Hello, today I want to tell you about loops. If you are a technician of the SDH network you will have used them a lot to sectionalize network faults but if you come from the packet networks, you will be careful, a loop on an ethernet port can cause the loss of network services.
Let´s to talk about SDH loops. The loops made in both physical and logical Optical Networks (Made in the management platform) in line ports or tributaries are standardized procedures to sectionalize faults, perform acceptance tests and commissioning of optical equipment. The logical loops automatically generate alarms indicating their existence, but those that are carried out on the physical ports (either local or remote), alarms are only generated on the remote terminations of the services that transit through the loop line ports.
The services that transit on SDH paths will be affected in the event of loops at any level (VC12, VC3 or VC4), since these will not have termination, and in the SDH network the alarms of the paths in the originating terminal will close, not in the destination terminals of the configured routes, where they will acknowledge the affected service alarm as explained above.
Ethernet service.
The Ethernet over SDH service, as its name indicates, is nothing more than the process of transporting Ethernet frames over SDH frames using protocols defined for this purpose.
Port (External Ports)
The external ports of the Ethernet unit can reach speeds of 10M, FE, GE and 10GE, depending on the type of Ethernet card.
VC Trunk (Internal Ports)
VCTrunks are made up of virtual containers at various levels (VC12, VC3 or VC4).
In the case of Ethernet over SDH services, a loop at any level that involves the service can be disastrous, since by configuration the VCTrunks are logical ports of a virtual L2 LAN Switch, so a link would be made to a port Ethernet, creating a loop to L2.
In the case of EPL (Point-to-Point Connection): It affects only the ends and if there is a physical connection with a LAN Switch, it could be compromised.
In the case of EPLAN (Multipoint Point Connection): It affects all components of the Multipoint and if there is a physical connection with a LAN Switch it could be compromised.
SNCP Protection Scheme.
In the SNCP protection scheme, the service is sent concurrently on both paths (Work and Protection), then at the receiving end the best signal is selected, which initially coincides with the work path. The protection is activated when the work path detects an alarm associated with signal degradation (SD) or signal failure (SF).
Signal Failed (SF).
Conditions for the high order SNCP: R_LOS, R_LOF, R_LOC, MS_AIS, AU_AIS, AU_LOP, B2_EXC
Conditions for the low order SNCP: HP_LOM, TU_AIS, TU_LOP
Signal Degraded (SD).
Conditions for SNCP high order: B3_SD, B3_EXC, HP_UNEQ, HP_TIM
Conditions for the low order SNCP:
VC-12 level: BIP_SD, BIP_EXC, LP_UNEQ
VC-3 level: B3_SD_VC3, B3_EXC_VC3
VC-4 level: B3_SD_VC4, B3_EXC_VC4
In the event of a loop, these high-order signals that activate the protection are not present, so the system does not switch to the protection and therefore continues to send the services through the working path through the line port that is in loop. with the consequent impact on the service.
In this same sense, a service that has switched to protection as a result of any of these alarms (if it is configured reversed), returns to the original path or path when the alarms or events that generated the switch disappear. In the case at hand, a loop in a line port makes the alarms that triggered the switching disappear and allows the services to return to their original path, causing the effects of those configured by that address.
SNCP Looped line ports.
Okay, this is all. I hope it helps you and those of us from SDH be careful with network tests now with packet networks and the technicians of the packet world who do you think?.
