diff --git a/README.md b/README.md
index 8fafc23..98f81a1 100644
--- a/README.md
+++ b/README.md
@@ -36,13 +36,14 @@ See [examples](examples/) or [integration testing](src/tests.rs) for basic usage
 ### Server
 
 Most operations are performed on `Stream` and `Sink`. There will be some options in [opts](src/opts.rs).
+The implementation details are obscured, and you can only see a very high level of abstraction, including the `Error` type, which is just `std::io::Error`.
 
 Keep polling `incoming` because it also serves as the router to every connections.
-Apply `Sink::poll_flush` to IO will trigger to flush all pending packets, `ACK`/`NACK`, and stale packets.
-Apply `Sink::poll_close` to IO will ensure that all data is received by the peer before returning (i.e It may keep resending infinitely.).
+Apply `Sink::poll_flush` to IO will trigger to flush all pending packets, `ACK`/`NACK`, and stale packets. So you have to call `poll_flush` periodically. You can configure the [flush strategy](src/opts.rs) you want.
+Apply `Sink::poll_close` to IO will ensure that all data is received by the peer before returning. It may keep resending infinitely unless you cancel the task. So you'd better set a timeout for each `poll_close`.
 
 > [!NOTE]
-> All calculations are lazy. You need to decide how long to flush once, and how long to wait when closing before considering the peer is disconnected.
+> All calculations are lazy. The state will not update if you do not poll it.
 
 ```rust
 use bytes::Bytes;
diff --git a/examples/tracing.rs b/examples/tracing.rs
index 8f2af27..89550e7 100644
--- a/examples/tracing.rs
+++ b/examples/tracing.rs
@@ -177,7 +177,7 @@ fn display(spans: Vec<SpanRecord>) {
         if list.is_empty() {
             continue;
         }
-        println!("{}", trace_id.0);
+        println!("trace_id: {}", trace_id.0);
         let l = &list[&SpanId::default()];
         for (i, root) in l.iter().enumerate() {
             dfs(&list, &spans_map, *root, 0, i == l.len() - 1);
diff --git a/src/client/conn/tokio.rs b/src/client/conn/tokio.rs
index 377f9b5..407b056 100644
--- a/src/client/conn/tokio.rs
+++ b/src/client/conn/tokio.rs
@@ -13,7 +13,7 @@ use crate::client::handler::online::HandleOnline;
 use crate::codec::frame::Framed;
 use crate::codec::{Decoded, Encoded};
 use crate::guard::HandleOutgoing;
-use crate::link::{Router, TransferLink};
+use crate::link::{Route, TransferLink};
 use crate::opts::Ping;
 use crate::state::{IncomingStateManage, OutgoingStateManage};
 use crate::utils::Logged;
@@ -57,10 +57,11 @@ impl ConnectTo for TokioUdpSocket {
             .frame_encoded(peer.mtu, config.codec_config(), Arc::clone(&link))
             .manage_outgoing_state(None);
 
-        let (mut router, route) = Router::new(Arc::clone(&link));
+        let (mut router, route) = Route::new(Arc::clone(&link));
 
         tokio::spawn(async move {
             while let Some(pack) = incoming.next().await {
+                // deliver the packet actively so that we do not miss ACK/NACK packets to advance the outgoing state
                 router.deliver(pack);
             }
         });
diff --git a/src/estimator.rs b/src/estimator.rs
index c9f763a..a04827c 100644
--- a/src/estimator.rs
+++ b/src/estimator.rs
@@ -42,6 +42,9 @@ impl RFC6298Impl {
 
     /// The current RTO estimation.
     pub(crate) fn rto(&self) -> Duration {
+        // TODO:
+        // RFC6298 2.4 suggests a minimum of 1 second, which may be
+        // a conservative choice for some applications.
         cmp::max(
             self.get() + cmp::max(TIMER_GRANULARITY, 4 * self.var),
             Duration::from_secs(1),
diff --git a/src/guard.rs b/src/guard.rs
index b3c0018..16947f4 100644
--- a/src/guard.rs
+++ b/src/guard.rs
@@ -362,6 +362,10 @@ impl ResendMap {
 
     /// `process_stales` collect all stale frames into buffer and remove the expired entries
     fn process_stales(&mut self, buffer: &mut VecDeque<Frame>) {
+        if self.map.is_empty() {
+            return;
+        }
+
         let now = Instant::now();
         if now < self.last_record_expired_at {
             trace!(
@@ -384,6 +388,7 @@ impl ResendMap {
             }
         });
         debug_assert!(min_expired_at > now);
+        // update the last record expired at
         self.last_record_expired_at = min_expired_at;
 
         let len = self.map.len();
diff --git a/src/link.rs b/src/link.rs
index 6f779cb..d6b05f1 100644
--- a/src/link.rs
+++ b/src/link.rs
@@ -19,6 +19,7 @@ pub(crate) type SharedLink = Arc<TransferLink>;
 
 /// Transfer data and task between stream and sink.
 pub(crate) struct TransferLink {
+    // incoming ack with receive timestamp
     incoming_ack: ConcurrentQueue<(AckOrNack, Instant)>,
     incoming_nack: ConcurrentQueue<AckOrNack>,
     forward_waking: AtomicBool,
@@ -98,17 +99,19 @@ impl TransferLink {
                 dropped.total_cnt()
             );
         }
-        // wake up after sends ack
+        // wake up after receiving an ack
         if self.should_waking() {
             let c_id = ConnId::new(self.role.guid(), self.peer.guid);
+            let mut cnt = 0;
             for waker in Reactor::get().cancel_all_timers(c_id) {
                 // safe to panic
                 waker.wake();
-                debug!(
-                    "[{}] wake up a certain waker after receives ack on connection: {c_id:?}",
-                    self.role
-                );
+                cnt += 1;
             }
+            debug!(
+                "[{}] wake up {cnt} wakers after receives ack on connection: {c_id:?}",
+                self.role
+            );
         }
     }
 
@@ -173,14 +176,14 @@ impl TransferLink {
     }
 }
 
-/// Router for incoming packets
-pub(crate) struct Router {
+/// A route for incoming packets
+pub(crate) struct Route {
     router_tx: Sender<FrameSet<FramesMut>>,
     link: SharedLink,
     seq_read: u24,
 }
 
-impl Router {
+impl Route {
     pub(crate) fn new(link: SharedLink) -> (Self, impl Stream<Item = FrameSet<FramesMut>>) {
         let (router_tx, router_rx) = async_channel::unbounded();
         (
@@ -200,7 +203,8 @@ impl Router {
         }
         match pack {
             connected::Packet::FrameSet(frames) => {
-                // TODO: use lock free concurrent queue to avoid lock
+                // TODO: use lock free concurrent queue to buffer the outgoing ack/nack to avoid
+                // locking the mutex
 
                 self.link.outgoing_ack.lock().push(Reverse(frames.seq_num));
 
diff --git a/src/packet/connected/frame_set.rs b/src/packet/connected/frame_set.rs
index 963e735..272ddc1 100644
--- a/src/packet/connected/frame_set.rs
+++ b/src/packet/connected/frame_set.rs
@@ -390,7 +390,8 @@ impl FrameBody {
             }),
             PackType::DisconnectNotification => Ok(Self::DisconnectNotification),
             PackType::DetectLostConnections => Ok(Self::DetectLostConnections),
-            _ => Ok(Self::User(buf)),
+            _ => Ok(Self::User(buf)), /* we rely on the user to handle this even it is not a user
+                                       * packet */
         }
     }
 
diff --git a/src/packet/mod.rs b/src/packet/mod.rs
index 04f5ba7..3d8364a 100644
--- a/src/packet/mod.rs
+++ b/src/packet/mod.rs
@@ -19,9 +19,9 @@ macro_rules! read_buf {
 
 pub(in crate::packet) use read_buf;
 
-const VALID_FLAG: u8 = 0b1000_0000;
-const ACK_FLAG: u8 = 0b1100_0000;
-const NACK_FLAG: u8 = 0b1010_0000;
+const VALID_FLAG: u8 = 0b1000_0000; // A valid user frame
+const ACK_FLAG: u8 = 0b1100_0000;  // A valid user frame which contains an ACK frame
+const NACK_FLAG: u8 = 0b1010_0000; // A valid user frame which contains a NACK frame
 
 const PARTED_FLAG: u8 = 0b0001_0000;
 const CONTINUOUS_SEND_FLAG: u8 = 0b0000_1000;
@@ -38,7 +38,7 @@ pub(crate) const FRAGMENT_PART_SIZE: usize = 10;
 /// others are encapsulated in a `FrameSet` data packet and appear as the first byte of the body
 #[derive(Debug, Clone, Copy, PartialEq, Eq)]
 #[repr(u8)]
-#[allow(dead_code)] // may used in future
+#[allow(dead_code)] // We do not want follow the whole RakNet design
 pub(crate) enum PackType {
     ConnectedPing = 0x00,
     UnconnectedPing1 = 0x01,
@@ -50,6 +50,17 @@ pub(crate) enum PackType {
     OpenConnectionRequest2 = 0x07,
     OpenConnectionReply2 = 0x08,
     ConnectionRequest = 0x09,
+
+    // Some packet related to security, we do not support them now
+    RemoteSystemRequiresPublicKey = 0x0A,
+    OurSystemRequiresSecurity = 0x0B,
+    PublicKeyMismatch = 0x0C,
+    OutOfBandInternal = 0x0D,
+    // Related to `_WITH_ACK_RECEIPT` packets
+    SndReceiptAcked = 0x0E,
+    SndReceiptLoss = 0x0F,
+
+    // User packet types
     ConnectionRequestAccepted = 0x10,
     ConnectionRequestFailed = 0x11,
     AlreadyConnected = 0x12,
@@ -58,6 +69,7 @@ pub(crate) enum PackType {
     DisconnectNotification = 0x15,
     ConnectionLost = 0x16,
     ConnectionBanned = 0x17,
+    InvalidPassword = 0x18,
     IncompatibleProtocolVersion = 0x19,
     IpRecentlyConnected = 0x1a,
     Timestamp = 0x1b,
@@ -85,6 +97,12 @@ impl PackType {
             0x08 => Ok(PackType::OpenConnectionReply2),
             0x09 => Ok(PackType::ConnectionRequest),
             0x10 => Ok(PackType::ConnectionRequestAccepted),
+            0x0A => Ok(PackType::RemoteSystemRequiresPublicKey),
+            0x0B => Ok(PackType::OurSystemRequiresSecurity),
+            0x0C => Ok(PackType::PublicKeyMismatch),
+            0x0D => Ok(PackType::OutOfBandInternal),
+            0x0E => Ok(PackType::SndReceiptAcked),
+            0x0F => Ok(PackType::SndReceiptLoss),
             0x11 => Ok(PackType::ConnectionRequestFailed),
             0x12 => Ok(PackType::AlreadyConnected),
             0x13 => Ok(PackType::NewIncomingConnection),
@@ -92,6 +110,7 @@ impl PackType {
             0x15 => Ok(PackType::DisconnectNotification),
             0x16 => Ok(PackType::ConnectionLost),
             0x17 => Ok(PackType::ConnectionBanned),
+            0x18 => Ok(PackType::InvalidPassword),
             0x19 => Ok(PackType::IncompatibleProtocolVersion),
             0x1a => Ok(PackType::IpRecentlyConnected),
             0x1b => Ok(PackType::Timestamp),
diff --git a/src/server/incoming/tokio.rs b/src/server/incoming/tokio.rs
index 606d093..a0bb9f8 100644
--- a/src/server/incoming/tokio.rs
+++ b/src/server/incoming/tokio.rs
@@ -18,7 +18,7 @@ use super::{Config, MakeIncoming};
 use crate::codec::frame::Framed;
 use crate::codec::{Decoded, Encoded};
 use crate::guard::HandleOutgoing;
-use crate::link::{Router, TransferLink};
+use crate::link::{Route, TransferLink};
 use crate::opts::TraceInfo;
 use crate::server::handler::offline::OfflineHandler;
 use crate::server::handler::online::HandleOnline;
@@ -32,7 +32,7 @@ pin_project! {
         offline: OfflineHandler<Framed<Arc<TokioUdpSocket>>>,
         config: Config,
         socket: Arc<TokioUdpSocket>,
-        routers: HashMap<SocketAddr, Router>,
+        router: HashMap<SocketAddr, Route>,
         close_events: Arc<ConcurrentQueue<SocketAddr>>,
     }
 }
@@ -55,7 +55,7 @@ impl MakeIncoming for TokioUdpSocket {
             ),
             socket,
             config,
-            routers: HashMap::new(),
+            router: HashMap::new(),
             close_events: Arc::new(ConcurrentQueue::unbounded()),
         }
     }
@@ -72,9 +72,10 @@ impl Stream for Incoming {
 
         let role = this.config.server_role();
         for ev in this.close_events.try_iter() {
-            this.routers
+            this.router
                 .remove(&ev)
                 .expect("closed a non-exist connection");
+            // TODO: could we keep the connection alive for a while? 0-RTT handshake?
             this.offline.as_mut().disconnect(&ev);
             debug!("[{role}] connection closed: {ev}");
         }
@@ -83,7 +84,7 @@ impl Stream for Incoming {
             let Some((pack, peer)) = ready!(this.offline.as_mut().poll_next(cx)) else {
                 return Poll::Ready(None);
             };
-            if let Some(entry) = this.routers.get_mut(&peer.addr) {
+            if let Some(entry) = this.router.get_mut(&peer.addr) {
                 if !entry.deliver(pack) {
                     error!("[{role}] connection was dropped before closed");
                 }
@@ -91,9 +92,9 @@ impl Stream for Incoming {
             }
 
             let link = TransferLink::new_arc(role, peer);
-            let (mut entry, route) = Router::new(Arc::clone(&link));
+            let (mut entry, route) = Route::new(Arc::clone(&link));
             entry.deliver(pack);
-            this.routers.insert(peer.addr, entry);
+            this.router.insert(peer.addr, entry);
 
             let dst = Framed::new(Arc::clone(this.socket), this.config.max_mtu as usize)
                 .handle_outgoing(Arc::clone(&link), this.config.send_buf_cap, peer, role)
diff --git a/src/tests.rs b/src/tests.rs
index 0ec33ed..3bbce10 100644
--- a/src/tests.rs
+++ b/src/tests.rs
@@ -9,7 +9,7 @@ use log::info;
 use tokio::net::UdpSocket;
 
 use crate::client::{self, ConnectTo};
-use crate::opts::{FlushStrategy, TraceInfo};
+use crate::opts::FlushStrategy;
 use crate::server::{self, MakeIncoming};
 use crate::utils::tests::test_trace_log_setup;
 use crate::{Message, Reliability};
@@ -60,7 +60,6 @@ async fn test_tokio_udp_works() {
                     tokio::select! {
                         Some(data) = reader.next() => {
                             sender.feed(Message::new(Reliability::Reliable, 0, data)).await.unwrap();
-                            info!("last trace id: {:?}", reader.last_trace_id());
                         }
                         _ = ticker.tick() => {
                             sender.flush().await.unwrap();