The following sections describe features of the Digital Network Interface hardware implementation that are important to note for purposes of application development.
3.3.1. SCbus Routing
Data is transmitted over the SCbus in 1024 time slots. At system initiation and download, the number of devices (analog interface, voice, digital network interface, facsimile, etc.) on each board and the number of SCbus time slots required to service these devices are determined. Only one Digital Network Interface device time slot can transmit on a specific SCbus time slot at a time. To assure this, the transmit of all devices are assigned to a specific and unique SCbus time slot at system initialization. This transmit assignment cannot be changed by the application.
When both voice and telephone network digital interface devices (T-1/E-1) are on a single SCbus board, these resources are treated as separate and independent devices.
3.3.2. Loss of Synchronization Alarm HandlingThe most critical error condition that can occur on a T-1 or E-1 line is Receive Loss of Synchronization (RLOS). This section describes the alarm conditions and signals associated with Digital Network Interface alarm handling and how they are indicated on a Digital Network Interface board.
T-1 Alarm HandlingFor T-1 applications, the T-1 compatible Digital Network Interface boards generate three alarm conditions to indicate RLOS:
A red alarm condition occurs when RLOS has existed for 2.5 seconds (default) on incoming data. This condition will exist until the synchronization has been recovered and remains recovered for 12 seconds (default).
A yellow alarm is sent by the receiving T-1 Digital Network Interface device to the transmitter device. The yellow alarm indicates to the transmitter device that a red alarm condition exists at the receiver device. The yellow alarm is sent for as long as the red alarm condition exists at the receiver device.
The blue alarm is a "keep alive" signal. When the T-1 Digital Network Interface device is used in a drop and insert configuration and it receives an RLOS for 2.5 seconds, a red alarm condition is entered on the T-1 Digital Network Interface side that received the RLOS. The configuration then transmits a blue alarm signal from the other Digital Network Interface connected via the SCbus cable to its T-1 span. The blue alarm signal informs the receiving station that there is a problem on the line and allows the receiving station to continue to derive its transmit clock from the received signal.
Figure 9. T-1 Alarm Conditions
E-1 Alarm HandlingFor E-1 applications, the E-1 compatible Digital Network Interface boards generate four alarm conditions to indicate loss of synchronization (FSERR or MFSERR):
A remote alarm is generated by the E-1 compatible Digital Network Interface device to indicate it has detected a loss of frame synchronization on the receive line (FSERR condition). The remote alarm is transmitted to the E-1 network. A remote alarm is returned to the network by setting bit 3 of time slot 0 in non-alignment frames to 1. ("Non-alignment frames" are those frames not carrying the 7-bit frame-sync pattern 0011011 in time slot 0.)
If the E-1 compatible Digital Network Interface device is in a drop-and-insert configuration, it also generates an unframed all 1s alarm. The unframed all 1s alarm is transmitted to the downstream device to indicate that the data it is receiving is unsynchronized at the frame level and is therefore unreliable. The downstream device must then transmit this alarm to the downstream network.
When the E-1 compatible Digital Network Interface device detects a recovery of frame synchronization, it will stop transmitting the remote and unframed all 1s alarms.
A distant multiframe alarm is generated by the E-1 compatible Digital Network Interface device to indicate it has detected a loss of multiframe synchronization on the receive line (MSFERR condition). The distant multiframe alarm is transmitted to the E-1 network. The Digital Network Interface device returns a distant multiframe alarm by setting the bit in position 2 of time slot 16 in frame 0 to 1.
If the E-1 compatible Digital Network Interface device is in a drop-and-insert configuration, it also generates a signaling all 1s alarm. A signaling all 1s alarm is generated by inserting all 1s in time slot 16. The signaling all 1s alarm is transmitted to the downstream device to indicate that the data it is receiving is unsynchronized at the multiframe level and is therefore unreliable. The downstream device must then transmit this alarm to the downstream network.
When the E-1 compatible Digital Network Interface device detects a recovery of multiframe synchronization, it will stop transmitting the distant multiframe and signaling all 1s alarms.
Figure 10. E-1 Loss of Synchronization Alarm Requirements
3.3.3. Digital Network Interface Hardware Alarm IndicatorsThe three LED's on the rear bracket of the Digital Network Interface board indicate the state of the signal being received. All LED indicators will remain lit until the Digital Network Interface firmware is downloaded to the device.
Red LED: The red LED lights up whenever the Digital Network Interface device detects RLOS.
Yellow LED: A yellow LED lights up whenever the Digital Network Interface device receives an alarm indicating that a network span is receiving unsynchronized data from the Digital Network Interface board.
Green LED: A green LED is lit whenever the Digital Network Interface board is receiving a signal.
Click here to contact Dialogic Customer Engineering
Copyright 2001, Dialogic Corporation