When field engineers patrol the NG SDH equipment by using the patrol software, the information “the type of SSN1 line board in cycle will lead to ECC cycle” is displayed in the patrol result.
Field engineers must know such a restriction. When the field engineers use the inloop function of the N1 series line board, the engineers must try to avoid the affect of this restriction.
The inloop of the SSN1 series line boards (with the board total capacity STM-16 or below) can result in the ECC loopback. When the IP protocol stack is used in the ECC communication, the board is in a non-gateway NE, and the communication with the gateway NE is implemented through the optical interface that delivers the inloop, a large number of inloop alarms are reported frequently after the inloop is delivered to the board.
When the inloop is set for the optical port or the first VC-4 channel of an SSN1 series line board, the ECC and subsequently the overhead bytes D1 to D12 are looped back.
Suppose the ECC communication uses the IP protocol stack, the board is in a non-gateway NE, and the communication between the board and gateway NE is implemented through the optical port that delivers the inloop.
Then, after the inloop is delivered, packets are transmitted discontinuously from the optical port and the packets are looped back to the optical port itself at the same time. Before an alarm is reported, the alarm must be reported to the gateway NE and then the alarm is transmitted through the optical port according to the routing requirement. As a result, the optical port transmits the packet to the gateway NE and receives the packet from the gateway NE. Because the destination address of the packet remains unchanged, the packet received is transmitted from the optical port again. Hence, the procedure repeats and a large number of packets are transmitted to the peer end. An IP packet includes the TTL field (Time to Live). The field is set to 255 in the first transmit. The field value is subtracted by 1 after each routing forward to prevent the endless forward of the packet. When the TTL value is 0, the packet is discarded. Hence, the IP packet can be transmitted for 255 times. This is why the LOOP_ALM is transiently reported for 255 times.
The 10 Gbit/s line boards of the N1 series and the N2 series line boards use different chips from the SSN1 series line boards. In the loopback of the optical port and the first VC-4 channel, the overhead bytes D1 to D12 in the first V-C4 are not looped back. Hence, the 10 Gbit/s line boards of the N1 series and the N2 series boards are not subject to such a specification restriction.
This problem also exists in most OptiX Metro SDH line boards.