Cisco Support Community
Showing results for 
Search instead for 
Did you mean: 

Welcome to Cisco Support Community. We would love to have your feedback.

For an introduction to the new site, click here. And see here for current known issues.

New Member

Does Cisco 1720 Router Supports ISDN Switch Type - VN6

I have a Cisco 1720 router installed in France and connect to a external NT1. The Local Telco switch is setup for switch-type = VN6. The router running IOS 12.1.17 IP Plus, does not have an option for VN6. The only switch type option in the router for France is VN3.

The Cisco 1720 router doesn't activate layer 1. Even when a ISDN call is initiated from router.

Router has been replaced and Telco stated that ISDN link from the NT1 back to the switch. The cable from the NT1 to the router is about 25ft. The cable tested ok.

Can someone let me know what I'm doing wrong with this setup.

Thanks in advance.


Re: Does Cisco 1720 Router Supports ISDN Switch Type - VN6

vn3 or basic-net3 would be the best choices for France.

Layer 1 issues should be related to the HW (box or cable); sounds like you have tested both. You might try to place the 1720 right at the switch with a shorter cable, to confirm if that makes a different. You might try another NT1, too.

You should check to see if the TEI's will be negotiated at power up or for each call; if the latter, then configure "isdn tei-neg first-call".

Finally, if you still have problems "debug isdn q921" (for TEI negotiation) and "debug isdn q931" (for call establishment) would be great to see. Keep in mind that you first need to get layer1 ACTIVE before you take this step.