diff --git a/tests/test_etcp_bbr.c b/tests/test_etcp_bbr.c
index 17e6fdb8..91b09337 100644
--- a/tests/test_etcp_bbr.c
+++ b/tests/test_etcp_bbr.c
@@ -2,6 +2,7 @@
 #include <string.h>
 #include <stdio.h>
 #include <stdlib.h>
+#include "../lib/debug_config.h"
 
 #define MSEG(s) do { test_total++; printf("TEST %d: %-50s ", test_total, s); fflush(stdout); } while(0)
 #define PASS()  do { puts("PASS"); test_passed++; } while(0)
@@ -34,6 +35,26 @@ static uint32_t run_ack(struct bbr* bbr, uint32_t acked, uint32_t rtt_us,
 
 /* --- tests --- */
 
+/* Одинаковая доставка байтов обязана давать одну скорость независимо от MTU. */
+static int test_byte_rate(void) {
+    MSEG("byte rate and BDP are independent of MSS");
+    const uint32_t sizes[] = {576, 1400};
+    for (unsigned i = 0; i < sizeof(sizes)/sizeof(sizes[0]); i++) {
+        struct bbr s = { .now_tb = 10000 }; bbr_init(&s);
+        s.mode = BBR_PROBE_BW; s.full_bw_reached = 1; s.cycle_idx = BBR_BW_PROBE_CRUISE;
+        s.cycle_mstamp_tb = s.now_tb; s.probe_wait_us = 2000000;
+        uint32_t cwnd = 100000, pacing = 0;
+        struct bbr_rate_sample rs = { .delivered = 10000, .interval_us = 10000, .rtt_us = 20000,
+            .acked_sacked = 1000, .tx_in_flight = 40000 };
+        bbr_main(&s, &rs, &cwnd, &pacing, sizes[i], 40000, 0);
+        DEBUG_INFO(DEBUG_CATEGORY_DEBUG, "BBR byte sample: MSS=%u delivered=10000 interval_us=10000 pace=%u cwnd=%u",
+            sizes[i], pacing, cwnd);
+        if (pacing != 990000) FAIL("1MB/s delivery must produce 990000B/s cruise pacing");
+        if (cwnd < 40000 || cwnd > 41000) FAIL("2*BDP plus ACK aggregation must be 40000..41000 bytes");
+    }
+    PASS(); return 0;
+}
+
 static int test_init(void)
 {
     MSEG("bbr_init — startup mode");
@@ -148,6 +169,8 @@ static int test_probe_rtt(void)
 
 int main(void)
 {
+    debug_config_init(); debug_set_level(DEBUG_LEVEL_ERROR); debug_set_category_level(DEBUG_CATEGORY_DEBUG, DEBUG_LEVEL_INFO);
+    test_byte_rate();
     test_init();
     test_startup_growth();
     test_full_bw();