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© Tieline Research Pty. Ltd. 2019

Bridge-IT Manual v4.0

Important Note:

Tieline FEC can only be configured for use with the Music and

MusicPLUS algorithms.

Configuring RFC 2733 FEC in the Codec

1. Press the

HOME

button to return to the

Home

screen.

2. Use the navigation buttons on the front panel to select

Connect

and press the

button.

3. Select

and press the

button.

4. Select

Sessionless

and press the

button.

5. Select peer-to-peer (

P-to-P

) and press the

button.

6. Use the down

navigation button to select

Setup

and press the

button.

7. Navigate to

FEC

and press

8. Select

Enable

and press

9. Select the

FEC Percentage

and press

10. Select the

FEC Delay

used by the codec and press

Important Notes:

The

FEC Delay

configured should take into account the packet arrival (jitter buffer)

strategy at the remote codec. For example, if the maximum jitter buffer at the remote
codec is 1000 ms, the FEC Delay setting should be lower, to ensure there is enough
time for FEC packets to arrive and replace lost packets prior to audio playout.

By default, the codec will use the audio stream IP address as the remote FEC IP
address as well. This can be adjusted in the

Program Manager panel

in the HTML5

Toolbox web-GUI.

The default local and remote UDP audio FEC ports are 9002.

Any of the available algorithms can be selected when configuring RFC 2733 FEC in the
codec.

How does FEC work?

If you enter a FEC setting of 20% and you are losing one packet in every five sent, the lost packet
will be replaced by FEC to maintain the quality of the connection. If you are losing more packets
than this, say one in three, it will be necessary to increase the FEC setting to 33% to compensate.

Note

: There is an inverse relationship between FEC settings and the jitter-buffer millisecond

setting that you use for IP connections.

So  why  not  use  100%  FEC  every  time?  The  answer  is  because  you  need  twice  the  bit  rate  to
achieve  full  redundancy  and  depending  on  the  link  conditions,  this  could  potentially  cause  more
drop-outs  because  of  network  congestion  than  it  fixes.  Here  is  a  simple  rule  to  remember: Your
maximum  uplink  speed  is  all  the  bandwidth  you  have  to  play  with.  As  a  rule  of  thumb,  try  not  to
exceed  more  than  80%  of  your  maximum  bandwidth.  If  your  link  is  shared,  be  even  more
conservative.

You should also consider the remote end too. What is their maximum upload speed? Is the
connection shared at either end? Your bit rates, FEC settings and buffer rates must be pre-
configured at both ends before you connect, so it's always better to set your connection speed and
balance your FEC according to the available uplink bandwidth at each end for best performance.

As an example, if you want 15 kHz mono (using the Tieline Music Algorithm) you will need at least
a 24kbps connection for audio. Adding 100% FEC will add another 24kbps making your bit rate
48kbps plus some overhead of around 10kbps is required. If you're on a 64kbps uplink, you should
consider reducing your FEC to minimize the likelihood of exceeding your bandwidth capacity.

Here is another example, if you want 15 kHz stereo, you need at least 56kbps for the audio. 100%
FEC requires at least 112kbps and 50% FEC requires at least 84kbps. If your uplink speed is