diff --git a/src/runtime2/communication.rs b/src/runtime2/communication.rs
index 4fee962a9b41daa870d84b2b60e71585d5b630a3..c4bee587535d12a0410fcc24ff6545f853431c3c 100644
--- a/src/runtime2/communication.rs
+++ b/src/runtime2/communication.rs
@@ -1,10 +1,14 @@
 use crate::protocol::eval::*;
 use super::runtime::*;
+use super::component::*;
 
 #[derive(Copy, Clone)]
 pub struct PortId(pub u32);
 
+
 impl PortId {
+    /// This value is not significant, it is chosen to make debugging easier: a
+    /// very large port number is more likely to shine a light on bugs.
     pub fn new_invalid() -> Self {
         return Self(u32::MAX);
     }
@@ -16,11 +20,13 @@ pub struct Peer {
     pub(crate) handle: CompHandle,
 }
 
+#[derive(Debug, PartialEq, Eq)]
 pub enum PortKind {
     Putter,
     Getter,
 }
 
+#[derive(Debug, PartialEq, Eq)]
 pub enum PortState {
     Open,
     Blocked,
@@ -41,22 +47,36 @@ pub struct Channel {
 }
 
 pub struct DataMessage {
-    pub source_port_id: PortId,
-    pub target_port_id: PortId,
+    pub data_header: MessageDataHeader,
+    pub sync_header: MessageSyncHeader,
     pub content: ValueGroup,
 }
 
+pub struct MessageSyncHeader {
+    pub sync_round: u32,
+}
+
+pub struct MessageDataHeader {
+    pub expected_mapping: Vec<(PortId, u32)>,
+    pub new_mapping: u32,
+    pub source_port: PortId,
+    pub target_port: PortId,
+}
+
 pub struct ControlMessage {
-    pub id: u32,
+    pub id: ControlId,
     pub sender_comp_id: CompId,
-    pub content: ControlContent,
+    pub target_port_id: Option<PortId>,
+    pub content: ControlMessageContent,
 }
 
-pub enum ControlContent {
+#[derive(Copy, Clone)]
+pub enum ControlMessageContent {
     Ack,
-    Ping,
-    PortPeerChangedBlock,
-    PortPeerChangedUnblock,
+    BlockPort(PortId),
+    UnblockPort(PortId),
+    PortPeerChangedBlock(PortId),
+    PortPeerChangedUnblock(PortId, CompId),
 }
 
 pub enum Message {
@@ -64,4 +84,15 @@ pub enum Message {
     Control(ControlMessage),
 }
 
+impl Message {
+    pub(crate) fn target_port(&self) -> Option<PortId> {
+        match self {
+            Message::Data(v) =>
+                return Some(v.data_header.target_port),
+            Message::Control(v) =>
+                return v.target_port_id,
+        }
+    }
+}
+