Network Interface Module (NIM)

 NIM is the short form of Net Interface Module, which is the interface unit for the access of various port devices in the SCWLL BSS system to the HIRS network. Based on the current overall design requirement, each HIRS frame of the BSC contains 18 NIM boards, of which 16 are working boards and two are standby boards, forming two N+1 backup systems. The active/standby switchover is implemented in the daisy chain mode. Each NIM board provides eight bi-directional 422 ports, with the supporting data rate being 8Mb/s. In addition, various clocks required for various devices, such as even second and chip signal, are also transmitted in form of differential signals through the 422 port of the NIM boards. 

   Basic structure and Functions of NIM

Control unit: Implements board startup, self-test, status error reporting, N+1 switchover etc.

DISCO logic: Transmits the data in the reception buffer to the UGATE of the NCM, or saves the data from the UGATE into the sending buffer.

HDLC logic: Receives the HDLC data frames from the CPM, NCM, SVICM or CDSU and save them into the buffer, or takes data from the sending buffer, converts them into the HDLC format and sends them to the CPM, NCM, SVICM or CDSU.

422 driving: Drives the HDLC data code flow, even second and CHIP signals.

GLTP driving: Drives the DISCO dual-bus data and control signals.

The NIM panel contains three indicators and one reset button, as shown in Figure 

RUN: A green indicator, blinking when the board works normally.

ALM: A red indicator, blinking in case of board failure.

ACT: A green indicator, lighting up when the board is in active state.