164 lines
6.4 KiB
C
164 lines
6.4 KiB
C
/*
|
|
* Copyright (C) 2008-2011 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
|
|
*/
|