diff --git a/tunnels/client/http2/http2_client.c b/tunnels/client/http2/http2_client.c
index 14ab1b8f..3abe4632 100644
--- a/tunnels/client/http2/http2_client.c
+++ b/tunnels/client/http2/http2_client.c
@@ -27,7 +27,7 @@ static void sendGrpcFinalData(tunnel_t *self, line_t *line, size_t stream_id)
     self->up->upStream(self->up, endstream_ctx);
 }
 
-static bool trySendRequest(tunnel_t *self, http2_client_con_state_t *con, size_t stream_id, shift_buffer_t *buf)
+static bool trySendRequest(tunnel_t *self, http2_client_con_state_t *con, int32_t stream_id, shift_buffer_t *buf)
 {
     line_t *line = con->line;
 
@@ -71,6 +71,13 @@ static bool trySendRequest(tunnel_t *self, http2_client_con_state_t *con, size_t
         // HTTP2 DATA framehd
         con->state = kH2SendData;
 
+        http2_client_child_con_state_t *stream = nghttp2_session_get_stream_user_data(con->session, stream_id);
+        stream->bytes_sent_nack += bufLen(buf);
+        if (stream->bytes_sent_nack > kMaxSendBeforeAck)
+        {
+            pauseLineDownSide(stream->line);
+        }
+
         // LOGD("HTTP2 SEND_DATA_FRAME_HD...\n");
         if (con->content_type == kApplicationGrpc)
         {
@@ -94,6 +101,7 @@ static bool trySendRequest(tunnel_t *self, http2_client_con_state_t *con, size_t
         framehd.stream_id = stream_id;
         shiftl(buf, HTTP2_FRAME_HDLEN);
         http2FrameHdPack(&framehd, rawBufMut(buf));
+
         context_t *req = newContext(line);
         req->payload   = buf;
         self->up->upStream(self->up, req);
@@ -140,7 +148,7 @@ static void flushWriteQueue(http2_client_con_state_t *con)
 static int onHeaderCallback(nghttp2_session *session, const nghttp2_frame *frame, const uint8_t *name, size_t namelen,
                             const uint8_t *value, size_t valuelen, uint8_t flags, void *userdata)
 {
-    (void) name;
+    // (void) name;
     (void) session;
     (void) namelen;
     (void) value;
@@ -152,7 +160,7 @@ static int onHeaderCallback(nghttp2_session *session, const nghttp2_frame *frame
     }
 
     // LOGD("onHeaderCallback\n");
-    printFrameHd(&frame->hd);
+    // printFrameHd(&frame->hd);
     // const char *name  = (const char *) _name;
     // const char *value = (const char *) _value;
     // LOGD("%s: %s\n", name, value);
@@ -180,6 +188,22 @@ static int onHeaderCallback(nghttp2_session *session, const nghttp2_frame *frame
     //         // req->headers["Host"] = value;
     //     }
     // }
+    http2_client_child_con_state_t *stream = nghttp2_session_get_stream_user_data(session, frame->hd.stream_id);
+    if (stream)
+    {
+        if (strcmp((const char *) name, "grpc-ack") == 0)
+        {
+            const int consumed = atoi((const char *) value);
+            if (stream->bytes_sent_nack > kMaxSendBeforeAck)
+            {
+                stream->bytes_sent_nack -= consumed;
+                if (stream->bytes_sent_nack < kMaxSendBeforeAck / 2)
+                {
+                    resumeLineDownSide(stream->line);
+                }
+            }
+        }
+    }
 
     return 0;
 }
@@ -227,6 +251,18 @@ static int onDataChunkRecvCallback(nghttp2_session *session, uint8_t flags, int3
                 stream->bytes_needed      = 0;
                 context_t *stream_data    = newContext(stream->line);
                 stream_data->payload      = gdata_buf;
+
+                stream->bytes_received_nack += bufLen(gdata_buf);
+                if (stream->bytes_sent_nack >= kMaxRecvBeforeAck)
+                {
+                    nghttp2_nv nvs[1];
+                    char       stri[32];
+                    sprintf(stri, "%d", (int) stream->bytes_sent_nack);
+                    nvs[0] = makeNV("grpc-ack", stri);
+                    nghttp2_submit_headers(con->session, NGHTTP2_FLAG_END_HEADERS, stream_id, NULL, &nvs[0], 1, NULL);
+                    stream->bytes_sent_nack = 0;
+                }
+
                 stream->tunnel->dw->downStream(stream->tunnel->dw, stream_data);
 
                 if (nghttp2_session_get_stream_user_data(session, stream_id))
@@ -244,6 +280,18 @@ static int onDataChunkRecvCallback(nghttp2_session *session, uint8_t flags, int3
         writeRaw(buf, data, len);
         context_t *stream_data = newContext(stream->line);
         stream_data->payload   = buf;
+
+        stream->bytes_received_nack += bufLen(buf);
+        if (stream->bytes_sent_nack >= kMaxRecvBeforeAck)
+        {
+            nghttp2_nv nvs[1];
+            char       stri[32];
+            sprintf(stri, "%d", (int) stream->bytes_sent_nack);
+            nvs[0] = makeNV("grpc-ack", stri);
+            nghttp2_submit_headers(con->session, NGHTTP2_FLAG_END_HEADERS, stream_id, NULL, &nvs[0], 1, NULL);
+            stream->bytes_sent_nack = 0;
+        }
+
         stream->tunnel->dw->downStream(stream->tunnel->dw, stream_data);
     }
 
@@ -510,7 +558,7 @@ tunnel_t *newHttp2Client(node_instance_context_t *instance_info)
 
     for (size_t i = 0; i < workers_count; i++)
     {
-        state->thread_cpool[i] = (thread_connection_pool_t){.round_index = 0, .cons = vec_cons_with_capacity(8)};
+        state->thread_cpool[i] = (thread_connection_pool_t) {.round_index = 0, .cons = vec_cons_with_capacity(8)};
     }
 
     if (! getStringFromJsonObject(&(state->host), settings, "host"))
@@ -557,7 +605,7 @@ api_result_t apiHttp2Client(tunnel_t *self, const char *msg)
 {
     (void) (self);
     (void) (msg);
-    return (api_result_t){0};
+    return (api_result_t) {0};
 }
 
 tunnel_t *destroyHttp2Client(tunnel_t *self)
@@ -568,5 +616,5 @@ tunnel_t *destroyHttp2Client(tunnel_t *self)
 
 tunnel_metadata_t getMetadataHttp2Client(void)
 {
-    return (tunnel_metadata_t){.version = 0001, .flags = 0x0};
+    return (tunnel_metadata_t) {.version = 0001, .flags = 0x0};
 }
diff --git a/tunnels/client/http2/types.h b/tunnels/client/http2/types.h
index 5a3f0e6d..fc07ac82 100644
--- a/tunnels/client/http2/types.h
+++ b/tunnels/client/http2/types.h
@@ -24,16 +24,26 @@ typedef enum
     kH2RecvData,
 } http2_session_state;
 
+enum{
+
+    kMaxRecvBeforeAck = (1 << 16),
+    kMaxSendBeforeAck = (1 << 20)
+};
+
 typedef struct http2_client_child_con_state_s
 {
     struct http2_client_child_con_state_s *prev, *next;
     int32_t                                stream_id;
     nghttp2_stream                        *ng_stream;
     buffer_stream_t                       *chunkbs; // used for grpc
-    size_t                                 bytes_needed;
     tunnel_t                              *tunnel;
     line_t                                *parent;
     line_t                                *line;
+    size_t                                 bytes_needed;
+    size_t                                 bytes_sent_nack;
+    size_t                                 bytes_received_nack;
+
+
 
 } http2_client_child_con_state_t;
 
diff --git a/tunnels/server/http2/helpers.h b/tunnels/server/http2/helpers.h
index 7e0814f6..3cb61d7b 100644
--- a/tunnels/server/http2/helpers.h
+++ b/tunnels/server/http2/helpers.h
@@ -5,7 +5,7 @@
 
 #define kMaxConcurrentStreams 0xffffffffU // NOLINT
 
-static nghttp2_nv makeNv(const char *name, const char *value)
+static nghttp2_nv makeNV(const char *name, const char *value)
 {
     nghttp2_nv nv;
     nv.name     = (uint8_t *) name;
diff --git a/tunnels/server/http2/http2_server.c b/tunnels/server/http2/http2_server.c
index a276a27e..0f0011f7 100644
--- a/tunnels/server/http2/http2_server.c
+++ b/tunnels/server/http2/http2_server.c
@@ -201,12 +201,12 @@ static int onFrameRecvCallback(nghttp2_session *session, const nghttp2_frame *fr
 
     nghttp2_nv nvs[10];
     int        nvlen = 0;
-    nvs[nvlen++]     = makeNv(":status", "200");
+    nvs[nvlen++]     = makeNV(":status", "200");
     if (con->content_type == kApplicationGrpc)
     {
         // correct content_type: application/grpc
-        nvs[nvlen++] = makeNv("content-type", httpContentTypeStr(kApplicationGrpc));
-        nvs[nvlen++] = makeNv("accept-encoding", "identity");
+        nvs[nvlen++] = makeNV("content-type", httpContentTypeStr(kApplicationGrpc));
+        nvs[nvlen++] = makeNV("accept-encoding", "identity");
     }
 
     int flags = NGHTTP2_FLAG_END_HEADERS;
@@ -403,7 +403,7 @@ static void downStream(tunnel_t *self, context_t *c)
             int flags = NGHTTP2_FLAG_END_STREAM | NGHTTP2_FLAG_END_HEADERS;
             if (con->content_type == kApplicationGrpc)
             {
-                nghttp2_nv nv = makeNv("grpc-status", "0");
+                nghttp2_nv nv = makeNV("grpc-status", "0");
                 nghttp2_submit_headers(con->session, flags, stream->stream_id, NULL, &nv, 1, NULL);
             }
             else