Siemens Simatic S7-200 System Manual page 304

S7-200 Programmable Controller System Manual
Security Callback
The callback function of the Modem module is optional and is configured with the Modem Expansion
wizard. The callback function provides additional security for the attached CPU by allowing access to the
CPU only from predefined telephone numbers. When the callback function is enabled, the Modem module
answers any incoming calls, verifies the caller, and then disconnects the line. If the caller is authorized, the
Modem module then dials a predefined telephone number for the caller, and allows access to the CPU.
The Modem module supports three callback modes:
-
Callback to a single predefined telephone number
-
Callback to multiple predefined telephone numbers
-
Callback to any telephone number
The callback mode is selected by checking the appropriate option in the Modem Expansion wizard and
then defining the callback telephone numbers. The callback telephone numbers are stored in the Modem
module configuration block stored in the data block of the attached CPU.
The simplest form of callback is to a single predefined telephone number. If only one callback number is
stored in the Modem module configuration block, whenever the Modem module answers an incoming call,
it notifies the caller that callback is enabled, disconnects the caller, and then dials the callback number
specified in the configuration block.
The Modem module also supports callback for multiple predefined telephone numbers. In this mode the
caller is asked for a telephone number. If the supplied number matches one of the predefined telephone
numbers in the Modem module configuration block, the Modem module disconnects the caller, and then
calls back using the matching telephone number from the configuration block. The user can configure up
to 250 callback numbers.
Where there are multiple predefined callback numbers, the callback number supplied when connecting to
the Modem module must be an exact match of the number in the configuration block of the Modem
module except for the first two digits. For example, if the configured callback is 91(123)4569999 because
of a need to dial an outside line (9) and long distance (1), the number supplied for the callback could be
any of the following:
10
-
91(123)4569999
-
1(123)4569999
-
(123)4569999
All of the above telephone number are considered to be a callback match. The Modem module uses the
callback telephone number from its configuration block when performing the callback, in this example
91(123)4569999. When configuring multiple callback numbers, make sure that all telephone numbers are
unique excluding the first two digits. Only the numeric characters in a telephone number are used when
comparing callback numbers. Characters such as commas or parenthesis are ignored when comparing
callback numbers.
The callback to any telephone number is set up in the Modem Expansion wizard by selecting the "Enable
callbacks to any phone number" option during the callback configuration. If this option is selected, the
Modem module answers an incoming call and requests a callback telephone number. After the telephone
number is supplied by the caller, the Modem module disconnects and dials that telephone number. This
callback mode only provides a means to allow telephone charges to be billed to the Modem module's
telephone connection and does not provide any security for the S7-200 CPU. The Modem module
password should be used for security if this callback mode is used.
The Modem module password and callback functions can be enabled at the same time. The Modem
module requires a caller to supply the correct password before handling the callback.
292