Configuring Forward Error Correction - Tieline Merlin PLUS User Manual

Important Note: The preceding table assumes Tieline Music is the algorithm in use. Do
not use PCM (linear uncompressed) audio over highly contended DSL/ADSL connections
without enough bandwidth to support the high connection bit rates required.
Relationship between the Jitter Buffer and Forward Error Correction (FEC)
If forward error correction is configured then additional data packets are sent over a connection to
replace any lost data packets. There is no need to modify jitter buffer settings if you are sending
FEC data, only if you are receiving FEC data.
The jitter buffer depth on the receive codec needs to be increased if FEC is employed. We
recommend you add 100ms to the fixed jitter buffer on a codec receiving FEC at a setting of 20%
and 20ms at a setting of 100%.
Tieline's auto jitter buffer detects the amount of FEC that is being used and automatically
compensates to increase the codec jitter buffer when this feature is enabled.
24.8

Configuring Forward Error Correction

There are two modes of Forward Error Correction (FEC) available in the codec:
1. Tieline FEC: Transmits a secondary stream of audio data packets over a single connection.
2. RFC 2733 compliant FEC (Sessionless connections only): Transmits audio packets over a
separate connection.
FEC is designed to increase the stability of UDP/IP connections in the event that data packets are
lost. FEC works by sending a secondary stream of audio packets over a connection so that if your
primary audio stream packets are lost or corrupted, then packets from the secondary stream can
be substituted to replace them. The amount of FEC required depends on the number of data
packets lost over the IP connection.
Both the local and remote codec FEC settings can be configured in the codec before dialing. FEC
should only be used if link quality displayed on the codec is below S:99 R:99, as it is of no benefit
otherwise.
Tieline and RFC2733 compliant FEC settings are outlined in the following table with their bit rate
ratios.
© Tieline Pty. Ltd. 2017
Connection
Private LAN
Local
National
International
Wireless Network
Satellite IP
Merlin PLUS WNET Manual v2.0
Jitter-Buffer Recommendation
60 milliseconds
100 - 200 milliseconds
100 - 300 milliseconds
100 – 400 milliseconds
250 - 750 milliseconds
500 - 999 milliseconds
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