Siemens SIMATIC S7-200 System Manual page 326

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
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Callback to multiple predefined telephone numbers
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Callback to any telephone number
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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:
91(123)4569999
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1(123)4569999
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(123)4569999
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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.
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