When Optix OSN3500 SSN1EMS4 single board carries out BPS protection, both GE interfaces and FE interfaces are protected by using single transmitter-selector-receiver. Since the EMS4 single board has a large number of ports (4GE & 16FE), it may be connected to multiple communication devices at the same time, and under normal circumstances, all of them are working on the primary single board, when there are services transmitted in both directions on the primary link. However, on the standby link, on the one hand, EMS4 will turn off the transmission of all ports, so the ports of the opposite-end equipment veneer will be in the Link down state; on the other hand, the opposite-end equipment veneer enables its transmission, although it does not send services, but the receive side of the standby EMS4 will not be in the Link down state. when BPS protection, when the primary veneer detects any port link failure ( Link Down), a single board hardware failure, or a single board going offline, the cross single board of the device will switch all the services on the primary single board to the standby single board to realize service protection. As shown in the solid line in Figure 2. the services of #1, #2, and #3 are inverted to the standby EMS4 and the corresponding standby communication equipment. during PPS protection, when the primary single board detects the link failure (Link Down) of any port, the cross single board of the equipment switches all the failed services on the primary single board to the standby single board to realize service protection. As shown by the solid line in Figure 3. Only the failed #1 service is switched to the standby EMS4 and the standby communication device at the opposite end.

Problem Description

The customer configures EPL service on EMS4 board, and VCTRUNK binds 5 VC12 services to two upper fibers respectively. After enabling LCAS function, when fiber breakage occurs, the data service is interrupted for about 150ms.

Customers ask us what is the protection reversal time of LCAS in this scenario, is there any standard?

Alarm Information

No

Processing

1. Standard time calculation

The multi-frame of VC12 is realized by the b2 bit of K4 bytes, 32 VC12 multi-frames form a virtual cascade multi-frame, and each VC12 multi-frame consists of 4 VC12s. Therefore, the period of the virtual cascade compound frame composed of VC12s is 32*4*0.125ms = 16ms

According to the standard description, the recovery time of the MFI can be 3~10 virtual cascade reframe cycles.

The MFI recovery time of VC12 is that:

3 MFI recovery re-framing cycles = 3 * 16ms = 48ms

10 MFI recovery reframe cycles = 10 * 16ms = 160ms

2. LCAS protection reversal time = fault detection time + single board service recovery time + LCAS troubleshooting time.

1) The fault detection time is related to the actual path length of the existing network.

2) The single board service recovery time is between 48ms~160ms according to the standard definition when VC12 is configured.

3) LCAS fault processing time,The LCAS task processing period of EMS4 is 200ms, which means the maximum processing time of LCAS task is 200ms.

4) Combined with the above calculation, the LCAS reversal time is around 200ms.

Root Cause

In ITU-T, the LCAS standard does not define the reversal time of LCAS protection, however, the LCAS protocol itself is based on the virtual cascade technology, and the virtual cascade technology standard has strict regulations on the service recovery operation in order to ensure the correct service recovery.

The low-order MFI recovery time is calculated as follows:

G.783 standard description:

8.2.5.2 VC-11 VC-12 VC-2 virtual concatenation multiframe alignment

Sink direction The extended overhead multiframe is recovered according to 8.2.3.1. The virtual concatenation frame number is recovered from bits 1-5 of the K4[2] multiframe sequence. The process will be in the out of multiframe (OOM) state when either the extended overhead multiframe alignment process is in the OOM or the extended overhead multiframe alignment process is in the OOM. in the OOM

The process will be in the out of multiframe (OOM) state when either the extended overhead multiframe alignment process is in the OOM state or when an error is encountered in the received and expected frame number from bits 1-5 of the K4[2] sequence. extended overhead multiframe process is in the IM state and two consecutive error-free frame numbers are recovered. The sequence number is recovered from bits 6-11 of the K4[2] sequence. The sequence number is recovered from bits 6-11 of the K4[2] sequence. A new sequence number is accepted if the received sequence has the same value in n consecutive extended overhead A new sequence number is accepted if the received sequence has the same value in n consecutive extended overhead multiframes, with 3 ≤ ?n ≤ ?10. The accepted sequence number is compared with the expected sequence number for detection of the dSQM defect.

Recommendations and Summary

The LCAS functionality is lossless in the scenario of adding or deleting bindings (provided that the actual traffic does not exceed the bandwidth size after deleting bindings or adding bindings). And it can't do lossless protection for the scenario of interrupting fiber.

The technical information related to this chapter and the SDH equipment troubleshooting process is provided by Shenzhen Optical Transmission Network Technology Co. ( www.opticaltrans.com), please retain! Huawei SDH Optical Transmission Equipment,SDH Transmission Equipment Sales