GatesAir PTR-255 Program Audio Codec Module
Intraplex Products Issue 2.1, February 2006
2.5 Auxiliary Data Channel
The PTR-255 supports one bi-directional auxiliary RS-232 data channel. This channel can be set
to run at rates up to 9.6 kbps as part of MPEG or G.722 audio transmission. The bi-directional
data channel is available both when the card is using the same audio coding algorithm in both
directions and also when the card is set up to run MPEG audio in one direction and G.722 audio
in the other direction.
When configuring the auxiliary data channel, keep in mind that as the aux data rate increases,
fewer bits are available for audio coding and at low bit rates this can have a noticeable effect on
the audio quality. In the MPEG format, aux data channel bits are taken from the overall MPEG
bitstream and affect both channels equally. In the G.722 format, all aux data bits are taken from
Channel 1 and have no effect on Channel 2.
2.6 Inverse Multiplexing
Inverse multiplexing (IMUX) is a method of synchronizing multiple B channels on an ISDN
circuit. On the PTR-255, IMUX is required when the card is being used in an IntraLink ISDN
shelf for MPEG Layer 2 or MPEG Layer 3 transmission at 128 kbps.
The PTR-255 provides two user-selectable IMUX methods: CCS-compatible and FHG
(Fraunhofer Group). For proper operation, you must select CCS-compatible IMUX for use with
MPEG Layer 2 and FHG IMUX for use with MPEG Layer 3.
2.7 Receive-Only Operation
The PTR-255 can be set to operate in receive-only mode by turning on both loopback switches.
When in this mode, all the receive settings operate normally but no transmit data is placed on the
multiplexer transmit bus.
2.8 Contact Closure Option
When the PTR-255 is equipped with an MA-556 module adapter, it will pass four contact
closures in each direction of the circuit, regardless of the audio coding methods in use. To use the
contact closure option, one of the auxiliary data channels must also be enabled (data rate other
than off selected).
Inputs are opto-isolated and can be controlled by a CMOS, open collector or LS TTL logic
outputs or by a switched 5V source.
Outputs are normally open SPST relay closures. The input and output options are illustrated in
Figure 5-3. Specifications for the relays appear in Section 8, Specifications.
2.9 Alerts/Alarms
The PTR-255 modules issue a card-level ALARM signal upon detection of an internal DSP
failure.
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