[Info-vax] VAX RDMs (Remote Diagnostic Modules)

[vaxorcist]

A question for former DEC technicians, System Managers & whoever
worked with RDMs:

Several of the bigger VAXen had an RDM (Remote Diagnostic Module) as
an option. In case of problems these RDM were connected via serial
line and modem to one of the DDCs (DEC Diagnostic Centers).

What kind of hardware was used on the other side (at the DEC
Diagnostic Centers)?

Surely a modem, but what else? Another RDM or a special module or
computer for
remote diagnosis?

My VAX-11/750 has got an RDM and I would like to use it one day.

Regards,

Ulli