TR-127 Ring Injection and Hook State Tool

The Broadband Forum TR-127 Ring Injection and Hook State Tool was developed by the UNH-IOL for the DSL Testing Service. It is a custom tool used to precisely inject ringing at various phase angles for specific time durations, as well as altering the hook state at various angles of ringing phase as specified in the TR-127 documentation.

Our custom in-house Broadband Forum TR-127 test tool uses a microcontroller to monitor an incoming ring signal and then precisely inject it onto the line at various phase angles. It also triggers an external CPE model to change the hook-state and simulate multiple phones on the CPE line. The tool can be interfaced via serial connection, and provides serial and on-board indicators of test status. For questions and comments, please contact Lincoln Lavoie.


  • Microcontroller driven for precision timing
  • Controlled via serial interface
  • Supports ADSL to VDSL2 testing
  • Precisely controls ringing and hook state for TR-127 sections 8.3 through 8.9
  • Simulates both European and North American telephone models
  • Can accept any arbitrary frequency
  • Ringing and hook state can be controlled manually
  • Automation allows for repeatable testing


The tool can determine incoming ring frequency automatically, allowing for arbitrary and uncommon ringing frequencies. The use of a microcontroller allows for precision timing control of the ringing signal and hook states according to the TR-127 document. The self testing features allow us to ensure the tool is calibrated and operating correctly with the aid of an oscilloscope. The tool also has an additional opto-isolated input to allow for expandability in the future.


The CO model board takes an incoming ring signal, determines the frequency, then uses the signal to inject ringing into the splitter according to TR-127 timing specifications. A microcontroller handles all of the timing to ensure precision. It can inject and remove the ringing, as well as trigger the CPE model at a range of phase angles. Specific parts of the TR-127 test are coded into the microcontroller as well to perfectly match the test specifications. Communicating with the board is done via serial terminal. It has an easy to use interface, allowing testers to run each part of the test independently in case a specific section needs to be retested. The CPE model board controls the phone models. These "ringers" can be added to the ports allowing the simulation of up to four 20 hz North American or European phones (TR-127 specifies only three). The array of ringers is pictured here. Each of these models a phone on the CPE side of the phone line.