diff --git a/include/server/IServerSocket.h b/include/server/IServerSocket.h
index c3f7af4..79ce209 100644
--- a/include/server/IServerSocket.h
+++ b/include/server/IServerSocket.h
@@ -14,6 +14,7 @@ class IServerSocket {
 	utils::Signal<PlayerID, const protocol::PacketBase&> OnReceive;
 
 	void Send(PlayerID a_PlayerId, const protocol::PacketBase& a_Packet);
+	void Broadcast(const protocol::PacketBase& a_Packet);
 
 	IServerSocket() {}
 	virtual ~IServerSocket() {}
diff --git a/include/server/IServerState.h b/include/server/IServerState.h
index 6b9f9ad..e79a5bf 100644
--- a/include/server/IServerState.h
+++ b/include/server/IServerState.h
@@ -9,10 +9,6 @@ namespace server {
 class Server;
 
 class IServerState : private utils::SlotGuard {
-  protected:
-	void SendPacket(PlayerID a_Id, const protocol::PacketBase& a_Packet);
-	void SetNewState(const std::shared_ptr<IServerState>& a_NewState);
-
   public:
 	virtual void HandlePacket(PlayerID a_Id, const protocol::PacketBase& a_Packet) = 0;
 	virtual void Update(float a_Delta) = 0;
@@ -22,6 +18,12 @@ class IServerState : private utils::SlotGuard {
 	IServerState();
 	virtual ~IServerState();
 
+  protected:
+	void SendPacket(PlayerID a_Id, const protocol::PacketBase& a_Packet);
+	void BroadcastPacket(const protocol::PacketBase& a_Packet);
+	void SetNewState(const std::shared_ptr<IServerState>& a_NewState);
+	virtual void Init() {}
+
   private:
 	Server* m_Server;
 
diff --git a/include/server/PlayerIds.h b/include/server/PlayerIds.h
index 6166a26..ca523ec 100644
--- a/include/server/PlayerIds.h
+++ b/include/server/PlayerIds.h
@@ -35,6 +35,14 @@ class PlayerIds {
 		m_PeerToPlayer.erase(a_PeerId);
 		m_PlayerToPeer.erase(playerId);
 	}
+
+	auto begin() {
+		return m_PeerToPlayer.begin();
+	}
+
+	auto end() {
+		return m_PeerToPlayer.end();
+	}
 };
 
 }  // namespace server
diff --git a/include/server/Server.h b/include/server/Server.h
index 77e79d6..83542c7 100644
--- a/include/server/Server.h
+++ b/include/server/Server.h
@@ -3,6 +3,7 @@
 #include <memory>
 #include <server/IServerSocket.h>
 #include <server/IServerState.h>
+#include <chrono>
 
 namespace td {
 namespace server {
@@ -11,19 +12,23 @@ class Server {
   private:
 	std::shared_ptr<IServerSocket> m_Socket;
 	std::shared_ptr<IServerState> m_State;
+	std::chrono::time_point<std::chrono::system_clock> m_LastTime;
 
   public:
-	Server(const std::shared_ptr<IServerSocket>& a_Socket) : m_Socket(a_Socket) {}
+	Server(const std::shared_ptr<IServerSocket>& a_Socket) : m_Socket(a_Socket), m_LastTime(std::chrono::system_clock::now()) {}
 
-	void Update(float a_Delta) {
-		m_State->Update(a_Delta);
-	}
+	void Update();
 
 	void UpdateState(const std::shared_ptr<IServerState>& a_State) {
 		m_State = a_State;
 		m_State->SetServer(this);
 	}
 
+  private:
+	void Update(float a_Delta) {
+		m_State->Update(a_Delta);
+	}
+
 	friend class IServerState;
 };
 
diff --git a/include/server/socket/FakeSocket.h b/include/server/socket/FakeSocket.h
index 20b4f05..cdb1893 100644
--- a/include/server/socket/FakeSocket.h
+++ b/include/server/socket/FakeSocket.h
@@ -12,6 +12,9 @@ class FakeSocket : public IServerSocket {
 
 	utils::Signal<PeerID, const protocol::PacketBase&> OnSend;
 
+	void ConnectFakePeer(PeerID a_Peer);
+	void DisconnectFakePeer(PeerID a_Peer);
+
   protected:
 	virtual void SendPeer(PeerID a_Peer, const protocol::PacketBase& a_Packet) override;
 };
diff --git a/include/server/state/GameState.h b/include/server/state/GameState.h
index 05b739b..83d8530 100644
--- a/include/server/state/GameState.h
+++ b/include/server/state/GameState.h
@@ -1,21 +1,33 @@
 #pragma once
 
 #include <server/IServerState.h>
+#include <td/game/World.h>
+#include <td/simulation/ServerSimulation.h>
 
 namespace td {
 namespace server {
 
-class GameState : public IServerState{
+class GameStateHandler;
+
+class GameState : public IServerState {
   private:
-	/* data */
+	std::shared_ptr<game::World> m_World;
+	sim::ServerSimulation m_Simulation;
+	float m_Time;
+
   public:
-	GameState(/* args */) {}
+	GameState(const std::shared_ptr<game::World>& a_World);
 	~GameState() {}
 
 	virtual void HandlePacket(PlayerID a_Id, const protocol::PacketBase& a_Packet) override;
 	virtual void Update(float a_Delta) override;
 	virtual void OnPlayerJoin(PlayerID a_Id) override;
 	virtual void OnPlayerLeave(PlayerID a_Id) override;
+
+  protected:
+	virtual void Init() override;
+
+	friend class GameStateHandler;
 };
 
 }  // namespace server
diff --git a/include/server/state/GameStateHandler.h b/include/server/state/GameStateHandler.h
new file mode 100644
index 0000000..afc202f
--- /dev/null
+++ b/include/server/state/GameStateHandler.h
@@ -0,0 +1,25 @@
+#pragma once
+
+#include <td/protocol/packet/Packets.h>
+
+namespace td {
+namespace server {
+
+class GameState;
+
+class GameStateHandler : public protocol::PacketHandler {
+  private:
+	GameState& m_GameState;
+	PlayerID m_PlayerId;
+
+	using protocol::PacketHandler::Handle;
+
+  public:
+	GameStateHandler(GameState& a_GameState, PlayerID a_PlayerId);
+
+	virtual void Handle(const protocol::packets::SpawnTroopPacket& a_Packet) override;
+	virtual void Handle(const protocol::packets::PlaceTowerPacket& a_Packet) override;
+};
+
+}  // namespace server
+}  // namespace td
diff --git a/include/server/state/LobbyState.h b/include/server/state/LobbyState.h
index f0ac688..e427139 100644
--- a/include/server/state/LobbyState.h
+++ b/include/server/state/LobbyState.h
@@ -5,11 +5,12 @@
 namespace td {
 namespace server {
 
+// this class is temporary useless
 class LobbyState : public IServerState {
   private:
-	/* data */
+	std::shared_ptr<game::World> m_World;
   public:
-	LobbyState(/* args */) {}
+	LobbyState(const std::shared_ptr<game::World>& a_World) : m_World(a_World) {}
 	~LobbyState() {}
 
 	virtual void HandlePacket(PlayerID a_Id, const protocol::PacketBase& a_Packet) override;
diff --git a/include/td/Maths.h b/include/td/Maths.h
index 023ea6d..aff9373 100644
--- a/include/td/Maths.h
+++ b/include/td/Maths.h
@@ -1,6 +1,6 @@
 #pragma once
 
-#include <cstdint>
+#include <sp/common/DataBufferOperators.h>
 
 namespace td {
 
@@ -183,6 +183,35 @@ T Lerp(T v0, T v1, T t) {
 
 }  // namespace maths
 
+template <typename T>
+sp::DataBuffer& operator<<(sp::DataBuffer& a_Buffer, const Vec2<T>& a_Vec) {
+	return a_Buffer << a_Vec.x << a_Vec.y;
+}
 
+template <typename T>
+sp::DataBuffer& operator>>(sp::DataBuffer& a_Buffer, Vec2<T>& a_Vec) {
+	return a_Buffer >> a_Vec.x >> a_Vec.y;
+}
+
+template <typename T>
+sp::DataBuffer& operator<<(sp::DataBuffer& a_Buffer, const Vec3<T>& a_Vec) {
+	return a_Buffer << a_Vec.x << a_Vec.y << a_Vec.z;
+}
+
+template <typename T>
+sp::DataBuffer& operator>>(sp::DataBuffer& a_Buffer, Vec3<T>& a_Vec) {
+	return a_Buffer >> a_Vec.x >> a_Vec.y >> a_Vec.z;
+}
+
+
+template <typename T>
+sp::DataBuffer& operator<<(sp::DataBuffer& a_Buffer, const Vec4<T>& a_Vec) {
+	return a_Buffer << a_Vec.x << a_Vec.y << a_Vec.z << a_Vec.w;
+}
+
+template <typename T>
+sp::DataBuffer& operator>>(sp::DataBuffer& a_Buffer, Vec4<T>& a_Vec) {
+	return a_Buffer >> a_Vec.x >> a_Vec.y >> a_Vec.z >> a_Vec.w;
+}
 
 }  // namespace td
diff --git a/include/td/Types.h b/include/td/Types.h
index cafc172..b126919 100644
--- a/include/td/Types.h
+++ b/include/td/Types.h
@@ -12,6 +12,10 @@ namespace td {
 
 using FpFloat = fpm::fixed_16_16;
 
+using StepTime = std::uint16_t;
+
+constexpr int STEP_TIME = 50;
+
 enum class TeamColor : std::int8_t {
 	None = -1,
 	Blue,
@@ -61,15 +65,11 @@ using TowerID = std::uint16_t;
 using PlayerID = std::uint8_t;
 using EntityID = std::uint16_t;
 
-struct TowerCoords {
-	std::int16_t x;
-	std::int16_t y;
-};
+using TowerCoords = Vec2<std::int16_t>;
 
 using EntityCoords = Vec2<FpFloat>;
 
 using PeerID = std::uint16_t;
-using StepsType = std::uint16_t;
 
 enum class Direction : std::uint8_t {
 	PositiveX = 1 << 0,
diff --git a/include/td/game/World.h b/include/td/game/World.h
index d941932..9177cd6 100644
--- a/include/td/game/World.h
+++ b/include/td/game/World.h
@@ -1,25 +1,25 @@
 #pragma once
 
-#include <td/simulation/WorldTicker.h>
 #include <td/game/WorldTypes.h>
 #include <td/protocol/packet/Packets.h>
+#include <td/simulation/WorldTicker.h>
 
 namespace td {
 namespace game {
 
 class World {
   protected:
+	// header
 	TowerTileColorPalette m_TowerPlacePalette;
 	Color m_WalkablePalette;
 	std::vector<Color> m_DecorationPalette;
 	Color m_Background;
-
-	ChunkList m_Chunks;
-
 	SpawnColorPalette m_SpawnColorPalette;
-
 	TilePalette m_TilePalette;
 
+	//data
+	ChunkList m_Chunks;
+
 	std::shared_ptr<sim::WorldSnapshot> m_CurrentState;
 	std::shared_ptr<sim::WorldSnapshot> m_NextState;
 
@@ -28,6 +28,7 @@ class World {
 
   public:
 	World();
+	World(World&&) = default;
 
 	bool LoadMap(const protocol::pdata::WorldHeader& worldHeader);
 	bool LoadMap(const protocol::pdata::WorldData& worldData);
@@ -130,8 +131,9 @@ class World {
   private:
 	void TickMobs(std::uint64_t delta);
 	void CleanDeadMobs();
-
 };
 
+using WorldPtr = std::shared_ptr<World>;
+
 }  // namespace game
 }  // namespace td
\ No newline at end of file
diff --git a/include/td/protocol/packet/PacketData.h b/include/td/protocol/packet/PacketData.h
index 8bdcc39..4e3ac86 100644
--- a/include/td/protocol/packet/PacketData.h
+++ b/include/td/protocol/packet/PacketData.h
@@ -7,7 +7,11 @@
 #include <td/game/WorldTypes.h>
 
 // Make it dynamic ?
+#ifdef NDEBUG
 #define LOCKSTEP_BUFFER_SIZE 10
+#else
+#define LOCKSTEP_BUFFER_SIZE 1
+#endif
 
 namespace td {
 namespace protocol {
@@ -45,7 +49,7 @@ struct PlayerLeave {
 
 struct PredictCommand {
 	CommandPtr m_Command;
-	std::uint16_t m_FrameNumber;
+	StepTime m_FrameNumber;
 };
 
 /** Keep alive */
@@ -73,7 +77,7 @@ struct BeginGame {
 };
 
 struct LockSteps {
-	std::uint16_t m_FirstFrameNumber;
+	StepTime m_FirstFrameNumber;
 	std::array<LockStep, LOCKSTEP_BUFFER_SIZE> m_LockSteps;
 };
 
@@ -95,6 +99,7 @@ struct WorldData {
 	game::ChunkList m_Chunks;
 };
 
+// TODO: spawn multiple troops at the same time
 struct SpawnTroop {
 	sp::BitField<EntityType, 5> m_Type;
 	sp::BitField<std::uint8_t, 3> m_Level;
diff --git a/include/td/protocol/packet/PacketSerialize.h b/include/td/protocol/packet/PacketSerialize.h
index 29c2331..9fd0328 100644
--- a/include/td/protocol/packet/PacketSerialize.h
+++ b/include/td/protocol/packet/PacketSerialize.h
@@ -4,36 +4,7 @@
 
 namespace td {
 
-template <typename T>
-sp::DataBuffer& operator<<(sp::DataBuffer& a_Buffer, const Vec2<T>& a_Vec) {
-	return a_Buffer << a_Vec.x << a_Vec.y;
-}
 
-template <typename T>
-sp::DataBuffer& operator>>(sp::DataBuffer& a_Buffer, Vec2<T>& a_Vec) {
-	return a_Buffer >> a_Vec.x >> a_Vec.y;
-}
-
-template <typename T>
-sp::DataBuffer& operator<<(sp::DataBuffer& a_Buffer, const Vec3<T>& a_Vec) {
-	return a_Buffer << a_Vec.x << a_Vec.y << a_Vec.z;
-}
-
-template <typename T>
-sp::DataBuffer& operator>>(sp::DataBuffer& a_Buffer, Vec3<T>& a_Vec) {
-	return a_Buffer >> a_Vec.x >> a_Vec.y >> a_Vec.z;
-}
-
-
-template <typename T>
-sp::DataBuffer& operator<<(sp::DataBuffer& a_Buffer, const Vec4<T>& a_Vec) {
-	return a_Buffer << a_Vec.x << a_Vec.y << a_Vec.z << a_Vec.w;
-}
-
-template <typename T>
-sp::DataBuffer& operator>>(sp::DataBuffer& a_Buffer, Vec4<T>& a_Vec) {
-	return a_Buffer >> a_Vec.x >> a_Vec.y >> a_Vec.z >> a_Vec.w;
-}
 
 namespace game {
 
diff --git a/include/td/simulation/GameHistory.h b/include/td/simulation/GameHistory.h
deleted file mode 100644
index 806286a..0000000
--- a/include/td/simulation/GameHistory.h
+++ /dev/null
@@ -1,31 +0,0 @@
-#pragma once
-
-#include <optional>
-#include <td/protocol/command/Commands.h>
-#include <td/protocol/packet/Packets.h>
-
-namespace td {
-namespace game {
-
-class GameHistory {
-  private:
-	using HistorySizeType = StepsType;
-
-	std::vector<std::optional<protocol::LockStep>> m_History;
-	
-  public:
-	GameHistory();
-
-	void SetLockStep(HistorySizeType a_Index, protocol::LockStep&& a_LockStep);
-
-	const protocol::LockStep& GetLockStep(HistorySizeType a_Index) const;
-
-	bool HasLockStep(HistorySizeType a_Index) const;
-
-	void FromPacket(td::protocol::pdata::LockSteps&& a_Steps);
-
-	td::protocol::packets::LockStepsPacket ToPacket(HistorySizeType a_StartIndex);
-};
-
-}  // namespace game
-}  // namespace td
diff --git a/include/td/simulation/ServerSimulation.h b/include/td/simulation/ServerSimulation.h
index aaadbad..599041f 100644
--- a/include/td/simulation/ServerSimulation.h
+++ b/include/td/simulation/ServerSimulation.h
@@ -25,6 +25,8 @@ class ServerSimulation : public protocol::CommandHandler {
 
 	protocol::packets::LockStepsPacket Update();
 
+	protocol::packets::LockStepsPacket MakePacket();
+
 	// no checks are done !
 
 	virtual void Handle(const protocol::commands::SpawnTroopCommand& a_SpawnTroop) override;
diff --git a/src/main.cpp b/src/main.cpp
index aa9f185..72ad7fb 100644
--- a/src/main.cpp
+++ b/src/main.cpp
@@ -1,9 +1,9 @@
 #include <iostream>
 
-#include <td/protocol/packet/PacketSerialize.h>
 #include <fstream>
 #include <td/game/World.h>
 #include <td/input/Display.h>
+#include <td/protocol/packet/PacketSerialize.h>
 #include <td/protocol/packet/Packets.h>
 #include <td/render/renderer/EntityRenderer.h>
 #include <td/render/renderer/TowerRenderer.h>
@@ -17,7 +17,7 @@
 
 #include <server/Server.h>
 #include <server/socket/FakeSocket.h>
-#include <server/state/LobbyState.h>
+#include <server/state/GameState.h>
 
 class WorldApply : public td::protocol::PacketHandler {
   private:
@@ -36,6 +36,24 @@ class WorldApply : public td::protocol::PacketHandler {
 	}
 };
 
+class ClientHandler : public td::protocol::PacketHandler {
+  private:
+	td::sim::ClientSimulation& m_Simulation;
+
+	using td::protocol::PacketHandler::Handle;
+
+  public:
+	ClientHandler(td::sim::ClientSimulation& a_Simulation) : m_Simulation(a_Simulation) {}
+
+	void Handle(const td::protocol::packets::LockStepsPacket& a_LockStep) {
+		m_Simulation.Handle(a_LockStep);
+	}
+
+	void Handle(const td::protocol::packets::PredictCommandPacket& a_Predict) {
+		m_Simulation.Handle(a_Predict);
+	}
+};
+
 void Save(const td::protocol::PacketBase& header, const td::protocol::PacketBase& data) {
 	auto comp = std::make_shared<sp::ZlibCompress>();
 
@@ -48,7 +66,7 @@ void Save(const td::protocol::PacketBase& header, const td::protocol::PacketBase
 	stream.WriteMessage(data, false);
 }
 
-td::game::World GetWorld() {
+td::game::WorldPtr GetWorld() {
 	auto comp = std::make_shared<sp::ZlibCompress>();
 
 	std::ifstream fStream("test/tdmap.tdmap2");
@@ -59,8 +77,8 @@ td::game::World GetWorld() {
 	auto header = stream.ReadMessage(td::protocol::PacketID::WorldHeader);
 	auto data = stream.ReadMessage(td::protocol::PacketID::WorldData);
 
-	td::game::World w;
-	auto wa = std::make_shared<WorldApply>(w);
+	auto w = std::make_shared<td::game::World>();
+	auto wa = std::make_shared<WorldApply>(*w);
 
 	td::protocol::PacketDispatcher d;
 	d.RegisterHandler(wa);
@@ -80,24 +98,12 @@ void FastForward(td::game::World& a_World, const td::sim::GameHistory& a_LockSte
 	}
 }
 
-td::sim::GameHistory GetCustomHistory() {
-	constexpr std::size_t MAX_COUNT = 20 * 60 * 40;
-
-	td::sim::GameHistory gh(MAX_COUNT);
-
-	auto spawn = td::protocol::CommandPtr(
-		std::make_shared<td::protocol::commands::SpawnTroopCommand>(td::EntityType::Zombie, 0, td::Vec2fp{td::FpFloat(77), td::FpFloat(13)}, 0));
-	gh[0].push_back(spawn);
-
-	auto tower = td::protocol::CommandPtr(
-		std::make_shared<td::protocol::commands::PlaceTowerCommand>(td::TowerType::Archer, 0, td::TowerCoords{77, 13}));
-	gh[0].push_back(tower);
-
-	return gh;
-}
-
 int main(int argc, char** argv) {
-	td::game::World w = GetWorld();
+	td::game::WorldPtr serverWorld = GetWorld();
+
+	// server
+	auto fakeSocket = std::make_shared<td::server::FakeSocket>();
+	td::server::Server server(fakeSocket);
 
 	// init GL context
 	td::Display display(1920, 1080, "Tower-Defense 2");
@@ -106,42 +112,40 @@ int main(int argc, char** argv) {
 
 	display.OnAspectRatioChange.Connect([&cam](float a_AspectRatio) { cam.UpdatePerspective(a_AspectRatio); });
 
-	td::sim::GameHistory gh = GetCustomHistory();
+	td::game::WorldPtr clientWorld = GetWorld();
 
 	td::render::RenderPipeline renderer;
-	renderer.AddRenderer<td::render::WorldRenderer>(cam, w);
-	renderer.AddRenderer<td::render::EntityRenderer>(cam, w);
-	renderer.AddRenderer<td::render::TowerRenderer>(cam, w);
+	renderer.AddRenderer<td::render::WorldRenderer>(cam, *clientWorld);
+	renderer.AddRenderer<td::render::EntityRenderer>(cam, *clientWorld);
+	renderer.AddRenderer<td::render::TowerRenderer>(cam, *clientWorld);
 
 	cam.SetCamPos({77, 7, 13});
 	cam.UpdatePerspective(display.GetAspectRatio());
 
-	td::sim::ClientSimulation simulation(w, 50);
+	td::sim::ClientSimulation simulation(*clientWorld, td::STEP_TIME);
+	ClientHandler clientHandler(simulation);
 
-	display.OnKeyDown.Connect([&simulation](SDL_Keycode key) {
-		static int counter = 0;
+	// temporary tests
+	display.OnKeyDown.Connect([&fakeSocket](SDL_Keycode key) {
 		if (key == SDLK_A) {
-			auto spawn = td::protocol::CommandPtr(
-				std::make_shared<td::protocol::commands::SpawnTroopCommand>(td::EntityType::Zombie, 0, td::Vec2fp{td::FpFloat(77), td::FpFloat(13)}, 0));
-			std::array<td::protocol::LockStep, LOCKSTEP_BUFFER_SIZE> steps{};
-			steps[0].push_back(spawn);
-			td::protocol::packets::LockStepsPacket packet{counter * LOCKSTEP_BUFFER_SIZE * 3, steps};
-			simulation.Handle(packet);
-			counter++;
+			fakeSocket->OnReceive(0, td::protocol::packets::SpawnTroopPacket(td::EntityType::Zombie, 1));
+		} else if (key == SDLK_Z) {
+			fakeSocket->OnReceive(0, td::protocol::packets::PlaceTowerPacket(td::TowerType::Archer, td::TowerCoords(77, 13)));
 		}
 	});
 
+	fakeSocket->ConnectFakePeer(0);
 
-	// server
-	auto socket = std::make_shared<td::server::FakeSocket>();
-	td::server::Server server(socket);
-	server.UpdateState(std::make_shared<td::server::LobbyState>());
-	server.Update(1.0f);
-	server.Update(1.0f);
-	socket->OnDisconnect(0);
+	// packets from the server to the client
+	fakeSocket->OnSend.Connect([&clientHandler](td::PeerID a_Peer, const td::protocol::PacketBase& a_Packet) {
+		a_Packet.Dispatch(clientHandler);
+	});
+
+	server.UpdateState(std::make_shared<td::server::GameState>(serverWorld));
 
 	while (!display.IsCloseRequested()) {
 		display.PollEvents();
+		server.Update();
 		float lerp = simulation.Update();
 		renderer.Render(lerp);
 		display.Update();
diff --git a/src/server/IServerSocket.cpp b/src/server/IServerSocket.cpp
index ccf9cda..3deeb4d 100644
--- a/src/server/IServerSocket.cpp
+++ b/src/server/IServerSocket.cpp
@@ -21,5 +21,11 @@ void IServerSocket::Send(PlayerID a_PlayerId, const protocol::PacketBase& a_Pack
 	SendPeer(m_Ids.GetPeerId(a_PlayerId), a_Packet);
 }
 
+void IServerSocket::Broadcast(const protocol::PacketBase& a_Packet) {
+	for (auto [peerId, playerId] : m_Ids) {
+		SendPeer(peerId, a_Packet);
+	}
+}
+
 }  // namespace server
 }  // namespace td
diff --git a/src/server/IServerState.cpp b/src/server/IServerState.cpp
index cdd9f04..3f99642 100644
--- a/src/server/IServerState.cpp
+++ b/src/server/IServerState.cpp
@@ -10,6 +10,7 @@ void IServerState::SetServer(Server* a_Server) {
 	Connect(m_Server->m_Socket->OnConnect, std::bind(&IServerState::OnPlayerJoin, this, std::placeholders::_1));
 	Connect(m_Server->m_Socket->OnDisconnect, std::bind(&IServerState::OnPlayerLeave, this, std::placeholders::_1));
 	Connect(m_Server->m_Socket->OnReceive, std::bind(&IServerState::HandlePacket, this, std::placeholders::_1, std::placeholders::_2));
+	Init();
 }
 
 IServerState::IServerState() : m_Server(nullptr) {}
@@ -20,6 +21,10 @@ void IServerState::SendPacket(PlayerID a_Id, const protocol::PacketBase& a_Packe
 	m_Server->m_Socket->Send(a_Id, a_Packet);
 }
 
+void IServerState::BroadcastPacket(const protocol::PacketBase& a_Packet) {
+	m_Server->m_Socket->Broadcast(a_Packet);
+}
+
 void IServerState::SetNewState(const std::shared_ptr<IServerState>& a_NewState) {
 	m_Server->UpdateState(a_NewState);
 }
diff --git a/src/server/Server.cpp b/src/server/Server.cpp
index b648900..453e3af 100644
--- a/src/server/Server.cpp
+++ b/src/server/Server.cpp
@@ -1 +1,14 @@
-#include <server/Server.h>
\ No newline at end of file
+#include <server/Server.h>
+
+namespace td {
+namespace server {
+
+void Server::Update() {
+	auto timeElapsed = std::chrono::system_clock::now() - m_LastTime;
+	float timeSeconds = std::chrono::duration<float, std::chrono::seconds::period>(timeElapsed).count();
+	Update(timeSeconds);
+	m_LastTime = std::chrono::system_clock::now();
+}
+
+}  // namespace server
+}  // namespace td
diff --git a/src/server/socket/FakeSocket.cpp b/src/server/socket/FakeSocket.cpp
index ebe3a5d..aa2da4d 100644
--- a/src/server/socket/FakeSocket.cpp
+++ b/src/server/socket/FakeSocket.cpp
@@ -7,5 +7,13 @@ void FakeSocket::SendPeer(PeerID a_Peer, const protocol::PacketBase& a_Packet) {
 	OnSend(a_Peer, a_Packet);
 }
 
+void FakeSocket::ConnectFakePeer(PeerID a_Peer) {
+	OnConnectPeer(a_Peer);
+}
+
+void FakeSocket::DisconnectFakePeer(PeerID a_Peer) {
+	OnDisconnectPeer(a_Peer);
+}
+
 }  // namespace server
 }  // namespace td
diff --git a/src/server/state/GameState.cpp b/src/server/state/GameState.cpp
index 6a28183..8ea3ff4 100644
--- a/src/server/state/GameState.cpp
+++ b/src/server/state/GameState.cpp
@@ -1,25 +1,36 @@
 #include <server/state/GameState.h>
+#include <server/state/GameStateHandler.h>
 
 #include <iostream>
 
 namespace td {
 namespace server {
 
-void GameState::HandlePacket(PlayerID a_Id, const protocol::PacketBase& a_Packet) {
+GameState::GameState(const std::shared_ptr<game::World>& a_World) : m_World(a_World), m_Simulation(*m_World, STEP_TIME), m_Time(0) {}
 
+void GameState::Init() {
+	std::cout << "Switched to Game state !\n";
+	BroadcastPacket(m_Simulation.MakePacket());
+}
+
+void GameState::HandlePacket(PlayerID a_Id, const protocol::PacketBase& a_Packet) {
+	GameStateHandler handler(*this, a_Id);
+	a_Packet.Dispatch(handler);
 }
 
 void GameState::Update(float a_Delta) {
-	
+	static const float stepTimeSecond = static_cast<float>(STEP_TIME) / 1000.0f;
+	m_Time += a_Delta;
+	if (m_Time > stepTimeSecond) {
+		m_Time = std::fmod(m_Time, stepTimeSecond);
+		auto lockStepPacket = m_Simulation.Update();
+		BroadcastPacket(lockStepPacket);
+	}
 }
 
-void GameState::OnPlayerJoin(PlayerID a_Id) {
+void GameState::OnPlayerJoin(PlayerID a_Id) {}
 
-}
-
-void GameState::OnPlayerLeave(PlayerID a_Id) {
-	std::cout << "Game leave !" << std::endl;
-}
+void GameState::OnPlayerLeave(PlayerID a_Id) {}
 
 }  // namespace server
 }  // namespace td
diff --git a/src/server/state/GameStateHandler.cpp b/src/server/state/GameStateHandler.cpp
new file mode 100644
index 0000000..3b0e9fc
--- /dev/null
+++ b/src/server/state/GameStateHandler.cpp
@@ -0,0 +1,24 @@
+#include <server/state/GameState.h>
+#include <server/state/GameStateHandler.h>
+
+namespace td {
+namespace server {
+
+GameStateHandler::GameStateHandler(GameState& a_GameState, PlayerID a_PlayerId) : m_GameState(a_GameState), m_PlayerId(a_PlayerId) {}
+
+// TODO: redo this
+void GameStateHandler::Handle(const protocol::packets::SpawnTroopPacket& a_Packet) {
+	static const EntityCoords DEFAULT_POS(td::FpFloat(77), td::FpFloat(13));
+
+	td::protocol::commands::SpawnTroopCommand spawn(*a_Packet->m_Type, *a_Packet->m_Level, DEFAULT_POS, m_PlayerId);
+	m_GameState.m_Simulation.Handle(spawn);
+}
+
+// TODO: and this
+void GameStateHandler::Handle(const protocol::packets::PlaceTowerPacket& a_Packet) {
+	td::protocol::commands::PlaceTowerCommand place(a_Packet->m_Type, m_PlayerId, a_Packet->m_Position);
+	m_GameState.m_Simulation.Handle(place);
+}
+
+}  // namespace server
+}  // namespace td
diff --git a/src/server/state/LobbyState.cpp b/src/server/state/LobbyState.cpp
index 7db94e4..e9a1b1c 100644
--- a/src/server/state/LobbyState.cpp
+++ b/src/server/state/LobbyState.cpp
@@ -11,7 +11,7 @@ void LobbyState::HandlePacket(PlayerID a_Id, const protocol::PacketBase& a_Packe
 }
 
 void LobbyState::Update(float a_Delta) {
-	SetNewState(std::make_shared<GameState>());
+	SetNewState(std::make_shared<GameState>(m_World));
 }
 
 void LobbyState::OnPlayerJoin(PlayerID a_Id) {
@@ -19,7 +19,7 @@ void LobbyState::OnPlayerJoin(PlayerID a_Id) {
 }
 
 void LobbyState::OnPlayerLeave(PlayerID a_Id) {
-	std::cout << "Lobby leave !" << std::endl;
+
 }
 
 }  // namespace server
diff --git a/src/td/simulation/ClientSimulation.cpp b/src/td/simulation/ClientSimulation.cpp
index 7d43c36..e8045e6 100644
--- a/src/td/simulation/ClientSimulation.cpp
+++ b/src/td/simulation/ClientSimulation.cpp
@@ -2,6 +2,8 @@
 
 #include <chrono>
 
+#include <iostream>
+
 namespace td {
 namespace sim {
 
@@ -30,13 +32,13 @@ ClientSimulation::ClientSimulation(game::World& a_World, GameHistory&& a_History
 ClientSimulation::ClientSimulation(game::World& a_World, std::uint64_t a_StepTime) :
 	m_StepTime(a_StepTime),
 	m_World(a_World),
-	m_History(std::numeric_limits<std::uint16_t>::max()),
+	m_History(std::numeric_limits<StepTime>::max()),
 	m_CurrentTime(0),
 	m_LastTime(GetTime()),
 	m_CurrentStep(0),
 	m_LastSnapshot(std::make_shared<WorldSnapshot>()),
 	m_LastValidStep(0) {
-	Step();
+	// Step();
 }
 
 float ClientSimulation::Update() {
@@ -45,7 +47,7 @@ float ClientSimulation::Update() {
 	m_LastTime = GetTime();
 	if (m_CurrentTime > m_StepTime) {
 		Step();
-		m_CurrentTime -= m_StepTime;
+		m_CurrentTime %= m_StepTime;
 	}
 	return (float)m_CurrentTime / (float)m_StepTime;
 }
@@ -69,25 +71,25 @@ void ClientSimulation::Handle(const protocol::packets::LockStepsPacket& a_LockSt
 	FastReplay();
 }
 
-void ClientSimulation::Handle(const protocol::packets::PredictCommandPacket& a_Predict) {
-	
-}
+void ClientSimulation::Handle(const protocol::packets::PredictCommandPacket& a_Predict) {}
 
 void ClientSimulation::FastForward(std::size_t a_Count) {
 	for (std::size_t i = 0; i < a_Count; i++) {
 		Step();
 	}
+	std::cout << "Was behind " << a_Count << " ticks !\n";
 }
 
 void ClientSimulation::FastReplay() {
-	if (m_LastValidStep >= m_CurrentStep)
+	if (m_LastValidStep + 1 >= m_CurrentStep)
 		return;
 
 	m_World.ResetSnapshots(m_LastSnapshot, m_LastSnapshot);
 
+	// TODO: cover holes
 	const std::size_t stepCount = m_CurrentStep - m_LastValidStep;
 	m_CurrentStep = m_LastValidStep;
-	
+
 	FastForward(stepCount);
 }
 
diff --git a/src/td/simulation/GameHistory.cpp b/src/td/simulation/GameHistory.cpp
deleted file mode 100644
index fd36519..0000000
--- a/src/td/simulation/GameHistory.cpp
+++ /dev/null
@@ -1,36 +0,0 @@
-#include <td/simulation/GameHistory.h>
-
-namespace td {
-namespace game {
-
-GameHistory::GameHistory() : m_History(std::numeric_limits<HistorySizeType>::max()) {}
-
-void GameHistory::SetLockStep(HistorySizeType a_Index, protocol::LockStep&& a_LockStep) {
-	m_History[a_Index] = std::move(a_LockStep);
-}
-
-const protocol::LockStep& GameHistory::GetLockStep(HistorySizeType a_Index) const {
-	return *m_History[a_Index];
-}
-
-bool GameHistory::HasLockStep(HistorySizeType a_Index) const {
-	return m_History[a_Index].has_value();
-}
-
-void GameHistory::FromPacket(protocol::pdata::LockSteps&& a_Steps) {
-	for (int i = 0; i < LOCKSTEP_BUFFER_SIZE; i++) {
-		protocol::LockStep& step = a_Steps.m_LockSteps[i];
-		SetLockStep(i + a_Steps.m_FirstFrameNumber, std::move(step));
-	}
-}
-
-protocol::packets::LockStepsPacket GameHistory::ToPacket(HistorySizeType a_StartIndex) {
-	std::array<protocol::LockStep, LOCKSTEP_BUFFER_SIZE> steps;
-	for (int i = 0; i < LOCKSTEP_BUFFER_SIZE; i++) {
-		steps[i] = GetLockStep(a_StartIndex + i);
-	}
-	return {a_StartIndex, std::move(steps)};
-}
-
-}  // namespace game
-}  // namespace td
diff --git a/src/td/simulation/ServerSimulation.cpp b/src/td/simulation/ServerSimulation.cpp
index 497d866..bde94dd 100644
--- a/src/td/simulation/ServerSimulation.cpp
+++ b/src/td/simulation/ServerSimulation.cpp
@@ -4,20 +4,24 @@ namespace td {
 namespace sim {
 
 ServerSimulation::ServerSimulation(game::World& a_World, std::uint64_t a_StepTime) :
-	m_World(a_World), m_StepTime(a_StepTime), m_CurrentTime(0) {}
+	m_World(a_World), m_StepTime(a_StepTime), m_CurrentTime(0), m_History(std::numeric_limits<StepTime>::max()) {}
 
 protocol::packets::LockStepsPacket ServerSimulation::Update() {
 	std::lock_guard<std::mutex> lock(m_Mutex);
-	
+
 	m_World.Tick(m_History[m_CurrentTime], FpFloat(m_StepTime) / FpFloat(1000));
 	m_CurrentTime++;
 
+	return MakePacket();
+}
+
+protocol::packets::LockStepsPacket ServerSimulation::MakePacket() {
 	std::array<protocol::LockStep, LOCKSTEP_BUFFER_SIZE> nextSteps;
 	std::copy(m_History.begin() + m_CurrentTime, m_History.begin() + m_CurrentTime + nextSteps.size(), nextSteps.begin());
 	return {m_CurrentTime, std::move(nextSteps)};
 }
 
-template<typename T>
+template <typename T>
 void AddToCommandHistory(protocol::LockStep& a_LockStep, const T& a_Cmd) {
 	a_LockStep.push_back({std::make_shared<T>(a_Cmd)});
 }