */
+#define GSMTAP_TYPE_GSM_RLP		0x14	/* GSM RLP as per 3GPP TS 24.022 */
 
 /* ====== DO NOT MAKE UNAPPROVED MODIFICATIONS HERE ===== */
 #define GSMTAP_BURST_UNKNOWN		0x00