Changing PRI card line mode to T1 or E1 without moving the jumper

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The recommended way to set line mode on your Digium 1-, 2-, and 4-port (span) digital telephony cards is to set the jumper(s) on the card for either T1 or E1 mode for each span on the card. With the jumper off, the span is ready for T1 mode; with the jumper on, the span is ready for E1 mode. For more details about the jumpers, see the user manual for the single, dual, or quad span digital cards.

However, sometimes a card will have been installed in a server without first setting the jumper(s) correctly, and it may be inconvenient to remove the card from the server to access its jumper(s).  In this case, the “default_linemode” option can be passed when the card’s device driver is loaded.  For single-span cards, the device driver is wcte12xp; for dual-, quad-, and 8-span cards, the device driver is wct4xxp.

Note: The eight-span card (TE820) does not have jumpers. The “default_linemode” module parameter, for the wct4xxp device driver, is the only method to set the TE820 line mode.


Depending on how your Asterisk server loads the DAHDI device drivers, the “default_linemode” option must be set/passed in one of two places:

  • If your Asterisk server uses the DAHDI init script to load the DAHDI device drivers on boot (or if you execute the “service dahdi start” command, which runs the init script), you must set the “default_linemode” option in the/etc/modprobe.d/dahdi.conf file.

/etc/modprobe.d/dahdi.conf :

# You should place any module parameters for your DAHDI modules here
# Example:
# options wctdm24xxp latency=6
options wcte12xp default_linemode=e1
options wct4xxp default_linemode=t1

* In the preceding example, all single span cards (via device driver wcte12xp) are set to E1 mode; all 2-, 4-, and 8-span cards (via device driver wct4xxp) are set to T1 mode.

Then you would reload the DAHDI device drivers by first stopping asterisk, then restarting (stopping and starting) DAHDI using the init script:

# service asterisk stop
# service dahdi restart
# service asterisk start


* Remember that you will still need to configure /etc/dahdi/system.conf and /etc/asterisk/chan_dahdi.conf (or/etc/asterisk/dahdi-channels.conf) to use the proper B-channels and D-channels.

  • Following is an example of loading the DAHDI device drivers manually, to set the wcte12xp driver to T1 mode.
# modprobe dahdi
# modprobe wcte12xp default_linemode=t1
# dahdi_cfg -vv



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6 thoughts on “Changing PRI card line mode to T1 or E1 without moving the jumper

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