diff --git a/packages/acn/src/models.ts b/packages/acn/src/models.ts
index a339a25..8136fbc 100644
--- a/packages/acn/src/models.ts
+++ b/packages/acn/src/models.ts
@@ -19,3 +19,61 @@ export type RootLayerPDU = {
   header: string;
   data: Uint8Array;
 };
+
+export enum SessionDataTransportVectors {
+  REL_WRAP = 1,
+  UNREL_WRAP,
+  CHANNEL_PARAMS,
+  JOIN,
+  JOIN_REFUSE,
+  JOIN_ACCEPT,
+  LEAVE,
+  LEAVING,
+  CONNECT,
+  CONNECT_ACCEPT,
+  CONNECT_REFUSE,
+  DISCONNECT,
+  DISCONNECTING,
+  ACK,
+  NAK,
+  GET_SESSIONS,
+  SESSIONS,
+}
+
+export enum TransportLayerAddressTypes {
+  SDT_ADDR_NULL = 0,
+  SDT_ADDR_IPV4,
+  SDT_ADDR_IPV6,
+}
+
+export type SDTChannelParams = {
+  expiry: number;
+  nakOutboundFlag: number;
+  nakHoldoff: number;
+  nakModulus: number;
+  nakMaxWait: number;
+};
+
+export type TransportLayerAddress = {
+  type: TransportLayerAddressTypes;
+  port?: number;
+  address?: string;
+};
+
+export type SDTJOINData = {
+  componentID: string;
+  memberID: number;
+  channelNumber: number;
+  reciprocalChannel: number;
+  totalSequenceNumber: number;
+  reliableSequenceNumber: number;
+  destinationAddress: TransportLayerAddress;
+  channelParameters: SDTChannelParams;
+  adhocExpiry: number;
+};
+
+export type SessionDataTransportPDU = {
+  vector: SessionDataTransportVectors;
+  // TODO(jwetzell): cleanup these types
+  data: SDTJOINData | Uint8Array;
+};
diff --git a/packages/acn/src/pdu/index.ts b/packages/acn/src/pdu/index.ts
index 58670a5..07a880b 100644
--- a/packages/acn/src/pdu/index.ts
+++ b/packages/acn/src/pdu/index.ts
@@ -1,4 +1,6 @@
 import rlp from './rlp';
+import sdt from './sdt';
 export default {
   rlp,
+  sdt,
 };
diff --git a/packages/acn/src/pdu/sdt.ts b/packages/acn/src/pdu/sdt.ts
new file mode 100644
index 0000000..d9b2252
--- /dev/null
+++ b/packages/acn/src/pdu/sdt.ts
@@ -0,0 +1,96 @@
+import { SessionDataTransportPDU, SessionDataTransportVectors, TransportLayerAddress } from '../models';
+import { toHex } from '../utils';
+
+// TODO(jwetzell): work out flag inheritance, will need previous PDU
+
+export function decode(bytes: Uint8Array): SessionDataTransportPDU {
+  const view = new DataView(bytes.buffer, bytes.byteOffset, bytes.byteLength);
+  const flags = view.getUint8(0) >> 4;
+  const lengthFlag = ((flags >> 3) & 0x1) === 1;
+  const vectorFlag = ((flags >> 2) & 0x1) === 1;
+
+  if (!vectorFlag) {
+    throw new Error('SDT PDU must have a vector');
+  }
+
+  const dataFlag = (flags & 0x1) === 1;
+
+  if (!dataFlag) {
+    // TODO(jwetzell): idk know if this is true
+    throw new Error('SDT PDU must have data');
+  }
+
+  const lengthH = view.getUint8(0) & 0x0f;
+  let lengthOffset = 1;
+  const lengthL = view.getUint8(lengthOffset);
+
+  let length = (lengthH << 8) + lengthL;
+  console.log('length', length);
+  if (lengthFlag) {
+    lengthOffset += 1;
+    const lengthX = view.getUint8(lengthOffset);
+    length = (lengthH << 16) + (lengthL << 8) + lengthX;
+  }
+  let vectorOffset = lengthOffset + 1;
+
+  if (lengthFlag) {
+    vectorOffset += 1;
+  }
+
+  const vector = view.getUint8(vectorOffset);
+
+  const dataOffset = vectorOffset + 1;
+  // NOTE(jwetzell): flags/lengthH + lengthL + lengthX + vector
+  const dataLength = length - (1 + 1 + (lengthFlag ? 1 : 0) + 1);
+  const data = bytes.subarray(dataOffset, dataOffset + dataLength);
+
+  switch (vector) {
+    case SessionDataTransportVectors.JOIN:
+      const destinationAddress: TransportLayerAddress = {
+        type: view.getUint8(dataOffset + 30),
+      };
+
+      // TODO(jwetzell): handle IPv6, type === 2
+      if (destinationAddress.type === 1) {
+        // IPv4
+        destinationAddress.port = view.getUint16(dataOffset + 31);
+        destinationAddress.address = bytes.subarray(dataOffset + 33, dataOffset + 37).join('.');
+      }
+
+      const adhocExpiry = view.getUint8(dataOffset + 45);
+      const joinData = {
+        componentID: toHex(bytes.subarray(dataOffset, dataOffset + 16)),
+        memberID: view.getUint16(dataOffset + 16),
+        channelNumber: view.getUint16(dataOffset + 18),
+        reciprocalChannel: view.getUint16(dataOffset + 20),
+        totalSequenceNumber: view.getUint32(dataOffset + 22),
+        reliableSequenceNumber: view.getUint32(dataOffset + 26),
+        destinationAddress,
+        channelParameters: {
+          expiry: view.getUint8(dataOffset + 37),
+          nakOutboundFlag: view.getUint8(dataOffset + 38),
+          nakHoldoff: view.getUint16(dataOffset + 39),
+          nakModulus: view.getUint16(dataOffset + 41),
+          nakMaxWait: view.getUint16(dataOffset + 43),
+        },
+        adhocExpiry,
+      };
+      return {
+        vector,
+        data: joinData,
+      };
+
+    default:
+      console.error(`unhandled SDT vector: ${vector}`);
+      break;
+  }
+
+  return {
+    vector,
+    data,
+  };
+}
+
+export default {
+  decode,
+};