Static on T1/PRI line

Owned by Kelli Higdon
Last updated: Jul 08, 2024
2 min read

General

Static on a T1/PRI can be caused by many things. There are two causes which are the most common, they are timing and echo cancellation. Trouble shooting steps are below.

 

Troubleshooting

Troubleshooting PRI static may vary if the T1 line is connected to a channel bank or PRI line. Review the appropriate section for the hardware setup you are investigating.

 

Physical Connection (Cabling)

A poor physical cable between the PBXtra and the carrier can be the culprit of static on a PRI line. A quick method of testing this out is to replace the T1 cable between the PBXtra and the smart jack. You may need a straight-through (standard cat-5) cable, or you may need a http://help.fonality.com/index.php/T1_crossover_HOWTO .

Continued testing may also prove out an issue on the cabling down the line to the carrier. Only your carrier will be able to verify if this is the case.

 

Timing

Timing is supplied by the d-channel on channel 24 for T1's and the d-channel on channel 16 for E1's (non-US.) Generally setting the first port as the timing source will be sufficient unless there is a channel bank or the Telco has another port providing timing.

  1. Generally setting the timing on port 1 as the master timing source is sufficient. In the case of a channel bank see below.

  2. If the PRI provider only provides timing on another port simply change the timing source to that port.

  3. If there is a channel bank you will need to configure the first port as your normally would, then have the channel bank reference it as a timing source:

    1. Set the Timeclock Reference Clock to "1" (if the line in span 1 provides timing).

    2. Set the Timeclock to "Master".

Note: port = span

 

Echo

Echo cancellation can cause static when not configured properly.

  1. If the card has HWEC, use only HWEC and turn off software echo cancellation.

  2. If this does not resolve the problem try only software echo cancellation.

  3. For channel banks, you should disable HWEC cancellation by default and only enable it if the customer experiences echo, perform the same troubleshooting steps as above.

 

Firmware

V29 of the A104DM firmware can cause static and dropped calls, upgrade to V31.

 

Reference Articles

 

Configuration Files

  • /etc/wanpipe/wanpipe#.conf on the PBX server

  • /etc/asterisk/zapata.conf on the PBX server

  • /etc/asterisk/zaptel.conf on the PBX server

 

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