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CTS-ISDNLINK configuration


I have been looking at the admin guide for the new ISDN link box for telepresence and I think I have the gist of how the system should be configured.

I have some questions.

firstly I would like to confirm that the dial string as detailed in the admin guide states that if I was to dial one of the following strings I would be able to call an external ISDN number from the ISDN link box.

the dial string I understand it as is

Protocol SIP

<uri of ISDN link>:<ISDN number>

example below.

URI of ISDN link  =

IP of ISDN =

external ISDN number = 01234123456

So the dial options i believe are as follows


Firstly I would like confirmation that the above is correct?

Secondly I cannot see any documentation stating that there is a H.323 option, is this correct that the ISDN link is SIP only or is there a H.323 option available.

from what I understand it appears that the ISDNlink uses the technology prefix method of routing calls via an ISDN gateway and in this instance specifically only supports SIP, I would personally prefer greatly if H.323 was available I shall detail my reasons why below.

For a stand alone ISDN system it is often required that the system is used to dial to a new ad-hoc number that was not previously known and have not previously been provisioned for, so a nice simple dial string for the user to enter makes the process of placing this call far simpler, in the instance with the configuration detailed in the admin guide the user would need to dial a domain on the alphanumeric keypad, then enter the ISDN number which they wish to dial to, from my personal experience dialing URI's from the alphanumeric keypad is rather a laborious and drawn out process, and for persons that are not so technically savvy is far more complicated and difficult to understand.

With the above in mind and with experience configuring and running various other ISDN Gateways I am wondering, maybe hoping that there is a H.323 option on the ISDNlink which has simply not been documented and that we could indeed use a simple dial plan technology prefix in order to route calls via ISDN rather than having to specifically rely on the SIP method (or maybe I have just not found this information as yet).

for instance dial 9 for an outside line.

I thoroughly look forward to any reply and update about my questions above, and am very interested in understanding the reason for the ISDNlink being SIP only (as far as I can tell) and what the views are for Cisco with enabling H.323 on this box.

Cheers in advanced


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2 Replies 2

Marius Nedregaard
Cisco Employee
Cisco Employee

Hi David.

To dail you need to use this string, you need to specify x-h320.  Correct string:;x-h320number=XXXX

If you throw a VCS in the mix, then you can manipulate your dail strings using regex in order to get an easier dailstring.

The reason ( as I understand it) for the calling is that you should still be able to place regular sip and h323 calls from the system - and not lock it down for ISDN calls only

I will not be able to answer your qeustion regarding implementing H323 on the ISDN Link, I leave that for my peers.


Hi Marius

thank you very much for your response, you have confirmed that the dial string is more complex than i originally thought

so in the instance that there is no VCS involved in order to apply a transform the only option is;x-h320number=01234123456

for confirmation is this the exact dial string that the user would need to enter into the codec in order for the call to be routed out.

is there a method that would allow us to simply this dial string in a standalone solution?

Other than using the local directory.



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