Codec Tieline Gateway - Configuring Forward Error Correction

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© Tieline Research Pty. Ltd. 2021
Gateway and Gateway 4 Manual v1.2
24.10
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.
FEC Setting
Bit rate Ratios
Connection Use
Tieline
FEC
RFC
2733
FEC
100%
(Lowest
delay)
A simultaneous dual-redundant
stream (1:1 ratio) is sent from
the codec. Twice the
connection bit rate is required to
operate the codec using the
100% setting. E.g. if your
connection is 14,400Kbps, you
will require an additional 14,400
Kbps of bandwidth to allow for
the FEC data stream.
Recommended to
be used over
wireless and
international
connections.
Yes
Yes
50%
Additional data is sent by FEC
in a ratio of 2:1.
Recommended for
international &
national
connections
Yes
Yes
33%
Additional data is sent by FEC
in a ratio of 3:1.
Recommended for
national and local
connections.
Yes
Yes
25%
Additional data is sent by FEC
in a ratio of 4:1.
Recommended for
national and local
connections.
No
Yes
20%
Additional data is sent by FEC
in a ratio of 5:1.
Recommended for
local and LAN
connections.
Yes
Yes
10%(Highest
delay)
Additional data is sent by FEC
in a ratio of 10:1.
Recommended for
local and LAN
connections.
No
Yes
Off
FEC is off in the codec and the
connection bandwidth is equal
to the connection bit rate
setting in the codec.
Recommended for
wired LAN
connections &
managed T1 & E1
Yes
Yes