diff --git a/_includes/devdoc/ref_p2p_networking.md b/_includes/devdoc/ref_p2p_networking.md
index 99f04f71..83808565 100644
--- a/_includes/devdoc/ref_p2p_networking.md
+++ b/_includes/devdoc/ref_p2p_networking.md
@@ -1411,6 +1411,8 @@ bc8f5e5400000000 ............................ Epoch time: 1415483324
 {% autocrossref %}
 
 The following network messages all help control the InstantSend feature of Dash.
+InstantSend uses the masternode network to lock transaction inputs and enable
+secure, instantaneous transactions.
 
 {% endautocrossref %}
 
@@ -1419,6 +1421,10 @@ The following network messages all help control the InstantSend feature of Dash.
 
 {% autocrossref %}
 
+The `ix` message (transaction lock request) has the same structure as the `tx` message.
+The masternode network responds with `txlvote` messages if the transaction inputs
+can be locked.
+
 {% endautocrossref %}
 
 
@@ -1427,6 +1433,41 @@ The following network messages all help control the InstantSend feature of Dash.
 
 {% autocrossref %}
 
+The `txlvote` message ([transaction lock vote][msg_txlock_vote]{:#term-msg_txlock_vote}{:.term})
+is sent by masternodes to indicate approval of a transaction lock request
+`ix` message.
+
+| Bytes | Name | Data type | Required | Description |
+| ---------- | ----------- | --------- | -------- | -------- |
+| 32 | txHash | uint256 | Required | TXID of the transaction to lock
+| 36 | outPoint | outpoint | Required | The unspent outpoint to lock in this transaction
+| 36 | outpointMasternode | outpoint | Required | The outpoint of the masternode which is signing the vote
+| 66* | vchMasternodeSignature | char[] | Required | 66 bytes in most cases. Length (1 byte) + Signature (65 bytes)
+
+The following annotated hexdump shows a `txlvote` message. (The
+message header has been omitted.)
+
+{% highlight text %}
+3c121fb4a12b2f715e2f70a9fa282115
+be197dde14073959fb2a2b8e95a7418f ..... TXID
+
+Outpoint to lock
+| bb607995757c6a6efd6429215dcb3688
+| b252d34d835c81fed310fd905f487020 ... Outpoint TXID
+| 01000000 ........................... Outpoint index number (1)
+
+Masternode Outpoint
+| de9029c7e9b7eb7cd11f27ba670b2349
+| 0c3f0717b86ed949c316874589405cd2 ... Outpoint TXID
+| 00000000 ........................... Outpoint index number (0)
+
+1ccc39ffb9c62111a8c82823d3ce61d2
+380db4e8f76ec238d568908f37558a90
+4e79566a53663de12ec2be1183c87d61
+250e8ebd57be171be1d4b5e89b69c263
+88 ................................... Masternode Signature
+{% endhighlight %}
+
 {% endautocrossref %}
 
 
diff --git a/_includes/references.md b/_includes/references.md
index 1dadbe3d..26514428 100644
--- a/_includes/references.md
+++ b/_includes/references.md
@@ -213,6 +213,7 @@ http://opensource.org/licenses/MIT.
 [getheaders message]: /en/developer-reference#getheaders "A P2P protocol message used to request a range of block headers"
 [headers message]: /en/developer-reference#headers "A P2P protocol message containing one or more block headers"
 [inv message]: /en/developer-reference#inv "A P2P protocol message used to send inventories of transactions and blocks known to the transmitting peer"
+[ix message]: /en/developer-reference#ix "A P2P protocol message which sends a single serialized transaction via InstantSend"
 [mempool message]: /en/developer-reference#mempool "A P2P protocol message used to request one or more inv messages with currently-unconfirmed transactions"
 [merkleblock message]: /en/developer-reference#merkleblock "A P2P protocol message used to request a filtered block useful for SPV proofs"
 [notfound message]: /en/developer-reference#notfound "A P2P protocol message sent to indicate that the requested data was not available"
@@ -221,6 +222,7 @@ http://opensource.org/licenses/MIT.
 [reject message]: /en/developer-reference#reject "A P2P network message used to indicate a previously-received message was rejected for some reason"
 [sendheaders message]: /en/developer-reference#sendheaders "A P2P network message used to request new blocks be announced through headers messages rather than inv messages"
 [tx message]: /en/developer-reference#tx "A P2P protocol message which sends a single serialized transaction"
+[txlvote message]: /en/developer-reference#txlvote "A P2P protocol message which masternodes send in response to an ix (transaction lock request) message if the transaction inputs can be locked."
 [verack message]: /en/developer-reference#verack "A P2P network message sent in reply to a version message to confirm a connection has been established"
 [version message]: /en/developer-reference#version "A P2P network message sent at the begining of a connection to allow protocol version negotiation"