diff --git a/6.ts b/6.ts
index c1bb5cb..bd1cc7a 100644
--- a/6.ts
+++ b/6.ts
@@ -1,19 +1,24 @@
 import { BufReader } from "https://deno.land/std@0.157.0/io/buffer.ts";
+import { ByteSet, LengthType } from "https://deno.land/x/bytes@1.0.3/mod.ts";
 
 const PORT = 5588;
 
-type Road = number;
-type Dispatcher = Road[];
-type Location = number;
-type SpeedLimit = number;
-type Timestamp = number;
-type Plate = string;
 type Car = Plate;
 
-type U8 = number;
 type U16 = number;
 type U32 = number;
 
+type Deciseconds = U32;
+type Location = U16;
+type Plate = string;
+
+type Road = U16;
+type Mile = U16;
+
+type SpeedLimit = U16;
+type SpeedMPH100 = U16;
+type Timestamp = U32;
+
 interface Camera {
   road: Road;
   location: Location;
@@ -26,53 +31,444 @@ interface Report {
   timestamp: Timestamp;
 }
 
-// const tEnc = new TextEncoder();
+const tEnc = new TextEncoder();
+const tDec = new TextDecoder();
 
 console.log(`Starting TCP listener on on 0.0.0.0:${PORT}`);
 
-function chatSession(conn: Deno.Conn) {
-  const closeOnDisconnect = () => {
-    console.warn("Disconnected client");
-    try {
-      conn.close();
-    } catch (err) {
-      console.error("Error closing client connection:", err);
-    }
-  };
-
-  serve(conn).catch((e) => e).finally(closeOnDisconnect);
+function session(conn: Deno.Conn) {
+  serve(conn).catch((e) => console.error("Exception during session:", e))
+    .finally(() => disconnect(conn));
 }
 
 enum MessageType {
   ERROR = 0x10, // Server -> Client
   PLATE = 0x20, // Client -> Server
   TICKET = 0x21, // Server -> Client
+  WANT_HEARTBEAT = 0x40, // Client -> Server
+  HEARTBEAT = 0x41, // Server -> Client
+  I_AM_CAMERA = 0x80, // Client -> Server
+  I_AM_DISPATCHER = 0x81, // Client -> Server
 }
 
+console.log("Message Types:", MessageType);
+
 type ErrorMessage = [
   string, // msg
 ];
 
 type PlateMessage = [
-  string, // plate
-  U32, // timestamp
+  Plate,
+  Timestamp,
 ];
 
-interface TicketMessage {
+type TicketMessage = [
+  Plate, // plate
+  Road, // road
+  Mile, // mile1
+  Timestamp, // timestamp1
+  Mile, // mile2
+  Timestamp, // timestamp2
+  SpeedMPH100, // speed
+];
+
+type WantHeartbeatMessage = [
+  Deciseconds,
+];
+
+type HeartbeatMessage = [];
+
+type IAmCameraMessage = [
+  Road,
+  Mile,
+  SpeedLimit,
+];
+
+type IAmDispatcherMessage = [
+  Road[],
+];
+
+type Message =
+  | ErrorMessage
+  | PlateMessage
+  | TicketMessage
+  | WantHeartbeatMessage
+  | HeartbeatMessage
+  | IAmCameraMessage
+  | IAmDispatcherMessage;
+
+async function readU16(reader: BufReader): Promise<U16> {
+  const buf = await reader.readFull(new Uint8Array(2));
+  if (!buf) throw `unable to fill buffer of length 2 with U32 bytes`;
+  return ByteSet.from(buf, "big").read.uint16();
 }
 
-type Message = ErrorMessage | PlateMessage;
+async function readU32(reader: BufReader): Promise<U32> {
+  const buf = await reader.readFull(new Uint8Array(4));
+  if (!buf) throw `unable to fill buffer of length 4 with U32 bytes`;
+  return ByteSet.from(buf, "big").read.uint32();
+}
+
+async function readString(reader: BufReader): Promise<string> {
+  const len = await reader.readByte();
+  if (!len) throw "unable to read string length byte";
+  const buf = await reader.readFull(new Uint8Array(len));
+  if (!buf) throw `unable to fill buffer of length ${len} with string bytes`;
+  return tDec.decode(buf);
+}
+
+async function readArray<T>(
+  reader: BufReader,
+  readCallback: (r: BufReader) => Promise<T>,
+): Promise<T[]> {
+  const len = await reader.readByte();
+  if (!len) throw "unable to read array length byte";
+  const result = [];
+  while (result.length < len) {
+    result.push(await readCallback(reader));
+  }
+  if (result.length != len) {
+    throw new Error(
+      `unable to read array of length ${len} (got ${result.length})`,
+    );
+  }
+  return result;
+}
+
+async function seqRead<T extends Message>(
+  reader: BufReader,
+  seq: ((r: BufReader) => Promise<T[keyof T]>)[],
+): Promise<T> {
+  const result = [];
+  for (const f of seq) {
+    result.push(await f(reader));
+  }
+  return result as T; // TODO: cheating
+}
+
+async function readError(reader: BufReader): Promise<ErrorMessage> {
+  return await seqRead(reader, [readString]);
+}
+
+async function readPlate(reader: BufReader): Promise<PlateMessage> {
+  return await seqRead(reader, [readString, readU32]);
+}
+
+async function readTicket(reader: BufReader): Promise<TicketMessage> {
+  return await seqRead(reader, [
+    readString,
+    readU16,
+    readU16,
+    readU32,
+    readU16,
+    readU32,
+    readU16,
+  ]);
+}
+
+async function readWantHeartbeat(
+  reader: BufReader,
+): Promise<WantHeartbeatMessage> {
+  return await seqRead(reader, [readU32]);
+}
+
+async function readIAmCamera(reader: BufReader): Promise<IAmCameraMessage> {
+  return await seqRead(reader, [readU16, readU16, readU16]);
+}
+
+async function readMessage(
+  reader: BufReader,
+): Promise<{ type: MessageType; message: Message }> {
+  const type = await reader.readByte();
+  if (!type) throw new Error("Failed to read message type byte");
+  let message: Message | null = null;
+  switch (type) {
+    case MessageType.ERROR:
+      message = await readError(reader);
+      break;
+    case MessageType.PLATE:
+      message = await readPlate(reader);
+      break;
+    case MessageType.TICKET:
+      message = await readTicket(reader);
+      break;
+    case MessageType.WANT_HEARTBEAT:
+      message = await readWantHeartbeat(reader);
+      break;
+    case MessageType.HEARTBEAT:
+      message = [];
+      break;
+    case MessageType.I_AM_CAMERA:
+      message = await readIAmCamera(reader);
+      break;
+    case MessageType.I_AM_DISPATCHER:
+      message = [await readArray(reader, readU16)];
+      break;
+    default:
+      throw new Error(`failed to read message of type 0x${type.toString(16)}`);
+  }
+  return { type, message };
+}
+
+function dayOfTime(ts: Timestamp): number {
+  return Math.floor(ts / 86400);
+}
+
+const intervals = new Map<Deno.Conn, number>();
+const cameras = new Map<Deno.Conn, Camera>();
+const dispatchers = new Map<Deno.Conn, Road[]>();
+const observations = new Map<Plate, Map<Road, Map<Location, Timestamp>>>();
+const unsentTickets: TicketMessage[] = [];
+const dispatchedTicketDays = new Map<Plate, Set<number>>();
+
+function makeObservation(
+  plate: Plate,
+  road: Road,
+  location: Location,
+  when: Timestamp,
+  speedLimit: SpeedLimit,
+) {
+  let forPlate = observations.get(plate);
+  if (!forPlate) {
+    const newForPlate = new Map<Road, Map<Location, Timestamp>>();
+    observations.set(plate, newForPlate);
+    forPlate = newForPlate;
+  }
+  let forRoad = forPlate.get(road);
+  if (!forRoad) {
+    const newForRoad = new Map<Location, Timestamp>();
+    forPlate.set(road, newForRoad);
+    forRoad = newForRoad;
+  }
+
+  for (const [loc, ts] of forRoad.entries()) {
+    const distMiles = Math.abs(location - loc);
+    const deltaSecs = Math.abs(ts - when);
+    const speed = distMiles / (deltaSecs / 60 / 60);
+    console.log("Diff:", {
+      plate,
+      road,
+      loc,
+      ts,
+      location,
+      when,
+      distMiles,
+      deltaSecs,
+      speed,
+      speedLimit,
+      day: dayOfTime(when),
+    });
+    if (speed > speedLimit + 0.5) {
+      let [m1, t1] = [loc, ts];
+      let [m2, t2] = [location, when];
+      if (when < ts) {
+        [m2, t2] = [loc, ts];
+        [m1, t1] = [location, when];
+      }
+
+      // for now, we will send one ticket per observation - should work, given the constraints
+      dispatchTicket([
+        plate,
+        road,
+        m1,
+        t1,
+        m2,
+        t2,
+        Math.floor(speed * 100),
+      ]);
+      break;
+    }
+  }
+
+  console.log("Observation:", { plate, road, location, when });
+
+  forRoad.set(location, when);
+}
+
+function handleMessage(
+  conn: Deno.Conn,
+  type: MessageType,
+  message: Message,
+) {
+  console.debug("Message:", {
+    from: conn.remoteAddr,
+    type: MessageType[type.toString()],
+    message,
+  });
+  switch (type) {
+    case MessageType.WANT_HEARTBEAT: {
+      if (intervals.has(conn)) {
+        return sendErrorAndDisconnect(conn, "heartbeat already specified");
+      }
+      const [interval] = (message as WantHeartbeatMessage);
+      setIntervalFor(conn, interval);
+      break;
+    }
+    case MessageType.PLATE: {
+      const cam = cameras.get(conn);
+      if (!cam) return sendErrorAndDisconnect(conn, "not a camera");
+      const [plate, when] = (message as PlateMessage);
+      makeObservation(plate, cam.road, cam.location, when, cam.speedLimit);
+      break;
+    }
+    case MessageType.I_AM_CAMERA: {
+      if (cameras.has(conn) || dispatchers.has(conn)) {
+        sendErrorAndDisconnect(conn, "already identified");
+      }
+      const [road, location, speedLimit] = (message as IAmCameraMessage);
+      const camera: Camera = {
+        road,
+        location,
+        speedLimit,
+      };
+      cameras.set(conn, camera);
+      break;
+    }
+    case MessageType.I_AM_DISPATCHER: {
+      if (cameras.has(conn) || dispatchers.has(conn)) {
+        sendErrorAndDisconnect(conn, "already identified");
+      }
+      const [roads] = (message as IAmDispatcherMessage);
+      dispatchers.set(conn, roads);
+      for (let i = unsentTickets.length - 1; i >= 0; i--) {
+        const t = unsentTickets[i];
+        const [_, road] = t;
+        if (roads.includes(road)) {
+          unsentTickets.splice(i, 1);
+          sendTicket(conn, t);
+        }
+      }
+      break;
+    }
+    default:
+      console.warn("Unable to handle unknown message:", {
+        from: conn.remoteAddr,
+        type: MessageType[type.toString()],
+        message,
+      });
+      break;
+  }
+}
+
+function markPlateDay(plate: Plate, day: number) {
+  let forTicketDay = dispatchedTicketDays.get(plate);
+  if (!forTicketDay) {
+    const newForTicketDay = new Set<number>();
+    dispatchedTicketDays.set(plate, newForTicketDay);
+    forTicketDay = newForTicketDay;
+  }
+  forTicketDay.add(day);
+}
+
+function hasPlateDay(plate: Plate, day: number): boolean {
+  return !!(dispatchedTicketDays.get(plate)?.has(day));
+}
+
+function dispatchTicket(t: TicketMessage) {
+  let [plate, road, mile1, ts1, mile2, ts2, speed] = t;
+  let day1 = dayOfTime(ts1);
+  const day2 = dayOfTime(ts2);
+
+  while (day1 < day2) {
+    const nts1 = Math.max(ts1, day1 * 86400);
+    const nts2 = Math.min(((day1 + 1) * 86400) - 1, ts2);
+    console.log("Multi-day ticket:", day1, day2, nts1, nts2);
+    day1++;
+    ts1 = nts2 + 1;
+    dispatchTicket([plate, road, mile1, nts1, mile2, nts2, speed]);
+  }
+
+  if (hasPlateDay(plate, day1)) {
+    return;
+  }
+  markPlateDay(plate, day1);
+
+  let sent = false;
+  for (const [conn, roads] of dispatchers.entries()) {
+    if (roads.includes(road)) {
+      sent = true;
+      sendTicket(conn, t);
+      break;
+    }
+  }
+  if (!sent) unsentTickets.push(t);
+}
+
+async function sendTicket(conn: Deno.Conn, t: TicketMessage) {
+  const [plate, road, m1, t1, m2, t2, speed] = t;
+  console.log("Sending ticket:", t);
+  const plateBytes = tEnc.encode(plate);
+
+  const p = new ByteSet(
+    1 + 1 + plateBytes.length + 2 + 2 + 4 + 2 + 4 + 2,
+    "big",
+  );
+  p.write.uint8(MessageType.TICKET);
+  // p.write.uint8(plateBytes.length);
+  p.write.uint8Array(plateBytes, LengthType.Uint8);
+  p.write.uint16(road);
+  p.write.uint16(m1);
+  p.write.uint32(t1);
+  p.write.uint16(m2);
+  p.write.uint32(t2);
+  p.write.uint16(speed);
+  await conn.write(p.buffer);
+}
 
 async function serve(conn: Deno.Conn) {
   const reader = new BufReader(conn);
-  const type = await reader.peek(1);
-  if (!type) throw new Error("failed to peek start of packet");
-  console.log({ type }, 0x64);
-  // TODO: loop...
+  try {
+    while (true) {
+      const { type: type, message } = await readMessage(reader);
+      handleMessage(conn, type, message);
+    }
+  } finally {
+    clearIntervalFor(conn);
+  }
+}
+
+function disconnect(conn: Deno.Conn) {
+  console.log("Disconnecting:", conn.remoteAddr);
+  try {
+    conn.close();
+  } catch (_) {
+    console.debug("Failed to close connection (probably already closed)");
+  }
+  clearIntervalFor(conn);
+  cameras.delete(conn);
+  dispatchers.delete(conn);
+}
+
+async function sendErrorAndDisconnect(conn: Deno.Conn, msg: string) {
+  console.warn("Sending error:", msg);
+  await conn.write(new Uint8Array([MessageType.ERROR]));
+  await conn.write(tEnc.encode(msg));
+  disconnect(conn);
+}
+
+function setIntervalFor(conn: Deno.Conn, intervalDeciseconds: number) {
+  if (intervalDeciseconds <= 0) return;
+
+  intervals.set(
+    conn,
+    setInterval(() => {
+      try {
+        conn.write(new Uint8Array([MessageType.HEARTBEAT]));
+      } catch {
+        clearIntervalFor(conn);
+      }
+    }, intervalDeciseconds * 100 /* deciseconds to ms */),
+  );
+}
+
+function clearIntervalFor(conn: Deno.Conn) {
+  if (intervals.has(conn)) {
+    clearInterval(intervals.get(conn));
+    intervals.delete(conn);
+  }
 }
 
 for await (const conn of Deno.listen({ port: PORT })) {
   console.log("Connection established:", conn.remoteAddr);
-  chatSession(conn);
-  console.log("Connection closed:", conn.remoteAddr);
+  session(conn);
 }
diff --git a/deno.lock b/deno.lock
new file mode 100644
index 0000000..ed3ec25
--- /dev/null
+++ b/deno.lock
@@ -0,0 +1,18 @@
+{
+  "version": "2",
+  "remote": {
+    "https://deno.land/std@0.157.0/_util/assert.ts": "e94f2eb37cebd7f199952e242c77654e43333c1ac4c5c700e929ea3aa5489f74",
+    "https://deno.land/std@0.157.0/bytes/bytes_list.ts": "aba5e2369e77d426b10af1de0dcc4531acecec27f9b9056f4f7bfbf8ac147ab4",
+    "https://deno.land/std@0.157.0/bytes/equals.ts": "3c3558c3ae85526f84510aa2b48ab2ad7bdd899e2e0f5b7a8ffc85acb3a6043a",
+    "https://deno.land/std@0.157.0/bytes/mod.ts": "763f97d33051cc3f28af1a688dfe2830841192a9fea0cbaa55f927b49d49d0bf",
+    "https://deno.land/std@0.157.0/io/buffer.ts": "fae02290f52301c4e0188670e730cd902f9307fb732d79c4aa14ebdc82497289",
+    "https://deno.land/std@0.157.0/io/types.d.ts": "0cae3a62da7a37043661746c65c021058bae020b54e50c0e774916e5d4baee43",
+    "https://deno.land/x/bytes@1.0.3/mod.ts": "0df9e698738399cb6ab2ceaff1d64d45e1581d62c900e3cc6664d75556288fb8",
+    "https://deno.land/x/bytes@1.0.3/src/bitarray/BitArray.ts": "0b3ad2f03aee0bc5f1f047714e83fec43e9ccbab32b4113cb61925ac80fec62d",
+    "https://deno.land/x/bytes@1.0.3/src/bitarray/Read.ts": "f8e721c984a7297025de9406304cf96cf9778f999fa6ed064dfee5f3d4f9800d",
+    "https://deno.land/x/bytes@1.0.3/src/bitarray/Write.ts": "2ef36768c7d47b00e9100507452ce8ce9b14912bc0f1059926a022a719de7d9c",
+    "https://deno.land/x/bytes@1.0.3/src/byteset/ByteSet.ts": "9b7306cb12852cfaf6340378a87c9e5b33eba6de8c3d4c05ddc411bb3da2743c",
+    "https://deno.land/x/bytes@1.0.3/src/byteset/Read.ts": "761966c30456c6cc5b4a52c7e154139033b03e6b14c8cecea88f68ad3f0c2b66",
+    "https://deno.land/x/bytes@1.0.3/src/byteset/Write.ts": "9ec31b39bc1306960f70486e3e898cc38902f2ce3ba338912e1acdee6867b97e"
+  }
+}
diff --git a/readme.md b/readme.md
index e42d1f6..23c8cba 100644
--- a/readme.md
+++ b/readme.md
@@ -10,13 +10,7 @@ the `std` modules available to do as much as possible in a very asynchronous
 
 [Install Deno][deno#install]
 
-# Usage
-
-```bash
-deno run -A --unstable N.ts
-```
-
-## Example
+# Example Usage
 
 ```bash
 deno run -A --unstable 0.ts