Merge pull request #353 from ElPaisano/update/glossary

Add dcutr glossary entries

content/concepts/appendix/glossary.md

@@ -41,6 +41,10 @@ A libp2p connection is a communication channel that allows peers to read and wri
 
 Connections between peers are established via [transports](#transport), which can be thought of as "connection factories". For example, the TCP transport allows you to create connections that use TCP/IP as their underlying substrate.
 
+### DCUtR 
+
+Direct Connection Upgrade through Relay (DCUtR) is a protocol for establishing direct connections between nodes via hole punching, without a [signaling server](#signaling-server). DCUtR synchronizes and opens connections to each peer's predicted external addresses.
+
 ### Dial
 
 The process of opening a libp2p connection to another peer is known as "dialing", and accepting connections is known as ["listening"](#listen). Together, an implementation of dialing and listening forms a [transport](#transport).
@@ -207,6 +211,10 @@ The implementation of the libp2p handshake is called
 
 For details, see the [protocol negotiation article]({{< relref "/concepts/fundamentals/protocols.md#protocol-negotiation" >}}).
 
+### Signaling server
+
+A server or service that facilitates communication between nodes in a peer-to-peer network, specifically in context of setting up, maintaining and terminating a direct communication channel between two peers which are behind NATs. The server discovers the external IP address and port of the peers, and also relays messages between the peers to assist NAT traversal.
+
 ### Stream
 
 TODO: Distinguish between the various types of "stream". Could refer to

content/concepts/nat/dcutr.md

@@ -11,14 +11,7 @@ to scale and maintain, and may result in low-bandwidth, high-latency
 connections. [Hole punching]({{< relref "/concepts/nat/hole-punching.md" >}}) is another technique
 that enables NAT traversal by enabling two nodes behind NATs to communicate
 directly.  However, in addition to relay nodes, it requires another piece of
-infrastructure called signaling servers.
-
-> A signaling server is a server or service that facilitates communication
-> between nodes in a P2P network, specifically in context of setting up,
-> maintaining and terminating a direct communication channel between two peers
-> which are behind NATs. It helps in discovering the external IP address and
-> port of the peers and also in NAT traversal by relaying messages between the
-> peers.
+infrastructure called a [signaling server](../appendix/glossary.md#signaling-server).
 
 The good news is that libp2p offers a hole punching solution which eliminates
 the need for centralized signaling servers and allows the use of distributed