diff --git a/adsbus/proto.c b/adsbus/proto.c
index 73e9281..74305c0 100644
--- a/adsbus/proto.c
+++ b/adsbus/proto.c
@@ -1,11 +1,83 @@
+#include <assert.h>
+#include <string.h>
+
 #include "buf.h"
 #include "packet.h"
+#include "server.h"
 
+#include "adsb.pb-c.h"
 #include "proto.h"
 
+#define PROTO_MAGIC "aDsB"
+
+static void proto_obj_to_buf(Adsb *wrapper, struct buf *buf) {
+	assert(!buf->length);
+	assert(adsb__get_packed_size(wrapper) <= BUF_LEN_MAX);
+	buf->length = adsb__pack(wrapper, (uint8_t *) buf_at(buf, 0));
+	assert(buf->length);
+}
+
+static void proto_serialize_packet(struct packet *packet, AdsbPacket *out, size_t len) {
+	out->source_id = (char *) packet->source_id;
+	if (packet->mlat_timestamp) {
+		out->mlat_timestamp = packet->mlat_timestamp;
+		out->has_mlat_timestamp = true;
+	}
+	if (packet->rssi) {
+		out->rssi = packet->rssi;
+		out->has_rssi = true;
+	}
+	out->payload.data = packet->payload;
+	out->payload.len = len;
+}
+
+static void proto_serialize_mode_s_short(struct packet *packet, struct buf *buf) {
+	AdsbPacket packet_out = ADSB_PACKET__INIT;
+	proto_serialize_packet(packet, &packet_out, 7);
+	Adsb wrapper = ADSB__INIT;
+	wrapper.mode_s_short = &packet_out;
+	proto_obj_to_buf(&wrapper, buf);
+}
+
+static void proto_serialize_mode_s_long(struct packet *packet, struct buf *buf) {
+	AdsbPacket packet_out = ADSB_PACKET__INIT;
+	proto_serialize_packet(packet, &packet_out, 14);
+	Adsb wrapper = ADSB__INIT;
+	wrapper.mode_s_short = &packet_out;
+	proto_obj_to_buf(&wrapper, buf);
+}
+
 bool proto_parse(struct buf *buf, struct packet *packet, void *state_in) {
 	return false;
 }
 
 void proto_serialize(struct packet *packet, struct buf *buf) {
+	if (!packet) {
+		AdsbHeader header = ADSB_HEADER__INIT;
+		header.magic = PROTO_MAGIC;
+		header.server_version = server_version;
+		header.server_id = server_id;
+		header.mlat_timestamp_mhz = PACKET_MLAT_MHZ;
+		header.mlat_timestamp_max = PACKET_MLAT_MAX;
+		header.rssi_max = PACKET_RSSI_MAX;
+
+		Adsb wrapper = ADSB__INIT;
+		wrapper.header = &header;
+
+		proto_obj_to_buf(&wrapper, buf);
+		return;
+	}
+
+	switch (packet->type) {
+		case PACKET_TYPE_NONE:
+			break;
+
+		case PACKET_TYPE_MODE_S_SHORT:
+			proto_serialize_mode_s_short(packet, buf);
+			break;
+
+		case PACKET_TYPE_MODE_S_LONG:
+			proto_serialize_mode_s_long(packet, buf);
+			break;
+	}
 }
diff --git a/adsbus/send.c b/adsbus/send.c
index 34ac7fb..d4ea899 100644
--- a/adsbus/send.c
+++ b/adsbus/send.c
@@ -11,6 +11,7 @@
 #include "buf.h"
 #include "json.h"
 #include "peer.h"
+#include "proto.h"
 #include "raw.h"
 #include "stats.h"
 #include "uuid.h"
@@ -43,6 +44,10 @@ struct serializer {
 		.name = "json",
 		.serialize = json_serialize,
 	},
+	{
+		.name = "proto",
+		.serialize = proto_serialize,
+	},
 	{
 		.name = "raw",
 		.serialize = raw_serialize,