Article #ETM229B
Synopsis
A Secure Transmission Unit (STU-III) is a secure telecommunications device designed to operate as both an ordinary telephone and a secure instrument over the telephone network. A STU unit is used to protect the transmission of sensitive or classified information.
Because the unit can be used as an ordinary telephone, it is possible for a call to not go into secure mode. You can define TeleWall® Policy Rules to detect whether a call has gone secure and terminate the call if it is not in secure mode.
Versions Affected
Applies to all versions of the ETM® System.
More Information
The table below is an example of STU Rules.
Note: “STU Lines” in the Source and Destination columns is a user-defined Phone Number Group containing telephone numbers that connect to STU-III Units.
| STU Policy | |||||||||
| No. | Call Direction | Source | Destination | Call Type | Time | Call Duration | Action | Track | Comments |
| 1 | Any | Any | Any | STU | Any | 01:00 | Allow | EmailLog | Notify of long STU calls |
| 2 | Inbound | Any | STU Lines | ! STU | Any | 00:01 | Terminate | EmailLog | Terminate calls that do not go secure |
| 3 | Outbound | STU Lines | Any | ! STU | Any | 00:01 | Terminate | EmailLog | Terminate calls that do not go secure |
| 4 | Any | Any | Any | STU | Any | Any | Allow | Log | Log all STU calls |
The Rules in the example are processed against calls as follows:
Rule 1
The Policy is looking for any calls with call type of STU-III and call duration of 1 hour. Processing pauses at Rule 1 until call type is determined.
- If the call type is identified as STU-III, processing continues with the next Rule while it waits for the 1-hour duration to be reached. Rule 1 is reprocessed every 15 seconds until the 1-hour duration is reached or the call ends. If the call lasts 1 hour, an email notification is sent, and the call is logged in the TeleWall Policy Log.
- If the call is not STU-III, or if a STU-III call does not last 1 hour, Rule 1 does not fire.
Rule 2
The purpose of Rule 2 is to terminate any inbound calls to STU Lines that do not go secure within the first minute (i.e., the call type is identified as anything except STU). Rule 2 is looking for inbound calls from any source with a call type of anything other than STU-III and a call duration of 1 minute.
- If the call is an inbound call to STU Lines and does not have a call type of STU-III, Rule 2 is skipped while it waits for the 1-minute duration to be reached. After all of the subsequent Rules are processed, Rule 2 is reprocessed every 15 seconds until the 1-minute call duration is reached or the call ends.
- If the call type is STU-III, this Rule does not fire.
Rule 3
The purpose of Rule 3 is to terminate any outbound calls from STU Lines that do not go secure within the first minute (i.e., the call type is identified as anything except STU). Rule 3 is looking for outbound calls from STU Lines to any destination with a call type of anything other than STU-III and a call duration of 1 minute. (Note that if SMDR is providing outbound source, these calls will not be terminated, because SMDR is not available until after the call ends.)
- If the call is an outbound call from STU Lines and does not have a call type of STU-III, Rule 3 is skipped while it waits for the 1-minute duration to be reached. After subsequent Rules are processed, Rule 3 is reprocessed every 15 seconds until the 1-minute call duration is reached or the call ends.
- If the call type is STU-III, this Rule does not fire.
Rule 4
The purpose of Rule 4 is to ensure that STU calls that go secure are allowed to complete. If the call has a call type of STU and did not trigger any of the previous Rules, the call is allowed and is logged in the TeleWall Policy Log.
For example, when processing inbound STU-III call to STU Lines:
- Rule 1 specifies call duration of 1 hour. Processing moves to Rule 2.
- Rule 2 specifies that any inbound call to STU Lines that does not go secure within 1 minute should be terminated. The call is identified as STU; the Rule does not fire.
- Rule 3 applies to outbound calls; the Rule does not fire.
- Rule 4 specifies that any STU call that did not trigger previous Rules should be logged and allowed. The Rule fires and the call is logged.
- Rule 1 is reprocessed every 15 seconds (even if Rules 2, 3, or 4 fire) until the call duration reaches 1 hour or the call ends. If the call reaches a 1-hour duration, Rule 1 fires, triggering an email notification of a long STU call, and the call is logged in the TeleWall Policy Log.
Last Update: 2/26/02
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