The process of initializing the BRI involves the initialization of the TE and  NT. The TE will be either locally powered or by central exchange power sources.   When the TE is powered on for the first time, or when it is in low-power consumption mode it will be in inactive state. For activation  purposes it uses signals INFO 1 to INFO 4 as specified by ITU Recommendation I.430.

When the TE is powered on for the first time or when it has lost frame synchronization, it sends an activation request by  sending INFO 1 signal to NT and waits for response from NT.  At the first receipt of any signal  it stops sending INFO 1 signal  and waits for INFO 2 (activation signal) or INFO 4 signal. +  Once it receives activation signal, it sends INFO 3 as a response. Then it will be waiting for  normal INFO 4 frames. The reception of INFO 4 also indicates the BRI has been operational and is activated. Thus during the actual data transfer, the TE sends INFO 3 frames and the NT sends INFO4 frames.

 The transmission  of signals looks something like this.

 
       TE                                          NT
 
      INFO 0  ----------------->

                   <----------------    INFO 0 (no line signal)

      INFO 1 ------------------>

                    <----------------   INFO 2 (activation signal).

      INFO 3  ----------------->

                     <----------------   INFO 4 (normal frame).              Fig .    TE initialization.