GatesAir PT-353, Инструкция по установке и эксплуатации, Страница: 13 / 55

2 – Functional Description PT/PR-353 Program Audio Module Installation & Operation Manual
Version 1.1
GatesAir 2-3
Intraplex Products
The PR-353 module can generate these alarms and alerts:
●
If the framer has lost sync with the PT-353 module, an out-of-frame error occurs, generating an
alarm condition. The contact closes on the MA-509 or MA-559 module adapter, and the yellow
indicator light on the power supply turns on.
● If the FRMLS signal from the common module is closed, the shelf has lost framing information.
The contact closes on the MA-509 or MA-559 module adapter, and the yellow indicator light on the
power supply turns on.
● If the framer determines there are too many errors in the audio stream for Reed-Solomon forward
error correction (FEC), a mute condition occurs and an out-of-frame error generates an alarm
condition. The contact closes on the MA-509 or MA-559 module adapter, and the yellow indicator
light on the power supply turns on.
2.6 Rate Adaptation
Rate adaptation allows the PR-353 to replicate or lock onto the incoming AES input stream from the
PT-353 module, thus alleviating the need for the data to be locked to the transmission medium, such
as a T1 line. The PR-353 module at the transmitter effectively locks onto the incoming data stream
instead of the incoming T1 clock.
Using this method of transport removes the need for sample rate converters on any part of the
transmission path, providing the AES stream is the same as the PT-353 and PR-353 board
configurations. The lock range of the receiver is on the order of 0.01% of the incoming AES source at
the PT-353 end. If a signal is applied to the PR-353 module which is outside of the 0.01% clock
tolerance, errors occur at the PR-353 module, regardless of the status of the Reed-Solomon FEC. In
such situations, the sample rate converter on the PT-353 module (SW6) must be engaged.
There is one condition that cannot be used for rate adaptation. When using a T1 link at a 48 ksps
sampling rate, the entire 24 time slots of the T1 transmission are used, leaving no room for any
overhead including rate adaptation.
2.7 Reed-Solomon Forward Error Correction
The TDM link is protected by Reed-Solomon FEC, which can correct up to two symbol (byte) errors in
every eight frames, which corresponds to a bit error rate (BER) over 10-4. When received by the PR-
353 module, each eight frame block contains either no errors, correctable errors, or uncorrected
errors. If there are no errors or correctable errors, the errors are corrected and the data (both the
audio and the auxiliary) are processed normally. A yellow ERR indicator is flashed for 0.1 second for
each correctable block.
Note: Consecutive errors at a rate up to 10-3 can be removed; however, random errors at this rate
cannot be corrected.
If a block contains uncorrected errors, it is used in its uncorrected form. However, if three consecutive
uncorrected blocks are received, the PR-353 module enters a soft-mute state, (the audio is faded to
zero over a period of 1-2 milliseconds) and the ERR indicator light turns on. The PR-353 module exits
the soft-mute state (fading up the audio) and the ERR indicator light turns off once three consecutive
correctable (or error-free) blocks have been received. Error correction is not available for two-channel,
48ksps bandwidth applications on a T1 network, as there is insufficient bandwidth.
2.8 External Timing
The PR-353 module can use an external timing source, allowing the PT-353 module to lock to the local
equipment clock. This external source is automatically selected from
●
AES input stream
● RS-422