Howto BERT (Bit Error Rate Test)

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BeroFix ist capable of doing a BERT (Bit Error Rate Test) over an PSTN line to measure the quality of the line. This is possible with am appfs - Firmware > 2.1

A BERT requires two instances:

1.Audio-Echo-Loop
2.Pattern Transceiver

Audio Echo Loop

In beroFix you can setup an Audio-Echo-Loop by adding a Dialplan Rule PSTN->SIP (e.g. ISDN->SIP). The SIP Destiantion Address can be any IP Address. BeroFix will not really send a SIP Call to this address, it's just a matter that the dialplan requires a SIP Destination.

This Special Dialplan Rule must now be modified with the Advanced Settings Editor. Under "More" you must add the following line:

rtp_loopback=1

When you now call-in via ISDN and this dialplan rule matches (make sure to define a DID for this test in the Destination Dialplan Field), then the call will be answered and the audio will be echoed back to the sender.


Pattern Transceiver

To start the pattern transceiver, you need to setup a SIP->PSTN Call via berofix (e.g. a SIP->ISDN call). This call should be terminated at the Audio-Echo-Loop, so that all Audio will be echoed back.

The Pattern Transceiver is currently started via the telnet interface. First of all you need to enable the telnet interface in the Security Settings in the GUI under Preferences->Security.

Just set the telnet interface ACL to:

0.0.0.0/0

Now you need to connect to berofix's telnet interface. You can simply do that with telnet in linux or with putty in windows:

telnet 10.0.0.2 54322 (linux)

putty  - use a "raw" Socket, to the berofix IP Address, with the Port 54322, 
         Set the terminal parameter "Implicit CR in every LF"  (windows)


The first thing, that you see in the telnet interface is the help screen. When you enter "k" you will see a list of currently running calls with some detailed call-info.

You must now identify the SIP->ISDN Call that we just initiated, where we want to start the BERT Transceiver. The output of "k" looks like:

k
LISTING CALL OPERATIONS COMPACT
01 CS=SM_CALL_ACTIVE I2S OAD= DAD=25938918 P/C=2:2 SIPF=NA SIPT=NA RTP=5000:172.20.0.102:14772 CT=00:03:36 BRDG=NO MCA=15/240(g711_20) MCR=0/240() MFL=MSP_VOICE_ACTIVE TS=3

The first column is the Call index (01). On This index you can start the BERT with:

bert1 (index 01, without 0) 

Now the BERT is started and you can periodically issue an

sbert1 (fetch statistic info)
lbert1 (show statistic info from last fetch via sbert1)

The output shows you the Amount of Bits that are sent and received and the amounts of Bad-Bits that are received. Don't worry if you find some Bad Bits, those come up during the initiation of the BERT. If the bad bid numbers grows over time, then you've got a line quality problem.