diff --git a/Cargo.toml b/Cargo.toml
index 4c4cdad..a2f4c44 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -39,6 +39,7 @@ futures = "0.3"
 crc32fast = "1"
 intmap = "2"
 moka = { version = "0.12", optional = true, features = ["sync"] }
+tokio = { version = "1.27.0", features = ["rt", "sync"], optional = true}
 
 [target.'cfg(not(target_arch = "wasm32"))'.dependencies]
 random-access-disk = { version = "3", default-features = false }
@@ -59,9 +60,9 @@ test-log = { version = "0.2.11", default-features = false, features = ["trace"]
 tracing-subscriber = { version = "0.3.16", features = ["env-filter", "fmt"] }
 
 [features]
-default = ["async-std", "sparse"]
+default = ["tokio", "sparse"]
 sparse = ["random-access-disk/sparse"]
-tokio = ["random-access-disk/tokio"]
+tokio = ["dep:tokio", "random-access-disk/tokio"]
 async-std = ["random-access-disk/async-std"]
 cache = ["moka"]
 # Used only in interoperability tests under tests/js-interop which use the javascript version of hypercore
diff --git a/src/common/node.rs b/src/common/node.rs
index 7e339d3..c0a9dfc 100644
--- a/src/common/node.rs
+++ b/src/common/node.rs
@@ -20,10 +20,15 @@ pub(crate) struct NodeByteRange {
 // disk.
 #[derive(Debug, Clone, PartialEq, Eq)]
 pub struct Node {
+    /// TODO document me
     pub(crate) index: u64,
+    /// hash of the data in this node
     pub(crate) hash: Vec<u8>,
+    /// number of bytes of the data
     pub(crate) length: u64,
     pub(crate) parent: u64,
+    /// The data. Other metadata in this struct is provided before the actual data.
+    /// so it is optional
     pub(crate) data: Option<Vec<u8>>,
     pub(crate) blank: bool,
 }
diff --git a/src/common/peer.rs b/src/common/peer.rs
index c71b981..11de57d 100644
--- a/src/common/peer.rs
+++ b/src/common/peer.rs
@@ -1,6 +1,8 @@
 //! Types needed for passing information with with peers.
 //! hypercore-protocol-rs uses these types and wraps them
 //! into wire messages.
+use std::fmt::Display;
+
 use crate::Node;
 
 #[derive(Debug, Clone, PartialEq)]
@@ -104,14 +106,27 @@ pub struct DataSeek {
 #[derive(Debug, Clone, PartialEq)]
 /// TODO: Document
 pub struct DataUpgrade {
-    /// TODO: Document
+    /// starting block of this upgrade response
     pub start: u64,
-    /// TODO: Document
+    /// number of blocks in this upgrade response
     pub length: u64,
-    /// TODO: Document
+    /// the metadata nodes?
     pub nodes: Vec<Node>,
     /// TODO: Document
     pub additional_nodes: Vec<Node>,
     /// TODO: Document
     pub signature: Vec<u8>,
 }
+
+impl Display for DataUpgrade {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        write!(
+            f,
+            "DataUpgrade(start: {}, length: {}, nodes: {:?}, .., signature: {})",
+            self.start,
+            self.length,
+            self.nodes,
+            self.signature.len()
+        )
+    }
+}
diff --git a/src/core.rs b/src/core.rs
index 886ff98..a950dc9 100644
--- a/src/core.rs
+++ b/src/core.rs
@@ -3,8 +3,12 @@ use ed25519_dalek::Signature;
 use futures::future::Either;
 use std::convert::TryFrom;
 use std::fmt::Debug;
+#[cfg(feature = "tokio")]
+use tokio::sync::broadcast::{self, Receiver, Sender};
 use tracing::instrument;
 
+#[cfg(feature = "tokio")]
+static MAX_EVENT_QUEUE_CAPACITY: usize = 32;
 #[cfg(feature = "cache")]
 use crate::common::cache::CacheOptions;
 use crate::{
@@ -37,6 +41,24 @@ impl HypercoreOptions {
     }
 }
 
+#[derive(Debug)]
+#[cfg(feature = "tokio")]
+struct Events {
+    /// Sends a notification to the replicator that core is upgraded
+    on_upgrade: Sender<()>,
+    /// Notify receiver to get block over the network.
+    on_get: Sender<(u64, Sender<()>)>,
+}
+
+#[cfg(feature = "tokio")]
+impl Events {
+    fn new() -> Self {
+        let (on_upgrade, _) = broadcast::channel(MAX_EVENT_QUEUE_CAPACITY);
+        let (on_get, _) = broadcast::channel(MAX_EVENT_QUEUE_CAPACITY);
+        Self { on_upgrade, on_get }
+    }
+}
+
 /// Hypercore is an append-only log structure.
 #[derive(Debug)]
 pub struct Hypercore {
@@ -48,6 +70,8 @@ pub struct Hypercore {
     pub(crate) bitfield: Bitfield,
     skip_flush_count: u8, // autoFlush in Javascript
     header: Header,
+    #[cfg(feature = "tokio")]
+    events: Events,
 }
 
 /// Response from append, matches that of the Javascript result
@@ -247,6 +271,8 @@ impl Hypercore {
             bitfield,
             header,
             skip_flush_count: 0,
+            #[cfg(feature = "tokio")]
+            events: Events::new(),
         })
     }
 
@@ -323,6 +349,11 @@ impl Hypercore {
             }
         }
 
+        // NB: send() returns an error when there are no receivers. Which is the case when there is
+        // no replication. We ignore the error. No recievers is ok.
+        #[cfg(feature = "tokio")]
+        let _ = self.events.on_upgrade.send(());
+
         // Return the new value
         Ok(AppendOutcome {
             length: self.tree.length,
@@ -330,10 +361,40 @@ impl Hypercore {
         })
     }
 
+    #[cfg(feature = "tokio")]
+    /// Subscribe to upgrade events
+    pub fn on_upgrade(&self) -> Receiver<()> {
+        self.events.on_upgrade.subscribe()
+    }
+
+    #[cfg(feature = "tokio")]
+    /// Notify listeners of a get request
+    pub fn on_get(&self, index: u64) -> Receiver<()> {
+        let (tx, rx) = broadcast::channel(1);
+        let _ = self.events.on_get.send((index, tx));
+        rx
+    }
+
+    #[cfg(feature = "tokio")]
+    /// Subscribe to `.get` requests
+    pub fn on_get_subscribe(&self) -> Receiver<(u64, Sender<()>)> {
+        self.events.on_get.subscribe()
+    }
+
     /// Read value at given index, if any.
     #[instrument(err, skip(self))]
     pub async fn get(&mut self, index: u64) -> Result<Option<Vec<u8>>, HypercoreError> {
         if !self.bitfield.get(index) {
+            // not in this core
+            // try getting it over the network
+            #[cfg(feature = "tokio")]
+            {
+                let mut rx = self.on_get(index);
+                //let res = rx.recv().await.unwrap();
+                tokio::spawn(async move {
+                    let _ = rx.recv().await;
+                });
+            }
             return Ok(None);
         }