Subrata -
CON-SSSNT is a Solution Support contract and provides accelerated response time of 30 minutes for Sev1/2 compared to Smart Net Total Care (SNTC) 60 minutes for Sev1/2. It isn't possible to determine or published a resolution time metric as every case/issue is different.
For onsite support when a RMA's device is installed at a customer site, there are onsite support options. For Solution Support the SKU is CON-SSCS-WSC385SE for SNTC it is CON-OS-WSC385SE. However these services are not associated with the initial device deployment or installation. They are only for replacement of RMA devices.
Hope this helps,
Teresa