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ISDN Crossover cable???

ISDN Crossover cable???

I have a two Cisco routers (1-1004, 1-2516) that I want to connect via ISDN interfaces, just for practice (CCNA). Is there a way to do this with just a crossover cable? I don't want to spend $1100 for an ISDN simulator. Any help would be appreciated.


RE: ISDN Crossover cable???

To my knowledge you cannot connect two ISDN devices back-to-back.  The reason is because ISDN depends on signalling on the D-channel.  Without a D-channel it is not ISDN.  ISDN CPE devices normally do not have a means of generating a D-channel.

RE: ISDN Crossover cable???

I'm trying the very same thing with two cisco 1004 routers with a U interface (American model) so far I've got the Link lights up by connecting the pin 4-5 together on the Serial interface (RG-45). As for the programing side of things, I trying to force the lines to be leased-line type as to avoid the dialing tone issue and use ppp encapsulation with no success. I'd love to hear from anyone who has gotten further than this.

RE: ISDN Crossover cable???

ISDN cable pin assignments: Pin3 TX+, Pin4 RX+, Pin5 RX-, Pin6 TX-.  A crossover cable would be pins 3 to 4 and pins 5 to 6.  I haven't tried it yet to see if it actually works.

RE: ISDN Crossover cable???


In Europe we dial out on one number and receive on the other using MSN (Multi Subscriber Numbering). ISDN has two independent channels.

To do this in the US you need to ask your supplier to set up a different number on each of the B channels.

We did this at a trade show in the US last year and it worked ok...

To the best of my knowledge crossover will not work as the call answer process is a data stream on the D channel.


RE: ISDN Crossover cable???

It's already been suggested by another contributor.. but here is the definitive answer...

  You cannot back to back ISDN devices. Q931 protocol has two different definitions for the Network device and the Exchange device.

  As suggested elswhere, the cheapest test is an ISDN line.. call yourself from one B channel to the other. This can be difficult on some devices - thecheaper ones often can't cope with it and become confused.

  Otherwise you need an ISDN simulator. These start around £2500 from memory. EmuTel make very acceptable ones.

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