diff --git a/src/quic_tp.c b/src/quic_tp.c
new file mode 100644
index 0000000..522ff57
--- /dev/null
+++ b/src/quic_tp.c
@@ -0,0 +1,570 @@
+#include <haproxy/global.h>
+#include <haproxy/ncbuf-t.h>
+#include <haproxy/net_helper.h>
+#include <haproxy/quic_enc.h>
+#include <haproxy/quic_tp.h>
+#include <haproxy/xprt_quic-t.h>
+
+#define QUIC_MAX_UDP_PAYLOAD_SIZE     2048
+
+/* This is the values of some QUIC transport parameters when absent.
+ * Should be used to initialize any transport parameters (local or remote)
+ * before updating them with customized values.
+ */
+struct quic_transport_params quic_dflt_transport_params = {
+	.max_udp_payload_size = QUIC_MAX_UDP_PAYLOAD_SIZE,
+	.ack_delay_exponent   = QUIC_DFLT_ACK_DELAY_COMPONENT,
+	.max_ack_delay        = QUIC_DFLT_MAX_ACK_DELAY,
+	.active_connection_id_limit = QUIC_ACTIVE_CONNECTION_ID_LIMIT,
+};
+
+/* Initialize <dst> transport parameters with default values (when absent)
+ * from <quic_dflt_transport_params>.
+ * Never fails.
+ */
+static void quic_dflt_transport_params_cpy(struct quic_transport_params *dst)
+{
+	dst->max_udp_payload_size = quic_dflt_transport_params.max_udp_payload_size;
+	dst->ack_delay_exponent   = quic_dflt_transport_params.ack_delay_exponent;
+	dst->max_ack_delay        = quic_dflt_transport_params.max_ack_delay;
+	dst->active_connection_id_limit = quic_dflt_transport_params.active_connection_id_limit;
+}
+
+/* Initialize <p> transport parameters. <server> is a boolean, set if TPs are
+ * used by a server (haproxy frontend) else this is for a client (haproxy
+ * backend).
+ *
+ * This must only be used for haproxy local parameters. To initialize peer
+ * parameters, see quic_dflt_transport_params_cpy().
+ *
+ * Never fails.
+ */
+void quic_transport_params_init(struct quic_transport_params *p, int server)
+{
+	const uint64_t ncb_size = global.tune.bufsize - NCB_RESERVED_SZ;
+	const int max_streams_bidi = 100;
+	const int max_streams_uni = 3;
+
+	/* Set RFC default values for unspecified parameters. */
+	quic_dflt_transport_params_cpy(p);
+
+	p->max_idle_timeout                    = 30000;
+
+	p->initial_max_streams_bidi            = max_streams_bidi;
+	p->initial_max_streams_uni             = max_streams_uni;
+	p->initial_max_stream_data_bidi_local  = ncb_size;
+	p->initial_max_stream_data_bidi_remote = ncb_size;
+	p->initial_max_stream_data_uni         = ncb_size;
+	p->initial_max_data = (max_streams_bidi + max_streams_uni) * ncb_size;
+
+	if (server)
+		p->with_stateless_reset_token  = 1;
+
+	p->active_connection_id_limit          = 8;
+
+	p->retry_source_connection_id.len = 0;
+}
+
+/* Encode <addr> preferred address transport parameter in <buf> without its
+ * "type+len" prefix. Note that the IP addresses must be encoded in network byte
+ * order.
+ * So ->ipv4_addr and ->ipv6_addr, which are buffers, must contained values
+ * already encoded in network byte order.
+ * It is the responsibility of the caller to check there is enough room in <buf> to encode
+ * this address.
+ * Never fails.
+ */
+static void quic_transport_param_enc_pref_addr_val(unsigned char **buf,
+                                                   const unsigned char *end,
+                                                   struct tp_preferred_address *addr)
+{
+	write_n16(*buf, addr->ipv4_port);
+	*buf += sizeof addr->ipv4_port;
+
+	memcpy(*buf, addr->ipv4_addr, sizeof addr->ipv4_addr);
+	*buf += sizeof addr->ipv4_addr;
+
+	write_n16(*buf, addr->ipv6_port);
+	*buf += sizeof addr->ipv6_port;
+
+	memcpy(*buf, addr->ipv6_addr, sizeof addr->ipv6_addr);
+	*buf += sizeof addr->ipv6_addr;
+
+	*(*buf)++ = addr->cid.len;
+	if (addr->cid.len) {
+		memcpy(*buf, addr->cid.data, addr->cid.len);
+		*buf += addr->cid.len;
+	}
+
+	memcpy(*buf, addr->stateless_reset_token, sizeof addr->stateless_reset_token);
+	*buf += sizeof addr->stateless_reset_token;
+}
+
+/* Decode into <addr> preferred address transport parameter found in <*buf> buffer.
+ * Returns 1 if succeeded, 0 if not.
+ */
+static int quic_transport_param_dec_pref_addr(struct tp_preferred_address *addr,
+                                              const unsigned char **buf,
+                                              const unsigned char *end)
+{
+	ssize_t addr_len;
+
+	addr_len = sizeof addr->ipv4_port + sizeof addr->ipv4_addr;
+	addr_len += sizeof addr->ipv6_port + sizeof addr->ipv6_addr;
+	addr_len += sizeof addr->cid.len;
+
+	if (end - *buf < addr_len)
+		return 0;
+
+	addr->ipv4_port = read_n16(*buf);
+	*buf += sizeof addr->ipv4_port;
+
+	memcpy(addr->ipv4_addr, *buf, sizeof addr->ipv4_addr);
+	*buf += sizeof addr->ipv4_addr;
+
+	addr->ipv6_port = read_n16(*buf);
+	*buf += sizeof addr->ipv6_port;
+
+	memcpy(addr->ipv6_addr, *buf, sizeof addr->ipv6_addr);
+	*buf += sizeof addr->ipv6_addr;
+
+	addr->cid.len = *(*buf)++;
+	if (addr->cid.len) {
+		if (end - *buf > addr->cid.len || addr->cid.len > sizeof addr->cid.data)
+			return 0;
+		memcpy(addr->cid.data, *buf, addr->cid.len);
+		*buf += addr->cid.len;
+	}
+
+	if (end - *buf != sizeof addr->stateless_reset_token)
+		return 0;
+
+	memcpy(addr->stateless_reset_token, *buf, end - *buf);
+	*buf += sizeof addr->stateless_reset_token;
+
+	return *buf == end;
+}
+
+/* Decode into <p> struct a transport parameter found in <*buf> buffer with
+ * <type> as type and <len> as length, depending on <server> boolean value which
+ * must be set to 1 for a server (haproxy listener) or 0 for a client (connection
+ * to an haproxy server).
+ */
+static int quic_transport_param_decode(struct quic_transport_params *p,
+                                       int server, uint64_t type,
+                                       const unsigned char **buf, size_t len)
+{
+	const unsigned char *end = *buf + len;
+
+	switch (type) {
+	case QUIC_TP_ORIGINAL_DESTINATION_CONNECTION_ID:
+		if (!server || len > sizeof p->original_destination_connection_id.data)
+			return 0;
+
+		if (len)
+			memcpy(p->original_destination_connection_id.data, *buf, len);
+		p->original_destination_connection_id.len = len;
+		*buf += len;
+		p->original_destination_connection_id_present = 1;
+		break;
+	case QUIC_TP_INITIAL_SOURCE_CONNECTION_ID:
+		if (len > sizeof p->initial_source_connection_id.data)
+			return 0;
+
+		if (len)
+			memcpy(p->initial_source_connection_id.data, *buf, len);
+		p->initial_source_connection_id.len = len;
+		*buf += len;
+		p->initial_source_connection_id_present = 1;
+		break;
+	case QUIC_TP_STATELESS_RESET_TOKEN:
+		if (!server || len != sizeof p->stateless_reset_token)
+			return 0;
+		memcpy(p->stateless_reset_token, *buf, len);
+		*buf += len;
+		p->with_stateless_reset_token = 1;
+		break;
+	case QUIC_TP_PREFERRED_ADDRESS:
+		if (!server)
+			return 0;
+		if (!quic_transport_param_dec_pref_addr(&p->preferred_address, buf, *buf + len))
+			return 0;
+		p->with_preferred_address = 1;
+		break;
+	case QUIC_TP_MAX_IDLE_TIMEOUT:
+		if (!quic_dec_int(&p->max_idle_timeout, buf, end))
+			return 0;
+		break;
+	case QUIC_TP_MAX_UDP_PAYLOAD_SIZE:
+		if (!quic_dec_int(&p->max_udp_payload_size, buf, end))
+			return 0;
+		break;
+	case QUIC_TP_INITIAL_MAX_DATA:
+		if (!quic_dec_int(&p->initial_max_data, buf, end))
+			return 0;
+		break;
+	case QUIC_TP_INITIAL_MAX_STREAM_DATA_BIDI_LOCAL:
+		if (!quic_dec_int(&p->initial_max_stream_data_bidi_local, buf, end))
+			return 0;
+		break;
+	case QUIC_TP_INITIAL_MAX_STREAM_DATA_BIDI_REMOTE:
+		if (!quic_dec_int(&p->initial_max_stream_data_bidi_remote, buf, end))
+			return 0;
+		break;
+	case QUIC_TP_INITIAL_MAX_STREAM_DATA_UNI:
+		if (!quic_dec_int(&p->initial_max_stream_data_uni, buf, end))
+			return 0;
+		break;
+	case QUIC_TP_INITIAL_MAX_STREAMS_BIDI:
+		if (!quic_dec_int(&p->initial_max_streams_bidi, buf, end))
+			return 0;
+		break;
+	case QUIC_TP_INITIAL_MAX_STREAMS_UNI:
+		if (!quic_dec_int(&p->initial_max_streams_uni, buf, end))
+			return 0;
+		break;
+	case QUIC_TP_ACK_DELAY_EXPONENT:
+		if (!quic_dec_int(&p->ack_delay_exponent, buf, end) ||
+			p->ack_delay_exponent > QUIC_TP_ACK_DELAY_EXPONENT_LIMIT)
+			return 0;
+		break;
+	case QUIC_TP_MAX_ACK_DELAY:
+		if (!quic_dec_int(&p->max_ack_delay, buf, end) ||
+			p->max_ack_delay > QUIC_TP_MAX_ACK_DELAY_LIMIT)
+			return 0;
+		break;
+	case QUIC_TP_DISABLE_ACTIVE_MIGRATION:
+		/* Zero-length parameter type. */
+		if (len != 0)
+			return 0;
+		p->disable_active_migration = 1;
+		break;
+	case QUIC_TP_ACTIVE_CONNECTION_ID_LIMIT:
+		if (!quic_dec_int(&p->active_connection_id_limit, buf, end))
+			return 0;
+		break;
+	default:
+		*buf += len;
+	};
+
+	return *buf == end;
+}
+
+/* Encode <type> and <len> variable length values in <buf>.
+ * Returns 1 if succeeded, 0 if not.
+ */
+static int quic_transport_param_encode_type_len(unsigned char **buf,
+                                                const unsigned char *end,
+                                                uint64_t type, uint64_t len)
+{
+	return quic_enc_int(buf, end, type) && quic_enc_int(buf, end, len);
+}
+
+/* Decode variable length type and length values of a QUIC transport parameter
+ * into <type> and <len> found in <*buf> buffer.
+ * Returns 1 if succeeded, 0 if not.
+ */
+static int quic_transport_param_decode_type_len(uint64_t *type, uint64_t *len,
+                                                const unsigned char **buf,
+                                                const unsigned char *end)
+{
+	return quic_dec_int(type, buf, end) && quic_dec_int(len, buf, end);
+}
+
+/* Encode <param> bytes stream with <type> as type and <length> as length into buf.
+ * Returns 1 if succeeded, 0 if not.
+ */
+static int quic_transport_param_enc_mem(unsigned char **buf, const unsigned char *end,
+                                        uint64_t type, void *param, uint64_t length)
+{
+	if (!quic_transport_param_encode_type_len(buf, end, type, length))
+		return 0;
+
+	if (end - *buf < length)
+		return 0;
+
+	if (length)
+		memcpy(*buf, param, length);
+	*buf += length;
+
+	return 1;
+}
+
+/* Encode <val> 64-bits value as variable length integer into <buf>.
+ * Returns 1 if succeeded, 0 if not.
+ */
+static int quic_transport_param_enc_int(unsigned char **buf,
+                                        const unsigned char *end,
+                                        uint64_t type, uint64_t val)
+{
+	size_t len;
+
+	len = quic_int_getsize(val);
+
+	return len && quic_transport_param_encode_type_len(buf, end, type, len) &&
+		quic_enc_int(buf, end, val);
+}
+
+/* Returns the required length in bytes to encode <cid> QUIC connection ID. */
+static inline size_t sizeof_quic_cid(const struct tp_cid *cid)
+{
+	return sizeof cid->len + cid->len;
+}
+
+/* Encode <addr> preferred address into <buf>.
+ * Note that the IP addresses must be encoded in network byte order.
+ * So ->ipv4_addr and ->ipv6_addr, which are buffers, must contained
+ * values already encoded in network byte order.
+ * Returns 1 if succeeded, 0 if not.
+ */
+static int quic_transport_param_enc_pref_addr(unsigned char **buf,
+                                              const unsigned char *end,
+                                              struct tp_preferred_address *addr)
+{
+	uint64_t addr_len = 0;
+
+	addr_len += sizeof addr->ipv4_port + sizeof addr->ipv4_addr;
+	addr_len += sizeof addr->ipv6_port + sizeof addr->ipv6_addr;
+	addr_len += sizeof_quic_cid(&addr->cid);
+	addr_len += sizeof addr->stateless_reset_token;
+
+	if (!quic_transport_param_encode_type_len(buf, end, QUIC_TP_PREFERRED_ADDRESS, addr_len))
+		return 0;
+
+	if (end - *buf < addr_len)
+		return 0;
+
+	quic_transport_param_enc_pref_addr_val(buf, end, addr);
+
+	return 1;
+}
+
+/* Encode <p> transport parameter into <buf> depending on <server> value which
+ * must be set to 1 for a server (haproxy listener) or 0 for a client
+ * (connection to a haproxy server).
+ * Return the number of bytes consumed if succeeded, 0 if not.
+ */
+int quic_transport_params_encode(unsigned char *buf,
+                                 const unsigned char *end,
+                                 struct quic_transport_params *p,
+                                 int server)
+{
+	unsigned char *head;
+	unsigned char *pos;
+
+	head = pos = buf;
+	if (server) {
+		if (!quic_transport_param_enc_mem(&pos, end,
+		                                  QUIC_TP_ORIGINAL_DESTINATION_CONNECTION_ID,
+		                                  p->original_destination_connection_id.data,
+		                                  p->original_destination_connection_id.len))
+			return 0;
+
+		if (p->retry_source_connection_id.len) {
+			if (!quic_transport_param_enc_mem(&pos, end,
+			                                  QUIC_TP_RETRY_SOURCE_CONNECTION_ID,
+			                                  p->retry_source_connection_id.data,
+			                                  p->retry_source_connection_id.len))
+				return 0;
+		}
+
+		if (p->with_stateless_reset_token &&
+			!quic_transport_param_enc_mem(&pos, end, QUIC_TP_STATELESS_RESET_TOKEN,
+			                              p->stateless_reset_token,
+			                              sizeof p->stateless_reset_token))
+			return 0;
+		if (p->with_preferred_address &&
+			!quic_transport_param_enc_pref_addr(&pos, end, &p->preferred_address))
+			return 0;
+	}
+
+	if (!quic_transport_param_enc_mem(&pos, end,
+	                                  QUIC_TP_INITIAL_SOURCE_CONNECTION_ID,
+	                                  p->initial_source_connection_id.data,
+	                                  p->initial_source_connection_id.len))
+		return 0;
+
+	if (p->max_idle_timeout &&
+	    !quic_transport_param_enc_int(&pos, end, QUIC_TP_MAX_IDLE_TIMEOUT, p->max_idle_timeout))
+		return 0;
+
+	/*
+	 * "max_packet_size" transport parameter must be transmitted only if different
+	 * of the default value.
+	 */
+	if (p->max_udp_payload_size != QUIC_DFLT_MAX_UDP_PAYLOAD_SIZE &&
+	    !quic_transport_param_enc_int(&pos, end, QUIC_TP_MAX_UDP_PAYLOAD_SIZE, p->max_udp_payload_size))
+		return 0;
+
+	if (p->initial_max_data &&
+	    !quic_transport_param_enc_int(&pos, end, QUIC_TP_INITIAL_MAX_DATA, p->initial_max_data))
+	    return 0;
+
+	if (p->initial_max_stream_data_bidi_local &&
+	    !quic_transport_param_enc_int(&pos, end, QUIC_TP_INITIAL_MAX_STREAM_DATA_BIDI_LOCAL,
+	                                          p->initial_max_stream_data_bidi_local))
+	    return 0;
+
+	if (p->initial_max_stream_data_bidi_remote &&
+	    !quic_transport_param_enc_int(&pos, end, QUIC_TP_INITIAL_MAX_STREAM_DATA_BIDI_REMOTE,
+	                                          p->initial_max_stream_data_bidi_remote))
+	    return 0;
+
+	if (p->initial_max_stream_data_uni &&
+	    !quic_transport_param_enc_int(&pos, end, QUIC_TP_INITIAL_MAX_STREAM_DATA_UNI,
+	                                          p->initial_max_stream_data_uni))
+	    return 0;
+
+	if (p->initial_max_streams_bidi &&
+	    !quic_transport_param_enc_int(&pos, end, QUIC_TP_INITIAL_MAX_STREAMS_BIDI,
+	                                          p->initial_max_streams_bidi))
+	    return 0;
+
+	if (p->initial_max_streams_uni &&
+	    !quic_transport_param_enc_int(&pos, end, QUIC_TP_INITIAL_MAX_STREAMS_UNI,
+	                                          p->initial_max_streams_uni))
+	    return 0;
+
+	/*
+	 * "ack_delay_exponent" transport parameter must be transmitted only if different
+	 * of the default value.
+	 */
+	if (p->ack_delay_exponent != QUIC_DFLT_ACK_DELAY_COMPONENT  &&
+	    !quic_transport_param_enc_int(&pos, end, QUIC_TP_ACK_DELAY_EXPONENT, p->ack_delay_exponent))
+	    return 0;
+
+	/*
+	 * "max_ack_delay" transport parameter must be transmitted only if different
+	 * of the default value.
+	 */
+	if (p->max_ack_delay != QUIC_DFLT_MAX_ACK_DELAY &&
+	    !quic_transport_param_enc_int(&pos, end, QUIC_TP_MAX_ACK_DELAY, p->max_ack_delay))
+	    return 0;
+
+	/* 0-length value */
+	if (p->disable_active_migration &&
+	    !quic_transport_param_encode_type_len(&pos, end, QUIC_TP_DISABLE_ACTIVE_MIGRATION, 0))
+		return 0;
+
+	if (p->active_connection_id_limit &&
+	    p->active_connection_id_limit != QUIC_ACTIVE_CONNECTION_ID_LIMIT &&
+	    !quic_transport_param_enc_int(&pos, end, QUIC_TP_ACTIVE_CONNECTION_ID_LIMIT,
+	                                  p->active_connection_id_limit))
+	    return 0;
+
+	return pos - head;
+}
+
+/* Decode transport parameters found in <buf> buffer into <p>, depending on
+ * <server> boolean value which must be set to 1 for a server (haproxy listener)
+ * or 0 for a client (connection to a haproxy server).
+ * Returns 1 if succeeded, 0 if not.
+ */
+static int quic_transport_params_decode(struct quic_transport_params *p, int server,
+                                        const unsigned char *buf,
+                                        const unsigned char *end)
+{
+	const unsigned char *pos;
+
+	pos = buf;
+
+	while (pos != end) {
+		uint64_t type, len;
+
+		if (!quic_transport_param_decode_type_len(&type, &len, &pos, end))
+			return 0;
+
+		if (end - pos < len)
+			return 0;
+
+		if (!quic_transport_param_decode(p, server, type, &pos, len))
+			return 0;
+	}
+
+	/*
+	 * A server MUST send original_destination_connection_id transport parameter.
+	 * initial_source_connection_id must be present both for server and client.
+	 */
+	if ((server && !p->original_destination_connection_id_present) ||
+	    !p->initial_source_connection_id_present)
+		return 0;
+
+	return 1;
+}
+
+/* Store transport parameters found in <buf> buffer into <qc> QUIC connection
+ * depending on <server> value which must be 1 for a server (haproxy listener)
+ * or 0 for a client (connection to a haproxy server).
+ * Note that peer transport parameters are stored in the TX part of the connection:
+ * they are used to send packets to the peer with its transport parameters as
+ * limitations.
+ * Returns 1 if succeeded, 0 if not.
+ */
+int quic_transport_params_store(struct quic_conn *qc, int server,
+                                const unsigned char *buf,
+                                const unsigned char *end)
+{
+	struct quic_transport_params *tx_params = &qc->tx.params;
+	struct quic_transport_params *rx_params = &qc->rx.params;
+
+	/* initialize peer TPs to RFC default value */
+	quic_dflt_transport_params_cpy(tx_params);
+
+	if (!quic_transport_params_decode(tx_params, server, buf, end))
+		return 0;
+
+	if (tx_params->max_ack_delay)
+		qc->max_ack_delay = tx_params->max_ack_delay;
+
+	if (tx_params->max_idle_timeout && rx_params->max_idle_timeout)
+		qc->max_idle_timeout =
+			QUIC_MIN(tx_params->max_idle_timeout, rx_params->max_idle_timeout);
+	else
+		qc->max_idle_timeout =
+			QUIC_MAX(tx_params->max_idle_timeout, rx_params->max_idle_timeout);
+
+	return 1;
+}
+
+/* QUIC server (or haproxy listener) only function.
+ * Initialize the local transport parameters <rx_params> from <listener_params>
+ * coming from configuration and Initial packet information (destintation
+ * connection ID, source connection ID, original destination connection ID,
+ * and if a token was present denoted by <token> boolean value.
+ * Returns 1 if succeeded, 0 if not.
+ */
+int qc_lstnr_params_init(struct quic_conn *qc,
+                         const struct quic_transport_params *listener_params,
+                         const unsigned char *stateless_reset_token,
+                         const unsigned char *dcid, size_t dcidlen,
+                         const unsigned char *scid, size_t scidlen,
+                         const unsigned char *odcid, size_t odcidlen, int token)
+{
+	struct quic_transport_params *rx_params = &qc->rx.params;
+	struct tp_cid *odcid_param = &rx_params->original_destination_connection_id;
+
+	/* Copy the transport parameters. */
+	*rx_params = *listener_params;
+	/* Copy the stateless reset token */
+	memcpy(rx_params->stateless_reset_token, stateless_reset_token,
+	       sizeof rx_params->stateless_reset_token);
+	/* Copy original_destination_connection_id transport parameter. */
+	if (token) {
+		memcpy(odcid_param->data, odcid, odcidlen);
+		odcid_param->len = odcidlen;
+		/* Copy retry_source_connection_id transport parameter. */
+		memcpy(rx_params->retry_source_connection_id.data, dcid, dcidlen);
+		rx_params->retry_source_connection_id.len = dcidlen;
+	}
+	else {
+		memcpy(odcid_param->data, dcid, dcidlen);
+		odcid_param->len = dcidlen;
+	}
+
+	/* Copy the initial source connection ID. */
+	memcpy(rx_params->initial_source_connection_id.data, scid, scidlen);
+	rx_params->initial_source_connection_id.len = scidlen;
+
+	return 1;
+}
+