diff --git a/sim/src/main/scala/agent.scala b/sim/src/main/scala/agent.scala
index 8b3d650c..e4badc3c 100644
--- a/sim/src/main/scala/agent.scala
+++ b/sim/src/main/scala/agent.scala
@@ -1,3 +1,5 @@
+package sim
+
 import cats.Monad
 import cats.effect.kernel.{Async, Clock}
 import cats.effect.std.{AtomicCell, Queue}
diff --git a/sim/src/main/scala/blockchain.scala b/sim/src/main/scala/blockchain.scala
index 698cf59f..3033fc74 100644
--- a/sim/src/main/scala/blockchain.scala
+++ b/sim/src/main/scala/blockchain.scala
@@ -1,3 +1,5 @@
+package sim
+
 import cats.Monad
 import cats.effect.std.Random
 import cats.effect.{Clock, Sync, Temporal}
@@ -9,10 +11,7 @@ import fs2.Stream
 
 import scala.concurrent.duration.*
 
-case class Account(value: String)
-
-case class Transaction(id: Long, account: Account, change: Long)
-case class Block(txs: Vector[Transaction], seqNum: Int)
+import sim.env.*
 
 /** L1 robust ledger system.
  */
diff --git a/sim/src/main/scala/env/ledger.scala b/sim/src/main/scala/env/ledger.scala
index 44a0ea71..32ed01ab 100644
--- a/sim/src/main/scala/env/ledger.scala
+++ b/sim/src/main/scala/env/ledger.scala
@@ -1,23 +1,39 @@
-package env
+package sim.env
+import cats.effect.{ExitCode, IO, IOApp}
 
-case class Rejection()
+case class Address(v: String)
+
+case class VrfPublicKey(value: String)  // HexString
+case class KesPublicKey(value: String)  // HexString
+case class DsigPublicKey(value: String) // HexString
+
+case class Account(
+    address: Address,
+    stake: Long,
+    vrfPk: VrfPublicKey,
+    kesPk: KesPublicKey,
+    dsigPk: DsigPublicKey
+)
+
+case class Transaction(id: Long, account: Account, change: Long)
 
 case class BlockId(value: Long)
 
-/** @type
-  *   B - Block
-  * @type
-  *   S - State
-  */
-trait Ledger[B, S, F[_]]:
+case class Block(id: BlockId, seqNum: Int)
+
+case class State(verAccounts: Vector[Account]) // set of verification keys to store in the Ledger
+
+trait Ledger[F[_]]:
   /** Add a new block to the ledger.
     */
-  def add(block: B): F[Either[Rejection, S]]
+  def add(block: Block): F[Unit]
 
   /** Get all blocks at the given height.
     */
-  def getAll(height: Int): F[List[B]]
+  def getAll(height: Int): F[List[Block]]
 
   /** Get specific block.
     */
-  def get(id: BlockId): F[Option[B]]
+  def get(id: BlockId): F[Option[Block]]
+  
+  def addParticipant(acc: Account): F[Unit]
diff --git a/sim/src/main/scala/main.scala b/sim/src/main/scala/main.scala
index fa7c42ae..63c99b92 100644
--- a/sim/src/main/scala/main.scala
+++ b/sim/src/main/scala/main.scala
@@ -3,6 +3,8 @@ import cats.syntax.show.*
 
 import scala.concurrent.duration.*
 
+import sim.*
+
 object Main extends IOApp {
   override def run(args: List[String]): IO[ExitCode] =
     for
diff --git a/sim/src/main/scala/protocol/spectrum.scala b/sim/src/main/scala/protocol/spectrum.scala
new file mode 100644
index 00000000..150c3638
--- /dev/null
+++ b/sim/src/main/scala/protocol/spectrum.scala
@@ -0,0 +1,57 @@
+package sim.spectrum
+
+import cats.Monad
+import cats.effect.IO
+import cats.effect.kernel.{Async, Clock}
+import cats.effect.std.{AtomicCell, Queue}
+import cats.syntax.applicative.*
+import cats.syntax.flatMap.*
+import cats.syntax.foldable.*
+import cats.syntax.functor.*
+import cats.syntax.traverse.*
+import sim.*
+import sim.env.*
+
+import scala.concurrent.duration.*
+import scala.language.postfixOps
+
+
+sealed trait SpectrumMsg
+case class NewBlock(block: Block) extends SpectrumMsg
+case class GetBlock(blockId: BlockId)  extends SpectrumMsg
+case class Register(newAcc: Account)  extends SpectrumMsg
+
+
+final class Spectrum[F[_]: Monad](
+                                   selfAddr: Addr,
+                                   // abstract interface to Ledger, so you dont have to care about impl.
+                                   ledger: Ledger[F],
+                                   // queue of pending output commands waiting to be returned from poll().
+                                   pendingOutputs: Queue[F, (Addr, AgentOut[SpectrumMsg])]
+                                 ) extends Agent[SpectrumMsg, F]:
+  def getAddr: F[Addr] = selfAddr.pure
+
+  def injectMessage(srcAddr: Addr, m: SpectrumMsg): F[Unit] =
+    m match
+      case NewBlock(block) => ledger.add(block)
+      case Register(account) => ledger.addParticipant(account)
+      case GetBlock(blockId) =>
+        for
+          maybeBlock <- ledger.get(blockId)
+          _ <- maybeBlock match
+            case None =>
+              // do nothing
+              ().pure
+            case Some(block) =>
+              // if the requested block is found locally we send it to the peer which requested it
+              pendingOutputs.offer(srcAddr -> SendMessage(NewBlock(block)))
+        yield ()
+
+  def injectConnReq(peerAddr: Addr, handshake: SpectrumMsg): F[Either[Reject, SpectrumMsg]] = ???
+
+  def injectConnLost(peerAddr: Addr): F[Unit] = ???
+
+  def injectConnEstablished(peerAddr: Addr, handshake: SpectrumMsg): F[Unit] = ???
+
+  def poll: F[Option[(Addr, AgentOut[SpectrumMsg])]] =
+    pendingOutputs.tryTake
\ No newline at end of file
diff --git a/sim/src/main/scala/swarm.scala b/sim/src/main/scala/swarm.scala
index 08110b68..f9b5d0c6 100644
--- a/sim/src/main/scala/swarm.scala
+++ b/sim/src/main/scala/swarm.scala
@@ -1,3 +1,5 @@
+package sim
+
 import cats.effect.kernel.Async
 import cats.effect.std.{AtomicCell, Random}
 import cats.effect.syntax.spawn.*