Hello,
Today i will share with you how long is the switchover time of LCAS fiber breakage protection for EMS4 board.
Problem Description
The customer uses the EMS4 board to configure EPL services, and VCTRUNK binds 5 VC12 services to two optical fibers for transmission. After enabling the LCAS function, when a fiber break occurs, the data service will be interrupted for about 150ms.
Customers inquired about the protection switching time of our LCAS in this scenario, and is there any standard?
Process
1. Standard time calculation
The VC12 multiframe is realized by the b2 bit of the K4 byte. 32 VC12 multiframes form a virtual concatenated multiframe, and each VC12 multiframe is composed of 4 VC12s. Therefore, the virtual concatenation multi-frame period composed of VC12 is 32*4*0.125ms = 16ms
According to the standard description, the recovery time of MFI can be 3-10 virtual concatenation multi-frame periods.
The MFI recovery time of VC12 is:
3 MFI recovery multi-frame period = 3 * 16ms = 48ms
10 MFI recovery multiframe period = 10 * 16ms = 160ms
2. LCAS protection switching time = failure detection time + single board business recovery time + LCAS failure processing time.
a) The fault detection time is related to the actual path length of the existing network.
b) In the case of VC12 configuration, the service recovery time of the single board is defined by the standard and the recovery time is between 48ms and 160ms.
c) LCAS fault processing time. The processing cycle of LCAS task of EMS4 is 200ms, which means that the longest processing time of LCAS task is 200ms.
d) Combined with the above calculation method, the LCAS switching time is about 200ms.
Cause
In ITU-T, the LCAS standard does not define the switching time of the LCAS protection. However, the LCAS protocol itself is based on the virtual concatenation technology. In order to ensure the correct recovery of the service, the virtual concatenation technology standard has strict regulations on the service recovery operation.
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 state or when an error is encountered in the received and expected frame number from bits 1-5 of the K4[2] sequence. The process enters the IM state when the 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. 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.
Conclusion
With the LCAS function in the scenario of adding, deleting, and binding, the service is lossless (precondition: the actual traffic does not exceed the bandwidth after deleting the binding or adding the binding). However, lossless protection cannot be achieved for the scene where the fiber is interrupted.
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