diff --git a/chirpstack/Cargo.toml b/chirpstack/Cargo.toml
index 4fc89991..e0850c1e 100644
--- a/chirpstack/Cargo.toml
+++ b/chirpstack/Cargo.toml
@@ -55,6 +55,7 @@
     "diesel",
     "regions",
     "crypto",
+    "applayer",
   ] }
   backend = { path = "../backend" }
 
diff --git a/lrwn/Cargo.toml b/lrwn/Cargo.toml
index e6d607f3..87dbc36e 100644
--- a/lrwn/Cargo.toml
+++ b/lrwn/Cargo.toml
@@ -33,3 +33,4 @@
   serde = ["dep:serde"]
   crypto = ["dep:cmac", "dep:aes"]
   regions = []
+  applayer = []
diff --git a/lrwn/src/applayer/clocksync/mod.rs b/lrwn/src/applayer/clocksync/mod.rs
new file mode 100644
index 00000000..a3a6d96c
--- /dev/null
+++ b/lrwn/src/applayer/clocksync/mod.rs
@@ -0,0 +1 @@
+pub mod v1;
diff --git a/lrwn/src/applayer/clocksync/v1.rs b/lrwn/src/applayer/clocksync/v1.rs
new file mode 100644
index 00000000..53207e03
--- /dev/null
+++ b/lrwn/src/applayer/clocksync/v1.rs
@@ -0,0 +1,559 @@
+use std::time::Duration;
+
+use anyhow::Result;
+
+use crate::applayer::PayloadCodec;
+
+pub enum Cid {
+    PackageVersionReq,
+    PackageVersionAns,
+    AppTimeReq,
+    AppTimeAns,
+    DeviceAppTimePeropdicityReq,
+    DeviceAppTimePeropdicityAns,
+    ForceDeviceResyncReq,
+}
+
+impl Cid {
+    pub fn from_u8(uplink: bool, value: u8) -> Result<Cid> {
+        Ok(match uplink {
+            true => match value {
+                0x00 => Cid::PackageVersionAns,
+                0x01 => Cid::AppTimeReq,
+                0x02 => Cid::DeviceAppTimePeropdicityAns,
+                _ => return Err(anyhow!("Invalid CID: {}", value)),
+            },
+            false => match value {
+                0x00 => Cid::PackageVersionReq,
+                0x01 => Cid::AppTimeAns,
+                0x02 => Cid::DeviceAppTimePeropdicityReq,
+                0x03 => Cid::ForceDeviceResyncReq,
+                _ => return Err(anyhow!("Invalid CID: {}", value)),
+            },
+        })
+    }
+
+    pub fn to_u8(&self) -> u8 {
+        match self {
+            Cid::PackageVersionReq | Cid::PackageVersionAns => 0x00,
+            Cid::AppTimeReq | Cid::AppTimeAns => 0x01,
+            Cid::DeviceAppTimePeropdicityReq | Cid::DeviceAppTimePeropdicityAns => 0x02,
+            Cid::ForceDeviceResyncReq => 0x03,
+        }
+    }
+}
+
+#[derive(Debug, PartialEq)]
+pub enum Payload {
+    PackageVersionReq,
+    PackageVersionAns(PackageVersionAnsPayload),
+    AppTimeReq(AppTimeReqPayload),
+    AppTimeAns(AppTimeAnsPayload),
+    DeviceAppTimePeropdicityReq(DeviceAppTimePeriodicityReqPayload),
+    DeviceAppTimePeropdicityAns(DeviceAppTimePeriodicityAnsPayload),
+    ForceDeviceResyncReq(ForceDeviceResyncReqPayload),
+}
+
+impl Payload {
+    pub fn cid(&self) -> Cid {
+        match self {
+            Self::PackageVersionReq => Cid::PackageVersionReq,
+            Self::PackageVersionAns(_) => Cid::PackageVersionAns,
+            Self::AppTimeReq(_) => Cid::AppTimeReq,
+            Self::AppTimeAns(_) => Cid::AppTimeAns,
+            Self::DeviceAppTimePeropdicityReq(_) => Cid::DeviceAppTimePeropdicityReq,
+            Self::DeviceAppTimePeropdicityAns(_) => Cid::DeviceAppTimePeropdicityAns,
+            Self::ForceDeviceResyncReq(_) => Cid::ForceDeviceResyncReq,
+        }
+    }
+
+    pub fn from_slice(uplink: bool, b: &[u8]) -> Result<Self> {
+        if b.is_empty() {
+            return Err(anyhow!("At least one byte is expected"));
+        }
+
+        let cid = Cid::from_u8(uplink, b[0])?;
+
+        Ok(match cid {
+            Cid::PackageVersionReq => Payload::PackageVersionReq,
+            Cid::PackageVersionAns => {
+                Payload::PackageVersionAns(PackageVersionAnsPayload::decode(&b[1..])?)
+            }
+            Cid::AppTimeReq => Payload::AppTimeReq(AppTimeReqPayload::decode(&b[1..])?),
+            Cid::AppTimeAns => Payload::AppTimeAns(AppTimeAnsPayload::decode(&b[1..])?),
+            Cid::DeviceAppTimePeropdicityReq => Payload::DeviceAppTimePeropdicityReq(
+                DeviceAppTimePeriodicityReqPayload::decode(&b[1..])?,
+            ),
+            Cid::DeviceAppTimePeropdicityAns => Payload::DeviceAppTimePeropdicityAns(
+                DeviceAppTimePeriodicityAnsPayload::decode(&b[1..])?,
+            ),
+            Cid::ForceDeviceResyncReq => {
+                Payload::ForceDeviceResyncReq(ForceDeviceResyncReqPayload::decode(&b[1..])?)
+            }
+        })
+    }
+
+    pub fn to_vec(&self) -> Result<Vec<u8>> {
+        let mut out = vec![self.cid().to_u8()];
+
+        match self {
+            Self::PackageVersionReq => {}
+            Self::PackageVersionAns(pl) => out.extend_from_slice(&pl.encode()?),
+            Self::AppTimeReq(pl) => out.extend_from_slice(&pl.encode()?),
+            Self::AppTimeAns(pl) => out.extend_from_slice(&pl.encode()?),
+            Self::DeviceAppTimePeropdicityReq(pl) => out.extend_from_slice(&pl.encode()?),
+            Self::DeviceAppTimePeropdicityAns(pl) => out.extend_from_slice(&pl.encode()?),
+            Self::ForceDeviceResyncReq(pl) => out.extend_from_slice(&pl.encode()?),
+        };
+
+        Ok(out)
+    }
+}
+
+#[derive(Debug, PartialEq)]
+pub struct PackageVersionAnsPayload {
+    pub package_identifier: u8,
+    pub package_version: u8,
+}
+
+impl PayloadCodec for PackageVersionAnsPayload {
+    fn decode(b: &[u8]) -> Result<Self> {
+        if b.len() != 2 {
+            return Err(anyhow!("Expected 2 bytes"));
+        }
+
+        Ok(PackageVersionAnsPayload {
+            package_identifier: b[0],
+            package_version: b[1],
+        })
+    }
+    fn encode(&self) -> Result<Vec<u8>> {
+        Ok(vec![self.package_identifier, self.package_version])
+    }
+}
+
+#[derive(Debug, PartialEq)]
+pub struct AppTimeReqPayload {
+    pub device_time: Duration, // Duration since GPS Epoch
+    pub param: AppTimeReqPayloadParam,
+}
+
+impl PayloadCodec for AppTimeReqPayload {
+    fn decode(b: &[u8]) -> Result<Self> {
+        if b.len() != 5 {
+            return Err(anyhow!("Expected 5 bytes"));
+        }
+
+        let mut device_time: [u8; 4] = [0; 4];
+        device_time.copy_from_slice(&b[0..4]);
+        let device_time_secs = u32::from_le_bytes(device_time);
+
+        Ok(AppTimeReqPayload {
+            device_time: Duration::new(device_time_secs.into(), 0),
+            param: AppTimeReqPayloadParam {
+                token_req: b[4] & 0x0f,
+                ans_required: b[4] & 0x10 != 0,
+            },
+        })
+    }
+
+    fn encode(&self) -> Result<Vec<u8>> {
+        if self.param.token_req > 15 {
+            return Err(anyhow!("Max token_req value is 15"));
+        }
+
+        let mut b = vec![0; 5];
+        b[0..4].copy_from_slice(&(self.device_time.as_secs() as u32).to_le_bytes());
+        b[4] = self.param.token_req;
+
+        if self.param.ans_required {
+            b[4] |= 0x10;
+        }
+
+        Ok(b)
+    }
+}
+
+#[derive(Debug, PartialEq)]
+pub struct AppTimeReqPayloadParam {
+    pub token_req: u8,
+    pub ans_required: bool,
+}
+
+#[derive(Debug, PartialEq)]
+pub struct AppTimeAnsPayload {
+    pub time_correction: Duration,
+    pub param: AppTimeAnsPayloadParam,
+}
+
+impl PayloadCodec for AppTimeAnsPayload {
+    fn decode(b: &[u8]) -> Result<Self> {
+        if b.len() != 5 {
+            return Err(anyhow!("Expected 5 bytes"));
+        }
+
+        let mut time_correction: [u8; 4] = [0; 4];
+        time_correction.copy_from_slice(&b[0..4]);
+        let time_correction_secs = u32::from_le_bytes(time_correction);
+
+        Ok(AppTimeAnsPayload {
+            time_correction: Duration::new(time_correction_secs.into(), 0),
+            param: AppTimeAnsPayloadParam {
+                token_ans: b[4] & 0x0f,
+            },
+        })
+    }
+
+    fn encode(&self) -> Result<Vec<u8>> {
+        if self.param.token_ans > 15 {
+            return Err(anyhow!("Max token_ans value is 15"));
+        }
+
+        let mut b = vec![0; 5];
+        b[0..4].copy_from_slice(&(self.time_correction.as_secs() as u32).to_le_bytes());
+        b[4] = self.param.token_ans;
+
+        Ok(b)
+    }
+}
+
+#[derive(Debug, PartialEq)]
+pub struct AppTimeAnsPayloadParam {
+    pub token_ans: u8,
+}
+
+#[derive(Debug, PartialEq)]
+pub struct DeviceAppTimePeriodicityReqPayload {
+    pub period: u8,
+}
+
+impl PayloadCodec for DeviceAppTimePeriodicityReqPayload {
+    fn decode(b: &[u8]) -> Result<Self> {
+        if b.len() != 1 {
+            return Err(anyhow!("Expected 1 byte"));
+        }
+
+        Ok(DeviceAppTimePeriodicityReqPayload {
+            period: b[0] & 0x0f,
+        })
+    }
+
+    fn encode(&self) -> Result<Vec<u8>> {
+        if self.period > 15 {
+            return Err(anyhow!("Max period value is 15"));
+        }
+
+        Ok(vec![self.period])
+    }
+}
+
+#[derive(Debug, PartialEq)]
+pub struct DeviceAppTimePeriodicityAnsPayload {
+    pub status: DeviceAppTimePeriodicityAnsPayloadStatus,
+    pub time: Duration,
+}
+
+impl PayloadCodec for DeviceAppTimePeriodicityAnsPayload {
+    fn decode(b: &[u8]) -> Result<Self> {
+        if b.len() != 5 {
+            return Err(anyhow!("Expected 5 bytes"));
+        }
+
+        let mut time: [u8; 4] = [0; 4];
+        time.copy_from_slice(&b[1..5]);
+        let time_secs = u32::from_le_bytes(time);
+
+        Ok(DeviceAppTimePeriodicityAnsPayload {
+            status: DeviceAppTimePeriodicityAnsPayloadStatus {
+                not_supported: b[0] & 0x01 != 0,
+            },
+            time: Duration::new(time_secs.into(), 0),
+        })
+    }
+
+    fn encode(&self) -> Result<Vec<u8>> {
+        let mut b = vec![0; 5];
+        if self.status.not_supported {
+            b[0] |= 0x01;
+        }
+
+        b[1..5].copy_from_slice(&(self.time.as_secs() as u32).to_le_bytes());
+        Ok(b)
+    }
+}
+
+#[derive(Debug, PartialEq)]
+pub struct DeviceAppTimePeriodicityAnsPayloadStatus {
+    pub not_supported: bool,
+}
+
+#[derive(Debug, PartialEq)]
+pub struct ForceDeviceResyncReqPayload {
+    pub force_conf: ForceDeviceResyncReqPayloadForceConf,
+}
+
+impl PayloadCodec for ForceDeviceResyncReqPayload {
+    fn decode(b: &[u8]) -> Result<Self> {
+        if b.len() != 1 {
+            return Err(anyhow!("Expected 1 byte"));
+        }
+
+        Ok(ForceDeviceResyncReqPayload {
+            force_conf: ForceDeviceResyncReqPayloadForceConf {
+                nb_transmissions: b[0] & 0x07,
+            },
+        })
+    }
+
+    fn encode(&self) -> Result<Vec<u8>> {
+        if self.force_conf.nb_transmissions > 7 {
+            return Err(anyhow!("Max nb_transmissions is 7"));
+        }
+
+        Ok(vec![self.force_conf.nb_transmissions])
+    }
+}
+
+#[derive(Debug, PartialEq)]
+pub struct ForceDeviceResyncReqPayloadForceConf {
+    pub nb_transmissions: u8,
+}
+
+#[cfg(test)]
+mod test {
+    use super::*;
+
+    struct CommandTest {
+        name: String,
+        uplink: bool,
+        command: Payload,
+        bytes: Vec<u8>,
+        expected_error: Option<String>,
+    }
+
+    #[test]
+    fn test_package_version_req() {
+        let encode_tests = [CommandTest {
+            name: "encode PackageVersionReq".into(),
+            uplink: false,
+            command: Payload::PackageVersionReq,
+            bytes: vec![0x00],
+            expected_error: None,
+        }];
+
+        let decode_tests = [CommandTest {
+            name: "decode PackageVersionReq".into(),
+            uplink: false,
+            command: Payload::PackageVersionReq,
+            bytes: vec![0x00],
+            expected_error: None,
+        }];
+
+        run_tests_encode(&encode_tests);
+        run_tests_decode(&decode_tests);
+    }
+
+    #[test]
+    fn test_package_version_ans() {
+        let encode_tests = [CommandTest {
+            name: "encode PackageVersionAns".into(),
+            uplink: true,
+            command: Payload::PackageVersionAns(PackageVersionAnsPayload {
+                package_identifier: 1,
+                package_version: 1,
+            }),
+            bytes: vec![0x00, 0x01, 0x01],
+            expected_error: None,
+        }];
+
+        let decode_tests = [CommandTest {
+            name: "decode PackageVersionAns".into(),
+            uplink: true,
+            command: Payload::PackageVersionAns(PackageVersionAnsPayload {
+                package_identifier: 1,
+                package_version: 1,
+            }),
+            bytes: vec![0x00, 0x01, 0x01],
+            expected_error: None,
+        }];
+
+        run_tests_encode(&encode_tests);
+        run_tests_decode(&decode_tests);
+    }
+
+    #[test]
+    fn test_app_time_req() {
+        let encode_tests = [CommandTest {
+            name: "encode AppTimeReq".into(),
+            uplink: true,
+            command: Payload::AppTimeReq(AppTimeReqPayload {
+                device_time: Duration::from_secs(1024),
+                param: AppTimeReqPayloadParam {
+                    token_req: 15,
+                    ans_required: true,
+                },
+            }),
+            bytes: vec![0x01, 0x00, 0x04, 0x00, 0x00, 0x1f],
+            expected_error: None,
+        }];
+
+        let decode_tests = [CommandTest {
+            name: "decode AppTimeReq".into(),
+            uplink: true,
+            command: Payload::AppTimeReq(AppTimeReqPayload {
+                device_time: Duration::from_secs(1024),
+                param: AppTimeReqPayloadParam {
+                    token_req: 15,
+                    ans_required: true,
+                },
+            }),
+            bytes: vec![0x01, 0x00, 0x04, 0x00, 0x00, 0x1f],
+            expected_error: None,
+        }];
+
+        run_tests_encode(&encode_tests);
+        run_tests_decode(&decode_tests);
+    }
+
+    #[test]
+    fn test_app_time_ans() {
+        let encode_tests = [CommandTest {
+            name: "encode AppTimeAns".into(),
+            uplink: false,
+            command: Payload::AppTimeAns(AppTimeAnsPayload {
+                time_correction: Duration::from_secs(1024),
+                param: AppTimeAnsPayloadParam { token_ans: 15 },
+            }),
+            bytes: vec![0x01, 0x00, 0x04, 0x00, 0x00, 0x0f],
+            expected_error: None,
+        }];
+
+        let decode_tests = [CommandTest {
+            name: "decode AppTimeAns".into(),
+            uplink: false,
+            command: Payload::AppTimeAns(AppTimeAnsPayload {
+                time_correction: Duration::from_secs(1024),
+                param: AppTimeAnsPayloadParam { token_ans: 15 },
+            }),
+            bytes: vec![0x01, 0x00, 0x04, 0x00, 0x00, 0x0f],
+            expected_error: None,
+        }];
+
+        run_tests_encode(&encode_tests);
+        run_tests_decode(&decode_tests);
+    }
+
+    #[test]
+    fn test_device_app_time_periodicity_req() {
+        let encode_tests = [CommandTest {
+            name: "encode DeviceAppTimePeropdicityReq".into(),
+            uplink: false,
+            command: Payload::DeviceAppTimePeropdicityReq(DeviceAppTimePeriodicityReqPayload {
+                period: 15,
+            }),
+            bytes: vec![0x02, 0x0f],
+            expected_error: None,
+        }];
+
+        let decode_tests = [CommandTest {
+            name: "decode DeviceAppTimePeropdicityReq".into(),
+            uplink: false,
+            command: Payload::DeviceAppTimePeropdicityReq(DeviceAppTimePeriodicityReqPayload {
+                period: 15,
+            }),
+            bytes: vec![0x02, 0x0f],
+            expected_error: None,
+        }];
+
+        run_tests_encode(&encode_tests);
+        run_tests_decode(&decode_tests);
+    }
+
+    #[test]
+    fn test_device_app_time_periodicity_ans() {
+        let encode_tests = [CommandTest {
+            name: "encode DeviceAppTimePeropdicityAns".into(),
+            uplink: true,
+            command: Payload::DeviceAppTimePeropdicityAns(DeviceAppTimePeriodicityAnsPayload {
+                status: DeviceAppTimePeriodicityAnsPayloadStatus {
+                    not_supported: true,
+                },
+                time: Duration::from_secs(1024),
+            }),
+            bytes: vec![0x02, 0x01, 0x00, 0x04, 0x00, 0x00],
+            expected_error: None,
+        }];
+
+        let decode_tests = [CommandTest {
+            name: "decode DeviceAppTimePeropdicityAns".into(),
+            uplink: true,
+            command: Payload::DeviceAppTimePeropdicityAns(DeviceAppTimePeriodicityAnsPayload {
+                status: DeviceAppTimePeriodicityAnsPayloadStatus {
+                    not_supported: true,
+                },
+                time: Duration::from_secs(1024),
+            }),
+            bytes: vec![0x02, 0x01, 0x00, 0x04, 0x00, 0x00],
+            expected_error: None,
+        }];
+
+        run_tests_encode(&encode_tests);
+        run_tests_decode(&decode_tests);
+    }
+
+    #[test]
+    fn test_force_device_resync_req() {
+        let encode_tests = [CommandTest {
+            name: "encode ForceDeviceResyncReq".into(),
+            uplink: false,
+            command: Payload::ForceDeviceResyncReq(ForceDeviceResyncReqPayload {
+                force_conf: ForceDeviceResyncReqPayloadForceConf {
+                    nb_transmissions: 7,
+                },
+            }),
+            bytes: vec![0x03, 0x07],
+            expected_error: None,
+        }];
+
+        let decode_tests = [CommandTest {
+            name: "decode ForceDeviceResyncReq".into(),
+            uplink: false,
+            command: Payload::ForceDeviceResyncReq(ForceDeviceResyncReqPayload {
+                force_conf: ForceDeviceResyncReqPayloadForceConf {
+                    nb_transmissions: 7,
+                },
+            }),
+            bytes: vec![0x03, 0x07],
+            expected_error: None,
+        }];
+
+        run_tests_encode(&encode_tests);
+        run_tests_decode(&decode_tests);
+    }
+
+    fn run_tests_encode(tests: &[CommandTest]) {
+        for tst in tests {
+            println!("> {}", tst.name);
+            let resp = tst.command.to_vec();
+            if let Some(e) = &tst.expected_error {
+                assert!(resp.is_err());
+                assert_eq!(e, &resp.err().unwrap().to_string());
+            } else {
+                assert_eq!(tst.bytes, resp.unwrap());
+            }
+        }
+    }
+
+    fn run_tests_decode(tests: &[CommandTest]) {
+        for tst in tests {
+            println!("> {}", tst.name);
+            let resp = Payload::from_slice(tst.uplink, &tst.bytes);
+            if let Some(e) = &tst.expected_error {
+                assert!(resp.is_err());
+                assert_eq!(e, &resp.err().unwrap().to_string());
+            } else {
+                assert_eq!(tst.command, resp.unwrap());
+            }
+        }
+    }
+}
diff --git a/lrwn/src/applayer/mod.rs b/lrwn/src/applayer/mod.rs
new file mode 100644
index 00000000..ee002523
--- /dev/null
+++ b/lrwn/src/applayer/mod.rs
@@ -0,0 +1,8 @@
+use anyhow::Result;
+
+pub mod clocksync;
+
+pub trait PayloadCodec<Struct = Self> {
+    fn decode(b: &[u8]) -> Result<Struct>;
+    fn encode(&self) -> Result<Vec<u8>>;
+}
diff --git a/lrwn/src/lib.rs b/lrwn/src/lib.rs
index 1fb117b6..e087d819 100644
--- a/lrwn/src/lib.rs
+++ b/lrwn/src/lib.rs
@@ -21,6 +21,8 @@ pub use self::phy_payload::*;
 pub use self::relay::*;
 
 mod aes128;
+#[cfg(feature = "applayer")]
+pub mod applayer;
 mod cflist;
 mod devaddr;
 mod dl_settings;