The SDH Huawei OSN3500 transmission equipment EMS4 single board accesses and handles 4-channel GE services and 16-channel FE services. Adopting hot-swappable SFP optical interfaces, the transmission distance can reach up to 550m for multimode fiber and 10km for single-mode fiber (40km and 80km optical modules can also be selected according to the actual needs). 1000Base-SX/LX/ZX Ethernet optical interfaces support self-negotiation to meet the IEEE802.3z standard. Supports 10Base-T/100Base-TX when used with ETF8; 100Base-FX when used with EFF8. Supports frame lengths from 64 Byte to 9216 Byte, and Jumbo frames up to 9216 Byte. Maximum uplink: 2.5Gbit/s, virtual cascade: VC-12, VC-3, VC-4, VC12-Xv (X≤64), VC3-Xv (X≤24), VC4-Xv (X≤8), supports EVPL service based on PORT+VLAN. Supports up to 4000 IP-based ingress services, up to 4000 VCTRUNK-based ingress services, and up to 8000 LINK services. Supports forwarding function of Layer 2 switching, user side switching and SDH network side switching. Supports 512 blacklists and 512 static MAC addresses. Supports source MAC address self-learning function with MAC address table size of 128 k. Supports manual link aggregation and static link aggregation. Supports inner loopback for Ethernet ports (PHY layer).

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

None

Processing

1. Standard time calculation

The reframe of VC12 is realized by K4 bytes of b2 bits, 32 VC12 reframes form a virtual cascade reframe, and each VC12 reframe 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 re-framing 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) 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.

Suggestions and Summary

LCAS function has no loss of service in the scenario of adding or deleting bindings (premise: 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