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MPEG NOTES
If the unit is fitted with our MPEG layer II codec some extra facilities become available.
MODE OF OPERATION
Our MPEG codec will try to establish lock with the codec at the other end of the ISDN line.
It will attempt communication in MPEG at 16, 24, 32 or 48KHz sampling as well as G722.
This is achieved by looking at the incoming data and locking onto it. Initially our MPEG
codec sends MPEG at 24KHz sampling and so if there is one of our units at both ends of the
ISDN line they will settle for this mode.
It is possible to force the codec into any desired mode, but remember that a codec lock will
only be achieved if the codec at the other end of the ISDN line is operating in the same mode.
To force the mode you must 'dial' special codes after the line connection has been made.
These codes are printed on the rear panel 'CODEC TYPE' label.
AVAILABLE
OPTIONS
CODE TO FORCE OPTION
MODE
G722 = *722
MPEG = *888
AUTO = *000
SAMPLE FREQU
16KHz = *16
24KHz = *24
32KHz = *32
48KHz = *48
DATA RATE
56KBits/Sec = *56
64KBits/Sec = *64
After the call is terminated the unit resets itself to the automatic mode.
AUXILIARY DATA INSTALLATION
If this unit is fitted with an MPEG codec it is possible to fit a 9 pin D socket to the rear panel.
The latest version of our GSGC4 and 5 have a hole already punched for this connector, but if
you are fitting an MPEG codec to an older GSGC5 and require the auxiliary data facility, it
will be necessary to punch a hole or replace the rear panel.
This is a serial port operating at a fixed 9600 baud. It is pin compatible with a PC and
provides a data path to another similarly equipped unit at the other end of the ISDN link. The
data and audio channels can be used simultaneously and the data has no noticeable effect on
the audio quality. This data path only operates if the codec is in the MPEG mode.