(ASCEND) ISDN data as voice [aka DOV, DOSBS] and Siemens switches?

[Gene Hastings <hastings@info-ren.org>]

I've been told that data over voice does not and cannot work on 
Siemens switches and was wondering if anyone can shed some light on 
the mechanism and accuracy of this assertion.

The background:

We work with a number of non-profit and community groups who have 
been benefiting from the use of data connections made as ISDN voice 
calls for their Internet Connections. Recently, one such group 
installed a new connection which would not establish  a full 
connection; the router on one end would dial, the other end would 
answer, but a framed connection (PPP or MPP) was never established. A 
service call was placed and the technician reported no problem. 
Interestingly, it was mentioned in passing that the CO serving this 
location had a Siemens switch.

I was able to speak with an engineer at our ILEC who has often been 
informative in the past, and he promptly told me that data over voice 
did not work on Siemens switches, and could not be made to work on 
them. He confessed that it had been some months since he had learned 
of this, so he did not recall precisely why it was not possible.

[The equipment at the problem site is an Ascend Pipeline 75, of 
recent revision. The other end of the attempted connection has been 
several different Pipelines (to no avail) on a #5ESS switch.]


This leaves me with a number of questions.

Has anyone heard of this phenomenon before? Is it unconditionally 
true, or a feature of some other condition?

If it is so, how so? I had understand that, barring the transit of 
analog facilities, a voice call made between two ISDN connections was 
of necessity digital end-to-end. While I can imagine the application 
of various kinds of signal processing on the voice call, I don't know 
enough of the internals to speculate as to whether this sort of thing 
is actually happening.

Is there any configuration or provisioning change which could be made 
on the line or on the CPE which might have a chance of working?

Are there any traces or diagnostics on the P75 I can examine, either 
directly or via Syslog or SNMP, which would confirm that this 
incompatibility is the source of the failure to connect, and not some 
other factor?

Thanks,
Gene Hastings

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