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Connect a Cisco t1 csu/dsu to ATLAS 550 T1 Network module

I have some T1 CSU/DSU cards for Cisco routers. Presently I have two cards installed on two routers connected in a back to back configuration using a t1 crossover cable. They've been configured in a master/slave setup and work fine with full connectivity.

This is the configuration of the slave device:

interface Serial0/0


ip address

service-module t1 timeslots 1-24

service-module t1 linecode b8zs

service-module t1 framing esf

service-module t1 clock source line

My ATLAS 550 has two T1 Network Interface Modules. I would like to connect a Cisco router to each module and pass the traffic through to the other router. This is for a testing environment

I've connected the above device to one of the modules but don't get a carrier detect light.

My questions:

Is it possible to do what I'm trying?

What type of cable do I need between the Cisco card and T1 module? I tried a standard straight Through Ethernet cable and didn't get a carrier detect. Using the crossover T1 cable I get a carrier detect and Layer 1 shows as 'up' on the Cisco router. Layer 2 is down.

Do I need to use ppp for Layer 2 on the Cisco device?

What configurations do I need on the ADTRAN 550? I've set the linecode and framing but I'm not sure about the other settings on the T1 modules and to switch between them.

Any help would be appreciated since I haven't really found this scenario on the web.

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3 Replies
Honored Contributor
Honored Contributor

Re: Connect a Cisco t1 csu/dsu to ATLAS 550 T1 Network module

You may need a T1 crossover cable between the Cisco and the Atlas as well, try that.

Linecode and framing should be all that's needed to bring up carrier detect.

Have you made a T1 loopback plug to verify that the interfaces are working?  8-pin plug, connect pins 1 and 5 together also connect pins 2 and 4 together.

And here's something that will make this kind of thing easier in the future:

ThinkGeek has these from time to time, a true lifesaver.  I've also seen them at Fry's

Not applicable

Re: Connect a Cisco t1 csu/dsu to ATLAS 550 T1 Network module

As Jay mentioned (and you discovered on your own) you will need a T1 cross-over cable between the ATLAS and the Ciscos. The ATLAS will have to be configured. If there is no configuration, then the ATLAS will generate a T1 signal but won't connect that T1 interface to anything. If you want to use the ATLAS simply to connect one Cisco to another then you can map the two T1 interfaces to each other (under Dedicated Maps) and map all 24 DS0s. This will pass everything directly from one T1 interface to the other.

If you want the ATLAS to terminate the IP connection and route the IP traffic then you will need to do PPP encapsulation and configure the ATLAS to terminate each PPP link. Here is a link on configuring PPP endpoints in the ATLAS

Hope this helps,


Re: Connect a Cisco t1 csu/dsu to ATLAS 550 T1 Network module

Thanks to the both of you for your quick responses. I used the crossover T1 and set the 24 DSOs in the dedicated map. It works fine.