Add "tvb_reported_length()" to get the "reported length" of a tvbuff

(i.e., the amount of data that was in the packet, even if not all of it
was captured), for use when dissecting packets containing data that
fills the packet (we want the dissector to try to dissect all of it; if
it runs past the end of the captured data, we want it to throw an
exception so that we'll put a "Short Frame" note in the protocol tree).

This means we always want a tvbuff to have a real reported length value,
so we make it an unsigned integer, and don't bother checking it for -1,
as it should never be -1.

If the reported length passed in to "tvb_set_subset()" is -1, set the
reported length to the reported length of the tvbuff of which the new
tvbuff will be a subset minus the offset in that tvbuff of the subset,
so that "-1" means "what's left of the packet after we chop off the
header".  This is necessary in order to ensure that all tvbuffs have a
real reported length value.

Have "dissect_packet()" set the reported length of the top-level tvbuff
to the reported length of the frame, so that we start out with a tvbuff
with a real reported length value.

Have "tvb_offset_exists()" return FALSE if the offset is past the end of
the tvbuff.

If the offset passed to it is postitive, have "compute_offset_length()"
check for that it's not more than one byte past the end of the tvbuff -
if it's just past the end, we don't want the check to fail, as we don't
want attempts to create a subset tvbuff containing zero bytes to fail;
that would be done if a captured packet was all header and no payload,
and we'd want the dissector of the payload, not the dissector of the
header, to throw an exception, as the problem isn't with the protocol
for the header, it's with the protocol for the payload.

Convert the ATM dissector, the SSCOP dissector, the Q.2931 dissector,
and the Q.931 dissector to use tvbuffs.

Make the LAPD dissector set up a tvbuff for the Q.931 dissector (it's
not converted yet).

svn path=/trunk/; revision=2023

1 files changed, 313 insertions, 303 deletions

diff --git a/packet-q931.c b/packet-q931.c
index 001f33afb2..547c7361a8 100644
--- a/packet-q931.c
+++ b/packet-q931.c
@@ -2,7 +2,7 @@
  * Routines for Q.931 frame disassembly
  * Guy Harris <guy@alum.mit.edu>
  *
- * $Id: packet-q931.c,v 1.14 2000/05/11 08:15:39 gram Exp $
+ * $Id: packet-q931.c,v 1.15 2000/05/29 08:57:38 guy Exp $
  *
  * Ethereal - Network traffic analyzer
  * By Gerald Combs <gerald@zing.org>
@@ -310,25 +310,25 @@ static const value_string q931_repeat_indication_vals[] = {
  * Dissect a Segmented message information element.
  */
 static void
-dissect_q931_segmented_message_ie(const u_char *pd, int offset, int len,
+dissect_q931_segmented_message_ie(tvbuff_t *tvb, int offset, int len,
     proto_tree *tree)
 {
 	if (len != 2) {
-		proto_tree_add_text(tree, NullTVB, offset, len,
+		proto_tree_add_text(tree, tvb, offset, len,
 		    "Segmented message: length is %d, should be 2\n", len);
 		return;
 	}
-	if (pd[offset] & 0x80) {
-		proto_tree_add_text(tree, NullTVB, offset, 1,
+	if (tvb_get_guint8(tvb, offset) & 0x80) {
+		proto_tree_add_text(tree, tvb, offset, 1,
 		    "First segment: %u segments remaining",
-		    pd[offset] & 0x7F);
+		    tvb_get_guint8(tvb, offset) & 0x7F);
 	} else {
-		proto_tree_add_text(tree, NullTVB, offset, 1,
+		proto_tree_add_text(tree, tvb, offset, 1,
 		    "Not first segment: %u segments remaining",
-		    pd[offset] & 0x7F);
+		    tvb_get_guint8(tvb, offset) & 0x7F);
 	}
-	proto_tree_add_text(tree, NullTVB, offset + 1, 1,
-	    "Segmented message type: %u\n", pd[offset + 1]);
+	proto_tree_add_text(tree, tvb, offset + 1, 1,
+	    "Segmented message type: %u\n", tvb_get_guint8(tvb, offset + 1));
 }
 
 /*
@@ -507,7 +507,7 @@ static const value_string q931_uil3_vals[] = {
 };
 
 void
-dissect_q931_bearer_capability_ie(const u_char *pd, int offset, int len,
+dissect_q931_bearer_capability_ie(tvbuff_t *tvb, int offset, int len,
     proto_tree *tree)
 {
 	guint8 octet;
@@ -520,9 +520,9 @@ dissect_q931_bearer_capability_ie(const u_char *pd, int offset, int len,
 
 	if (len == 0)
 		return;
-	octet = pd[offset];
+	octet = tvb_get_guint8(tvb, offset);
 	coding_standard = octet & 0x60;
-	proto_tree_add_text(tree, NullTVB, offset, 1,
+	proto_tree_add_text(tree, tvb, offset, 1,
 	    "Coding standard: %s",
 	    val_to_str(coding_standard, q931_bc_coding_standard_vals, NULL));
 	if (coding_standard != Q931_ITU_STANDARDIZED_CODING) {
@@ -530,11 +530,12 @@ dissect_q931_bearer_capability_ie(const u_char *pd, int offset, int len,
 		 * We don't know how the bearer capability is encoded,
 		 * so just dump it as data and be done with it.
 		 */
-		proto_tree_add_text(tree, NullTVB, offset,
-		    len, "Data: %s", bytes_to_str(&pd[offset], len));
+		proto_tree_add_text(tree, tvb, offset,
+		    len, "Data: %s",
+		    bytes_to_str(tvb_get_ptr(tvb, offset, len), len));
 		return;
 	}
-	proto_tree_add_text(tree, NullTVB, offset, 1,
+	proto_tree_add_text(tree, tvb, offset, 1,
 	    "Information transfer capability: %s",
 	    val_to_str(octet & 0x1F, q931_information_transfer_capability_vals,
 	      "Unknown (0x%02X)"));
@@ -547,8 +548,8 @@ dissect_q931_bearer_capability_ie(const u_char *pd, int offset, int len,
 	if (!(octet & Q931_IE_VL_EXTENSION)) {
 		if (len == 0)
 			return;
-		octet = pd[offset];
-		proto_tree_add_text(tree, NullTVB, offset, 1,
+		octet = tvb_get_guint8(tvb, offset);
+		proto_tree_add_text(tree, tvb, offset, 1,
 		    "Out-band negotiation %spossible",
 		    (octet & 0x40) ? "" : "not ");
 		offset += 1;
@@ -557,13 +558,13 @@ dissect_q931_bearer_capability_ie(const u_char *pd, int offset, int len,
 
 	if (len == 0)
 		return;
-	octet = pd[offset];
-	proto_tree_add_text(tree, NullTVB, offset, 1,
+	octet = tvb_get_guint8(tvb, offset);
+	proto_tree_add_text(tree, tvb, offset, 1,
 	    "Transfer mode: %s",
 	    val_to_str(octet & 0x60, q931_transfer_mode_vals,
 	      "Unknown (0x%02X)"));
 	it_rate = octet & 0x1F;
-	proto_tree_add_text(tree, NullTVB, offset, 1,
+	proto_tree_add_text(tree, tvb, offset, 1,
 	    "Information transfer rate: %s",
 	    val_to_str(it_rate, q931_information_transfer_rate_vals,
 	      "Unknown (0x%02X)"));
@@ -573,19 +574,19 @@ dissect_q931_bearer_capability_ie(const u_char *pd, int offset, int len,
 	if (it_rate == Q931_IT_RATE_MULTIRATE) {
 		if (len == 0)
 			return;
-		proto_tree_add_text(tree, NullTVB, offset, 1, "Rate multiplier: %u", pd[offset]);
+		proto_tree_add_text(tree, tvb, offset, 1, "Rate multiplier: %u", tvb_get_guint8(tvb, offset));
 		offset += 1;
 		len -= 1;
 	}
 
 	if (len == 0)
 		return;
-	octet = pd[offset];
+	octet = tvb_get_guint8(tvb, offset);
 	if ((octet & 0x60) == 0x20) {
 		/*
 		 * Layer 1 information.
 		 */
-		proto_tree_add_text(tree, NullTVB, offset, 1,
+		proto_tree_add_text(tree, tvb, offset, 1,
 		    "User information layer 1 protocol: %s",
 		    val_to_str(octet & 0x1F, q931_uil1_vals,
 		      "Unknown (0x%02X)"));
@@ -596,14 +597,14 @@ dissect_q931_bearer_capability_ie(const u_char *pd, int offset, int len,
 			goto l1_done;
 		if (len == 0)
 			return;
-		octet = pd[offset];
-		proto_tree_add_text(tree, NullTVB, offset, 1,
+		octet = tvb_get_guint8(tvb, offset);
+		proto_tree_add_text(tree, tvb, offset, 1,
 		    "Layer 1 is %s",
 		    (octet & 0x40) ? "Asynchronous" : "Synchronous");
-		proto_tree_add_text(tree, NullTVB, offset, 1,
+		proto_tree_add_text(tree, tvb, offset, 1,
 		    "Layer 1 in-band negotiation is %spossible",
 		    (octet & 0x20) ? "" : "not ");
-		proto_tree_add_text(tree, NullTVB, offset, 1,
+		proto_tree_add_text(tree, tvb, offset, 1,
 		    "User rate: %s",
 		    val_to_str(octet & 0x1F, q931_l1_user_rate_vals,
 		      "Unknown (0x%02X)"));
@@ -614,21 +615,21 @@ dissect_q931_bearer_capability_ie(const u_char *pd, int offset, int len,
 			goto l1_done;
 		if (len == 0)
 			return;
-		octet = pd[offset];
-		proto_tree_add_text(tree, NullTVB, offset, 1,
+		octet = tvb_get_guint8(tvb, offset);
+		proto_tree_add_text(tree, tvb, offset, 1,
 		    "Intermediate rate: %s",
 		      val_to_str(octet & 0x60, q931_l1_intermediate_rate_vals,
 		       "Unknown (0x%X)"));
-		proto_tree_add_text(tree, NullTVB, offset, 1,
+		proto_tree_add_text(tree, tvb, offset, 1,
 		    "%s to send data with network independent clock",
 		    (octet & 0x10) ? "Required" : "Not required");
-		proto_tree_add_text(tree, NullTVB, offset, 1,
+		proto_tree_add_text(tree, tvb, offset, 1,
 		    "%s accept data with network independent clock",
 		    (octet & 0x08) ? "Can" : "Cannot");
-		proto_tree_add_text(tree, NullTVB, offset, 1,
+		proto_tree_add_text(tree, tvb, offset, 1,
 		    "%s to send data with flow control mechanism",
 		    (octet & 0x04) ? "Required" : "Not required");
-		proto_tree_add_text(tree, NullTVB, offset, 1,
+		proto_tree_add_text(tree, tvb, offset, 1,
 		    "%s accept data with flow control mechanism",
 		    (octet & 0x02) ? "Can" : "Cannot");
 		offset += 1;
@@ -638,23 +639,23 @@ dissect_q931_bearer_capability_ie(const u_char *pd, int offset, int len,
 			goto l1_done;
 		if (len == 0)
 			return;
-		octet = pd[offset];
-		proto_tree_add_text(tree, NullTVB, offset, 1,
+		octet = tvb_get_guint8(tvb, offset);
+		proto_tree_add_text(tree, tvb, offset, 1,
 		    "Rate adaption header %sincluded",
 		    (octet & 0x40) ? "" : "not ");
-		proto_tree_add_text(tree, NullTVB, offset, 1,
+		proto_tree_add_text(tree, tvb, offset, 1,
 		    "Multiple frame establishment %ssupported",
 		    (octet & 0x20) ? "" : "not ");
-		proto_tree_add_text(tree, NullTVB, offset, 1,
+		proto_tree_add_text(tree, tvb, offset, 1,
 		    "%s mode of operation",
 		    (octet & 0x10) ? "Protocol sensitive" : "Bit transparent");
-		proto_tree_add_text(tree, NullTVB, offset, 1,
+		proto_tree_add_text(tree, tvb, offset, 1,
 		    (octet & 0x08) ?
 		      "Full protocol negotiation" : "LLI = 256 only");
-		proto_tree_add_text(tree, NullTVB, offset, 1,
+		proto_tree_add_text(tree, tvb, offset, 1,
 		    "Message originator is %s",
 		    (octet & 0x04) ? "Assignor only" : "Default assignee");
-		proto_tree_add_text(tree, NullTVB, offset, 1,
+		proto_tree_add_text(tree, tvb, offset, 1,
 		    "Negotiation is done %s",
 		    (octet & 0x02) ? "in-band" : "out-of-band");
 		offset += 1;
@@ -664,16 +665,16 @@ dissect_q931_bearer_capability_ie(const u_char *pd, int offset, int len,
 			goto l1_done;
 		if (len == 0)
 			return;
-		octet = pd[offset];
-		proto_tree_add_text(tree, NullTVB, offset, 1,
+		octet = tvb_get_guint8(tvb, offset);
+		proto_tree_add_text(tree, tvb, offset, 1,
 		    "Stop bits: %s",
 		      val_to_str(octet & 0x60, q931_l1_stop_bits_vals,
 		       "Unknown (0x%X)"));
-		proto_tree_add_text(tree, NullTVB, offset, 1,
+		proto_tree_add_text(tree, tvb, offset, 1,
 		    "Data bits: %s",
 		      val_to_str(octet & 0x18, q931_l1_data_bits_vals,
 		       "Unknown (0x%X)"));
-		proto_tree_add_text(tree, NullTVB, offset, 1,
+		proto_tree_add_text(tree, tvb, offset, 1,
 		    "Parity: %s",
 		      val_to_str(octet & 0x08, q931_l1_parity_vals,
 		       "Unknown (0x%X)"));
@@ -682,20 +683,20 @@ dissect_q931_bearer_capability_ie(const u_char *pd, int offset, int len,
 			goto l1_done;
 		if (len == 0)
 			return;
-		octet = pd[offset];
-		proto_tree_add_text(tree, NullTVB, offset, 1,
+		octet = tvb_get_guint8(tvb, offset);
+		proto_tree_add_text(tree, tvb, offset, 1,
 		    "%s duplex",
 		    (octet & 0x40) ? "Full" : "Half");
 		modem_type = octet & 0x3F;
 		if (modem_type <= 0x5 ||
 		    (modem_type >= 0x20 && modem_type <= 0x2F)) {
-			proto_tree_add_text(tree, NullTVB, offset, 1,
+			proto_tree_add_text(tree, tvb, offset, 1,
 			    "Modem type: National use 0x%02X", modem_type);
 		} else if (modem_type >= 0x30) {
-			proto_tree_add_text(tree, NullTVB, offset, 1,
+			proto_tree_add_text(tree, tvb, offset, 1,
 			    "Modem type: User specified 0x%02X", modem_type);
 		} else {
-			proto_tree_add_text(tree, NullTVB, offset, 1,
+			proto_tree_add_text(tree, tvb, offset, 1,
 			    "Modem type: %s",
 			      val_to_str(modem_type, q931_l1_modem_type_vals,
 			      NULL));
@@ -708,13 +709,13 @@ l1_done:
 
 	if (len == 0)
 		return;
-	octet = pd[offset];
+	octet = tvb_get_guint8(tvb, offset);
 	if ((octet & 0x60) == 0x40) {
 		/*
 		 * Layer 2 information.
 		 */
 		uil2_protocol = octet & 0x1F;
-		proto_tree_add_text(tree, NullTVB, offset, 1,
+		proto_tree_add_text(tree, tvb, offset, 1,
 		    "User information layer 2 protocol: %s",
 		    val_to_str(uil2_protocol, q931_uil2_vals,
 		      "Unknown (0x%02X)"));
@@ -728,13 +729,13 @@ l1_done:
 			goto l2_done;
 		if (len == 0)
 			return;
-		octet = pd[offset];
+		octet = tvb_get_guint8(tvb, offset);
 		if (uil2_protocol == Q931_UIL2_USER_SPEC) {
-			proto_tree_add_text(tree, NullTVB, offset, 1,
+			proto_tree_add_text(tree, tvb, offset, 1,
 			    "User-specified layer 2 protocol information: 0x%02X",
 			    octet & 0x7F);
 		} else {
-			proto_tree_add_text(tree, NullTVB, offset, 1,
+			proto_tree_add_text(tree, tvb, offset, 1,
 			    "Mode: %s",
 			    val_to_str(octet & 0x60, q931_mode_vals,
 			      "Unknown (0x%02X)"));
@@ -746,8 +747,8 @@ l1_done:
 			goto l2_done;
 		if (len == 0)
 			return;
-		octet = pd[offset];
-		proto_tree_add_text(tree, NullTVB, offset, 1,
+		octet = tvb_get_guint8(tvb, offset);
+		proto_tree_add_text(tree, tvb, offset, 1,
 		    "Window size: %u k", octet & 0x7F);
 		offset += 1;
 		len -= 1;
@@ -757,13 +758,13 @@ l2_done:
 
 	if (len == 0)
 		return;
-	octet = pd[offset];
+	octet = tvb_get_guint8(tvb, offset);
 	if ((octet & 0x60) == 0x60) {
 		/*
 		 * Layer 3 information.
 		 */
 		uil3_protocol = octet & 0x1F;
-		proto_tree_add_text(tree, NullTVB, offset, 1,
+		proto_tree_add_text(tree, tvb, offset, 1,
 		    "User information layer 3 protocol: %s",
 		    val_to_str(uil3_protocol, q931_uil3_vals,
 		      "Unknown (0x%02X)"));
@@ -778,13 +779,13 @@ l2_done:
 			goto l3_done;
 		if (len == 0)
 			return;
-		octet = pd[offset];
+		octet = tvb_get_guint8(tvb, offset);
 		switch (uil3_protocol) {
 
 		case Q931_UIL3_X25_PL:
 		case Q931_UIL3_ISO_8208:
 		case Q931_UIL3_X223:
-			proto_tree_add_text(tree, NullTVB, offset, 1,
+			proto_tree_add_text(tree, tvb, offset, 1,
 			    "Mode: %s",
 			    val_to_str(octet & 0x60, q931_mode_vals,
 			      "Unknown (0x%02X)"));
@@ -795,8 +796,8 @@ l2_done:
 				goto l3_done;
 			if (len == 0)
 				return;
-			octet = pd[offset];
-			proto_tree_add_text(tree, NullTVB, offset, 1,
+			octet = tvb_get_guint8(tvb, offset);
+			proto_tree_add_text(tree, tvb, offset, 1,
 			    "Default packet size: %u", octet & 0x0F);
 			offset += 1;
 			len -= 1;
@@ -805,15 +806,15 @@ l2_done:
 				goto l3_done;
 			if (len == 0)
 				return;
-			octet = pd[offset];
-			proto_tree_add_text(tree, NullTVB, offset, 1,
+			octet = tvb_get_guint8(tvb, offset);
+			proto_tree_add_text(tree, tvb, offset, 1,
 			    "Packet window size: %u", octet & 0x7F);
 			offset += 1;
 			len -= 1;
 			break;
 
 		case Q931_UIL3_USER_SPEC:
-			proto_tree_add_text(tree, NullTVB, offset, 1,
+			proto_tree_add_text(tree, tvb, offset, 1,
 			    "Default packet size: %u octets",
 			    1 << (octet & 0x0F));
 			offset += 1;
@@ -826,9 +827,9 @@ l2_done:
 				goto l3_done;
 			if (len == 0)
 				return;
-			octet = pd[offset + 1];
+			octet = tvb_get_guint8(tvb, offset + 1);
 			add_l3_info |= (octet & 0x0F);
-			proto_tree_add_text(tree, NullTVB, offset, 2,
+			proto_tree_add_text(tree, tvb, offset, 2,
 			    "Additional layer 3 protocol information: %s",
 			    val_to_str(add_l3_info, nlpid_vals,
 			      "Unknown (0x%02X)"));
@@ -966,7 +967,7 @@ static const value_string q931_cause_code_vals[] = {
 };
 
 static void
-dissect_q931_cause_ie(const u_char *pd, int offset, int len,
+dissect_q931_cause_ie(tvbuff_t *tvb, int offset, int len,
     proto_tree *tree)
 {
 	guint8 octet;
@@ -974,9 +975,9 @@ dissect_q931_cause_ie(const u_char *pd, int offset, int len,
 
 	if (len == 0)
 		return;
-	octet = pd[offset];
+	octet = tvb_get_guint8(tvb, offset);
 	coding_standard = octet & 0x60;
-	proto_tree_add_text(tree, NullTVB, offset, 1,
+	proto_tree_add_text(tree, tvb, offset, 1,
 	    "Coding standard: %s",
 	    val_to_str(coding_standard, q931_cause_coding_standard_vals, NULL));
 	if (coding_standard != Q931_ITU_STANDARDIZED_CODING) {
@@ -984,11 +985,12 @@ dissect_q931_cause_ie(const u_char *pd, int offset, int len,
 		 * We don't know how the cause is encoded,
 		 * so just dump it as data and be done with it.
 		 */
-		proto_tree_add_text(tree, NullTVB, offset,
-		    len, "Data: %s", bytes_to_str(&pd[offset], len));
+		proto_tree_add_text(tree, tvb, offset,
+		    len, "Data: %s",
+		    bytes_to_str(tvb_get_ptr(tvb, offset, len), len));
 		return;
 	}
-	proto_tree_add_text(tree, NullTVB, offset, 1,
+	proto_tree_add_text(tree, tvb, offset, 1,
 	    "Location: %s",
 	    val_to_str(octet & 0x0F, q931_cause_location_vals,
 	      "Unknown (0x%X)"));
@@ -998,8 +1000,8 @@ dissect_q931_cause_ie(const u_char *pd, int offset, int len,
 	if (!(octet & Q931_IE_VL_EXTENSION)) {
 		if (len == 0)
 			return;
-		octet = pd[offset];
-		proto_tree_add_text(tree, NullTVB, offset, 1,
+		octet = tvb_get_guint8(tvb, offset);
+		proto_tree_add_text(tree, tvb, offset, 1,
 		    "Recommendation: %s",
 		    val_to_str(octet & 0x7F, q931_cause_recommendation_vals,
 		      "Unknown (0x%X)"));
@@ -1009,8 +1011,8 @@ dissect_q931_cause_ie(const u_char *pd, int offset, int len,
 
 	if (len == 0)
 		return;
-	octet = pd[offset];
-	proto_tree_add_text(tree, NullTVB, offset, 1,
+	octet = tvb_get_guint8(tvb, offset);
+	proto_tree_add_text(tree, tvb, offset, 1,
 	    "Cause value: %s",
 	    val_to_str(octet & 0x7F, q931_cause_code_vals,
 	      "Unknown (0x%X)"));
@@ -1019,9 +1021,9 @@ dissect_q931_cause_ie(const u_char *pd, int offset, int len,
 
 	if (len == 0)
 		return;
-	proto_tree_add_text(tree, NullTVB, offset, len,
+	proto_tree_add_text(tree, tvb, offset, len,
 	    "Diagnostics: %s",
-	    bytes_to_str(&pd[offset], len));
+	    bytes_to_str(tvb_get_ptr(tvb, offset, len), len));
 }
 
 /*
@@ -1058,7 +1060,7 @@ static const value_string q931_call_state_vals[] = {
 };
 
 static void
-dissect_q931_call_state_ie(const u_char *pd, int offset, int len,
+dissect_q931_call_state_ie(tvbuff_t *tvb, int offset, int len,
     proto_tree *tree)
 {
 	guint8 octet;
@@ -1066,9 +1068,9 @@ dissect_q931_call_state_ie(const u_char *pd, int offset, int len,
 
 	if (len == 0)
 		return;
-	octet = pd[offset];
+	octet = tvb_get_guint8(tvb, offset);
 	coding_standard = octet & 0x60;
-	proto_tree_add_text(tree, NullTVB, offset, 1,
+	proto_tree_add_text(tree, tvb, offset, 1,
 	    "Coding standard: %s",
 	    val_to_str(coding_standard, q931_coding_standard_vals, NULL));
 	if (coding_standard != Q931_ITU_STANDARDIZED_CODING) {
@@ -1076,11 +1078,12 @@ dissect_q931_call_state_ie(const u_char *pd, int offset, int len,
 		 * We don't know how the call state is encoded,
 		 * so just dump it as data and be done with it.
 		 */
-		proto_tree_add_text(tree, NullTVB, offset,
-		    len, "Data: %s", bytes_to_str(&pd[offset], len));
+		proto_tree_add_text(tree, tvb, offset,
+		    len, "Data: %s",
+		    bytes_to_str(tvb_get_ptr(tvb, offset, len), len));
 		return;
 	}
-	proto_tree_add_text(tree, NullTVB, offset, 1,
+	proto_tree_add_text(tree, tvb, offset, 1,
 	    "Call state: %s",
 	    val_to_str(octet & 0x3F, q931_call_state_vals,
 	      "Unknown (0x%02X)"));
@@ -1118,7 +1121,7 @@ static const value_string q931_element_type_vals[] = {
 };
 
 static void
-dissect_q931_channel_identification_ie(const u_char *pd, int offset, int len,
+dissect_q931_channel_identification_ie(tvbuff_t *tvb, int offset, int len,
     proto_tree *tree)
 {
 	guint8 octet;
@@ -1128,26 +1131,26 @@ dissect_q931_channel_identification_ie(const u_char *pd, int offset, int len,
 
 	if (len == 0)
 		return;
-	octet = pd[offset];
-	proto_tree_add_text(tree, NullTVB, offset, 1,
+	octet = tvb_get_guint8(tvb, offset);
+	proto_tree_add_text(tree, tvb, offset, 1,
 	    "Interface %s identified",
 	    (octet & Q931_INTERFACE_IDENTIFIED) ? "explicitly" : "implicitly");
-	proto_tree_add_text(tree, NullTVB, offset, 1,
+	proto_tree_add_text(tree, tvb, offset, 1,
 	    "%s interface",
 	    (octet & Q931_NOT_BASIC_CHANNEL) ? "Not basic" : "Basic");
-	proto_tree_add_text(tree, NullTVB, offset, 1,
+	proto_tree_add_text(tree, tvb, offset, 1,
 	    "Indicated channel is %s",
 	    (octet & 0x08) ? "required" : "preferred");
-	proto_tree_add_text(tree, NullTVB, offset, 1,
+	proto_tree_add_text(tree, tvb, offset, 1,
 	    "Indicated channel is %sthe D-channel",
 	    (octet & 0x04) ? "" : "not ");
 	if (octet & Q931_NOT_BASIC_CHANNEL) {
-		proto_tree_add_text(tree, NullTVB, offset, 1,
+		proto_tree_add_text(tree, tvb, offset, 1,
 		    "Channel selection: %s",
 		    val_to_str(octet & 0x03, q931_not_basic_channel_selection_vals,
 		      NULL));
 	} else {
-		proto_tree_add_text(tree, NullTVB, offset, 1,
+		proto_tree_add_text(tree, tvb, offset, 1,
 		    "Channel selection: %s",
 		    val_to_str(octet & 0x03, q931_basic_channel_selection_vals,
 		      NULL));
@@ -1161,7 +1164,7 @@ dissect_q931_channel_identification_ie(const u_char *pd, int offset, int len,
 		do {
 			if (len == 0)
 				break;
-			octet = pd[offset];
+			octet = tvb_get_guint8(tvb, offset);
 			offset += 1;
 			len -= 1;
 			identifier_len++;
@@ -1172,9 +1175,10 @@ dissect_q931_channel_identification_ie(const u_char *pd, int offset, int len,
 		 * last octet of the interface identifier?
 		 */
 		if (identifier_len != 0) {
-			proto_tree_add_text(tree, NullTVB, identifier_offset,
+			proto_tree_add_text(tree, tvb, identifier_offset,
 			    identifier_len, "Interface identifier: %s",
-			    bytes_to_str(&pd[identifier_offset],
+			    bytes_to_str(
+			      tvb_get_ptr(tvb, identifier_offset, identifier_len),
 			      identifier_len));
 		}
 	}
@@ -1182,9 +1186,9 @@ dissect_q931_channel_identification_ie(const u_char *pd, int offset, int len,
 	if (octet & Q931_NOT_BASIC_CHANNEL) {
 		if (len == 0)
 			return;
-		octet = pd[offset];
+		octet = tvb_get_guint8(tvb, offset);
 		coding_standard = octet & 0x60;
-		proto_tree_add_text(tree, NullTVB, offset, 1,
+		proto_tree_add_text(tree, tvb, offset, 1,
 		    "Coding standard: %s",
 		    val_to_str(coding_standard, q931_coding_standard_vals,
 		      NULL));
@@ -1194,14 +1198,15 @@ dissect_q931_channel_identification_ie(const u_char *pd, int offset, int len,
 			 * encoded, so just dump it as data and be done
 			 * with it.
 			 */
-			proto_tree_add_text(tree, NullTVB, offset,
-			    len, "Data: %s", bytes_to_str(&pd[offset], len));
+			proto_tree_add_text(tree, tvb, offset,
+			    len, "Data: %s",
+			    bytes_to_str(tvb_get_ptr(tvb, offset, len), len));
 			return;
 		}
-		proto_tree_add_text(tree, NullTVB, offset, 1,
+		proto_tree_add_text(tree, tvb, offset, 1,
 		    "Channel is indicated by %s",
 		    (octet & Q931_IS_SLOT_MAP) ? "slot map" : "number");
-		proto_tree_add_text(tree, NullTVB, offset, 1,
+		proto_tree_add_text(tree, tvb, offset, 1,
 		    "%s type: %s",
 		    (octet & Q931_IS_SLOT_MAP) ? "Map element" : "Channel",
 		    val_to_str(octet & 0x0F, q931_element_type_vals,
@@ -1227,7 +1232,7 @@ static const value_string q931_progress_description_vals[] = {
 };
 
 void
-dissect_q931_progress_indicator_ie(const u_char *pd, int offset, int len,
+dissect_q931_progress_indicator_ie(tvbuff_t *tvb, int offset, int len,
     proto_tree *tree)
 {
 	guint8 octet;
@@ -1235,9 +1240,9 @@ dissect_q931_progress_indicator_ie(const u_char *pd, int offset, int len,
 
 	if (len == 0)
 		return;
-	octet = pd[offset];
+	octet = tvb_get_guint8(tvb, offset);
 	coding_standard = octet & 0x60;
-	proto_tree_add_text(tree, NullTVB, offset, 1,
+	proto_tree_add_text(tree, tvb, offset, 1,
 	    "Coding standard: %s",
 	    val_to_str(coding_standard, q931_cause_coding_standard_vals, NULL));
 	if (coding_standard != Q931_ITU_STANDARDIZED_CODING) {
@@ -1245,11 +1250,12 @@ dissect_q931_progress_indicator_ie(const u_char *pd, int offset, int len,
 		 * We don't know how the progress indicator is encoded,
 		 * so just dump it as data and be done with it.
 		 */
-		proto_tree_add_text(tree, NullTVB, offset,
-		    len, "Data: %s", bytes_to_str(&pd[offset], len));
+		proto_tree_add_text(tree, tvb, offset,
+		    len, "Data: %s",
+		    bytes_to_str(tvb_get_ptr(tvb, offset, len), len));
 		return;
 	}
-	proto_tree_add_text(tree, NullTVB, offset, 1,
+	proto_tree_add_text(tree, tvb, offset, 1,
 	    "Location: %s",
 	    val_to_str(octet & 0x0F, q931_cause_location_vals,
 	      "Unknown (0x%X)"));
@@ -1258,8 +1264,8 @@ dissect_q931_progress_indicator_ie(const u_char *pd, int offset, int len,
 
 	if (len == 0)
 		return;
-	octet = pd[offset];
-	proto_tree_add_text(tree, NullTVB, offset, 1,
+	octet = tvb_get_guint8(tvb, offset);
+	proto_tree_add_text(tree, tvb, offset, 1,
 	    "Progress description: %s",
 	    val_to_str(octet & 0x7F, q931_progress_description_vals,
 	      "Unknown (0x%02X)"));
@@ -1284,7 +1290,7 @@ static const value_string q931_netid_plan_vals[] = {
 };
 
 static void
-dissect_q931_ns_facilities_ie(const u_char *pd, int offset, int len,
+dissect_q931_ns_facilities_ie(tvbuff_t *tvb, int offset, int len,
     proto_tree *tree)
 {
 	guint8 octet;
@@ -1292,9 +1298,9 @@ dissect_q931_ns_facilities_ie(const u_char *pd, int offset, int len,
 
 	if (len == 0)
 		return;
-	octet = pd[offset];
+	octet = tvb_get_guint8(tvb, offset);
 	netid_len = octet & 0x7F;
-	proto_tree_add_text(tree, NullTVB, offset, 1,
+	proto_tree_add_text(tree, tvb, offset, 1,
 	    "Network identification length: %u",
 	    netid_len);
 	offset += 1;
@@ -1302,12 +1308,12 @@ dissect_q931_ns_facilities_ie(const u_char *pd, int offset, int len,
 	if (netid_len != 0) {
 		if (len == 0)
 			return;
-		octet = pd[offset];
-		proto_tree_add_text(tree, NullTVB, offset, 1,
+		octet = tvb_get_guint8(tvb, offset);
+		proto_tree_add_text(tree, tvb, offset, 1,
 		    "Type of network identification: %s",
 		    val_to_str(octet & 0x70, q931_netid_type_vals,
 		      "Unknown (0x%02X)"));
-		proto_tree_add_text(tree, NullTVB, offset, 1,
+		proto_tree_add_text(tree, tvb, offset, 1,
 		    "Network identification plan: %s",
 		    val_to_str(octet & 0x0F, q931_netid_plan_vals,
 		      "Unknown (0x%02X)"));
@@ -1320,9 +1326,10 @@ dissect_q931_ns_facilities_ie(const u_char *pd, int offset, int len,
 		if (netid_len > len)
 			netid_len = len;
 		if (netid_len != 0) {
-			proto_tree_add_text(tree, NullTVB, offset, netid_len,
+			proto_tree_add_text(tree, tvb, offset, netid_len,
 			    "Network identification: %.*s",
-			    netid_len, &pd[offset]);
+			    netid_len,
+			    tvb_get_ptr(tvb, offset, netid_len));
 			offset += netid_len;
 			len -= netid_len;
 		}
@@ -1334,9 +1341,9 @@ dissect_q931_ns_facilities_ie(const u_char *pd, int offset, int len,
 	 */
 	 if (len == 0)
 	 	return;
-	proto_tree_add_text(tree, NullTVB, offset,
+	proto_tree_add_text(tree, tvb, offset,
 	    len, "Network-specific facility specification: %s",
-	    bytes_to_str(&pd[offset], len));
+	    bytes_to_str(tvb_get_ptr(tvb, offset, len), len));
 }
 
 /*
@@ -1350,15 +1357,15 @@ static const value_string q931_notification_description_vals[] = {
 };
 
 static void
-dissect_q931_notification_indicator_ie(const u_char *pd, int offset, int len,
+dissect_q931_notification_indicator_ie(tvbuff_t *tvb, int offset, int len,
     proto_tree *tree)
 {
 	guint8 octet;
 
 	if (len == 0)
 		return;
-	octet = pd[offset];
-	proto_tree_add_text(tree, NullTVB, offset, 1,
+	octet = tvb_get_guint8(tvb, offset);
+	proto_tree_add_text(tree, tvb, offset, 1,
 	    "Notification description: %s",
 	    val_to_str(octet & 0x7F, q931_notification_description_vals,
 	      "Unknown (0x%02X)"));
@@ -1368,11 +1375,11 @@ dissect_q931_notification_indicator_ie(const u_char *pd, int offset, int len,
  * Dissect a Date/time information element.
  */
 static void
-dissect_q931_date_time_ie(const u_char *pd, int offset, int len,
+dissect_q931_date_time_ie(tvbuff_t *tvb, int offset, int len,
     proto_tree *tree)
 {
 	if (len != 6) {
-		proto_tree_add_text(tree, NullTVB, offset, len,
+		proto_tree_add_text(tree, tvb, offset, len,
 		    "Date/time: length is %d, should be 6\n", len);
 		return;
 	}
@@ -1380,10 +1387,10 @@ dissect_q931_date_time_ie(const u_char *pd, int offset, int len,
 	 * XXX - what is "year" relative to?  Is "month" 0-origin or
 	 * 1-origin?  Q.931 doesn't say....
 	 */
-	proto_tree_add_text(tree, NullTVB, offset, 6,
+	proto_tree_add_text(tree, tvb, offset, 6,
 	    "Date/time: %02u-%02u-%02u %02u:%02u:%02u",
-	    pd[offset + 0], pd[offset + 1], pd[offset + 2],
-	    pd[offset + 3], pd[offset + 4], pd[offset + 5]);
+	    tvb_get_guint8(tvb, offset + 0), tvb_get_guint8(tvb, offset + 1), tvb_get_guint8(tvb, offset + 2),
+	    tvb_get_guint8(tvb, offset + 3), tvb_get_guint8(tvb, offset + 4), tvb_get_guint8(tvb, offset + 5));
 }
 
 /*
@@ -1414,17 +1421,17 @@ static const value_string q931_signal_vals[] = {
 };
 
 static void
-dissect_q931_signal_ie(const u_char *pd, int offset, int len,
+dissect_q931_signal_ie(tvbuff_t *tvb, int offset, int len,
     proto_tree *tree)
 {
 	if (len != 1) {
-		proto_tree_add_text(tree, NullTVB, offset, len,
+		proto_tree_add_text(tree, tvb, offset, len,
 		    "Signal: length is %d, should be 1\n", len);
 		return;
 	}
-	proto_tree_add_text(tree, NullTVB, offset, 1,
+	proto_tree_add_text(tree, tvb, offset, 1,
 	    "Signal: %s",
-	    val_to_str(pd[offset], q931_signal_vals, "Unknown (0x%02X)"));
+	    val_to_str(tvb_get_guint8(tvb, offset), q931_signal_vals, "Unknown (0x%02X)"));
 }
 
 /*
@@ -1446,34 +1453,34 @@ static const value_string q931_throughput_class_vals[] = {
 };
 
 static void
-dissect_q931_information_rate_ie(const u_char *pd, int offset, int len,
+dissect_q931_information_rate_ie(tvbuff_t *tvb, int offset, int len,
     proto_tree *tree)
 {
 	if (len != 4) {
-		proto_tree_add_text(tree, NullTVB, offset, len,
+		proto_tree_add_text(tree, tvb, offset, len,
 		    "Information rate: length is %d, should be 4\n", len);
 		return;
 	}
-	proto_tree_add_text(tree, NullTVB, offset + 0, 1,
+	proto_tree_add_text(tree, tvb, offset + 0, 1,
 	    "Incoming information rate: %s",
-	    val_to_str(pd[offset + 0] & 0x1F, q931_throughput_class_vals,
+	    val_to_str(tvb_get_guint8(tvb, offset + 0) & 0x1F, q931_throughput_class_vals,
 	      "Unknown (0x%02X)"));
-	proto_tree_add_text(tree, NullTVB, offset + 1, 1,
+	proto_tree_add_text(tree, tvb, offset + 1, 1,
 	    "Outgoing information rate: %s",
-	    val_to_str(pd[offset + 1] & 0x1F, q931_throughput_class_vals,
+	    val_to_str(tvb_get_guint8(tvb, offset + 1) & 0x1F, q931_throughput_class_vals,
 	      "Unknown (0x%02X)"));
-	proto_tree_add_text(tree, NullTVB, offset + 2, 1,
+	proto_tree_add_text(tree, tvb, offset + 2, 1,
 	    "Minimum incoming information rate: %s",
-	    val_to_str(pd[offset + 2] & 0x1F, q931_throughput_class_vals,
+	    val_to_str(tvb_get_guint8(tvb, offset + 2) & 0x1F, q931_throughput_class_vals,
 	      "Unknown (0x%02X)"));
-	proto_tree_add_text(tree, NullTVB, offset + 3, 1,
+	proto_tree_add_text(tree, tvb, offset + 3, 1,
 	    "Minimum outgoing information rate: %s",
-	    val_to_str(pd[offset + 3] & 0x1F, q931_throughput_class_vals,
+	    val_to_str(tvb_get_guint8(tvb, offset + 3) & 0x1F, q931_throughput_class_vals,
 	      "Unknown (0x%02X)"));
 }
 
 static int
-dissect_q931_guint16_value(const u_char *pd, int offset, int len,
+dissect_q931_guint16_value(tvbuff_t *tvb, int offset, int len,
     proto_tree *tree, char *label)
 {
 	guint8 octet;
@@ -1482,7 +1489,7 @@ dissect_q931_guint16_value(const u_char *pd, int offset, int len,
 
 	value_len = 0;
 
-	octet = pd[offset];
+	octet = tvb_get_guint8(tvb, offset);
 	if (octet & Q931_IE_VL_EXTENSION) {
 		/*
 		 * Only one octet long - error.
@@ -1500,7 +1507,7 @@ dissect_q931_guint16_value(const u_char *pd, int offset, int len,
 		 */
 		goto past_end;
 	}
-	octet = pd[offset];
+	octet = tvb_get_guint8(tvb, offset);
 	if (octet & Q931_IE_VL_EXTENSION) {
 		/*
 		 * Only two octets long - error.
@@ -1518,7 +1525,7 @@ dissect_q931_guint16_value(const u_char *pd, int offset, int len,
 		 */
 		goto past_end;
 	}
-	octet = pd[offset];
+	octet = tvb_get_guint8(tvb, offset);
 	if (!(octet & Q931_IE_VL_EXTENSION)) {
 		/*
 		 * More than three octets long - error.
@@ -1530,17 +1537,17 @@ dissect_q931_guint16_value(const u_char *pd, int offset, int len,
 	len -= 1;
 	value_len++;
 
-	proto_tree_add_text(tree, NullTVB, offset, value_len, "%s: %u ms", label,
+	proto_tree_add_text(tree, tvb, offset, value_len, "%s: %u ms", label,
 	    value);
 	return value_len;
 
 past_end:
-	proto_tree_add_text(tree, NullTVB, offset, len,
+	proto_tree_add_text(tree, tvb, offset, len,
 	    "%s goes past end of information element", label);
 	return -1;
 
 bad_length:
-	proto_tree_add_text(tree, NullTVB, offset, len, "%s isn't 3 octets long",
+	proto_tree_add_text(tree, tvb, offset, len, "%s isn't 3 octets long",
 	    label);
 	return -1;
 }
@@ -1549,14 +1556,14 @@ bad_length:
  * Dissect an End-to-end transit delay information element.
  */
 static void
-dissect_q931_e2e_transit_delay_ie(const u_char *pd, int offset, int len,
+dissect_q931_e2e_transit_delay_ie(tvbuff_t *tvb, int offset, int len,
     proto_tree *tree)
 {
 	int value_len;
 
 	if (len == 0)
 		return;
-	value_len = dissect_q931_guint16_value(pd, offset, len, tree,
+	value_len = dissect_q931_guint16_value(tvb, offset, len, tree,
 	    "Cumulative transit delay");
 	if (value_len < 0)
 		return;	/* error */
@@ -1565,7 +1572,7 @@ dissect_q931_e2e_transit_delay_ie(const u_char *pd, int offset, int len,
 
 	if (len == 0)
 		return;
-	value_len = dissect_q931_guint16_value(pd, offset, len, tree,
+	value_len = dissect_q931_guint16_value(tvb, offset, len, tree,
 	    "Requested end-to-end transit delay");
 	if (value_len < 0)
 		return;	/* error */
@@ -1574,7 +1581,7 @@ dissect_q931_e2e_transit_delay_ie(const u_char *pd, int offset, int len,
 
 	if (len == 0)
 		return;
-	value_len = dissect_q931_guint16_value(pd, offset, len, tree,
+	value_len = dissect_q931_guint16_value(tvb, offset, len, tree,
 	    "Maximum end-to-end transit delay");
 }
 
@@ -1582,12 +1589,12 @@ dissect_q931_e2e_transit_delay_ie(const u_char *pd, int offset, int len,
  * Dissect a Transit delay selection and indication information element.
  */
 static void
-dissect_q931_td_selection_and_int_ie(const u_char *pd, int offset, int len,
+dissect_q931_td_selection_and_int_ie(tvbuff_t *tvb, int offset, int len,
     proto_tree *tree)
 {
 	if (len == 0)
 		return;
-	dissect_q931_guint16_value(pd, offset, len, tree,
+	dissect_q931_guint16_value(tvb, offset, len, tree,
 	    "Transit delay");
 }
 
@@ -1603,26 +1610,26 @@ static const value_string q931_fast_selected_vals[] = {
 };
 
 static void
-dissect_q931_pl_binary_parameters_ie(const u_char *pd, int offset, int len,
+dissect_q931_pl_binary_parameters_ie(tvbuff_t *tvb, int offset, int len,
     proto_tree *tree)
 {
 	guint8 octet;
 
 	if (len == 0)
 		return;
-	octet = pd[offset];
-	proto_tree_add_text(tree, NullTVB, offset, 1,
+	octet = tvb_get_guint8(tvb, offset);
+	proto_tree_add_text(tree, tvb, offset, 1,
 	    "Fast select: %s",
 	    val_to_str(octet & 0x18, q931_fast_selected_vals,
 	      NULL));
-	proto_tree_add_text(tree, NullTVB, offset, 1,
+	proto_tree_add_text(tree, tvb, offset, 1,
 	    "%s",
 	    (octet & 0x04) ? "No request/request denied" :
 	    		     "Request indicated/request accepted");
-	proto_tree_add_text(tree, NullTVB, offset, 1,
+	proto_tree_add_text(tree, tvb, offset, 1,
 	    "%s confirmation",
 	    (octet & 0x02) ? "Link-by-link" : "End-to-end");
-	proto_tree_add_text(tree, NullTVB, offset, 1,
+	proto_tree_add_text(tree, tvb, offset, 1,
 	    "Modulus %u sequencing",
 	    (octet & 0x01) ? 8 : 128);
 }
@@ -1631,40 +1638,40 @@ dissect_q931_pl_binary_parameters_ie(const u_char *pd, int offset, int len,
  * Dissect a Packet layer window size information element.
  */
 static void
-dissect_q931_pl_window_size_ie(const u_char *pd, int offset, int len,
+dissect_q931_pl_window_size_ie(tvbuff_t *tvb, int offset, int len,
     proto_tree *tree)
 {
 	if (len == 0)
 		return;
-	proto_tree_add_text(tree, NullTVB, offset, 1,
-	    "Forward value: %u", pd[offset] & 0x7F);
+	proto_tree_add_text(tree, tvb, offset, 1,
+	    "Forward value: %u", tvb_get_guint8(tvb, offset) & 0x7F);
 	offset += 1;
 	len -= 1;
 
 	if (len == 0)
 		return;
-	proto_tree_add_text(tree, NullTVB, offset, 1,
-	    "Backward value: %u", pd[offset] & 0x7F);
+	proto_tree_add_text(tree, tvb, offset, 1,
+	    "Backward value: %u", tvb_get_guint8(tvb, offset) & 0x7F);
 }
 
 /*
  * Dissect a Packet size information element.
  */
 static void
-dissect_q931_packet_size_ie(const u_char *pd, int offset, int len,
+dissect_q931_packet_size_ie(tvbuff_t *tvb, int offset, int len,
     proto_tree *tree)
 {
 	if (len == 0)
 		return;
-	proto_tree_add_text(tree, NullTVB, offset, 1,
-	    "Forward value: %u", pd[offset] & 0x7F);
+	proto_tree_add_text(tree, tvb, offset, 1,
+	    "Forward value: %u", tvb_get_guint8(tvb, offset) & 0x7F);
 	offset += 1;
 	len -= 1;
 
 	if (len == 0)
 		return;
-	proto_tree_add_text(tree, NullTVB, offset, 1,
-	    "Backward value: %u", pd[offset] & 0x7F);
+	proto_tree_add_text(tree, tvb, offset, 1,
+	    "Backward value: %u", tvb_get_guint8(tvb, offset) & 0x7F);
 }
 
 /*
@@ -1677,21 +1684,21 @@ static const value_string q931_cug_indication_vals[] = {
 };
 
 static void
-dissect_q931_cug_ie(const u_char *pd, int offset, int len, proto_tree *tree)
+dissect_q931_cug_ie(tvbuff_t *tvb, int offset, int len, proto_tree *tree)
 {
 	if (len == 0)
 		return;
-	proto_tree_add_text(tree, NullTVB, offset, 1,
+	proto_tree_add_text(tree, tvb, offset, 1,
 	    "CUG indication: %s",
-	    val_to_str(pd[offset] & 0x07, q931_cug_indication_vals,
+	    val_to_str(tvb_get_guint8(tvb, offset) & 0x07, q931_cug_indication_vals,
 	      "Unknown (0x%02X)"));
 	offset += 1;
 	len -= 1;
 
 	if (len == 0)
 		return;
-	proto_tree_add_text(tree, NullTVB, offset, len, "CUG index code: %.*s", len,
-	    &pd[offset]);
+	proto_tree_add_text(tree, tvb, offset, len, "CUG index code: %.*s", len,
+	    tvb_get_ptr(tvb, offset, len));
 }
 
 /*
@@ -1703,14 +1710,14 @@ static const value_string q931_reverse_charging_indication_vals[] = {
 };
 
 static void
-dissect_q931_reverse_charge_ind_ie(const u_char *pd, int offset, int len,
+dissect_q931_reverse_charge_ind_ie(tvbuff_t *tvb, int offset, int len,
     proto_tree *tree)
 {
 	if (len == 0)
 		return;
-	proto_tree_add_text(tree, NullTVB, offset, 1,
+	proto_tree_add_text(tree, tvb, offset, 1,
 	    "Reverse charging indication: %s",
-	    val_to_str(pd[offset] & 0x07, q931_reverse_charging_indication_vals,
+	    val_to_str(tvb_get_guint8(tvb, offset) & 0x07, q931_reverse_charging_indication_vals,
 	      "Unknown (0x%02X)"));
 }
 
@@ -1764,19 +1771,19 @@ static const value_string q931_redirection_reason_vals[] = {
 };
 
 static void
-dissect_q931_number_ie(const u_char *pd, int offset, int len,
+dissect_q931_number_ie(tvbuff_t *tvb, int offset, int len,
     proto_tree *tree)
 {
 	guint8 octet;
 
 	if (len == 0)
 		return;
-	octet = pd[offset];
-	proto_tree_add_text(tree, NullTVB, offset, 1,
+	octet = tvb_get_guint8(tvb, offset);
+	proto_tree_add_text(tree, tvb, offset, 1,
 	    "Type of number: %s",
 	    val_to_str(octet & 0x70, q931_number_type_vals,
 	      "Unknown (0x%02X)"));
-	proto_tree_add_text(tree, NullTVB, offset, 1,
+	proto_tree_add_text(tree, tvb, offset, 1,
 	    "Numbering plan: %s",
 	    val_to_str(octet & 0x0F, q931_numbering_plan_vals,
 	      "Unknown (0x%02X)"));
@@ -1786,12 +1793,12 @@ dissect_q931_number_ie(const u_char *pd, int offset, int len,
 	if (!(octet & Q931_IE_VL_EXTENSION)) {
 		if (len == 0)
 			return;
-		octet = pd[offset];
-		proto_tree_add_text(tree, NullTVB, offset, 1,
+		octet = tvb_get_guint8(tvb, offset);
+		proto_tree_add_text(tree, tvb, offset, 1,
 		    "Presentation indicator: %s",
 		    val_to_str(octet & 0x60, q931_presentation_indicator_vals,
 		      "Unknown (0x%X)"));
-		proto_tree_add_text(tree, NullTVB, offset, 1,
+		proto_tree_add_text(tree, tvb, offset, 1,
 		    "Screening indicator: %s",
 		    val_to_str(octet & 0x03, q931_screening_indicator_vals,
 		      "Unknown (0x%X)"));
@@ -1805,8 +1812,8 @@ dissect_q931_number_ie(const u_char *pd, int offset, int len,
 	if (!(octet & Q931_IE_VL_EXTENSION)) {
 		if (len == 0)
 			return;
-		octet = pd[offset];
-		proto_tree_add_text(tree, NullTVB, offset, 1,
+		octet = tvb_get_guint8(tvb, offset);
+		proto_tree_add_text(tree, tvb, offset, 1,
 		    "Reason for redirection: %s",
 		    val_to_str(octet & 0x0F, q931_redirection_reason_vals,
 		      "Unknown (0x%X)"));
@@ -1816,8 +1823,8 @@ dissect_q931_number_ie(const u_char *pd, int offset, int len,
 
 	if (len == 0)
 		return;
-	proto_tree_add_text(tree, NullTVB, offset, len, "Number: %.*s",
-	    len, &pd[offset]);
+	proto_tree_add_text(tree, tvb, offset, len, "Number: %.*s",
+	    len, tvb_get_ptr(tvb, offset, len));
 }
 
 /*
@@ -1836,19 +1843,19 @@ static const value_string q931_odd_even_indicator_vals[] = {
 };
 
 static void
-dissect_q931_party_subaddr_ie(const u_char *pd, int offset, int len,
+dissect_q931_party_subaddr_ie(tvbuff_t *tvb, int offset, int len,
     proto_tree *tree)
 {
 	guint8 octet;
 
 	if (len == 0)
 		return;
-	octet = pd[offset];
-	proto_tree_add_text(tree, NullTVB, offset, 1,
+	octet = tvb_get_guint8(tvb, offset);
+	proto_tree_add_text(tree, tvb, offset, 1,
 	    "Type of subaddress: %s",
 	    val_to_str(octet & 0x70, q931_subaddress_type_vals,
 	      "Unknown (0x%02X)"));
-	proto_tree_add_text(tree, NullTVB, offset, 1,
+	proto_tree_add_text(tree, tvb, offset, 1,
 	    "Odd/even indicator: %s",
 	    val_to_str(octet & 0x10, q931_odd_even_indicator_vals,
 	      NULL));
@@ -1857,8 +1864,8 @@ dissect_q931_party_subaddr_ie(const u_char *pd, int offset, int len,
 
 	if (len == 0)
 		return;
-	proto_tree_add_text(tree, NullTVB, offset, len, "Subaddress: %s",
-	    bytes_to_str(&pd[offset], len));
+	proto_tree_add_text(tree, tvb, offset, len, "Subaddress: %s",
+	    bytes_to_str(tvb_get_ptr(tvb, offset, len), len));
 }
 
 /*
@@ -1872,17 +1879,17 @@ static const value_string q931_restart_indicator_class_vals[] = {
 };
 
 static void
-dissect_q931_restart_indicator_ie(const u_char *pd, int offset, int len,
+dissect_q931_restart_indicator_ie(tvbuff_t *tvb, int offset, int len,
     proto_tree *tree)
 {
 	if (len != 1) {
-		proto_tree_add_text(tree, NullTVB, offset, len,
+		proto_tree_add_text(tree, tvb, offset, len,
 		    "Restart indicator: length is %d, should be 1\n", len);
 		return;
 	}
-	proto_tree_add_text(tree, NullTVB, offset, 1,
+	proto_tree_add_text(tree, tvb, offset, 1,
 	    "Restart indicator: %s",
-	    val_to_str(pd[offset] & 0x07, q931_restart_indicator_class_vals,
+	    val_to_str(tvb_get_guint8(tvb, offset) & 0x07, q931_restart_indicator_class_vals,
 	      "Unknown (0x%02X)"));
 }
 
@@ -1919,7 +1926,7 @@ static const value_string q931_audiovisual_characteristics_vals[] = {
 };
 
 void
-dissect_q931_high_layer_compat_ie(const u_char *pd, int offset, int len,
+dissect_q931_high_layer_compat_ie(tvbuff_t *tvb, int offset, int len,
     proto_tree *tree)
 {
 	guint8 octet;
@@ -1928,9 +1935,9 @@ dissect_q931_high_layer_compat_ie(const u_char *pd, int offset, int len,
 
 	if (len == 0)
 		return;
-	octet = pd[offset];
+	octet = tvb_get_guint8(tvb, offset);
 	coding_standard = octet & 0x60;
-	proto_tree_add_text(tree, NullTVB, offset, 1,
+	proto_tree_add_text(tree, tvb, offset, 1,
 	    "Coding standard: %s",
 	    val_to_str(coding_standard, q931_coding_standard_vals, NULL));
 	if (coding_standard != Q931_ITU_STANDARDIZED_CODING) {
@@ -1938,16 +1945,17 @@ dissect_q931_high_layer_compat_ie(const u_char *pd, int offset, int len,
 		 * We don't know how the call state is encoded,
 		 * so just dump it as data and be done with it.
 		 */
-		proto_tree_add_text(tree, NullTVB, offset,
-		    len, "Data: %s", bytes_to_str(&pd[offset], len));
+		proto_tree_add_text(tree, tvb, offset,
+		    len, "Data: %s",
+		    bytes_to_str(tvb_get_ptr(tvb, offset, len), len));
 		return;
 	}
 
 	if (len == 0)
 		return;
-	octet = pd[offset];
+	octet = tvb_get_guint8(tvb, offset);
 	characteristics = octet & 0x7F;
-	proto_tree_add_text(tree, NullTVB, offset, 1,
+	proto_tree_add_text(tree, tvb, offset, 1,
 	    "High layer characteristics identification: %s",
 	    val_to_str(characteristics, q931_high_layer_characteristics_vals,
 	      NULL));
@@ -1957,14 +1965,14 @@ dissect_q931_high_layer_compat_ie(const u_char *pd, int offset, int len,
 	if (!(octet & Q931_IE_VL_EXTENSION)) {
 		if (len == 0)
 			return;
-		octet = pd[offset];
+		octet = tvb_get_guint8(tvb, offset);
 		if (characteristics == Q931_AUDIOVISUAL) {
-			proto_tree_add_text(tree, NullTVB, offset, 1,
+			proto_tree_add_text(tree, tvb, offset, 1,
 			    "Extended audiovisual characteristics identification: %s",
 			    val_to_str(octet & 0x7F, q931_audiovisual_characteristics_vals,
 			      NULL));
 		} else {
-			proto_tree_add_text(tree, NullTVB, offset, 1,
+			proto_tree_add_text(tree, tvb, offset, 1,
 			    "Extended high layer characteristics identification: %s",
 			    val_to_str(octet & 0x7F, q931_high_layer_characteristics_vals,
 			      NULL));
@@ -1990,15 +1998,15 @@ static const value_string q931_protocol_discriminator_vals[] = {
 };
 
 static void
-dissect_q931_user_user_ie(const u_char *pd, int offset, int len,
+dissect_q931_user_user_ie(tvbuff_t *tvb, int offset, int len,
     proto_tree *tree)
 {
 	guint8 octet;
 
 	if (len == 0)
 		return;
-	octet = pd[offset];
-	proto_tree_add_text(tree, NullTVB, offset, 1,
+	octet = tvb_get_guint8(tvb, offset);
+	proto_tree_add_text(tree, tvb, offset, 1,
 	    "Protocol discriminator: %s",
 	    val_to_str(octet, q931_protocol_discriminator_vals,
 	    "Unknown (0x%02x)"));
@@ -2010,13 +2018,13 @@ dissect_q931_user_user_ie(const u_char *pd, int offset, int len,
 	switch (octet) {
 
 	case Q931_PROTOCOL_DISCRIMINATOR_IA5:
-		proto_tree_add_text(tree, NullTVB, offset, len, "User information: %.*s",
-		    len, &pd[offset]);
+		proto_tree_add_text(tree, tvb, offset, len, "User information: %.*s",
+		    len, tvb_get_ptr(tvb, offset, len));
 		break;
 
 	default:
-		proto_tree_add_text(tree, NullTVB, offset, len, "User information: %s",
-		    bytes_to_str(&pd[offset], len));
+		proto_tree_add_text(tree, tvb, offset, len, "User information: %s",
+		    bytes_to_str(tvb_get_ptr(tvb, offset, len), len));
 		break;
 	}
 }
@@ -2025,12 +2033,12 @@ dissect_q931_user_user_ie(const u_char *pd, int offset, int len,
  * Dissect information elements consisting of ASCII^H^H^H^H^HIA5 text.
  */
 static void
-dissect_q931_ia5_ie(const u_char *pd, int offset, int len, proto_tree *tree,
+dissect_q931_ia5_ie(tvbuff_t *tvb, int offset, int len, proto_tree *tree,
     char *label)
 {
 	if (len != 0) {
-		proto_tree_add_text(tree, NullTVB, offset, len, "%s: %.*s", label, len,
-		    &pd[offset]);
+		proto_tree_add_text(tree, tvb, offset, len, "%s: %.*s", label, len,
+		    tvb_get_ptr(tvb, offset, len));
 	}
 }
 
@@ -2044,8 +2052,10 @@ static const value_string q931_codeset_vals[] = {
 };
 
 void
-dissect_q931(const u_char *pd, int offset, frame_data *fd, proto_tree *tree)
+dissect_q931(tvbuff_t *tvb, packet_info *pinfo, proto_tree *tree)
 {
+	int		offset = 0;
+	guint		reported_length;
 	proto_tree	*q931_tree = NULL;
 	proto_item	*ti;
 	proto_tree	*ie_tree;
@@ -2057,36 +2067,38 @@ dissect_q931(const u_char *pd, int offset, frame_data *fd, proto_tree *tree)
 	int		codeset;
 	gboolean	non_locking_shift;
 
-	if (check_col(fd, COL_PROTOCOL))
-		col_add_str(fd, COL_PROTOCOL, "Q.931");
+	pinfo->current_proto = "Q.931";
+
+	if (check_col(pinfo->fd, COL_PROTOCOL))
+		col_add_str(pinfo->fd, COL_PROTOCOL, "Q.931");
 
 	if (tree) {
-		ti = proto_tree_add_item(tree, proto_q931, NullTVB, offset,
+		ti = proto_tree_add_item(tree, proto_q931, tvb, offset,
 		    END_OF_FRAME, NULL);
 		q931_tree = proto_item_add_subtree(ti, ett_q931);
 
-		proto_tree_add_item(q931_tree, hf_q931_discriminator, NullTVB, offset, 1, pd[offset]);
+		proto_tree_add_item(q931_tree, hf_q931_discriminator, tvb, offset, 1, tvb_get_guint8(tvb, offset));
 	}
 	offset += 1;
-	call_ref_len = pd[offset] & 0xF;	/* XXX - do as a bit field? */
+	call_ref_len = tvb_get_guint8(tvb, offset) & 0xF;	/* XXX - do as a bit field? */
 	if (q931_tree != NULL)
-		proto_tree_add_item(q931_tree, hf_q931_call_ref_len, NullTVB, offset, 1, call_ref_len);
+		proto_tree_add_item(q931_tree, hf_q931_call_ref_len, tvb, offset, 1, call_ref_len);
 	offset += 1;
 	if (call_ref_len != 0) {
 		/* XXX - split this into flag and value */
-		memcpy(call_ref, &pd[offset], call_ref_len);
+		tvb_memcpy(tvb, call_ref, offset, call_ref_len);
 		if (q931_tree != NULL)
-			proto_tree_add_item(q931_tree, hf_q931_call_ref, NullTVB, offset, call_ref_len, call_ref);
+			proto_tree_add_item(q931_tree, hf_q931_call_ref, tvb, offset, call_ref_len, call_ref);
 		offset += call_ref_len;
 	}
-	message_type = pd[offset];
-	if (check_col(fd, COL_INFO)) {
-		col_add_str(fd, COL_INFO,
+	message_type = tvb_get_guint8(tvb, offset);
+	if (check_col(pinfo->fd, COL_INFO)) {
+		col_add_str(pinfo->fd, COL_INFO,
 		    val_to_str(message_type, q931_message_type_vals,
 		      "Unknown message type (0x%02X)"));
 	}
 	if (q931_tree != NULL)
-		proto_tree_add_item(q931_tree, hf_q931_message_type, NullTVB, offset, 1, message_type);
+		proto_tree_add_item(q931_tree, hf_q931_message_type, tvb, offset, 1, message_type);
 	offset += 1;
 
 	/*
@@ -2094,8 +2106,9 @@ dissect_q931(const u_char *pd, int offset, frame_data *fd, proto_tree *tree)
 	 */
 	codeset = 0;	/* start out in codeset 0 */
 	non_locking_shift = TRUE;
-	while (IS_DATA_IN_FRAME(offset)) {
-		info_element = pd[offset];
+	reported_length = tvb_reported_length(tvb);
+	while (offset < reported_length) {
+		info_element = tvb_get_guint8(tvb, offset);
 
 		/*
 		 * Check for the single-octet IEs.
@@ -2107,7 +2120,7 @@ dissect_q931(const u_char *pd, int offset, frame_data *fd, proto_tree *tree)
 			    !(info_element & Q931_IE_SHIFT_LOCKING);
 			codeset = info_element & Q931_IE_SHIFT_CODESET;
 			if (q931_tree != NULL) {
-				proto_tree_add_text(q931_tree, NullTVB, offset, 1,
+				proto_tree_add_text(q931_tree, tvb, offset, 1,
 				    "%s shift to codeset %u: %s",
 				    (non_locking_shift ? "Non-locking" : "Locking"),
 				    codeset,
@@ -2122,21 +2135,21 @@ dissect_q931(const u_char *pd, int offset, frame_data *fd, proto_tree *tree)
 
 			case Q931_IE_MORE_DATA:
 				if (q931_tree != NULL) {
-					proto_tree_add_text(q931_tree, NullTVB, offset, 1,
+					proto_tree_add_text(q931_tree, tvb, offset, 1,
 					    "More data");
 				}
 				break;
 
 			case Q931_IE_SENDING_COMPLETE:
 				if (q931_tree != NULL) {
-					proto_tree_add_text(q931_tree, NullTVB, offset, 1,
+					proto_tree_add_text(q931_tree, tvb, offset, 1,
 					    "Sending complete");
 				}
 				break;
 
 			default:
 				if (q931_tree != NULL) {
-					proto_tree_add_text(q931_tree, NullTVB, offset, 1,
+					proto_tree_add_text(q931_tree, tvb, offset, 1,
 					    "Unknown information element (0x%02X",
 					    info_element);
 				}
@@ -2149,7 +2162,7 @@ dissect_q931(const u_char *pd, int offset, frame_data *fd, proto_tree *tree)
 
 		case Q931_IE_CONGESTION_LEVEL:
 			if (q931_tree != NULL) {
-				proto_tree_add_text(q931_tree, NullTVB, offset, 1,
+				proto_tree_add_text(q931_tree, tvb, offset, 1,
 				    "Congestion level: %s",
 				    val_to_str(info_element & Q931_IE_SO_IE_MASK,
 				      q931_congestion_level_vals,
@@ -2162,7 +2175,7 @@ dissect_q931(const u_char *pd, int offset, frame_data *fd, proto_tree *tree)
 
 		case Q931_IE_REPEAT_INDICATOR:
 			if (q931_tree != NULL) {
-				proto_tree_add_text(q931_tree, NullTVB, offset, 1,
+				proto_tree_add_text(q931_tree, tvb, offset, 1,
 				    "Repeat indicator: %s",
 				    val_to_str(info_element & Q931_IE_SO_IE_MASK,
 				      q931_repeat_indication_vals,
@@ -2180,162 +2193,159 @@ dissect_q931(const u_char *pd, int offset, frame_data *fd, proto_tree *tree)
 		/*
 		 * Variable-length IE.
 		 */
-		if (!BYTES_ARE_IN_FRAME(offset + 1, 1))
-			break;	/* ran past end of frame */
-		info_element_len = pd[offset + 1];
-		if (!BYTES_ARE_IN_FRAME(offset + 2, info_element_len))
-			break;	/* ran past end of frame */
+		info_element_len = tvb_get_guint8(tvb, offset + 1);
 		if (q931_tree != NULL) {
-			ti = proto_tree_add_text(q931_tree, NullTVB, offset,
+			ti = proto_tree_add_text(q931_tree, tvb, offset,
 			    1+1+info_element_len, "%s",
 			    val_to_str(info_element, q931_info_element_vals,
 			      "Unknown information element (0x%02X)"));
 			ie_tree = proto_item_add_subtree(ti, ett_q931_ie);
-			proto_tree_add_text(ie_tree, NullTVB, offset, 1,
+			proto_tree_add_text(ie_tree, tvb, offset, 1,
 			    "Information element: %s",
 			    val_to_str(info_element, q931_info_element_vals,
 			      "Unknown (0x%02X)"));
-			proto_tree_add_text(ie_tree, NullTVB, offset + 1, 1,
+			proto_tree_add_text(ie_tree, tvb, offset + 1, 1,
 			    "Length: %u", info_element_len);
 
 			switch (info_element) {
 
 			case Q931_IE_SEGMENTED_MESSAGE:
-				dissect_q931_segmented_message_ie(pd,
+				dissect_q931_segmented_message_ie(tvb,
 				    offset + 2, info_element_len, ie_tree);
 				break;
 
 			case Q931_IE_BEARER_CAPABILITY:
 			case Q931_IE_LOW_LAYER_COMPAT:
-				dissect_q931_bearer_capability_ie(pd,
+				dissect_q931_bearer_capability_ie(tvb,
 				    offset + 2, info_element_len, ie_tree);
 				break;
 
 			case Q931_IE_CAUSE:
-				dissect_q931_cause_ie(pd,
+				dissect_q931_cause_ie(tvb,
 				    offset + 2, info_element_len, ie_tree);
 				break;
 
 			case Q931_IE_CALL_STATE:
-				dissect_q931_call_state_ie(pd,
+				dissect_q931_call_state_ie(tvb,
 				    offset + 2, info_element_len, ie_tree);
 				break;
 
 			case Q931_IE_CHANNEL_IDENTIFICATION:
-				dissect_q931_channel_identification_ie(pd,
+				dissect_q931_channel_identification_ie(tvb,
 				    offset + 2, info_element_len, ie_tree);
 				break;
 
 			case Q931_IE_PROGRESS_INDICATOR:
-				dissect_q931_progress_indicator_ie(pd,
+				dissect_q931_progress_indicator_ie(tvb,
 				    offset + 2, info_element_len, ie_tree);
 				break;
 
 			case Q931_IE_NETWORK_SPECIFIC_FACIL:
 			case Q931_IE_TRANSIT_NETWORK_SEL:
-				dissect_q931_ns_facilities_ie(pd,
+				dissect_q931_ns_facilities_ie(tvb,
 				    offset + 2, info_element_len, ie_tree);
 				break;
 
 			case Q931_IE_NOTIFICATION_INDICATOR:
-				dissect_q931_notification_indicator_ie(pd,
+				dissect_q931_notification_indicator_ie(tvb,
 				    offset + 2, info_element_len, ie_tree);
 				break;
 
 			case Q931_IE_DISPLAY:
-				dissect_q931_ia5_ie(pd, offset + 2,
+				dissect_q931_ia5_ie(tvb, offset + 2,
 				    info_element_len, ie_tree,
 				    "Display information");
 				break;
 
 			case Q931_IE_DATE_TIME:
-				dissect_q931_date_time_ie(pd,
+				dissect_q931_date_time_ie(tvb,
 				    offset + 2, info_element_len, ie_tree);
 				break;
 
 			case Q931_IE_KEYPAD_FACILITY:
-				dissect_q931_ia5_ie(pd, offset + 2,
+				dissect_q931_ia5_ie(tvb, offset + 2,
 				    info_element_len, ie_tree,
 				    "Keypad facility");
 				break;
 
 			case Q931_IE_SIGNAL:
-				dissect_q931_signal_ie(pd,
+				dissect_q931_signal_ie(tvb,
 				    offset + 2, info_element_len, ie_tree);
 				break;
 
 			case Q931_IE_INFORMATION_RATE:
-				dissect_q931_information_rate_ie(pd,
+				dissect_q931_information_rate_ie(tvb,
 				    offset + 2, info_element_len, ie_tree);
 				break;
 
 			case Q931_IE_E2E_TRANSIT_DELAY:
-				dissect_q931_e2e_transit_delay_ie(pd,
+				dissect_q931_e2e_transit_delay_ie(tvb,
 				    offset + 2, info_element_len, ie_tree);
 				break;
 
 			case Q931_IE_TD_SELECTION_AND_INT:
-				dissect_q931_td_selection_and_int_ie(pd,
+				dissect_q931_td_selection_and_int_ie(tvb,
 				    offset + 2, info_element_len, ie_tree);
 				break;
 
 			case Q931_IE_PL_BINARY_PARAMETERS:
-				dissect_q931_pl_binary_parameters_ie(pd,
+				dissect_q931_pl_binary_parameters_ie(tvb,
 				    offset + 2, info_element_len, ie_tree);
 				break;
 
 			case Q931_IE_PL_WINDOW_SIZE:
-				dissect_q931_pl_window_size_ie(pd,
+				dissect_q931_pl_window_size_ie(tvb,
 				    offset + 2, info_element_len, ie_tree);
 				break;
 
 			case Q931_IE_PACKET_SIZE:
-				dissect_q931_packet_size_ie(pd,
+				dissect_q931_packet_size_ie(tvb,
 				    offset + 2, info_element_len, ie_tree);
 				break;
 
 			case Q931_IE_CUG:
-				dissect_q931_cug_ie(pd,
+				dissect_q931_cug_ie(tvb,
 				    offset + 2, info_element_len, ie_tree);
 				break;
 
 			case Q931_IE_REVERSE_CHARGE_IND:
-				dissect_q931_reverse_charge_ind_ie(pd,
+				dissect_q931_reverse_charge_ind_ie(tvb,
 				    offset + 2, info_element_len, ie_tree);
 				break;
 
 			case Q931_IE_CALLING_PARTY_NUMBER:
 			case Q931_IE_CALLED_PARTY_NUMBER:
 			case Q931_IE_REDIRECTING_NUMBER:
-				dissect_q931_number_ie(pd,
+				dissect_q931_number_ie(tvb,
 				    offset + 2, info_element_len, ie_tree);
 				break;
 
 			case Q931_IE_CALLING_PARTY_SUBADDR:
 			case Q931_IE_CALLED_PARTY_SUBADDR:
-				dissect_q931_party_subaddr_ie(pd,
+				dissect_q931_party_subaddr_ie(tvb,
 				    offset + 2, info_element_len, ie_tree);
 				break;
 
 			case Q931_IE_RESTART_INDICATOR:
-				dissect_q931_restart_indicator_ie(pd,
+				dissect_q931_restart_indicator_ie(tvb,
 				    offset + 2, info_element_len, ie_tree);
 				break;
 
 			case Q931_IE_HIGH_LAYER_COMPAT:
-				dissect_q931_high_layer_compat_ie(pd,
+				dissect_q931_high_layer_compat_ie(tvb,
 				    offset + 2, info_element_len, ie_tree);
 				break;
 
 			case Q931_IE_USER_USER:
-				dissect_q931_user_user_ie(pd,
+				dissect_q931_user_user_ie(tvb,
 				    offset + 2, info_element_len, ie_tree);
 				break;
 
 			default:
-				proto_tree_add_text(ie_tree, NullTVB, offset + 2,
+				proto_tree_add_text(ie_tree, tvb, offset + 2,
 				    info_element_len, "Data: %s",
-				    bytes_to_str(&pd[offset + 2],
+				    bytes_to_str(
+				      tvb_get_ptr(tvb, offset + 2, info_element_len),
 				      info_element_len));
 				break;
 			}
@@ -2349,30 +2359,30 @@ dissect_q931(const u_char *pd, int offset, frame_data *fd, proto_tree *tree)
 void
 proto_register_q931(void)
 {
-    static hf_register_info hf[] = {
-	{ &hf_q931_discriminator,
-	  { "Protocol discriminator", "q931.disc", FT_UINT8, BASE_HEX, NULL, 0x0, 
-	  	"" }},
-
-	{ &hf_q931_call_ref_len,
-	  { "Call reference value length", "q931.call_ref_len", FT_UINT8, BASE_DEC, NULL, 0x0,
-	  	"" }},
-
-	{ &hf_q931_call_ref,
-	  { "Call reference value", "q931.call_ref", FT_BYTES, BASE_HEX, NULL, 0x0,
-	  	"" }},
-
-	{ &hf_q931_message_type,
-	  { "Message type", "q931.message_type", FT_UINT8, BASE_HEX, VALS(q931_message_type_vals), 0x0,
-	  	"" }},
-
-    };
-    static gint *ett[] = {
-        &ett_q931,
-        &ett_q931_ie,
-    };
-
-    proto_q931 = proto_register_protocol ("Q.931", "q931");
-    proto_register_field_array (proto_q931, hf, array_length(hf));
-    proto_register_subtree_array(ett, array_length(ett));
+	static hf_register_info hf[] = {
+		{ &hf_q931_discriminator,
+		  { "Protocol discriminator", "q931.disc", FT_UINT8, BASE_HEX, NULL, 0x0, 
+		  	"" }},
+
+		{ &hf_q931_call_ref_len,
+		  { "Call reference value length", "q931.call_ref_len", FT_UINT8, BASE_DEC, NULL, 0x0,
+		  	"" }},
+
+		{ &hf_q931_call_ref,
+		  { "Call reference value", "q931.call_ref", FT_BYTES, BASE_HEX, NULL, 0x0,
+		  	"" }},
+
+		{ &hf_q931_message_type,
+		  { "Message type", "q931.message_type", FT_UINT8, BASE_HEX, VALS(q931_message_type_vals), 0x0,
+		  	"" }},
+
+	    };
+	static gint *ett[] = {
+		&ett_q931,
+		&ett_q931_ie,
+	};
+
+	proto_q931 = proto_register_protocol ("Q.931", "q931");
+	proto_register_field_array (proto_q931, hf, array_length(hf));
+	proto_register_subtree_array(ett, array_length(ett));
 }