diff --git a/trunk/src/app/srs_app_rtc_conn.cpp b/trunk/src/app/srs_app_rtc_conn.cpp
index 3e8f686f8..0cf4e9bd4 100644
--- a/trunk/src/app/srs_app_rtc_conn.cpp
+++ b/trunk/src/app/srs_app_rtc_conn.cpp
@@ -1334,7 +1334,6 @@ SrsRtcServer::SrsRtcServer()
 {
     timer = new SrsHourGlass(this, 1 * SRS_UTIME_SECONDS);
 
-    mmstfd = NULL;
     waiting_msgs = false;
     cond = srs_cond_new();
     trd = new SrsDummyCoroutine();
@@ -1415,6 +1414,9 @@ srs_error_t SrsRtcServer::listen_udp()
             return srs_error_wrap(err, "listen %s:%d", ip.c_str(), port);
         }
 
+        // We will use all FDs to sendmmsg.
+        stfds.push_back(listener->stfd());
+
         srs_trace("rtc listen at udp://%s:%d, fd=%d", ip.c_str(), port, listener->fd());
         listeners.push_back(listener);
     }
@@ -1642,8 +1644,6 @@ mmsghdr* SrsRtcServer::fetch()
 
 void SrsRtcServer::sendmmsg(srs_netfd_t stfd, mmsghdr* /*hdr*/)
 {
-    mmstfd = stfd;
-
     if (waiting_msgs) {
         waiting_msgs = false;
         srs_cond_signal(cond);
@@ -1670,12 +1670,15 @@ srs_error_t SrsRtcServer::cycle()
 
     uint64_t nn_msgs = 0;
     uint64_t nn_msgs_last = 0;
-    uint64_t nn_msgs_max = 0;
-    uint64_t nn_loop = 0;
-    uint64_t nn_wait = 0;
+    int nn_msgs_max = 0;
+    int nn_loop = 0;
+    int nn_wait = 0;
     srs_utime_t time_last = srs_get_system_time();
     SrsStatistic* stat = SrsStatistic::instance();
 
+    // We use FDs to send out messages, by round-trip algorithm.
+    uint32_t fd_index = 0;
+
     SrsPithyPrint* pprint = SrsPithyPrint::create_rtc_send();
     SrsAutoFree(SrsPithyPrint, pprint);
 
@@ -1698,12 +1701,12 @@ srs_error_t SrsRtcServer::cycle()
         cache.swap(hotspot);
         cache_pos = 0;
 
-        mmsghdr* p = &hotspot[0];
-        mmsghdr* end = p + pos;
-        srs_netfd_t stfd = mmstfd;
+        srs_netfd_t stfd = NULL;
+        mmsghdr* p = &hotspot[0]; mmsghdr* end = p + pos;
         for (; p < end; p += max_sendmmsg) {
             int vlen = (int)(end - p);
             vlen = srs_min(max_sendmmsg, vlen);
+            stfd = stfds.at((fd_index++) % stfds.size());
 
             int r0 = srs_sendmmsg(stfd, p, (unsigned int)vlen, 0, SRS_UTIME_NO_TIMEOUT);
             if (r0 != vlen) {
@@ -1719,6 +1722,7 @@ srs_error_t SrsRtcServer::cycle()
 
         pprint->elapse();
         if (pprint->can_print()) {
+            // TODO: FIXME: Extract a PPS calculator.
             int pps_average = 0; int pps_last = 0;
             if (true) {
                 if (srs_get_system_time() > srs_get_system_startup_time()) {
@@ -1736,7 +1740,7 @@ srs_error_t SrsRtcServer::cycle()
                 pps_unit = "(k)"; pps_last /= 10000; pps_average /= 10000;
             }
 
-            srs_trace("-> RTC #%d SEND %d, pps %d/%d%s, schedule %" PRId64 "/%" PRId64 "/%" PRId64 ", sessions %d by sendmmsg %d",
+            srs_trace("-> RTC #%d SEND %d, pps %d/%d%s, schedule %d/%d/%d, sessions %d by sendmmsg %d",
                 srs_netfd_fileno(stfd), pos, pps_average, pps_last, pps_unit.c_str(), nn_loop, nn_wait, nn_msgs_max, (int)map_username_session.size(), max_sendmmsg);
             nn_msgs_last = nn_msgs; time_last = srs_get_system_time();
             nn_loop = nn_wait = nn_msgs_max = 0;
diff --git a/trunk/src/app/srs_app_rtc_conn.hpp b/trunk/src/app/srs_app_rtc_conn.hpp
index e63f2109b..9eb518018 100644
--- a/trunk/src/app/srs_app_rtc_conn.hpp
+++ b/trunk/src/app/srs_app_rtc_conn.hpp
@@ -240,7 +240,7 @@ private:
     srs_cond_t cond;
     bool waiting_msgs;
     // TODO: FIXME: Support multiple stfd.
-    srs_netfd_t mmstfd;
+    std::vector<srs_netfd_t> stfds;
     // Hotspot msgs, we are working on it.
     // @remark We will wait util all messages are ready.
     std::vector<mmsghdr> hotspot;