<chapter xmlns="http://docbook.org/ns/docbook" xml:id="chapter.overview">
<title>System Overview</title>
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<sect1 xml:id="sect.overview.introducting_rivendell">
<title>Introducing Rivendell</title>
<para>
Rivendell is a digital audio content management and delivery system
that is targeted for use in professional radio broadcast environments.
It includes robust tools for the acquisition, organization, management
and play out of audio material from and to a diverse array of sources
and destinations. Support for a wide variety of external third party
hardware devices and software packages commonly used in the radio
industry is featured, including interfaces for:
</para>
<para>
<itemizedlist>
<listitem>Audio Routing Switchers</listitem>
<listitem>Satellite Downlink Receivers</listitem>
<listitem>Audio Mixing Consoles</listitem>
<listitem>Commercial Traffic and Music Scheduling Systems</listitem>
</itemizedlist>
</para>
<para>
Rivendell is made available under the terms of the
<link linkend="appendix.gplv2">GNU General Public License,
version 2</link>.
As such, it comes with <emphasis>absolutely no warranty</emphasis>,
not even the implied
warranties of merchantability or fitness for a particular purpose.
See the full text of the GPLv2 for details.
</para>
<para>
Rivendell has been designed and developed from the ground up to run
on the popular and highly stable <trademark>GNU/Linux</trademark>
operating system.
Selected tools (mostly having to do with log generation) have also
been ported to run in the Microsoft <trademark>Windows</trademark>
environment as well.
Full source code as well as binary installation packages for Windows
and select Linux distributions are available on line.
</para>
<para>
Rivendell has been designed to be able to operate in a wide variety
of roles, ranging from single, self-contained workstations to large,
multi-station clusters consisting of multiple workstations and
centralized servers. Also included are redundancy and hot-standby
capabilities to allow for reliable operation even in the presence of
hardware faults.
</para>
<para>
Rivendell is implemented as a set of interactive tools or 'modules'
that collectively provide the complete functionality of the system.
Briefly, these modules and their functions are:
</para>
<para>
<variablelist>
<varlistentry>
<term>RDAdmin</term>
<listitem>
System wide configuration
</listitem>
</varlistentry>
<varlistentry>
<term><link linkend="chapter.rdlibrary">RDLibrary</link></term>
<listitem>
Library content management
</listitem>
</varlistentry>
<varlistentry>
<term><link linkend="chapter.rdcatch">RDCatch</link></term>
<listitem>
Automatic event scheduler
</listitem>
</varlistentry>
<varlistentry>
<term><link linkend="chapter.rdairplay">RDAirPlay</link></term>
<listitem>
On-air play out application
</listitem>
</varlistentry>
<varlistentry>
<term><link linkend="chapter.rdlogedit">RDLogEdit</link></term>
<listitem>
Log editing and voicetracking tool
</listitem>
</varlistentry>
<varlistentry>
<term><link linkend="chapter.rdlogmanager">RDLogManager</link></term>
<listitem>
Automated log generation and interface utility
</listitem>
</varlistentry>
<varlistentry>
<term><link linkend="chapter.rdlogin">RDLogin</link></term>
<listitem>
Set the current user on a Rivendell host
</listitem>
</varlistentry>
<varlistentry>
<term>RDCartSlots</term>
<listitem>
Emulate a traditional broadcast cart machine
</listitem>
</varlistentry>
<varlistentry>
<term>RDPanel</term>
<listitem>
Large "cart wall" application
</listitem>
</varlistentry>
<varlistentry>
<term>RDCastManager</term>
<listitem>
Podcast feed manager
</listitem>
</varlistentry>
</variablelist>
</para>
<para>
The operation of each of these modules is explained in detail in the
chapters that follow. However, we first need to cover some basic
concepts common to all Rivendell modules.
</para>
<sect2 xml:id="sect.overview.the_rivendell_object_paradigm">
<title>The Rivendell Object Paradigm</title>
<para>
All Rivendell modules make use of the following four classes of
system resources:
</para>
<para>
<itemizedlist>
<listitem>
<link linkend="sect.overview.hosts">Hosts</link>
</listitem>
<listitem>
<link linkend="sect.overview.users">Users</link>
</listitem>
<listitem>
<link linkend="sect.overview.groups">Groups</link>
</listitem>
<listitem>
<link linkend="sect.overview.services">Services</link>
</listitem>
</itemizedlist>
</para>
<para>
We'll cover each of these concepts in turn.
</para>
<sect3 xml:id="sect.overview.hosts">
<title>Hosts</title>
<para>
Every physical computer within a given network that is running
Rivendell software is referred to as a <emphasis>host</emphasis>.
Any host in a
Rivendell network can be individually configured and controlled
from any other host (provided the system administrator has enabled
this capability). Hosts can be used for a wide variety of
applications, including content ingestion and management,
automatic recording (sometimes referred to as netcatching),
on-air play out or log (sometimes also referred to as playlist)
generation. It is also possible for a single host to perform all
of these functions.
</para>
</sect3>
<sect3 xml:id="sect.overview.users">
<title>Users</title>
<para>
Every host on a Rivendell network has one or more
<emphasis>users</emphasis> available
to it. In this context, a 'user' is merely a set of access
policies established by the system administrator that defines what
tasks a given host is or is not allowed to perform. Every host
has at least one user, called the <emphasis>default user</emphasis>.
As the name
suggests, this is the set of user policies that are loaded by
default when the system starts up. It is also possible to change
the user currently in use on a given host by running the RDLogin
module.
</para>
</sect3>
<sect3 xml:id="sect.overview.groups">
<title>Groups</title>
<para>
A Rivendell <emphasis>group</emphasis> is a system of categories
that is used by the
audio library to classify and organize the audio within the library.
Groups are a very powerful capability, and many operations within
Rivendell can be specified on the basis of group membership.
The actual classification scheme, including the number of available
groups and their names, is completely arbitrary so as to allow each
facility to tailor a schema that best fits its own operational
requirements. Designing and implementing the group schema is one
of the most important tasks facing the Rivendell system
administrator, as a well-designed schema can make long-term
maintenance and management of the system substantially easier
vis-a-vis a poorly thought out one. We will cover groups in
detail in the chapters devoted to the RDLibrary and RDAdmin modules.
</para>
</sect3>
<sect3 xml:id="sect.overview.services">
<title>Services</title>
<para>
Every facility at which Rivendell is deployed is presumed to have
one or more ultimate destinations for which audio is intended.
These could be radio stations (e.g. WAVA), satellite uplink
channels, live Internet audio streams, or any mix of the above.
Each of these sorts of destinations is referred to in Rivendell
as a <emphasis>service</emphasis>, and certain parameters,
particularly as regards
audio play out and log (playlist) creation, can be configured on
the basis of what particular service is being referenced.
</para>
</sect3>
</sect2>
<sect2 xml:id="sect.overview.the_rivendell_hardware_paradigm">
<title>The Rivendell Hardware Paradigm</title>
<para>
In addition to the core computer hardware (CPU, motherboard, etc),
each Rivendell host typically interacts with specialized hardware
required to accomplish the task at hand. Three main categories of
such 'special' hardware are of interest to us here, the three being
audio adapters, serial ports and GPIO/switcher devices. We'll
cover each below.
</para>
<sect3 xml:id="sect.overview.audio_adapters">
<title>Audio Adapters</title>
<para>
An <emphasis>audio adapter</emphasis> in Rivendell is simply a
device or facility for
getting audio into and/or out of a host on a realtime basis.
Most commonly this will be a sound card, although other, more
exotic possibilities (using TCP/IP networking or direct routing
to other audio applications) also exist. The three main classes
of audio adapters supported by Rivendell are:
</para>
<para>
<variablelist>
<varlistentry>
<term>Advanced Linux Sound Architecture (ALSA)</term>
<listitem>
<para>
The standard Linux sound card driver starting with the 2.6.x
kernel series, ALSA supports a huge array of commercially
available sound cards, ranging from entry level 'game' cards
to high-end cards aimed at professional audio uses.
More information, including a current list of supported
cards, is available at the ALSA web site,
http://www.alsa-project.org/.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term>HPI Adapters</term>
<listitem>
<para>
These are high-performance sound cards manufactured by
AudioScience Corporation. Designed and built specifically
for broadcast automation applications, many feature advanced
capabilities (such as on-board MPEG codecs and AES3 i/o)
specially aimed for use in that setting. They are so-called
because Rivendell uses AudioScience's special 'HPI' driver
to access and control them. More information is available
at AudioScience's web site, http://www.audioscience.com/.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term>JACK Audio Interconnect Kit</term>
<listitem>
<para>
JACK is not a particular set of hardware devices, but rather
an audio 'framework' that allows compliant applications to
share audio resources and route audio in realtime amongst
themselves. JACK is different from similar efforts within
the Linux realm in that it was designed from the ground up
for professional audio work, with particular focus upon
low-latency operation and synchronous execution of all
clients. More information can be found at the JACK web
site, http://jackit.sourceforge.net/.
</para>
</listitem>
</varlistentry>
</variablelist>
</para>
</sect3>
<sect3 xml:id="sect.overview.serial_ports">
<title>Serial Ports</title>
<para>
Commonly known in the DOS/Windows world as 'COM ports',
<emphasis>serial ports</emphasis> are often used to communicate
with outboard gear, such as
satellite receivers and audio switchers. Up to eight serial ports
can be accessed simultaneously by each Rivendell host.
</para>
</sect3>
<sect3 xml:id="sect.overview.gpio_switcher_devices">
<title>GPIO/Switcher Devices</title>
<para>
Because these capabilities are often (although not always)
bundled together in the same device, Rivendell lumps GPIO and
switcher devices together within the same class.
<emphasis>GPIO</emphasis> stands
for 'General Purpose Input Output'. As the name implies, these
devices can be used to interface to a huge variety of outboard
equipment by means of control lines. <emphasis>GPI</emphasis>
(General Purpose Input)
lines can be used to sense changes in an outboard system's state
(and Rivendell programmed to take various actions on the basis of
that), while <emphasis>GPO</emphasis> (General Purpose Output)
lines can be used to
send commands to an outboard system. The actual physical
interfacing of GPIO devices is complex and generally beyond
the scope of this document. Readers are encouraged to consult
a good handbook on radio engineering for more information.
A current list of GPIO/Switcher devices supported by Rivendell
can be found in 'docs/GPIO.txt' file in the Rivendell sources.
</para>
</sect3>
</sect2>
</sect1>
</chapter>