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+/* $Id$ */
+/* 
+ * Copyright (C) 2008-2009 Teluu Inc. (http://www.teluu.com)
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA 
+ */
+
+
+/**
+@defgroup PJNATH_TURN TURN: Traversal Using Relays around NAT
+@brief TURN protocol implementation
+@ingroup PJNATH
+
+\section turn_intro_sec Introduction to TURN
+
+When a direct communication path cannot be found, it is necessary to
+use the services of an intermediate host that acts as a relay for the
+packets.  This relay typically sits in the public Internet and relays
+packets between two hosts that both sit behind NATs.
+
+TURN allows a host behind a NAT (called the TURN client) to request that 
+another host (called the TURN server) act as a relay.  The client can 
+arrange for the server to relay packets to and from certain other hosts
+(called peers) and can control aspects of how the relaying is done.
+The client does this by obtaining an IP address and port on the
+server, called the relayed-transport-address.  When a peer sends a
+packet to the relayed-transport-address, the server relays the packet
+to the client.  When the client sends a data packet to the server,
+the server relays it to the appropriate peer using the relayed-
+transport-address as the source.
+
+
+\section turn_op_sec Overview of TURN operations
+
+<b>Discovering TURN server</b>.\n
+Client learns the IP address of the TURN
+server either through some privisioning or by querying DNS SRV records
+for TURN service for the specified domain. Client may use UDP or TCP (or
+TLS) to connect to the TURN server.
+
+<b>Authentication</b>.\n
+All TURN operations requires the use of authentication
+(it uses STUN long term autentication method), hence client must be
+configured with the correct credential to use the service.
+
+<b>Allocation</b>.\n
+Client creates one "relay port" (or called <b>relayed-transport-address</b>
+in TURN terminology) in the TURN server by sending TURN \a Allocate request,
+hence this process is called creating allocation. Once the allocation is 
+successful, client will be given the IP address and port of the "relay 
+port" in the Allocate response.
+
+<b>Sending data through the relay</b>.\n
+Once allocation has been created, client may send data to any remote 
+endpoints (called peers in TURN terminology) via the "relay port". It does 
+so by sending Send Indication to the TURN server, giving the peer address 
+in the indication message. But note that at this point peers are not allowed
+to send data towards the client (via the "relay port") before permission is 
+installed for that peer.
+
+<b>Creating permissions</b>.\n
+Permission needs to be created in the TURN server so that a peer can send 
+data to the client via the relay port (a peer in this case is identified by
+its IP address). Without this, when the TURN server receives data from the
+peer in the "relay port", it will drop this data.
+
+<b>Receiving data from peers</b>.\n
+Once permission has been installed for the peer, any data received by the 
+TURN server (from that peer) in the "relay port" will be relayed back to 
+client by using Data Indication.
+
+<b>Using ChannelData</b>.\n
+TURN provides optimized framing to the data by using ChannelData 
+packetization. The client activates this format by sending ChannelBind 
+request to the TURN server, which provides (channel) binding which maps a 
+particular peer address with a channel number. Data sent or received to/for
+this peer will then use ChannelData format instead of Send or Data 
+Indications.
+
+<b>Refreshing the allocation, permissions, and channel bindings</b>.\n
+Allocations, permissions, and channel bindings need to be refreshed
+periodically by client, or otherwise they will expire.
+
+<b>Destroying the allocation</b>.\n
+Once the "relay port" is no longer needed, client destroys the allocation
+by sending Refresh request with LIFETIME attribute set to zero.
+
+
+\section turn_org_sec Library organizations
+
+The TURN functionalities in PJNATH primarily consist of 
+\ref PJNATH_TURN_SOCK and \ref PJNATH_TURN_SESSION. Please see more
+below.
+
+
+\section turn_using_sec Using TURN transport
+
+The \ref PJNATH_TURN_SOCK is a ready to use object for relaying
+application data via a TURN server, by managing all the operations
+above.
+
+Among other things it provides the following features:
+ - resolution of the TURN server with DNS SRV
+ - interface to create allocation, permissions, and channel
+   bindings
+ - interface to send and receive packets through the relay
+ - provides callback to notify the application about incoming data
+ - managing the allocation, permissions, and channel bindings
+
+Please see \ref PJNATH_TURN_SOCK for more documentation about and
+on how to use this object.
+
+
+\section turn_owntransport_sec Creating custom TURN transport
+
+The \ref PJNATH_TURN_SESSION is a transport-independent object to
+manage a client TURN session. It contains the core logic for managing
+the TURN client session as listed in TURN operations above, but
+in transport-independent manner (i.e. it doesn't have a socket), so
+that developer can integrate TURN client functionality into existing
+framework that already has its own means to send and receive data,
+or to support new transport types to TURN, such as TLS.
+
+You can create your own (custom) TURN transport by wrapping this
+into your own object, and provide it with the means to send and
+receive packets.
+
+Please see \ref PJNATH_TURN_SESSION for more information.
+
+
+\section turn_samples_sec Samples
+
+The \ref turn_client_sample is a sample application to use the
+\ref PJNATH_TURN_SOCK. Also there is a sample TURN server in
+the distribution as well. 
+
+Also see <b>\ref samples_page</b> for other samples.
+
+ */
+
+
+/**
+ * @defgroup PJNATH_TURN_SOCK TURN client transport
+ * @brief Client transport utilizing TURN relay
+ * @ingroup PJNATH_TURN
+ */
+
+/**
+ * @defgroup PJNATH_TURN_SESSION TURN client session
+ * @brief Transport independent TURN client session
+ * @ingroup PJNATH_TURN
+ */