diff --git a/libsponge/tcp_sender.cc b/libsponge/tcp_sender.cc
index eeff693..03c4f1a 100644
--- a/libsponge/tcp_sender.cc
+++ b/libsponge/tcp_sender.cc
@@ -20,9 +20,8 @@ using namespace std;
 TCPSender::TCPSender(const size_t capacity, const uint16_t retx_timeout, const std::optional<WrappingInt32> fixed_isn)
     : _isn(fixed_isn.value_or(WrappingInt32{random_device()()}))
     , _initial_retransmission_timeout{retx_timeout}
-    , _stream(capacity) {
-    _timer.reinit(_initial_retransmission_timeout);
-}
+    , _stream(capacity)
+    , _timer(retx_timeout) {}
 
 uint64_t TCPSender::bytes_in_flight() const { return _next_seqno - _unack_seqno; }
 
@@ -50,6 +49,7 @@ void TCPSender::fill_window() {
             _next_seqno += seg.length_in_sequence_space();
             hdr.syn = false;
             hdr.seqno = next_seqno();
+            _timer.start();
             if (sendptr >= data.size())
                 break;
             payload = data.substr(sendptr, TCPConfig::MAX_PAYLOAD_SIZE);
@@ -65,8 +65,8 @@ void TCPSender::fill_window() {
         _segments_out.push(seg);
         _outstandings.push(seg);
         _next_seqno += seg.length_in_sequence_space();
+        _timer.start();
     }
-    _timer.start();
 }
 
 //! \param ackno The remote receiver's ackno (acknowledgment number)
@@ -81,7 +81,7 @@ void TCPSender::ack_received(const WrappingInt32 ackno, const uint16_t window_si
         if (abs_ackno >= _unack_seqno + _outstandings.front().length_in_sequence_space()) {
             _unack_seqno += _outstandings.front().length_in_sequence_space();
             _outstandings.pop();
-            _timer.reinit(_initial_retransmission_timeout);
+            _timer.reset_init(_initial_retransmission_timeout);
         } else {
             break;
         }
@@ -95,18 +95,19 @@ void TCPSender::ack_received(const WrappingInt32 ackno, const uint16_t window_si
 
 //! \param[in] ms_since_last_tick the number of milliseconds since the last call to this method
 void TCPSender::tick(const size_t ms_since_last_tick) {
-    if (!_timer.started())
+    if (!_timer.is_started())
         return;
-    _timer.count_down(ms_since_last_tick);
-    if (!_timer.expired())
+    _timer.tick(ms_since_last_tick);
+    if (!_timer.is_expired())
         return;
     _segments_out.push(_outstandings.front());
     if (_window_size > 0)
-        _timer.consec_retrans();
+        _timer.retransmit();
     _timer.reset();
+    _timer.start();
 }
 
-unsigned int TCPSender::consecutive_retransmissions() const { return _timer.consec_retrans_count(); }
+unsigned int TCPSender::consecutive_retransmissions() const { return _timer.consecutive_retransmissions(); }
 
 void TCPSender::send_empty_segment() {
     TCPHeader hdr;
diff --git a/libsponge/tcp_sender.hh b/libsponge/tcp_sender.hh
index d878aff..a4b5abf 100644
--- a/libsponge/tcp_sender.hh
+++ b/libsponge/tcp_sender.hh
@@ -14,36 +14,39 @@
 //! God knows what this class does
 class TCPTimer {
   private:
-    size_t RTO{0};
-    size_t rt_count{0};
-    size_t ti_count{0};
-    bool timer_on{false};
+    size_t RTO;
+    size_t _cr_count{0};
+    size_t _ti_count;
+    bool _is_started{false};
 
   public:
-    TCPTimer() = default;
-    void reinit(uint32_t initial_RTO) {
-        RTO = initial_RTO;
-        ti_count = RTO;
-        rt_count = 0;
-        timer_on = false;
+    TCPTimer(uint32_t initial_retransmission_timeout)
+        : RTO(initial_retransmission_timeout), _ti_count(initial_retransmission_timeout) {}
+    void reset_init(uint32_t initial_retransmission_timeout) {
+        RTO = initial_retransmission_timeout;
+        _ti_count = RTO;
+        _cr_count = 0;
+        _is_started = false;
     }
-    void reset() { ti_count = RTO; }
-    size_t cur_RTO() const { return RTO; }
-    void start() { timer_on = true; }
-    bool started() const { return timer_on; }
-    void stop() { timer_on = false; }
-    bool expired() const { return ti_count == 0; }
-    void count_down(size_t milli_sec) {
-        if (ti_count >= milli_sec)
-            ti_count -= milli_sec;
+    void reset() {
+        _ti_count = RTO;
+        _is_started = false;
+    }
+    void start() { _is_started = true; }
+    void stop() { _is_started = false; }
+    void tick(size_t milli_sec) {
+        if (_ti_count >= milli_sec)
+            _ti_count -= milli_sec;
         else
-            ti_count = 0;
+            _ti_count = 0;
     }
-    void consec_retrans() {
-        rt_count++;
+    void retransmit() {
+        _cr_count++;
         RTO <<= 1;
     }
-    size_t consec_retrans_count() const { return rt_count; }
+    bool is_started() const { return _is_started; }
+    bool is_expired() const { return _ti_count == 0; }
+    size_t consecutive_retransmissions() const { return _cr_count; }
 };
 
 //! \brief The "sender" part of a TCP implementation.
@@ -73,7 +76,7 @@ class TCPSender {
     //! current window size, default (and at least) should be 1 byte according to the handout
     uint16_t _window_size{1};
     std::queue<TCPSegment> _outstandings{};
-    TCPTimer _timer{};
+    TCPTimer _timer;
 
   public:
     //! Initialize a TCPSender