diff --git a/architecture.md b/architecture.md
index 762aacd..e635e2a 100644
--- a/architecture.md
+++ b/architecture.md
@@ -126,20 +126,23 @@ Header fields:
 
 | Field | Size | Purpose |
 |---|---|---|
-| `message_type` | 2 bytes | Distinguishes video frame, control request, control response |
-| `channel_id` | 2 bytes | For video: identifies the stream. For control: identifies the request/response pair (correlation ID) |
+| `message_type` | 2 bytes | Determines how the payload is interpreted |
 | `payload_length` | 4 bytes | Byte length of the following payload |
 
-**Message types:**
+The header is intentionally minimal. Any node — including a relay that does not recognise a message type — can skip or forward the frame by reading exactly `payload_length` bytes without needing to understand the payload. All message-specific identifiers (stream ID, correlation ID, etc.) live inside the payload and are handled by the relevant message type handler.
 
-| Value | Meaning |
-|---|---|
-| `0x0001` | Video frame |
-| `0x0002` | Control request |
-| `0x0003` | Control response |
-| `0x0004` | Stream event |
+**Message types and their payload structure:**
 
-Video frame payloads are raw compressed frames. Control payloads are binary-serialized structures — see [Protocol Serialization](#protocol-serialization). Stream events carry lifecycle signals for a channel — see [Device Resilience](#device-resilience).
+| Value | Type | Payload starts with |
+|---|---|---|
+| `0x0001` | Video frame | `stream_id` (u16), then compressed frame data |
+| `0x0002` | Control request | `request_id` (u16), then command-specific fields |
+| `0x0003` | Control response | `request_id` (u16), then result-specific fields |
+| `0x0004` | Stream event | `stream_id` (u16), `event_code` (u8), then event-specific fields |
+
+Node-level messages (not tied to any stream or request) have no prefix beyond the header — the payload begins with the message-specific fields directly.
+
+Control payloads are binary-serialized structures — see [Protocol Serialization](#protocol-serialization). Stream events carry lifecycle signals — see [Device Resilience](#device-resilience).
 
 ### Unified Control and Video on One Connection
 
diff --git a/dev/cli/transport_cli.c b/dev/cli/transport_cli.c
index 18490b2..8bc029b 100644
--- a/dev/cli/transport_cli.c
+++ b/dev/cli/transport_cli.c
@@ -13,8 +13,8 @@ static void server_on_frame(struct Transport_Conn *conn,
 {
 	(void)userdata;
 
-	printf("recv  type=0x%04x channel=%u length=%u",
-		frame->message_type, frame->channel_id, frame->payload_length);
+	printf("recv  type=0x%04x length=%u",
+		frame->message_type, frame->payload_length);
 
 	if (frame->payload_length > 0) {
 		uint32_t show = frame->payload_length < 8 ? frame->payload_length : 8;
@@ -28,7 +28,7 @@ static void server_on_frame(struct Transport_Conn *conn,
 	printf("\n");
 
 	struct App_Error err = transport_send_frame(conn,
-		frame->message_type, frame->channel_id,
+		frame->message_type,
 		frame->payload, frame->payload_length);
 
 	if (!APP_IS_OK(err)) {
@@ -90,8 +90,8 @@ static void client_on_frame(struct Transport_Conn *conn,
 	struct Transport_Frame *frame, void *userdata)
 {
 	(void)conn; (void)userdata;
-	printf("echo  type=0x%04x channel=%u length=%u\n",
-		frame->message_type, frame->channel_id, frame->payload_length);
+	printf("echo  type=0x%04x length=%u\n",
+		frame->message_type, frame->payload_length);
 	free(frame->payload);
 }
 
@@ -123,15 +123,15 @@ static void cmd_client(int argc, char **argv) {
 
 	printf("connected to %s:%u\n", host, port);
 
-	for (uint16_t i = 0; i < 3; i++) {
+	for (int i = 0; i < 3; i++) {
 		uint8_t payload[] = { 0xde, 0xad, 0xbe, 0xef, (uint8_t)i };
-		err = transport_send_frame(conn, 0x0001, i, payload, sizeof(payload));
+		err = transport_send_frame(conn, 0x0001, payload, sizeof(payload));
 		if (!APP_IS_OK(err)) {
-			fprintf(stderr, "send failed on frame %u (errno %d)\n",
+			fprintf(stderr, "send failed on frame %d (errno %d)\n",
 				i, err.detail.syscall.err_no);
 			break;
 		}
-		printf("sent  type=0x0001 channel=%u length=5\n", i);
+		printf("sent  type=0x0001 length=5\n");
 	}
 
 	sleep(1);
diff --git a/include/transport.h b/include/transport.h
index 376505f..03b38b1 100644
--- a/include/transport.h
+++ b/include/transport.h
@@ -3,7 +3,7 @@
 #include <stdint.h>
 #include "error.h"
 
-#define TRANSPORT_FRAME_HEADER_SIZE    8u
+#define TRANSPORT_FRAME_HEADER_SIZE    6u
 #define TRANSPORT_DEFAULT_MAX_PAYLOAD  (16u * 1024u * 1024u)
 
 struct Transport_Conn;
@@ -13,10 +13,13 @@ struct Transport_Server;
  * A received frame. payload is malloc'd by the transport layer;
  * the on_frame callback takes ownership and must free it.
  * payload is NULL when payload_length is 0.
+ *
+ * The header carries only message_type and payload_length.
+ * All message-specific fields (stream_id, request_id, etc.) are
+ * the first bytes of the payload, interpreted by the message handler.
  */
 struct Transport_Frame {
 	uint16_t  message_type;
-	uint16_t  channel_id;
 	uint32_t  payload_length;
 	uint8_t  *payload;
 };
@@ -77,7 +80,6 @@ struct App_Error  transport_connect(struct Transport_Conn **out,
  */
 struct App_Error  transport_send_frame(struct Transport_Conn *conn,
 	uint16_t        message_type,
-	uint16_t        channel_id,
 	const uint8_t  *payload,
 	uint32_t        length);
 
diff --git a/src/modules/transport/transport.c b/src/modules/transport/transport.c
index e57e601..425d134 100644
--- a/src/modules/transport/transport.c
+++ b/src/modules/transport/transport.c
@@ -61,8 +61,7 @@ static void *conn_read_thread_fn(void *arg) {
 
 		struct Transport_Frame frame;
 		frame.message_type   = get_u16(header_buf, 0);
-		frame.channel_id     = get_u16(header_buf, 2);
-		frame.payload_length = get_u32(header_buf, 4);
+		frame.payload_length = get_u32(header_buf, 2);
 
 		if (frame.payload_length > conn->max_payload) {
 			break;
@@ -287,13 +286,12 @@ struct App_Error transport_connect(struct Transport_Conn **out,
 }
 
 struct App_Error transport_send_frame(struct Transport_Conn *conn,
-	uint16_t message_type, uint16_t channel_id,
+	uint16_t message_type,
 	const uint8_t *payload, uint32_t length)
 {
 	uint8_t header[TRANSPORT_FRAME_HEADER_SIZE];
 	put_u16(header, 0, message_type);
-	put_u16(header, 2, channel_id);
-	put_u32(header, 4, length);
+	put_u32(header, 2, length);
 
 	pthread_mutex_lock(&conn->write_mutex);
 	int ok = write_exact(conn->fd, header, TRANSPORT_FRAME_HEADER_SIZE);