GatesAir PTR-255 Program Audio Codec Module
Intraplex Products Issue 2.1, February 2006
4.2.1 Local Loopback
In a local loopback (Figure 4-2), the PTR-255 encodes the incoming audio as specified by the
transmit configuration settings, places the resulting data on the multiplexer bus for transmission
to the far end of the link and also passes the data stream to the receive side of the card where it is
decoded and handed back to the user. This loopback is useful for testing the user's equipment, the
connection to the PTR-255 and most of the circuitry on the channel module itself.
While a local loopback is active, the transmit-side configuration settings override the receive-side
configuration settings. For example, if the card is set to transmit 128 kbps MPEG Layer 2 audio
and to receive one channel of G.722 audio only, when the loopback is active the receive output
will be 128 kbps MPEG Layer 2 audio. Once the loopback is turned off, the receive side returns
to its previous configuration.
Aggregate
Circuit
(T1, E1,
ISDN, etc.)
Local
Loopback
Audio
Port
Location 1 Location 2
Audio
Port
PTR-255 PTR-255
Figure 4-2
Local Loopback
4.2.2 Network Loopback
When a network loopback is active (Figure 4-3), the PTR-255 passes the incoming data stream to
the receive side of the card where it is decoded and handed to the user as usual, but it also turns
around this receive data stream and sends it back out to the far end over the network. Activating
this loopback at Location 1 is useful for testing the user’s equipment and PTR-255 at Location 2,
as well as the network connection.
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