T1 alarms include red alarm, yellow alarm and “blue alarm”. Alarms generation and pass-on can be illustrated as the following diagram in the figure below (color is used to denote the nature of alarm). When there is a connection break between the two multiplexers, the one on the right (downstream) will detect a loss of signal (and a loss of frame) and flag a “red” alarm. Meanwhile, it will also send a RAI alarm (“yellow” alarm) to its counterpart multiplexer (upstream) and forward an AIS alarm (“blue” alarm) to its downstream network element. RAI stands for Remote Alarm Indication. The transmission of RAI in T1 facility varies between SF format and ESF format. In SF format, RAI is transmitted by setting the Bit #2 position of every time slot in the trunk to “0”. In ESF format, RAI is transmitted by transmitting the 16-bit pattern “1111111100000000” in its data link bit (J1 SF/ESF RAI transmission is different. AIS stands for Alarm Indication Signal. It is indicated by transmitting an unframed “all ones” bit stream to the downstream device. The reception of such stream indicates that the transmitting device of such stream is on “blue” alarm status. Refer to application note AN-856 for more details. For other questions not addressed by the Knowledge Base, please submit a technical support request.


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AN-856 IDT Transceivers Handling of T1/E1/J1 Signaling,Alarms and Errors Application Note PDF 197 KB