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New Member

Back to Back T1 CSU/DSU for testing

I have a customer who is deploying 105 new 2600 series routers. The routers will have the T1 CSU/DSU built into a WIC slot. They have a frame relay WAN and our goal is to provide a lab that will allow me to setup a 3600 with 6 internal T1 CSU/DSUs as a frame relay switch then use crossover rj-45 cables to make a CSU/DSU back to back connections. This will test the CSU setup and allow testing of the frame config, I will also be able to test 6 at a time and move some data end to end.

I have info to make the router a frame switch.

But I can find nothing on how to make the back to back CSU/DSU config work.

I also need pin outs for the rj-45 crossover cables.

Thanks for your help!!

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New Member

Re: Back to Back T1 CSU/DSU for testing

I do know to put the T1 CSU into a hardwired loop, you would short pins 1 - 4, 2-5. Therefore, I would try pining the RJ45 cables the same way. As far as getting the two CSUs to communictate back-to-back, I believe you have to set the encapulation to HDLC. I remember pulling up a document on CCO some time back, but fail to find it now (lack of time...sorry).

Hope this helps!



Re: Back to Back T1 CSU/DSU for testing

See this link for the proper pin-outs of your cable:

As for the config you need to make the T1 work, the only non-default interface setting that you need to enter is "service-module t1 clock source internal" on one end - NOT BOTH (sorry for the scream, there are no italics here).



Cisco Employee

Re: Back to Back T1 CSU/DSU for testing

Here is the link which talks about that hard loopback test on T1 line with pinout.

You can build crossover cable with it.

New Member

Re: Back to Back T1 CSU/DSU for testing

One thing I have noticed with running T1 WIC CSU/DSU back to back is that the links can run too "hot" with a short cable you might need to knock down the db level on both ends of the T-1 with the following interface command:

service-module t1 lbo -7.5db

As for the T-1 cross-over cable:

1 goes to 4

2 goes to 5

New Member

Re: Back to Back T1 CSU/DSU for testing

The last time I set this up on a 2611, I was unable to do frame relay switching between T1 ports in the same WAN slot. Had to drop another dual T1 card in the second slot to simulate the frame switch. Just an FYI to prevent frustration. The crossover should work fine with the following:






New Member

Re: Back to Back T1 CSU/DSU for testing

Sounds familiar.....

We are about 20% down the road in rolling out 103 remote site 1760's over Frame, terminating in a 3600 at the core (via demuxed DS3).

Recently tackeled the addition of a lab setup in the same office as the 3600 and wanted to spoof the clock rate to simulate half of each remote's CIR (for data test bandwidth allocation, the actual FR will also be running VoIP but the lab will not).

Keep in mind, our Cisco partner for the project is building the configs and shipping all equipment. Between myself and another Engr. have years of hands on experience with IOS but are not the experts. It took some time to get the lab setup to work correctly for us.

The basic setup we used were WIC-T1-CSU/DSU's on each end of the line, and a Cat5 cable between them.

The only Ser. encapsulation proto that we could get to bring the line up was HDLC.

I believe the clocks were set to internal on the 3600 side, and line on the remote 1760 end, also set the timeslots on each to 2 (half the 256k CIR).

Luckily I happened to have a OEM crimped RJ-48X cable - sitting unused for years now - that we eventually threw on the host 3600 end to bring it up.

Straight-through and Cross-over pinned out RJ-45 cables would produce a Carrier Link and remote alarms. The RJ-48X uses 1,2,4, and 5 as others have already posted.

If there is anyway to simulate an actual FR serial link (define local DLCI's through me off), other than our current setup and what others have suggested I'd be interested as well. Not sure if it'll affect the VoIP lab eventually but a mirrored setup would be cool.