Further improve bandwidth estimation for type 2 MTU probe replies.

This patch adds timestamp information to type 2 MTU probe replies. This
timestamp can then be used by the recipient to estimate bandwidth more
accurately, as jitter in the RX direction won't affect the results.

diff --git a/src/net_packet.c b/src/net_packet.c
index d700fd6..1254e48 100644 (file)
--- a/src/net_packet.c
+++ b/src/net_packet.c
@@ -189,6 +189,11 @@ static void mtu_probe_h(node_t *n, vpn_packet_t *packet, length_t len) {
                        uint8_t* data = packet->data;
                        *data++ = 2;
                        uint16_t len16 = htons(len); memcpy(data, &len16, 2); data += 2;
+                       struct timeval now;
+                       gettimeofday(&now, NULL);
+                       uint32_t sec = htonl(now.tv_sec); memcpy(data, &sec, 4); data += 4;
+                       uint32_t usec = htonl(now.tv_usec); memcpy(data, &usec, 4); data += 4;
+                       packet->len = data - packet->data;
                } else {
                        /* Legacy protocol: n won't understand type 2 probe replies. */
                        packet->data[0] = 1;
@@ -244,19 +249,30 @@ static void mtu_probe_h(node_t *n, vpn_packet_t *packet, length_t len) {
                /* Calculate RTT and bandwidth.
                   The RTT is the time between the MTU probe burst was sent and the first
                   reply is received. The bandwidth is measured using the time between the
-                  arrival of the first and third probe reply.
+                  arrival of the first and third probe reply (or type 2 probe requests).
                 */
 
                struct timeval now, diff;
                gettimeofday(&now, NULL);
                timersub(&now, &n->probe_time, &diff);
+
+               struct timeval probe_timestamp = now;
+               if (packet->data[0] == 2 && packet->len >= 11) {
+                       uint32_t sec; memcpy(&sec, packet->data + 3, 4);
+                       uint32_t usec; memcpy(&usec, packet->data + 7, 4);
+                       probe_timestamp.tv_sec = ntohl(sec);
+                       probe_timestamp.tv_usec = ntohl(usec);
+               }
+               
                n->probe_counter++;
 
                if(n->probe_counter == 1) {
                        n->rtt = diff.tv_sec + diff.tv_usec * 1e-6;
-                       n->probe_time = now;
+                       n->probe_time = probe_timestamp;
                } else if(n->probe_counter == 3) {
-                       n->bandwidth = 2.0 * probelen / (diff.tv_sec + diff.tv_usec * 1e-6);
+                       struct timeval probe_timestamp_diff;
+                       timersub(&probe_timestamp, &n->probe_time, &probe_timestamp_diff);
+                       n->bandwidth = 2.0 * probelen / (probe_timestamp_diff.tv_sec + probe_timestamp_diff.tv_usec * 1e-6);
                        logger(DEBUG_TRAFFIC, LOG_DEBUG, "%s (%s) RTT %.2f ms, burst bandwidth %.3f Mbit/s, rx packet loss %.2f %%", n->name, n->hostname, n->rtt * 1e3, n->bandwidth * 8e-6, n->packetloss * 1e2);
                }
        }