Liberator S BRENT Converter

BRENT Converter

The BRENT Converter is based on the Liberator “S” platform and all features on the Liberator “S” are available on the BRENT Converter. The BRENT Converter is a powerful and useful tool for many situations. It is designed to simplify BRENT installations and to provide a more cost effective, reliable and manageable solution for applications where multiple BRENTs are required (for videoconferencing, for example). It also enables BRENTs to use more reliable PRI services, which may also be delivered over fibre to improve security. To ensure more reliable BRENT operation with ISDN in other countries, including the USA, SPIDs etc are handled and there are a number of configuration options to help the BRENTs to function under different conditions and on a huge variety of networks. BRENT can be troublesome and difficult to interoperate with non-UK ISDN services but the Brent Converter assists in overcoming these issues. It also has many flexible features, such as Number Manipulation, which often come in useful in the more unusual applications often associated with BRENTs.


  • Specific additional functionality for the BRENT encryptor phone
  • Converts PRI ISDN to BRI
  • Both “Red” and “Black” sides
  • Converts between Euro (ETSI) and ANSI (USA) BRI
  • Based on the popular Liberator “S” product but with extra capabilities for BRENT applications

As well as the extensive capabilities of the Liberator “S”, the BRENT Converter has a number of features specifically for this application.

“ B” Channel Reservation
By way of illustration we have used a real, installed application below, where BRENTs are required for videoconferencing and used with MCUs (Multi-Conference Units).

BRENT diagram

If the MCU makes an out-going call on the PRI it can utilise any timeslot. Furthermore, calls to multiple BRENTs may be made at the same time. If calls to the same remote BRENT converter are not sent from a single central-site BRENT, calls get “crossed” and fail. Clearly there needs to be some intelligence to handle, order and route calls to the appropriate local encryptor. The BRENT Converter, when it receives a call to a specific destination number (DDI) on its PRI port routes the call to an available BRENT. It then reserves the second “B” channel on that BRENT until it receives another call on the PRI for the same destination number. In this way the two BRI calls to a remote BRENT will always originate from a single central BRENT and calls cannot get crossed. This facility overcomes one of the most troublesome limitations of the BRENT to provide reliable  multi-call sessions.

Call Connect Delay
When in Secure Mode BRENTs take a period of time to exchange keys, handle other “handshakes” and “lock”. Once the BRENTs are locked the attached application/DTE then has end-to-end communications. However, the BRENT “Red S” interface passes the attached DTE a Call Connect message as soon as the ISDN call itself is answered (on the Black interface) - not once there is an actual available data path for the application when the BRENT is synchronised and no longer using the ISDN channel for its own purposes. This means the attached DTE can start to transfer data or try to communicate with its partner device at the other end of the link whilst there is no end-to-end circuit available because the BRENT is still performing its synchronisation exchanges. This can cause data loss or lead the attached device to give up and close the call so the application never works. This is common on terrestrial links but becomes even more obvious on satellite links where the BRENT key exchange etc takes even longer. The intelligence in the BRENT Converter means the Call Connect message from the red “S” bus on the BRENT to the attached device can be delayed for a user-configurable period of time. This ensures an end-to-end data path exists for the attached devices as soon as the call is connected.

Call Timers
Some internal ISDN state machine call timers have been modified to better suit the requirements of the BRENT.

Whilst standard on both the Liberator and the BRENT Converter, the extensive diagnostics and tools make identifying and resolving connectivity issues possible and far more simple than with just a BRENT. For example, traces can capture all low-level ISDN messaging and these can be forwarded as a file to our experts here for analysis and advice should that be needed. An additional small application can convert the ISDN trace data in to a more human readable format.

Live Demo of FRM220 Chassis

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