Index: uspace/srv/net/tcp/Makefile
===================================================================
--- uspace/srv/net/tcp/Makefile	(revision b33d140f53df46bff63409f9e614b46f85b8db6f)
+++ uspace/srv/net/tcp/Makefile	(revision 868b0e91e9888be12b528f09fbdf09945369c5cd)
@@ -51,3 +51,10 @@
 	ucall.c
 
+TEST_SOURCES = \
+	pdu.c \
+	segment.c \
+	seq_no.c \
+	test/main.c \
+	test/pdu.c
+
 include $(USPACE_PREFIX)/Makefile.common
Index: uspace/srv/net/tcp/segment.c
===================================================================
--- uspace/srv/net/tcp/segment.c	(revision b33d140f53df46bff63409f9e614b46f85b8db6f)
+++ uspace/srv/net/tcp/segment.c	(revision 868b0e91e9888be12b528f09fbdf09945369c5cd)
@@ -43,5 +43,5 @@
 
 /** Alocate new segment structure. */
-tcp_segment_t *tcp_segment_new(void)
+static tcp_segment_t *tcp_segment_new(void)
 {
 	return calloc(1, sizeof(tcp_segment_t));
Index: uspace/srv/net/tcp/segment.h
===================================================================
--- uspace/srv/net/tcp/segment.h	(revision b33d140f53df46bff63409f9e614b46f85b8db6f)
+++ uspace/srv/net/tcp/segment.h	(revision 868b0e91e9888be12b528f09fbdf09945369c5cd)
@@ -40,5 +40,4 @@
 #include "tcp_type.h"
 
-extern tcp_segment_t *tcp_segment_new(void);
 extern void tcp_segment_delete(tcp_segment_t *);
 extern tcp_segment_t *tcp_segment_dup(tcp_segment_t *);
Index: uspace/srv/net/tcp/test/main.c
===================================================================
--- uspace/srv/net/tcp/test/main.c	(revision 868b0e91e9888be12b528f09fbdf09945369c5cd)
+++ uspace/srv/net/tcp/test/main.c	(revision 868b0e91e9888be12b528f09fbdf09945369c5cd)
@@ -0,0 +1,35 @@
+/*
+ * Copyright (c) 2017 Jiri Svobda
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ *
+ * - Redistributions of source code must retain the above copyright
+ *   notice, this list of conditions and the following disclaimer.
+ * - Redistributions in binary form must reproduce the above copyright
+ *   notice, this list of conditions and the following disclaimer in the
+ *   documentation and/or other materials provided with the distribution.
+ * - The name of the author may not be used to endorse or promote products
+ *   derived from this software without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
+ * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
+ * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
+ * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
+ * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
+ * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+ * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+ * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+ * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
+ * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#include <pcut/pcut.h>
+
+PCUT_INIT
+
+PCUT_IMPORT(pdu);
+
+PCUT_MAIN()
Index: uspace/srv/net/tcp/test/pdu.c
===================================================================
--- uspace/srv/net/tcp/test/pdu.c	(revision 868b0e91e9888be12b528f09fbdf09945369c5cd)
+++ uspace/srv/net/tcp/test/pdu.c	(revision 868b0e91e9888be12b528f09fbdf09945369c5cd)
@@ -0,0 +1,131 @@
+/*
+ * Copyright (c) 2017 Jiri Svoboda
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ *
+ * - Redistributions of source code must retain the above copyright
+ *   notice, this list of conditions and the following disclaimer.
+ * - Redistributions in binary form must reproduce the above copyright
+ *   notice, this list of conditions and the following disclaimer in the
+ *   documentation and/or other materials provided with the distribution.
+ * - The name of the author may not be used to endorse or promote products
+ *   derived from this software without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
+ * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
+ * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
+ * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
+ * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
+ * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+ * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+ * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+ * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
+ * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#include <errno.h>
+#include <inet/endpoint.h>
+#include <pcut/pcut.h>
+#include <str.h>
+#include <stdlib.h>
+
+#include "../pdu.h"
+#include "../segment.h"
+
+/** Verify that two segments have the same content */
+static void pdu_seg_cmp(tcp_segment_t *a, tcp_segment_t *b)
+{
+	PCUT_ASSERT_INT_EQUALS(a->ctrl, b->ctrl);
+	PCUT_ASSERT_INT_EQUALS(a->seq, b->seq);
+	PCUT_ASSERT_INT_EQUALS(a->ack, b->ack);
+	PCUT_ASSERT_INT_EQUALS(a->len, b->len);
+	PCUT_ASSERT_INT_EQUALS(a->wnd, b->wnd);
+	PCUT_ASSERT_INT_EQUALS(a->up, b->up);
+	PCUT_ASSERT_INT_EQUALS(tcp_segment_text_size(a),
+	    tcp_segment_text_size(b));
+	if (tcp_segment_text_size(a) != 0)
+		PCUT_ASSERT_NOT_NULL(a->data);
+	if (tcp_segment_text_size(b) != 0)
+		PCUT_ASSERT_NOT_NULL(b->data);
+	if (tcp_segment_text_size(a) != 0) {
+		PCUT_ASSERT_INT_EQUALS(0, memcmp(a->data, b->data,
+		    tcp_segment_text_size(a)));
+	}
+}
+
+PCUT_INIT
+
+PCUT_TEST_SUITE(pdu);
+
+/** Test encode/decode round trip for control PDU */
+PCUT_TEST(encdec_syn)
+{
+	tcp_segment_t *seg, *dseg;
+	tcp_pdu_t *pdu;
+	inet_ep2_t epp, depp;
+	int rc;
+
+	inet_ep2_init(&epp);
+	inet_addr(&epp.local.addr, 1, 2, 3, 4);
+	inet_addr(&epp.remote.addr, 5, 6, 7, 8);
+
+	seg = tcp_segment_make_ctrl(CTL_SYN);
+	PCUT_ASSERT_NOT_NULL(seg);
+
+	seg->seq = 20;
+	seg->ack = 19;
+	seg->wnd = 18;
+	seg->up = 17;
+
+	rc = tcp_pdu_encode(&epp, seg, &pdu);
+	PCUT_ASSERT_INT_EQUALS(EOK, rc);
+	rc = tcp_pdu_decode(pdu, &depp, &dseg);
+	PCUT_ASSERT_INT_EQUALS(EOK, rc);
+
+	pdu_seg_cmp(seg, dseg);
+	tcp_segment_delete(seg);
+}
+
+/** Test encode/decode round trip for data PDU */
+PCUT_TEST(encdec_data)
+{
+	tcp_segment_t *seg, *dseg;
+	tcp_pdu_t *pdu;
+	inet_ep2_t epp, depp;
+	uint8_t *data;
+	size_t i, dsize;
+	int rc;
+
+	inet_ep2_init(&epp);
+	inet_addr(&epp.local.addr, 1, 2, 3, 4);
+	inet_addr(&epp.remote.addr, 5, 6, 7, 8);
+
+	dsize = 15;
+	data = malloc(dsize);
+	PCUT_ASSERT_NOT_NULL(data);
+
+	for (i = 0; i < dsize; i++)
+		data[i] = (uint8_t) i;
+
+	seg = tcp_segment_make_data(CTL_SYN, data, dsize);
+	PCUT_ASSERT_NOT_NULL(seg);
+
+	seg->seq = 20;
+	seg->ack = 19;
+	seg->wnd = 18;
+	seg->up = 17;
+
+	rc = tcp_pdu_encode(&epp, seg, &pdu);
+	PCUT_ASSERT_INT_EQUALS(EOK, rc);
+	rc = tcp_pdu_decode(pdu, &depp, &dseg);
+	PCUT_ASSERT_INT_EQUALS(EOK, rc);
+
+	pdu_seg_cmp(seg, dseg);
+	tcp_segment_delete(seg);
+	free(data);
+}
+
+PCUT_EXPORT(pdu);
