The MIB module is defined to configure the Announcements
feature on the Media Gateway Card.

The Media Gateway Card will have the capability to 
play pre-recorded local announcements in switched 
VoIP solutions only.  Under the control of a call agent,
announcements can be played in either direction over 
existing connections (calls) or towards the Time
Division Multiplexed (TDM) network on a TDM endpoint
that is terminated on the the Media Gateway Card.

A large number of different announcements may be cached
on the Media Gateway Card for immediate play out.
A persistent announcement store, called the Announcement
file server, will exist in the packet network and hold
all the announcements in the network. Announcements will 
be downloaded on demand as announcement files from
the configured announcement store. Downloaded announcement
files will be stored on the Media Gateway Card as either 
'permanent' or 'dynamic' announcement files. Permanent
files on the Media Gateway Card are exempt from being
refreshed, replaced, or removed without explicit
provisioning actions.  Dynamic announcement files will
not persist across resets.  Permanent announcement files
will be reloaded, if possible, following a reset. Dynamic
announcement files are automatically 'aged'. 'Aged'
files are re-fetched from the Announcement file server.
Dynamic Announcement files can be replaced on the 
Media Gateway Card if the Announcement memory on the
card is full and additional Announcement files are to 
be downloaded. The file(s) to be replaced will be
determined according to some Least Recently Used(LRU)
algorithm.

Announcements can be played over established connections
and unconnected TDM endpoints in any encoding supported
by the Media Gateway Card in its current configuration.
Announcement files must be encoded in G.729a to be
played on G.729ab connections or, if G.729ab has been
chosen as the preferred codec, unconnected endpoints.

The Announcement file server will reside on an IP network 
reachable from the Media Gateway Card using TFTP.
The user will configure the Announcement file server 
node name on the the Media Gateway Card.
The Announcement file server will have a 'main' file
directory for Announcements. If the Announcement prefix
path is configured to begin with a '/' then the 
directory is absolute. If the prefix path is configured
to begin without a '/' then it will be relative to the
default TFTP server directory. If no prefix path is
configured then the Announcement 'main' directory and
the TFTP default directory will be the same. The user
must configure subdirectories within the main
Announcement directory for each encoding that
Announcements may be played in. These subdirectories must
be of the following names: 'g711u', 'g711a', 'g726_40k',
'g726_32k', 'g726_24k', 'g726_16k', 'g729_a',
'g7231_high_rate', 'g7231_a_high_rate', 'g7231_low_rate', 
'g7231_a_low_rate'.


The Media Gateway Card maintains an Announcement cache in
resident memory. The cache is populated on demand with
dynamic files or provisioned with permanent files. That
is to say that when an Announcement is requested to be
played it will first be retrieved from the Announcement
file server and placed in the on-board Announcement cache.
Subsequent requests for the same Announcement will not
require retrieval of the Announcement file from the
Announcement file server.  Note that an Announcement in
one encoding is a different file than the same
Announcement in a different encoding.

The 'Announcement aging' policy is provisionable for 
dynamic files. Once a dynamic Announcement has 'aged'
in the on-board cache it will be 'refreshed' by being 
retrieved again from the Announcement file server.  
The age time determines the maximum time before an updated
Announcement file is automatically propagated to the card.
Shorter age times will result in more frequent file
server access. Changing the 'age' time does not affect
the age times of dynamic Announcement files currently
loaded. However, once these files are refreshed, they
will then use the new 'age' time.

Announcements may also be provisioned as 'permanent'.  
A permanent Announcement will be fetched from the 
Announcement file server and 'frozen' in the Media
Gateway Card Announcement cache.  Permanent
Announcements will be excluded from aging (and being
automatically refreshed) and excluded from being 
replaced if the Announcement cache becomes full.  
Permanent Announcements can only be removed from the
cache explicitly by user through command line
interface or through a Network Manager. If the Media
Gateway Card is reset, permanent Announcements will be
re-fetched from the Announcement file server as soon
as the card becomes active. The Announcement encoding
must be specified when provisioning permanent
Announcements.