ITU-T G.703 2048 kbit/s (PCM) interface

Interface states, processes, remote feeding

• Interface states:
  The interface has 6 operation states:

                                                   
                                              received        transmitted
    State:     Description:                   frame           frame
                                                  by the interface
  
      F0  - power off state                   ------          -----
      F1  - operation state                   normal          normal
      F2  - RAI is in the received frame      normal+RAI      normal
      F3  - no received signal                ------          normal+RAI
      F4  - AIS                               AIS             normal+RAI
      F5  - RCRC                              normal+RCRC+RAI normal+RAI+RCRC
      

• Interface processes:
  Synchronization: there is a separated process for the PCM frame and for the CRC multiframe (the CAS is in the museum)
  • PCM frame synchronization:
    According to the recommendation of ITU-T G.706, steps of the synchronization are the following:
    1. Search for a frame synchronous code (Frame Alignment Signal 0011011) in the PCM signal flow.
    2. If we find a frame synchronous code, we should verify after a frame time (125 us), that the value of the second bit of the service code (Non Frame Alignment Signal) is 1.
    3. After the next frame time we should find another frame synchronous code in the PCM signal flow.
    After that there is a synchronized state, and then can go the synchronization of CAS and CRC multiframes.

    Loosing the synchronization:
    PCM frame synch will vanish after receiving 3 wrong frame synchronous codes following each other.

    Recovery of synchronization:
    PCM frame synch will recover after receiving 2 perfect frame synchronous codes following each other.

  • CAS multiframe synchronization:
    Steps of the CAS multiframe synchronization:
    1. Searching for a multiframe synchronous code word ( 0000 ) in the 16. timeslot of the PCM signal flow.
    2. If we find a multiframe synchronous code, we should find a next multiframe synchronous code after a multiframe time in the PCM signal flow.
    Then there is a synchronized state.

    Loosing the synchronization:
    CAS multiframe synch will vanish after receiving 2 wrong multiframe synchronous codes following each other.

    Recovery of synchronization:
    CAS multiframe synch will recover after receiving 1 perfect multiframe synchronous code, if the frame synch has already been recovered.

  • CRC-4 multiframe synchronization:
    Steps of the CRC-4 multiframe synchronization:
    1. Searching for a multiframe synchronous code ( 001011 ) in the 0. timeslot of the PCM signal flow.
    2. If we find a multiframe synchronous code, we should find after a multiframe time the next multiframe synchronous code in the 0. timeslot.
    Then there is a synchronized state Loosing the synchronization:
    CRC-4 multiframe will vanish, if the number of CRC errors/sec exceeds 914.

    Recovery of synchronization:
    CRC-4 multiframe synch will recover after receiving 2 perfect CRC-4 multiframe synchronous code, if the PCM frame synch has already been recovered.

• Remote feeding:
  At the interface we usually do not apply any remote feedings.

     Interface realization:
    ----------------------
    Many firms produce these interface realizing circuits in an integrated implementation. 
    Types that can be found in laboratory environment: 

    Manufacturer:  Mark of type:

    MITEL  (USA)    MH89790
    DALLAS (USA)    DS2153Q