diff --git a/tuic/src/protocol/mod.rs b/tuic/src/protocol/mod.rs
index 406ebc3..8368314 100644
--- a/tuic/src/protocol/mod.rs
+++ b/tuic/src/protocol/mod.rs
@@ -1,11 +1,10 @@
 mod address;
+mod authenticate;
 mod connect;
 mod dissociate;
 mod heartbeat;
 mod packet;
 
-pub mod authenticate;
-
 pub use self::{
     address::Address, authenticate::Authenticate, connect::Connect, dissociate::Dissociate,
     heartbeat::Heartbeat, packet::Packet,
diff --git a/tuic/src/prototype/authenticate.rs b/tuic/src/prototype/authenticate.rs
index fbccf57..fa02069 100644
--- a/tuic/src/prototype/authenticate.rs
+++ b/tuic/src/prototype/authenticate.rs
@@ -1,20 +1,37 @@
-use super::TaskRegister;
+use super::{
+    side::{self, Side, SideMarker},
+    TaskRegister,
+};
 use crate::protocol::{Authenticate as AuthenticateHeader, Header};
 
-pub struct Authenticate {
+pub struct Authenticate<M>
+where
+    M: SideMarker,
+{
+    inner: Side<Tx, Rx>,
+    _marker: M,
+}
+
+pub struct Tx {
     header: Header,
     _task_reg: TaskRegister,
 }
 
-impl Authenticate {
+pub struct Rx;
+
+impl Authenticate<side::Tx> {
     pub(super) fn new(task_reg: TaskRegister, token: [u8; 8]) -> Self {
         Self {
-            header: Header::Authenticate(AuthenticateHeader::new(token)),
-            _task_reg: task_reg,
+            inner: Side::Tx(Tx {
+                header: Header::Authenticate(AuthenticateHeader::new(token)),
+                _task_reg: task_reg,
+            }),
+            _marker: side::Tx,
         }
     }
 
     pub fn header(&self) -> &Header {
-        &self.header
+        let Side::Tx(tx) = &self.inner else { unreachable!() };
+        &tx.header
     }
 }
diff --git a/tuic/src/prototype/connect.rs b/tuic/src/prototype/connect.rs
index fddac8e..391c2d0 100644
--- a/tuic/src/prototype/connect.rs
+++ b/tuic/src/prototype/connect.rs
@@ -1,20 +1,37 @@
-use super::TaskRegister;
+use super::{
+    side::{self, Side, SideMarker},
+    TaskRegister,
+};
 use crate::protocol::{Address, Connect as ConnectHeader, Header};
 
-pub struct Connect {
+pub struct Connect<M>
+where
+    M: SideMarker,
+{
+    inner: Side<Tx, Rx>,
+    _marker: M,
+}
+
+struct Tx {
     header: Header,
     _task_reg: TaskRegister,
 }
 
-impl Connect {
+struct Rx;
+
+impl Connect<side::Tx> {
     pub(super) fn new(task_reg: TaskRegister, addr: Address) -> Self {
         Self {
-            header: Header::Connect(ConnectHeader::new(addr)),
-            _task_reg: task_reg,
+            inner: Side::Tx(Tx {
+                header: Header::Connect(ConnectHeader::new(addr)),
+                _task_reg: task_reg,
+            }),
+            _marker: side::Tx,
         }
     }
 
     pub fn header(&self) -> &Header {
-        &self.header
+        let Side::Tx(tx) = &self.inner else { unreachable!() };
+        &tx.header
     }
 }
diff --git a/tuic/src/prototype/dissociate.rs b/tuic/src/prototype/dissociate.rs
index abf5cef..c1088f5 100644
--- a/tuic/src/prototype/dissociate.rs
+++ b/tuic/src/prototype/dissociate.rs
@@ -1,20 +1,32 @@
-use super::TaskRegister;
+use super::side::{self, Side, SideMarker};
 use crate::protocol::{Dissociate as DissociateHeader, Header};
 
-pub struct Dissociate {
-    header: Header,
-    _task_reg: TaskRegister,
+pub struct Dissociate<M>
+where
+    M: SideMarker,
+{
+    inner: Side<Tx, Rx>,
+    _marker: M,
 }
 
-impl Dissociate {
-    pub(super) fn new(task_reg: TaskRegister, assoc_id: u16) -> Self {
+pub struct Tx {
+    header: Header,
+}
+
+pub struct Rx;
+
+impl Dissociate<side::Tx> {
+    pub(super) fn new(assoc_id: u16) -> Self {
         Self {
-            header: Header::Dissociate(DissociateHeader::new(assoc_id)),
-            _task_reg: task_reg,
+            inner: Side::Tx(Tx {
+                header: Header::Dissociate(DissociateHeader::new(assoc_id)),
+            }),
+            _marker: side::Tx,
         }
     }
 
     pub fn header(&self) -> &Header {
-        &self.header
+        let Side::Tx(tx) = &self.inner else { unreachable!() };
+        &tx.header
     }
 }
diff --git a/tuic/src/prototype/heartbeat.rs b/tuic/src/prototype/heartbeat.rs
index 369a7ec..17ecdfc 100644
--- a/tuic/src/prototype/heartbeat.rs
+++ b/tuic/src/prototype/heartbeat.rs
@@ -1,17 +1,32 @@
+use super::side::{self, Side, SideMarker};
 use crate::protocol::{Header, Heartbeat as HeartbeatHeader};
 
-pub struct Heartbeat {
+pub struct Heartbeat<M>
+where
+    M: SideMarker,
+{
+    inner: Side<Tx, Rx>,
+    _marker: M,
+}
+
+pub struct Tx {
     header: Header,
 }
 
-impl Heartbeat {
+pub struct Rx;
+
+impl Heartbeat<side::Tx> {
     pub(super) fn new() -> Self {
         Self {
-            header: Header::Heartbeat(HeartbeatHeader::new()),
+            inner: Side::Tx(Tx {
+                header: Header::Heartbeat(HeartbeatHeader::new()),
+            }),
+            _marker: side::Tx,
         }
     }
 
     pub fn header(&self) -> &Header {
-        &self.header
+        let Side::Tx(tx) = &self.inner else { unreachable!() };
+        &tx.header
     }
 }
diff --git a/tuic/src/prototype/mod.rs b/tuic/src/prototype/mod.rs
index b96f414..4f8c5e9 100644
--- a/tuic/src/prototype/mod.rs
+++ b/tuic/src/prototype/mod.rs
@@ -15,8 +15,11 @@ mod heartbeat;
 mod packet;
 
 pub use self::{
-    authenticate::Authenticate, connect::Connect, dissociate::Dissociate, heartbeat::Heartbeat,
-    packet::Packet,
+    authenticate::Authenticate,
+    connect::Connect,
+    dissociate::Dissociate,
+    heartbeat::Heartbeat,
+    packet::{Fragment, Packet},
 };
 
 pub struct Connection {
@@ -34,31 +37,28 @@ impl Connection {
         }
     }
 
-    pub fn authenticate(&self, token: [u8; 8]) -> Authenticate {
+    pub fn send_authenticate(&self, token: [u8; 8]) -> Authenticate<side::Tx> {
         Authenticate::new(self.local_active_task_count.reg(), token)
     }
 
-    pub fn connect(&self, addr: Address) -> Connect {
-        Connect::new(self.local_active_task_count.reg(), addr)
+    pub fn send_connect(&self, addr: Address) -> Connect<side::Tx> {
+        Connect::<side::Tx>::new(self.local_active_task_count.reg(), addr)
     }
 
-    pub fn packet<'a>(
+    pub fn send_packet(
         &self,
         assoc_id: u16,
         addr: Address,
-        payload: &'a [u8],
-        frag_len: usize,
-    ) -> Packet<'a> {
-        self.udp_sessions
-            .lock()
-            .send(assoc_id, addr, payload, frag_len)
+        max_pkt_size: usize,
+    ) -> Packet<side::Tx> {
+        self.udp_sessions.lock().send(assoc_id, addr, max_pkt_size)
     }
 
-    pub fn dissociate(&self, assoc_id: u16) -> Dissociate {
+    pub fn send_dissociate(&self, assoc_id: u16) -> Dissociate<side::Tx> {
         self.udp_sessions.lock().dissociate(assoc_id)
     }
 
-    pub fn heartbeat(&self) -> Heartbeat {
+    pub fn send_heartbeat(&self) -> Heartbeat<side::Tx> {
         Heartbeat::new()
     }
 
@@ -98,22 +98,16 @@ impl UdpSessions {
         }
     }
 
-    fn send<'a>(
-        &mut self,
-        assoc_id: u16,
-        addr: Address,
-        payload: &'a [u8],
-        frag_len: usize,
-    ) -> Packet<'a> {
+    fn send<'a>(&mut self, assoc_id: u16, addr: Address, max_pkt_size: usize) -> Packet<side::Tx> {
         self.sessions
             .entry(assoc_id)
             .or_insert_with(|| UdpSession::new(self.local_active_task_count.reg()))
-            .send(assoc_id, addr, payload, frag_len)
+            .send(assoc_id, addr, max_pkt_size)
     }
 
-    fn dissociate(&mut self, assoc_id: u16) -> Dissociate {
+    fn dissociate(&mut self, assoc_id: u16) -> Dissociate<side::Tx> {
         self.sessions.remove(&assoc_id);
-        Dissociate::new(self.local_active_task_count.reg(), assoc_id)
+        Dissociate::new(assoc_id)
     }
 }
 
@@ -130,19 +124,26 @@ impl UdpSession {
         }
     }
 
-    fn send<'a>(
-        &self,
-        assoc_id: u16,
-        addr: Address,
-        payload: &'a [u8],
-        frag_len: usize,
-    ) -> Packet<'a> {
+    fn send<'a>(&self, assoc_id: u16, addr: Address, max_pkt_size: usize) -> Packet<side::Tx> {
         Packet::new(
             assoc_id,
             self.next_pkt_id.fetch_add(1, Ordering::AcqRel),
             addr,
-            payload,
-            frag_len,
+            max_pkt_size,
         )
     }
 }
+
+pub mod side {
+    pub struct Tx;
+    pub struct Rx;
+
+    pub trait SideMarker {}
+    impl SideMarker for Tx {}
+    impl SideMarker for Rx {}
+
+    pub(super) enum Side<T, R> {
+        Tx(T),
+        Rx(R),
+    }
+}
diff --git a/tuic/src/prototype/packet.rs b/tuic/src/prototype/packet.rs
index ccd17fc..4a139c6 100644
--- a/tuic/src/prototype/packet.rs
+++ b/tuic/src/prototype/packet.rs
@@ -1,23 +1,60 @@
+use super::side::{self, Side, SideMarker};
 use crate::protocol::{Address, Header, Packet as PacketHeader};
 
-pub struct Packet<'a> {
+pub struct Packet<M>
+where
+    M: SideMarker,
+{
+    inner: Side<Tx, Rx>,
+    _marker: M,
+}
+
+pub struct Tx {
+    assoc_id: u16,
+    pkt_id: u16,
+    addr: Address,
+    max_pkt_size: usize,
+}
+
+pub struct Rx;
+
+impl Packet<side::Tx> {
+    pub(super) fn new(assoc_id: u16, pkt_id: u16, addr: Address, max_pkt_size: usize) -> Self {
+        Self {
+            inner: Side::Tx(Tx {
+                assoc_id,
+                pkt_id,
+                addr,
+                max_pkt_size,
+            }),
+            _marker: side::Tx,
+        }
+    }
+
+    pub fn into_fragments<'a>(self, payload: &'a [u8]) -> Fragment<'a> {
+        let Side::Tx(tx) = self.inner else { unreachable!() };
+        Fragment::new(tx.assoc_id, tx.pkt_id, tx.addr, tx.max_pkt_size, payload)
+    }
+}
+
+pub struct Fragment<'a> {
     assoc_id: u16,
     pkt_id: u16,
     addr: Address,
-    payload: &'a [u8],
     max_pkt_size: usize,
     frag_total: u8,
     next_frag_id: u8,
     next_frag_start: usize,
+    payload: &'a [u8],
 }
 
-impl<'a> Packet<'a> {
-    pub(super) fn new(
+impl<'a> Fragment<'a> {
+    fn new(
         assoc_id: u16,
         pkt_id: u16,
         addr: Address,
-        payload: &'a [u8],
         max_pkt_size: usize,
+        payload: &'a [u8],
     ) -> Self {
         let first_frag_size = max_pkt_size - PacketHeader::len_without_addr() - addr.len();
         let frag_size_addr_none =
@@ -33,16 +70,16 @@ impl<'a> Packet<'a> {
             assoc_id,
             pkt_id,
             addr,
-            payload,
             max_pkt_size,
             frag_total,
             next_frag_id: 0,
             next_frag_start: 0,
+            payload,
         }
     }
 }
 
-impl<'a> Iterator for Packet<'a> {
+impl<'a> Iterator for Fragment<'a> {
     type Item = (Header, &'a [u8]);
 
     fn next(&mut self) -> Option<Self::Item> {
@@ -72,7 +109,7 @@ impl<'a> Iterator for Packet<'a> {
     }
 }
 
-impl ExactSizeIterator for Packet<'_> {
+impl ExactSizeIterator for Fragment<'_> {
     fn len(&self) -> usize {
         self.frag_total as usize
     }