An example of the network topology is shown on the first slide.
The customer has a 1+0 microwave SDH backbone and a PDH lease line from another operator from the same source MUX to remote MUX site. They want to use
the PDH lease line as protection to the primary SDH path. However SNCP cannot be configured on PDH links and hence switching would not occur.
The solution is shown in the second slide. Optical connectivity between BSC and Metro 1000 is shown as an example.
1. If the customer provides traffic from BSC/other vendor MUX etc optically then 4 optical ports will be required to set up the configuration. If the traffic is connected
electrically from the source then 3 optical ports will be required.
2. Port-1 is optically connected to the BSC which is the sink for SNCP
3. Port-2 is optically connected to the SDH microwave backbone which is the working path
4. Port-3 will be the protection path for SNCP which is hard patched using optical fiber with Port-4 which is in turn configured with the electrical board of the MUX and subsequently pathed with the lease line operator's MUX's DDF (electrical ports).
5. SNCP is configured on Ports-1, 2 & 3 with Port-2 as working source, Port-3 as protection source and Port-1 as the sink.
Since SNCP cannot be configured on PDH links, switching of traffic will not occur leaving the network unprotected. In this case it is possible to create the PDH service
as an optical link initially and then configured with electrical board so that the SNCP is in fact configured with optical ports as working as well as protection paths.
If the microwave link is down/disabled/cut traffic will now shift to Port-3 (patched with Port-4 and then to electrical card) however it will not shift back when PDH link is down. Now depending on the customer's requirement, SNCP will be configured as
revertive or non revertive:
1. Revertive case:
In case this protection is being used in a less dense area where traffic switching is does not affect many users during the day then the customer may opt for
revertive SNCP. Also it may be used when the lease line media is unreliable and has frequent cuts (I have experienced such cases on field), the customer may
want to revert traffic immediately the microwave media is normal again to avoid long down time. Another reason may be the customer does not have man power
to monitor the network 24x7, so the traffic cannot be manually switched in case PDH link goes down while SDH link is up (I have experienced this on field as well)
2. Non revertive
The customer has man power to monitor 24x7 and switch to working path late night when number of users is less thereby limiting the affect on users. The lease
line is from a reliable operator and rarely suffers from cuts. This mode is more preffered as it minimizes affect on the network.