## Channels

Each peer connection is multiplexed into channels.
<hr />

### PEX channel

The PEX channel is used to exchange peer addresses.

<table>
  <tr>
    <td><b>Channel</b></td>
    <td>"PEX"</td>
  </tr>
  <tr>
    <td><b>Messages</b></td>
    <td>
      <ul>
        <li>pexRequestMsg</li>
        <li>pexResponseMsg</li>
      </ul>
    </td>
  </tr>
</table>
<hr />

### Block channel

The block channel is used to propagate block or header information to new peers or peers catching up with the blockchain.

<table>
  <tr>
    <td><b>Channel</b></td>
    <td>"block"</td>
  </tr>
  <tr>
    <td><b>Messages</b></td>
    <td>
      <ul>
        <li>RequestMsg</li>
        <li>BlockMsg</li>
        <li>HeaderMsg</li>
      </ul>
    </td>
  </tr>
  <tr>
    <td><b>Notes</b></td>
    <td>
      Nodes should only advertise having a header or block at height 'h' if it also has all the headers or blocks less than 'h'.  Thus for each peer we need only keep track of two integers -- one for the most recent header height 'h_h' and one for the most recent block height 'h_b', where 'h_b' &lt;= 'h_h'.
    </td>
  </tr>
</table>
<hr />

### Mempool channel

The mempool channel is used for broadcasting new transactions that haven't yet entered the blockchain.  It uses a lossy bloom filter on either end, but with sufficient fanout and filter nonce updates every new block, all transactions will eventually reach every node.

<table>
  <tr>
    <td><b>Channel</b></td>
    <td>"mempool"</td>
  </tr>
  <tr>
    <td><b>Messages</b></td>
    <td>
      <ul>
        <li>MempoolTxMsg</li>
      </ul>
    </td>
  </tr>
  <tr>
    <td><b>Notes</b></td>
    <td>
      Instead of keeping a perfect inventory of what peers have, we use a lossy filter.<br/>
      Bloom filter (n:10k, p:0.02 -> k:6, m:10KB)<br/>
      Each peer's filter has a random nonce that scrambles the message hashes.<br/>
      The filter & nonce refreshes every new block.<br/>
    </td>
  </tr>
</table>
<hr />

### Consensus channel

The consensus channel broadcasts all information used in the rounds of the Tendermint consensus mechanism.

<table>
  <tr>
    <td><b>Channel</b></td>
    <td>"consensus"</td>
  </tr>
  <tr>
    <td><b>Messages</b></td>
    <td>
      <ul>
        <li>ProposalMsg</li>
        <li>VoteMsg</li>
        <li>NewBlockMsg</li>
      </ul>
    </td>
  </tr>
  <tr>
    <td><b>Notes</b></td>
    <td>
      How do optimize/balance propagation speed & bandwidth utilization?
    </td>
  </tr>
</table>

## Resources

* http://www.upnp-hacks.org/upnp.html